Short communication: Effect of the addition of Bifidobacterium monocultures on the physical, chemical, and sensory characteristics of fermented goat milk

J. Dairy Sci. 100:1–8 https://doi.org/10.3168/jds.2017-12818 © American Dairy Science Association®, 2017.

Short communication: Effect of the addition of Bifidobacterium monocultures on the physical, chemical, and sensory characteristics of fermented goat milk A. Mituniewicz-Małek,* M. Ziarno,†1 I. Dmytrów,* and J. Balejko‡

*Department of Dairy Technology and Food Storage, Food Science and Fisheries Faculty, West Pomeranian Technological University, 71-459 Szczecin, Poland †Division of Milk Biotechnology, Department of Biotechnology, Microbiology and Food Evaluation, Faculty of Food Sciences, Warsaw University of Life Sciences—SGGW, 02-776 Warsaw, Poland ‡Department of Process Engineering, Food Science and Fisheries Faculty, West Pomeranian Technological University, 71-459 Szczecin, Poland

ABSTRACT

Short Communication

The aim of the study was to use 3 monocultures of Bifidobacterium (Bifidobacterium animalis ssp. lactis AD600, Bifidobacterium animalis ssp. lactis BB-12, and Bifidobacterium longum AD50) in fermented goat milk to assess the microbial, physicochemical, rheological, and sensory quality of beverages during a 3-wk storage period at 5°C. The results indicated that selected bifidobacteria may be used for production of fermented goat milk because they comply with the minimum standards specified by the Food and Agriculture Organization of the United Nations and the World Health Organization during the entire period of storage. However, goat milk fermented by Bif. longum AD50 had less than 106 cfu/g after 21 d of storage. The acidity, acetaldehyde content, viscosity, and hardness of fermented goat milk beverages depended on the strain and the storage period. Sensory properties were similar and acceptable, with a tendency for the quality to be reduced with an extended storage time. Depending on the monoculture of bifidobacteria used to manufacture fermented goat milk, the product had a different pH value. Titratable acidity in all fermented goat milk increased significantly along with the time of storage. Our study has shown that monocultures of bifidobacteria had a significant effect on the content of acetaldehyde, but the lowest effect over the entire storage period was observed in goat milk fermented by Bif. animalis ssp. lactis BB-12. This sample also had the lowest viscosity values compared with other samples and the best organoleptic properties during a 3-wk storage period. Key words: milk processing, goat milk, lactic acid bacteria, fermentation, cold storage

Fermented dairy products are a crucial part of the human diet in many regions of the world. The most popular fermented milks, predominantly yogurts, are mainly made of cow milk. However, the growing demand for alternative dairy products such as fermented goat milk supplemented with several ingredients, such as fruit, cereals, or pro- and prebiotics (Coda et al., 2012; Eke et al., 2013; Velez-Ruiz et al., 2013), has been observed. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host (FAO/WHO, 2001, 2002; Mohania at al., 2013; Hill et al., 2014). Probiotic microorganisms mainly consist of lactic acid bacteria of the Lactobacillus genus as well as the Bifidobacterium genus, namely Bifidobacterium longum and Bifidobacterium bifidum (Cebeci and Gurakan, 2003; Avonts et al., 2004). It is quite uncommon to ferment a milk with just one monoculture of probiotics such as the Bifidobacterium genus. A pure probiotic fermentation of milk usually leads to products with relatively specific tastes of low sensory acceptance. In technological practice, other starter cultures (e.g., yogurt bacteria) are normally used as a background fermentation culture compensating for these disadvantages (Baron et al., 2000; Gueimonde et al., 2004; Zaręba et al., 2008; Mazochi et al., 2010). Attempts are being made to produce milk products fermented only by monocultures of probiotic cultures (Mituniewicz-Małek et al., 2013; Slačanac et al., 2013). However, it is difficult to produce fermented goat milk with properties comparable with those of fermented cow milk. Bifidobacteria have been suggested to have probiotic or beneficial effects in humans and are therefore used in probiotic dairy products (Fuller and Gibson, 1997). The aim of this study was to use commercial monocultures of Bifidobacterium spp. (Bifidobacterium animalis ssp. lactis and Bif. longum) in the manufacture of fermented goat milk and the assessment

Received March 2, 2017. Accepted May 26, 2017. 1 Corresponding author: [email protected]

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MITUNIEWICZ-MAŁEK ET AL.

of the quality of the obtained beverages during a 3-wk storage period (5 ± 1°C). The raw material in the experimental manufacture of fermented milk products was pooled goat milk purchased from the Jasionek Hodowla Kóz organic farm in Cewlino near Koszalin, Poland. The following 3 commercially available strains were used: Bif. animalis ssp. lactis AD600 (Abiasa, Tui, Spain), Bif. longum AD50 (Abiasa), and Bif. animalis ssp. lactis BB-12 (Chr. Hansen, Hoersholm, Denmark). Goat milk was pasteurized using a batch method (85°C for 15–20 min), cooled down to 40°C, and normalized by adding goat milk powder (Danmis, Wyszyny, Poland) up to 14% of DM. Next, the milk was divided into 3 batches, and each batch was inoculated with 1 of 3 previously activated cultures of Bifidobacterium spp. (in the form of a bulk activated at 40°C for 5 h, which was added to the milk samples in the amount of 5%). Incubation was carried out at 40°C until the formation of curd after approximately 5 h. The end of the fermentation was based on the experimental results of the goat milk fermentation by this group of starter cultures (Mituniewicz-Małek et al., 2014) and based on the pH and fermentation curve set in the culture specification. Next, the samples of fermented goat milk were cooled down to 5 ± 1°C and stored at the same temperature for 3 wk. As a result, 3 types of samples of fermented goat milk were obtained in this study: goat milk fermented by Bif. animalis ssp. lactis AD600 (FNP-A), goat milk fermented by Bif. longum AD50 (FNP-B), and goat milk fermented by Bif. animalis ssp. lactis BB-12 (FNP-C). The samples were tested after d 1, 7, 14, and 21. Physicochemical analysis included determination of titratable acidity in Soxhlet-Henkel degrees, active acidity with a pH meter (IQ 150, Spectrum Technologies, Bridgend, UK), and acetaldehyde content (Lees and Jago, 1969). Rheological analysis included measurements of viscosity and texture. Viscosity was measured using a double gap system of coaxial cylinders in a rheometer (AR2000, American Instruments, Hartland, WI). Apparent viscosity was determined at a coagulation rate ranging from 1 to 400/s and at a constant temperature of the sample (Peltier module). Texture profile analysis was performed with a TA.XT Plus texture analyzer with a computer set (Stable Micro Systems, Surrey, UK). Fermented goat milk samples (in 220-mL cups) were penetrated by an aluminum cylinder (20 mm diameter) to the depth of 15 mm at a speed of 5 mm/s and a press force of 1 N (Domagała and Juszczak, 2004). Hardness, as a major parameter of texture (Salvador and Fiszman, 2004), was only measured and discussed. Organoleptic evaluations were conducted by trained participants (consumers of fermented goat milk) according to ISO (1998). The appearance, taste, smell, and consistency Journal of Dairy Science Vol. 100 No. 9, 2017

of samples were evaluated on a 5-point scale where 1 is the worst score (appearance: 1 = separation of the serum, precipitate; taste: 1 = tastes enough sweet, offflavor; smell: 1 = odor feebly marked, strange odor; consistency: 1 = insufficiently precipitate, not the corresponding color filler) and 5 is the best score (appearance: 5 = appearance without separation of the serum; taste: 5 = tastes pure; smell: 5 = fermented, without foreign flavor; consistency: 5 = homogeneous, viscous, dense, the corresponding color filler). Microbial analysis included a viable cell count of starter bacteria in fermented goat milk after 24 h of fermentation (d 1) and again after d 7, 14, and 21 of storage at 5 ± 1°C. To count viable bacteria, the plate method was applied in 2 replicates for 3 independent replicates of each sample (ISO, 2010). A relevant dilution of samples was prepared in sterile peptone water (10 g/L). Viable counts were enumerated on De Man, Rogosa and Sharpe agar (Merck, Kenilworth, NJ) fortified with cysteine hydrochloride at an amount of 0.05% (wt/vol; Sigma-Aldrich, St. Louis, MO) at pH 5.7 after 72 h of anaerobic incubation of plates (Anaerocult A system, Merck) at 37°C (Simpson et al., 2004). The viable counts were expressed as the number of colony-forming units per gram. The microbiological analysis also included the determination of the contaminating yeasts and molds (YGC agar, Merck). The obtained results of microbial, physicochemical, and rheological analyses were statistically analyzed. These are expressed as arithmetic means and standard deviations. The statistical analyses were carried out by 2-way ANOVA with repeated measures and tests to determine the differences in 2 dependent and independent means (Student’s t-test). The statistical significance of all the tests was P = 0.05. Table 1 shows the mean results of sensory evaluations, the physicochemical and rheological properties of fermented goat milk within 3 wk of cold storage, and the results of 2-way ANOVA. Statistically significant differences among the strains were observed as well as significant effects of storage time on titratable acidity, pH, acetaldehyde content, viscosity, and hardness. Moreover, significant interactions were reported in all fermented goat milk samples between both tested factors and compared with all the quality indicators, such as titratable acidity, pH, content of acetaldehyde, viscosity, and hardness. The titratable acidity of fermented goat milk varied from 31.07 to 54.00 Soxhlet-Henkel degrees. The highest value during the 3-wk storage period was observed in FNP-B, and the lowest value was observed in FNP-C (Table 1). Titratable acidity in all fermented goat milk samples increased significantly along with the time of storage (Table 1). As far as active acidity is concerned, different pH levels were observed in samples within the time of study

Different superscripts within a row show significant difference (P < 0.05). FNP-A = beverage inoculated with Bifidobacterium animalis ssp. lactis AD600; FNP-B = beverage inoculated with Bifidobacterium longum AD50; FNP-C = beverage inoculated with Bifidobacterium animalis ssp. lactis BB-12. 1

4.08d 0.664b 1.371e 0.669c 4.27c 1.399c 1.085e 0.644c 4.44c 0.338d 0.344c 0.383a 4.54b 2.283a 0.990d 0.687c 4.33c 0.935b 0.693a 0.475a 4.60b 0.767b 0.150b 0.116b 4.84a 2.118a 0.702a 0.403a

4.24c 1.473c 0.377c 0.441a

3.00 46.27b 4.63 45.73b 4.75 37.47a 4.75 37.47a

Sensory evaluation (points) Titratable acidity (Soxhlet  Henkel degrees) pH Acetaldehyde (mg/L) Viscosity (mPa/s) Hardness (N)

a–f

4.38a 0.442e 0.394c 0.237e 4.99a 0.560b 0.249c 0.272e 5.20e 0.661b 0.034f 0.127b 5.32e 1.246c 0.309c 0.286e

3.75d 36.13a 4.13 36.27a 4.63 32.13e 4.88 31.07e 3.38 54.00d 4.75 51.07d 4.63 42.00b 4.50 44.67b

b

1  

c

21

b

14 Property

1

a

7

a

FNP-A

Table 1. Quality properties of fermented beverages made of goat milk on d 1, 7, 14, and 211

7

b

FNP-B

14

b

21

d

 

1

a

7

b

FNP-C

14

e

21

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(Table 1). The highest pH (4.38–5.32) was observed in FNP-C samples, and the lowest pH (4.08–4.54) was observed in FNP-B samples. In the product fermented by Bif. animalis ssp. lactis AD600, active acidity ranged from 4.24 to 4.84. However, a significant decrease in pH was observed after the last day of storage (d 21) in all fermented goat milk compared with the values obtained on d 1. Acidity is one of key factors allowing a fermented goat milk to be fit for human consumption. Viable cultures of bacteria are the basis for the manufacture of fermented goat milk, and bacterial activity causes changes in beverage acidity during storage (Birollo at al., 2000). Our study has shown that fermented goat milk had different values for titratable and active acidity depending on the monoculture of Bif. longum and Bif. animalis ssp. lactis used in the manufacturing process. Similar results were obtained by Kongo et al. (2006). Mituniewicz-Małek et al. (2013) also observed that the type of inoculum affects the acidity of goat milk fermented by a monoculture (Lactobacillus paracasei, Lactobacillus casei, and Lactobacillus acidophilus). In addition, results obtained in our study confirmed a significant effect of storage period on the tested properties. Danków et al. (2000) tested fermented milk made of goat milk and observed a significant effect of storage period on both titratable and active acidity. Similar conclusions were made by Baron et al. (2000) when testing milk fermented by Bifidobacterium breve, Bif. longum, Bif. bifidum, and Bifidobacterium infantis. The same was the case for Bozanic and Tratnik (2001), who tested goat milk fermented by Bif. bifidum BB-12. Mituniewicz-Małek et al. (2013) reported an increase in titratable acidity and a significant decrease in pH in goat milk samples inoculated with probiotic bacteria between d 1 and 21 of storage. Bonczar and Wszołek (1997) explained the fluctuations in acidity of fermented milk during cold storage on the basis of the fermentation activity of the microorganisms present, which still ingest lactose at 4°C, although this process is significantly slower than at the optimal growth temperature. Flavor carriers are produced in the metabolism of carbohydrates, lipids, proteins, and citrates (Rysstad et al., 1990; Zaręba et al., 2012). The variety of components affecting the flavor of fermented milk depends on the properties of the bacterial strains used. Acetaldehyde is a typical yogurt metabolite, and it significantly contributes to the product’s organoleptic quality. Nosova et al. (2000) and Margolles and Sánchez (2012) discovered bifidobacteria strains possessing the ability to produce acetaldehyde. During our 3-wk study, the content of acetaldehyde in the samples ranged from 0.338 to 2.283 mg/L. The lowest concentration was observed in FNP-C and the highest was observed in FNP-B after d 21 and Journal of Dairy Science Vol. 100 No. 9, 2017

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d 1, respectively (Table 1). Also, the lowest fluctuations in the content of acetaldehyde were observed in FNPC over the entire storage period. Nevertheless, after 3 wk the acetaldehyde content in all fermented goat milk samples decreased significantly compared with the results obtained on d 1 (Table 1). Our study has shown that monocultures of bifidobacteria have a significant effect on the content of acetaldehyde. A noteworthy result was obtained with the strains of Bif. longum AD50 and Bif. animalis ssp. lactis AD600, which produced a significant amount of acetaldehyde; Bif. animalis ssp. lactis BB-12 showed a lower production of acetaldehyde. A low level of acetaldehyde in fermented goat milk samples was reported by Mituniewicz-Małek et al. (2011a) and Zaręba et al. (2012). According to Rysstad et al. (1990), high levels of acetaldehyde are not likely to occur in fermented goat milk because goat milk, compared with cow milk, contains more than 20 times more free glycine, which inhibits threonine aldolase, an enzyme converting threonine into acetaldehyde and glycine. In addition, along with extending storage, acetaldehyde content decreases successively, as has been confirmed in the available literature (Ozer at al., 2007) as well as in our study. Texture, along with taste and odor, is considered an important quality indicator of fermented goat milk that determines whether such products are attractive components of a basic human diet (Jaworska and Hejduk, 2008; Mituniewicz-Małek et al., 2011b). Hardness and viscosity demonstrate a significant influence over customer preferences, whereas the quality of curd depends on the texture profile of the milk used, the production technology, the additives, and particularly the type and activity of cultures (Bonczar and Reguła, 2003; Gustaw and Nastaj, 2007; Zare et al., 2011). Our research has shown differences in viscosity depending on the type of bifidobacteria monoculture and the storage time of fermented goat milk samples. The viscosity of our fermented goat milk samples ranged from 0.034 to 1.371 mPa/s; the highest values were observed in a beverage inoculated with Bif. longum AD50, and the lowest values were observed in those samples inoculated with Bif. animalis ssp. lactis BB-12. A significant decrease in the viscosity of the fermented goat milk as well as in FNP-A was observed after a comparison between d 1 and 7, whereas a significant increase was reported on d 14 and 21 (Table 1). Also, in terms of hardness, the highest and lowest values were observed in FNPB and FNP-C, respectively. The hardness of the third sample ranged from 0.116 to 0.475 N. In addition, after 1 wk of storage, hardness, similar to viscosity, was significantly lower compared with the tests carried out on d 1, and a significant increase in this value was observed after d 14 and 21 (Table 1). The type of Journal of Dairy Science Vol. 100 No. 9, 2017

inoculum and its composition may alter the physical characteristics of a product by affecting its texture and appearance (Bonczar et al., 2002; Hassan et al., 2002; Domagała and Juszczak, 2004; Domagała and Wszołek, 2008). In addition, Bensimira et al. (2010) reported a significant effect of incubation temperature on the rheological properties of manufactured fermented goat milks. One of the most frequently occurring flaws in the texture of fermented milk is overly loose consistency of beverages produced by the thermostat method as well as excessively liquid consistency and low viscosity of beverages produced by the batch method (Pazakova et al., 1999). These flaws particularly apply to fermented milks made of goat milk because, compared with cow milk, their consistency is less cohesive and has lower viscosity (Domagała and Wszołek, 2008; Danków and Pikul, 2011). Moreover, the chemical composition of goat milk fluctuates depending on the season of the year, causing changes in texture. This hampers production of a product of standard quality throughout the entire lactation period (Domagała and Wszołek, 2000). To minimize the differences in the content of the major components of goat milk and thereby to obtain fermented milks of desirable texture, the milk is enhanced with nonfat DM. Another crucial factor affecting the quality properties of fermented milk beverages is the appropriate choice of starter cultures (Hassan et al., 2002; Domagała and Juszczak, 2004). The results of our study confirm the effect of the monocultures of Bif. longum and Bif. animalis ssp. lactis on the texture of fermented goat milks. In recent years, similar results have been obtained in fermented milks made of goat milk inoculated with relevant cultures and commercial probiotic cultures (Mituniewicz-Małek et al., 2013; Teichert et al., 2015). Domagała (2005) showed that the duration of storage has a significant effect on texture properties of fermented goat milk, and this has been confirmed by many authors (Karademir et al., 2002; Uysal et al., 2003; Salvador and Fiszman, 2004; Tratnik et al., 2006; Domagała and Wszołek, 2008) and by our study. The apparent viscosity of goat yogurt increased during the storage, whereas its hardness remained unchanged; this was also observed by Karademir et al. (2002). In contrast, Uysal et al. (2003) reported increased hardness in yogurts made of goat milk and mixed cow and goat milk after 14 d of storage. The effect of cold storage on texture parameters of fermented goat milks was also observed by Mituniewicz-Małek et al. (2013, 2015). A statistically significant effect of cold storage on cohesiveness was reported by Teichert et al. (2015), who observed that cohesiveness in fermented goat milk inoculated with thickening cultures significantly decreased after only 2 wk of storage. A similar situation was observed for viscosity, whereas the

SHORT COMMUNICATION: ADDITION OF BIFIDOBACTERIUM MONOCULTURES

hardness and consistency of fermented goat milk under study did not change significantly in cold storage. The metabolic activity of the bacteria modifies not only rheological but also organoleptic properties of the product that are crucial from both consumers’ and manufacturers’ perspectives. A sensory analysis has shown that our fermented goat milks had desirable sensory values during the 3-wk storage period (Table 1). When evaluations of all the samples were carried out on certain days, the results were similar. This made choosing the fermented goat milk with the most acceptable properties difficult. The sensory scores of the products were higher in the first 2 wk of the study (4.13–4.88 points) compared with wk 3 (3.00–3.75 points). It has been shown, however, that in the early weeks samples FNP-A and FNP-C were more acceptable than FNP-B. All the samples had homogeneous curd with no expulsion of whey (syneresis) or any gas release. The texture was quite compact once it had been mixed; it showed a tendency to ductility, which is particularly typical of bifidobacteria. The odor and taste were typical for fermented beverages; however, a goat milk flavor was detectable. The FNP-C samples from the final week were rated better than the other fermented goat milk samples. The differences in the titratable acidity, acetaldehyde content, texture, or viscosity were important for the sensory acceptance of the products. Lower scores of samples after d 21 resulted from the production of a slight expulsion of whey, a more detectable goaty aftertaste, and a looser texture. The results of a consumer preference survey showed that flavor, odor, and consistency were the key factors determining whether a fermented goat milk was accepted by consumers (Skrzypczak and Gustaw, 2012). Our study has shown that fermented goat milk inoculated with monocultures of Bifidobacterium maintained a desirable sensory quality for 3 wk; however, when the storage time was extended, the sensory quality decreased. Decreased sensory quality combined with a more detectable goaty aftertaste has also been reported by other authors (Kudełka, 2009; Mituniewicz-Małek et al., 2013). However, Mituniewicz-Małek et al. (2013, 2015) reported similar results on the consistency of fermented goat milk inoculated with probiotic monocultures. Moreover, this study has revealed that in fermented goat milk inoculated with monocultures of Bif. animalis ssp. lactis AD600, Bif. longum AD50, and Bif. animalis ssp. lactis BB-12, the total sensory quality was not significantly affected by the type of inoculum. This is consistent with Domagała and Wszołek (2008). Mazochi et al. (2010) and Salva et al. (2011) obtained similar results in fermented goat milk manufactured with probiotic bacteria of Bifidobacterium or Lactobacillus. They reported that it is possible to manufacture

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fermented goat milk beverages supplemented with probiotics. This is all the more important because a significant group of consumers finds these products’ sensory properties pleasant, although a little specific. Table 2 shows the cell count of bifidobacteria (expressed as a logarithm of cfu/g). The initial viable cell count of bifidobacteria in fermented goat milk was 6.7, 6.8, and 7.4 log cfu/g in milk samples inoculated with Bif. animalis ssp. lactis AD600, Bif. longum AD50, and Bif. animalis ssp. lactis BB-12, respectively. All fermented goat milk samples were free of yeasts and molds. Generally, yogurts and fermented milks are evaluated for 28 to 35 d—that is, the shelf life of the products. The fermented goat milks examined in our study were evaluated for only 3 wk because we did not expect that these samples would show a longer shelf life. When 3 types of fermented goat milk were compared, it was shown that the survival rate of bifidobacteria depended on their type or strain. When samples were stored at refrigerated temperature (5 ± 1°C), the bifidobacteria cell count decreased in 2 types of fermented goat milk (FNP-A and FNP-B); however, statistically significant differences were observed after d 14 (Table 2). The population of bifidobacteria in the third sample (FNP-C) did not change significantly until the last day of the study. Health benefits from consuming fermented goat milk with probiotic bacteria strains depend on the high survival rate of the bacteria. The viable cell count of probiotic bacteria in fermented milk should be a minimum of 6 log cfu/g, as recommended by Codex Alimentarius Commission (2003). This criterion has to be met within the product’s entire shelf life. It is expected that bifidobacteria will show good survival rates during the storage period of products; however, the literature cites various survival rates of bifidobacteria strains and lactic acid bacteria in fermented milk (Vinderola et al., 2000; Gueimonde et al., 2004; Zaręba et al., 2008). Some authors report that lactic acid bacteria and bifidobacteria are more active in goat milk fermentation compared with cow milk fermentation due to the specific composition and structure of goat milk—namely, the higher content of some mineral compounds and short-chain fatty acids as well as the better bioavailability of proteins (Slačanac et al., 2013). Two types of fermented goat milk (FNP-A and FNP-C) could be considered probiotic products during the 21 d of storage, and FNP-B could be considered a probiotic product only for 14 d (considering 106 cfu/g as the minimum). One of the explanations for the higher survival of BB-12 is the lower acidity of the products (Table 1) and the differences between strains used in this study. This last hypothesis is in line with the results of Baron et al. (2000), who demonstrated that the survival rate of Bif. bifidum R071, Bif. breve R070, Journal of Dairy Science Vol. 100 No. 9, 2017

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Bif. infantis R033, and Bif. longum R175 in fermented milk depended on the bifidobacteria strain. Bozanic and Tratnik (2001) proved that the supplementation of goat and cow fermented milk (skim milk powder and whey protein concentrate powder) did not have any effect on the survival rate of bifidobacteria, which was dependent on fermentation only. This is consistent with Kongo et al.’s (2006) results that tested the survival rate of Bif. animalis in fermented products made of goat milk and stored at 5 to 7°C for 10 d. Seelee et al. (2006) stated that the viable cell count of bifidobacteria was 6.5 log cfu/g in goat milk yogurts stored at 4°C for 21 d. Zaręba et al. (2008) revealed that the cell counts of Bif. animalis ssp. lactis BB-12 in fermented and unfermented cow milk stored at 6°C for 4 wk met the therapeutic minimum criteria until the end of the sample storage. Therefore, most authors report good survival rates for many species of bifidobacteria in fermented goat milk (Ziarno et al., 2011; da Silva et al., 2013; Mituniewicz-Małek et al., 2013, 2014; Shori and Baba, 2014). In contrast, Mazochi et al. (2010) observed a decrease in the population of bifidobacteria in yogurts made of goat milk inoculated with Bif. longum, Bif. breve, Bifidobacterium pseudolongum, or Bif. bifidum. The monocultures of Bif. animalis ssp. lactis AD600, Bif. animalis ssp. lactis BB-12, and Bif. longum AD50 may be used in the manufacture of fermented goat milk that complies with the therapeutic minimum for probiotic bacteria (6.0 log cfu/g), as specified by FAO/WHO (2002), within 21 or 14 d of cold storage, respectively. Therefore, fermented goat milk may be an alternative to other probiotic dairy products from which consumers expect health-promoting benefits. The acidity, acetaldehyde content, viscosity, and hardness were dependent on the strain used for manufacture and the period of cold storage. Based on our results, Bif. animalis ssp. lactis AD600 and Bif. animalis ssp. lactis BB-12 are recommended for the production of fermented goat milk. Within 21 d of cold storage, regardless of the inoculum used, the tested products had very similar sensory propTable 2. Survival rate of bifidobacteria (log cfu/g) in fermented goat milk stored refrigerated for 21 d1 (mean ± SD; n = 6) Storage time (d) 1 7 14 21

FNP-A 6.7 6.5 6.1 6.0

± ± ± ±

a

0.1 0.1ac 0.3c 0.4cd

FNP-B 6.8 6.6 6.0 5.6

± ± ± ±

a

0.1 0.1ac 0.4c 0.3cd

FNP-C 7.4 7.4 7.3 7.0

± ± ± ±

0.2b 0.1b 0.1b 0.5ab

a–d Different superscripts within a row show significant difference (P < 0.05). 1 FNP-A = beverage inoculated with Bifidobacterium animalis ssp. lactis AD600; FNP-B = beverage inoculated with Bifidobacterium longum AD50; FNP-C = beverage inoculated with Bifidobacterium animalis ssp. lactis BB-12.

Journal of Dairy Science Vol. 100 No. 9, 2017

erties that were desirable. With the passage of time, all fermented goat milks became less attractive in terms of their quality. Titratable acidity in all fermented goat milk increased significantly along with the time of storage. Depending on the monoculture of bifidobacteria used to manufacture fermented goat milk, pH values were different. Our study has shown that monocultures of bifidobacteria had a significant effect on the content of acetaldehyde, but the lowest fluctuations in the content of acetaldehyde were observed in goat milk fermented by Bif. animalis ssp. lactis BB-12 within the entire storage. This sample also demonstrated the lowest viscosity values. The choice of the type of inoculum also altered the physical characteristics of fermented goat milk by affecting its hardness and organoleptic properties. A sensory analysis has shown that our fermented goat milks had desirable sensory values during a 3-wk storage period. Samples of goat milk fermented by Bif. animalis ssp. lactis BB-12 taken from the final week of storage were evaluated more highly than the other fermented goat milk samples. ACKNOWLEDGMENTS

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