Determination of some quality properties of ice cream fermented with kefir culture and flavored with mint (Menthaspicata L.)

doi:10.21203/rs.3.rs-3964946/v1

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Research Article

Determination of some quality properties of ice cream fermented with kefir culture and flavored with mint (Menthaspicata L.)

https://doi.org/10.21203/rs.3.rs-3964946/v1

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Kefir is a healthy fermented dairy product, while ice cream is one of the most consumed dairy products. In this study, the mint flavor was added in different proportions (0 (KI), 0.2% (KIM2), 0.4% (KIM4), and 0.6% (KIM6)) to ice cream fermented with kefir culture. The study investigated the microbiological, antioxidant, thermal, rheological, textural, compositional, and sensory properties of kefir ice cream samples during 45-day storage. The lactic bacilli, lactic cocci, and Leuconostoc counts of samples were around 8 log CFU/g, while the yeast counts were less than 4 log CFU/g. The addition of mint flavor did not have a negative effect on the microbiological properties of the samples. Values of IC₅₀ and total phenolic content (except for samples KIM2 and KIM6) values did not differ significantly among samples and during storage (P<0.05). The pH and melting rate values of the samples decreased with the addition of mint flavor, while acidity values increased. Sample KI usually had the lowest values for thermal properties. The overrun, a*, WI, and hardness values of the samples decreased based on the mint flavor concentration, whereas the viscosity (at 50 rpm) and consistency coefficient values increased. Samples KI and KIM2 were scored higher than other samples for all sensory properties. As a result, 0.2% mint flavored kefir ice cream could be produced.

Probiotic ice cream

antioxidant activity

thermal properties

mint aroma

microbiota

Ice cream which has a wide range of tastes, high commercial potential, and acceptable sensory properties, is a frozen dairy product known and consumed by people of all ages. Probiotic cultures and healthy ingredients can be used in ice cream formulations. Therefore, ice cream has a potential that can be diversified and improved (Januário et al. 2018). Ice cream is a suitable medium for probiotic bacteria (Guler-Akin et al. 2016). Many lactic acid bacteria and fungi can be used in probiotic ice cream (Di Criscio et al. 2010).

Kefir is a fermented dairy product that contains a variety of microorganisms, including lactic acid bacteria, acetic acid bacteria, and yeast. The production of kefir involves using kefir grains and cultures (Ürkek et al. 2011; Gul et al. 2015). Kefir has numerous health benefits, including antimicrobial, antitumor, antioxidant, antimutagenic, cholesterol-lowering, immune system-stimulating, and anti-apoptotic effects (Hertzler and Clancy 2003). It is considered a probiotic dairy product due to its probiotic bacteria content (Gul et al. 2015). Kefir is a drinkable product with a slightly sour, refreshing taste (Otles and Cagindi 2003; Yilmaz-Ersan et al. 2018).

Different ingredients can be added different ingredients to balance the flavor of probiotic ice cream (Hanafi et al. 2022). Mint (Menthaspicata L.) belongs to the Labiatae family, a perennial and aromatic plant (Baliga and Rao 2010). The essential oil obtained from mint is commonly used as a flavoring agent in tea, ice cream, toothpaste, chewing gum, and confectionery formulations (Verma et al. 2018). Mint chocolate chip ice cream is one of the most popular ice cream flavors. Some of the countries with the highest consumption of mint chocolate chip ice cream are Ecuador, Madagascar, New Zealand, Russia, and Tunisia (Anonymous 2021).

The objectives of the research were a) to determine the effects of mint and storage on microbiological, some physicochemical, sensory properties, and antioxidant activity b) to investigate the thermal and rheological properties of mint chocolate chip ice cream.

Material

Raw milk was purchased from the Şiran Dairy Products Plant in Gümüşhane, Turkey. The characteristics of the raw milk are shown in Table 1. Kefir starter culture was obtained from CHOOZIT® Kefir DC (LYO 1000 l, Danisco, Germany). Skimmed milk powder was provided by Aynes Dairy Products Co. (Turkey), and mint flavor by Aromsa Co. (İstanbul, Turkey). The stabilizer (salep), emulsifier, and sugar were provided by local markets.

Table 1

The properties of raw milk
Parameters	Raw milk
Fat (%)	3.4
Total solids (%)	8.5
Specific gravity (g/ml)	1.0288
Protein (%)	3.1
Lactose (%)	4.6
Ash (%)	0.6
Freezing point ℃	-0.539
Conductivity (mS/cm)	5.0

Ice cream production

The ice cream mix recipe was adjusted as milk 72%, sugar 17%, butter 6.25%, emulsifier %0.2, stabilizer (salep) 0.2%, and skimmed milk powder 3.85%. The mixture was pasteurized at 85 ℃ for 25 s. then cooled to 25 ℃ and divided equally into four glass containers. Kefir starter culture was added to each part and kept at 25 ℃ for 24 h for fermentation. The fermented mixtures were kept at + 4 ℃ (refrigerator) for one night. A mint flavor was added before an ice cream maker (Sage BCI 600 BSS., Australia) was used to make kefir ice cream (KIC). The samples were coded as no mint KI, 0.2% mint KIM2, 0.4% mint KIM4 and 0.6% mint KIM6.

Methods

Microbiological analyses

The lactic bacilli, lactic cocci, Leuconostoc, and yeast counts of the samples were determined to assess the microbiological properties of the samples. The analyses were performed using decimal serial dilutions. Lactic bacilli on De Man-Rogosa-Sharpe agar (Biolife, Italy) and lactic cocci on M17 agar (Condalab, Madrid, Spain) were determined anaerobically at 30°C for 48–72 h and anaerobically at 30°C for 72 h, respectively. Leuconostoc counts were determined on Mayeux, Sandine & Elliker (MSE; Condalab, Madrid, Spain) agar aerobically at 22°C for 120 h (García Fontán et al. 2006). Dichloran-Rose Bengal Chloramphenicol agar (DRBC, Merck, Germany) for yeast colonies was used after incubation at 25°C for 5–7 days (Jarvis 1973).

Antioxidant activity

The extract of ice cream samples for DPPH free radical scavenging activity and TPC analysis was obtained with the method with some modifications according to Şengül et al. (Şengül et al. 2012).

Total phenolic content (TPC)

TPC values were determined by the colorimetric method described by Gülçin et al. (Gülçin et al. 2002). The prepared extract (10 mL) and 10 mL ethanol (90%, v/v) were placed in an orbital shaker and shaken for 30 min. One mL of the mixture, 46 mL of deionised water and 1 mL of Folin-Ciocalteu were placed in a glass jar and allowed to stand for 3 min at room temperature. 2% Na₂CO₃ (w/v; Merck, Germany) was added to the mixture and shaken at 210 rpm for 2 hours. The absorbance of the prepared mixture was determined using a visible spectrophotometer (DU 730 Beckman Coulter, Inc., Fullerton, CA) at 760 nm against blank samples. The results obtained were expressed as micrograms of gallic acid equivalents per milligram of sample (µg GAE/mg).

Scavenging activity on 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free radicals

0.06 mM DPPH (in ethanol v/v) was prepared. DPPH (2000 µL) and 100, 150, 200 and 250 µL extracts were transferred to flasks. The same amounts of extracts were transferred to another flask and then completed with absolute ethanol. This mixture was used as a blank. All mixtures were vortexed and kept in the dark for 30 min. The absorbance values of the samples were then measured using a visible spectrophotometer (DU 730 Beckman Coulter, Inc., Fullerton, CA) at 517 nm against the blank (Gülçin 2010). The IC50 values of the samples were calculated with the obtained linear regression using the absorbance values. The IC50 values were expressed as µg/ml.

Thermal measurements

The thermal properties of the ice cream samples were determined using a Differential Scanning Calorimetry (DSC) instrument (EXTAR DSC 7020, Hitachi High-Tech Corporation, Tokyo, Japan). Weighted (15 g) samples in aluminum pans were placed in the DSC. The instrument was standardized with mercury and indium. The analysis was performed as follows: (a) cooling to -80°C at 10°C/min; (b) heating between − 80 and − 40°C and tempering at the same temperatures for 30 min to allow maximum ice formation; (c) cooling to -80°C at 10°C/min and isothermal hold for 5 min; and (d) heating between − 80 and 20°C at 5°C/min (Blond 1994).

Proximate analyses

The total solids, ash, fat, protein, pH and titratable acid content of the ice cream samples were determined using gravimetric methods (AOAC 1990). The overrun ratio was measured using the method as defined by Akbari et al. (Akbari et al. 2016). Overrun values were calculated according to Equal.

$$\text{Overrun }\left(\text{%}\right)\text{= }\frac{\left(\text{weight of mix}\right)\text{-}\left(\text{weight of ice cream}\right)}{\text{weight of ice cream}}\text{×100}$$

To determine the first drop time, 25g of each sample was weighed and held on a wire mesh at 20°C. The fall time of the first drop was recorded in seconds (Güven and Karaca 2002). The amount of melted ice cream samples was determined every 10 min for 70 min. The melting rate was calculated by linear regression and expressed in g/min.

A colorimeter (Minolta Colorimeter CR-400, Osaka, Japan) machine was used for L*, a*, b*, the saturation (C*) and Hue angel (H°) values. The colorimetric measurements were performed in triplicate and with calibration at Y = 92.5, x = 0.3060, y = 0.3310. The white index (WI) was calculated according to method described by Kurt and Atalar (Kurt and Atalar 2018). The equation was below.

$$\text{WI=100-}\sqrt{{\text{(100-}{\text{L}}^{\text{*}}\text{)}}^{\text{2}}\text{+(}{{\text{a}}^{\text{*}}\text{)}}^{\text{2}}\text{+(}{{\text{b}}^{\text{*}}\text{)}}^{\text{2}}}$$

Viscosity measurements at 20 and 50 rpm were made using a Brookfield Viscometer Model DV-II (Stoughton, MA, USA). Rheological properties were determined using the power law model after measurements at 5, 10, 20, 50 and 100 rpm. The consistency coefficient (K, Pa.sⁿ) and the flow index (n) were calculated from the power law model. All viscosity values were determined using spindle no. 6. The power law model was calculated according to below the Equation.

$$\text{η=}{\text{K}\text{γ}}^{\left(\text{n}\text{-1}\right)}$$

η: apparent viscosity (Pa.s)

K coefficient consistency (Pa.sⁿ)

γ: shear rate (rpm)

n flow behaviour index

Instrumental Hardness

A texture analyzer (TA-XT plus Texture Analyzer Stable Micro Systems Ltd, Godalming, Surrey, UK) was used to measure the hardness of the samples. Hardness values were determined using probe no. P5 at -2°C and − 6°C. The instrument evaluation conditions for pre-test and test, post-test speed force and distance were 2 mm/s, 5 mm/s, 10 g and 10 mm respectively.

Sensory test

The sensory test of ice cream samples was rated by nine semi-trained panelists according to the hedonic scale. The ice cream samples were rated from worst 1 to best 9. The panelists were four women and five men aged between 20 and 40. The samples were evaluated in terms of color, rubbery texture, taste, melting in the mouth, resistance to melting and overall acceptability by the panelists (Meilgaard et al. 1999). The required ethical approval for the sensory test was obtained from the Research Ethics Committee of Gümüshane University (approval no. 2021/1 and date 04/02/2021).

Statistical analyses

All data were analyzed using the SPSS17 statistical software package. Significant differences were identified using one-way ANOVA analysis and Duncan's multiple comparison tests. The study was carried out in two replications. The pH, acidity, first drip time, melting rate, antioxidant activity, microbiological, and sensory analyses were conducted during 45 days of storage (2, 15, 30 and 45 days), while other analyses were carried out only at the beginning of storage.

Microbiological properties

Lactic bacilli, lactic cocci, Leuconostoc, and yeast counts of the ice cream samples are shown in Table 2. Lactic bacilli count of the samples were higher at the end of storage than at the beginning of storage except for sample KIM2, but the changes were not statistically significant (P > 0.05). Only on the 15th day of storage, the differences between the samples were statistically significant (P < 0.05). The number of lactic cocci of sample KI increased at the end of storage, whereas sample KIM4 decreased (P < 0.05). There were no significant differences between samples during storage in terms of lactic cocci and Leuconostoc counts (P > 0.05). The Leuconostoc counts of the samples increased at the 45th day of storage according to the second day of storage. Except for sample KIM4, the differences were not statistically significant (P > 0.05). Lactic bacilli, lactic cocci and Leuconostoc counts of all samples were > 8 log CFU/g (Table 2).

Table 2

Microbiological properties of the produced kefir ice creams using the mint aroma (log CFU/g)
Parameters	Storage (days)	KI	KIM2	KIM4	KIM6
Lactic bacilli	2	8.34 ± 0.26A,a	8.44 ± 0.10A,a	8.36 ± 0.07A,a	8.43 ± 0.22A,a
	15	8.29 ± 0.02A,ab	7.70 ± 0.07A,b	8.32 ± 0.07A,a	7.86 ± 0.42A,ab
	30	8.33 ± 0.12A,a	7.96 ± 0.12A,a	8.21 ± 0.24A,a	8.54 ± 0.33A,a
	45	8.56 ± 0.02A,a	7.95 ± 0.54A,a	8.43 ± 0.01A,a	8.51 ± 0.10A,a
Lactic cocci	2	8.68 ± 0.13A,a	8.71 ± 0.08A,a	8.71 ± 0.13A,a	8.68 ± 0.19A,a
	15	8.43 ± 0.00AB,a	8.17 ± 0.98A,a	8.87 ± 0.03A,a	8.26 ± 1.02A,a
	30	8.09 ± 0.20B,a	8.47 ± 0.03A,a	8.88 ± 0.12A,a	8.52 ± 0.61A,a
	45	8.72 ± 0.08A,a	8.01 ± 0.53A,a	8.32 ± 0.14B,a	8.49 ± 0.24A,a
Leuconostoc	2	8.35 ± 0.01A,a	8.36 ± 0.12A,a	8.38 ± 0.06C,a	8.47 ± 0.06A,a
	15	8.54 ± 0.53A,a	7.94 ± 1.33A,a	8.95 ± 0.14A,a	8.33 ± 0.90A,a
	30	8.63 ± 0.23A,a	8.32 ± 0.13A,a	8.79 ± 0.14AB,a	8.51 ± 0.69A,a
	45	8.83 ± 0.00A,a	8.63 ± 0.04A,a	8.61 ± 0.05BC,a	8.60 ± 0.21A,a
Yeast	2	4.01 ± 0.07A,a	3.95 ± 0.10AB,a	3.77 ± 0.08A,a	3.89 ± 0.17AB,a
	15	3.89 ± 0.09AB,a	4.00 ± 0.03A,a	3.99 ± 0.10A,a	4.20 ± 0.51A,a
	30	3.68 ± 0.13B,a	3.96 ± 0.04AB,a	3.97 ± 0.35A,a	3.83 ± 0.19AB,a
	45	3.91 ± 0.04AB,a	3.64 ± 0.21B,a	3.60 ± 0.14A,ab	3.27 ± 0.06B,b
Different capital letters (A, B, C, D) indicate statistical significant in the columns, while different small letters (a, b, c, d) indicate in the rows (P < 0.05). KI: kefir ice cream without mint aroma, KIM2: kefir ice cream containing 0.2% mint aroma, KIM4: kefir ice cream containing 0.4% mint aroma, KIM6: kefir ice cream containing 0.6% mint aroma,

O’Brien et al. (O’Brien et al. 2016) found that lactic bacilli, lactic cocci counts of traditionally and commercially produced frozen kefir samples decreased at the end of storage (day 30). They determined lactic bacilli counts to be 7.24 log CFU/mL (traditional) and 6.33 log CFU/mL (commercial), and lactic cocci counts to be 6.24 log CFU/mL (traditional) and 5.44 log CFU/mL (commercial) at the end of storage. Sarica and Coşkun (Sarica and Coşkun 2022) investigated some properties of frozen kefir samples prepared from cow’s and goat’s milk lactic bacilli, lactic cocci, and Leuconostoc counts during 45 days. They found a decrease in the number of lactic bacilli, lactic cocci, and Leuconostoc counts at the end of storage. The results obtained in the present study were not consistent with those reported by O’Brien et al. [24] and by Sarica and Coşkun [25] and were higher than their results at the end of storage.

The yeast counts of the samples ranged from 3.77 log CFU/g to 4.01 log CFU/g on the second day of storage, while at the end of storage they ranged from 3.27 log CFU/g to 3.91 log CFU/g (Table 2). All samples had lower yeast counts at the end of storage than on the 2nd day of storage (P < 0.05), except KIM4. At the end of storage, sample KIM6 had the lowest yeast count (3.27 log CFU/g). There were no noticeable differences observed between the samples during the remaining storage days, as per the statistical analysis (P > 0.05).O’Brien et al. [24] determined yeast counts between 8.83 log CFU/g (day 1) and 6.82 log CFU/g (day 30) in traditional samples, and 7.20 log CFU/g (day 1) and 4.38 log CFU/g (day 30) in commercial samples. Sarica and Coşkun [25] found a decrease during storage and at the end of storage was less than 2 log CFU/mL. Similarly, Köroğlu (Köroğlu 2015) and Al (Al 2018) found a decreasing yeast count in KIC samples at the end of storage. The results of the present study were lower than those reported by O’Brien et al. [24], while they were higher than those reported by Sarica and Coşkun [25], by Köroğlu (Köroğlu 2015) and by Al (Al 2018).

Kefir must not contain less than 7 log CFU/g of specific microorganisms and 4 log CFU/g according to legal requirements (Turkish Food Codex 2009; Codex Alimentarius Commission 2022). All KIC samples complied with the legal requirements for lactic bacilli, lactic cocci, Leuconostoc counts, but not for yeast counts.

Antioxidant activity

The DPPH radical scavenging activities of the samples were determined as IC50 values. There is an inverse relationship between DPPH radical scavenging activities and IC50 values. During the whole storage period, there was no significant difference in IC50 values between samples (P > 0.05; Table 3). At the end of storage, IC50 values ranged from 588.77 µg/mg to 697 µg/mg.

Table 3

Antioxidant capacity of the produced kefir ice creams using the mint aroma
Parameters	Storage (days)	KI	KIM2	KIM4	KIM6
DPPH (IC₅₀, µg/mg)	2	736.22 ± 72.03A,a	740.07 ± 146.47A,a	698.94 ± 112.31A,a	594.75 ± 239.20A,a
	15	565.81 ± 72.28A,a	547.98 ± 82.96A,a	544.07 ± 61.21A,a	515.59 ± 21.64A,a
	30	746.40 ± 99.77A,a	651.40 ± 3.49A,a	595.98 ± 29.01A,a	637.67 ± 129.28A,a
	45	588.77 ± 2.44A,a	697.55 ± 68.87A,a	644.76 ± 90.75A,a	629.65 ± 28.85A,a
TPC (µg GAE/mg)	2	75.54 ± 6.90A,a	71.88 ± 8.62B,a	71.88 ± 5.17A,a	88.95 ± 1.72AB,a
	15	76.76 ± 18.96A,a	67.00 ± 5.17B,a	76.76 ± 15.51A,a	86.51 ± 5.17AB,a
	30	95.04 ± 6.90A,a	87.73 ± 3.45A,a	95.04 ± 10.34A,a	103.57 ± 5.17A,a
	45	86.51 ± 1.72A,a	74.32 ± 12.07AB,a	88.95 ± 5.17A,a	77.98 ± 10.34B,a
Different capital letters (A, B, C, D) indicate statistical significant in the columns, while different small letters (a, b, c, d) indicate in the rows (P < 0.05). TPC: total phenolic components, DPPH: 2,2-diphenyl-1-picryl-hydrazyl. KI: kefir ice cream without mint aroma, KIM2: kefir ice cream containing 0.2% mint aroma, KIM4: kefir ice cream containing 0.4% mint aroma, KIM6: kefir ice cream containing 0.6% mint aroma,

The TPC values of the samples are shown in Table 3. Sample KIM2 had higher TPC values at the end of storage than at the beginning of storage, while sample KIM4 had a lower value at the end of storage (P < 0.05). Sample KIM6 had the highest TPC values except for the 45th day of storage. However, these differences were not statistically significant (P > 0.05).

Akca and Akpinar (Akca and Akpinar 2021b) found that the TPC and antioxidant capacity of ice cream containing sesame, pomegranate and grape seed oils were between 45.50-70.63 mg GAE/g and 23.31–37.43%, respectively. Amin et al. (Amin et al. 2023) determined TPC and DPPH values of ice cream made with chia seed oil to be 0.11–5.19 mg GAE/mL and 5.62–51.18%, respectively. They observed that TPC and DPPH values increased with increasing chia seed oil concentration.

The IC50 and TPC values of the mint flavor were 195.28 µg/mg and 392.46 µg GAE/mg, respectively. The mint flavor did not affect the IC50 and TPC values of the ice cream samples. This situation may have been caused by the lower amount of mint flavoring used.

Some quality parameters

KIC samples had the lowest pH values at the end of storage (Table 4). However, these changes were statistically significant only for samples KI (pH 4.67) and KIM4 (pH 4.92) (P < 0.045). Throughout the entire storage period, the KIM2 sample exhibited the highest pH values. The acidity values of the KIC samples showed no significant differences during the whole storage, except for sample KIM4 (P > 0.05). The acidity of sample KIM6 was lower than the other samples on the 2nd and 15th day of storage (P > 0.05). At the end of storage, the acidity values were between 0.68% and 0.82% (Table 4) and the differences among the samples were not significant (P > 0.05). Köroğlu [26] found the pH and acidity values of KIC samples to be between 5.85–6.13 and 0.25–0.26%, respectively, during 30 days of storage. Al [27] found that pH and acidity values of KIC samples changed between 5.51–6.38 and 0.18-036% during 90-day storage, respectively. The pH values obtained in the present study were lower than those reported by Köroğlu [26] and by Al [27], while the acidity values were higher.

Table 4

pH, acidity, first dripping and melting rate values of the produced kefir ice creams using the mint aroma
Parameters	Storage (days)	KI	KIM2	KIM4	KIM6
pH	2	4.85 ± 0.00B,b	4.97 ± 0.00A,a	4.73 ± 0.00B,d	4.77 ± 0.03A,c
	15	4.87 ± 0.01AB,b	4.97 ± 0.01A,a	4.74 ± 0.02B,c	4.77 ± 0.01A,c
	30	4.89 ± 0.01A,b	4.98 ± 0.04A,a	4.81 ± 0.02A,bc	4.79 ± 0.05A,c
	45	4.67 ± 0.02C,b	4.92 ± 0.08A,a	4.65 ± 0.01C,b	4.72 ± 0.01A,b
Acidity (% lactic acid)	2	0.77 ± 0.01A,b	0.77 ± 0.03A,b	0.77 ± 0.03AB,b	0.86 ± 0.00A,a
	15	0.78 ± 0.03A,ab	0.69 ± 0.08A,b	0.85 ± 0.07A,ab	0.90 ± 0.06A,a
	30	0.85 ± 0.03A,ab	0.79 ± 0.04A,b	0.90 ± 0.00A,a	0.85 ± 0.01A,ab
	45	0.82 ± 0.09A,a	0.68 ± 0.04A,a	0.70 ± 0.06B,a	0.82 ± 0.07A,a
First dripping time (sn)	2	2580.00 ± 0.00A,a	2850.00 ± 381.84A,a	3000.00 ± 169.71A,a	2640.00 ± 84.85A,a
	15	2970.00 ± 127.28A,a	2490.00 ± 42.43A,b	2880.00 ± 169.71A,a	2910.00 ± 42.43A,a
	30	3030.00 ± 212.13A,a	2610.00 ± 466.69A,a	2700.00 ± 84.85A,a	3150.00 ± 381.84A,a
	45	2850.00 ± 212.13A,a	2610.00 ± 721.25A,a	2550.00 ± 466.69A,a	2580.00 ± 254.56A,a
Melting rate (g/min)	2	0.59 ± 0.00B,c	0.86 ± 0.03A,a	0.79 ± 0.02A,b	0.87 ± 0.01A,a
	15	0.62 ± 0.05B,b	0.85 ± 0.03A,a	0.80 ± 0.04A,a	0.81 ± 0.01A,a
	30	0.80 ± 0.06A,a	0.74 ± 0.01B,ab	0.82 ± 0.03A,a	0.68 ± 0.03B,b
	45	0.79 ± 0.02A,a	0.63 ± 0.01C,b	0.66 ± 0.02B,b	0.65 ± 0.04B,b
Different capital letters (A, B, C, D) indicate statistical significant in the columns, while different small letters (a, b, c, d) indicate in the rows (P < 0.05). KI: kefir ice cream without mint aroma, KIM2: kefir ice cream containing 0.2% mint aroma, KIM4: kefir ice cream containing 0.4% mint aroma, KIM6: kefir ice cream containing 0.6% mint aroma.

Lactic acid bacteria have the importance of pH (decreasing) and acidity values (increasing) due to fermentation (Ranadheera et al. 2012; Sah et al. 2016). The lactic acid bacteria count increased at the end of storage (Table 2). The differences in lactic acid bacteria counts may have caused the changes in pH and acidity. The first dripping times and melting rates of the KIC samples are presented in Table 4. The differences in first dripping times were not statistically significant among the KIC samples (except at 15 days) and during storage (P > 0.05). The melting rates of the KIC samples containing mint flavor decreased significantly at the end of storage, while those of the control sample increased (P < 0.05). Kanca et al. (Kanca et al. 2023) investigated some properties of ice cream samples to which kefir was added at different rates. They found that the first dripping times and melting rates of the samples were lowest at 1920 s and 0.66 g/min, and highest at 2400 s and 0.80 g/min, respectively. The first dripping values reported by Kanca et al. (Kanca et al. 2023) were lower than ours and the melting values were similar. The low pH values have an important effect on the melting resistance of ice cream. Research has shown that the structure of proteins is affected by low pH values, which results in high melting resistance (Favaro-Trindade et al. 2007).

Thermal properties

The midpoint and offset temperatures of glass transition (T_g′) decreased as a function of mint flavor concentration, while the onset temperatures showed no significant (P > 0.05) changes (Table 5). The onset and midpoint temperatures of melting (T_m′) were highest for sample KI, while the offset temperatures did not change significantly among the samples (P > 0.05). Similarly, Ürkek (Ürkek 2021) determined glass transition and melting temperatures of ice cream samples containing a mixture of chia seed powder and salep between (-55.56 ℃)-(-37.77 ℃) and (-36.17)-( -26.33 ℃), respectively. Ertugay et al. (Ertugay et al. 2020) reported similar results when they investigated some properties of ice cream with added Kavılca fibre.

Table 5

Thermal properties of the produced kefir ice creams using the mint aroma
Parameters		KI	KIM2	KIM4	KIM6
T_g′ (glass transition temperature)	Onset °C	-53.96 ± 3.12a	-52.63 ± 0.14a	-54.93 ± 0.45a	-52.74 ± 1.21a
	Midpoint °C	-47.36 ± 0.22c	-47.75 ± 0.02b	-48.73 ± 0.01a	-48.84 ± 0.16a
	Offset °C	-41.33 ± 1.99b	-42.13 ± 0.64ab	-44.94 ± 0.17a	-43.44 ± 0.98ab
T_m′ (melting temperature)	Onset °C	-35.12 ± 1.01b	-37.78 ± 0.35a	-38.06 ± 0.48a	-38.89 ± 1.17a
	Midpoint °C	-32.02 ± 0.02b	-32.61 ± 0.97ab	-33.54 ± 0.07a	-33.36 ± 0.34ab
	Offset °C	-29.71 ± 0.04a	-28.79 ± 0.28a	-29.59 ± 0.58a	-28.58 ± 2.19a
Freezing point temperature, T_f (°C)		-14.10 ± 0.08a	-15.37 ± 0.96a	-14.98 ± 1.28a	-13.77 ± 1.99a
Heat of ice freezing, ΔH (J/g)		171.50 ± 34.65b	111.50 ± 4.95a	96.00 ± 5.66a	133.00 ± 4.24ab
Melting point temperature, T_m (°C)		3.07 ± 0.16b	1.30 ± 0.18a	2.44 ± 0.73ab	1.30 ± 0.60a
Heat of ice melting, ΔH (J/g)		190.00 ± 56.57a	134.50 ± 6.36a	147.50 ± 3.54a	142.00 ± 4.24a
Different small letters (a, b, c, d) indicate statistical significant in the rows (P < 0.05). KI: kefir ice cream without mint aroma, KIM2: kefir ice cream containing 0.2% mint aroma, KIM4: kefir ice cream containing 0.4% mint aroma, KIM6: kefir ice cream containing 0.6% mint aroma.

The freezing point (T_f) and melting point (T_m) temperatures were determined between (-13.77 ℃)-(-15.37 ℃) and 1.30–3.07℃, respectively (Table 5). Ice freezing values were lower in the mint flavored KIC samples than in the control sample. The heat of melting values showed irregular changes and these changes were not significant (P > 0.05). Similar results were reported by Ertugay et al. (Ertugay et al. 2020) and Kavaz Yuksel (Kavaz Yuksel 2015) who studied some characteristics of ice cream containing sloe berries. It was found that many factors such as water holding capacity, serum phase ratio, soluble matter rate, freezing ratio and protein interactions on T_g′, T_m′, T_f and T_m values of ice cream (Soukoulis et al. 2009). Changes in pH and acidity affected protein interactions (Kneifel et al. 1991; Soukoulis and Tzia 2008). The difference in thermal properties may have been caused by changes in pH and acidity due to microbial activity.

Proximate analysis

There were slight differences in the total solids, ash, fat, and protein values of the KIC samples (Table 6), but these were not significant (P > 0.05). Similarly, Kanca et al. (Kanca et al. 2023) found no statistical significance in the total solids, ash, fat and protein values of ice cream.

Table 6

Proximate composition of the produced kefir ice creams using the mint aroma
Parameters	KI	KIM2	KIM4	KIM6
Total solids (%)	36.81 ± 0.23a	37.01 ± 0.35a	37.01 ± 0.20a	37.23 ± 0.11a
Ash (%)	0.81 ± 0.00a	0.79 ± 0.03a	0.78 ± 0.00a	0.78 ± 0.01a
Fat (%)	10.00 ± 0.28a	10.30 ± 0.42a	10.10 ± 0.42a	10.90 ± 0.42a
Protein (%)	3.77 ± 0.26a	3.63 ± 0.04a	3.75 ± 0.11a	3.66 ± 0.45a
Overrun (%)	40.26 ± 0.95a	35.15 ± 0.76b	32.50 ± 0.77c	32.44 ± 0.95c
Viscosity at 20 rpm (cP)	12807.38 ± 1709.16a	13203.45 ± 2511.01a	14488.44 ± 729.54a	14554.92 ± 1773.43a
Viscosity at 50 rpm (cP)	6630.08 ± 721.37ab	6266.83 ± 219.44b	7614.35 ± 358.45a	7638.51 ± 244.46a
Consistency coefficient (K; Pa.sⁿ)	60.60 ± 11.15ab	54.46 ± 12.20b	57.29 ± 0.99ab	78.30 ± 1.00a
Flow behavior index (n)	0.41 ± 0.11a	0.48 ± 0.04a	0.48 ± 0.00a	0.40 ± 0.01a
R²	0.98 ± 0.01	0.92 ± 0.04	0.94 ± 0.01	0.99 ± 0.01
L*	97.04 ± 0.38a	96.46 ± 1.44a	97.76 ± 0.45a	97.31 ± 0.09a
a*	-0.91 ± 0.30a	-1.47 ± 0.63ab	-2.13 ± 0.00b	-2.15 ± 0.01b
b*	2.69 ± 0.08a	3.38 ± 1.93a	5.06 ± 0.33a	4.99 ± 0.27a
C*	2.84 ± 0.18a	3.68 ± 2.02a	5.49 ± 0.30a	5.43 ± 0.25a
H°	108.40 ± 5.37a	114.40 ± 3.54a	112.80 ± 01.27a	113.20 ± 0.99a
WI	95.90 ± 0.39a	94.61 ± 0.11b	94.06 ± 0.11b	93.94 ± 0.26b
Hardness (N)	106.19 ± 2.31a	102.36 ± 7.91a	69.23 ± 6.57b	42.19 ± 2.11c
Different small letters (a, b, c, d) indicate statistical significant in the rows (P < 0.05). KI: kefir ice cream without mint aroma, KIM2: kefir ice cream containing 0.2% mint aroma, KIM4: kefir ice cream containing 0.4% mint aroma, KIM6: kefir ice cream containing 0.6% mint aroma.

The overrun values of the samples decreased in the mint flavored KIC samples and the control sample had the highest overrun value (40.26%). Kanca et al. (Kanca et al. 2023) found the lowest overrun value in the control sample. Salem et al. (Salem et al. 2005) produced ice cream with Lb. acidophilus, B. bifidum, Lb. reuteri, Lb. gasseri and Lb. rhamnosus. They obtained the highest overrun value in the control sample. The results of the present study are in agreement with those reported by Salem et al. (Salem et al. 2005) but were not in harmony with those reported by Kanca et al. (Kanca et al. 2023). Many factors affect the overrun values of ice cream, such as the protein structure, acidity, and freezing point. Changes in the volume increase of ice creams containing microorganisms may be due to the use of different levels of acidity and cultures, which affect the freezing point and the structure of the protein (Salem et al. 2005). Fat globules, protein/emulsifier and production process affect overrun (Kurultay et al. 2010; Ürkek 2021).

The viscosity values at 20 and 50 rpm of the KI sample were lower than those of the mint flavored samples (Table 6). However, this difference was significant only at 50 rpm (P < 0.05). Salem et al. (Salem et al. 2005)d roğlu [26] reported that the control samples had lower viscosity than samples containing microorganisms. These findings are similar to our study.

The K values of the KIC samples decreased with the addition of 0.2% mint flavor and increased in the other samples (P < 0.05). Kanca et al. (Kanca et al. 2023) found that the K values of ice cream samples containing kefir changed significantly. The results reported by Kanca et al. (Kanca et al. 2023) were not coherent with the present study. All samples had n values between 0.40 and 0.48, and pseudoplastic behavior (Table 6). Many researchers found the flow behavior of ice cream samples as pseudoplastic behavior (Aloğlu et al. 2018; Ürkek et al. 2022; Kanca et al. 2023).

It has been reported that an increase in the water-holding capacity of milk proteins has a positive effect on viscosity, overrun and melting. The water-holding capacity of milk proteins increases as the pH decreases towards the isoelectric point (Kneifel et al. 1991). In addition, exopolysaccharides affect the viscosity and rheological properties of products, and kefir cultures could be produced with exopolysaccharides (Yang et al. 2022). Differences in viscosity and K values may have been caused by pH and microbial content.

The colorimetric parameters of the KIC samples did not show any significant changes in terms of L*, b*, C* and H° (P > 0.05; Table 6). Sample KI had the highest a* (-0.91) and WI (95.90) values. The L* values were ranged from 0.92 to 0.99, whereas the WI values varied from 93.94 to 95.90 (Table 6). Öztürk et al. (Öztürk et al. 2018) stated that the color parameters of ice cream samples containing Lactobacillus casei 431 and white-dark myrtus fruit were not affected by the addition of Lactobacillus casei 431.

Instrumental hardness

As can be seen from Table 6, the hardness values of the KIC samples decreased with the concentration of mint flavor concentration. The hardness values of samples KI and KIM2 were the statistically equal (P > 0.05), while these results were higher than other samples (P < 0.05). Kanca et al. (Kanca et al. 2023) found no significant difference between ice cream samples in terms of hardness values. These results are not consistent with those reported by Kanca et al. (Kanca et al. 2023) and by Acu et al. (Acu et al. 2021) who investigated some properties of ice cream samples with probiotic starter culture and raspberry added.

There is an inverse relationship between viscosity and hardness (Kurt and Atalar 2018). The hardness values affect the ice crystal size, ice phase and water holding capacity (Muse and Hartel 2004; Ürkek 2021). As shown in Table 6, the viscosity values increased while the hardness values decreased.

Sensory test

The sensory test scores of the KIC samples are shown in Fig. 1. All sensory test scores of sample KI were generally the highest during 45 days. The flavor scores of sample KIM6 were the lowest at the end of storage. The overall acceptability of the KIC samples ranged from 6.39 to 7.51, while the flavor scores varied from 5.30 to 7.19. The melting in mouth and resistance to melting scores of the KIC samples showed no significant change between samples and during storage (P > 0.5). Sample KIM2 did have the highest scores after than sample KI in terms of flavor and overall acceptability. Color, taste, melting in mouth and overall acceptability scores of sample KIM2 were higher at the end of storage than at the beginning of storage (P < 0.05). Kanca et al. (Kanca et al. 2023) found that sensory scores of ice creams with high kefir content were usually lower than other samples. Salem et al. (Salem et al. 2005) reported that the total sensory score of the control sample was higher than other samples containing probiotic bacteria.

This study found that the use of mint flavor only had a significant effect on acidity, pH, melting rate (P < 0.01) and WI values (P < 0.05), while storage affected acidity, melting rate, yeast (P < 0.01), lactic bacilli and pH (P < 0.05). Lactic bacilli, lactic cocci, and Leuconostoc counts of all samples conformed with legal requirements, whereas yeast counts were not. The highest sensory score was recorded in the KI sample, followed by the sample with 0.2% mint flavor. Kefir cultures with 0.2% mint flavor can be used for ice cream production. Because the sample KIM2 has impressive microbiological properties and sensory scores among the samples containing mint flavor. Thus, a novel ice cream could be produced and contribute to the dairy industry.

Acknowledgements

The study has been supported by the Gümüşhane University Scientific Research Projects Coordination Department (Grant Number: 21.B0430.02.01). The authors thank support from Aromsa Food Aroma and Additives Industry and Trade Inc. (Kocaeli, Turkey) for used mint flavors in the research.

Author Contribution Feyza Öztürk: investigation, data curation, formal analysis. Bayram Ürkek: supervision, investigation, formal analysis, data curation, software, methodology, project administration, writing–original draft, writing–review and editing. Mustafa Şengül: conceptualization, formal analysis, writing–original draft, writing–review and editing.

Conflict of Interest The authors declare that they have no conflict of interest financial interests or personal.

Data availability The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Funding No funding was obtained for this study.

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No competing interests reported.

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Determination of some quality properties of ice cream fermented with kefir culture and flavored with mint (Menthaspicata L.)

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Abstract

Figures

Introduction

Material and Method

Material

Ice cream production

Methods

Microbiological analyses

Antioxidant activity

Total phenolic content (TPC)

Scavenging activity on 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free radicals

Thermal measurements

Proximate analyses

Instrumental Hardness

Sensory test

Statistical analyses

Results and Discussion

Microbiological properties

Antioxidant activity

Some quality parameters

Thermal properties

Proximate analysis

Instrumental hardness

Sensory test

Conclusion

Declarations

References

Additional Declarations

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