Performance of different microbial cultures in potentially probiotic and prebiotic yoghurts from cow and goat milks

Lactobacillus acidophilus or Bifidobacterium animalis subsp. lactis Bb‐12 and green banana pulp were used in order to obtain potentially probiotic and prebiotic yoghurts, which were compared over a 45‐day storage period. Goat milk yoghurts demonstrated probiotic effects up to 45 days of storage. Cow milk yoghurts produced with B. animalis subsp. lactis Bb‐12 showed a probiotic effect reduction during the storage period (1.74 log CFU/g). The type of milk affected the yoghurts’ chemical and physicochemical properties. Sensory acceptance was also affected, where cow milk yoghurts were better accepted than goat milk ones.     

Physicochemical,microbiological, rheological,and sensory properties of yoghurts with new polysaccharide extracts from Lactarius volemus Fr. using three probiotics

Polysaccharide extracts (0.05 ~ 0.15% w/w) from Lactarius volemus Fr. were used as growth factors and were incorporated into three different probiotic yoghurts. Yoghurts with polysaccharide extracts had a significantly improved water‐retention capacity and reduced pH (P < 0.05). Polysaccharide extracts also significantly increased the viable count and essential amino acid content in the probiotic yoghurts (P < 0.05). The best sensory properties were achieved with the addition of 0.10% polysaccharide extracts. Our study suggests that polysaccharide extracts from L. volemus Fr. are a highly efficient growth factor for shortening the fermentation period and improving the quality of probiotic yoghurts.     

Functional and technological aspects of whey powder and whey protein products

Commercial whey powder, whey protein concentrates and whey protein isolates (WPIs) were evaluated for certain functional properties and for their application in full‐fat and nonfat yoghurts. The functional properties of whey products varied, and the highest functionality was recorded in samples with high protein levels. Whey powder had the lowest foaming performance and emulsifying capacity, while WPIs possessed the best functional properties of all the other samples. Curd tension (CT), viscosity and syneresis were improved in yoghurts made using fortified cow's milk or reconstituted skim milk with any whey products, while whey powder had no impact on CT.     

Effects of somatic cell counts on the physicochemical and rheological properties of yoghurt made from sheep’s milk

In the present work, yoghurts were made from sheep’s milk with two different somatic cell count (SCC), at low (200 000 cells mL^?1) and high (750 000 cells mL^?1) levels. The characteristics of the final product were analysed for pH, acidity, protein, total solids, fat, syneresis, water holding capacity (WHC) and apparent viscosity. Samples were analysed on days 1, 7 and 14 after production of yoghurts. The SCC had no significant effect either on the acidity or pH of the yoghurt at 24 h (P > 0.05) but a significant effect (P < 0.05) was observed at 168 h. No effects of SCC were observed on total solids and fat content of the yoghurt after 24 and 168 h. High SCC (HSCC) yoghurt had higher protein content (P < 0.05). The yoghurt with the highest SCC had the highest level of syneresis. Viscosity of HSCC yoghurt was higher than that of the low SCC yoghurt on days 1, 7 and 14 of storage. The flow properties also showed that the low SCC yoghurt was softer than that from milk with high content in somatic cells.     

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     

The effect of heat treatment of ovine milk on the compositional and sensory properties of set yoghurt

The aim of this study was to investigate the effect of heat treatment of ovine milk at 60 °C/5 min and 90 °C/5 min (control group) on the compositional and sensory properties of set yoghurt (n = 40). The concentration of apparent casein and total whey protein were significantly higher while sensory properties (except consistency) were not significantly different from the yoghurts in control group (P < 0.05). The results showed that ovine set yoghurt produced by heat treatment at low temperature possessed higher amount of preserved inherent functional and nutritional properties of milk than yoghurt produced by heat treatment at high temperature.     

Physicochemical properties of probiotic frozen yoghurt made from camel milk

The purpose of this research was to determine and compare the physicochemical properties of probiotic frozen yoghurts made from camel and cow milks. The results showed that the viscosity of frozen yoghurt made from camel milk was significantly higher (P < 0.05) than that from cow milk. Less fat was destabilised in frozen yoghurt made from camel milk. The frozen yoghurt made from camel milk required more time for melting than that from cow milk. Flavour scores of the frozen yoghurt made from camel milk constituents were significantly lower (P < 0.05) than those made from cow milk.     

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.     

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     

Physical properties and microstructure of yoghurts supplemented with milk protein hydrolysates

The physical properties and the microstructure of yoghurts containing probiotic bacteria, and supplemented with milk protein hydrolysates, were studied. Three casein hydrolysates and three whey protein hydrolysates were added to milk at a concentration ranging from 0.25 to 4 g L⁻¹. The milks were then fermented with either of two different cultures. The resulting yoghurts with added hydrolysates were compared to the control yoghurt without supplementation. For both cultures, addition of hydrolysates decreased the complex viscosity and graininess in yoghurts. The addition of hydrolysates also reduced fermentation time. Microstructural observations showed a more open and less branched structure in yoghurts when milk protein hydrolysates were incorporated. The difference in fermentation time between milks with different levels of added hydrolysates could partially explain the differences in microstructure and physical properties of the final yoghurts.     

Suitability of high-dynamic-pressure-treated milk for the production of yoghurt

The aim of this work was to evaluate, using the response surface methodology, the effects of different levels of high-pressure homogenization (HPH) on the microbiological and rheological characteristics of yoghurts having different contents of fat and milk solids. The HPH treatment of milk resulted a useful tool to obtain yoghurts having a greater variety of textures associated to a high microbiological quality. In fact, all the yoghurt types obtained by using milk treated with different levels of pressure were characterized by cell loads of the starter cultures higher than 8 log₁₀ cfu ml⁻¹ immediately after the fermentation and than 7 log₁₀ cfu ml⁻¹ after 60 days of storage at 4°C. The HPH treatment seems to favor the growth of Streptococcus thermophilus with respect to that of Lactobacillus delbrueckii subsp. bulgaricus, regardless of the level of pressure applied. The use of a Central Composite Design (CCD) and the polynomial models obtained permitted to individuate the levels of the three independent variables (pressure level, milk solids and fat concentration) able to maximize the growth of starters during the fermentation process, to minimize their viability loss during the refrigerated storage as well as to define their effects on the product viscosity.     

Encapsulation in an alginate–goats’ milk–inulin matrix improves survival of probiotic Bifidobacterium in simulated gastrointestinal conditions and goats’ milk yoghurt

In this work, a new encapsulating matrix, alginate–goats’ milk–inulin, was used to encapsulate Bifidobacterium animalis subsp. lactis BB‐12. The addition of inulin resulted in capsules with a compact structure, and a higher probiotic cell count under simulated gastrointestinal conditions and in probiotic goats’ milk yoghurt during refrigerated storage. Encapsulation of the probiotic bacteria led to slower post‐acidification yoghurts. The results of this study showed that the alginate–goats’ milk–inulin matrix has potential to be used as a new encapsulation material to encapsulate probiotics for use in goats’ milk‐based probiotic fermented dairy products, avoiding the cross‐contamination caused by using capsules based on cows’ milk.     

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.     

Pigment from red fermented rice as colouring agent for stirred skimmed milk yoghurts

Yoghurt is one of the most popular fermented milk products worldwide and is becoming more and more popular in China. In this study, the pigment of red fermented rice (RFR) by Monascus spp., which have been used as natural edible pigments in Asian countries for more than a thousand years, were applied to colour yoghurts. The colour stabilities, physicochemical characters and organoleptic qualities of the yoghurts containing 0 (control), 1.25, 2.5 and 5.0 pigment units/mL of milk, were measured after 1, 4, 7 and 14 days of storage at 4 °C. The results revealed that the colours of the yoghurts were stable during the storage period, and there was no significant effect (P > 0.05) of RFR pigment concentration tested on physicochemical properties and organoleptic characteristics of the yoghurts. This investigation demonstrates that RFR pigment could be used as a colourant in yoghurts.     

RELATION BETWEEN SENSORY TEXTURE PROPERTIES AND EXOPOLYSACCHARIDE DISTRIBUTION IN SET AND IN STIRRED YOGHURTS PRODUCED WITH DIFFERENT STARTER CULTURES

Set yoghurts produced with seven different exopolysaccharide‐producing starter cultures were subjected to sensory texture profiling including texture evaluation before and after a stirring procedure carried out by trained assessors. The microstructure of four selected yoghurts was investigated by confocal laser scanning microscopy with special focus on the distribution of exopolysaccharides (EPS) in the protein network. Two different types of microstructures were observed, one in which EPS were associated with the protein network and another where EPS appeared to be incompatible with the protein; as a consequence, the EPS were situated in the void spaces in the protein network. The latter yoghurts were less ropy and had higher serum separation than the yoghurts where EPS were associated with the protein, and they exhibited a significant increase in mouth thickness as a result of stirring. Yoghurts in which the EPS were associated with protein had high ropiness, low serum separation and appeared more resistant to stirring. The nature of EPS‐protein interactions is extremely important for the textural effects of EPS in fermented milk products, and such interactions depend on the specific starter culture used.     

Modifying the microstructure of low-fat yoghurt by microfluidisation of milk at different pressures to enhance rheological and sensory properties

The effects of microfluidisation of milk at different pressures, prior to heat treatment, on structural and sensory properties of low-fat stirred yoghurt, were investigated. Low-fat yoghurts prepared from microfluidised milk were compared with low-fat (1.5%) and full-fat (3.5%) control yoghurts made with homogenised (20/5 MPa) milk. The microstructure of low-fat yoghurts prepared with microfluidised milk consisted of smaller and more uniform fat globules, well incorporated into more interconnected fat-protein gel networks, compared with those of control yoghurts. This modification in microstructure caused significant changes in gel particle size, sensory profile and rheological behaviour. Microfluidisation increased the gel particle size, gel strength and viscosity; marked beneficial effects were found at higher pressures (50–150 MPa). Microfluidising milk at 50–150 MPa increased the gel strength by 171–195% and viscosity by 98–103%, creating low-fat yoghurts with creaminess and desirable texture properties similar to, or better than, full-fat conventional yoghurt.     

A comparison of selected quality characteristics of yoghurts prepared from thermosonicated and conventionally heated milks

Thermosonication (TS) of preheated (45 °C) milk (0.1%, 1.5% and 3.5% fat) for 10 min at an ultrasound frequency of 24 kHz allowed the preparation of yoghurts with rheological properties superior to those of control yoghurts produced from conventionally heated milk (90 °C for 10 min). Texture profile analysis and flow curves showed that yoghurts from the TS milks had stronger gel structures which displayed higher water-holding capacities (WHC) and lower syneresis. Based on averaged data from a sensory panel (n = 30), TS yoghurts showed superior texture and colour properties and samples with a fat content of 0.1% scored best in terms of overall acceptability. Retentions of water-soluble (thiamine and riboflavin) and fat-soluble (retinol and tocopherol) vitamins were similar in TS and conventionally prepared yoghurts.     

Comparative analysis of physicochemical,rheological, sensory and flavour properties of yoghurts using a new probiotic Bacillus coagulans 13002 with traditional yoghurt starter

Bacillus coagulans 13002 (13002) as a new potential starter was incorporated into the yoghurts for fermentation in this study. We compared three groups of yoghurt, including Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (SL), 13002 (BCS), and 13002 and SL (BCS + SL). Compared with the combination of SL and BCS, the group of BCS + SL exhibited better flavour, higher titratable acidity, cohesiveness and richer volatile compounds, suggesting that the combination of BCS and SL was more efficient to produce the best sensory properties of yoghurt (P < 0.05). The production of volatile compounds in fermentation with and without the addition of BCS was mainly affected by aldehydes, ketones, esters and hydrocarbons, respectively. Furthermore, BCS additions into traditional starters resulted in increasing organic acids and speeding up the usage of sucrose and lactose during the fermentation period of yoghurt. Our study suggested that BCS is a favourable starter supplement for improving the quality of probiotic yoghurts.     

Comparison of the effects of high-pressure microfluidization and conventional homogenization of milk on particle size,water retention and texture of non-fat and low-fat yoghurts

The effect of high-pressure homogenization using a Microfluidizer^® on texture, water-holding capacity, and extent of syneresis on stirred yoghurts was compared with that of conventional homogenization. The effect of homogenization condition on particle size was also assessed in milk and in yoghurt. Stirred yoghurts were prepared from recombined milk samples (0 and 1.5% fat) heat-treated (95 °C, 2 min) and then treated by conventional valve homogenization at 25 MPa or microfluidization at 150 MPa. Homogenization conditions influenced the particle size in milk, gel particle size, and textural quality of stirred yoghurts in a manner dependent upon fat content. Milk microfluidized at 150 MPa had smaller particle size than homogenized milk, but resulted in larger particles in yoghurt. Microfluidization of low-fat milk modified the microstructure of yoghurt, giving more interconnectivity in the protein networks with embedded fat globules, but with similar texture profiles and water retention compared with yoghurt made from conventionally homogenized milk.