Regulation and optimization of water activity and quality of intermediate-moisture potato frozen cake

ABSTRACT

The deterioration of cakes during frozen storage is a notorious phenomenon. This study aimed to evaluate the effects of cryoprotectants (collagen peptide, sericin peptide, and curdlan) on the intermediate-moisture cake during frozen storage. The results showed that cryoprotectants had a positive impact on water state and properties of products. Compared with the control group, the intermediate-moisture cake with better water-holding capacity had better texture characteristics and flavor than the others had, including alleviating the decrement of hardness and chewiness and promoting the augment of sensory evaluation. This study provided more comprehensive theories for the effects of cryoprotectants on intermediate-moisture cake quality from the perspective of water state.

RESUMEN

El deterioro experimentado por los pasteles durante su almacenamiento congelado es notorio. Este estudio se propuso evaluar los efectos provocados por los crioprotectores (péptido de colágeno, péptido de sericina y curdlán) en el pastel de humedad intermedia durante el almacenamiento congelado. Los resultados dan cuenta de que los crioprotectores ejercieron un impacto positivo en el estado del agua y las propiedades de los productos. En comparación con el grupo de control, el pastel de humedad intermedia con mayor capacidad de retención de agua presenta mejores características de textura y sabor que los demás. Ello incluye la mitigación de la disminución de la dureza y la masticabilidad y el aumento de sus propiedades durante la evaluación sensorial. Este estudio aportó teorías más completas sobre los efectos de los crioprotectores en la calidad del pastel de humedad intermedia desde la perspectiva del estado del agua.

KEYWORDS:

• Intermediate-moisture
• frozen cake
• cryoprotectants
• water-holding capacity

PALABRAS CLAVE:

• Humedad intermedia
• pastel congelado
• crioprotectores
• capacidad de retención de agua

1. Introduction

Cakes are highly appreciated by consumers because of their good taste, beneficial nutritional profile and ready-to-eat convenience. However, great majority of cakes circulating in the market are not ready-to-sell, led to the development of methods for the production and preservation of bakery products such as freezing technology. Although this technique enables businesses to reduce production cost and time due to its advantages on centralized manufacturing and distribution process (Selomulyo & Zhou, 2007), the deterioration during frozen storage is a notorious phenomenon. For example, the moisture migration and redistribution causing localized softening and drying, and the formation and growth of ice crystals causing structural distortion (Cauvain, 1998; He & Hoseney, 1990). Thus, the amount of unfrozen water in matrix is a major cause of product degradation during frozen storage. To improve the stability of frozen cakes, the control of water content and the addition of improvers might overcome these problems.

Intermediate moisture foods (IMFs) generally refer to a group of foods with 10%–50% (w/w) moisture content and the water activity between 0.65 and 0.9 (Prabhakar, 2014). In general, IMFs are considered as microbiologically stable at room temperature and can maintain certain initial characteristics of fresh food products (N. Y. N. Y. Lu et al., 2016). Soft cakes, such as Parfait, usually have a short shelf life at room temperature. When its water activity is controlled at 0.687–0.810, its shelf life at room temperature will be prolonged to 3 months. If stored under refrigeration, the shelf life will be even longer (Jelen, 2000).

Although IMFs have a longer shelf life during frozen storage, the growth and recrystallization of ice caused by the repeated fluctuation of temperature will lead to a destruction of the structure, thus hindering the development of such products. In the food industry, adding cryoprotectants is one of the most effective methods to alleviate the quality deterioration of foods during frozen storage. Traditional commercial cryoprotectant, such as polyphosphates, sugars, alcohols, and their compounds, are no longer conform with the current consumers’ pursuit of health.

Antifreeze proteins (AFPs) are peptides and glycopeptides that can depress freezing point and modify the morphology of ice crystals (Xu et al., 2016). They also can inhibit the recrystallization of ice crystals by binding to the surface of ice crystals through an adsorption-inhibition mechanism (Clarke et al., 2002). Studies have shown that collagen peptide can be used as a cryoprotectant to improve bread quality and affect the moisture migration of dough during frozen storage (Xu et al., 2016). Sericin peptide has the function of antifreezing protection which can prevent cells and tissues from freezing denaturation (Tsujimoto et al., 2001). Adding a certain amount of sericin peptide into frozen food can not only improve the nutritional value of the product, but also improve the texture characteristics of the product (Gong et al., 2019).

Hydrocolloids can compete for water with polymers like protein and starch, thereby controlling the migration of water and improving the stability of products during frozen storage (Selomulyo & Zhou, 2007). Curdlan, a kind of polysaccharide produced by microorganism fermentation, can be used as stabilizer, thickener, or texturizer in food. It also can be used as cryoprotectant due to its strong hydrophilicity and freeze-thawed stability (Cong et al., 2004). Liang et al. (Liang et al., 2021) reported that curdlan could improve the quality and gluten network of frozen-cooked noodles by preventing ice crystals from growth and recrystallization.

Therefore, this study evaluate the effects of cryoprotectants (collagen peptide, sericin peptide, curdlan) on the quality of intermediate-moisture cake during frozen storage. The effects of cryoprotectants on the water content, water activity, water mobility, textural characteristics, and sensory quality of cakes before and after frozen storage were systematically investigated. The aim of this study is to offer some new scientific insight for quality improvement of intermediate-moisture frozen cake during frozen storage, and expand the application potential of collagen peptide, sericin peptide, and curdlan in food industry.

2. Materials and methods

2.1. Materials

Low-gluten flour (gluten≤9.5%) was purchased from Jiangsu Xinliang Flour Co., Ltd (Jiangsu, china). Sucrose was purchased from Guangzhou Fuzheng Food Co., Ltd (Guangzhou, china). Double-effect baking powder (Disodium dihydrogen pyrophosphate≤40%, Natrium Bicarbonate≥30%, corn starch, Calcium carbonate≥8%, calcium bis≤5%, Glyceryl Monostearate≤2%) was purchased from Angel Yeast Co., Ltd (Hubei, china). Eggs was purchased from Changshu Yongqing Agricultural Products Trading Co., Ltd (Changshu, china). Colza oil was purchased from Yihai Kerry Food Marketing Co., Ltd (Shanghai, china). Honey was purchased from Shanghai Guanshengyuan Bee Products Co., Ltd (Shanghai, china). Potato whole flour was purchased from Inner Mongolia Xisen Potato Whole Flour Co., Ltd (Inner Mongolia, china).

2.2. Preparation of intermediate-moisture potato frozen cake

The cake was prepared with 225 g wheat flour, 42 g potato flour, 140 g sucrose, 10 g baking powder, 240 g egg, 100 g oil, 140 g honey, 1.125 g whey powder, 1.125 g monoglyceride, and 1.125 g thickening agent. Cakes with collagen peptide, sericin peptide, and curdlan contained 0.225 g, 1.125 g, or 2.25 g collagen peptide, sericin peptide, and curdlan (0.1%, 0.5%, and 1.0% wheat flour basis). The addition of three different cryoprotectants were optimized by using a three-level and three-factor orthogonal experiment (Table 1). Cake with no cryoprotectant was used as control. Then, the cake paste was mixed in a vertical mixer. The cake paste was immediately divided into 100 g and transferred to a paper tray, then baked at 190°C/180°C for 28 minutes. Cooling the baked cake to room temperature and stored at −18°C for 0, and 4 weeks.

Table 1. Formula optimization for the adding of three different cryoprotectants by using orthogonal experiment (L9 (43)).

Tabla 1. Optimización de la fórmula para la adición de tres crioprotectores diferentes mediante un experimento ortogonal (L9 (43))

	Collagen peptide (%)	Sericin peptide (%)	Curdlan (%)
Control	0	0	0
1	0.1	0.1	0.1
2	0.1	0.5	0.5
3	0.1	1	1
4	0.5	0.1	0.5
5	0.5	0.5	1
6	0.5	1	0.1
7	1	0.1	1
8	1	0.5	0.1
9	1	1	0.5

2.3. Determination of water activity and water content

The methods of testing the water activity and water content as described by Shima et al. (Mehrabi et al., 2017) were used with a brief modification. Equilibration at room temperature for 2 hours, the water activity of the core part in the cake piece was measured at room temperature using an H-BD5m water activity tester. The water content of the samples before and after freezing was determined by the weight discrepancy after drying at 105°C.

2.4. Water mobility determination

The water mobility of cake samples was determined using LF-NMR Analyzer (Niumag Corporation, Shanghai, China) according to the method described by Li et al. (Li et al., 2014) with some modification. Fragments of 10 mm × 10 mm × 10 mm were sealed in PET/PE bags. The spin-spin relaxation time (T2) of samples was performed by running Carr-Purcell-Meiboom-Gill (CPMG) sequences. The measurement parameters were the proton resonance frequency of 24.5 MHz, the test period TW was 1500 ms, the cumulative sampling number was 5000, and RGI was 20.0.

2.5. Texture profile analysis (TPA)

Fragments of 40 × 20 × 20 mm were dissected from the center part of freeze-thawed cake. Texture parameters were measured using a texture analyzer equipped with a P36 probe (Stable Microsystems TA-XT2i, Scarsdale, NY, USA). The test parameters were set as follows: pre-test speed 2.0 mm/s, test speed 1.0 mm/s, post-test speed 4.0 mm/s, and compression degree at 20%. The measured parameters include hardness and chewiness (Karaoğlu et al., 2008).

2.6. Sensory evaluation

Six screened assessors rated the cake in terms of appearance, internal structure, hardness, viscosity, and flavor. The scoring criteria is shown in Table 2.

Table 2. Cake sensory evaluation standard.

Tabla 2. Norma de evaluación sensorial del pastel

Content	Evaluation standard
Appearance (10 points)	The surface is smooth without spots, ring patterns, the stomata are evenly distributed and the upper part has a large arc (8 ~ 10 points). The surface is slightly bubbled, ring-shaped, slightly contracted and deformed, and the upper part has a certain arc (5 ~ 7 points). The surface has deep ring patterns, shrinkage and deformation and depression, and the upper arc is small (2 ~ 4 points).
Internal structure (30 points)	Bright yellow or pale yellow, shiny, uniform pores, smooth, and delicate (23 ~ 30 points). Yellow or light yellow matte, slightly larger and rough, uneven, no solid part (16 ~ 22 points). Dark yellow, large and rough stomata, tight stomata at the bottom, and a few solid parts (8 ~ 15 points).
Hardness (10 points)	Soft and elastic, recovers quickly when pressed (8 ~ 10 points). Soft and elastic, press to recover slowly (5 ~ 7 points). Poor flexibility, difficult to recover after pressing (2 ~ 4 points).
Viscosity (10 points)	Not stick teeth (8 ~ 10 points). Slightly stick teeth (5 ~ 7 points). Very stick teeth (2 ~ 4 points).
Flavor (20 points)	Pure taste, soft, delicate, and slightly moist (16 ~ 20 points). Soft, slightly tough, and slightly dry (12 ~ 15 points). Loose, dry, tough, rough, or sticky teeth (6 ~ 11 points).

2.7. Statistical analysis

All experiments were run in triplicate unless specified and the experimental data was expressed as means (standard deviations, SDs) of three independent experiments. All statistical analyses were performed by using SPSS 19.0 for variance analysis and Minitab 17.0 for range analysis. The significance level of P < .05 was used.

3. Results and discussion

3.1. Regulating effect of cryoprotectants on the water activity and water content of potato frozen cake

As shown in Table 3, all the samples prepared based on the formula in Table 1 could meet the requirements of IMFs. The water activity of groups 1–9 was lower than those of the control group, while the water content was higher than those of the control group after 4 weeks frozen storage. The decrease of water activity and the increase of water content indicated that the water holding capacity of the cakes had been enhanced Kong et al. (Kong et al., 2016) reported that large ice crystals could cause physical damage to the food structure, which lead to the decrease of water holding capacity. They confirmed that AFPs could reduce the size of ice crystals and prevent the formation of large ice crystals, resulting a preservation of cellular structure. Wu et al. also reported that sericin peptides could interact with water molecules through hydrogen bonding, hydrophobic interactions, and non-bonding interactions, which could prevent water from forming ice (Wu et al., 2015). As reported by Nguyen et al., the structural match and hydrogen bond formation between ice surface and the collagen peptide could bind collagen peptide to ice, which could inhibit ice growth (Nguyen et al., 2018). Curdlan could form helical structure by the bonding of hydrogen bonds with water molecules, and the structure will not change during freezing and thawing, thus curdlan could significantly improve the water-holding capacity of frozen products (Hatakeyama et al., 2016).

Table 3. Regulating effect of water activity and water content potato frozen cake by the adding of different cryoprotectant.

Tabla 3. Efecto regulador de la actividad del agua y del contenido de agua del pastel de papa congelado mediante la adición de diferentes crioprotectores

	Collagen peptide (%)	Sericin peptide (%)	Curdlan (%)	Water activity		Water Content
				0 week	4 week	0 week		4 week
Control	0	0	0	0.736 ± 0.018^a	0.715 ± 0.010^b	20.077 ± 0.037^b		20.513 ± 0.929 ^f
1	0.1	0.1	0.1	0.715 ± 0.009^abc	0.690 ± 0.006^b	23.770 ± 0.144^a		21.047 ± 0.506^def
2	0.1	0.5	0.5	0.719 ± 0.001^abc	0.697 ± 0.006^b	24.370 ± 0.208^a		21.920 ± 1.065^cde
3	0.1	1	1	0.727 ± 0.009^abc	0.689 ± 0.004^b	23.830 ± 0.096^a		20.420 ± 0.653 ^f
4	0.5	0.1	0.5	0.722 ± 0.005^abc	0.700 ± 0.009^b	23.997 ± 0.346^a		22.370 ± 0.033^bcd
5	0.5	0.5	1	0.704 ± 0.020^bc	0.711 ± 0.003^b	19.857 ± 1.209^b		23.130 ± 0.059^bc
6	0.5	1	0.1	0.708 ± 0.019^abc	0.697 ± 0.011^b	19.907 ± 0.611^b		23.590 ± 0.215^ab
7	1	0.1	1	0.701 ± 0.006 ^c	0.705 ± 0.016^b	18.853 ± 1.685^b		24.527 ± 0.373^a
8	1	0.5	0.1	0.703 ± 0.003^bc	0.686 ± 0.002^b	19.240 ± 0.397^b		23.117 ± 0.796^bc
9	1	1	0.5	0.705 ± 0.002^abc	0.693 ± 0.005^b	19.913 ± 0.719^b		23.043 ± 0.640^bc
T1j	0.7203	0.7127	0.7087
	0.6920	0.6983	0.6910
	23.99	22.21	20.97
	21.13	22.65	22.58
T2j	0.7113	0.7087	0.7153
	0.7027	0.6980	0.6967
	21.25	21.16	20.76
	23.03	22.72	22.44
T3j	0.7030	0.7133	0.7107
	0.6947	0.6930	0.7017
	19.34	21.22	20.85
	23.56	22.35	22.69
Rj	0.0173	0.0047	0.0067
	0.0107	0.0053	0.1107
	4.65	1.05	1.91
	2.43	0.37	0.25

Different superscripts within the same column indicate significant difference according to the Fisher PLSD test at the 0.05 confidence level.

The basic cake control formula with the adding of 0.5% basic additive was used as the control group.

T_ij refers to the mean value of evaluation index for each level of one factor.

R value refers to the range value.

Los distintos superíndices dentro de la misma columna indican diferencias significativas según la prueba PLSD de Fisher a un nivel de confianza de 0.05. Como grupo de control se utilizó la fórmula de control del pastel básico con la adición de 0.5% de aditivo básico.

Tij se refiere al valor medio del índice de evaluación para cada nivel de un factor.

El valor R se refiere al valor del rango.

From the R value by the range analysis (Table 3), it could be seen that after 4 weeks frozen storage, curdlan had the greatest impact on water activity, followed by collagen peptide, and sericin peptide had the smallest effect. Collagen peptide had the greatest impact on water content, followed by sericin peptide, and curdlan had the smallest effect.

It had been widely reported that moisture had an important influence on the delicate taste and bulky appearance of cakes. Generally, cakes with low water content had poor taste and appearance. However, high water content would lead to high water activity of the products, which affect the safety of the products. Since all the tested samples were intermediate-moisture food with water activities lower than 0.9, the higher water content of frozen cakes the better quality of them. From Table 3, we found group 7 had the highest water content, and the adding amount for the cryoprotectants of it was 1% collagen peptide, 0.1% sericin peptide, and 1% curdlan, respectively. This result was almost agreed with the above referred result that the high content adding of collagen peptide and curdlan would help to increase the water content, leading to a better water holding capacity.

3.2. Effect of cryoprotectants on the water mobility of potato frozen cake

The formation and recrystallization of ice crystals during frozen storage will destroy the network structure of cakes and cause the migration of water in them, which will reduce their water holding capacity (Matuda et al., 2008). Therefore, it is necessary to investigate the water mobility in frozen cakes for further understanding the effect of cryoprotectants on decreasing the quality deterioration of frozen cakes during frozen storage.

Figure 1 was the T2 relaxation time distribution curve of a sample. The curve showed two peaks: T21 (1 ~ 10 ms), T22 (10 ~ 100 ms), which represented deep bound water and semi-bond water, respectively (Doona & Baik, 2007). The deep bound water, which is closely combined with gluten, starch, etc. will not move during frozen storage, while the semibound water will migrate and form ice crystals during the frozen storage.

Figure 1. Nuclear magnetic resonance T₂ spectroscopy.Figura 1. Espectroscopia de resonancia magnética nuclear T₂

The peak area ratio of T21 and T22 were presented in Figure 2. Compared with the control group, the proportion of deep bound water in experimental groups was higher than that in the control group after 4 weeks frozen storage, indicating that the water holding capacity of potato frozen cakes were improved. Groups 6–8 had the highest proportion of deep bound water. Collagen peptide and sericin peptide could bind on ice surface to inhibit the formation and recrystallization of ice crystals, thereby reducing the damage of the gluten network of the cake and increasing the deep-bound water content of the system. This result was consistent with the results of water migration of pig skin antifreeze peptides reported by Xu et al. (Xu et al., 2016) and the antifreeze effect of sericin on dough reported by Gong et al. (Gong et al., 2019). Williams et al. had reported that curdlan could form irreversible gel at high temperatures to hold moisture in meat and flour products, and the gel formed can maintain stability under pH 2–12 and freeze-thaw conditions (Williams et al., 2011).

Figure 2. Proportion of deep bound water in cakes frozen at 4 (dark grey) weeks.Figura 2. Proporción de agua ligada en profundidad en los pasteles congelados a las cuatro semanas (gris oscuro)

Combined with the above results of water activity and water content in Table 3, it could be inferred that the addition of collagen peptide and curdlan could reduce the migration of water in the intermediate-moisture potato frozen cake, thus increasing the water holding capacity and decreasing mechanical damage during frozen storage.

3.3. Effect of cryoprotectants on the texture characteristics of potato frozen cake

Results of TPA test for all potato frozen cakes were illustrated in Table 4. In this study, the hardness and chewiness of cake were used to evaluate the quality of potato frozen cakes. Hardness is an important index for evaluating cake quality, which is closely associated with human perception of freshness. Chewiness refers to the time required to chew the cake to the suitable for swallowing (T. M. T. M. Lu et al., 2010). Therefore, high values of chewiness are related with dense, which is not desirable in cakes. As shown in Table 4, the hardness and chewiness of cakes gradually increased with frozen storage time. The increase in the hardness and chewiness as a consequence of frozen storage indicates the destruction of gluten network by ice crystals during the freezing process (Yadav et al., 2009).

Table 4. Regulating effect of hardness and chewiness of potato frozen cake by the adding of different cryoprotectant.

Tabla 4. Efecto regulador de la dureza y la masticabilidad del pastel de papa congelado mediante la adición de diferentes crioprotectores

	Collagen peptide (%)	Sericin peptide (%)	Curdlan (%)	Hardness /g		Chewiness /g
				0 week	4 week	0 week		4 week
Control	0	0	0	756.988 ± 138.32^ab	1897.463 ± 232.66^abc	548.933 ± 92.31^a		1160.875 ± 124.42^ab
1	0.1	0.1	0.1	888.150 ± 70.36^a	1934.938 ± 365.66^abc	594.543 ± 45.00^a		1160.875 ± 124.42^ab
2	0.1	0.5	0.5	839.433 ± 102.65^a	1923.695 ± 90.77^abc	554.970 ± 62.82^a		1189.375 ± 161.73^ab
3	0.1	1	1	594.598 ± 96.20 ^c	1828.76 ± 236.73^abc	430.095 ± 69.66^b		993.683 ± 48.56^bc
4	0.5	0.1	0.5	585.853 ± 112.43 ^c	1715.088 ± 196.69^bc	397.595 ± 77.41^b		967.945 ± 144.81^bc
5	0.5	0.5	1	624.578 ± 38.92 ^c	2091.080 ± 385.93^ab	420.470 ± 33.33^b		960.120 ± 92.86^bc
6	0.5	1	0.1	523.393 ± 47.29 ^c	1796.280 ± 213.73^abc	353.730 ± 30.07^b		1235.755 ± 267.91^a
7	1	0.1	1	861.918 ± 21.78^a	1857.490 ± 378.54^abc	551.303 ± 20.06^a		989.468 ± 160.07^bc
8	1	0.5	0.1	637.065 ± 107.13^bc	1638.890 ± 186.96 ^c	425.068 ± 72.79^b		870.088 ± 198.29 ^c
9	1	1	0.5	861.918 ± 92.36^a	2191.010 ± 82.05^a	550.775 ± 57.08^a		859.963 ± 117.57 ^c
T1j	774.060	778.640	682.869
	1895.483	1825.839	1790.036
	526.536	514.48	457.78
	1114.644	1039.429	1088.906
T2j	577.941	700.359	762.401
	1867.483	1884.555	1943.264
	390.598	466.836	501.113
	1054.607	1006.528	1005.761
T3j	786.967	659.970	693.698
	1895.797	1938.683	1925.777
	509.049	444.867	467.289
	906.506	1029.8	981.09
Rj	209.026	118.671	79.532
	28.315	102.845	153.288
	135.938	69.614	43.333
	208.138	32.902	107.816

Different superscripts within the same column indicate significant difference according to the Fisher PLSD test at the 0.05 confidence level.

T_ij refers to the mean value of evaluation index for each level of one factor.

R_j value refers to the range value.

Los distintos superEDndices dentro de la misma columna indican diferencias significativas según la prueba PLSD de Fisher a un nivel de confianza de 0.05.

Tij se refiere al valor medio del índice de evaluación para cada nivel de un factor.

El valor Rj se refiere al valor del rango.

The hardness and chewiness of groups 3, 4, 5, 6, and 8 were significantly (P < .05) lower than those of the control group before freezing. After four weeks frozen storage, the hardness and chewiness of groups 3, 4, 6, 7, and 8 were lower than those of the control group. The improvement was similar to the phenomenon of water migration, which further proved that there was a certain correlation between water migration and product quality during frozen storage. Lahtinen et al. (Lahtinen et al., 1998) reported that water content is the most important factor affecting the softness of cakes. Mehmet et al. (Karaoglu et al., 2008) also reported a significant negative correlation between water content of cakes and cake firmness. Thus, the improvement of water holding capacity of cakes might be helpful to reduce its hardness and chewiness, and delay its quality deterioration during frozen storage.

Meanwhile, from the R value by the range analysis (Table 4), it could be seen that before freezing, collagen peptide had the largest impact on the hardness and chewiness of the cakes. After 4 weeks frozen storage, collagen peptide had the greatest impact on the chewiness. Thus, among the three cryoprotectants, collagen peptide had the greatest influence on the hardness and chewiness before and after frozen storage. This result was similar to the results of water activity and water content. High content of collagen peptides could improve the texture of cakes, which might be due to the inhibition of ice crystals (Nguyen et al., 2018). In addition, collagen peptides could also modify ice crystals to make them smaller and more evenly distributed, thus making the texture of cake delicate and soft (Ling et al., 2018).

3.4. Sensory evaluation of cake

According to the sensory evaluation scores in Table 5, after 4 weeks frozen storage, groups 7 and 8 had similar sensory evaluation scores with the control group. Meanwhile, as the R value shown in Table 6, it could be seen that after 4 weeks frozen storage, collagen peptide had the greatest impact on the sensory evaluation, followed by curdlan, and sericin peptide had the smallest effect. This result almost agreed with the above result that the high content addition of collagen peptide could help to increase the quality of cakes. Therefore, we could realize that the intermediate moisture cake with better water holding capacity would have better sensory quality after freezing.

Table 5. Sensory evaluation score.

Tabla 5. Puntuación de la evaluación sensorial

	Collagen peptide (%)	Sericin peptide (%)	Curdlan (%)	4 weeks
Control	0	0	0	65.4 ± 7.27^a
1	0.1	0.1	0.1	62.8 ± 4.66^a
2	0.1	0.5	0.5	64.4 ± 5.90^a
3	0.1	1	1	62.8 ± 3.19^a
4	0.5	0.1	0.5	63.2 ± 5.45^a
5	0.5	0.5	1	60.4 ± 5.94^a
6	0.5	1	0.1	61.4 ± 6.62^a
7	1	0.1	1	63.4 ± 6.58^a
8	1	0.5	0.1	65.0 ± 5.79^a
9	1	1	0.5	63.2 ± 5.76^a
T1j	63.33	63.13	63.07
T2j	61.75	63.27	63.60
T3j	63.87	62.47	62.20
Rj	2.20	0.80	1.40

Different superscripts within the same column indicate significant difference according to the Fisher PLSD test at the 0.05 confidence level.

T_ij refers to the mean value of evaluation index for each level of one factor.

R_j value refers to the range value.

Los distintos superíndices dentro de la misma columna indican una diferencia significativa según la prueba PLSD de Fisher a un nivel de confianza de 0.05.

Tij se refiere al valor medio del índice de evaluación para cada nivel de un factor.

El valor Rj se refiere al valor del rango.

4. Conclusion

This study investigated the effects of cryoprotectants in frozen intermediate moisture cake. Collagen peptide, sericin peptide and curdlan were added in frozen intermediate moisture cakes to weaken the quality deterioration of cakes during frozen storage. The underlying mechanism of cryoprotectants on quality regulation and optimization during frozen storage was elucidated from water state and properties. In addition, the texture and sensory properties were also explored to analyze the quality of frozen cakes. The results showed that the improvement of water holding capacity improved the quality of intermediate-moisture cakes during frozen storage, including alleviating the decrement of hardness and chewiness and promoting the augment of sensory evaluation. The results provided a theoretical basis and technical reference for revealing the effects of cryoprotectants on water mobility, texture and flavor of intermediate-moisture cake during frozen storage, and expand the application potential of collagen peptide, sericin peptide and curdlan in food industry.

Acknowledgments

This work was funded by the Natural Science Foundation of China (Grant No. 31972017) and the National Key R&D Program of China (Grant No: 2016YFD0400206).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Natural Science Foundation of China [31972017]; Research Startup Fund of Yibin University [2013QD04]; National Key R&D Program of China [2016YFD0400206].