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RESEARCH ARTICLE

The effects of inulin combined with galacto-oligosaccharide on the various properties of synbiotic soy cheese containing Lactobacillus acidophilus KLDS 1.0738

X. Zhang, Y. Li, J.J. Yang, X.Y. Ma, X.D. Jia, A.L. Li, P. Du

Key Laboratory of Dairy Science, Ministry of Education, Food College, Northeast Agriculture University, Harbin, China

Corresponding Author: A.L. Li, [email protected]; P. Du, [email protected]

Received: 10 April 2020 / Accepted: 10 June 2020 / Published: 15 July 2020

Abstract

This study aimed to evaluate the compatibility of L. acidophilus KLDS 1.0738 (LA-1.0738) with different prebiotic carbohydrates to develop a synbiotic soft soy cheese. It was observed that the addition of 4% (m/v) prebiotics mixture (galacto-oligosaccharide:inulin = 1:3) to soy cheese significantly improved the growth of LA-1.0738, making it no less than 8.2 log colony-forming unit (CFU)/g during the 28-day storage period, but had limited influence on the viability of S. thermophilus KLDS T1C2 (STT1C2). Meanwhile, because of the presence of prebiotics, soy cheese fermented by LA-1.0738 in co-culture with STT1C2 exhibited higher values of acidity, proteolysis and lipolysis index as well as better texture properties and sensory acceptance. These results suggested that the selected combination of prebiotics could be used as functional ingredients to manufacture soy cheese to maintain the survival of desired LA-1.0738, which contributed to improve the texture and sensory features of soy cheese.

Keywords: L. acidophilus KLDS 1.0738, prebiotic, synbiotic, soy cheese

 

1. Introduction

With people’s emphasis on diet and health, consumers’ demand for nutritious and functional food is growing. Probiotics are living microorganisms which can effectively enhance human health when taken in adequate dose, including removing constipation, alleviating diarrhoea, lowering cholesterol and promoting immunity (Hana et al., 2016; Plaza-Diaz et al., 2014). Fermented dairy products containing probiotics are already one of the most popular commercial functional foods such as milk beverage, yogurt and cheese (Cassani et al., 2020). Among these, cheese is considered a better carrier of probiotics. Owing to its more dense texture and relatively higher fat content, it provides a suitable protective effect for the survival of probiotics in the gastrointestinal environment (Ong et al., 2005). The soymilk, rich in plant protein, phospholipids and isoflavones, is one of the important sources of high-quality nutrients for people in oriental countries (Chen et al., 2012) and is often called green cow’s milk. There have been increasing interests in the use of probiotic-added soymilk to develop soy cheese, which also known as a tofu derivatives (Chaturika and Hyun-Dong, 2018). For example, the soy cream cheese prepared with L. acidophilus FTCC 0291 has been reported to contain angiotensin converting enzyme (ACE) inhibitory bioactive peptide, which is responsible for reducing high blood pressure (Liong et al., 2010). The soy-cheese spread prepared with L. casei NCDC-0017 exhibited higher antioxidant activity than the cheese sauce (Kumar et al., 2018). Therefore, the application of probiotics in soybean products can not only enhance the nutritional value of soy-based products but also expand the variety of non-dairy functional food.

The viability of probiotics during fermentation and storage determines the health effects of fermented products. Most previous research has focused on combining prebiotic ingredients to maintain or even improve the viability of probiotic strains in dairy products (Langa et al., 2019; Sebnem et al., 2019). Currently, Santos et al. (2019) indicated that adding inulin (IN) to fermented soymilk could not only efficiently promote the survival of Lactococcus, Lactobacillus and yeast in kefir grains but also improve the sensory acceptability of beverage during the 14-day shelf life. Furthermore, in vitro and in vivo experiments have suggested that synbiotic products generally tend to have better probiotic effects than either probiotics or prebiotics alone (Le et al., 2019; Samadrita et al., 2019). Nowadays, synbiotic soybean products have been studied almost exclusively in the fermented soy milk or soy yoghurt. However, a few studies have done research on symbiotic soybean cheese.

In our previous study, we screened a strain of L. acidophilus 1.0738 with probiotic characteristics, which had a strong tolerance to acid and bile salt and had a relief effect on intestinal inflammation in animal experiments (Li et al., 2017a). In the present study, we adopted L. acidophilus strain and different prebiotic oligosaccharides to develop a potentially synbiotic soft soybean cheese. The protective effect of different prebiotics on the survival of L. acidophilus in soy cheese was explored. Moreover, the changes in physicochemical and microbiological, and texture and sensory properties of probiotic soybean cheese were analysed during storage.

2. Materials and methods

Probiotic strains and prebiotics

L. acidophilus KLDS 1.0738 (LA-1.0738) and S. thermophilus KLDS T1C2 (STT1C2) obtained from Key Laboratory of Dairy Science, Ministry of Education (Northeast Agricultural University, Harbin, China) were cultured in DeMan–Rogosa–Sharpe (MRS) agar (Sigma, US) and M17 broth (Huankai Microbial, China) at 37 °C for 24 h, respectively. After three consecutive transfers, the inoculum concentration of L. acidophilus and S. thermophilus starter was adjusted to 9 log CFU/g for making soy cheese.

Commercial prebiotics were added to soy cheese: fructo-oligosaccharides (FOS) and oligoisomaltose (IMO) were purchased from RYON Co. Ltd. (Shanghai, China), galacto-oligosaccharides (GOS) was purchased from BIOTOPPED Co. Ltd. (Beijing, China), and mannan-oligosaccharides (MOS) and IN were purchased from Shanghai Yuanye Bio-Technology Co. Ltd. (Shanghai, Chain).

Selection of suitable probiotics

The experiment in this section is divided into three parts. Firstly, we used MRS-dex (MRS without glucose) to analyse the effects of different prebiotics (FOS, IMO, GOS, MOS and IN) on the growth of LA-1.0738, that is, after incubating at 37 °C for 24 h, the optical density (OD600) of LA-1.0738 in MRS-dex containing different prebiotics was determined using a CHEMUSB4-UV-VIS spectrophotometer (Ocean Optics, Inc., US). Then we also used the OD600 value of LA-1.0738 as an indicator to evaluate the appropriate dosage of prebiotic (0–5%, m/v) added to the MRS-dex. Finally, we evaluated the effects of different proportions of probiotic combinations (GOS and IN ratios of 1:1, 1:2, 1:3, 2:1 and 3:1) on the growth of LA-1.0738, including investigating the OD600 value in MRS-dex and the number of viable bacteria in soy cheese.

Preparation of synbiotic soy cheese

Soy cheese was made according to the method described by Matias et al. (2014). Briefly, soybeans (soy:water = 1:3, w/v) soaked overnight were ground and sieved to obtain soy milk. After adding with 4% (m/v) prebiotics mixture (galacto-oligosaccharide:IN = 1:3), the soy milk was sterilised in HVE-50 autoclave (Hirayama, Japan) at 0.1 MPa, 121 °C for 20 min and cooled to 37 °C. Subsequently, 5% (v/v) lactic acid bacteria (LA-1.0738:STT1C = 1:1) was inoculated into soy milk for fermentation, followed by adding 3% (g/L) CaCl2 solution for coagulation until pH 4.8 was obtained. Then the curd was cut into 2 × 2 × 2 cm cubes and drained completely, vacuum-packed in a sealed plastic bag and stored at 4 °C for 28 days. Three formulations of soy cheese were produced each with LA-1.0738 alone (P), LA-1.0738 and STT1C2 combination (PS) and LA-1.0738, STT1C2 and prebiotics compound (PSP).

Physico-chemical analyses

The pH value was measured using a digital pH-meter (METTLER TOLEDO, Zurich, Switzerland). Total acidity and free fatty acid (FFA) content were determined according to the Association of Official Analytical Chemists (AOAC, 2000) Method Nos. 935.57 and 940.28, respectively. The pH 4.6 soluble nitrogen (pH 4.6 SN) was determined according to the method of Feeney et al. (2001).

Instrumental texture profile analysis (TPA)

Texture properties of soft soy cheese were determined at room temperature (25 °C), using a texture analyser (TA-XT2i, Stable Micro Systems, Surrey, UK). The metallic cylinder probe was P/0.5S (20 mm in diameter), the compression distance was 10 mm, the contact force was 0.2 N, the pre-test and test speed was 1.0 mm s–1, and the post-test speed was 10 mm s–1. Parameters consisted of hardness, springiness, cohesiveness, gumminess and resilience. The value of texture was the mean value of quintuplicates.

Microbiological analysis

Changes of viable LA-1.0738 and STT1C2 numbers in soy cheese were monitored weekly during storage period (1 up to 28 days). For this purpose, 25 g of duplicate soy cheese sample was diluted with 225 ml of 0.1% (g/ml) peptone water in Bag Mixer 400 (Interscience, St. Nom, France) and submitted to serial dilutions with the same diluent. LA-1.0738 was counted by pour-plating 1 ml of each dilution in modified MRS agar containing maltose (BioFroxx, Germany), after 48 h of aerobic incubation at 37 °C. STT1C2 was counted by pour-plating 1 ml of each dilution in M17 agar (Huankai Microbial, China) with added lactose (Oxoid, Britain), followed by incubation at 37 °C for 48 h.

Sensory analysis

The sensory properties of the final product were evaluated at 25 °C by 15 trained judges (seven males and eight females), who were students, aged 20–30 years, at Northeast Agricultural University, China. The samples (P, PS and PSP) were placed in separate plastic pots, encoded with three random digits, and provided to trained panelists. According to the method described by Hough (2010), 15 trained panelists were invited to rate the sensory attributes of soy cheese for texture, mouth feel, appearance, taste and overall acceptability using a 9-point intensity scale, with 1 being the lowest score and 9 the highest. Results were given as the average of three trials for each of the samples, which formed a radial graph.

Compositional analysis of final products

The composition of final products was estimated using official methods (AOAC, 2000): moisture (Method No. 968.11), proteins (Method No. 99120), ash (Method No. 94546) and fat (Method No. 989.05). The yield of soybean cheese was calculated with the following equation:

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Statistical analysis

Data analysis was carried out using SPSS Inc. software (version 22.0) (SPSS Inc., Chicago, IL, USA). One-way analysis of variance was used to study the significant difference between mean values at a significance level of P = 0.05. Mean comparisons were carried out using Tukey’s test. Principal component analysis (PCA) data was performed using the Origin 2018 for Windows statistical software package (Origin Lab Co., Northampton, MA). All experimental data were expressed as mean ± standard deviation (SD).

3. Results and discussion

The effect of different prebiotics on L. acidophilus growth

The effectiveness of synbiotic depends on the ability of probiotics to utilise prebiotic (Ann et al., 2007), which is strain-specific and dose-dependent (Santichai et al., 2019). As shown in Figure 1a, compared with the non-prebiotic MRS-dex (control group), the addition of prebiotics significantly increased the OD600 of LA-1.0738 in MRS-dex. In particular, the value of OD600 in GOS and IN groups was higher than those of other oligosaccharide groups. Many studies have confirmed that L. acidophilus could use GOS and/or IN, and the underlying mechanism was that L. acidophilus could activate a precursor of enzymes β-fructosidase and β-galactosidases, necessary for the utilisation of IN and GOS (Andersen et al.; Endo et al., 2012). Although the growth of LA-1.0738 showed the highest OD600 value when the amount of GOS and IN added reached 5%, it was not significant compared to the 4% group (Figure 1b). In addition, when the ratio of GOS:IN is 1:3, the OD600 value of probiotics in MRS-dex medium (Figure 1c) and the number of viable bacteria in soy cheese (Figure 1d) were significantly higher than those in other groups. Ambalam et al. (2015) also indicated that the combination of different prebiotics promoted the growth of L. paracasei F8 and L. plantarum F44 more effectively than done by single prebiotic. Accordingly, we added 4% prebiotic (GOS:IN = 1:3) in subsequent experiments to produce probiotic soy cheese.



Fig 1

Figure 1. The effects of prebiotics on the growth of LA-1.0738: (a) Changes in OD600 for L. acidophilus in MRS-dex with different prebiotics; (b) changes in OD600 for L. acidophilus in MRS-dex with different concentrations of prebiotics; (c) changes in OD600 for L. acidophilusin MRS-dex with different IN to GOS ratios; (d) changes of viable counts of L. acidophilus in soy cheese with different IN to GOS ratios. Note: C, control group; FOS, fructo-oligosaccharides; MOS, mannan-oligosaccharides; IMO, oligoisomaltose; GOS, galacto-oligosaccharides; IN, inulin; MRS–dex, MRS without glucose. Different letters on top of the bars denote significant difference (P < 0.05). Error bars represent the mean ± standard deviation values of triplicate experiments.

Viability of LA-1.0738 and STT1C2 during storage

Previous studies mostly used pure culture bacteria to ferment soybean products (Liong et al., 2010; Rui et al., 2017). There are few studies on soy cheese fermented with mixed probiotics and yogurt starter. In our study, the individual LA-1.0738 was difficult to grow well in the soy cheese, the number of viable bacteria decreased significantly in the first 20 days, and there was almost no change between 21 and 28 days, resulting in the LA-1.0738 numbers dropping to 6.58 log CFU/g in the final product. Although the population of LA-1.0738 in the soy cheese fermented by LA-1.0738–STT1C2 combination also showed a downward trend between 14 and 28 days, but the amount of LA-1.0738 always remained above 7 log CFU/g (Table 1), suggesting that LA-1.0738 survived much better in the presence of STT1C2. Consistent with the observed symbiotic results of LA-1.0738 and STT1C2, Matias et al. (2014) also found that L. acidophilus La-5 and B. animalis Bb-12 maintained satisfactory probiotic counts (>6 log CFU/g) in soy cheese after co-cultivation with S. thermophile starter.

Table 1. The viable counts of L. acidophilus KLDS 1.0738 and S. thermophilus T1C2 in soy cheese during storage period of 28 days at 4 °C.
Microorganism Time (days) log CFU/g
P PS PSP
L. acidophilus 0 8.67 ± 0.19Ac 8.77 ± 0.06Ac 8.93 ± 0.05Ab
7 8.01 ± 0.13Ab 8.58 ± 0.10Bc 8.77 ± 0.04Bb
14 7.59 ± 0.07Ab 8.12 ± 0.09Bb 8.32 ± 0.02Ba
21 6.92 ± 0.09Aa 7.86 ± 0.04Bab 8.21 ± 0.07Ca
28 6.58 ± 0.04Aa 7.84 ± 0.05Ba 8.2 ± 0.08Ca
0 8.48 ± 0.08Aa 8.51 ± 0.18Aa 8.61 ± 0.05Aa
7 8.47 ± 0.05Aa 8.57 ± 0.11Aa 8.51 ± 0.07Aa
14 8.46 ± 0.07Aa 8.49 ± 0.06Aa 8.48 ± 0.10Aa
21 8.28 ± O.05Aa 8.28 ± 0.08Aa 8.32 ± 0.15Aa
28 8.24 ± 0.09Aa 8.27 ± 0.08Aa 8.29 ± 0.07Aa
A,B,CSignificant statistical differences (P < 0.05) in the same row.
a,b,cSignificant statistical differences (P < 0.05) in the same column.
All values correspond to the mean ± standard deviation values of triplicate experiments.
P: LA1.0738; PS: LA1.0738 +STT1C2; PSP: LA1.0738 +STT1C2 + prebiotics mixture.

Next, we further evaluated the protective effect of prebiotcs on the survival of probiotic organisms. As shown in Table 1, compared with the LA-1.0738 alone group or the STT1C2 starter co-culture group, the LA-1.0738 counts in the GOS–IN group increased significantly during storage (P < 0.05), which was not less than 8.2 log CFU/g on day 28. Similar finding was reported by Mishra and Mishra (2018), who found improvements in the growth of L. acidophilus in the symbiotic soy milk supplemented with IN and FOS. Unlike LA-1.0738, we observed that the prebiotics had little effect on STT1C2 counts, varying between 8.29 and 8.61 log CFU/g (Table 1), which might be related to the lack of oligosaccharide degrading enzymes in the S. thermophilus. Our previous studies have confirmed that the minimum amount of LA-1.0738 to produce health effects was 6–7 log CFU/g daily product consumption (Wang et al., 2018), suggesting the potential benefits of soy cheese as probiotic vehicle.

Physico-chemical analysis of soy cheese during storage

It is evident in Table 2 that compared with the group with LA-1.0738 alone, the pH value of soy cheese containing starter or prebiotic decreased during the storage period of 1–14 days, and the titration acidity increased (P < 0.05). Although the pH (4.17) of soy cheese with prebiotics after 28 days of storage was lower than the pH of soy cheese with starter (4.23), there was no significant difference between the two groups (P > 0.05). This decrease in pH value was similar to the observation made by Bergamini et al. (2009). In addition, all soy cheese formulas showed strong proteolytic and lipolytic abilities during 7–21 days, reaching maximum on day 28 (Table 2). Compared with the LA-1.0738 alone group, the mixed fermentation group of probiotics and starter had better results, and their pH 4.6 SN and FFA values increased by 15.10% and 7.33%, respectively, at the end of storage. Consistent with our results, Li et al. (2019) reported that L. plantarum, B. animalis Bb-12 and S. thermophilus-mixed fermented milk had higher titratable acidity, proteolytic activity and lipolytic capacity than the pure S. thermophilus group. We further observed that, compared with the LA-1.0738 alone group and the supplemented yogurt starter group, the FFA of soy cheese with prebiotics increased significantly (P < 0.05) and reached the highest value in 28 days (7.81%). Similarly, Rodrigues et al. (2012) also observed that the addition of FOS and IN (ratio 1:1) positively promoted lipolysis action and FFA production of cheese containing L. casei-01 and B. lactis B94 during storage.

Table 2. Changes in the physicochemical characteristics of cheese samples during storage time.
Cheese Time (d) pH Total acidity (%) pH 4.6 SN (%) FFA (%)
P 0 4.5 ± 0.03Ab 0.50 ± 0.05Aa 9.42 ± 0.07Aa 5.05 ± 0.13Aa
7 4.51 ± 0.03Bb 0.52 ± 0.01Aab 9.83 ± 0.08Aa 5.72 ± 0.05Ab
14 4.39 ± 0.02Bab 0.56 ± 0.03Bab 11.20 ± 0.19Ab 6.01 ± 0.05Abc
21 4.31 ± 0.03Bab 0.59 ± 0.02Bab 12.58 ± 0.01Ac 6.47 ± 0.19Ac
28 4.29 ± 0.05Aa 0.64 ± 0.04Bb 13.90 ± 0.07Ac 6.60 ± 0.27Ac
PS 0 4.52 ± 0.02Ab 0.54 ± 0.01Aa 9.13 ± 0.05Aa 5.21 ± 0.13Aa
7 4.35 ± 0.07ABab 0.60 ± 0.04Aab 11.45 ± 0.50Bb 5.28 ± 0.11Aa
14 4.29 ± 0.02Aa 0.68 ± 0.01Ab 13.70 ± 0.52Bbc 6.31 ± 0.14Ab
21 4.31 ± 0.03ABa 0.69 ± 0.02Ab 14.90 ± 0.15Bc 7.20 ± 0.07Ab
28 4.23 ± 0.07Aa 0.70 ± 0.03Ab 15.10 ± 1.20ABc 7.33 ± 0.11Ab
PSP 0 4.51 ± 0.04Ac 0.54 ± 0.02Aa 9.13 ± 0.21Aa 5.01 ± 0.13Aa
7 4.32 ± 0.02Abc 0.62 ± 0.03Ab 10.95 ± 0.10Ba 6.87 ± 0.06Bb
14 4.21 ± 0.03Ab 0.66 ± 0.01Abc 14.35 ± 0.92Bb 7.23 ± 0.19Bbc
21 4.19 ± 0.02Ab 0.70 ± 0.02Ac 15.04 ± 1.74Bb 7.67 ± 0.16Bc
28 4.17 ± 0.01Aab 0.73 ± 0.02Ac 15.81 ± 0.09ABb 7.81 ± 0.24Bc
A,B,CSignificant statistical differences among different cheese in the same column (P < 0.05).
a,b,cSignificant statistical differences among different days in the same column (P < 0.05).
All values correspond to the mean ± standard deviation values of triplicate experiments.
P: LA1.0738; PS: LA1.0738 +STT1C2; PSP: LA1.0738 +STT1C2 + prebiotics mixture; FFA: free fatty acid; SN: soluble nitrogen.

Textural properties of soy cheese during storage

It is observed in Table 3 that the hardness of the three groups of soy cheese increased significantly(P < 0.05)during storage and reached their maximum values on the 28th day, which were 757.42, 674.60 and 624.32 g, respectively. According to literature, it was speculated that the extracellular polysaccharides or bioactive ingredients produced by probiotics could increase viscosity, the water retention capacity, which thereby increased the hardness in the final product (Welman and Maddox, 2003). These results were supported by Li et al. (2017b), who pointed out that the addition of L. acidophilus to tofu could improve the hardness of tofu and make its texture more dense and stable than that of ordinary fermented tofu.

Table 3. Textural properties of soy cheese during storage time.
Texture parameter Time (d) Cheese
P PS PSP
Hardness (g) 0 481.10 ± 5.64Ba 470.82 ± 9.13ABa 427.51 ± 11.17Aa
7 582.40 ± 18.26Bb 506.33 ± 34.35ABa 456.01 ± 21.32Aab
14 601.54 ± 21.14Bb 621.60 ± 27.14ABb 514.39 ± 9.24Ab
21 703.53 ± 17.11Bc 636.29 ± 34.09Ab 590.25 ± 18.10Ac
28 757.42 ± 30.69Bc 674.60 ± 30.44ABb 624.32 ± 24.54Ac
Springiness (mm) 0 0.68 ± 0.01Ba 0.68 ± 0.01Ba 0.61 ± 0.01Aa
7 0.73 ± 0.01Ba 0.71 ± 0.02Aa 0.64 ± 0.01Aa
14 0.81 ± 0.02Bb 0.73 ± 0.01ABab 0.71 ± 0.02Ab
21 0.86 ± 0.02Bbc 0.79 ± 0.02ABbc 0.76 ± 0.02Ac
28 0.92 ± 0.02Bc 0.82 ± 0.03Ac 0.79 ± 0.01Ac
Cohesiveness (g.sec) 0 0.52 ± 0.02Aa 0.51 ± 0.03Aa 0.54 ± 0.02Aa
7 0.59 ± 0.01Ab 0.56 ± 0.01Aa 0.61 ± 0.03Aab
14 0.60 ± 0.03Ab 0.66 ± 0.01Ab 0.64 ± 0.01Aab
21 0.62 ± 0.01Ab 0.64 ± 0.01Ab 0.65 ± 0.03Ab
28 0.63 ± 0.01Ab 0.73 ± 0.03Ab 0.68 ± 0.02Ab
Gumminess (g) 0 195.35 ± 829Aa 188.57 ± 12.15Aa 196.80 ± 8.57Aa
7 215.42 ± 14.73Aa 231.93 ± 19.66Aa 225.68 ± 20.32Aa
14 454.59 ± 5.27Ab 412.61 ± 17.33Ab 421.83 ± 35.64Ab
21 576.34 ± 15.50Ac 560.39 ± 21.24Ac 569.81 ± 28.41Ac
28 596.76 ± 13.26Ac 591.73 ± 29.23Ac 589.20 ± 33.68Ac
Chewiness (g.sec) 0 137.51 ± 9.00Aa 145.01 ± 13.43Aa 140.14 ± 8.07Aa
7 198.53 ± 19.63Aa 165.21 ± 7.94Aa 193.20 ± 13.52Ab
14 381.30 ± 18.25Bb 335.15 ± 11.36ABb 310.02 ± 3.35Ac
21 507.85 ± 15.11Bc 445.75 ± 17.24ABc 436.67 ± 11.25Ad
28 566.72 ± 20.17Bb 483.05 ± 15.58ABb 463.31 ± 12.85Ad
Resilience 0 0.18 ± 0.01Aa 0.18 ± 0.01Aa 0.18 ± 0.02Aa
7 0.19 ± 0.02Aa 0.19 ± 0.02Aa 0.20 ± 0.01Aa
14 0.22 ± 0.03Aa 0.20 ± 0.02Aa 0.21 ± 0.02Aa
21 0.25 ± 0.03Aa 0.24 ± 0.01Aa 0.23 ± 0.02Aa
28 0.27 ± 0.02Aa 0.26 ± 0.01Aa 0.25 ± 0.02Aa
A,BSignificant statistical differences (P < 0.05) in the same row.
a,b,c,dSignificant statistical differences (P < 0.05) in the same column.
All values correspond to the mean ± standard deviation values of quintuplicate experiments.
P: LA1.0738; PS: LA1.0738 +STT1C2; PSP: LA1.0738 +STT1C2 + prebiotics mixture.

Furthermore, the scores for hardness, springiness and chewiness of soy cheese added with starter or prebiotics were lower than that of the probiotics alone group, especially the group with added prebiotics. The PCA results showed that the group with LA-1.0738 added alone significantly deviated from the other two groups (P < 0.05), while the yogurt starter-added group was clustered more closely with the prebiotics-added group (Figure 2). This result was positively related to the degree of hydrolysis of soy cheese. Similar to our findings, Barbosa et al. (2016) found that the addition of IN could improve the proteolytic activity of goat cheese containing L. acidophilus La-5 and B. animalis Bb-12 during storage, thereby reducing the hardness of product.



Fig 2

Figure 2. Principal component analysis of the textural parameters of cheese during storage. Note: P, LA-1.0738; PS, LA-1.0738 + STT1C2; PSP, LA-1.0738 + STT1C2 + prebiotics mixture.

Sensory evaluation of soy cheese

Figure 3 shows the trend of soy cheese in acceptability. The soy cheese with LA-1.0738 added alone had the lowest texture, mouth feel and overall acceptability scores, which might be related to consumers’ inability to accept its rich hardness (Gomes et al., 2011), although the yogurt starter addition group and the prebiotic addition group had similar texture, appearance and flavour. However, the soy cheese with added prebiotics had a better taste and overall acceptance. Similarly, Bedani et al. (2013) reported that the synbiotic soy beverages containing IN, L. acidophilus La-5, B. animalis Bb-12 and S. thermophilus were more acceptable. Cardarelli et al. (2007) also found that adding IN helped to improve the mouth feel and texture of petit-suisse cheese containing S. thermophilus and L. acidophilus.



Fig 3

Figure 3. Sensory evaluation of cheese samples at the end of storage. Note: P, LA-1.0738; PS, LA-1.0738 + STT1C2; PSP, LA-1.0738 + STT1C2 + prebiotics mixture.

Gross composition of soy cheese

As shown in Table 4, the addition of GOS and IN mixture resulted in the lowering of protein and fat content in the finished soy cheese, which might be due to the prebiotics increasing the activity of probiotics, resulting in more intense proteolysis and lipolysis (Valle et al., 2019). Although the protein and fat content of the co-culture group of STT1C2 and LA-1.0738 was lower than that of the probiotics alone group, the difference between the two groups was not significant. Moreover, the addition of starter or prebiotic had no significant effect on the yield (65.57 vs. 72.09 g per 100 g), moisture (64.38 vs. 68.20 g per 100 g) and ash (0.62 vs. 0.66 g per 100 g) of the soy cheese.

Table 4. Chemical composition of cheese samples at the end of ripening (28 days).
Samples Yield (g/100 g ) Moisture (g/100 g) Ash (g/100 g) Protein (g/100 g) Fat (g/100 g)
P 65.57 ± 2.61a 64.38 ± 1.02a 0.62 ± 0.01a 11.63 ± 0.06b 9.64 ± 0.05b
PS 71.67 ± 2.51a 68.20 ± 1.01a 0.64 ± 0.01a 9.22 ± 0.52a 8.56 ± 0.04a
PSP 72.09 ± 2.32a 67.92 ± 0.05a 0.66 ± 0.01a 8.73 ± 0.05a 8.215 ± 0.17a
a,bSignificant statistical differences (P < 0.05) in the same column.
All values correspond to the mean ± standard deviation values of triplicate experiments.
P, LA1.0738; PS, LA1.0738 + STT1C2; PSP, LA1.0738 + STT1C2 + prebiotics mixture.

4. Conclusion

The newly developed synbiotic soy cheese in this study might be a suitable carrier of probiotic LA-1.0738, in which the viable bacteria remained at the recommended functional level of above 108 CFU/g after 28 days of storage. Furthermore, the addition of probiotic and GOS:IN combination significantly improved the technological, physicochemical and sensory characteristics of soy cheese compared with the addition of only LA-1.0738. Further research is required to clarify the specific mechanisms involved in this synbiotic effect in responding to consumer health, and to confirm the effectiveness of the product in vivo.

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