Effects of Fermentation and Storage on the Concentration of Orotic Acid and Uric Acid in Skim Milk

Skim milk (SM) and skim milk yogurt (SMY) were produced and analyzed using high performance liquid chromatography (HPLC) for the presence of two organic acids–orotic acid (OA) and uric acid (UA). The concentration of OA in SM and SMY at 0 days was 106.2 and 46.1 ppm, respectively. After fermentation OA concentration was 56% lower (P <0.05) in SMY than in nonfermented SM. UA content of SM and SMY at 0 days was 23.3 and 20.1 ppm, respectively. Unlike OA, the UA contents were not significantly altered after fermentation. No significant differences were detected in the concentrations of OA and UA when values of SM and SMY of 0 days were compared with those after 3 days storage.     

Growth of probiotic bacteria and bifidobacteria in a soy yogurt formulation

Soy beverage and cows' milk yogurts were produced with Steptococcus thermophilus (ATCC 4356) and Lactobacillus delbrueckii subsp. bulgaricus (IM 025). The drop in pH during fermentation was faster in the soy beverage than in cows' milk, but the final pH values were similar. Yogurts were prepared with a yogurt starter in conjunction with either the probiotic bacteria Lactobacillus johnsonii NCC533 (La-1), Lactobacillus rhamnosus ATCC 53103 (GG) or human derived bifidobacteria. The presence of the probiotic bacteria did not affect the growth of the yogurt strains. Approximately 2 log increases in both L. rhamnosus GG and L. johnsonii La-1 were observed when each was added with the yogurt strains in both cows' milk and the soy beverage. Two of the five bifidobacteria strains grew well in the cows' milk and soy beverage during fermentation with the yogurt bacteria. High pressure liquid chromatography (HPLC) analyses showed that the probiotic bacteria and the bifidobacteria were using different sugars to support their growth, depending on whether the bacteria were growing in cows' milk or soy beverage.     

Effect of Consuming Yogurts Prepared with Three Culture Strains on Human Serum Lipoproteins

Ten human adult males' usual diets were modified by incorporating 681g nonfat, unpasteurized yogurt daily throughout three 14-21 day periods. A different set of select culture strains, two commercial and one patented, were used for yogurt production in the three dietary periods. Including yogurt daily in the diet significantly reduced fasting total serum cholesterol 10-12% in human adult males on some days, but serum cholesterol returned towards control values with continued yogurt consumption. Serum triglycerides and the proportions of serum lipoproteins were not significantly influenced by increasing yogurt consumption. Differences in concentrations of uric, orotic and hydroxymethylglutaric-like acids in the yogurts were insufficient to account for the differences in temporary hypocholesterolemic effects of yogurt consumption seen between strains.     

Physiochemical Properties,Microstructure, and Probiotic Survivability of Nonfat Goats’ Milk Yogurt Using Heat‐Treated Whey Protein Concentrate as Fat Replacer

There is a market demand for nonfat fermented goats’ milk products. A nonfat goats’ milk yogurt containing probiotics (Lactobacillus acidophilus, and Bifidobacterium spp.) was developed using heat‐treated whey protein concentrate (HWPC) as a fat replacer and pectin as a thickening agent. Yogurts containing untreated whey protein concentrate (WPC) and pectin, and the one with only pectin were also prepared. Skim cows’ milk yogurt with pectin was also made as a control. The yogurts were analyzed for chemical composition, water holding capacity (syneresis), microstructure, changes in pH and viscosity, mold, yeast and coliform counts, and probiotic survivability during storage at 4 °C for 10 wk. The results showed that the nonfat goats’ milk yogurt made with 1.2% HWPC (WPC solution heated at 85 °C for 30 min at pH 8.5) and 0.35% pectin had significantly higher viscosity (P < 0.01) than any of the other yogurts and lower syneresis than the goats’ yogurt with only pectin (P < 0.01). Viscosity and pH of all the yogurt samples did not change much throughout storage. Bifidobacterium spp. remained stable and was above 10⁶CFU g^‐1 during the 10‐wk storage. However, the population of Lactobacillus acidophilus dropped to below 10⁶CFU g^‐1 after 2 wk of storage. Microstructure analysis of the nonfat goats’ milk yogurt by scanning electron microscopy revealed that HWPC interacted with casein micelles to form a relatively compact network in the yogurt gel. The results indicated that HWPC could be used as a fat replacer for improving the consistency of nonfat goats’ milk yogurt and other similar products.     

Determination of antioxidant activity of bioactive peptide fractions obtained from yogurt

In this study, physicochemical and microbiological properties of traditional and commercial yogurt samples were determined during 4 wk of storage. Proteolytic activity, which occurs during the storage period of yogurt samples, was also determined. Peptide fractions obtained from yogurts were investigated and the effect of proteolysis on peptide release during storage was determined. The antioxidant activities of peptides released from yogurt water-soluble extracts (WSE) and from HPLC fractions were determined by 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods. The antioxidant activity of WSE from traditional yogurt was greater than that of WSE from commercial yogurts. In analysis by the ABTS method, mean values increased from 7.697 to 8.739 mM Trolox/g in commercial yogurts, and from 10.115 to 13.182 mM Trolox/g in traditional yogurts during storage. Antioxidant activities of peptides released from HPLC fractions of selected yogurt samples increased 10 to 200 times. In all yogurt samples, the greatest antioxidant activity was shown in the F2 fraction. After further fractionation of yogurt samples, the fractions coded as F2.2, F2.3, F4.3, and F4.4 had the highest antioxidant activity values. Total antioxidant activity of yogurts was low but after purification of peptides by fractionation in HPLC, peptide fractions with high antioxidant activity were obtained.     

Microbial, physical and sensory properties of yogurt supplemented with lentil flour

In this study, skim milk (9.5% w/v solid content) was supplemented with 1-3% (w/v) lentil flour or skim milk powder, inoculated with a yogurt culture, fermented and stored at 4 °C. Acid production during the fermentation, microbial growth, physical properties (pH, syneresis, and color), rheological properties (dynamic oscillation temperature sweep test at 4-50 °C), during 28 days of refrigerated storage and also sensory properties (flavor, mouth feel, overall acceptance and color) after production, were studied. Milk supplementation with 1-3% lentil flour enhanced acid production during fermentation, but the microbial population (CFU) of both S. thermophilus and L. delbrueckii subsp. bulgaricus were in the same range in all lentil flour and skim milk powder supplemented yogurts. The average pH of samples decreased from 4.5 to 4.1 after 28 days storage. Syneresis in 1-2% lentil flour supplemented yogurts was significantly higher than all other samples; however, greater lentil supplementation (3%) resulted in the lowest syneresis during the 28 days storage. With respect to color, “a” and “L” values did not significantly differ in all samples and remained constant after 28 days whereas “b” value increased as a result of lentil supplementation. Yogurt with 3% lentil flour showed higher storage (G') and loss (G?) moduli in comparison with samples supplemented with 1-3% skim milk powder and the non-supplemented control yogurt. Storage modulus (G') was higher than loss modulus (G?) in all samples and at all temperatures between 4 and 50 °C and they showed a hysteresis loop over this temperature range when the samples were heated and cooled. 1-2% lentil flour supplemented yogurt showed comparable sensory properties in comparison with 1-2% skim milk powder supplemented yogurt and the control sample.     

Effects of 4 Probiotic Strains in Coculture with Traditional Starters on the Flavor Profile of Yogurt

To study the influence of probiotics on the flavor profile of yogurt, 4 probiotics, including Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus rhamnosus, and Lactobacillus casei, were cofermented with traditional starters. The changes of bacterial growth, acid contents and volatile compounds of yogurt were investigated during fermentation and refrigerated storage. The strains that exhibited a low growth rate in milk did not significantly affect the bacterial population dynamics, acidity, or organic acid content during fermentation and storage. However, high viability and enhancement of postacidification were clearly observed in the samples that contained strains with a high growth rate in milk, particularly L. casei. A total of 45 volatile compounds, detected in most samples, were identified by headspace solid‐phase micro‐extraction followed by gas chromatography‐mass spectrometry. Among these compounds, ketones and aldehydes were the most abundant. The presence of either L. rhamnosus or L. plantarum did not significantly affect the major volatile compounds, while contributions of L. casei and L. acidophilus were found in the formation of minor volatile metabolites. Electronic nose measurements exhibited a good discrimination of samples that contained different probiotics during refrigerated storage.     

Viability of Bifidobacteria Strains in Yogurt with Added Oat Beta-Glucan and Corn Starch during Cold Storage

Abstract: Probiotics must be consumed at a level of 10⁷ CFU/mL for successful colonization of the gut. In yogurts containing beneficial cultures, the survival of probiotic strains can quickly decline below this critical concentration during cold storage. We hypothesized that beta-glucan would increase the viability of bifidobacteria strains in yogurt during cold storage. Yogurts were produced containing 0.44% beta-glucan (concentrated or freeze-dried) extracted from whole oat flour and/or 1.33% modified corn starch, and bifidobacteria (B. breve or B. longum) at a concentration of at least 10⁹ CFU/mL. All yogurts were stored at 4 °C. Bifidobacteria and yogurt cultures, Streptococcus thermophilus and Lactobacillus delbureckii subsp. bulgaricus, were enumerated from undisturbed aliquots before fermentation, after fermentation, and once a week for 5 wk. S. thermophilus and L. bulgaricus maintained a concentration of at least 10⁸ CFU/mL in yogurts containing concentrated or freeze-dried beta-glucan regardless of starch addition, and in the control with no added beta-glucan or starch. Similarly, the probiotic, Bifidobacterium breve, survived above a therapeutic level in all treatments. The addition of beta-glucan prolonged the survival of Bifidobacterium longum at a concentration of at least 10⁷ CFU/mL by up to 2 wk on average beyond the control. Further, the inclusion of concentrated beta-glucan in yogurt improved survival of B. longum above 10⁷ CFU/mL by 1 wk longer than did freeze-dried beta-glucan. Study results suggest that beta-glucan has a protective effect on bifidobacteria in yogurt when stressed by low-temperature storage. Practical Application: This study suggests that beta-glucan (oat fiber) may improve bifidobacteria survival in yogurt during refrigerated storage.     

Lactic acid production and rheological properties of yogurt made from milk acidified with carbon dioxide

The influence of milk acidification up to pH 6.0 with CO₂ on D ‐ and L ‐lactic acid production and lactose consumption by yogurt starter, changes in the pH, and rheological and sensory properties of yogurt were studied. A slight influence of CO₂ on lactic acid production during yogurt manufacture was detected. No significant changes in lactic acid concentration were observed during storage, although the final concentration was significantly lower in control than in pH 6.2 and 6.0 acidified samples. A great influence of CO₂ on D ‐lactic acid production was not observed. Yogurt manufactured from milk with lower pH values showed lower final pH values after 7 days of storage. The viscosity was similar in all analysed samples. No significant differences in sensory characteristics between unacidified and acidified yogurts were detected. © 1999 Society of Chemical Industry     

Survival and Metabolic Activity of Microencapsulated Bifidobacterium longum in Stirred Yogurt

ABSTRACT: Live cells of Bifidobacterium longum, microencapsulated in K‐carrageenan, were added to stirred yogurt after fermentation (pH 4.6) and stored at 4.4 °C for 30 d. Cell enumeration indicated no decline of encapsulated cell number in yogurt samples, while there was significant reduction in nonencapsulated cell population (89.3% for B. longum B6 and 91.8% for B. longum ATCC 15708). Ion‐exchange high‐performance liquid chromatography showed comparable amounts of lactic and acetic acids in all samples, indicating little metabolic activity by bifidobacteria in experimental yogurts. Consumer sensory analysis of blackberry‐flavored yogurts revealed that samples containing encapsulated bifidobacteria had a grainy texture. Results suggested that microencapsulation protected bifidobacteria from the low pH of yogurt.     

Survival of free and encapsulated probiotic bacteria and their effect on the sensory properties of yoghurt

The survival and effect of free and calcium-induced alginate-starch encapsulated probiotic bacteria (Lactobacillus acidophilus and Bifidobacterium lactis) on pH, exopolysaccharide production and influence on the sensory attributes of yogurt were studied over 7 weeks storage. Addition of probiotic bacteria (free or encapsulated) reduced acid development in yogurt during storage. Post-acidification in yogurt with encapsulated probiotic bacteria was slower compared to yogurt with free probiotic bacteria. More exopolysaccharides were observed in yogurts with probiotic cultures compared to those without probiotic cultures. The results showed that there was an increased survival of 2 and 1 log cell numbers of L. acidophilus and B. lactis, respectively due to protection of cells by microencapsulation. The addition of probiotic cultures either in the free or encapsulated states did not significantly affect appearance and colour, acidity, flavour and after taste of the yogurts over the storage period. There were, however, significant differences (P<0.05) in the texture (smoothness) of the yogurts. This study has shown that incorporation of free and encapsulated probiotic bacteria do not substantially alter the overall sensory characteristics of yogurts and microencapsulation helps to enhance the survival of probiotic bacteria in yogurts during storage.     

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.     

The effect of inulin as a fat replacer on the quality of set-type low-fat yogurt manufacture

The influence of different levels of inulin on the quality of fat-free yogurt production was investigated. Inulin was added to milk containing 0.1% of milk fat to give inulin levels of 1, 2 and 3%. The experimental yogurts were compared with control yogurt produced from whole milk. The total solids content of milk was standardized to 14% by adding skim milk powder to the experimental yogurt. The chemical composition, pH, titratable acidity, whey separation, consistency, acetaldehyde and volatile fatty acidity contents were determined in the experimental yogurts after 1, 7 and 15 days. Sensory properties of the yogurts were evaluated during storage. The addition of inulin at more than 1% increased whey separation and consistency. Acetaldehyde, pH and titratable acidity were not influenced by addition of inulin. Tyrosine and volatile fatty acidity levels were negatively affected by inulin addition. With respect to the organoleptic quality of yogurt, inulin addition caused a decrease in organoleptic scores: the control yogurt had the highest score, and the lowest score was obtained in yogurt samples containing 3% of inulin. Overall, the yogurt containing 1% of inulin was similar in quality characteristics to control yogurt made with whole milk.     

Donkey Milk for Manufacture of Novel Functional Fermented Beverages

The aim of this work was to investigate on the functional features of a donkey milk probiotic berevage as a novel food. Particularly, it was to study the decrease of lactose content and the antioxidant activity of standard yogurt (YC) and probiotic yogurt (YP; Lactobacillus acidophilus, Lactobacillus casei) from donkey milk during the storage up to 30 d at 4 ºC. The evolution of lactose content using enzymatic‐spectrophotometric kits was analyzed. Antioxidant activity of yogurt was measured using 2,2’‐azino‐bis‐3‐ethylbenzothiazoline‐6‐sulfonic acid (ABTS), ferric reducing antioxidant power (FRAP), and thiol assays. Parallel consumer sensory studies were carried out as consumer test in order to gain information about the impact of these novel fermented beverages on sensory perceptions. The statistical analysis has shown significant effect of studied factors. The results showed that the lactose content gradually decreased during storage in both yogurts, reaching values of 2.36% and 2.10% in YC and YP, respectively, at 30 d (P < 0.05). During storage of both yogurt types, the antioxidant activity increased, but YP showed a higher antioxidant activity than YC. The results suggest that the antioxidant activity of yogurt samples was affected by cultures of lactic acid bacteria (LAB). We conclude that the fermented donkey milk could be configured as health and nutraceutical food, which aims to meet nutritional requirements of certain consumers groups with lactose or cow milk protein intolerance.     

Antioxidant activity and flavor compounds of hickory yogurt

Hickory milk and reconstituted milk (about 12 g/100 g total solid) were mixed in the proportion of 3:7 by volume to prepare hickory milk yogurt. Cow milk yogurt was used as control. The acidity and total count of lactic acid bacteria of hickory milk yogurt were not significantly different from cow milk yogurt (p > 0.05). Compared with cow milk yogurt, hickory milk yogurt had higher total solids, fat, crude protein, and amino acids, but lower ash and not-fat solids. Sensory evaluation showed that the appearance and flavor scores of hickory milk yogurt had no significant difference from cow milk yogurt (p > 0.05), but the texture score was significantly higher (p < 0.05). IC₅₀ values in relation to 1,1-diphenyl-2-picrylhydrazyl scavenging activity and inhibition of lipid peroxidation (46.88 and 26.70 g/L) of hickory milk yogurt were significantly lower than those of cow milk yogurt which suggested that the antioxidant activity of hickory milk yogurt was significantly higher than cow milk yogurt (p < 0.05). There were 30 and 28 kinds of volatile compounds identified in hickory milk yogurt and cow milk yogurt, respectively. Compared with cow milk yogurt, the concentration of acetaldehyde, hexanal, nonanal, 2-nonanone, caproic acid, heptylic acid, and nonanoic acid in hickory milk yogurt increased significantly, and the concentration of benzaldehyde, 2,3-pentanedione, 2,3-butanedione, 3-hydroxy-2-butanone, acetic acid, butyric acid, and benzoic acid decreased significantly (p < 0.05).     

Industrial yogurt manufacture: monitoring of fermentation process and improvement of final product quality

Lactic acid fermentation during the production of skim milk and whole fat set-style yogurt was continuously monitored by measuring pH. The modified Gompertz model was successfully applied to describe the pH decline and viscosity development during the fermentation process. The viscosity and incubation time data were also fitted to linear models against ln(pH). The investigation of the yogurt quality improvement practices included 2 different heat treatments (80°C for 30 min and 95°C for 10 min), 3 milk protein fortifying agents (skim milk powder, whey powder, and milk protein concentrate) added at 2.0%, and 4 hydrocolloids (κ-carrageenan, xanthan, guar gum, and pectin) added at 0.01% to whole fat and skim yogurts. Heat treatment significantly affected viscosity and acetaldehyde development without influencing incubation time and acidity. The addition of whey powder shortened the incubation time but had a detrimental effect on consistency, firmness, and overall acceptance of yogurts. On the other hand, addition of skim milk powder improved the textural quality and decreased the vulnerability of yogurts to syneresis. Anionic stabilizers (κ-carrageenan and pectin) had a poor effect on the texture and palatability of yogurts. However, neutral gums (xanthan and guar gum) improved texture and prevented the wheying-off defect. Skim milk yogurts exhibited longer incubation times and higher viscosities, whereas they were rated higher during sensory evaluation than whole fat yogurts.     

Fat-free yogurt made using a galactose-positive exopolysaccharide-producing recombinant strain of Streptococcus thermophilus

To prevent textural defects in low-fat and fat-free yogurts, fat substitutes are routinely added to milk. In situ production of exopolysaccharides (EPS) by starter cultures is an acknowledged alternative to the addition of biothickeners. With the aim of increasing in situ EPS production, a recombinant galactose-positive EPS⁺Streptococcus thermophilus strain, RD-534-S1, was generated and compared with the parent galactose-negative EPS⁺ strain RD-534. The RD-534-S1 strain produced up to 84 mg/L of EPS during a single-strain milk fermentation process, which represented 1.3 times more than the EPS produced by strain RD-534. Under conditions that mimic industrial yogurt production, the starter culture consisting of RD-534-S1 and (EPS⁻) Lactobacillus bulgaricus L210R strain (RD-534-S1/L210R) led to an EPS production increase of 1.65-fold as compared with RD-534-S1 alone. However, the amount of EPS produced did not differ from that found in yogurts produced using an isogenic starter culture that included the parent S. thermophilus strain RD-534 and Lb. bulgaricus L210R (RD-534/L210R). Moreover, the gel characteristics of set-style yogurt and the rheological properties of stirred-style yogurt produced using RD-534-S1/L210R were similar to the values obtained for yogurts made with RD-534/L210R. In conclusion, it is possible to increase the production of EPS by ropy S. thermophilus strains through genetic engineering of galactose metabolism. However, when used in combination with Lb. bulgaricus for yogurt manufacture, the EPS overproduction of recombinant strain is not significant.     

Fermentation and Properties of Calcium-fortified Soy Milk Yogurt

Calcium-fortified soy milk yogurt containing 190 mg calcium/100g was produced and evaluated for textural and microstructural properties. The soy milk base contained 10% full fat soy flour, 2.25% soy protein isolate, 2.75% high fructose corn syrup, 1.55% calcium lactogluconate, and 1.25% potassium citrate. The mixture was heated 5 min at 80°C, cooled to 42°C, and inoculated with yogurt cultures. Calcium-fortified soy milk required a higher rate of inoculation (5%) than non-fortified soy milk (2.5%) and had higher titratable acidity and more syneresis. Calciumfortified soy milk yogurts showed comparable gel strength with that of commercial regular yogurt. Gels from nonfortified soy milk yogurts were hard and brittle. Addition of calcium did not significantly affect microstructure of the yogurts.     

Effects of fructooligosaccharide and whey protein concentrate on the viability of starter culture in reduced-fat probiotic yogurt during storage

ABSTRACT:  Viability of yogurt starter cultures and Bifidobacterium animalis was assessed during 28 d storage in reduced-fat yogurts containing 1.5% milk fat supplemented with 1.5% fructooligosaccharide or whey protein concentrate. These properties were examined in comparison with control yogurts containing 1.5% and 3% milk fat and no supplement. Although fructooligosaccharide improved the viability of Streptococcus thermophilus , Lactobacillus delbrueckii subs. bulgaricus, and Bifidobacterium animalis , the highest growth was obtained when milk was supplemented with whey protein concentrate in reduced-fat yogurt ( P < 0.05). Supplementation with 1.5% whey protein concentrate in reduced-fat yogurt increased the viable counts of S. thermophilus , L. delbrueckii subs. bulgaricus, and B. animalis by 1 log cycle in the 1st week of storage when compared to control sample. Similar improvement in the growth of both yogurt bacteria and B. animalis was also obtained in the full-fat yogurt containing 3% milk fat and no supplement. Addition of whey protein concentrate also resulted in the highest content of lactic and acetic acids ( P < 0.05). A gradual increase was obtained in organic acid contents during the storage.     

Short communication: Biogenic amine formation during fermentation in functional sheep milk yogurts

The present study evaluated biogenic amine (BA) content during the fermentation period in functional sheep milk yogurts. Four treatments were prepared and assessed: natural (NSY), prebiotic (PreSY), probiotic (ProSY), and synbiotic (SynSY). Biogenic amines (putrescine, cadaverine, spermidine, spermine, and tyramine), proteolysis activity, and pH were measured during each hour of fermentation. Grumixama pulp was added to all formulations as a technological strategy and potential substrate for bacteria during fermentation. The yogurt and probiotic bacteria were viable (≥7 log cfu·mL⁻¹) on d 0. The pH levels of the functional sheep milk yogurts had a more pronounced decrease than did the control of NSY. However, all yogurt samples underwent gradual decreases in pH until final fermentation. Proteolytic activity remained constant in all treatments during fermentation. The NSY, PreSY, ProSY, and SynSY presented the same behavior for all BA, with differences in concentration. Putrescine, cadaverine, and spermidine contents decreased, whereas spermine remained constant and tyramine increased. We conclude that fermentation of functional sheep milk yogurts can produce tyramine.