Encapsulation increases the in vitro bioaccessibility of probiotics in yoghurt

This study examined the encapsulation efficacy of probiotics in yoghurts, product physicochemical properties, the best timing to add encapsulated probiotics during yoghurt manufacturing (before or after fermentation) and their in vitro bioaccessibility. Three different yoghurt types were produced including plain and with encapsulated probiotics added before and after fermentation. A significant (P < 0.05) reduction in total probiotic count was observed in yoghurts containing encapsulated probiotics after 21 days of refrigerated storage. However, the total probiotic count increased during the in vitro colonic fermentation when yoghurts containing encapsulated probiotics were used, indicating increased bioaccessibility of probiotics in the colon.     

Potential application of Saccharomyces boulardii as a probiotic in goat's yoghurt: survival and organoleptic effects

Potential application of Saccharomyces boulardii in yoghurts could offer an alternative probiotic product to people suffering from antibiotic‐associated diarrhoea whilst on treatment. Three different yoghurts were made using goat's milk. Yoghurt 1 was the control with only starter culture added to the milk. For Yoghurt 2, S. boulardii was added in parallel with the starter culture, and for Yoghurt 3, the yeast was added after the yoghurt was coagulated by the starter. Duplicate counts for lactic acid bacteria (LAB) and S. boulardii alongside organoleptic assessment were carried out every 3 days following manufacture and storage at 6 °C. Our results demonstrate that S. boulardii can survive in high numbers for the period of 4 weeks tested without significant changes in taste. Very important is the fact that the presence of the yeast stimulated the survival of the LAB, which in both yeast yoghurts were significantly higher than in the control.     

乳酸菌发酵酸豆乳香气成分检测分析及评价

采用顶空固相微萃取(SPME)与气相色谱- 质谱(GC-MS)联用检测分析技术,并结合感官评分法对保加利亚乳杆菌、瑞士乳杆菌和嗜热链球菌3 种乳酸菌混合发酵的豆乳进行香气分析和评价,探讨不同乳酸杆菌及其与嗜热链球菌按比例混合发酵对酸豆乳香气的影响。感官评定结果表明,乳酸菌种及其混合比例对发酵酸豆乳的香气有明显影响。香气检测分析发现,对比发酵前样品,发酵后酸豆乳中酮类、酸类含量显著增加,而醛类和醇类含量明显减少,3 种酸豆乳中相同关键香气成分含量有差异。感官评定与香气检测分析结果一致,1:1 的保加利亚乳杆菌和嗜热链球菌组成的菌种产香浓郁,产酸力高,是豆乳发酵的优选菌种。     

Stevia‐fortified yoghurt: Stability,antioxidant activity and in vitro digestion behaviour

In this study, yoghurt samples were fortified with 0.25% and 0.5% freeze‐dried stevia extract (FSE). The control and stevia‐fortified yoghurts were evaluated and compared for the viability of the starter cultures, physicochemical properties, total phenolic content (TPC) and antioxidant activity throughout 30 days of storage. In addition, TPC and antioxidant activity were evaluated during in vitro gastrointestinal digestion. The results showed that the yoghurt matrix preserved the TPC, antioxidant capacity and total solids during storage, while the acidity, synaeresis and counts of the starter cultures of the final product were not significantly affected. However, addition of 0.5% FSE exerted a buffering effect on the system. After simulated digestion, the values of TPC and antioxidant activity of the fortified yoghurts increased in relation to the undigested fractions. These findings showed the feasibility of employing FSE as a functional ingredient in the manufacture of yoghurts with potential antioxidant properties.     

Viability of Lactobacillus acidophilus in rice bran‐enriched stirred yoghurt and the physicochemical and sensory characteristics of product during refrigerated storage

This study was aimed at investigating the fortification of probiotic yoghurt with rice bran to increase nutritional properties of the product. The different levels of rice bran (0.3%, 0.6%, 0.9% and 1.2%) were incorporated into milk. The yoghurt samples were produced after pasteurisation, addition of starter culture and 1% Lactobacillus acidophilus suspension (6 × 10⁸ CFU mL^?1) and incubation. During sample storage in refrigerator, the viability of L. acidophilus, viscosity and physicochemical and sensory properties of product were investigated. Rice bran significantly increased the viability of L. acidophilus (P < 0.05). In addition, all probiotic yoghurts incorporating rice bran indicated higher viscosity and acidity and lower pH and syneresis compared to plain yoghurts. Furthermore, increments in rice bran incorporation levels resulted in a reduction in consumers' sample preferences. In general, the addition of rice bran at a suitable level could increase L. acidophilus viability and improve quality attributes of yoghurt.     

Flavour profiles and survival of starter cultures of yoghurt produced from high-pressure homogenized milk

Volatile carbonyl compounds, organic acids and yoghurt bacteria counts were investigated in yoghurts made from ultra-high pressure homogenized milk. Yoghurts were manufactured from milk treated using ultra-high pressure homogenization at 200 or 300 MPa and at 30 °C or 40 °C, and compared with those produced from heat-treated milk with 3% added skim milk powder. To study the evolution of these parameters, samples were analysed after days 1, 14 and 28 of storage. Yoghurts from milk heat-treated or treated at 300 MPa had very similar profiles of organic acids and volatile compounds, as well as similar bacterial counts of both starter cultures. In comparison, yoghurts from milk treated at 200 MPa at either 30 °C or 40 °C gave different profiles, together with a sharp decrease in counts of lactobacilli. During storage, only slight differences in flavour compounds and yoghurt bacteria counts were detected, except in those samples from milk treated at 200 MPa.     

Development of yoghurt from ovine milk with enhanced texture and flavour properties

Six commercial starter cultures, all blends of Streptococcus thermophilus sp. and Lactobacillus bulgaricus sp., were compared for enhanced texture and flavour in yoghurt prepared from ovine milk. The fermentation patterns differed between starters, with YF‐L903 (E) showing the fastest fermentation but slower post‐acidification. YC‐X11 (A) produced the slowest acidification, while YC‐380 (B) resulted in the fastest post‐acidification. Textural and colour properties were affected significantly by the culture used. YF‐L903 (E) enhanced the firmness and luminosity of the yoghurt over storage, increasing mouthfeel and creaminess, as compared to yoghurts prepared with the other starter cultures starters studied.     

Comparison of volatile compounds in yoghurts made from cows’, buffaloes’, ewes’ and goats’ milks

The composition of the volatile fraction of yoghurts made from cows’, buffaloes’, ewes’ and goats’ milks was investigated during the 28 days of storage at 4 °C using solid‐phase microextraction technique (SPME) and gas chromatography coupled to mass spectrometry analysis (GC/MS). A total of 34 volatile compounds were identified in yoghurts during their storage at 4 °C, including aldehydes, ketones, alcohols, esters, acids, terpenes, hydrocarbons and sulphur compounds. In this study, acetaldehyde, diacetyl and acetoin, considered as the major compounds of yoghurt, were detected in all yoghurts.     

Effect of Greek-style yoghurt manufacturing processes on starter and probiotic bacteria populations during storage

This study compared viable counts of Streptococcus thermophilus (starter) and Lactobacillus helveticus R0052 (probiotic), as a function of two manufacturing processes of Greek-style (GS) yoghurt: centrifugation of a curd (GS-CF process) or ultrafiltration of milk prior to fermentation (GS-UF process). Fresh GS-UF and GS-CF yoghurts had between 3 and 7 times higher counts of Lb. helveticus R0052 and S. thermophilus than the regular stirred yoghurt (Control). Strain R0052 was three times more stable in the GS-CF yoghurt than in the Control over the 44 d storage period. The highest lactose content (44 g L⁻¹) was obtained in the Control, while 60% less was obtained in the GS-UF yoghurt; the opposite trend was observed for lactic acid and galactose. Free amino acid levels were 33% higher in the GS products. GS yoghurt can be 10 times better than traditional yoghurt to deliver probiotic bacteria, as a function of the process used.     

Physical characteristics of yoghurts made using exopolysaccharide-producing starter cultures and varying casein to whey protein ratios

This study investigated the physical characteristics of set and stirred yoghurts made at 9% (w/w) total solids with various casein (CN)-to-whey protein (WP) ratios and with exopolysaccharide (EPS)-producing starter cultures (capsular or ropy) during storage. The yoghurt was evaluated for composition, firmness and syneresis of set yoghurt, and for the flow curve and the area of hysteresis loop between the upward and downward curve of stirred yoghurt. Viable counts of starter bacteria and concentrations of lactic acid and EPS in the yoghurt were also determined. EPS concentration did not decrease during storage for 28 d. Firmness and syneresis of set yoghurt decreased when the CN-to-WP ratio was reduced from ratio 4:1 to 1:1 and when EPS starter cultures (especially ropy EPS) were used. Stirred yoghurt with a CN-to-WP ratio of 3:1 and made using ropy EPS-producing starter cultures had a higher shear stress and hysteresis loop area than yoghurt made using capsular EPS- or non-EPS-producing starter cultures. The results suggested that the physical characteristics of set and stirred yoghurts can be improved by varying CN-to-WP ratio and by the use of EPS-producing starter cultures.     

Survival of Lactobacillus casei and functional characteristics of reduced sugar red beetroot yoghurt with natural sugar substitutes

In this study, probiotic gel fermentation and functional characteristics of reduced sugar yoghurt with red beetroot bioactive components and steviol glycosides from Stevia rebaudiana extracts as natural source of noncaloric sweeteners were investigated. A significant increase in Lactobacillus casei viability and fermented gel network and a decrease in syneresis were determined in yoghurt sweetened with steviol glycosides and high content of red beetroot bioactive components such as total phenolics, anthocyanins and total antioxidant capacity (DPPH and FRAP). The survival of L. casei was maintained within probiotic and therapeutic levels (>9 log₁₀ CFU/g), due to the possible prebiotic effect of steviol glycosides and fermentable fibres and phenolic compounds of red beetroot during 28 days of cold storage of the probiotic yoghurts. Colour properties (L*, a*, b*, ΔE*, C*, h*) and such sensory properties as smoothness, sweetness astringency were significantly affected. The highest organic acid content was found in red beetroot enriched yoghurt with stevia, while the most dominant organic acids were butyric, lactic, malic and citric. As a result, it was determined that fermented milk products, which are supported by phytochemical and steviol glycoside interactions, have adequate nutritional effects, high probiotic viability and acceptable sensory properties     

Lactobacillus Gasseri LGZ 1029 in yogurt: rheological behaviour and volatile compound composition

Yogurt preserves and enhances nutritional value of milk. In this study, we have compared several strains to determine the physicochemical, sensory, rheological and aroma characteristics of different yogurts. We used Lactobacillus gasseri LGZ 1029 (LG), commercial probiotic L. rhamnosus (LGG) and traditional fermentation strains Streptococcus thermophilus and L. bulgaricus (SL). Results showed that the flavour and texture characteristics of mixed-strain yogurts were obviously better than in single-strain yogurts. Addition of LG increased pseudoplastic behaviour, as shown by Herschel–Bulkley model analysis of rheological behaviour. The LG + SL group also had both the highest viscosity consistency index and thickening ability. In addition, a total of 57 volatile compounds were detected in yogurts and the fermentation with the addition of LG was mainly affected by ketones. Our study suggested that a yogurt with new attributes can be produced by using LGZ 1029.     

Ethyl carbamate formation regulated by Saccharomyces cerevisiae ZJU in the processing of Chinese yellow rice wine

Ethyl carbamate (EC) is a probable carcinogen existing in most fermented foods. Throughout traditional fermentation processes, the Chinese fermentation starter plays an important role, but it contains varieties of microorganisms which make inhibiting EC efficiently become a challenge. Therefore, the traditional fermentation starter is substituted with a single yeast strain (Saccharomyces cerevisiae ZJU) to regulate EC catabolism. In this work, S. cerevisiae ZJU can reduce EC formation and the data of EC concentration show that there is 85.6% reduction of EC at most using S. cerevisiae ZJU instead of the traditional fermentation starter. Extracellular urea and citrulline were the leading precursors of EC. The content of amino acids and volatile flavour compounds in the experimental group has no significant influence compared to the natural fermentation. The findings in this work suggest that EC can be regulated by means of the fermentation starters variation.     

The effect of starter cultures on proteolytic changes and amino acid content in fermented sausages

The main objective of this work was to examine the effects of using five types of commercial starter cultures in fermented sausages. During the fermentation stage, changes in proteolytic characteristics were observed in fermented sausages. Proteolytic activity was high in Ls_b + Sc:(Lactobacillus sakei + Staphylococcus carnosus) and Pp + Sx:(Pediococcus pentosaceus + Staphylococcus xylosus) starter-inoculated sausages during processing. Moreover, a slight increase in proteolytic activity was detected during storage in both these sausages. Sarcoplasmic and myofibrillar proteins were also affected by this starter culture addition, during the fermentation, ripening and intense proteolysis were observed in both the fermented sausages. The content of free amino acids was similar at the beginning of the fermentation stage for all the studied batches. However, the high differences in the content of free amino acids at the end of the process could be attributed to the starter culture activity.     

Effect of starter cultures on the quality of Suan yu,a Chinese traditional fermented freshwater fish

The generation of volatile compounds of four starter cultures composed of isolated microorganisms from traditional Suan yu was investigated. The cultures included two pure starters (PS1: Lactobacillus plantarum 120 and PS2: Pediococcus pentosaceus 220) and two mixed starters (MS1: L. plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31 at 1:1:1; MS2: P. pentosaceus 220, S. xylosus 135 and S. cerevisiae 31 at 1:1:1). Naturally fermented Suan yu was used as control. The volatile compounds were collected from the headspace of the samples by Solid‐phase microextraction and analysed by gas chromatography–mass spectrometry. The type and total content of volatile compounds in the mixed‐starter‐fermented fish were higher than those of the pure‐starter‐fermented samples and control. A total of seventy nine and eighty volatile compounds were detected in Suan yu fermented with MS1 and MS2, respectively, with ethanol as the predominant compound and hexanal, ethyl acetate, 3‐methylbutanol, 3‐hydroxy‐2‐butanone, hexanoic acid ethyl ester and 2,3‐butanedione as the other compounds. Furthermore, the sensorial acceptance of the different products with mixed starter cultures seemed to improve the quality of Suan yu products.     

Sensory properties of soy yoghurts prepared from yellow and black soymilk using Streptococcus infantarius 12 and Weisellia sp. 4

BACKGROUND: Soy yoghurts containing enhanced bioactive isoflavone aglycones were prepared from combinations of yellow (YS) and black soymilk (BS) (YS:BS = 100:0, 70:30, 50:50 and 0:100, v/v) by fermentation with Streptococcus infantarius 12 and Weisellia sp. 4 at 37 °C for 10 h. Sensory properties of the bioactive soy yoghurts were investigated. Furthermore, other characteristics including the contents of isoflavones, viable cell numbers, pH, colour and DPPH radical scavenging activity were investigated. RESULTS: One hundred percent YS yoghurt showed the highest scores of all sensory attributes while 100% BS yoghurt was the lowest for colour and smoothness. The overall acceptability scores were 5.9 and 5.2 for 100% YS and 100% BS yoghurts, respectively (9‐point scale). The L‐values of soy yoghurts decreased as the percentage BS increased, indicating darkening of soy yoghurts. The contents of bioactive isoflavone aglycones (daidzein and genistein) in soy yoghurts remarkably increased (>1300 mg kg^?1) by fermentation. Viable cell numbers and pH of soy yoghurts ranged from 8.4 × 10⁸ to 9.6 × 10⁸ CFU g^?1 and 4.43 to 4.54, respectively. DPPH radical scavenging activity significantly increased as the percentage BS increased (P < 0.05). CONCLUSION: One hundred percent YS yoghurt was better for overall sensory properties while 100% BS yogurt was more bioactive in terms of the isoflavone aglycone contents and DPPH radical scavenging activity compared to other yoghurts. Copyright © 2008 Society of Chemical Industry     

Physical characteristics of set yoghurt made with altered casein to whey protein ratios and EPS-producing starter cultures at 9 and 14% total solids

This study investigated firmness and syneresis of set yoghurts made at the CN to WP ratios of 4:1, 3:1, 2:1 and 1:1 using non-EPS-, capsular EPS- and ropy EPS-producing starter cultures. The yoghurts were made at 9 and 14% (w/w) total solids. The total solids, total protein, the concentration of lactose and the ratios of CN to WP as well as the protein's profiles (native- polyacrylamide gel electrophoresis) in heated and unheated milk blends were investigated. The level of soluble denatured whey protein aggregates in heated milk was also determined. The concentration of EPS, firmness and level of spontaneous syneresis in set yoghurt were monitored weekly throughout 28 days of storage. The microstructure of the set yoghurt made with milk blends at the CN to WP ratio of 4:1 and using three types of starter cultures was carried out after 1 day of storage. There was no difference in the total solids, total protein and lactose concentration of liquid milk blends, except the CN to WP ratios. There was no difference in whey protein denaturation between milk blends. The level of soluble denatured whey protein aggregates in heated milk blends decreased with reducing CN to WP ratio. The firmness and the level of spontaneous syneresis in set yoghurts decreased as the CN to WP ratios were reduced. The use of EPS-producing starter cultures reduced firmness and syneresis and changed the protein matrix in the microstructure of set yoghurts made at 9% (w/w) total solids compared to the control products. These were not observed in set yoghurts made at 14% (w/w) total solids.     

Proteolytic degradation of ewe milk proteins during fermentation of yoghurts and storage

Yoghurts are mostly produced from cow milk and to a very limited extent from ewe milk. The evolution of caseins and whey proteins in ovine milk submitted to different thermal treatments (63 degrees C/30 min; 73 degrees C/15 min; 85 degrees C/10 min or 96 degrees C/5 min) was followed during fermentation of yoghurts and during their storage up to 14 days, using two different sets of starters. One set of starter LAB was a "ropy" culture (YC-191), which is a well-defined mixed strain culture containing Streptococcus thermophilus ST-143 and Lactobacillus delbrueckii subsp. bulgaricus (LB-18 and LB-CH2). The other set of starter bacteria (YC-460) was a standard yoghurt culture("non-ropy") containing mixed strain culture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Contents of free amino groups in produced yoghurts increased gradually during the fermentation, up to a maximal value obtained after 4 h fermentation, then they did not change significantly during storage of yoghurt produced with YC-191 starter. In contrary, a large drop in the amount of free amino groups was observed in the first 24 h of storage in the case of yoghurt made with YC-460 indicating that microorganisms continue still to grow in low temperatures. During fermentation and storage of both yoghurt types, alpha-lactalbumin was hydrolyzed to a slightly bigger extent than beta-lactoglobulin. During fermentation, beta-casein was slightly more degraded than alpha(s)-caseins; however, the opposite was observed during storage up to 14 days. Generally, a more intense heat pretreatment led to a higher degradation of whey proteins and caseins during fermentation and storage. Differences in proteolytic activity between the two starters used (whey proteins more degraded by YC-191; caseins more degraded by YC-460) may lead to improvement in production and formulation of yoghurts differing in their physicochemical and rheological properties.     

Effect of autochthonous starter cultures on the volatile flavour compounds of Chinese traditional fermented fish (Suan yu)

Effect of autochthonous starter cultures on the volatile flavour compounds of Chinese traditional fermented fish was studied. Lactobacillus plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31, isolated from Suan yu, were selected as starter cultures. Volatiles were extracted by headspace solid‐phase microextraction (SPME) and analysed by gas chromatography–mass spectrometry technology (GC‐MS). Esters and alcohols were the main components of volatiles, accounting for over 50 percentage points in all samples. The highest content of esters (3034.54 μg kg^?1) was observed in S1 inoculated with L. plantarum 120, while the highest content of alcohols (2164.53 μg kg^?1) and ketones (379.98 μg kg^?1) was detected in S3 inoculated with S. cerevisiae 31. The content of acids and aldehydes was lower in inoculated samples. Principal component analysis revealed that the volatile composition was primarily influenced by the nature of the starter cultures. L. plantarum 120 and S. xylosus 135 could accelerate fermentation.