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Article

Effect of the Addition of Soy Beverage and Propionic Bacteria on Selected Quality Characteristics of Cow’s Milk Yoghurt Products

by
Małgorzata Ziarno
1,*,
Dorota Zaręba
2,
Wiktoria Dryzek
3,
Rozeta Hassaliu
4 and
Tomasz Florowski
5
1
Division of Milk Technology, Department of Food Technology and Assessment, Institute of Food Science, Warsaw University of Life Sciences–SGGW (WULS–SGGW), 02-787 Warsaw, Poland
2
Professor E. Pijanowski Catering School Complex in Warsaw, 04-110 Warsaw, Poland
3
Faculty of Biology and Biotechnology, Warsaw University of Life Sciences–SGGW (WULS–SGGW), 02-787 Warsaw, Poland
4
Faculty of Biotechnology and Food, Agricultural University of Tirana, 1029 Tirana, Albania
5
Division of Meat Technology, Department of Food Technology and Assessment, Institute of Food Science, Warsaw University of Life Sciences–SGGW (WULS–SGGW), 02-787 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2022, 12(24), 12603; https://doi.org/10.3390/app122412603
Submission received: 21 November 2022 / Revised: 5 December 2022 / Accepted: 7 December 2022 / Published: 8 December 2022
(This article belongs to the Special Issue Functional Dairy Products)
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Abstract

:

Featured Application

The study showed the possibility of producing innovative vegetarian yoghurt products with plant-based ingredients, such as a soya beverage with symbiotic lactic acid bacteria and propionic acid bacteria starter cultures. This opens the way for the future development of functional cow’s milk–soya fermented products, such as yoghurts, which combine the effects of both lactic acid bacteria and propionic acid bacteria.

Abstract

Many diet trends have emerged over the last few years, including plant-based diets with soya as an important component, while fermented milk beverages have been an integral part of the human diet for thousands of years. However, there is little research on the potential of using propionic bacteria for dairy or plant-based food fermentation. The aim of this study was to evaluate the effects of soy beverage addition and propionic bacterium application on the quality of dairy yoghurt products. Three variants of the products—based on cow’s milk, soya beverages, and mixtures of both—were prepared and then fermented with yoghurt bacteria, propionic bacteria or a mixture thereof. It was found that it is possible to obtain functional yoghurt products based on cow’s milk, as well as milk–soya blends, using a mixture of yoghurt and propionic cultures. The resulting milk, milk–soya, and soya yoghurt products displayed pH values in the correct range and a stable bacterial population during refrigerated storage for 21 days. The refrigerated storage time and the type of culture starter used significantly determined the quality characteristics of the milk, milk–soya and soya yoghurt products, such as their firmness, adhesiveness, and water-holding capacity.

1. Introduction

The dairy industry is one of the main pillars of the food sector. Fermented dairy drinks, such as yoghurt, are hugely popular. Fermentation is one of the oldest known methods of making practical use of the activities of microorganisms. Fermentation processes have been known to mankind since prehistoric times, and developments in science and technology in this field have allowed them to be improved and used in many areas [1,2,3]. In the dairy industry, lactic acid fermentation bacteria in particular have been used in the production of fermented milk products, such as yoghurts.
Fermented foods are a major source of live bacteria in the human diet. According to the World Health Organization’s (WHO) definition, yoghurt is a fermented dairy product obtained by acidifying and coagulating milk with yoghurt bacteria, such as Streptococcus thermophilus or Lactobacillus delbrueckii subsp. bulgaricus, among others [4]. In new-generation yoghurts, the use of other bacterial cultures is permitted [4]. The content of viable bacterial cells in the final product should be a minimum of 107 per 1 mL or 1 g [5]. Fermented products are the main natural source of beneficial microflora in the human diet. Fermented milk products have been an integral part of the human diet for thousands of years. Since their beneficial effects on human health were first studied over 100 years ago, there is a growing interest in both the production and consumption of yoghurt [6].
However, over the last few years, many diet trends have emerged. Some of these have been short-lived, while others have caught on so well that they have become popular worldwide. One such example is the plant-based diet. A wide range of probiotic fermented dairy-free beverages are produced worldwide using a variety of plant matrices [7]. It is believed that a plant-based diet has more health benefits for the human body than a diet containing animal products [8,9,10]. This results in the restriction or total exclusion of animal products, with the aim of obtaining all the nutrients necessary for the body to function properly [11,12,13]. These diets employ legumes, particularly soya. Soya beverages contain high-quality proteins, isoflavones, unsaturated fatty acids, as well as carbohydrates, which, on the one hand, may cause some digestive discomfort, but on the other hand, are increasingly recognized as prebiotic substances [14,15,16,17,18,19,20]. They can also provide protection against many diseases, including cardiovascular disease, diabetes, and cancer [21,22].
The aim of this research was to analyze the effect of the addition of a soya beverage to cow’s milk in different proportions, and to evaluate selected quality parameters of the obtained yoghurt products. Research concerning the fermentation of soya beverages or their addition to a milk matrix is not advanced [23,24,25]. To date, there is a lack of scientific data on the fermentation of such matrices using propionic bacteria, either alone or in a mixture with standard lactic acid bacteria starters, such as yoghurt bacteria. Equally little information is available in the literature on the use of propionic bacteria in plant food matrices. Propionibacterium freudenreichii is a beneficial bacterium that modulates intestinal microflora, enhances motility, and reduces inflammation [26]. P. freudenreichii has been marketed as a probiotic in functional food supplements and used as a biopreservative and protective culture in food in several countries for years [26,27]. Milks fermented using P. freudenreichii may provide a source of riboflavin [28], enhance drug treatments [29], or counteract the harmful effects of some drugs [30,31], without adverse sensory properties [32].
Therefore, the aim of this study was to test the effect of the addition of a soy beverage and the application of propionic bacteria on selected quality characteristics of cow’s milk yoghurt products. This will open up the possibility of producing innovative functional dairy yoghurt products with plant-based ingredients, such as soya beverages with symbiotic lactic acid bacteria and propionic acid bacteria.

2. Materials and Methods

Marketed homogenized UHT milk with 2% fat (OSM Łowicz, Łowicz, Poland) and natural UHT soy beverage with 1.7% fat (Frias, Burgos, Spain) were used. Two industrial starter cultures designed for the dairy industry were used to carry out the fermentation: (1) yoghurt bacteria starter POB 010 (Dalton Biotecnologie S.r.l., Villa Raspa, Italy); and (2) propionic bacteria starter Propionicii 000F0004 (Dalton Biotecnologie S.r.l., Villa Raspa, Italy). Yoghurt starter POB 010 contains bacteria of the following species: S. thermophilus and L. delbrueckii subsp. bulgaricus. It is a freeze-dried DVI (Direct Vat Inoculation) culture, whose carrier is dextrose. The bacteria in it produce lactic acid and have an acidifying effect on the raw material. According to the information provided by the manufacturer, it has a good taste and produces exopolysaccharides during fermentation. Propionic bacteria starter Propionicii 000F0004 contains bacteria of the species P. freudenreichii subsp. shermanii. It is a freeze-dried DVI bacterial culture on the carrier dextrose. The manufacturer recommends using the starter in combination with mesophilic and/or thermophilic cultures to produce Swiss-type cheeses such as Emmentaler, Gruyere, or Greve. The starter gives the products their characteristic propionic aroma.

2.1. Preparation of Fermented Milk, Milk–Soya, and Soya Yoghurt Products

Three beverage variants—one based on cow’s milk, a soya beverage, and mixtures thereof in proportions of 2:1, 1:1, 1:2—were prepared (Table 1) in portions of 120 mL each in pre-sterilized glass jars. Then, they were inoculated with the appropriate bacterial starters. The first variant was fermented with a yoghurt bacteria starter only, the second variant with a mixture of yoghurt and propionic bacteria starters (in a 1:1 weight ratio), while the third variant was fermented with a propionic bacteria starter only. Samples prepared in this way were then used for fermentation. The separate portions of yoghurt products were prepared in separate glass jars for each day of analysis.
In the first two experiments, the fermentation kinetics of the beverages mentioned above were determined. To this end, the fermentation was carried out at two different temperatures: 37 °C and 45 °C. During the fermentation process, the pH of the samples was measured every two hours. On the basis of these measurements, the temperature and fermentation time of the relevant samples were selected.
Samples of fermented milk, milk–soya, and soya yoghurt products were obtained in three further experiments via the fermentation of beverages based on cow’s milk, soya beverage, and a mixture thereof at 45 °C for 18 h. After fermentation, the samples were placed in a refrigerator (5 °C), where they were kept for 21 days and subjected to appropriate analyses every 7 days.

2.2. Analysis of Fermented Milk, Milk–Soya, and Soya Yoghurt Products

2.2.1. pH Measurement

A CPO–505 pH meter (Elmetron, Zabrze, Poland) was used for the measurements [10,20]. The pH meter was equipped with a universal electrode combined with a temperature sensor, designed to measure liquid and semi-liquid samples. The results were recorded to two decimal places. Each measurement was performed in duplicate.

2.2.2. Texture Determination—Hardness and Adhesion

As part of the texture analysis, two parameters were examined: hardness and adhesiveness. A Brookfield CT3 10K texturometer (AMETEK Brookfield, Middleboro, MA, USA) with a TA4/1000 cylindrical probe (38.1 mm in diameter and 20 mm high) was used for the analysis [10]. Samples at a constant temperature of 5 °C were subjected to probing. The force used in the tests was 0.04 N. The probe was moved toward the specimen at a speed of 2 mm/s and in the opposite direction at 4.5 mm/s. Ten measurements per second were taken. From the start of the measurement, the probe traveled a distance of 25 mm into the sample at a speed of 1 mm/s. One cycle of measurement was made for each type of fermented beverage. Hardness was defined as the force required to deform the sample, while adhesiveness was defined as the force required to detach the probe from the test sample. The results were processed using the TexturePro CT V1.4 Build 17 software supplied with the measurement set. The final results are averages over two replicates, expressed to two decimal places.

2.2.3. Water-Holding Capacity (WHC) Determination

Water-holding capacity (otherwise known as water-binding capacity or water-absorption capacity) is a measure of the total amount of water that can be absorbed per gram of sample [10,20]. Water holding capacity determination was performed at 0, 7, 14, and 21 days of refrigerated sample storage. Forty grams each of fermented sample were weighed into 50 mL falcon-type test tubes. The samples were then subjected to centrifugation in a laboratory centrifuge (MPRW MPW–350R, MPW, Warsaw, Poland) at 3250× g and 4 °C for 20 min. After centrifugation, the supernatant was poured off from the precipitate and the test tubes were weighed again. The measurement result (S) was expressed as the ratio of the weight of the remaining precipitate to the initial sample weight, according to the formula: S = (the weight of the remaining precipitate in grams)/(the initial sample weight in grams) × 100%. The determination was performed three times, and the final result is presented as the mean value and standard deviation recorded to two decimal places.

2.2.4. Determination of the Microflora Population

The test was performed using the traditional method with the following microbiological media: (1) M17 agar (Merck, Darmstadt, Germany) for the determination of the total number of cells of bacteria of the species S. thermophilus; (2) MRS agar (Merck, Darmstadt, Germany) for the determination of lactobacilli of the genus Lactobacillus; and (3) medium for Propionibacterium spp. prepared on the basis of Atlas [32]. The microbiological media were prepared according to the recommendations given by the manufacturers and sterilized in an autoclave at 121 °C for 15 min. Prior to analyses, standard microbiological decimal dilutions of samples were prepared in sterile Ringer’s fluid (Sigma-Aldrich, Burlington, VT, USA), previously prepared according to the manufacturer’s instructions and sterilized in an autoclave for 15 min at 121 °C. Petri dishes with sample cultures were then incubated at 37 °C under the atmospheric conditions recommended for each group of microorganisms: (1) aerobic for S. thermophilus (for 72 h); and (2) anaerobic for bacteria of the genus Lactobacillus (for 72 h) and Propionibacterium spp. (for 7 days) [10,20,32]. At the end of the incubation, the number of colonies grown was determined and the result was recorded as the decimal logarithm calculated from the number of colony-forming units converted to 1 g (colony-forming units in 1 g, CFU/g) of the initial beverage sample. The result was obtained from the average of two replicates and recorded to one decimal place.
At the same time, the microbiological purity of the fermented beverage samples was checked by analyzing the absence of contaminating microflora, i.e., molds, yeasts and Enterobacteriaceae. YGC agar (Merck, Darmstadt, Germany) was used to detect the presence of molds and yeasts, while VRB agar (Merck, Darmstadt, Germany) was used to quantify Enterobacteriaceae. Petri dishes with sample cultures were then incubated at 25 °C for 5 days and 37 °C for 24–48 h, respectively.

2.2.5. Determination of Selected Carbohydrates

The content of selected carbohydrates was analyzed using high-performance liquid chromatography (HPLC) coupled with a refractive index detector (RID). This determination can be divided into the following steps: extraction, HPLC analysis, and data integration.
Extraction. The sample preparation was carried out according to the methodology described by Ziarno et al. [20] without any modification. Into falcon-type test tubes, 8 g of beverage sample was weighed and 32 g of methanol (HPLC-grade; Sigma-Aldrich, Burlington, VT, USA) was added. After capping and mixing, the falcon-type test tubes were placed in an ultrasonic water bath for 30 min at 30 °C. Then, they were centrifuged in a laboratory centrifuge (MPRW MPW–350R, “MPW Med. Instruments” Spółdzielnia Pracy, Warsaw, Poland) at 16,000× g at 4 °C to obtain the supernatant. The supernatant fluid was then filtered through a syringe nylon filter with a pore size of 0.45 µL (CHEMLAND, Stargard, Poland) and concentrated eight times in a water bath at 75 °C before being placed in chromatography vials.
HPLC analysis. An HPLC analysis was performed using a kit consisting of a DeltaChromTM Pump, a Sykam InjectorNeedle Injection Valve, S 6020, a DeltaChromTM Temperature Control Unit, a Sykam Detector, RI Detector S 3580, a Cosmosil Guard Column Sugar–D precolumn (10 mm × 4.6 mm, 5 μm; Cosmosil, Nacalai Tesque, Kyoto, Japan), and a Cosmosil Sugar–D chromatography column (250 mm × 4.6 mm, 5 μm; Cosmosil, Nacalai Tesque, Kyoto, Japan). The chromatographic analysis parameters were as follows: flow rate—1 mL/min, column temperature—30 °C. RI detector settings: range—10,000 mV, and sample rate—2 Hz. The mobile phase of the HPLC analysis is a mixture of acetonitrile (HPLC-grade; Sigma-Aldrich, Burlington, VT, USA) and ultrapure deionized water, in a 60:40 weight ratio. All analyses were performed in duplicate.
Data integration. Once the analysis was complete, the resulting files were identified by comparing the retention times with those of standards of selected carbohydrates (1% aqueous solutions of fructose, glucose, galactose, lactose, sucrose, raffinose, stachyose, and verbascose, among others; Sigma-Aldrich, Burlington, VT, USA) analyzed in the same way. The content of selected carbohydrates in the samples was calculated from the area under the peak of the respective sugar, taking into account the degree of concentration of the initial sample. The final result of the content of selected carbohydrates in the beverage samples was reported as mg per 100 g, to 2 decimal places.

2.3. Statistical Analysis

Based on the results of the above-mentioned analyses, a two- or three-factor analysis of variance (MANOVA) was performed and the statistical significance (p = 0.05) of the differences between the means was estimated using Tukey’s HSD test. The Statgraphics Centurion XVII statistical software was used for this statistical analysis.

3. Results and Discussion

The symbiosis between lactic acid bacteria and propionic bacteria, with their simultaneous use in food, is well-documented in rennet Swiss-type cheeses, e.g., Emmental. The thermophilic lactic acid bacteria used in these cheeses develop in the curd during the early stages of cheese production, converting some of the lactose into lactic acid. With this activity, the lactic acid bacteria make active use of their own proteolytic potential, which the propionic bacteria do not have. Thus, propionic bacteria can benefit from the proteolytic products of milk protein metabolism, i.e., peptides, amino acids, and non-protein nitrogen, resulting from the activity of lactic acid bacteria [33,34,35,36,37]. The symbiosis of propionic bacteria and lactobacilli is also known in medicine. Mixtures of propionic bacteria and lactic acid bacilli have been shown to restore the normal composition and function of the intestinal microflora in premature infants born by caesarean section and in infants following antibiotic therapy [38].

3.1. The Fermentation Kinetic of Milk, Milk–Soya, and Soya Beverages

Over the 24 h of fermentation at 37 °C, the pH values of the beverages with the yoghurt bacteria starter decreased to the greatest extent in the first 3 h, although the pH of the soya beverage decreased the slowest (Figure 1a). Changes in the pH of these beverages fermented at 45 °C were observed for all samples during the first 5 h of the process (Figure 1b). After this time, the rate of pH change slowed but continued on a downward trajectory. Like at fermentation at 37 °C, the soy beverage showed the weakest predisposition to changes in pH value.
In the case of beverages with yoghurt and propionic starters, the pH reduction was also most pronounced in the soy beverage (Figure 1c,d) at both 37 °C and 45 °C. In each case, the pH decreased most rapidly during the first 5 h of the process.
Under both temperature conditions of fermentation with the propionic starter alone, a significantly later pH reduction response was noted than in the fermentation of the previously discussed samples (Figure 1e,f). At 37 °C, no significant change was observed in the first 7 h of the fermentation process, and at 45 °C, changes in pH values only started to be observed after 5 h of fermentation.
A statistical analysis showed that both the duration of fermentation and the type of bacterial starter used had a significant effect on the pH of the analyzed beverages fermented at 37 °C and 45 °C.
According to the literature [39], the pH of fermented dairy beverages should be in the range of 4.0 to 4.5. As reported by Zárate [40], although bacteria of the P. freudenreichii subsp. shermanii species are capable of fermenting lactose, they show poor growth in milk due to the lack of proteases capable of hydrolyzing milk casein. In this study, pH values between 4.0 and 4.5 in practically every fermentation variant were obtained. Only in variants of beverages fermented only with yoghurt bacteria or mixtures with propionic bacteria, fermented at 45 °C, were pH values slightly lower than those in the range given above obtained after 24 h. Therefore, after analyzing all the acidification curves, it was concluded that fermenting for 18 h at 45 °C would be most beneficial.

3.2. Analysis of Fermented Milk, Milk–Soya, and Soya Yoghurt Products

3.2.1. pH Value

Table 2 shows the variation in pH value in all yoghurt products. Due to the long fermentation times of the beverages, their initial pH was low, but this resulted in the very good post-fermentation stability of the yoghurt products during 21 days of refrigerated storage. The pH values of almost all samples were significantly unchanged (p > 0.05) after 21 days, but there were significant differences between beverage types. Lower pH values were found in yoghurt products derived from milk–soy beverages than from cow’s milk or soy beverages. This may indicate some synergistic effect of the compositions of milk–soy beverages on the acidifying activity of the bacteria used to ferment these yoghurt products. The acidity of the yoghurt products was dependent on the microbial composition of the starter culture used in the experiment; beverages fermented with a yoghurt culture or a mixture of yoghurt and propionic bacteria were the most acidified, compared to beverages fermented with propionic bacteria only. It is worth noting the pH value of the soya beverage fermented by yoghurt bacteria, which increased during the first seven days of storage at low temperature and then began to decrease to a level statistically comparable to that observed immediately after fermentation. Such changes in the pH of yoghurt products were the result of the post-fermentation changes (resulting in different buffering capacities of samples due to changes in the protein fraction and acid content) which did not completely stop at the end of fermentation and continued during the first week of cold storage of the samples.
It should be mentioned that many authors have noted that the composition of fermentable beverages is important for the final pH value and its changes during cold storage, which are determined by the buffer capacity of the beverage, the different non-protein nitrogen and vitamin contents, and the availability of fermentable carbohydrates which are necessary for the growth of microorganisms [25,41,42,43]. Additionally, the type of starter culture influences the pH of yoghurt samples [26,44,45]. Results consistent with this study were obtained by Yerlikaya et al. [27], who studied Propionibacterium shermanii subsp. freudenreichii in dairy beverage production. The cited researchers reported significantly more effective pH reduction when Propionibacterium bacteria were used together with lactic acid bacteria than when they were used alone. They also showed that propionic acid bacteria were significantly more effective in lowering the pH of the tested yoghurts when combined with Lactobacillus acidophilus, Bifidobacterium animalis subsp. lactis, Lacticaseibacillus rhamnosus, and Lacticaseibacillus casei.
Many authors have observed changes in the pH of yoghurt products during cold storage; this is explained by the metabolic activity of the starter culture bacteria, which continue to break down the available carbohydrates, albeit at a much slower rate than at their optimum temperature [25,46,47,48,49,50,51,52]. In the case of the yoghurt products studied in this research, such changes in pH were not observed, which was the result of the initial low pH value (caused by the long fermentation time) and the high degree of attenuation of the available sugars (as described below).

3.2.2. Texture

Figure 2a,c,e show that the hardness was significantly higher for all the fermented milk yoghurt product samples compared to yoghurt products obtained from a mixture of milk–soya or soya yoghurt products alone during all storage periods. It follows that the addition of a soya beverage significantly reduces the hardness of the resulting milk curd. The effects of storage time, type of starter, and type of beverage used to obtain milk, milk–soya, and soya yoghurt products on their hardness were noted. An increase in hardness during refrigeration was found in almost every stored sample; these changes were already statistically significant after 7 or 14 days of cold storage. The magnitude of the changes depended on the bacterial culture used to ferment the beverages; the greatest changes were observed when a propionic bacteria starter was used. These changes were not reflected in the absence of changes in pH values, as described earlier.
The type of starter used, the composition of the yoghurt products, and the cold storage time also had a statistically significant effect on the adhesiveness of milk, milk–soya, and soya yoghurt products (Figure 2b,d,f). The highest adhesion values were measured in the milk-based yoghurt products (the exception was the propionic bacterium-fermented yoghurt products, which initially showed adherence at the same level as the other yoghurt samples), while the lowest values were measured in the soya-based yoghurt products. During the storage of the cow’s milk yoghurt product samples and the 2:1 milk–soya mixture, a statistically significant increase in adhesiveness was noted, while in the other yoghurt samples, changes were variable and unpredictable (showing no apparent relationships). The acidifying properties of the propionic bacteria, which are weaker than those of the yoghurt starter culture, did not improve the adhesion values of the yoghurt samples.
The firmness of yoghurt products is one of the most important quality criteria. The production of yoghurt and yoghurt-like products that are free from texture defects continues to be a problem in the dairy industry [53,54]. The texture (i.e., both the hardness and adhesiveness) of yoghurt products depends on the composition of the raw material, the type of bacterial culture used, the fermentation method, and the texturing additives, among other things [47,48,52,55,56,57,58,59,60,61,62,63]. In contrast, Vinderola et al. [64] determined that the rheological properties of fermented milk products depend on the acidity (the higher the acidity, the greater the hardness). Of course, there are also available studies suggesting that the type of milk used and the culture have no effect on the hardness [58,65,66] of the analyzed yoghurts [67,68].
The composition of the proteins present in fermented beverages is extremely important [25]. This is supported by this study, which observed differences in the firmness and adhesiveness of milk, milk–soya, and soya yoghurt products. For example, Tang et al. [69] showed that increasing the content of soya β−conglycinin increases the stiffness of the gel, although it significantly reduces the water retention capacity of the gel. The textural characteristics of cow’s and soya milk gels can be effectively correlated with their microstructure [70]. However, Ashna et al. [25] suggested the formation of some bonds between soya and cow’s milk proteins in samples with the addition of soya beverage, which, in their study, appeared to be more compact, with a regular distribution of the protein network and an increase in gel strength during cold storage, compared to milk samples. During fermentation, the proteolysis of both dairy and soya proteins occurs, leading to a homogeneous and dense microstructure. The differences in the hardness and adhesiveness of milk, milk–soya, and soya yoghurt products are also caused by the difference in the isoelectric point between cow’s milk and soya beverage; the different protein fractions of soya milk have an electrical point ranging from 5.07 to 5.88, while cow’s milk has an electrical point of 4.6 [71,72]. Since the yoghurt samples in this study were characterized by very low pH values (described above), the above information may explain the recorded hardness and adhesiveness values of the analyzed samples. The acidifying properties of the propionic bacteria, which are weaker than those of the yoghurt starter culture, did not improve the textural characteristics of these yoghurt samples. Furthermore, these results are in line with observations made by Park et al. [73], who, using a mixture of skim milk and soya beverage in yoghurt production, found that increasing the proportion of soya beverage led to a decrease in the gel strength of the product.

3.2.3. Water-Holding Capacity (WHC)

Water-holding capacity is defined as the ability to retain the aqueous phase in the resulting gel and is usually the inverse of the syneresis resulting from the shrinkage of the protein gel network, which is associated with the inability of the gel network to hold the liquid phase [74]. In this study, the WHC value is determined by the type of starter culture and the type of beverage used to make the yoghurt, as well as the storage time of the samples (Figure 3a–c). The addition of a soya beverage to cow’s milk statistically significantly reduced the WHC value, depending on the amount added (in general, the greater the addition, the lower the WHC value). The WHC value was influenced by the microbial composition of the starter culture used, which is probably explained by the acidifying properties of the bacteria used. The lowest WHC values were recorded for samples fermented with propionic bacteria culture only (Figure 3c), while a mixture of yoghurt bacteria and propionic bacteria cultures (Figure 3b) yielded WHC values comparable to those found for samples fermented with yoghurt bacteria culture only (Figure 3a). In some samples, the WHC value changed significantly during refrigerated storage; however, the direction of these changes varied according to the type of starter culture and the type of beverage used to make the yoghurt.
Gumus and Gharibzahedi [72] indicated that syneresis and the water-holding capacity are determined by the shrinkage of the gel caused by the lowering of the pH value. In this respect, the literature data are highly contradictory. Osman and Razig [49] found that the use of soya beverage in yoghurt production leads to an increase in the amount of whey secreted during cold storage (i.e., a decrease in WHC values). In contrast, Ashna et al. [25] showed that the secretion of the aqueous phase decreases (and thus, the WHC value increases) during the cold storage of samples; indeed, the smallest amount of secreted aqueous phase (highest WHC value) was revealed in yoghurt samples in which cow’s milk was replaced with the highest amount of soya milk. Additionally, Szajnar et al. [59] showed a tendency for syneresis to decrease with increased storage time of milk yoghurts.
However, it should be noted that the structure of the protein gel, and therefore, its hardness, can also determine the WHC value. Research has confirmed this. Ashna et al. [25] suggested that the syneresis and WHC value may be due to the total solids of the beverage being fermented. Moreover, Malaki et al. [75] indicated that the denaturing effect of the milk and soya proteins and the formation of their joint complexes during heat treatment are decisive for the syneresis and WHC value. In these experiments, cow’s milk and soya beverage were separately subjected to UHT treatment, which may have determined the WHC values obtained and influenced the observed changes in these values during refrigerated storage. In addition, Domagała and Wszołek [68] showed a statistically significant effect of the type of starter culture used on the syneresis of different variants of milk yoghurt.

3.2.4. Microflora Population

The microbiological quality of yoghurt depends on the presence of an adequate quantity of live and active microflora in the starter culture throughout the shelf life of the product. Table 3 shows the microbiological quality of milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored for 21 days. The initial population of lactic bacteria, both S. thermophilus and L. delbrueckii subsp. bulgaricus, did not depend statistically significantly on the type of beverage fermented with these bacteria. This was also the case for propionic bacteria; their initial cell count was the same in all yoghurt product samples, regardless of whether these bacteria were used for fermentation alone or in a mixture with yoghurt bacteria. For all yoghurt product samples fermented by only yoghurt bacteria, the invariability of the S. thermophilus bacterial population was noted up to the 21st day of storage of the samples. In the case of samples fermented with a mixture of yoghurt cultures of bacteria and propionic bacteria, only one significant population change was noted—these were samples of a mixture of cow’s milk and soya beverage in a ratio of 1:2. However, it is difficult to find a scientific justification for these changes, especially as they were not reflected either in the absence of changes in pH (described above) or in the determined carbohydrate levels (described below). As for the L. delbrueckii subsp. bulgaricus bacteria, in most of the yoghurt products tested, they had good survival rates up to the 21st day of storage. Only two exceptions to these observations were noted. The first was samples of a 1:2 mixture of cow’s milk and soya beverage, the same samples in which strange changes in the S. thermophilus bacteria population were noted. The second case was samples of soya beverage. Again, it is difficult for us to find a justification for the changes observed in these two yoghurt product samples, especially as they were not reflected in either the lack of change in pH (described above) or in the determined carbohydrate levels (described below). Perhaps there was some unpredictable environmental factor (e.g., related to the refrigerated sample storage equipment) which may have generated heat stress in the assayed lactobacilli. It was also observed that there was no variability in the cell population of P. freudenreichii subsp. shermanii bacteria over the course of the refrigerated storage of all the yoghurt product variants tested.
The results indicate the absence of molds and yeasts, as well as Enterobacteriaceae family bacteria, in 1 g of each yoghurt product sample. The results obtained from the analysis of all samples indicate a highly acceptable hygienic and sanitary quality of the milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures.
According to Zaręba et al. [76], the survival rate of lactic acid bacteria in fermented cow’s milk depends on the type, species, and strain of the bacteria used. No less important is the effect of storage time [44,77,78]. As indicated in studies by Beal et al. [44] and Shori et al. [79], a reduction in the yoghurt microflora population may be related to a progressive reduction in the pH of yoghurt products during refrigerated storage. The results in this work, obtained with samples with low acidity and no change in acidity during storage, seem to confirm this finding. Additionally, Vinderola et al. [80] showed no significant change in the number of viable bacterial cells when studying the viability of yoghurt microflora in Argentine yoghurts stored at 5 °C for 4 weeks.
Researchers have observed a symbiosis between the S. thermophilus and L. delbrueckii subsp. bulgaricus found in commercial yoghurt cultures [81]. S. thermophilus produce substances that stimulate lactobacilli growth, including lactic, pyruvic, and formic acids, as well as carbon dioxide. L. delbrueckii subsp. bulgaricus, on the other hand, have proteolytic enzymes and release oligopeptides and free amino acids that can be used as a nitrogen source for S. thermophilus during fermentation. In addition, S. thermophilus absorb oxygen, thereby creating favorable conditions for the growth of the lactobacilli [81]. As mentioned earlier, texture is an important characteristic of yoghurt products, and it can also be affected by the action of yoghurt bacteria resulting from the interactions among milk proteins, acids, and the exopolysaccharides produced by these bacteria [82,83,84,85]. As this research indicates, the yoghurt bacterial cell population can be high in yoghurts and remain at an appropriate level throughout the cold storage period; this may also partly determine the textural characteristics of the yoghurt.
The low temperature of yoghurt storage is a physical factor that affects the interior of microbial cells by determining specific mechanisms regulating the intracellular environment, metabolism, structure, and functional stability of the membrane and cell wall components, as well as the conformational stability of proteins and enzyme activity. Key in this situation are the mechanisms responsible for adaptation to low temperatures, particularly a certain adaptive system common to many microorganisms involving the biosynthesis of specific, low-molecular-weight proteins called cold shock proteins (CSPs) [86,87,88,89,90]. The insufficiently rapid reaction of bacterial cells resulting in damage to the apparatus responsible for the synthesis of endogenous proteins may be responsible for the gradual extinction of viable bacterial cells during the low-temperature storage of yoghurts. This might explain the two cases of significant reduction in the lactobacilli population in the yoghurt samples (the samples obtained from a 1:2 mixture of cow’s milk and soya beverage and from soya beverages alone).
Furthermore, in the case of propionic bacteria, a certain symbiosis with lactic acid bacteria can be noted. Tarnaud et al. [26] observed that P. freudenreichii does not grow in soy milk, but that such growth occurs in the presence of L. plantarum, which is capable of releasing amino acids from soy protein. The quoted authors explained the lack of growth of the strain they used, P. freudenreichii, by its inability to utilize the respective carbon or nitrogen sources present in soy milk, or both at the same time. Meanwhile, these capacities are strain-dependent, as in the case of lactic acid bacteria [36,90,91].

3.2.5. Selected Carbohydrates Content

In our study, the cow’s milk before fermentation contained 4.60 g of lactose per 100 g, with no detectable amounts of glucose or galactose. In comparison, the soya beverage contained sucrose (0.255 g), raffinose (0.048 g), stachyose (0.344 g), and verbascose (0.010) g/100 g; meanwhile, glucose, galactose, and maltose were not detected.
The concentrations of selected carbohydrates in all yoghurt product variants are shown in Table 4. In the cow’s milk yoghurt product variants, the glucose, galactose, and lactose contents were determined on all the days of storage. The other yoghurt product variants were assayed for glucose, galactose, maltose, lactose, sucrose, raffinose, stachyose, and verbascose. Samples of cow’s milk yoghurt products showed the presence of significant amounts of lactose, but the lactose content did not change during cold storage of the yoghurt samples, regardless of the type of bacterial starter culture used for milk fermentation. As for glucose and galactose, their amounts were either undetectable or trace; these values did not change during the refrigerated storage of the cow’s milk yoghurt product samples. Cow’s milk–soya yoghurt product samples were also characterized by significant lactose contents and low or undetectable contents of the other analyzed carbohydrates. In each case, their concentrations did not change in a statistically significant way during the 21 days of refrigerated storage of the yoghurt samples. The addition of propionic bacteria to the yoghurt bacterium starter culture or the use of propionic bacteria starter culture alone for beverage fermentation did not result in significant changes in the concentrations of the analyzed carbohydrates during the cold storage of these yoghurt product samples. The situation was different for variants of soya yoghurt products stored in a refrigerator. Lactose was not found in them, and only small amounts of glucose, galactose, maltose, raffinose, and verbascose were detected. Their contents did not change during the refrigerated storage of the yoghurt samples, regardless of the type of bacterial starter culture used in their fermentation.
Propionic bacteria are known to ferment numerous carbohydrates, including lactose, glucose, and trehalose [92]. The P. freudenreichii strain CIRM BIA129 studied by Loux et al. [91] uses lactose, glucose, and galactose, in addition to D–fructose, inositol, and gluconate, but not sucrose and raffinose. The P. freudenreichii examined by Tarnaud et al. [26] was unable to metabolize the sucrose and raffinose present in soya milk. From these results, it can be concluded that the applied propionic bacteria showed the ability to ferment lactose and its hydrolysis products, as well as sucrose, raffinose, stachyose, and verbascose. The study showed that propionic bacteria found suitable conditions for carbohydrate fermentation in both cow’s milk and milk–soya beverages, as well as soya beverages, but to varying degrees, which may explain the different acidity values, live cell populations, and concentrations of selected carbohydrates observed at the time. The presence of soluble oligosaccharides and simpler sugars, including stachyose, raffinose, and sucrose, in the soy beverage—which are also able to be metabolized by many species of lactic acid bacteria—was also confirmed by Hassanzadeh–Rostami et al. [93].

4. Conclusions

This work, to the authors’ knowledge, represents one of the only studies on the use of P. freudenreichii for the fermentation of milk or mixtures of milk with soya beverage to produce yoghurt products. It is possible to obtain various functional yoghurt products based on cow’s milk, as well as a milk–soya blend, using a mixture of yoghurt and propionic starter cultures. The use of propionic bacteria requires a longer fermentation time and a slightly higher process temperature. It was possible to demonstrate that the use of lactic acid bacteria in the form of a yoghurt starter culture, a yoghurt starter in combination with propionic bacteria, as well as a propionic bacteria starter culture alone, maintains the correct pH in cow’s milk, milk–soya, and soya yoghurt products during 21 days of refrigerated storage. The survival rate of S. thermophilus, L. delbrueckii subsp. bulgaricus and P. freudenreichii in yoghurt products depends on the type of starter used and changes during storage. The use of propionic acid fermentation bacteria allows the full attenuation of glucose, stachyose, and verbascose in soya yoghurts. However, refrigerated storage time, as well as the type of starter used, significantly determine the quality characteristics of milk, milk–soya, and soya yoghurt products, such as their firmness, adhesiveness, and water-holding capacity.
The presented research results do not exhaust the research scope of scientific or applied interest. For the development of new products, sensory or organoleptic evaluations are extremely important. In this research, such an evaluation was not conducted. There are indications that the addition of propionic bacteria did not impair the organoleptic characteristics of the obtained functional milk, milk–soy, and soy fermented yoghurt products and improved their nutritional value. In the future, it would be worthwhile to continue this research, including organoleptic evaluations and evaluations of nutritional parameters (e.g., B vitamin levels and protein digestibility).

Author Contributions

Conceptualization, M.Z., D.Z. and R.H.; methodology, M.Z., D.Z. and T.F.; software, M.Z. and R.H.; validation, M.Z., D.Z. and R.H.; formal analysis, M.Z. and T.F.; investigation, M.Z., W.D. and T.F.; resources, M.Z.; data curation, M.Z., D.Z. and R.H.; writing—original draft preparation, M.Z. and D.Z.; writing—review and editing, M.Z.; visualization, M.Z.; supervision, M.Z.; project administration, M.Z.; funding acquisition, M.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The Authors gratefully acknowledge the Institute of Food Sciences of Warsaw University of Life Sciences WULS–SGGW for supporting and providing necessary infrastructure and research stuff and AGM INNOTECH Sp. z o. o. (Kalisz, Poland) for providing the culture starter bacteria.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 12 12603 g001 550
Figure 1. (a–f) The fermentation kinetics (mean values) of milk, milk–soya, and soya beverages with different starter cultures (yoghurt bacteria starter (a,b); propionic bacteria starter (e,f); a mixture thereof (1:1) (c,d)) at two different fermentation temperatures (37 °C (a,c,e) and 45 °C (b,d,f)).
Figure 1. (a–f) The fermentation kinetics (mean values) of milk, milk–soya, and soya beverages with different starter cultures (yoghurt bacteria starter (a,b); propionic bacteria starter (e,f); a mixture thereof (1:1) (c,d)) at two different fermentation temperatures (37 °C (a,c,e) and 45 °C (b,d,f)).
Applsci 12 12603 g001
Applsci 12 12603 g002 550
Figure 2. (a–f) Changes in the hardness (a,c,e) and adhesiveness (b,d,f) of milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations). a,b,c,d,e,f,g,h,i—The same letters on each chart mean there are no statistically significant differences between the compared numerical values (p < 0.05).
Figure 2. (a–f) Changes in the hardness (a,c,e) and adhesiveness (b,d,f) of milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations). a,b,c,d,e,f,g,h,i—The same letters on each chart mean there are no statistically significant differences between the compared numerical values (p < 0.05).
Applsci 12 12603 g002
Applsci 12 12603 g003a 550Applsci 12 12603 g003b 550
Figure 3. (a–c) Changes in water-holding capacity (WHC) of milk, milk–soya, and soya yoghurt products obtained from beverages fermented by different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations). a,b,c,d,e—The same letters on each chart mean there are no statistically significant differences between the compared numerical values (p < 0.05).
Figure 3. (a–c) Changes in water-holding capacity (WHC) of milk, milk–soya, and soya yoghurt products obtained from beverages fermented by different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations). a,b,c,d,e—The same letters on each chart mean there are no statistically significant differences between the compared numerical values (p < 0.05).
Applsci 12 12603 g003aApplsci 12 12603 g003b
Table
Table 1. The schedule for the preparation of milk, milk–soya, and soya beverages fermented using different starter cultures and stored at 5 °C for 21 days.
Table 1. The schedule for the preparation of milk, milk–soya, and soya beverages fermented using different starter cultures and stored at 5 °C for 21 days.
Beverages ReceivedVariants 1: Yoghurt Bacteria Fermented BeveragesVariants 2: Yoghurt and Propionic Bacteria (1:1) Fermented BeveragesVariants 3: Propionic Bacteria Fermented Beverages
cow’s milkxxx
milk–soya (2:1)xxx
milk–soya (1:1)xxx
milk–soya (1:2)xxx
soya beveragexxx
Table
Table 2. pH values of milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations).
Table 2. pH values of milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations).
Type of BeverageStorage Time [Days]071421
Yoghurt Bacteria Fermented Beverages
cow’s milk4.05 b,c ± 0.054.01 b ± 0.054.02 b ± 0.054.01 b ± 0.05
milk–soya (2:1)3.94 a ± 0.043.93 a ± 0.043.92 a ± 0.043.92 a ± 0.04
milk–soya (1:1)3.93 a ± 0.043.90 a ± 0.043.91 a ± 0.043.90 a ± 0.04
milk–soya (1:2)3.92 a ± 0.043.92 a ± 0.043.90 a ± 0.043.90 a ± 0.04
soya beverage4.11 c ± 0.054.38 f ± 0.044.21 d,e ± 0.054.13 c,d ± 0.05
Yoghurt and Propionic Bacteria (1:1) Fermented Beverages
cow’s milk4.01 b ± 0.054.00 b ± 0.043.97 a,b ± 0.043.99 b ± 0.04
milk–soya (2:1)3.92 a ± 0.053.91 a ± 0.053.89 a ± 0.043.89 a ± 0.04
milk–soya (1:1)3.91 a ± 0.043.90 b ± 0.053.88 a ± 0.043.88 a ± 0.04
milk–soya (1:2)3.90 a ± 0.043.88 a ± 0.053.87 a ± 0.053.93 a ± 0.04
soya beverage4.13 c,d ± 0.054.11 c ± 0.044.11 c ± 0.054.14 c,d ± 0.05
Propionic Bacteria Fermented Beverages
cow’s milk4.31 f ± 0.054.37 f ± 0.054.23 e ± 0.054.36 f ± 0.05
milk–soya (2:1)3.98 b ± 0.054.02 b ± 0.054.03 b ± 0.054.05 b,c ± 0.05
milk–soya (1:1)3.96 a,b ± 0.054.00 b ± 0.043.98 b ± 0.044.00 b ± 0.05
milk–soya (1:2)4.01 b ± 0.044.03 b ± 0.054.00 b ± 0.044.04 b,c ± 0.06
soya beverage4.26 e ± 0.054.22 d ± 0.054.29 e ± 0.064.25 e ± 0.06
a,b,c,d,e,f The same letters within the whole column denote no statistically significant differences (p < 0.05).
Table
Table 3. Microflora population of milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations).
Table 3. Microflora population of milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations).
Type of BeverageStorage Time [days]071421
Yoghurt Bacteria Fermented Beverages
S. thermophilus population [log(CFU/g)]
cow’s milk7.9 a ± 0.18.2 a ± 0.18.2 a ± 0.17.9 a ± 0.1
milk–soya (2:1)7.9 a ± 0.18.4 a ± 0.18.4 a ± 0.17.9 a ± 0.1
milk–soya (1:1)7.9 a ± 0.18.4 a ± 0.18.6 a,b ± 0.17.9 a ± 0.1
milk–soya (1:2)7.7 a ± 0.18.4 a ± 0.18.7 a,b ± 0.17.9 a ± 0.1
soya beverage7.4 a ± 0.18.5 a ± 0.18.8 b ± 0.18.0 a ± 0.1
Lactobacillus spp. population [log(CFU/g)]
cow’s milk7.4 a ± 0.17.7 a ± 0.17.9 a ± 0.17.9 a ± 0.1
milk–soya (2:1)7.5 a ± 0.17.8 a ± 0.18.0 a ± 0.17.4 a ± 0.1
milk–soya (1:1)7.6 a ± 0.17.9 a ± 0.18.1 a ± 0.17.1 a,b ± 0.1
milk–soya (1:2)7.6 a ± 0.18.0 a ± 0.18.0 a ± 0.26.8 b ± 0.2
soya beverage7.4 a ± 0.18.1 a ± 0.18.1 a ± 0.16.8 b ± 0.2
Yoghurt and Propionic Bacteria (1:1) Fermented Beverages
S. thermophilus population [log(CFU/g)]
cow’s milk7.5 a ± 0.17.8 a ± 0.17.8 a ± 0.18.2 a ± 0.1
milk–soya (2:1)7.6 a ± 0.17.8 a ± 0.17.7 a ± 0.18.3 a,b ± 0.1
milk–soya (1:1)7.6 a ± 0.17.8 a ± 0.17.8 a ± 0.18.3 a,b ± 0.1
milk–soya (1:2)7.7 a ± 0.17.8 a ± 0.17.8 a ± 0.18.6 b ± 0.1
soya beverage7.6 a ± 0.17.6 a ± 0.17.7 a ± 0.18.1 a ± 0.1
Lactobacillus spp. population [log(CFU/g)]
cow’s milk7.2 a ± 0.47.3 a ± 0.17.8 a ± 0.17.7 a ± 0.1
milk–soya (2:1)7.4 a ± 0.17.6 a ± 0.18.0 a ± 0.18.0 a ± 0.1
milk–soya (1:1)7.7 a ± 0.17.7 a ± 0.17.9 a ± 0.17.9 a ± 0.1
milk–soya (1:2)7.7 a ± 0.17.9 a ± 0.17.9 a ± 0.28.1 a ± 0.1
soya beverage7.8 a ± 0.17.7 a ± 0.27.9 a ± 0.18.0 a ± 0.1
Propionibacterium spp. population [log(CFU/g)]
cow’s milk5.7 a ± 0.15.8 a ± 0.15.6 a ± 0.15.4 a ± 0.1
milk–soya (2:1)5.6 a ± 0.15.7 a ± 0.15.7 a ± 0.15.7 a ± 0.1
milk–soya (1:1)5.7 a ± 0.15.7 a ± 0.15.7 a ± 0.15.8 a ± 0.1
milk–soya (1:2)5.8 a ± 0.15.8 a ± 0.15.8 a ± 0.15.6 a ± 0.1
soya beverage5.9 a ± 0.15.6 a ± 0.15.8 a ± 0.15.8 a ± 0.1
Propionic Bacteria Fermented Beverages
Propionibacterium spp. population [log(CFU/g)]
cow’s milk5.7 a ± 0.15.3 a ± 0.15.4 a ± 0.15.7 a ± 0.1
milk–soya (2:1)5.4 a ± 0.15.1 a ± 0.15.5 a ± 0.15.5 a ± 0.2
milk–soya (1:1)5.7 a ± 0.15.1 a ± 0.35.6 a ± 0.15.6 a ± 0.2
milk–soya (1:2)5.8 a ± 0.15.6 a ± 0.15.7 a ± 0.15.5 a ± 0.1
soya beverage5.8 a ± 0.15.7 a ± 0.15.6 a ± 0.25.3 a ± 0.1
a,b—The same letters in the part of the table concerning individual microorganisms in yoghurt products means there are no statistically significant differences between the compared numerical values (p < 0.05).
Table
Table 4. Selected carbohydrate contents (g/100 g) in milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations).
Table 4. Selected carbohydrate contents (g/100 g) in milk, milk–soya, and soya yoghurt products obtained from beverages fermented using different starter cultures and stored at 5 °C for 21 days (mean values and standard deviations).
Type of CarbohydrateStorage Time [days]071421
Cow’s Milk Yoghurt Products
yoghurt bacteria fermented beverages
glucosend1ndndnd
galactose0.01 a ± 0.000.01 a ± 0.010.01 a ± 0.010.01 a ± 0.01
lactose0.44 b ± 0.030.43 b ± 0.020.40 b ± 0.020.42 b ± 0.03
yoghurt and propionic bacteria (1:1) fermented beverages
glucose<0.01 a<0.01 a<0.01 a<0.01 a
galactose0.01 a ± 0.010.01 a ± 0.000.01 a ± 0.01<0.01 a
lactose0.42 b ± 0.030.45 b ± 0.030.40 b ± 0.020.34 b ± 0.03
propionic bacteria fermented beverages
glucose0.01 a ± 0.010.01 a ± 0.000.01 a ± 0.000.01 a ± 0.01
galactose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.49 b ± 0.030.48 b ± 0.020.50 b ± 0.030.47 b ± 0.02
Milk–Soya (2:1) Yoghurt Products
yoghurt bacteria fermented beverages
glucosendndndnd
galactose0.01 a ± 0.010.01 a ± 0.010.01 a ± 0.010.01 a ± 0.01
maltose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.34 b ± 0.020.33 b ± 0.020.31 b ± 0.030.29 b ± 0.02
sucrose<0.01 a<0.01 a<0.01 a<0.01 a
raffinosendndndnd
stachyosendndndnd
verbascosendndndnd
yoghurt and propionic bacteria (1:1) fermented beverages
glucosendndndnd
galactose0.01 a ± 0.010.01 a ± 0.000.01 a ± 0.010.01 a ± 0.00
maltose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.25 b ± 0.020.26 b ± 0.020.23 b ± 0.020.27 b ± 0.02
sucrosendndndnd
raffinose<0.01 a<0.01 a<0.01 a<0.01 a
stachyosendndndnd
verbascosendndndnd
propionic bacteria fermented beverages
glucosendndndnd
galactose0.01 a ± 0.000.01 a ± 0.010.01 a ± 0.000.01 a ± 0.01
maltose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.27 b ± 0.020.27 b ± 0.030.26 b ± 0.030.26 b ± 0.02
sucrosendndndnd
raffinosendndndnd
stachyosendndndnd
verbascose<0.01 a<0.01 a<0.01 a<0.01 a
Milk–Soya (1:1) Yoghurt Products
yoghurt bacteria fermented beverages
glucosendndndnd
galactose0.01 a ± 0.000.01 a ± 0.010.03 a ± 0.000.01 a ± 0.00
maltose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.18 b ± 0.020.20 b ± 0.020.21 b ± 0.020.20 b ± 0.02
sucrose<0.01 a<0.01 a<0.01 a<0.01 a
raffinose<0.01 a<0.01 a<0.01 a<0.01 a
stachyose<0.01 a<0.01 a<0.01 a<0.01 a
verbascose<0.01 a<0.01 a<0.01 a<0.01 a
yoghurt and propionic bacteria (1:1) fermented beverages
glucose<0.01 a<0.01 a<0.01 a<0.01 a
galactose<0.01 a<0.01 a<0.01 a<0.01 a
maltose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.13 b ± 0.020.21 b ± 0.020.21 b ± 0.020.20 b ± 0.02
sucrosendndndnd
raffinose<0.01 a<0.01 a<0.01 a<0.01 a
stachyose<0.01 a<0.01 a<0.01 a<0.01 a
verbascosendndndnd
propionic bacteria fermented beverages
glucosendndndnd
galactose0.01 a ± 0.000.01 a ± 0.010.01 a ± 0.010.01 a ± 0.00
maltose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.24 b ± 0.020.18 b ± 0.020.17 b ± 0.030.22 b ± 0.02
sucrose<0.01 a<0.01 a<0.01 a<0.01 a
raffinosendndndnd
stachyosendndndnd
verbascosendndndnd
Milk–Soya (1:2) Yoghurt Products
yoghurt bacteria fermented beverages
glucosendndndnd
galactose0.01 ± 0.01<0.010.01 ± 0.000.01 ± 0.01
maltose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.12 ± 0.020.10 ± 0.020.01 ± 0.010.11 ± 0.02
sucrose<0.01 a<0.01 a<0.01 a<0.01 a
raffinose<0.01 a<0.01 a<0.01 a<0.01 a
stachyose<0.01 a<0.01 a<0.01 a<0.01 a
verbascose<0.01 a<0.01 a<0.01 a<0.01 a
yoghurt and propionic bacteria (1:1) fermented beverages
glucosendndndnd
galactose0.01 a ± 0.000.01 a ± 0.01<0.01 a0.01 a ± 0.01
maltose<0.01 a<0.01 a<0.01 a<0.01 a
lactose0.09 b ± 0.010.12 b ± 0.010.08 b ± 0.020.10 b ± 0.02
sucrosendndndnd
raffinose<0.01 a<0.01 a<0.01 a<0.01 a
stachyose<0.01 a<0.01 a<0.01 a<0.01 a
verbascosendndndnd
propionic bacteria fermented beverages
glucosendndndnd
galactose0.01 a ± 0.01<0.01 a0.01 a ± 0.000.01 a ± 0.01
maltose0.01 a ± 0.000.01 a ± 0.010.01 a ± 0.010.01 a ± 0.01
lactose0.12 b ± 0.020.10 b ± 0.020.12 b ± 0.020.13 b ± 0.02
sucrosendndndnd
raffinosendndndnd
stachyosendndndnd
verbascosendndndnd
Soya Yoghurt Products
yoghurt bacteria fermented beverages
glucose<0.01 a<0.01 a<0.01 a<0.01 a
galactose<0.01 a<0.01 a<0.01 a<0.01 a
maltose<0.01 a0.01 a ± 0.010.03 a ± 0.010.01 a ± 0.01
lactosendndndnd
sucrosendndndnd
raffinose<0.01 a<0.01 a<0.01 a<0.01 a
stachyosendndndnd
verbascose<0.01 a<0.01 a<0.01 a<0.01 a
yoghurt and propionic bacteria (1:1) fermented beverages
glucose<0.01 a<0.01 a<0.01 a<0.01 a
galactose<0.01 a<0.01 a<0.01 a<0.01 a
maltose0.01 a ± 0.000.01 a ± 0.010.01 a ± 0.010.02 a ± 0.01
lactosendndndnd
sucrosendndndnd
raffinose<0.01 a<0.01 a<0.01 a<0.01 a
stachyosendndndnd
verbascose<0.01 a<0.01 a<0.01 a<0.01 a
propionic bacteria fermented beverages
glucose<0.01 a<0.01 a<0.01 a<0.01 a
galactose<0.01 a<0.01 a<0.01 a<0.01 a
maltose0.01 a ± 0.010.01 a ± 0.000.01 a ± 0.010.01 a ± 0.00
lactosendndndnd
sucrosendndndnd
raffinose<0.01 a<0.01 a<0.01 a<0.01 a
stachyosendndndnd
verbascose<0.01 a<0.01 a<0.01 a<0.01 a
a,b—The same letters in the part of the table concerning individual yoghurt products mean there are no statistically significant differences between the compared numerical values (p < 0.05); nd—not detected.
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Ziarno, M.; Zaręba, D.; Dryzek, W.; Hassaliu, R.; Florowski, T. Effect of the Addition of Soy Beverage and Propionic Bacteria on Selected Quality Characteristics of Cow’s Milk Yoghurt Products. Appl. Sci. 2022, 12, 12603. https://doi.org/10.3390/app122412603

AMA Style

Ziarno M, Zaręba D, Dryzek W, Hassaliu R, Florowski T. Effect of the Addition of Soy Beverage and Propionic Bacteria on Selected Quality Characteristics of Cow’s Milk Yoghurt Products. Applied Sciences. 2022; 12(24):12603. https://doi.org/10.3390/app122412603

Chicago/Turabian Style

Ziarno, Małgorzata, Dorota Zaręba, Wiktoria Dryzek, Rozeta Hassaliu, and Tomasz Florowski. 2022. "Effect of the Addition of Soy Beverage and Propionic Bacteria on Selected Quality Characteristics of Cow’s Milk Yoghurt Products" Applied Sciences 12, no. 24: 12603. https://doi.org/10.3390/app122412603

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