Typical Yogurt Research Articles

Use of Fourier Transform Infrared Spectroscopy for Monitoring the Shelf Life and Safety of Yogurts Supplemented With a Lactobacillus plantarum Strain With Probiotic Potential.

The current study aimed to explore the performance of a probiotic Lactobacillus strain as an adjunct culture in yogurt production and to assess Fourier transform infrared spectroscopy as a rapid, noninvasive analytical technique to evaluate the quality and the shelf life of yogurt during storage. In this respect, bovine milk (full-fat) was inoculated with the typical yogurt starter culture without (control case) or with the further addition of Lactobacillus plantarum T571 as an adjunct (probiotic case). The milk was also inoculated with a cocktail mixture of three strains of Listeria monocytogenes in two different initial levels of inoculum, and the fermentation process was followed. Accordingly, yogurt samples were stored at 4 and 12°C, and microbiological, physicochemical, molecular, and sensory analyses were performed during storage. Results showed that the lactic acid bacteria exceeded 7 log CFU/g during storage in all samples, where the probiotic samples displayed higher acidity, lower pH, and reduced counts of Lb. monocytogenes in a shorter period than the control ones at both temperatures. Pulsed-field gel electrophoresis verified the presence of the probiotic strain until the end of storage at both temperatures and in adequate amounts, whereas the survival and the distribution of Listeria strains depended on the case. The sensory evaluation showed that the probiotic samples had desirable organoleptic characteristics, similar to the control. Finally, the spectral data collected from the yogurt samples during storage were correlated with microbiological counts and sensory data. Partial least squares and support vector machine regression and classification models were developed to provide quantitative estimations of yogurt microbiological counts and qualitative estimations of their sensory status, respectively, based on Fourier transform infrared fingerprints. The developed models exhibited satisfactory performance, and the acquired results were promising for the rapid estimation of the microbiological counts and sensory status of yogurt.

Effect of manufacturing processes and storage on aroma compounds and sensory properties of yoghurt

The goal of this study was to examine how yoghurt manufacturing processes influence the synthesis of aromas and to examine links with sensory properties. A traditional product with 4% protein (control) and two Greek-style yoghurts with 10% protein were made using curd centrifugation or milk ultrafiltration. Of 32 potentially aromatic compounds, six were detected only in yoghurt, six showed no changes between milk and yoghurt, 12 increased following fermentation or storage, and eight showed lower concentrations in yoghurt than in the initial milk. For the six compounds that appeared only after fermentation and the 12 others with higher levels in yoghurt than in milk, volatiles were found to increase by 27% on average during storage. The Greek-style yoghurts had higher “perception of acidity” and lower “smoothness” than did the control. Positive or negative correlations between “typical yoghurt flavour” and 12 volatiles were found.

Effect of different tea extracts on the physicochemical and sensory parameters of stirred probiotic yoghurts.

In yoghurt production, additives and flavours are added after the fermentation process, but in the case of yoghurts with the addition of tea extracts all studies concern set-type yoghurts. For this reason, the aim of this study was to analyse the effect of green, black, red (Pu-erh) and white tea extracts addition on sensory characteristics, pH, viscosity and colour of stirred probiotic yoghurts stored for two weeks. Skim milk powder (10% w/w), sucrose (4% w/w) and typical yoghurt cultures with the addition of Lactobacillus acidophilus LA-5 were applied for yoghurt manufacture. Then yoghurts were stirred and 4, 8, 12% black, red, green and white tea extracts were added. The samples were analysed after 1, 3, 7 and 14 days of storage at 5ºC. Instrumental colour (L*a*b*) determination, rheological measurements and sensory evaluation were carried out. The pH analysis of the final yoghurt samples showed that the type and quantity of tea extract addition had little effect. Apparent viscosity was affected by 12% addition of tea extracts but not by storage time. The instrumental analysis of the colour confirmed the visual assessment. Sensory evaluation revealed that yoghurts with the addition of green tea extract were the most accepted. The addition of extracts made of red, black and white tea resulted in lower values of all the sensory characteristics tested. The stirring method can be applied to the production of probiotic yoghurts with various tea extracts. The acidity of the yoghurts was practically not affected by the addition of the infusion derived from the different types of tea. 4% addition of tea extract did not affect the viscosity of the yoghurts. The best sensory scores among tea yoghurts were obtained by yoghurt with 4% green tea addition.

CHARACTERIZATION OF HAZELNUT MILK FERMENTED BY LACTOBACILLUS DELBRUECKII SUBSP. BULGARICUS AND STREPTOCOCCUS THERMOPHILUS

Raw hazelnut milk were used to develop new plant-based fermented product using commercial starter mix containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains in order to address the current demand for health promoting and functional plant-based dairy-like products. The pH, titratable acidity (TA), serum separation (SS), protein content, fat content and ash content of fermented product were found to be 4.95, 1.25 g lactic acid/ 100 mL, 28.00%, 2.60%, 7.03% and 0.66%, respectively. Fermented hazelnut milk demonstrated non-Newtonian pseudoplastic flow behavior and it’s structure was more predominantly elastic than viscous. Sensory analysis showed that some attributes of fermented hazelnut milk such as color, aroma, consistency, typical yoghurt odor and overall acceptability were less appreciated than Ayran (commercial cow milk yogurt drink) whereas some other attributes were found as satisfying.

Bacterial Diversity in Traditional Doogh in Comparison to Industrial Doogh

Forty-four samples of traditional Doogh and yoghurt were collected from 13 regions of 4 provinces in west of Iran (13 area) and analyzed using molecular methods including PCR, denaturing gradient gel electrophoresis (DGGE) of 16S rDNA, and sequencing. Moreover, collected samples as well as samples from industrially Doogh were analyzed with quantitative real-time PCR (RT-PCR). Analyzed 16S rRNA gene sequences of Doogh samples could be allocated to the presence of Lactobacillus spp. The typical yoghurt starter culture bacteria included four different Lactobacillus species with possible probiotic properties, L. acidophilus, L. helveticus, L. kefiranofaciens, and L. amylovorus. DGGE of traditional Doogh and yoghurt and RT-PCR of traditional Doogh and yoghurt and also industrial Doogh samples demonstrated that traditional Doogh and yoghurt show a higher abundance of total bacteria and lactobacilli and a higher bacterial diversity, respectively. Considering diversity and higher probiotic bacteria content in traditional Doogh, consumers’ healthiness in tribes and villages could be promoted with these indigenous products.

Influence of yogurt fermentation and refrigerated storage on the stability of protein toxin contaminants

Dairy products sold in a ready-to-eat form present the risk that adulterants persisting through manufacturing, storage, and distribution would reach consumers. Pathogenic microbes, including shigatoxigenic strains of Escherichia coli and the toxins they produce, are common food safety hazards associated with dairy products. Ricin and abrin are plant-derived ribosome-inactivating protein toxins related to the shiga-like toxins produced by E. coli. Limited information exists on the effects of manufacturing processes on the stabilities of these heat-resistant ribosome-inactivating proteins in the presence of foods. The goal of this study was to determine how typical yogurt manufacturing and storage processes influence ribosome-inactivating protein toxins. Ricin and abrin were added to skim or whole milk and batch pasteurized. Complete inactivation of both toxins was observed after 30 minutes at 85 °C. If the toxins were added after pasteurization, the levels of ricin and abrin in yogurt and their cytotoxic activities did not change significantly during fermentation or refrigerated storage for 4 weeks. The activities of ricin and abrin were inhibited by skim milk, nonfat yogurt, whole milk, and whole milk yogurt. The results showed minimal effects of the toxins on yogurt pH and %titratable acidity but inhibitory effects of yogurt on toxin activity.

DEVELOPMENT OF SET AND DRINKING SESAME YOGHURT FROM DECORTICATED SESAME SEED

Sesame yoghurt developed from sesame seed fortified with different fortifiers resulted in yoghurt that lacks the typical yogurt texture. This study aimed to dev elop set and drinking yoghurt from sesame milk. Gums were used to develop sesame set yoghurt and sesame yoghurt drink. The best set yoghurt was produced from the sesame milk fortified with 2% Cheese Dried Whey (CDW) plus 0.6% pectin and 0.2% CMC. The best yoghurt drink was produced from sesame milk fortified with dried whey plus 0.2% guar gum and pasteurized at 75°C for 5 min.

Effect of milk fat replacement by polyunsaturated fatty acids on the microbiological, rheological and sensorial properties of fermented milks

AbstractA modified milk (W3DD) where fat had been replaced by oils enriched in ω‐3 polyunsaturated fatty acids was used for the manufacture of a set‐type fermented product. In order to improve the organoleptic properties of the product, 30 g l−1 whey protein concentrate (WPC) was added during the manufacturing process. Samples were fermented employing a commercial probiotic starter culture (ABT‐2), which contained Streptococcus thermophilus ST‐20Y, Lactobacillus acidophilus LA‐5 and Bifidobacterium lactis BB‐12. The acidification process was dependent on the WPC addition, which favoured the increase of viable counts, but fermentation was not influenced by the milk fat composition. The highest counts of the probiotic strains, L acidophilus LA‐5 (3.3 × 105 cfu g−1) and B lactis BB‐12 (5.5 × 107 cfu g−1), after 21 days of storage at 4 °C, were found in fermented products derived from W3DD supplemented with WPC. Addition of WPC also increased the firmness of the products and reduced syneresis. No apparent colour changes due to fat composition or WPC supplementation were observed in the products. Milk fat replacement by oils rich in ω‐3 polyunsaturated fatty acids had a negative influence on the product texture but did not affect the typical yoghurt flavour. These defects were overcome by the addition of 30 g l−1 WPC, which improved the appearance, texture and general acceptability scores in the product. Copyright © 2004 Society of Chemical Industry

Impact of engineered Streptococcus thermophilus trains overexpressing glyA gene on folic acid and acetaldehyde production in fermented milk

The typical yogurt flavor is caused by acetaldehyde produced through many different pathways by the yogurt starter bacteria L. bulgaricus and S. thermophilus. The attention was focused on one specific reaction for acetaldehyde and folic acid formation catalyzed by serine hydroxymethyltransferase (SHMT), encoded by the glyA gene. In S. thermophilus, this enzyme SHMT also plays the typical role of the enzyme threonine aldolase (TA) that is the interconvertion of threonine into glycine and acetaldehyde. The behavior of engineered S. thermophilus strains in milk fermentation is described, folic acid and acetaldehyde production were measured and pH and counts were followed. The engineered S. thermophilus strains StA2305 and StB2305, have the glyA gene (encoding the enzyme serine hydroxymethyltransferase) overexpressed. These engineered strains showed normal growth in milk when it was supplemented with Casitione. When they were used in milk fermentation it was observed an increase in folic acid and in acetaldehyde production by StA2305 and for StB2305 it was noticed a significative increase in folic acid formation.

Formulations and Processing of Yogurt Affect the Microbial Quality of Carbonated Yogurt

Carbonation, flavor, culture type, pH, and storage time were varied to investigate the effects of these variables and their interactions on the growth of both typical and nontypical yogurt cultures and some contaminating bacteria. Two types of yogurt cultures (YC-470 and YC-180) were used as the source of typical yogurt bacteria, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. In addition, Lactobacillus acidophilus (LA-K) and Bifidobacterium longum ATCC 15707 were added as nontypical yogurt cultures to make sweetened low fat (1%) Swiss-style plain, strawberry, and lemon yogurts. Samples were incubated at 43°C until pH values of 5.0 or 4.2 were reached. Strawberry yogurts at low (4.2) and high (5.0) pHs were divided into three portions, which were separately inoculated with contaminating bacteria, Bacillus licheniformis ATCC 14580, Escherichia coli ATCC 11775, and Listeria monocytogenes Scott A. After incorporation of carbon dioxide (1.10 to 1.27vol.me of CO2 gas dissolved in water), the yogurt was stored at 4°C for a 90-d period. Carbon dioxide did not affect the growth of typical or nontypical yogurt bacteria. Also, CO2 did not inhibit the growth of undesirable microorganisms. In general, low levels of CO2 did not affect the bacterial population in yogurt. The microflora of yogurt were influenced by culture type, pH, flavor type, and storage time or their interactions.

Effects of Yogurt With and Without Active Cultures on Vaginal Candidal Infection in Women With Diabetes Mellitus

Introduction: Vaginal candidiasis is a common problem in women with diabetes mellitus. Consumption of yogurt may cause changes in vaginal flora not conducive to overgrowth of Candida.Methods: Seven diabetic women with chronic candidal vaginitis were randomly assigned to one of two treatments groups. Subjects received either frozen low-fat, aspartame-sweetened yogurt with or without typical yogurt organisms (Lactobacillus delbrueckii subsp. bulgahcus and Streptococcus salivarius subsp. thermophilus). The study was conducted in a double-blind manner. Subjects were instructed to consume 6 ounces of yogurt per day. At the study onset and at the end of the two month test period, subjects were asked questions about diabetes, candidiasis history and yogurt consumption. Random blood glucose levels, hemoglobin Ale, and vaginal pH were measured.Results: Hemoglobin Ale and blood glucose levels indicated poor glycemic control in the majority of subjects throughout the study. Both groups had a mean vaginal pH of 6.0 (normal pH 4.0–4.5) prior to yogurt consumption. At the end of the study, vaginal pH of the group consuming yogurt with active cultures decreased to 4.0 while the other group remained at pH 6.0. Subjects consuming yogurt with active cultures reported a decrease in vaginal candidiasis. The other group reported no change.Conclusion: Consumption of yogurt containing active yogurt organisms results in normalizing the vaginal pH which may decrease the incidence of candidal infections in women with diabetes mellitus.

Application of Ultrafiltered Sweet Buttermilk and Sweet Buttermilk Powder in the Manufacture of Nonfat and Low Fat Yogurts

Nonfat and low fat yogurts are soft, low in solids, and exhibit whey separation unless they are heavily stabilized. In this study, the quality of nonfat (9.55 to 10.39% total solids) and low fat (13.40%) yogurts that had been fortified with ultrafiltered sweet buttermilk or buttermilk powder was compared with that of a control yogurt that had been fortified with nonfat dry milk. The titratable acidity and pH of low fat yogurts were higher than those of nonfat yogurts. Low fat yogurt that had been fortified with ultrafiltered sweet buttermilk had the highest pH and titratable acidity. As shearing speed increased, the apparent viscosity of yogurts decreased, indicating a shear thinning property. At a high shearing speed, shearing time had little effect on the apparent viscosity. Nonfat yogurts with tested ingredients were similar to the control in flavor, appearance, texture, aroma, smoothness, and sourness. At a high level of fortification, ultrafiltered sweet buttermilk lacked typical yogurt flavor but had good appearance. The microstructures of nonfat yogurts were more open than those of low fat yogurts, possibly because of the higher protein contents of the latter. Ultrafiltered sweet buttermilk yielded the densest matrix. The addition of up to 4.8% sweet buttermilk powder to low fat yogurt mixes yielded a soft and smooth product.

CARBOHYDRATE UTILIZATION and GROWTH KINETICS IN the PRODUCTION of YOGURT FROM SOYMILK. PART II: EXPERIMENTAL and PARAMETER ESTIMATION RESULTS

Typical yogurt bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus, have been studied for their ability to utilize stachyose and other sugars in soymilk. Subculturing of the inocula on nonfat dry milk powder (NFDM) yielded bacteria that displayed oligosaccharide formation during fermentation of soymilk. However, storage of stock cultures on soymilk for 168 h or longer resulted in stachyose hydrolysis during fermentation. Values of the maximum specific growth rate for mixed cultures of Lactobacillus bulgaricus and Streptococcus thermophilus grown on soymilk at 44°C were estimated using the covariate adjustment method which allows biomass, substrate, and product data to be employed, simultaneously. Point estimates were 0.341, 0.296, and 0.478 h−1 for soymilk fermentation by inocula subcultured on 11% NFDM, for inocula stored in soymilk for greater than 168 h, and for inocula prepared as a mixed culture, respectively. the available electron balance (A.E.B.) was employed to check the consistency of the data using biomass, substrate and product measurements.

A yoghurt-like product made by fermenting ultrafiltered milk containing elevated whey proteins withLactobacillus acidophilus

SUMMARYA fermented milk with typical yoghurt flavour and aroma was prepared using a human strain ofLactobacillus acidophilus. Growth of the lactobacillus was stimulated when the whey proteins of the ultrafiltered skim-milk substrate were increased by addition of ultrafiltered Cheddar cheese whey. Fermentation, which was carried out at 37 °C, was accelerated by addition of lactase. The resulting product had a smooth consistency, a pH of 4⋅2, acetaldehyde levels up to 15 p.p.m. and no off-flavours.L. acidophilusremained viable at a level of approx. 108colony forming units/ml, with no impairment of quality, for up to 14 d at 4 °C.