Heat-treated Yogurt Research Articles

Honey Added to Yogurt with Bifidobacterium animalis subsp. lactis DN-173 010/CNCM I-2494 Supports Probiotic Enrichment but Does Not Reduce Intestinal Transit Time in Healthy Adults: A Randomized, Controlled, Crossover Trial

BackgroundHoney improves probiotic survival in vitro. However, if this effect translates to humans has not been investigated. ObjectivesWe aimed to determine effects of honey plus yogurt containing the probiotic Bifidobacterium animalis subsp. lactis DN-173 010/CNCM I-2494 (B. animalis) on intestinal transit time, probiotic enrichment, digestive health, mood, and cognition in adults. MethodsSixty-six healthy adults (34 female; 33.6 ± 9.8 y; 24.6 ± 3.0 kg/m2) in a crossover trial were randomly assigned to 2-wk yogurt conditions in a counterbalanced order with ≥4-wk washout: 1) Honey (HON): yogurt plus honey and 2) Negative Control (NC): heat-treated yogurt plus sugar. Of the participants, n = 62 completed the trial, and n = 37 (17 female; 32.0 ± 8.3 y; 25.0 ± 2.9 kg/m2) elected to enroll in a third condition (a nonrandomized study extension) after ≥4-wk washout with a reference Positive Control (PC): yogurt plus sugar. At baseline and end of each of the 3 conditions, intestinal transit time was measured with dye capsules; probiotic abundance with fecal DNA 16S sequencing; digestive health with symptom/function records, Bristol stool consistency, Gastrointestinal Tolerability, and Gastrointestinal Quality of Life Index; mood with Positive and Negative Affect Schedule-Short Form, Depression Anxiety Stress Scales-42, Patient-Reported Outcomes Measurement Information System questionnaires, and an emotional image task; and cognition with a spatial reconstruction task. Data were analyzed using linear mixed-effects models (LMMs) with significance at P ≤ 0.05. Baseline and end data were included in the LMM, with fixed effects being treatment, time, treatment by time interaction, and baseline covariate, and the random effect being the participant. ResultsB. animalis was enriched in HON (d = 3.54; P = 0.0002) compared to controls with linear discriminant analysis effect size. Intestinal transit time, gastrointestinal health, mood, and cognition did not differ between conditions (LMM: Ps > 0.05). ConclusionsYogurt + honey enriched B. animalis but did not reduce intestinal transit time or have other functional gastrointestinal, mood, or cognitive effects in adults.This trial was registered at www.clinicaltrials.gov as NCT04187950 and NCT04901390.

The effect of dairy products on liver fat and metabolic risk markers in males with abdominal obesity – a four-arm randomized controlled trial

In recent years, epidemiological studies have reported links between the consumption of fermented dairy products, such as yogurt, and health; however, evidence from human intervention trials is scarce and inconsistent. We aimed to investigate the effect of consumption of four different types of dairy products (two fermented and two non-fermented) on liver fat (primary outcome) and metabolic risk markers in males with abdominal obesity. In this parallel randomized controlled trial with four arms, 100 males aged 30-70 years, with body mass index 28.0-45.0kg/m2, and waist circumference ≥102cm underwent a 16-weeks intervention where they were instructed to consume 400g/day of either milk, yogurt, heat-treated yogurt, or acidified milk as part of their habitual diet. Liver fat was measured by magnetic resonance imaging. In the complete case analyses (n=80), no effects of the intervention or differences between groups were detected in anthropometry or body composition including liver fat. Moreover, no effects were detected in inflammatory markers. Main effects of time were detected in blood pressure (decrease; P<0.001), insulin (decrease; P<0.001), C-peptide (decrease; P=0.040), homeostatic model assessment for insulin resistance (decrease; P<0.001), total cholesterol (decrease; P=0.016), low-density lipoprotein (decrease; P=0.033), high-density lipoprotein (decrease; P=0.006), and alanine transaminase (decrease; P=0.019). Interactions between group and time failed to reach significance. In conclusion, findings from our study do not confirm that fermented yogurt products are superior in reducing liver fat or improving metabolic risk markers compared to non-fermented milk products. In fact, all intervention products (both fermented yogurt products and non-fermented milk products) did not affect liver fat and caused largely similar modest favorable changes in some metabolic risk markers. The study was registered at www. gov (# NCT04755530).

Efficacy of pasteurised yoghurt in improving chronic constipation: A randomised, double-blind, placebo-controlled trial

One hundred and eighteen constipation subjects were fed a placebo or treatment (pasteurised yoghurt) for 7 weeks in a double-blind, randomised, placebo-controlled study. The results suggested that pasteurised yoghurt was effective in improving constipation. The subjects who ingested pasteurised yoghurt showed a significant increase in their defecation frequency following one week of the intervention. Constipation symptoms such as straining, lumpy or hard stool, and sensations of incomplete evacuation and anorectal blockage were all ameliorated. The numbers of faecal bifidobacteria and lactobacilli, and the short-chain fatty acid concentrations increased significantly in the treatment groups. In this study, pasteurised yoghurt with non-viable probiotics was found to exert a positive effect on constipation in adults, proving that heat-treated yoghurt can improve constipation. This function of pasteurised yoghurt may provide a new application for lactic acid bacteria.

Effect of Radio Frequency Heating on Yoghurt, I: Technological Applicability, Shelf-Life and Sensorial Quality.

This first part of a two-part study focuses on the technical feasibility of applying radio frequency (RF) heating at different temperatures (58, 65 and 72 °C) to a stirred yoghurt gel after culturing. For comparison, a convectional (CV) heating process was also applied. The aim was to increase the yoghurt shelf-life, by preventing post-acidification and the growth of yeasts and molds. At the same time, the viability of lactic acid bacteria (LAB) was investigated in view of existing legal regulations for yoghurts. Additionally, the yoghurt color, aroma and taste profiles were evaluated. It was found that the application of RF heating was effective for the rapid attainment of homogenous temperatures of 58 and 65 °C, respectively. For RF heating at 72 °C, it was not possible to establish a stable heating regime, since in some cases, there was significant overheating followed by strong contraction of the yoghurt curd and whey separation. Hence, it was decided not to continue with the RF heating series at 72 °C. In the case of CV heating, heat transfer limitations were observed, and prolonged heating was required. Nevertheless, we showed that yeasts and molds survived neither the RF nor CV heat treatment. LAB were found not to survive the CV treatment, but these beneficial microorganisms were still present in reduced numbers after RF heating to 58 and 65 °C. This important observation is most likely related to the mildness of RF treatment. While post-acidification was not observed on yoghurt storage, slight color changes occurred after heat treatment. The flavor and taste profiles were shown to be similar to the reference product. Furthermore, a trained sensory panel was not able to distinguish between, for example, the reference yoghurt and the RF 65 °C sample by triangular testing (α = 5%), showing the potential of novel strategies for further improvements of heat-treated yoghurt.

Competition between yogurt probiotics and periodontal pathogens in vitro

Objective. To investigate the competition between probiotics in bio-yogurt and periodontal pathogens in vitro. Material and methods. The antimicrobial activity of bio-yogurt was studied by agar diffusion assays, using eight species of putative periodontal pathogens and a ‘protective bacteria’ as indicator strains. Four probiotic bacterial species (Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, and Bifidobacterium) were isolated from yogurt and used to rate the competitive exclusion between probiotics and periodontal pathogens. Results. Fresh yogurt inhibited all the periodontal pathogens included in this work, showing inhibition zones ranging from 9.3 (standard deviation 0.6) mm to 17.3 (standard deviation 1.7) mm, whereas heat-treated yogurt showed lower antimicrobial activity. In addition, neither fresh yogurt nor heat-treated yogurt inhibited the ‘protective bacteria’, Streptococcus sanguinis. The competition between yogurt probiotics and periodontal pathogens depended on the sequence of inoculation. When probiotics were inoculated first, Bifidobacterium inhibited Porphyromonas gingivalis, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, Porphyromonas circumdentaria, and Prevotella nigrescens; L. acidophilus inhibited P. gingivalis, A. actinomycetemcomitans, P. circumdentaria, P. nigrescens, and Peptostreptococcus anaerobius; L. bulgaricus inhibited P. gingivalis, A. actinomycetemcomitans, and P. nigrescens; and S. thermophilus inhibited P. gingivalis, F. nucleatum, and P. nigrescens. However, their antimicrobial properties were reduced when both species (probiotics and periodontal pathogens) were inoculated simultaneously. When periodontal pathogens were inoculated first, Prevotella intermedia inhibited Bifidobacterium and S. thermophilus. Conclusions. The results demonstrated that bio-yogurt and the probiotics that it contains are capable of inhibiting specific periodontal pathogens but have no effect on the periodontal protective bacteria.

Effect of Fortification with Various Types of Milk Proteins on the Rheological Properties and Permeability of Nonfat Set Yogurt

Yogurt base was prepared from reconstituted skim milk powder (SMP) with 2.5% protein and fortified with additional 1% protein (wt/wt) from 4 different milk protein sources: SMP, milk protein isolate (MPI), micellar casein (MC), and sodium caseinate (NaCN). Heat-treated yogurt mixes were fermented at 40 degrees C with a commercial yogurt culture until pH 4.6. During fermentation pH was monitored, and storage modulus (G') and loss tangent (LT) were measured using dynamic oscillatory rheology. Yield stress (sigma(yield)) and permeability of gels were analyzed at pH 4.6. Addition of NaCN significantly reduced buffering capacity of yogurt mix by apparently solubilizing part of the indigenous colloidal calcium phosphate (CCP) in reconstituted SMP. Use of different types of milk protein did not affect pH development except for MC, which had the slowest fermentation due to its very high buffering. NaCN-fortified yogurt had the highest G' and sigma(yield) values at pH 4.6, as well as maximum LT values. Partial removal of CCP by NaCN before fermentation may have increased rearrangements in yogurt gel. Soluble casein molecules in NaCN-fortified milks may have helped to increase G' and LT values of yogurt gels by increasing the number of cross-links between strands. Use of MC increased the CCP content but resulted in low G' and sigma(yield) at pH 4.6, high LT and high permeability. The G' value at pH 4.6 of yogurts increased in the order: SMP = MC < MPI < NaCN. Type of milk protein used to standardize the protein content had a significant impact on physical properties of yogurt. Practical Application: In yogurt processing, it is common to add additional milk solids to improve viscosity and textural attributes. There are many different types of milk protein powders that could potentially be used for fortification purposes. This study suggests that the type of milk protein used for fortification impacts yogurt properties and sodium caseinate gave the best textural results.

Antibacterial activity of yoghurt against viridans streptococci in vitro

Objective Yoghurt consumption leads to a selective decrease in the oral level of mutans streptococci. It is not clear whether this decrease is due to the bactericidal activity of yoghurt or other mechanisms. The present study investigated the differences in susceptibility to yoghurt between several strains of viridans streptococci. Design The sources of variation were minimised, at the expense of the external validity of the study, using culture collection strains. Each strain was tested separately on five occasions in planktonic form and logarithmic growth phase. Two strains of each of the following Streptococcus species were tested: mutans, sobrinus, gordonii, oralis, parasanguinis and sanguinis. One millilitre [10 8 colony-forming units (cfu)] of each strain was incubated (37 °C, 60 min) with 9 mL of fat-free plain yoghurt containing Streptococcus thermophilus and Lactobacillus bulgaricus (10 8 and 10 7 cfu/g, respectively) in gently vortexed tubes. Survival rates were calculated every 15 min by dividing the number of viable cells, obtained using conventional laboratory procedures, by the baseline number. Results Survival rates were 8% ( S. mutans 6519T), 12% ( S. mutans 31738), 35% ( S. oralis 25671) and >50% (all other species tested) after 15 min, and 0.01% ( S. mutans) and >10% (all other species tested) after 30 min. Overall, S. parasanguinis and S. sobrinus were the most resistant species. When heat-treated yoghurt (<10 cfu/g bacteria and inactivated bacteriocins) was used, this antibacterial activity was not found. Conclusion In vitro, yoghurt with live bacteria showed selective anti-mutans activity, suggesting that the overall decrease in mutans streptococci in vivo could be due to a bactericidal effect on S. mutans but not on S. sobrinus.

Molecular analysis of yogurt containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in human intestinal microbiota

BackgroundYogurt has traditionally been considered a probiotic-carrier food with health-promoting effects. Despite the universal assumption of this assertion, several researchers have evaluated the real capability of the yogurt bacteria Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus to survive and proliferate in the human intestine and have found contradictory results. ObjectiveThis double-blind crossover study assessed the qualitative and quantitative effects of fresh and heat-treated yogurt on bacterial intestinal microbiota from healthy subjects. DesignThe subjects were divided into experimental (n = 63) and control (n = 16) groups. The experimental group consumed fresh and heat-treated yogurt for 15 d according to a crossover design with a washout period of 2 wk. Three different fecal samples per individual were recovered: at baseline, after fresh yogurt intake, and after heat-treated yogurt intake. Qualitative changes in microbiota were studied by denaturing gel gradient electrophoresis (DGGE) with universal and lactic acid bacteria (LAB) 16S-rRNA primers. Quantitative changes in LAB, Clostridium coccoides, Clostridium perfringens, and Bacteroides groups were analyzed by real-time polymerase chain reaction. ResultsA particular DGGE stable band pattern was observed in each sample. No significant qualitative differences were detected in any fecal sample. However, a significantly higher density of LAB and C. perfringens and a significant decrease in the density of Bacteroides was observed after consumption of both types of yogurt. Microbiota density was not significantly different between the fresh and heat-treated yogurt groups, except for LAB, which was significantly greater in the fresh yogurt group. ConclusionThe main change in human microbiota observed after yogurt consumption was an increase in the density of LAB and C. perfringens to the detriment of Bacteroides. Bacterial changes were not different after the consumption of fresh and heat-treated yogurt.

Effect of a fermented milk containing Bifidobacterium animalis DN‐173 010 on the health‐related quality of life and symptoms in irritable bowel syndrome in adults in primary care: a multicentre, randomized, double‐blind, controlled trial

Health-related quality of life (HRQoL) has been rarely evaluated as a primary endpoint in the assessment of the effect of probiotics on the irritable bowel syndrome (IBS). To study the effects of fermented milk containing Bifidobacterium animalis DN-173 010 and yoghurt strains on the IBS in a multicentre, double-blind, controlled trial. A total of 274 primary care adults with constipation-predominant IBS (Rome II) were randomized to consume for 6 weeks either the test fermented milk or a heat-treated yoghurt (control). HRQoL and digestive symptoms were assessed after 3 and 6 weeks on an intention-to-treat population of 267 subjects. The HRQoL discomfort score, the primary endpoint, improved (P < 0.001) in both groups at weeks 3 and 6. The responder rate for the HRQoL discomfort score was higher (65.2 vs. 47.7%, P < 0.005), as was the decrease in bloating score [0.56 +/- (s.d.)1.01 vs. 0.31 +/- 0.87, P = 0.03], at week 3 in the test vs. the control group. In those subjects with <3 stools/week, stool frequency increased (P < 0.001) over 6 weeks in the test vs. control group. This study suggests a beneficial effect of a probiotic food on discomfort HRQoL score and bloating in constipation-predominant IBS, and on stool frequency in subjects with <3 stools/week.

Mesure de la digestibilité des protéines par la méthode des différences porto-artérielles chez l’espèce porcine

This paper gives an overview of the current in vivo methods used to evaluate nutritional quality of proteins. It present in the first part methods used to assess digestibility of proteins, the interest and constraints of portal measurements and finally questions regarding digestive interactions between alimentary nitrogen and endogenous nitrogen are discussed. The second part of this paper is focused on the presentation of a study which was aimed to determine 15N porto-arterial kinetics after ingestion of 15N labelled milk, yogurt or heat treated yogurt. It indicates an original method which combines 15N isotope protein labelling and postprandial porto-arterial measurements in growing pigs. 15N portal absorption in the growing pig were performed after ingestion of uniformly (0.2509 APE) labelled 15N milk (M), yogurt (Y) and heat treated yogurt (HY). The highest porto-arterial differences of 15N were found in the period between 30 min and 90 min after ingestion. Main absorption of nitrogen from M and HY occurs during the 0-120 min time period (about 74% for M and 68% for HY). For Y, a larger displayed absorption period over the 0-240 min time period was observed. 15N absorption rate is close to 75% for each studied milk product, suggesting that M, Y and HY deliver nearly the same amounts of nitrogen to the organism. These results also indicate that major part of proteins are absorbed within the 240 min postprandial period.

Interrelationships between dairy product intake, microflora metabolism, faecal properties and plasmid dissemination in gnotobiotic mice

We previously described the effects of intake of dairy products on plasmid dissemination in the digestive tract of gnotobiotic mice associated with human faecal flora (HFF) and found that yoghurt, heat-treated yoghurt (HTY) and milk reduced population levels of transconjugants compared with findings in mice fed a standard mouse diet. In the case of lactose intake, transconjugants were not detected. The aim of the present study was to assess the possible interrelationships between these observations and other variables (bacterial ecology, pH, moisture, enzyme activities, short-chain fatty acid (SCFA) contents, lactic acid contents). Much of the interest of the present comparison lies in the fact that the animals were homogeneous in terms of age, gender, food and intestinal microflora, owing to the gnotobiotic mouse model maintained in sterile isolators. We observed no variation in SCFA and lactic acid contents or in the population levels of strictly anaerobic strains of Bacteroides and Bifidobacterium, and of the facultative anaerobic recipient Escherichia coli PG1 strain. The main modifications were the reduction of population levels of transconjugants in mice receiving yoghurt, HTY and milk, and concomitantly an increase of beta-galactosidase and a decrease of beta-glucosidase activities, compared with control mice fed a standard diet. Total inhibition of plasmid transfer was observed in HFF mice consuming lactose, and concomitantly the two enzyme activities (beta-glucosidase and beta-galactosidase) were increased, compared with the findings in control mice fed a standard diet. In axenic mice consuming lactose, plasmid transfer occurred, beta-galactosidase was not detected and beta-glucosidase was decreased. It is therefore proposed that these two enzyme activities influence plasmid transfer and persistence of transconjugants in the digestive tract of HFF associated mice. When both activities were increased there was a total inhibition of plasmid transfer (case of lactose intake). When beta-galactosidase increased and beta-glucosidase decreased (case of yoghurt, HTY and milk), plasmid transfer occurred at a lower efficiency than in the control group, resulting in lower population levels of transconjugants.

15N as a marker to assess portal absorption of nitrogen from milk, yogurt and heat-treated yogurt in the growing pig.

Milk and yogurt constitute a major source of dietary protein. The nutritive value of dietary proteins is linked to subsequent postprandial amino acid availability in the portal blood (Rérat, 1988). Portal absorption of nutrients cannot be studied in humans, but pigs provide a valid model for studying protein digestion in humans (Rowan et al. 1994).Since stable isotopes are suitable to distinguish the exogenous from endogenous protein fraction in the intestinal lumen, intrinsic isotopic labelling of milk proteins has been considered a useful technique for nutritional investigations (Gaudichon et al. 1995; Gaudichon et al. 1999; Mahé et al. 1994). Recently, the use of 15N-labelled milk proteins were used to distinguish exogenous from endogenous N fractions in the human intestine after ingestion of 15N-milk or 15N-yogurt (Gaudichon et al. 1995). These authors pointed out that the jejunal flux of 15N was different for milk and yogurt. It is known that milk proteins and lactose undergo preliminary hydrolysis during lactic fermentation (Tamine &amp; Deeth, 1980). It is also suggested that lactic fermentation enhances the nutritional value of milk proteins (Vass et al. 1984).

Survival of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in the terminal ileum of fistulated Göttingen minipigs.

The ability of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus administered in yogurt to survive the passage through the upper gastrointestinal tract was investigated with Göttingen minipigs that were fitted with ileum T-cannulas. After ingestion of yogurt containing viable microorganisms, ileostomy samples were collected nearly every hour beginning 3 h after food uptake. Living L. delbrueckii subsp. bulgaricus and S. thermophilus were detected in the magnitude of 10(6) to 10(7) per gram of intestinal contents (wet weight) in all animals under investigation. A calculation of the minimum amount of surviving bacteria that had been administered is presented. Total DNA extracted from ileostomy samples was subjected to PCR, which was species specific for L. delbrueckii and S. thermophilus and subspecies specific for L. delbrueckii subsp. bulgaricus. All three bacterial groups could be detected by PCR after yogurt uptake but not after uptake of a semisynthetic diet. One pig apparently had developed an endogenous L. delbrueckii flora. When heat-treated yogurt was administered, L. delbrueckii was detected in all animals. S. thermophilus or L. delbrueckii subsp. bulgaricus was not detected, indicating that heat-inactivated cells and their DNAs had already been digested and their own L. delbrueckii flora had been stimulated for growth.

Influence of a Probiotic Yoghurt on the Status of Vitamins B1, B2 and B6 in the Healthy Adult Human

Background/Aims: The main reason for this study was to determine whether yoghurt bacteria, being rich in some water-soluble vitamins, release them or utilize vitamins from their surroundings. Our study was trying to determine for the first time, if the viable bacteria of probiotic yoghurt are able to influence the parameters of the B-vitamin (B₁, B₂, B₆) status of the healthy adult human. Methods: The test yoghurt was commercially available probiotic yoghurt prepared with Streptococcus thermophilus and Lactobacillus acidophilus, enriched with Lactobacillus casei GG. Different chemical forms of all investigated B-vitamins were determined by HPLC methods. In order to determine the influence of the yoghurt flora, each of 12 subjects consumed four yoghurt portions 125 g each ( = 500 g) a day, containing thermally inactivated cultures during the first 2-week period and yoghurt without heat treatment during the second 2-week period. Results: The heat treatment of the probiotic yoghurt caused negligible changes in vitamin contents. The plasma levels of thiamin decreased significantly (p < 0.01) after the first 2-week period and kept on decreasing during the second 2-week period. A similar trend was found in the urinary excretion. The plasma levels of the B₂-vitamers were different. The flavin adenine dinucleotide concentrations increased significantly (p < 0.01) after the consumption of heat-treated yoghurt and decreased significantly (p < 0.05) after the following 2 weeks, in which the subjects received the untreated yoghurt. In contrast, the flavin mononucleotide plasma levels decreased during the first 2-week period and increased during the second part of the study, but the change was not statistically significant. The free riboflavin concentrations in plasma and urine showed a continuous but not significant increase. The concentrations of pyridoxal-5-phosphate in plasma increased after the consumption of yoghurt with the inactivated bacteria and decreased in the second part of the study. However, the differences were not significant. The excretion of thiamin, B₂- and B₆-vitamers in the faeces did not significantly change throughout the study period (p > 0.05). Conclusions: Our observations show that the bacterial flora of the examined yoghurt does not influence the vitamin B₁, B₂ and B₆ status of man. It seems likely that even lactobacilli of the ‘probiotic’ type which are vitamin B consumers can decrease the bioavailability of these vitamins for man. Obviously a thermal death of the cells did not induce a release of physiologically active vitamins.

Portal absorption of 45Ca from labelled milk, yoghurt or heat treated yoghurt in the growing pig

The aim of this experiment was to study portal absorption of calcium in the growing pig after ingestion of extrinsic labelled 45Ca milk (M), yoghurt (Y) or heat treated yoghurt (HY). Portal levels of 45Ca are high very soon (15 min) after ingestion of M, Y and HY and decrease after 60 min. An absorption peak was observed at 30 min for M and HY and at 60 min for Y. The highest porto-arterial differences were observed between 15 and 60 min for each milk product, indicating that absorption mainly occurs during the first hour postprandial (about 50% for M, 44% for Y and 42% for HY). 45Ca portal absorption rate is close to 80% for the three dairy products, suggesting that M, Y and HY deliver nearly the same amounts of 45Ca to the organism.

Portal absorption of 15N and amino nitrogen in the growing pig after ingestion of labelled milk, yogurt or heat-treated yogurt.

The aim of this experiment was to study 15N and amino-nitrogen (AN) portal absorption in the growing pig after ingestion of uniformly (0.2509 APE) labelled 15N milk (M), yogurt ingested just after manufacturing (Y0), yogurt stored for 21 d at 4 degrees C (Y21) and heat-treated yogurt (HY). The highest porto-arterial differences (PAD) in 15N and AN were found in the period between 30 min and 90 min after ingestion. The absorption of nitrogen from M and HY mainly occurred during the 0-120 min time period (about 70% for M and 67% for HY). For Y0 and Y21, a larger displayed absorption period over the 0-240 min time period was observed. Y0 and Y21 presented a quite similar portal absorption profile. The 15N absorption rate was close to 80% for each studied milk product, suggesting that under our experimental conditions, dairy products (M, Y0, Y21 and HY) deliver nearly the same amounts of nitrogen to the organism. AN absorption rates were around 78% with a higher variability between the milk products. These results also indicate that most of the proteins were absorbed within the 240 min postprandial period.

Rheological Monitoring of Structure Development and Rebodying of Set-Style Yoghurt

AbstractThe present work was undertaken in order to evaluate the rheological changes of set-style yoghurt at different incubation times, during production. The study of rheological changes of milk destined to set-style yoghurt production, in different processing stages prior to fermentation was accomplished using steady and oscillatory shear, while the study of the influence of storage time was also carried out using steady shear. Set-style yoghurt samples with 2 and 3 hours of fermentation exhibited a major structural breakdown during upward shear rate sweep experiments as expected, since the protein network was initially intact. Both samples exhibited two points of sudden decay. For T2 the these points occured at shear stresses of 38 Pa and 77 Pa and for T3 at 47 Pa and 80-83 Pa. The first point corresponds to the main break-up of protein network and the second one to the disruption of primary-aggregates, breaking the portion of casein network that was associated with exopolyssacharides produced by lactic acid bacteria. Structural analysis performed by means of oscillatory measurements indicate that the protein network is already partially formed after 2 hours, albeit full development is only achieved after longer periods. Heat-treated milk, evaporated milk and set-style yoghurt samples with 0 and 1 hour incubation times showed an apparent yield stress value of approximately 0.4 Pa and a strong shear-thinning behaviour afterwards. At higher shear stresses (approximately 1.6 Pa), however, the behaviour changed to shear-thickening, this effect being attributed to flow-induced interactions between the milk components. For the latter sample, a further change in flow behaviour occurred at a stress of 8 Pa, which is probably due to the breakdown of the weak protein network that had formed during incubation.

Effects of Yogurt Ingestion on Mucosal and Systemic Cytokine Gene Expression in the Mouse

To assess the potential for ingestion of yogurt to modulate immunity, its effects on basal gene expression of cytokines in systemic and mucosal sites were determined in mice. Yogurts were manufactured from pasteurized nonfat dry milk using five commercial starter cultures with or without Bifidobacterium sp. and Lactobacillus acidophilus. Treatment mice were fed the AIN-93G diet mixed 1:1 with unheated yogurt or heat-treated yogurt (wt/wt) for 2 and 4 weeks, and control mice were fed the AIN-93G diet mixed 1:1 (wt/wt) with nonfat dry milk. The viability of the various bacterial groups in unheated yogurts was maintained above 106 CFU/g throughout the feeding period. The yogurt-feeding regimens did not significantly affect weight gain. Relative mRNA levels in spleen, mesenteric lymph nodes, or Peyer's patches for the cytokines interferon-γ, tumor necrosis factor-α, interleukin-2, -4, and -6, and the “housekeeping gene” β2-microglobulin were determined by reverse transcriptase–polymerase chain reaction in conjunction with hybridization analysis. Prolonged feeding of some yogurts decreased expression of several cytokine mRNAs, the depression of tumor necrosis factor-α mRNA in the spleen being the most prominent effect. Heat-treated yogurts were more effective in altering cytokine mRNA expression than were unheated yogurts containing viable organisms. Generally, yogurts either had no effect or decreased specific cytokine mRNA in the test organs, regardless of whether they contained Bifidobacterium sp. and L. acidophilus. These results suggest that, in contrast with previous studies in vitro, some yogurt formulations may reduce rather than stimulate basal cytokine expression and that these effects are most prominent in the systemic compartment.

In vitro antibacterial effect of yogurt onEscherichia coli

We investigated the bactericidal and bacteriostatic effects of yogurt on three strains of Escherichia coli: human toxigenic (078:H11), rabbit pathogenic (RDEC-1) and rabbit nonpathogenic [015:K14(L):H4]. Approximately 10(6) organisms were incubated in yogurt, milk, broth, and modifications of these materials. Aliquots were removed at various intervals and plated on MacConkey's agar for enumeration of E. coli. Yogurt was bactericidal (at least 5 log10 reduction in bacterial counts) to all three strains of E. coli with less than 10 CFU/ml remaining by 9 hr. In contrast, all three strains replicated rapidly in milk and broth, reaching maximum concentrations by 9 hr. The E. coli strains survived and multiplied in milk acidified to the same pH as the yogurt. Yogurt (native pH 4.1-4.4) in which the pH was brought up to and maintained at pH 5.5 or pH 7 for 8 hr was not bactericidal to E. coli. Heat-treated yogurt and the filtered supernatant of centrifuged yogurt (both containing no yogurt bacteria) were only bacteriostatic. We conclude that both live yogurt bacteria and a pH near 4.5 are necessary for the bactericidal activity of yogurt. The possibility that yogurt ingestion could protect against infection via other foods contaminated with pathogenic E. coli merits further in vivo investigation.