Physico-chemical properties of ϒ-irradiated cassava starches
The moisture content of untreated and ϒ-irradiated cassava starches was observed to be 7.87 %, 7.37 %, 6.71 % and 6.37 % for 0, 5, 7.5 and 10 kGy is given in Table 1. Similar result showed by Gani et al., 2012; Adzahan et al., (2009), they reported that the moisture content was decreased as the doses increased in the study of lotus stem and various starch (wheat, sago and tapioca). Production of free radicals and high energy due to irradiation cleaved the glycosidic bond thus results large molecule convert into small molecules of starch. In present study, showed that the moisture content was decreased with increasing gamma-irradiated doses due to the adsorption desorption process. The study showed that the hygroscopicity of the cassava starch lowered down due to increasing radiation doses. The highest fat content was observed for untreated starch (0.47 %) and the lowest was found in 10 kGy (0.19 %). Similar trend showed in wheat and chickpea starch by Bashir et al., 2016; Bashir and Manjeet Aggarwal, 2017. Present study showed that the fat value was decreased with increasing the irradiation doses because due to irradiation the molecular structure was changed and to disrupt the double bonds of fatty acids (Yalmaz and Gecgel, 2007). Protein content was found in the range between 0.07-0.17 % from 0 to 10 kGy. The protein was increased when the irradiation doses was increased. 10 kGy had highest protein content whereas 0 kGy found to be lowest. When the starch was treated with ϒ-irradiation so it can disintegrate the non-covalent bonds (hydrogen and disulfide bond) due to the generation of free radicals which may loss of structural and conformational integrity of protein. Bashir et al., 2016 reported the protein content was increased in wheat starch as the doses increased in the range between 0.39 to 0.40 % from 0 to 10 kGy. The fibre content ranged 0.20 %, 0.25 %, 0.27 %, 0.32 % from 0 to 5 kGy. The fibre content was increases as the irradiation doses were increased. (Grundy et al., 2016) has been reported that the higher level of fibre has tendency to lose moisture during drying due to weak water-fibre interaction. When the fibre is present along with starch which reveal that the limited amount of water available in the food system. The ash content for 0 to 10 kGy ranged between 0.057-0.074 %. Ash was slightly increased as the irradiated doses increased. Khan et al., 2018 reported the same trend in peach sample. Similar result shown in ϒ-irradiated wheat starch by (Bashir et al., 2016). The composition of ash in cassava is influenced by minerals content in the soil has been reported by Niba et al., (2001). Ash content is a measure of inorganic impurities, it represents the total mineral contents which is used as a measurement of quality of starch in the food industry. The pH of the samples for 0 to 10 kGy ranged between 4.16 to 3.23. Similar result observed in lotus starch and rice starch has been reported by Gani et al., (2012); Kumar et al., (2017). Similar results were observed by another researcher Wani et al., (2014); Verma et al., (2018). Due to ϒ-irradiation the starch molecule could be broken into carboxylic acid (Ghali et al., 1979). Present study revealed that the chemical structure of the starch molecule was changed so the pH may slightly affect. The amylose content of cassava starch is shown in Table 1. AAC increased with an increase in irradiation dose. For 0 kGy amylose was found to be 20.85 % which increased to 22.56 % for 10 kGy starch. The amylose content is the basis of classifying starches into waxy, semi-waxy, normal/regular and high-amylose types when amylose content is 0-2%, 3-15% 20-35%, and higher than 40% of the total starch, respectively (Tester et al., 2004; Morante et al., 2016; Botticella et al., 2018). Increasing the amylose content by ϒ-irradiation may defined the degradation of the amylopectin structures/branches and also the production of low molecular weight fractions (Chung et al., 2009; Chung and Liu, 2010). Similar results for the increased amylose content were reported for corn (Roushidi et al., 1983); rice (Bao et al., 2005); potato (Singh et al., 2010), bean (Rayas-Duarte and Rupnow, 1993). The cassava starch has been used in the production of fish cracker due to their good expansion property (Adzahan et al., 2009). The amylose content is an important aspect for food processing because it affects the gelatinization and retrogradation properties.
Table 1: Proximate composition of the cassava starches
Parameters
|
Irradiation dose (kGy)
|
Untreated
|
5.0
|
7.50
|
10.0
|
Moisture (%)
|
7.87±0.06
|
7.37±0.10
|
6.71±0.05
|
6.37±0.08
|
Fat (%)
|
0.47±0.03
|
0.35±0.01
|
0.28±0.02
|
0.19±0.01
|
Protein (%)
|
0.07±0.01
|
0.08±0.01
|
0.12±0.01
|
0.17±0.02
|
Fibre (%)
|
0.20±0.01
|
0.25±0.01
|
0.27±0.02
|
0.32±0.01
|
Amylose (%)
|
20.85±0.11
|
21.32±0.01
|
21.83±0.03
|
22.56±0.01
|
Ash (%)
|
0.057±0.001
|
0.067±0.001
|
0.068±0.002
|
0.074±0.003
|
pH
|
4.16±0.07
|
4.08±0.02
|
3.74±0.06
|
3.23±0.03
|
Carbohydrate (%)
|
91.32±0.00
|
91.86±0.01
|
92.52±0.01
|
92.87±0.00
|
Energy (kcal)
|
369.85±0.005
|
370.98±0.01
|
374.46±0.011
|
373.93±0.01
|
Flow properties
he flow properties of the cassava starch is presented in Table 2. The bulk density of the samples was observed for 0 kGy (0.554 g/cc), 5 kGy (0.557 g/cc), 7.5 kGy (0.557 g/cc) and 10 kGy (0.555 g/cc). The tapped density of a powder represents its random dense packing. Present study showed that there were no significant changes in bulk and tapped density with increasing the doses it indicates that ϒ-irradiation didn’t produce any damage to the polymer. But tapped density of the starches was higher than the bulk density ranged 0.831 g/cc, 0.831 g/cc, 0.835 g/cc, 0.831 g/cc (T3) for 0, 5, 7.5 and 10 kGy doses. This is due to some factors viz size, solid density, geometry and surface properties of the flour material (Iwe et al., 2016). Higher tapped density is suitable to the packaging and the greater amount of material is packed with in a constant unit volume (Toan, 2018).
Porosity of untreated and irradiated cassava starch were ranged in between 32.97-33.24 % respectively. Porosity is a measure of void space present in a material. Porosity is one of the main indicators that determines the quality of bakery products and characterizes their structure, volume and level of digestibility. The porous structure is most characteristic of bakery products and determines their quality (Petrusha et al., 2018).
Table 2: Density and flow properties of cassava starches
Parameters
|
Irradiation dose (kGy)
|
0
|
5
|
7.5
|
10
|
Bulk density (g/cc)
|
0.554±0.003
|
0.557±0.001
|
0.557±0.003
|
0.555±0.000
|
Tapped density (g/cc)
|
0.831±0.008
|
0.831±0.002
|
0.835±0.001
|
0.831±0.001
|
Porosity (%).
|
32.97±0.37
|
32.99±0.30
|
33.34±0.49
|
33.24±0.07
|
Carr’s index (%)
|
32.97±0.37
|
32.99±0.30
|
33.34±0.49
|
33.24±0.07
|
Hausner ratio
|
1.492±0.008
|
1.492±0.006
|
1.50±0.011
|
1.498±0.001
|
Carr’s index and Hausner’s ratio are a measure of the flowability and compressibility of a powder (Staniforth 1996). The Carr’s percentage indicates the aptitude of a material to diminish in volume while Hausner’s index shows the antiparticle friction. The values of C.I for untreated and irradiated cassava starch were ranged in between 32.97-33.24 % which was higher than the 15 % (for good flowability). It means untreated and irradiated cassava starch indicate that poor flowability. The score of Carr’s index (%) of 5–10, 12–16, 18–21 and 23–28 represent excellent, good, fair and poor flowability (Falade, 2019). Hausner ratio of the samples was found to be higher than 1.25 (for good flow). It seems that the Hausner ratio indicates that poor flow property of both the starches. Hausner value less than 1.25 indicates good flow and greater than 1.25 indicates poor flow (Staniforth (1996).
Color Quest
The color values of cassava starch are presented in Table 3. The “L” value of the flour ranged from 97.53-96.83, The highest value was found for 0 kGy whereas lowest value found in 10 kGy irradiated starch. Present study showed that the lightness of the cassava flour is closed to whiteness. The a* value for 0 kGy, 5 kGy, 7.5 kGy and 10 kGy were found to be -0.46, -0.31, -0.27 and -0.25 respectively. The a* value of the samples was decreased as the doses was increased it indicate the green color was fell down as the doses increased. b* value was ranged in between 92.96 -96.43 for untreated and irradiated starch. It showed that there was the enhancement of the yellow color when the doses were increased. Similar trend showed for “L” and “b” have been reported for corn starch (Kang et al., 1999), sago starch (Pimpa et al., 2007), chestnut starch (Correia et al., 2012), bean starch (Sofi et al., 2013) and Indian horse chestnut (Wani et al., 2014). The effect of γ- irradiation changed the color of cassava starch this alteration may be due to the Maillard reaction between sugars and protein or transformation of residual phenolics (Lee et al., 2003; Sokhey and Hanna, 1993).
Table 3: Color quest of the cassava starches
Parameters
|
Irradiation dose (kGy)
|
0
|
5
|
7.5
|
10
|
L*
|
94.05±0.04
|
91.58±0.03
|
85.48±0.62
|
81.40±0.52
|
a*
|
-0.93±0.01
|
-0.64±0.00
|
-0.38±0.00
|
-0.15±0.01
|
b*
|
9.14±0.04
|
12.12±0.02
|
12.18±0.01
|
12.28±0.11
|
Whiteness index
|
82.33±0.41
|
79.60±0.78
|
78.16±0.20
|
74.43±0.30
|
Functional Properties of Cassava starches
Water and Oil absorption capacity: The WAC and OAC of starch samples are given in Table 4. WAC increased from 1.72 to 1.97 g/g of starch on increasing the dose from 0 to 10 kGy. High WAC represent the presence of the minerals especially high phosphorus. The WAC increased with increased the doses of irradiation due to the degradation of the starch into simple sugars (like glucose, dextrin etc.) which had higher affinity for water than starch (Wani et al., 2014). Similar results showed in ϒ-irradiated lotus, kidney bean, broad bean starch reported by (Gani et al., 2012; Gani et al., 2013; Sofi et al., 2013). Similarly, Verma et al., 2018 has been reported for potato starch WAC increased from 84.10 to 93.24 g/g of starch on increasing the dose from 0 to 20 kGy. The high WAC is useful in the preparation of the soups, gravies and also to make food items like bread, sausages etc. WAC deals with the size, shape, proteins, lipids, pH and salt (Ezeocha et al., 2011), it plays a crucial role in the function of protein in various food items like in soups, bread, making dough and in bakery products (Adeyeye and Aye, 1998).
The OAC was also increased with increased doses of the untreated and cassava starch ranged in between 1.80-1.99 g/g respectively. OAC shows the binding capacity between fat and protein for the manufacturing of the food products. When starch was treated with irradiation which may cause the denaturation of protein and disintegrate the physical structure of amylopectin chain and unfolding of proteins (Abu et al., 2006; Sofi et al., 2013) therefore, the starch had the ability to entrap/bind the oil. Similar results have been reported by (Chandra et al., 2015; Bhat et al., 2016).
Table 4: Functional properties of the cassava starches
Parameters
|
Irradiation dose (kGy)
|
0
|
5
|
7.5
|
10
|
WAC (g/g)
|
1.72±0.006
|
1.80±0.003
|
1.86±0.008
|
1.97±0.002
|
OAC (g/g)
|
1.80±0.004
|
1.86±0.008
|
1.95±0.011
|
1.99±0.399
|
EA (%)
|
26.02±1.55
|
37.24±1.08
|
38.79±1.58
|
50.25±1.15
|
ES (%)
|
63.07±1.53
|
55.02±0.91
|
52.55±1.18
|
48.14±0.915
|
FC (%)
|
0.87±0.02
|
0.84±0.01
|
0.86±0.01
|
0.87±0.02
|
FS (%)
|
93.18±0.01
|
93.14±0.01
|
93.17±0.01
|
93.16±0.02
|
GT (°C)
|
62.39±0.31
|
62.28±0.22
|
62.26±0.20
|
62.03±0.15
|
LGC (%)
|
8%
|
6%
|
6%
|
4%
|
Emulsion activity and stability: The emulsion activity and emulsion stability for untreated and irradiated starches are presented in Table 4.4. Emulsifying activity is defined as the maximum amount of oil that can be emulsified by a fixed amount of the protein, while stability of the emulsion is defined as the rate of phase separation in water and oil during storage of the emulsion (Pearce and Kinsella, 1978). The emulsion activity for 0, 5, 7.5 and 10 kGy treated starch were found to be 26.02 %, 37.24 %, 38.79 and 50.25 % respectively with increasing the doses. The emulsion stability was gradually decreased with increased the doses from 0 to 10 kGy ranged between 63.07-48.14 % respectively. Present study revealed that the properties of emulsion activity and stability were changed after irradiation. The increment of the emulsion activity and the reduction of the emulsion stability might be due to the disintegration and aggregated the protein molecules when the starch was treated with the dosage of irradiation. In various studies showed that a good emulsifier acts as a barrier against lipid oxidation. Emulsion properties is an important aspect in the application of food industries like the formulation of agricultural products, use in coating etc.
Foam capacity and stability: The FC and FS of the cassava starch are presented in Table 4. The FC for 0, 5, 7.5 and 10 kGy were found 0.87 %, 0.84 %, 0.86 and 0.87 % respectively. The FC refers to the surface tension and interfacial area created by whipping the protein. The FC is corelated to the protein, the foam capacity increased when protein found to be high. In current study there is slightly decreased in foam capacity was observed in 5 and 7.5 kGy treated starch. FC were found to be 93.18 %, 93.14 %, 93.17 % 93.16 from 0 to 10 kGy doses. In the present study revealed that there were no significant changes after irradiation some minor decrements were shown in both foam capacity and foam stability. Actually, this is depended on the nature of the protein, when starch was treated with the dosage of the radiation so the nature of the protein was changed that may leads to change the foaming properties. Similar results shown in irradiated sorghum grains and sesame seeds by Ahmed et al., (2018); Hassana et al., (2018). Foaming properties is an important aspect in food industry and to improve the appearance or to maintain the consistency of the food products such as ice cream, cake etc. Several researchers also stated that gamma radiation caused no significant changes in foaming stability (Pednekar et al., 2010; Bhat et al., 2008).
Gelatinization temperature and Least gelation concentration: The gelatinization temperature and least gelation concentration of the cassava starch are presented in Table 4. For untreated and irradiated starch, the gelatinization temperature was found in between 62.390 C to 62.030 C. Irradiation didn’t show any significant effect, it was slightly decreased as the doses increased. Gelatinization is corelated to the property of the amylose and amylopectin chain. It is deal with the loss of birefringence and the crystallinity due to the breakage of the double bond and enhancing the leaching property of the amylopectin due to irradiation by Adzahan et al., (2009); Donovan, (1979); Evans and Haisman, (1982). It is a process where the starch granules form suspension in cold water at lower temperature. When heated prior to the storage at low temperature so the cellulose wall of the starch rupture and results swollen bump into each other and absorbed water. For 10 kGy treated cassava starch had least LGC (4 %) while 0 kGy had 8 % LGC. It was observed that the LGC was decreased as increased in doses from 0 to 10 kGy. Lower LGC had good ability to form the gel which is used in various food items. The gelation properties of the cassava starch could enhance their utilization in food industry which is required for the formation of gel (Chinma et al., 2013). Improvement of gelation capacity will be advantageous in hastening the food product preparation (Bhat et al., 2008).
Swelling power and solubility index: Swelling and solubility index of the untreated and irradiated starches is presented in Table 5. amylopectin plays a vital role for the swelling power, it means to trap the starch and retain the water within the structure, before and during gelatinization (Whistler and Daniel, 1985). The swelling power for 0, 5, 7.5 and 10 kGy treated cassava starch ranged 2.21-5.15 g, 2.74-5.36 g, 2.84-5.56 g, and 2.94-5.86 respectively at 50 to 900 C. The swelling power was increased with increasing temperature as well as radiation doses (0-10 kGy). The highest value was at 900 C for 10 kGy (2.94 g) while the lowest value observed at 500 for 0 kGy (2.21 g) treated starches. This variation showed due to the depolymerization of the amylopectin chain in the starch granules during irradiation and showed degradation of the starch granules chain at higher temperature with gelatinized the starch and denatured the protein matrix which may prevent the diffusion of water in to matrix of starch (Kumar et al., 2017). It plays an important role or to full fill the requirement of the food industry. It ascribes the classification of the starch from different botanical origin which indicate different swelling power at different temperature (Abioye et al., 2017). High swelling power showed the digestibility of starch is high and the usage of starch in a range of dietary application (Nuwamanya et al., 2010). Similar result has been reported by (Wani et al., (2014); Bashir and Aggarwal (2017); Verma et al., 2018, Jagannadham et al., 2014).
Solubility index deals with the degradation of the starch which is corelated to the amylose and amylopectin. The solubility of the samples was increased with the temperature along with doses. At temperature 90°C, swelling index increased at all doses of gamma irradiation. Similar results for increased solubility of sweet potato, cowpea and potato starch were demonstrated by (Ocloo et al., 2011; Verma et al., 2019). Similar trends followed by (Chung and Liu, 2010; Sofi et al., 2013). Increased in the solubility of the starch with the amylose due to the disruption of the starch granules because there is the establishment of H-bond with water when it is released in the solution therefore, amylose content was leached out.
Table 5: Swelling and Solubility index of the cassava starches
Parameters
|
Irradiation dose (kGy)
|
0
|
5
|
7.5
|
10
|
Swelling Power (g)
|
50° C
|
2.21±0.041
|
2.74±0.041
|
2.84±0.043
|
2.94±0.027
|
60° C
|
3.04±0.023
|
3.23±0.037
|
3.43±0.027
|
3.84±0.038
|
70° C
|
3.84±0.038
|
4.03±0.019
|
4.48±0.075
|
4.56±0.033
|
80° C
|
4.74±0.014
|
4.86±0.027
|
4.96±0.024
|
5.06±0.027
|
90° C
|
5.15±0.039
|
5.36±0.027
|
5.56±0.026
|
5.86±0.024
|
Solubility Index (g)
|
50° C
|
0.26±0.005
|
0.36±0.005
|
0.41±0.005
|
0.57±0.005
|
60° C
|
0.65±0.005
|
0.78±0.005
|
1.20±0.011
|
1.55±0.015
|
70° C
|
0.77±0.010
|
1.05±0.005
|
1.15±0.040
|
1.77±0.015
|
80° C
|
0.86±0.005
|
1.08±0.052
|
1.14±0.046
|
2.05±0.025
|
90° C
|
0.96±0.005
|
1.86±0.005
|
1.88±0.020
|
2.15±0.020
|
Syneresis: Syneresis is the separation of liquid from a gel its values depend on the storge time period. Syneresis of the untreated and irradiated starch is presented in Table 6 and was measured up to 120 h of storage. Syneresis was increased during storage period for 0, 5, 7.5, 10 kGy treated starch were ranged in between 1.94%-63.80 %, 1.74 %-61.64 %, 1.75 %-60.13 % and 1.34 %-59.04 % respectively. The highest value of syneresis was found for 10 kGy and lowest value found in untreated cassava starch at 120 h during storage at lower temperature. The syneresis value was increased with storage but decreased with the dosage. High syneresis value was found for 0 kGy ranged in between 1.94 % to 63.80 % while lowest value observed for 10 kGy treated starch ranged in between 1.34 % to 59.04 % during storage. Syneresis is the physical phenomenon in which the water is expelled and released from the starch gel (Karim et al., 2000). Syneresis occur due to the re-crystallization of the amylose in the granules of starch at low temperature in a loss of water from the gel structure (Arunyanart and Charoenrein, 2008). Similar results for syneresis were reported for irradiated kithul, rice, horse chestnut starch (Sudheesh et al., 2019; Ashwar et al., 2014); Wani et al., 2014). The increase in syneresis during storage could be attributed to the interaction of leached amylose chains which result in the release of water (Miles et al., 1985; Peera & Hoover, 1999; Wani et al., 2013) while decreased as the dosage increased due to the weak interaction of H-bond between amylose and amylopectin chain and to form simple sugar which have higher tendency for water.
Table 6: Syneresis (%) of the cassava starches
Time (h)
|
Irradiation dose (kGy)
|
0
|
5
|
7.5
|
10
|
0
|
1.94±0.02
|
1.75±0.03
|
1.74±0.03
|
1.34±0.04
|
24
|
55.96±0.16
|
54.55±0.42
|
53.07±0.97
|
51.77±0.51
|
48
|
59.50±0.18
|
56.96±0.12
|
56.29±1.08
|
55.33±1.40
|
72
|
59.98±0.18
|
57.92±0.09
|
57.57±0.24
|
56.80±0.25
|
96
|
60.80±1.84
|
60.63±0.02
|
59.50±0.17
|
58.48±0.04
|
120
|
63.80±0.15
|
61.64±0.56
|
60.13±0.02
|
59.04±0.06
|
Light transmittance
The effect of refrigerated storage on transmittance of untreated and irradiated starch gels is shown in Table 7. Transmittance is the fraction of incident light at a specified wavelength that passes through a sample. The light transmittance was decreased within increase in storage period at refrigeration temperature ranged in between 75.06-50.17, 75.66-51.22, 76.04-52.76 and 76.98-53.09 % from 0 to 10 kGy treated cassava starch. Light transmittance was increased as the dosage increased, ranged in between 75.66-76.98 %, 58.52-62.16 %, 61.24-62.89 %, 52.42-54.12 % and 50.17-53.09 kGy from 0 to 10 kGy. Similar result was observed in lotus starch, wheat starch, Indian beans, kithul irradiated starches (Gani et al., 2013; Bashir et al., 2016; Wani et al., 2010; Sudheesh et al., 2019). Present study suggested that the cassava starch could be used in the processing of jam, jellies confectionaries food items. Transparent gels can be used as carriers of active ingredients composed of oils, surfactants, vitamins, sunscreen agent and antioxidants in the formulation of multifunctional cosmetic gels (Comelles et al., 1992). Transmittance was increased due to disintegration of amylopectin, forming carboxyl group due to the production of free radicals, aggregation of amylose, intramolecular bonding and swollen granules when starch treated with irradiation starch these are the factors which are responsible for improving the starch gel clarity.
Table 7: Transmittance (%) of the cassava starches
Day (s)
|
Irradiation dose (kGy)
|
0
|
5
|
7.5
|
10
|
1
|
75.06±0.01
|
75.66±0.01
|
76.04±0.02
|
76.98±0.02
|
2
|
58.52±0.01
|
59.16±0.01
|
60.22±0.02
|
62.16±0.02
|
3
|
61.24±0.02
|
61.72±0.02
|
62.09±0.02
|
62.89±0.02
|
4
|
52.42±0.02
|
53.17±0.00
|
53.96±0.02
|
54.12±0.01
|
5
|
50.17±0.00
|
51.22±0.01
|
52.76±0.00
|
53.09±0.01
|
Scanning Electron Microscopy of cassava starches
The scanning electron microscopy of the untreated and irradiated starch is presented in fig 1. In present study showed the diameter/dimension of the granules which were calculated by using programing software, for untreated and irradiated starch granules showed same dimension of 10μ. The dimension of starch granules was stable after irradiation. Some regular, oblate, round shape distribution showed in untreated starch while some irregular, oval, polyhedral shape was observed in radiated starch. The scanning electron microscopy of the untreated and irradiated cassava starch revealed there is no fissure on the surface of the starch granules. As the doses increased it was observed that the shape of the granules was slightly changed it may be due to the clumping of the starch which indicate the aggregation of the starch due to the weak interaction between to starch-starch molecule (Singh et al., 2011) therefore, the amylose was leached out or to disintegrate the physical structure of the amylopectin chain and unfold the protein matrix (Abu et al., 2006; Sofi et al., 2013). Similar result showed in ϒ-irradiated oat, buckwheat, and potato starches has been reported by (Dar et al., 2018; Singh et al., 2011). Similar results for the chickpea starch were reported by Singh et al., 2004 and Elfaki et al., 1983.