A combination of cellulose nanocrystals (CNCs) and nano-fibrillated cellulose (NFC) was used as a sustainable substrate to immobilize anthocyanins in red cabbage extract (RCE) and prepare a pH-sensitive packaging film. The incorporation of RCE in the CNC/NFC suspension changed the morphology and increased the steady-state viscosity and storage modulus of the suspension. Three rheological models (i.e., Power-law, Herschel-Bulkley, and Nasiri-Ashrafizadeh) fitted the relationship between shear stress and shear rate for each suspension. The incorporation of RCE to the CNC/NFC suspension altered the physical, optical, and mechanical properties of the films and acted as a free radical scavenger. The incorporation of 50 wt.% RCE in the CNC/NFC film enhanced its elongation at break by around 855%. With the enhanced film flexibility, its tensile strength, however, declined. The developed indicator film contained 30 wt.% RCE demonstrated an optimum physical, mechanical, and optical properties with the lowest response time to alkaline pH, which has a great potential as a pH-sensitive film for use in the seafood packaging industry.
Research Article
pH-responsive Cellulose Nanomaterial Films Containing Anthocyanins for Intelligent and Active Food Packaging Applications
https://doi.org/10.21203/rs.3.rs-1763127/v1
This work is licensed under a CC BY 4.0 License
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Nanocellulose
Film-forming
pH sensor
Intelligent food packaging
Food packaging industry plays a crucial role in securing food supply and safety. Well-designed packaging facilitates the handling and storage of foods, protects them from contamination and spoilage, and improves their quality. Moreover, in modern marketing, advanced food packaging not only reduces the cost of the final product, but also makes the customers more satisfied (Müller and Schmid 2019). Despite significant development of bio-based polymers from renewable resources in recent years, petroleum-based plastics are still dominant in food packaging because of their low cost, and excellent physical and mechanical properties. However, non-biodegradable plastics detrimentally affect the environment, posing serious threats to the ecosystems. Consequently, a plethora of researches have been conducted to ameliorate the properties of biodegradable plastics as alternatives to recalcitrant synthetic polymers for food packaging application (Mangaraj et al. 2019).
In recent years, bio-based sensors and indicators have been employed to monitor the quality of the packaged foods as intelligent packaging (IP) films (Hu et al. 2021; Moradi et al. 2019; Nguyen et al. 2019; Sani et al. 2021). Because of the importance of freshness and quality of packaged foods, monitoring the quality and safety of the perishable food products during their transportation and storage is of great significance. IP includes designing a product that has the ability to sense, detect, and share information related to the quality of a product during transportation and its storage (Yam et al. 2005). Moreover, IP can provide precious data about the surrounding environment of the product (e.g., temperature, microbial growth, headspace gases, etc.), and prevents food spoilage and outbreaks of diseases caused by the spoilage of food products (Yousefi et al. 2019). Hence, a large number of studies have been conducted to develop IP systems using different indicators for extremely spoilable meat products and seafood (Cheng et al. 2013; Kuswandi et al. 2012; Yousefi et al. 2019), vegetables (Chen et al. 2018), and milk (Goodarzi et al. 2020; Weston et al. 2020). Deterioration of meat and seafood usually gives up volatile amines such as dimethylamine and trimethylamine. These gases contain total volatile basic nitrogen (TVBN) and most sensors have been employed to detect TVBN for monitoring the freshness of seafood (Cheng et al. 2013).
Research has been conducted to develop calorimetric indicators to monitor the quality of foods, which are detectable to naked eyes. Bhargava et al. (2020) summarized the properties and application of natural pigments extracted from plant and food wastes as indicators for bio-based active and smart food packaging films. Utilizing pigments extracted from agricultural and industrial food wastes such as husk, pulp, peel, barks, and bagasse not only helps save the environment, but also valorizes the food wastes as an economic approach. Etxabide et al. (2021) studied the stability of curcumin, betanin, and anthocyanin as natural colorants. Their results revealed that anthocyanin has proper color variations and broader color responses to different pHs before and during storage, which can be used in smart packaging films.
Anthocyanins are non-toxic natural phenolic compounds, which have antioxidant and antibacterial properties (Yousuf et al. 2016). These natural pigments can be found in various fruits and vegetables such as red cabbage, sweet potato, grapes, etc. (Prietto et al. 2017). Anthocyanins are extensively employed in the field of smart food packaging as pH indicators to monitor the freshness of foods. The selection of an appropriate platform for immobilizing the pH indicators substantially affects the efficiency of the final product. Various approaches have been utilized for the production of halochromic pH-sensitive films based on chitosan (Yong et al. 2019), starch (Vedove et al. 2021; Zhang et al. 2020), gums (Ma and Wang 2016; Wei et al. 2017), gelatins (Musso et al. 2019), bacterial nano fibrillated cellulose (Moradi et al. 2019), cellulose acetate nanofibrils (Aghaei et al. 2018), and their blends and nanocomposites.
Cellulose has attracted a significant attention in the recent decade as a renewable natural polymer with outstanding properties such as biodegradability, low price, abundance, relatively good mechanical, thermal, and optical properties. More recently, cellulose nanomaterials (CNMs), including nano-fibrillated cellulose (NFC), cellulose nanocrystals (CNCs), and bacterial nanocellulose (BNC), have generated significant academic and industrial interests (Mokhena and John 2020). Chemical and/or mechanical treatment of plant biomass leads to its disintegration and production of NFC. Strong acids are usually used to eliminate the amorphous portion of cellulose, resulting CNCs. BNC consists of ultrafine nanofibril, which is synthesized by some bacteria and has different physiochemical properties in comparison to plant-based CNMs (Ludwicka et al. 2020). The unique properties of CNMs, such as lightweight, good mechanical properties, large surface area, high chemical resistance, good optical properties, and the presence of reactive hydroxyl groups on its surface, have made CNMs a potential material for novel and emerging applications. Intermolecular and intramolecular hydrogen bonding of cellulose chains is responsible for the physico-mechanical properties and film-forming ability of CNM (Fang et al. 2019).
This study was intended to develop a CNM-based intelligent and pH sensitive film with incorporation the red cabbage extract, RCE, containing anthocyanins. The specific objectives were to demonstrate 1) combined CNC/NFC material as an appropriate substrate to immobilize the anthocyanins in RCE with enhanced pH responsiveness for monitoring the spoilage of seafood products, and 2) the use of RCE for improving the flexibility of the film to facilitate its application in the food packaging industry. The morphology, rheological behavior, physiochemical, pH responsiveness, and mechanical properties of the prepared suspensions and films were evaluated.
2.1. Materials
Commercially freeze-dried NFC (90% fines) was purchased from the University of Maine (Orono, ME, USA). Commercial CNC suspension (3 wt.% solid) was obtained from Alberta Innovates Technology Futures (AITF, Edmonton, Alberta, Canada). Red cabbage (Brassica oleracea var. capitata f. rubra) and fresh white shrimp (Litopenaeus setiferus) were purchased from local suppliers. Ethanol (98%) was purchased from Fisher Scientific Co (Hampton, NH, USA). 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical and anhydrous calcium chloride (CaCl2) was purchased from Alfa Aesar (Ward Hill, MA, USA).
2.2. Extraction of red cabbage anthocyanins
Red cabbage extract, RCE, was prepared according to methods used by Zhang et al. (2020) with some modifications. At first, 175 grams of pre-ground red cabbage were macerated with 250 mls of ethanol (70%). Ten mls of 1 M HCl were added to the extract solution to adjust the pH to 2.0 and the mixture was stored for 48 h in a refrigerator. After that, the sample was vacuum filtered and the obtained extract was neutralized to pH 7.0 with 1 M NaOH. A rotary evaporator (Yamato Scientific Co., model-RE 300, Japan) was utilized to concentrate the extract solution at 50˚C. Finally, the RCE was dried using a freeze dryer (Labconco, Kansas City, MO, USA) and stored for future use.
2.3. Preparation of pH indicator films
The target amount of NFC (1 wt.%) and CNC (3 wt.% solid content) suspensions was mixed together and diluted with DI water. Different percentages of RCE were added to the prepared NFC/CNC suspensions and the final suspensions were made homogeneous by stirring with a magnetic stirrer for 1 h followed by 30 min sonication in an ultrasonic bath. Finally, the resultant mixtures were poured into a Petri dish and air-dried under a fume hood for 24 h. For designating the prepared films, CCNF denotes the control CNC/NFC film with CNC/NFC mixing ratio of 75:25 based on dry material weight. CNR1, CNR2, CNR3, and CNR4 represent the CNC/NFC samples contained 20, 30, 40, and 50 wt.% freeze-dried RCE, respectively.
2.4. Characterization
2.4.1. Total anthocyanins content of RCE
A pH differential method according to the AOAC Official Method 2005.02 was used to determine the total anthocyanin content of RCE. In this method, the RCE was dissolved in two buffer solutions with pH of 1.0 and 4.5. The absorbance of solutions at each pH was measured at 530 nm and 700 nm, using an Evolution™ 350 UV–visible spectrophotometer (Thermo Fisher Scientific Inc., Waltham, MA, USA). The total anthocyanin concentration was calculated according to the following equations:
$$Anthocyanin Concentration=\frac{\varDelta A\times MW average\times DF\times 1000}{\epsilon \times L} \left[1\right]$$
$$\varDelta A={({A}_{530}-{A}_{700})}_{PH=1}-{\left({A}_{530}-{A}_{700}\right)}_{PH=4.5} \left[2\right]$$
where MW is the molecular weight for cyanidin-3-glucoside (cyd3-glu), i.e., 449.2 g/mol (considering that red cabbage anthocyanins are all derived from cyanidin-3-glucoside as the major anthocyanins core of red cabbage); DF = dilution factor; L = path length in cm; ɛ = 26,900 M extinction coefficient in L/ mol.cm for cyd-3-glu; and 1000 = conversion factor from g to mg.
2.4.2. CNM morphology and suspension properties
A transmission electron microscope (TEM) (JEM 1400, JEOL Inc., Peabody, MA, USA) with an accelerating voltage of 120 kV was used to analyze the morphology of CNCs and NFC. Each suspension was diluted to 0.005 wt. % using deionized water, followed by ultrasonic treatment for 20 minutes prior to the TEM operation. In order to enhance the contrast of TEM images, a droplet of each diluted suspension was placed on a Lacey carbon support grid (LC300-CU-100), then negatively stained with uranyl acetate (2 wt. %) solution and air dried. The dimensions of CNCs were determined by measuring the average length and width from 50 randomly chosen nanocrystals based on TEM images using Image J 1.53 software. To assess the colloidal stability of suspensions, the zeta potential (ζ) of diluted samples was measured using a nano ZS-Plus analyzer (Malvern Panalytical Inc., Westborough, MA, USA).
To evaluate the rheological properties of prepared suspensions before film casting, a stress-controlled rheometer (AR 2000, TA Instrument Inc., New Castle, DE) equipped with a cone- and- plate geometry was utilized. The cone angle and diameter of the test geometry were 2° and 40 mm, respectively. One mL of each suspension, which was vigorously stirred, was loaded at the center of the bottom plate. The steady-flow behavior was analyzed in the shear rate range of 0.01 to 100 s− 1 at 25°C. The rheological data (shear stress-shear rate curves) of prepared suspensions were fitted to Power-law (PL), Herschel-Bulkley (HB), and Nasiri-Ashrafizadeh (NA) models using the commercial software (Origin 8.0). The PL model is used to demonstrate the linear relationship between shear stress and shear rate on double logarithmic coordinates (Govier and Aziz 1972):
The HB model has the following form (Herschel and Bulkley 1926):
with the following restrictions \({\tau }_{0}\ge 0; b\ge 0; 0\le n\le 1; 0\le m\le 1\).
The oscillatory test was carried out using the same cone-and-plate geometry in the angular frequency (ω) range from 0.1 to 100 rad/s and constant strain (0.1%) to determine the storage modulus (G’) and loss modulus (G’’) of each suspension.
2.4.3. Film properties
Colorimetric analysis and light transmittance. In order to assess the responsiveness of the films to different pH solutions, a droplet of buffer solutions with different pHs was placed on the surface of the targeted film. The color parameters of the film before and after the exposure to different pH buffer solutions were determined using a color spectrophotometer (VS3-800, MetaVue™, X-Rite Inc., Grand Rapids, MI, USA.) at room temperature. The colorimeter measured the values of color indices including L-lightness, a - red to green, and b- yellow to blue. The total color difference ΔE was calculated according to the following equation:
\(\varDelta E=\sqrt{{(L-{L}^{*})}^{2}+{\left(a-{a}^{*}\right)}^{2}+{(b-{b}^{*})}^{2}}\) [6]
where L*, a* and b* are the color values of the control CNR2 film without contact to buffer solutions. The optical transparency of prepared films was evaluated by taking photos using a digital camera, and UV–vis light transmittance was also assessed by an Evolution™ 350 UV–visible spectrophotometer (Thermo Fisher Scientific Inc., Waltham, MA, USA).
Dynamic response of indicator films. Ultraviolet-visible (UV-Vis) absorption spectrum analysis was used to measure the dynamic response of indicator films. At first, the punched circular samples (D = 18 mm) were placed on the top of a vial contained 1M ammonia solution at room temperature, and the timer was started immediately. Then, the UV-Vis absorption spectrum of the indicator films was recorded periodically at different time intervals (0 to 60 minutes) in a wavelength range between 400 and 700 nm. The curves of response vs. time were fitted with a non-linear mathematical model using Origin Pro 9.5 software.
Physical properties. The thickness of films was obtained by taking five measurements with a digital micrometer (0.001 mm accuracy) after being conditioned at 25 oC and 75% relative humidity (RH). The equilibrium moisture content (EMC, %) test was conducted to investigate the dynamic moisture absorption of indicator films. At first, triplicate samples of each indicator film were dried in an oven at 70° C for 24 h till constant weight was reached. Then, they were placed inside a constant temperature and humidity incubator. At specified time intervals, indicator films were taken out from the incubator and weighted. The moisture content (%) versus time behavior for indicator films was recorded until the equilibrium at 25°C and 90% RH was established. The sample equilibrium moisture content (EMC, %) reached was determined as:
\(\text{E}MC \left(\%\right)=\frac{{W}_{i}-{W}_{f}}{{W}_{i}}\times 100\) [7]
in which, wi is the initial weight of dried films and wf is the final weight of the films after equilibrium at 85% RH. The moisture diffusion coefficient (D) of prepared films was determined using the Fick’s second law for a thin slab model, assuming one-dimensional water transport in thin films and a uniform concentration of water molecules within the films. The solution of Fick’s second law in the form of a slab model can be written as follows (Crank 1979):
\(\frac{{M}_{t}}{{M}_{e}}={4\left(\frac{Dt}{{L}^{2}}\right)}^{1/2}\{{\pi }^{-\frac{1}{2}}+2\sum _{n=1}^{\infty }{\left(-1\right)}^{n}ierfc\frac{nL}{2\sqrt{Dt}}\}\) [8]
where, Mt is moisture content at time t, Me is the final moisture at equilibrium, D represents the diffusivity of the moisture within the film, and L is the thickness of the film. For short times, the second term in the bracket can be disregarded, and the equation is simplified as follows:
Thus, the moisture diffusivity (D) can be obtained from the slope of the linear section of the Mt/Me against the square root of time plot.
Fourier transform infrared (FTIR) pattern. FTIR analysis was conducted to investigate the probable chemical interactions between RCE and cellulose chains. FTIR spectra of films were obtained by a spectrometer (VERTEX80, Bruker Corp, Billerica, MA, USA) with an attenuated total reflectance mode between 4000 and 400 cm− 1 wavenumbers.
X-ray diffraction (XRD) pattern. In order to evaluate the crystalline structure of the films, their XRD patterns were recorded with a Bruker Siemens D5000 X-ray diffractometer (Bruker Corp, Billerica, MA, USA) operated at 45 kV and 40 mA. Segal’s method (Segal et al. 1959) was employed to calculate the crystallinity index (CI, %) according to the following form:
\(\) \(CI \left(\%\right)= \frac{{I}_{200}-{I}_{Am}}{{I}_{200}}\times 100\) [10]
where I200 equals the maximum intensity at 22.6° and Iam is the minimum intensity at around 18°, which is associated with the amorphous regions of the cellulose.
Water vapor permeability (WVP). The water vapor permeability (WVP) was determined by measuring the water vapor transmission rate (WVTR) of the film, according to the desiccant method in ASTM E96 using anhydrous calcium chloride (CaCl2) as a desiccant. Film samples, in replicates of three, were mechanically sealed onto the vapometer cup assemblies (63.5 mm in diameter and 50.8 mm in height), which were filled with CaCl2. The assemblies were weighed and placed in an incubator set at 25 ˚C and a constant relative humidity (RH) of 85%. The weight of assemblies was measured periodically for three days. The following equations were used to calculate the WVP value (Karkhanis et al. 2018):
\(WVP=\frac{WVTR\times e}{{P}_{sat}({RH}_{out}-{RH}_{in})}\) [11]
\(WVTR=\frac{\varDelta w/t}{A}\) [12]
where e is the film thickness (m), 𝑃𝑠𝑎𝑡 is the saturated vapor pressure at the test temperature (3171 Pa), \({RH}_{out}\) is outside relative humidity (85%), \({RH}_{in}\) is inside relative humidity (≈ 0%), ΔW is the weight gain of the cups (g), t is time (h), and A is the effective area of exposed film (m2).
Mechanical properties. The tensile properties of the films after being conditioned at 25 oC and 75% RH were measured using an Instron 5900 testing machine (Instron Corp, Norwood, MA, USA) according to ASTM-D882 with a calibrated 90.7 kg capacity load cell. The dimensions of the samples were 50 mm in length and 5 mm in width. The samples were stretched until they fractured at a constant test speed of 3 𝑚𝑚/min. At least 5 specimens of each sample were tested, and the average values of fracture strength were reported.
Morphology. To evaluate the morphology of prepared films, the surface and cross-section of films after the tensile test was analyzed with a scanning electron microscope. Prior to SEM observations, a sputter-coater was used to coat the surface and cross-section of films with Pt. The morphology observations were conducted with a Quanta™ 3D DualBeam™ FEG FIB-SEM (FEI Co, Eindhoven, Netherlands) using a 5kV acceleration voltage.
Antioxidant activity. The antioxidant activity was analyzed by submerging 15 mg of film samples in 5 ml 1, 1-diphenyl-2-picrylhydrazyl (DPPH)/methanol solution (0.1 mM). The samples were kept in a dark place at room temperature for 1 hour. Subsequently, UV-vis spectroscopy was employed to determine the absorbance (Ab) values at 517 nm (Yao et al., 2020). DPPH radical scavenging capacity of films was calculated as follows:
\(Antioxidant activity \left(\%\right)=\frac{{Ab}_{DPPH}-{Ab}_{sample}}{{Ab}_{DPPH}} \times 100\) [13]
Shrimp freshness performance. To evaluate the film on the storage freshness of shrimps, a circular film sample (D = 5.1 cm) was used to seal each sample glass bottle that contained prepared shrimp samples. After preparation, the assembly was put in a dark place at 23˚C, and photographs were taken every 8 hours using a digital camera to evaluate film color change.
3.1. RCE properties
Figure 1a shows the UV-vis spectra of RCE in two different pH buffer solutions. The final result showed that the total RCE anthocyanins content of the solution was 154 mg/L with ethanol extraction. The chemical structure of cyanidin and color response of RCE solution in the presence of various buffer solutions (pH 1 to 13) are shown in Fig. 1b. The solution had a fast and distinguishable response to acidic, neutral, and basic pH. Digital photos of the CNR2 film, as optimized formulation based on its dynamic response to high pH, physical, and mechanical properties (section 3.3), after applying the buffer solution droplets with different pHs are also shown in Fig. 1b. Both RCE solution and films displayed distinguishable color changes from slight red to greenish-yellow in the presence of pH variation of 1 to13. The values of color indices (L, a, and b) and ΔE in different pH systems are shown in Fig. 1 (c-d). The addition of RCE into film formulation caused a slight purple color in the final films, which increased with the concentration of RCE. The CNR2 indicator film demonstrated a high value of L, indicating high brightness (lightness; 0 being pure black and 100 being pure white). The results of chroma a showed that in lower pH, the red color had a higher intensity (predominant flavylium cation structure). However, at higher pH, the green color (chalcone structure) was dominant (for chroma a: - being green and + being red). The negative values of chroma b show a greater blue intensity at a lower pH. The cyanidin has a greater tendency to yellow at a higher pH (for chroma b: - being blue and + being yellow) because it is degraded at higher pH and the color of the film turned into green or yellow (Jiang et al., 2020). The obtained ΔE values for CNR2 film show that the difference in colors is discernable by naked human eyes in a wide pH range. Preitto et al. (2017) also reported that a ΔE value higher than 5 is detectable by a naked eye. A schematic model of hydrogen bonding between RCE anthocyanins and CNC/NFC, and transformed chemical structure of anthocyanins at high pH values is illustrated in Fig. 1e.
3.2. Suspension structure and rheology
Morphology. The TEM images for CCNF, CNR2, and CNR4 suspension samples are shown in Fig. 2. The average width and length of the CNCs were 6.11 ± 1.62 nm and 136.45 ± 40.24 nm, respectively. The number of aggregated CNCs for all suspensions is typically larger than the number of isolated individual CNCs, which can be attributed to strong intermolecular hydrogen bonds between the CNCs in the drying step (Doh et al. 2020). However, the micrograph of CCNF (Fig. 2a) demonstrates more individual particles (blue circles) and end-to-end connected CNCs (yellow circles) than laterally agglomerated CNCs (red circles). More laterally agglomerated CNCs in the CNR2 (Fig. 2b) and CNR4 (Fig. 2c) samples could be related to the hydrogen bonding interactions between hydroxyl groups of RCE anthocyanins and CNCs.
The ζ value of the CCNF suspension was − 47.21 ± 2.59, and the incorporation of RCE to the CNC/NFC decreased the magnitudes of negative zeta-potential to -44.24 ± 2.7, -40.95 ± 1.13, and − 37.46 ± 1.8, and − 34.78 ± 1.88 for CNR1, CNR2, CNR3, and CNR4 samples, respectively. However, the absolute ζ values (> 30) confirm that all suspensions are fairly stable. Because the anthocyanins at neutral pH convey minor charges, changes in zeta potential were probably due to hydrogen bonding interactions between RCE, CNC, and NFC with increased concentration of the RCE in suspensions. Inam et al. (2022) reported that noncovalent interactions between polymeric nanoparticles and 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid (HEPES), as a zwitterionic molecule, play a crucial role in changing the zeta potential values. According to their report, hydrogen bonding interactions can suppress the zeta potential value of polymeric nanoparticles. Thus, hydroxyl groups of RCE anthocyanins can partially destabilize cellulose nanoparticles, leading to the ζ values reduction.
Rheological behavior. The rheological properties of a suspension substantially affect the quality of formed films. Thus, both steady-state shear flow and dynamic conditions were employed to evaluate the rheological properties of prepared suspensions. Figure 3a shows steady-state viscosities as a function of shear rate for the suspensions with different concentrations of RCE. All samples showed shear-thinning behavior, in which the viscosity of suspensions decreased with increased shear rate. This phenomenon is attributed to the disruption of the entangled network system of CNC/NFC suspensions with the increase of shear rate (Li et al. 2015). The incorporation of RCE to CNC/NFC increased the viscosity of suspensions along the whole shear rates, and the effect was more significant for samples CNR3 and CNR4. Due to the hydrogen bonding interactions and van der Waals forces among anthocyanin, CNC, and NFC, a non-covalent cross-linked structure can be formed, leading to increased viscosity of suspensions. Generally, some physical and chemical processes such as chain entanglement, hydrogen bonds, van der Waals forces, and ionic interaction may cause physical crosslinking between polymer chains (Liang et al. 2019).
Shear-thinning behavior of each suspension is different, which can be divided into different characteristic regions. For example, CCNF suspension demonstrated four characteristic regions. In regions I, the long nanofibers and rod-like CNCs oriented along the shear direction under the low shear force, causing a decrease of viscosity. In region II, the suspension showed a Newtonian plateau, which can be related to the formation of more entangled network of long NFC fibers during shearing (Li et al. 2015). Further increase of shear rate in region III, caused the destruction of the entangled NFC/CNC network, and a drop in the viscosity (slope III). Finally, as a result of the disruption of the entangled network, another plateau appeared in region IV. The addition of RCE changed the characteristic regions of the shear-thinning curves. The region IV was disappeared with the addition of RCE due to the formation of a physical cross-linked structure, which prevented the complete orientation of NFC and alignment of liquid crystalline CNC phase. Higher concentration of RCE decreased the plateau length in region II, and this region was completely disappeared for CNR3 and CNR4 samples. Interestingly, CNR3 and CNR4 samples demonstrated only one characteristic region, and the slope of the shear-thinning curves for CNR3 and CNR4 samples were constant and lower during the whole shear rates. It was proposed that higher concentrations of RCE forms an isotropic physically crosslinked structure, leading to a continuous shear-thinning behavior within the whole studied shear rate range.
|
Rheological models |
Parameters |
Samples |
||||
|---|---|---|---|---|---|---|
|
CCNF |
CNR1 |
CNR2 |
CNR3 |
CNR4 |
||
|
PL |
K n R2 |
0.187 0.403 0.923 |
0.210 0.462 0.911 |
0.200 0.387 0.961 |
0.429 0.249 0.956 |
0.592 0.243 0.977 |
|
HB |
\({\tau }_{0}\) K n R2 |
-0.246 0.508 0.193 0.900 |
-0.294 0.616 0.233 0.895 |
0.024 0.164 0.451 0.985 |
-0.125 0.580 0.189 0.959 |
-0.083 0.696 0.203 0.981 |
|
NA |
\({\tau }_{0}\) K n-m R2 |
0.010 0.314 -0.086 0.942 |
0.017 0.308 0.155 0.972 |
0.027 0.255 -0.221 0.996 |
0.165 0.388 -0.192 0.964 |
0.162 0.723 -0.388 0.996 |
The rheological parameters of suspensions based on the PL, HB, and NA models are listed in Table 1. The NA model showed the highest R2 values, indicating that shear stress-shear rate curves were fitted the best using this model. The plots of shear stress-shear rate data for each suspension with the fitted lines of the NA model are shown in Fig. 3b. The determined parameters show higher yield stress (\({\tau }_{0})\) and consistency coefficient (K) for samples contained higher RCE concentration. Moreover, the flow behavior index (n) of samples decreased with the addition of RCE, demonstrating the shear thinning behavior of RCE contained samples. The HB model cannot describe the rheological behavior of suspensions well because it led to some negative yield stresses (τo). Figure 3c and Fig. 3d illustrate storage modulus - G' and loss modulus - G'' as a function of angular frequency for CNC/NFC suspensions containing different amounts of RCE, respectively. The incorporation of RCE into the CNC/NFC suspensions increased the values of G’ and reached to the maximum G’ values for sample CNR4. Both values of G’ and G’’ increased with the addition of RCE and G’>G” over the whole probed frequency range. This demonstrates that in the presence of RCE, the suspensions show gel-like behavior, which can be attributed to the formation of a physically cross-linked structure due to the hydrogen bonding between anthocyanin and hydroxyl groups of CNC and NFC. As a result, the non-covalent crosslinked structure strengthened the suspensions and led to the increment of storage modulus. This result is consistent with the more uniform distribution of small CNC lumps in the TEM images of suspensions contained RCE.
3.3. Film properties
Physical and optical properties. Thickness, equilibrium moisture content (EMC), and moisture diffusion coefficient data of the film samples are tabulated in Table 2. The incorporation of RCE into films increased the sample thickness, which could be attributed to the expansion of interlayer spacing of cellulose chains. Polyphenolic RCE anthocyanins interrupted the hydrogen bonding between dense cellulose chains, increased moisture absorption, expanded the polymer chain interlayers, and generally increased the thickness of films. Merz et al. (2020) reported a similar behavior by the addition of anthocyanins extract to chitosan and polyvinyl alcohol films.
The dynamic moisture content of the indicator films from 0 to 120 minutes at 90% RH is shown in Fig. 4a. As shown, the moisture content of the control CCNF and CNR1 film was lower than other indicator films. By the incorporation of higher amounts of RCE, the moisture absorption of films was increased over time until equilibrium was established. The increment of moisture absorption could be related to the presence of -OH groups of RCE, which can increase the hydrophilicity of indicator films and absorb more water molecules. Moreover, Pourjavaher et al. (2017) found similar results by the addition of RCE to bacterial cellulose nanofiber films. They suggested that the polyphenolic molecules of RCE can decrease intermolecular interactions of the bacterial cellulose network and facilitate the interaction of free side groups of bacterial cellulose with water. As a result, RCE molecules reduce the cohesion of the cellulose nanofiber matrix and increase moisture absorption.
The results (Table 2) showed that the incorporation of RCE increased the diffusion coefficient values of film samples from 0.85 ± 0.22 ×10− 5 for CCNF to 4.60 ± 1.32 ×10− 5 mm2/min for CNR4 sample, which confirms its impact on increased hygroscopicity of indicator films.
|
Sample |
25oC and 75% RH |
25oC and 90% RH |
|||
|---|---|---|---|---|---|
|
Sample Thickness (µm) |
Tensile Strength (MPa) |
Elongation at break (%) |
D (mm2/min ×10− 5) |
EMC (%) |
|
|
CCNF CNR1 CNR2 CNR3 CNR4 |
24 ± 3.4 35 ± 0.7 36 ± 1.8 46 ± 1.3 47 ± 0.7 |
60.20 ± 2.20 54.07 ± 1.28 29.60 ± 2.27 20.47 ± 0.38 09.22 ± 0.23 |
1.60 ± 0.18 2.52 ± 0.42 4.70 ± 0.75 6.93 ± 0.75 15.28 ± 0.90 |
0.85 ± 0.22 1.92 ± 0.52 3.18 ± 0.68 3.81 ± 0.87 4.60 ± 1.32 |
09.75 ± 1.60 11.31 ± 1.38 19.14 ± 1.52 21.36 ± 1.57 24.04 ± 1.06 |
Figure 5a shows the optical transparency (digital photographs) and light transmittance (UV-Vis spectrum) of the control CCNF and films containing different percentages of RCE. Clearly, with the addition of RCE in the film, the transparency and light transmittance declined because polyphenolic anthocyanin absorbs visible light in the range of 300–800 nm. Moreover, the higher thickness of CNR3 and CNR4 samples could cause light scattering and decrease the visible light transmittance. RCE containing films showed a transmittance peak in the 400–500 nm wavelength corresponding to the bluish-purple color of the film. The minimum transmittance occurs between 500–600 nm wavelength, because of the characteristic absorbance peak of cyanidin. These results show that the CNR2 film has the optimum transparency for food packaging application.
FTIR-ATR spectra. FTIR analysis was used to assess the hydrogen bonding interaction between CNC/NFC and the cyanidin of RCE. Figure 5b shows the FTIR absorption spectra of film samples with different loadings of RCE. Free O–H stretching vibration of the OH groups in cellulose molecules is discernable in the range between 3000–3500 cm− 1 (Li et al. 2014). The OH stretching (between 3000to 3500 cm− 1) and OH bending (1640 cm− 1) peaks for films incorporated with the higher percentage of RCE are much sharper and stronger, indicating the presence of a higher concentration of hydroxyl groups. The sharpness of the bands could be related to an increase in intramolecular and intermolecular hydrogen bonds and chain reordering (Abral et al. 2020). Two individual peaks are identified from all films between 3500 to 3000 cm− 1, i.e., 3300 and 3340 cm− 1. The former peak is assigned to intermolecular hydrogen bonding and the latter one to intramolecular hydrogen bonding. The peak at about 1640 cm− 1 is associated with the O–H bending of the absorbed water indicates the tendency of RCE loaded films to absorb higher moisture (Abral et al. 2020).
X-ray Crystallography. Figure 5c demonstrates the normalized XRD patterns of RCE and all five CNM-based films, where the cellulose Iβ crystalline structure with different intensities can be observed. All film samples exhibited three main characteristic peaks at 14.7˚, (110), 16.4˚ (1\(\stackrel{-}{1}0)\), 22.6˚ (200), and 34.5˚ (004) (Sun et al., 2018). The presence of a broad peak at around 2θ = 22.6 confirms the amorphous nature of RCE. Generally, the addition of higher amounts of RCE slightly decreased the intensity of peaks. This phenomenon could be attributed to the plasticizing effect of anthocyanins (more than 20 wt.%) that weakened the intermolecular hydrogen bonds between cellulose molecules (Chi et al., 2020). In order to better understand the effect of RCE on the crystalline structure of films, crystallinity index (CI) values of samples were calculated with data shown in Fig. 4d. The CI values for CCNF, CNR1, CNR2, CNR3, and CNR4 were 81.08%, 81.4%, 80.36%, 78%, and 76.2%, respectively. According to the literature, the total crystallinity range of AITF CNCs is from 88 to 94% (Reid et al. 2017). The CI value of CCNF sample shows that the addition of NFC decreased its crystallinity. The incorporation of RCE slightly decreased the crystallinity values of the films. However, the addition of 20 wt.% RCE had no significant effect on the crystalline parameters of the film for sample CNR1. The higher amounts of RCE can limit the probability of forming crystalline structure due to more hydrogen bonds formed among CNC, NFC, and RCE. Pourjavaher et al. (2017) also found similar results with the addition of RCE to bacterial cellulose nanofibers. According to their report, the incorporation of anthocyanins can break the inter- and intra-molecular hydrogen bonds of cellulose and reduce the crystalline structure. Similar results were also reported by researchers using different dyes and film matrices (Kang et al. 2020, Sun et al. 2017).
Dynamic response of indicator films. The relationship between color change and molecular structure of RCE anthocyanins was analyzed by using a UV-vis absorption spectrum. It is well known that chromogenic groups in the pigment molecule (conjugated π and the benzene ring) have particular absorption peaks in the UV-visible region (Huang et al. 2021). Figure 6 (a-d) demonstrates the UV-vis absorption spectra of pH indicator films exposed to 1M ammonia solution. For all films, the maximum absorption before ammonia exposure (t = 0) was located at around 561 nm. By incrementing ammonia gas exposure time, the absorption peak gradually shifted towards longer wavelengths and reached a maximum absorption peak at around 608 nm. The shift of UV-vis absorption peak of indicator films after exposure to ammonia gas can be described by the mechanism shown in Fig. 1. After the exposure of the film to the 1 M ammonia solution, the ammonia vapor diffuses into the film and ammonium ions (NH4+) and hydroxyl ions (OH−) form due to the hydrolysis reaction \(\left(\text{N}\text{H}3+\text{H}2\text{O}\to {{\text{N}\text{H}}_{4}}^{+}+{\text{O}\text{H}}^{-}\right).\) Consequently, the structure of anthocyanins is altered with the increase of OH− concentration (Ezati et al. 2019, Huang et al. 2021) and its color turn to green. In the alkaline pH, negatively charged prototrophic tautomers of the quinoidal bases are formed, which are contributed to the green color (Fig. 5b) (Rakic et al. 2019). In order to assess the dynamic response of prepared indicator films to ammonia gas, the relative ratio of absorbance at 561 nm and 608 nm (Response=A608/A561) was investigated. Figure 6e shows the scatter plot of Response vs. time and dynamic response fitting curve of indicator films. To understand the relation between response rate and RCE concentration, the time required for the Response to reach a critical value (A608/A561=1, dotted lines in Fig. 6e) was considered as response time. The fitting equations based on the Boltzmann mathematical model, and estimated response times of indicator films are tabulated in Table 3. The results showed that the response of the CNR2 film toward ammonia vapor is faster than other films. However, the low concentration of RCE in the CNR1 film caused a higher response time than that of the CNR2 film. The higher concentration of RCE in CNR3 and CNR4 films increased the response time. This phenomenon could be attributed to the higher anthocyanins content, which needed more OH− for the color transformation. Moreover, the deeper color of pigment can disturb the color change and cause the hysteresis phenomenon (Kang et al. 2020).
|
Sample |
Boltzmann Fitting equation |
R2 |
Response time (min) |
|---|---|---|---|
|
CNR1 |
\(y=1.1-0.2275/(1+(\text{e}\text{x}\text{p}(x-10.03))/10.51)\) |
0.996 |
15.94 |
|
CNR2 |
\(y=1.08-0.1706/(1+(\text{e}\text{x}\text{p}(x-21.86))/13.08)\) |
0.997 |
12.06 |
|
CNR3 |
\(y=1.05-0.206/(1+(\text{e}\text{x}\text{p}(x-4.05))/11.1)\) |
0.993 |
22.72 |
|
CNR4 |
\(y=1.04-0.17/(1+(\text{e}\text{x}\text{p}(x-19.25))/12.85)\) |
0.998 |
33.5 |
Antioxidant activity. Figure 6f shows the UV-Vis spectrum of pristine CCNF and halochromic film samples dissolved in DPPH/methanol solution after incubating in a dark place for 1 hour. The measured antioxidant activity value of the films showed that CCNF film had no significant antioxidant capacity (7.53%). In contrast, the antioxidant activity of the RCE contained films exhibited considerable DPPH radical scavenging ability. For example, the antioxidant capacity of CNR1, CNR2, CNR3, and CNR4 were 60.4, 80.3, 90.8, and 91.8%, respectively. The increment of the amount of RCE in the formulations led to higher polyphenol content and enhanced the antioxidant activity of the films. This behavior can be assigned to the intense antioxidant activity of phenolic OH groups of anthocyanins containing plenty of electrons. These electrons and hydrogen atoms can be donated to reactive free radicals to quench them (Sani et al. 2021; Yun et al. 2019; Zhang et al. 2019).
Film mechanical performance. Typical stress-strain curves and the results of tensile strength, elongation at break, and tensile modulus of the control film and RCE incorporated films are illustrated in Fig. 7 (a-d) with actual data summarized in Table 2. The CCNF control sample showed high tensile strength (≈ 60 MPa) and tensile modulus (≈ 7.4 GPa), but very low elongation at break (≈ 1.6%). The presence of RCE remarkably enhanced the elongation at break of films. The incorporation of 50 wt.% of RCE in the sample CNR4 increased the elongation at break of the film by around 855%. This behavior was attributed to the plasticizer role of polyphenolic RCE and chain networks restructuring because of inter and intramolecular hydrogen bonds, resulting in lower inter-molecular interactions among cellulose chains, which increased their interlayer spacing. Consequently, the mobility of cellulose chains can be increased. Moreover, the halochromic films absorb moisture, and the water molecules act as a plasticizer to enhance the ability of cellulose chains to move easily. Abral et al. also reported that humid conditions can increase the elongation at break and decrease the tensile strength of bacterial nanopaper (Abral et al. 2021). The loading of RCE decreased the tensile strength of the films. For example, tensile strength of the CNR4 film sample was decreased by 85%. This phenomenon could be related to the higher porosity of CNR4 film (SEM image -next section) due to the weakened intermolecular hydrogen bonding between CNCs and NFC in the presence of RCE. As a result, micro-voids as local defects are generated, which reduces the tensile strength of halochromic films because of stress concentrations around the micro-voids and easier crack initiation. The lower tensile strength of halochromic films can also be attributed to the air bubbles inside the film structure because of the higher viscosity of suspensions contained RCE. Pourjavaher et al. (2017) reported similar phenomenon by the incorporation of RCE to bacterial cellulose nanofibers. They attributed the increased elongation at break and reduced tensile strength and tensile modulus to the plasticizer role of RCE, which decreased the interactions between cellulose molecules.
Film microstructure. The top surface and cross-section morphology of CCNF, CNR2, and CNR4 films after the tensile test are displayed in Fig. 8. It can be seen that the top and cross-section surfaces of CCNF control film (Fig. 8a and 8d) were more homogenous in comparison to CNR2 (Fig. 8b and 8e) and CNR4 (Fig. 8c and 8f) films. This observation can be ascribed to the higher compactness of CNCs and NFC, leading to a more uniform structure. NFC bundles arranged in a layer-by-layer manner are clearly seen in the cross-section image (Fig. 8d) for CCNF system. However, the CNR2 and CNR4 film exhibited a low compact layer-by-layer structure with more pores and cavities (rough surfaces as observed in the SEM images). Thus, the incorporation of RCE expands the interlayer spacing of chains and separates CNCs and NFCs. The higher porosity of CNR4 (Fig. 8f) in comparison to the CNR2 (Fig. 8e) film results from the more interlayer expansion and separation of CNCs and NFC due to the new hydrogen bonding between RCE and cellulose chains, which interrupts the regular hydrogen bonding and self-assembly of CNCs and NFC system.
Water vapor permeability. The results of water vapor permeability (WVP) for control CCNF film, CNR2, and a commercial PLA-PBAT film (thickness = 0.008mm) showed that the value of WVP increased from 1.016 ± 0.023×10− 8 g/m.h.Pa for CCNF to 1.15 ± 0.032×10− 8 g/m.h.Pa for CNR2. However, the PLA-PBAT film revealed a lower WVP (2.7 ± 0.05×10− 9 g/m.h.Pa). Generally, unlike the PLA-PBA, the cellulose-based films have a hydrophilic structure and are more sensitive to moisture. The mechanism of permeation of water vapor is by diffusion of water vapor molecules through the porous structure of the films under a partial pressure difference (Basha et al. 2011). According to the XRD results, the presence of RCE decreased the crystallinity of films by interrupting the intermolecular hydrogen bonding and expanding the interlayer spacing of cellulose chains. Consequently, the compaction of CNC/NFC system was reduced and the diffusion of water vapor molecules into the film was facilitated. Hubbe et al. (2017) also reported that the crystalline regions play a crucial role in preventing the permeation of water vapor through the CNM films. Therefore, decreasing the crystallinity of the film could detrimentally affect the WVP. Moreover, they delineated the potential of plasticizer molecules to interrupt the H bonding within a nanocellulose-based film and increase the diffusion rate of water vapor molecules.
Film responsiveness to shrimp spoilage. Based on the aforementioned results, indicator films produced distinguishable color changes to be used for monitoring shrimp freshness. The CNR2 film was selected for the test. Figure 9a shows the color changes of the indicator film during 24 hours. In the initial stage, the color of the films was light purple and after 8 hours of storage at room temperature, the color turned to light green. With increased storage time to 16 and 24 hours, the green color deepened. However, the difference between green colors was not detectable after 24 hours. In order to better analyze the color change of the film during the spoilage, the color indices were determined using the colorimetric method. The values of a and b indices and the color difference (ΔE) are also illustrated in Fig. 9b and c. The results showed that the chroma a remarkably decreased, and chroma b increased after 8 hours (green color). The color difference data revealed that the color change is detectable by a naked eye. As a perishable food, shrimp can be quickly spoiled during storage and release various volatile basic nitrogen gases (ammonia and amines) because of spoilage microorganism and the breakdown of protein in the shrimp muscle (Zhang et al. 2020). The microbial and biochemical activity during storage of shrimp results in change of pH from acidic to neutral or alkaline range (Don et al. 2018). The production of volatile bases compounds in the headspace of the glass bottle can gradually increase the pH and change the color of the indicator film. According to these results, this CNM-based indicator film has a great potential to be employed for monitoring the freshness of shrimp and other seafood products.
CNC/NFC based halochromic films were prepared by loading different amounts of RCE to CNC/NFC suspension, followed by casting and drying at room temperature. It was found that RCE increased the viscosity and storage modulus (G’) of CNC/NFC suspension because of the predominant hydrogen bonding interactions between anthocyanin and cellulose chains and formation a partial physical crosslinked structure. Among the three rheological models (i.e., PL, HB, and NA), NA model performed the best in predicting the rheological properties of CNC/NFC/RCE suspensions. The indicator films showed fast and naked-eye detectable color changes in a wide range of pH buffer solutions and ammonia vapor exposure. The addition of RCE increased the thickness, porosity and improved the elongation at break and flexibility of films. Meanwhile, the tensile strength and tensile modulus decreased. Due to the hydrogen bonding interruption of abundant cyanidins in the RCE, the crystallinity of the RCE containing films slightly decreased. The CNR2 film demonstrated a higher water vapor permeability in comparison to that of the commercial PLA-PBAT film. With the increased RCE content, the films showed a significant antioxidant activity. The application of the halochromic CNC/NFC film for monitoring the freshness of packaged shrimps revealed its sensitivity for detecting the spoilage of seafood products.
Acknowledgments
This collaborative study was carried out with support from by National Institute of Forest Science, Seoul, Korea (FP0701-2021-02), USDA Specialty Crop Block Grant Program – Farm Bill (SCBGP–FB, USA), and Louisiana Board of Regents (LEQSF (2020–23)–RD–B–02, USA).
Declaration of interests
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Qinglin Wu reports financial support was provided by Louisiana State University.
Abral H, Ariksa J, Mahardika M, Handayani D, Aminah I, Sandrawati N, Sugiarti E, Muslimin A. N, Rosanti S. D (2020) Effect of heat treatment on thermal resistance, transparency and antimicrobial activity of sonicated ginger cellulose film. Carbohydr Polym 240:116287. https://doi.org/10.1016/j.carbpol.2020.116287
Abral H, Chairani M. K, Rizki M. D, Mahardika M, Handayani D, Sugiarti E, Muslimin A. N, Sapuan S.M, Ilyas R.A (2021) Characterization of compressed bacterial cellulose nanopaper film after exposure to dry and humid conditions. J Mater Res Technol 11:896-904. https://doi.org/10.1016/j.jmrt.2021.01.057
Aghaei Z, Emadzadeh B, Ghorani B, Kadkhodaee R (2018) Cellulose acetate nanofibres containing alizarin as a halochromic sensor for the qualitative assessment of rainbow trout fish spoilage. Food Bioproc Tech 11(5):1087-1095. https://doi.org/10.1007/s11947-017-2046-5
Basha R. K, Konno K, Kani H, Kimura T (2011) Water vapor transmission rate of biomass based film materials. Eng Agric Environ Food 4(2):37-42. https://doi.org/10.1016/S1881-8366(11)80018-2
Bhargava N, Sharanagat V. S, Mor R. S, Kumar K (2020) Active and intelligent biodegradable packaging films using food and food waste-derived bioactive compounds: A review. Trends Food Sci Technol 105:385-401. https://doi.org/10.1016/j.tifs.2020.09.015
Chen H.-z, Zhang M, Bhandari B, Guo Z (2018) Applicability of a colorimetric indicator label for monitoring freshness of fresh-cut green bell pepper. Postharvest Biol Technol 140:85-92. https://doi.org/10.1016/j.postharvbio.2018.02.011
Cheng J.-H, Dai Q, Sun D.-W, Zeng X.-A, Liu D, Pu H.-B (2013) Applications of non-destructive spectroscopic techniques for fish quality and safety evaluation and inspection. Trends Food Sci Technol 34(1):18-31. https://doi.org/10.1016/j.tifs.2013.08.005
Chi W, Cao L, Sun G, Meng F, Zhang C, Li J, Wang L (2020) Developing a highly pH-sensitive ĸ-carrageenan-based intelligent film incorporating grape skin powder via a cleaner process. J Clean Prod 244:118862. https://doi.org/10.1016/j.jclepro.2019.118862
Crank, J (1979) The mathematics of diffusion. Oxford university press.
Doh H, Dunno K. D, Whiteside W. S (2020) Preparation of novel seaweed nanocomposite film from brown seaweeds Laminaria japonica and Sargassum natans. Food Hydrocoll 105: 105744. https://doi.org/10.1016/j.foodhyd.2020.105744
Don S, Xavier K. M, Devi S. T, Nayak B. B, Kannuchamy N (2018) Identification of potential spoilage bacteria in farmed shrimp (Litopenaeus vannamei): Application of Relative Rate of Spoilage models in shelf life-prediction. Lwt 97:295-301. https://doi.org/10.1016/j.lwt.2018.07.006
Etxabide A, Kilmartin P. A, Maté J. I (2021) Color stability and pH-indicator ability of curcumin, anthocyanin and betanin containing colorants under different storage conditions for intelligent packaging development. Food control 121:107645. https://doi.org/10.1016/j.foodcont.2020.107645
Ezati P, Tajik H, Moradi M, Molaei R (2019) Intelligent pH-sensitive indicator based on starch-cellulose and alizarin dye to track freshness of rainbow trout fillet. Int J Biol Macromol 132:157-165. https://doi.org/10.1016/j.ijbiomac.2019.03.173
Fang Z, Hou G, Chen C, & Hu L (2019) Nanocellulose-based films and their emerging applications. Curr Opin Solid State Mater Sci 23(4):100764. https://doi.org/10.1016/j.cossms.2019.07.003
Goodarzi M. M, Moradi M, Tajik H, Forough M, Ezati P, Kuswandi B (2020) Development of an easy-to-use colorimetric pH label with starch and carrot anthocyanins for milk shelf life assessment. Int J Biol Macromol 153:240-247. https://doi.org/10.1016/j.ijbiomac.2020.03.014
Govier G. W, Aziz K (1972) The flow of complex mixtures in pipes (Vol. 469). Van Nostrand Reinhold Company New York.
Herschel W. H, Bulkley R (1926) Konsistenzmessungen von gummi-benzollösungen. Kolloid-Zeitschrift 39(4):291-300. https://doi.org/10.1007/BF01432034
Hu B, Pu H, Sun D.-W (2021) Multifunctional cellulose based substrates for SERS smart sensing: Principles, applications and emerging trends for food safety detection. Trends Food Sci Technol 110:304-320. https://doi.org/10.1016/j.tifs.2021.02.005
Huang, S, Wang G, Lin, H, Xiong Y, Liu X, Li H (2021) Preparation and dynamic response properties of colorimetric indicator films containing pH-sensitive anthocyanins. Sensors and Actuators Reports 3:100049. https://doi.org/10.1016/j.snr.2021.100049
Hubbe M. A, Ferrer A, Tyagi P, Yin Y, Salas C, Pal L, Rojas O. J (2017) Nanocellulose in thin films, coatings, and plies for packaging applications: A review. BioResources 12(1):2143-2233. https://doi.org/10.15376/biores.12.1.2143-2233
Inam W, Bhadane R, Akpolat R. N, Taiseer R. A, Filippov S. K, Salo‐Ahen O. M, Zhang H (2022) Interactions between polymeric nanoparticles and different buffers as investigated by zeta potential measurements and molecular dynamics simulations. View: 20210009. https://doi.org/10.1002/VIW.20210009
Jiang G, Hou X, Zeng X, Zhang C, Wu H, Shen G, Li S, Luo Q, Li M, Liu X, Chen A, Wang Z (2020) Preparation and characterization of indicator films from carboxymethyl-cellulose/starch and purple sweet potato (Ipomoea batatas (L.) lam) anthocyanins for monitoring fish freshness. Int J Biol Macromol 143:359-372. https://doi.org/10.1016/j.ijbiomac.2019.12.024
Kang S, Wang H, Xia L, Chen M, Li L, Cheng J, Jiang S (2020) Colorimetric film based on polyvinyl alcohol/okra mucilage polysaccharide incorporated with rose anthocyanins for shrimp freshness monitoring. Carbohydr Polym 229: 115402. https://doi.org/10.1016/j.carbpol.2019.115402
Karkhanis S. S, Stark N. M, Sabo R. C, Matuana L M (2018) Water vapor and oxygen barrier properties of extrusion-blown poly (lactic acid)/cellulose nanocrystals nanocomposite films. Compos Part A Appl Sci Manuf 114:204-211. https://doi.org/10.1016/j.compositesa.2018.08.025
Kuswandi B, Restyana A, Abdullah A, Heng L. Y, Ahmad M (2012) A novel colorimetric food package label for fish spoilage based on polyaniline film. Food control 25(1):184-189. https://doi.org/10.1016/j.foodcont.2011.10.008
Li J, Wang Y, Wei X, Wang F, Han D, Wang Q, Kong L (2014) Homogeneous isolation of nanocelluloses by controlling the shearing force and pressure in microenvironment. Carbohydr Polym 113:388-393. https://doi.org/10.1016/j.carbpol.2014.06.085
Liang L, Bhagia S, Li M, Huang C, Ragauskas A. J (2019) Cross-linked nanocellulosic materials and their applications. ChemSusChem 13(1):78-87. https://doi.org/10.1002/cssc.201901676
Li M.-C, Wu Q, Song K, Lee S, Qing Y, Wu Y (2015) Cellulose nanoparticles: structure–morphology–rheology relationships. ACS Sustain Chem Eng 3(5):821-832. https://doi.org/10.1021/acssuschemeng.5b00144
Ludwicka K, Kaczmarek M, Białkowska A (2020) Bacterial Nanocellulose—A Biobased Polymer for Active and Intelligent Food Packaging Applications: Recent Advances and Developments. Polymers 12(10):2209. https://doi.org/10.3390/polym12102209
Ma Q, Wang L (2016) Preparation of a visual pH-sensing film based on tara gum incorporating cellulose and extracts from grape skins. Sens Actuators B Chem 235:401-407. https://doi.org/10.1016/j.snb.2016.05.107
Mangaraj S, Yadav A, Bal L. M, Dash S, Mahanti N. K (2019) Application of biodegradable polymers in food packaging industry: a comprehensive review. J Packag Technol Res 3(1):77-96.https://doi.org/10.1007/s41783-018-0049-y
Merz B, Capello C, Leandro G. C, Moritz D. E, Monteiro A. R, Valencia G. A (2020) A novel colorimetric indicator film based on chitosan, polyvinyl alcohol and anthocyanins from jambolan (Syzygium cumini) fruit for monitoring shrimp freshness. Int J Biol Macromol 153:625-632. https://doi.org/10.1016/j.ijbiomac.2020.03.048
Mokhena T. C, John M. J (2020) Cellulose nanomaterials: New generation materials for solving global issues. Cellulose 27(3):1149-1194. https://doi.org/10.1007/s10570-019-02889-w
Moradi M, Tajik H, Almasi H, Forough M, Ezati P (2019) A novel pH-sensing indicator based on bacterial cellulose nanofibers and black carrot anthocyanins for monitoring fish freshness. Carbohydr Polym 222:115030. https://doi.org/10.1016/j.carbpol.2019.115030
Müller P, Schmid M (2019) Intelligent packaging in the food sector: A brief overview. Foods 8(1):16. https://doi.org/10.3390/foods8010016
Musso Y. S, Salgado P. R, Mauri A. N (2019) Smart gelatin films prepared using red cabbage (Brassica oleracea L.) extracts as solvent. Food Hydrocoll 89:674-681. https://doi.org/10.1016/j.foodhyd.2018.11.036
Nasiri M, Ashrafizadeh S (2010) Novel equation for the prediction of rheological parameters of drilling fluids in an annulus. Ind Eng Chem Res 49(7):3374-3385. https://doi.org/10.1021/ie9009233
Nguyen L. H, Naficy S, McConchie R, Dehghani F, Chandrawati R (2019) Polydiacetylene-based sensors to detect food spoilage at low temperatures. J Mater Chem C 7(7):1919-1926. https://doi.org/10.1039/c8tc05534c
Pourjavaher S, Almasi H, Meshkini S, Pirsa S, Parandi E (2017) Development of a colorimetric pH indicator based on bacterial cellulose nanofibers and red cabbage (Brassica oleraceae) extract. Carbohydr Polym 156: 193-201. https://doi.org/10.1016/j.carbpol.2016.09.027
Prietto L, Mirapalhete T. C, Pinto V. Z, Hoffmann J. F, Vanier N. L, Lim L.-T, Guerra Dias A.R, da Rosa Zavareze E (2017) pH-sensitive films containing anthocyanins extracted from black bean seed coat and red cabbage. Lwt 80:492-500. https://doi.org/10.1016/j.lwt.2017.03.006
Rakić V, Rinnan Å, Polak T, Skrt M, Miljković M, Ulrih N. P (2019) pH-induced structural forms of cyanidin and cyanidin 3-O-β-glucopyranoside. Dyes and Pigments 165:71-80. https://doi.org/10.1016/j.dyepig.2019.02.012
Reid MS, Villalobos M, Cranston ED (2017) Benchmarking cellulose nanocrystals: from the laboratory to industrial production. Langmuir 33(7):1583-1598.
Sani M. A, Tavassoli M, Hamishehkar H, McClements D. J (2021) Carbohydrate-based films containing pH-sensitive red barberry anthocyanins: Application as biodegradable smart food packaging materials. Carbohydr Polym 255:117488. https://doi.org/10.1016/j.carbpol.2020.117488
Segal L, Creely J. J, Martin Jr A, Conrad C (1959) An empirical method for estimating the degree of crystallinity of native cellulose using the X-ray diffractometer. Text Res J:29(10):786-794. https://doi.org/10.1177/004051755902901003
Sun L, Sun J, Chen L, Niu P, Yang X, Guo Y (2017) Preparation and characterization of chitosan film incorporated with thinned young apple polyphenols as an active packaging material. Carbohydr Polym 163: 81-91. https://doi.org/10.1016/j.carbpol.2017.01.016
Sun X, Wu Q, Zhang X, Ren S, Lei T, Li W, Xu G, Zhang Q (2018) Nanocellulose films with combined cellulose nanofibers and nanocrystals: tailored thermal, optical and mechanical properties. Cellulose 25(2):1103-1115. https://doi.org/10.1007/s10570-017-1627-9
Vedove T. M, Maniglia B. C, Tadini C. C (2021) Production of sustainable smart packaging based on cassava starch and anthocyanin by an extrusion process. J Food Eng 289:110274. https://doi.org/10.1016/j.jfoodeng.2020.110274
Wei, Y.-C, Cheng, C.-H, Ho, Y.-C, Tsai, M.-L, Mi, F.-L (2017) Active gellan gum/purple sweet potato composite films capable of monitoring pH variations. Food Hydrocoll 69:491-502. https://doi.org/10.1016/j.foodhyd.2017.03.010
Weston M, Phan M. A. T, Arcot J, Chandrawati R (2020) Anthocyanin-based sensors derived from food waste as an active use-by date indicator for milk. Food Chem 326:127017. https://doi.org/10.1016/j.foodchem.2020.127017
Yam K. L, Takhistov P. T, Miltz J (2005) Intelligent packaging: concepts and applications. J Food Sci 70(1):R1-R10. https://doi.org/10.1111/j.1365-2621.2005.tb09052.x
Yao X, Hu H, Qin Y, Liu J (2020) Development of antioxidant, antimicrobial and ammonia-sensitive films based on quaternary ammonium chitosan, polyvinyl alcohol and betalains-rich cactus pears (Opuntia ficus-indica) extract. Food Hydrocoll 106:105896. https://doi.org/10.1016/j.foodhyd.2020.105896
Yong H, Liu, J, Qin, Y, Bai, R, Zhang, X, & Liu, J (2019) Antioxidant and pH-sensitive films developed by incorporating purple and black rice extracts into chitosan matrix. Int J Biol Macromol 137:307-316. https://doi.org/10.1016/j.ijbiomac.2019.07.009
Yousefi H, Su H.-M, Imani S. M, Alkhaldi K, M. Filipe C. D, Didar T. F (2019) Intelligent food packaging: A review of smart sensing technologies for monitoring food quality. ACS sensors 4(4):808-821. https://doi.org/10.1021/acssensors.9b00440
Yousuf B, Gul K, Wani A. A, Singh P (2016) Health benefits of anthocyanins and their encapsulation for potential use in food systems: a review. Crit Rev Food Sci Nutr 56(13):2223-2230. https://doi.org/10.1080/10408398.2013.805316
Yun D, Cai H, Liu Y, Xiao L, Song J, Liu J (2019) Development of active and intelligent films based on cassava starch and Chinese bayberry (Myrica rubra Sieb. et Zucc.) anthocyanins. RSC adv 9(53):30905-30916. https://doi.org/10.1039/C9RA06628D
Zhang J, Zou X, Zhai X, Huang X, Jiang C, Holmes M (2019) Preparation of an intelligent pH film based on biodegradable polymers and roselle anthocyanins for monitoring pork freshness. Food Chem 272:306-312. https://doi.org/10.1016/j.foodchem.2018.08.041
Zhang K, Huang T.-S, Yan H, Hu X, Ren T (2020) Novel pH-sensitive films based on starch/polyvinyl alcohol and food anthocyanins as a visual indicator of shrimp deterioration. Int J Biol Macromol 145:768-776. https://doi.org/10.1016/j.ijbiomac.2019.12.159
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SynopsisThe develop halochromic CNC/NFC films containing anthocyanins provide a sensitive way for monitoring the freshness of packaged seafood products.