Utilization of Reconstituted Whey Powder and Microbial Transglutaminase in Ayran (Drinking Yogurt) Production.

Research background: In industrial ayran production, milk is diluted to the desired protein content (2% (m/V)) prior to fermentation by yogurt starter cultures by partial replacement of cheese whey in reconstituted form with potable water. This may be an alternative way of protein recovery from cheese by-products as well as reducing the production costs since less milk is used in ayran production. On the other hand, the balance between milk caseins and whey proteins is disturbed when cheese whey is added to milk for ayran production, which likely leads to a time-dependent phase separation during cold storage. Modification of ayran matrix by enzymatic crosslinking of proteins may be a solution to overcome this potential physical instability of ayran. This topic has not been explored to date, and the present study was designed to investigate the possibilities of utilization of reconstituted whey powder (RWP) and microbial transglutaminase (MTG) in ayran production. Experimental approach: Milk was diluted to obtain 2% protein level using RWP and potable water. The aim of utilization of RWP was to meet 5, 10 or 15% of the protein content of the final product. RWP solutions were obtained by calculating the amounts of whey powder required to meet the specified ratios and mixing it with the water required for dilution. We prepared eight different ayran samples divided in three groups, namely group A: prepared by partially diluting milk with RWP to obtain 5, 10 or 15% of total protein amount in the product, group AMTG: prepared by adding microbial transglutaminase (0.5 U per g of protein) to group A samples, and control group without RWP and with or without the addition of MTG. The gross composition, physical (phase separation and viscosity, chemical (volatile and peptide profiles and SDS-PAGE electrophoresis patterns) and sensory properties of the samples were evaluated throughout 15 days of storage with weekly intervals. Results and conclusions: Since the amounts of whey powder used to obtain RWP were different, dry matter levels of the samples differed. Using RWP in ayran production increased the phase separation slightly. Incorporation of MTG affected the physical properties of the ayran samples positively and prevented phase separation at a satisfactory level. SDS-PAGE electrophoretograms revealed that cross-linking between proteins triggered by MTG formed intense bonds at high molecular mass regions. The remaining parameters were not affected by MTG. Results revealed that the samples with 10% RWP with and without addition of MTG were determined as the formulations with the highest commercialization potential. Novelty and scientific contribution: Utilizing RWP in the production of ayran to reduce the protein content of the final product to the desired level is a new approach. Since complete replacement of RWP with potable water to dilute milk to reach 2% (m/V) protein likely leads to lower sensory scores, we have investigated a possibility of partial replacement of RWP with potable water. A time-dependent phase separation is the major challenge of industrial ayran production. This physical problem was largely eliminated by means of MTG-mediated cross-linking of milk proteins. The proposed novel ayran production method offers dairy industry reduction of production costs and contributes to sustainability in milk production since smaller volume of milk is used to reach desired protein content in the final product.

Acute and short-term effects of Lactobacillus paracasei subsp. paracasei 431 and inulin intake on appetite control and dietary intake: A two-phases randomized, double blind, placebo-controlled study.

This study aims to examine the acute and short-term effects of prebiotics, probiotics, and their combination on appetite, energy intake and satiety related hormones in two phases. The first phase was a randomized, double blind, placebo controlled crossover study. Prebiotic (16 g inulin), probiotic (Lactobacillus paracasei subsp. paracasei 431 (L. casei 431) (>106 cfu/ml), synbiotic (their combination) and control (16 g maltodextrin) dairy drinks were consumed by 16 healthy men with a standard breakfast on four separate test days, and the following satiety responses and ad libitum food intake at lunch and over 24 h were assessed. In the second phase, the effects of 21 days of synbiotic (n = 10) or control (n = 11) drink consumption on appetite sensation, energy intake, serum glucose, insulin, peptide YY, ghrelin, obestatin and adiponectin concentration were assessed in a randomized double-blind placebo-controlled design. In the first phase, energy intake values during ad libitum lunch were the lowest in the prebiotic drink, followed by probiotic, synbiotic and control drinks, respectively (p = 0.017); also the rest of the day and 24-h dietary energy intake was lower by prebiotic and probiotic drinks compared to the control drink (p < 0.05 for each). For short-term effects, no significant difference in anthropometric measurements, hunger-satiety scores and serum glucose, insulin, PYY, ghrelin, obestatin and adiponectin concentrations were recorded. Despite the potential of prebiotics and probiotics to reduce energy intake, further studies are required for a better understanding of their role in satiety related mechanisms.

Changes of proteolysis and angiotensin-I converting enzyme-inhibitory activity in white-brined cheese as affected by adjunct culture and ripening temperature.

The effects of use of adjunct cultures (Lactobacillus helveticus and Lb. casei) and ripening temperatures (6 or 12 °C) on proteolysis and angiotensin-I converting enzyme (ACE)-inhibitory activity in white-brined cheeses were investigated during 120 d ripening. Proteolysis was monitored by urea-polyacrylamide gel electrophoresis (urea-PAGE) and reversed phase-HPLC (RP-HPLC) of water-insoluble and -soluble fractions of the cheeses, respectively. Urea-PAGE patterns of the samples revealed that the intensities of the bands representing casein fractions decreased in the experimental cheeses, being more pronounced in the cheeses made with adjunct cultures. Similarly, peptide profiles and the concentrations of individual and total free amino acids were influenced by both the adjunct cultures and ripening temperatures. The ACE-inhibitory activity of the water-soluble extracts of the cheeses were higher in the cheeses made using adjunct cultures (especially Lb. helveticus) and ripened at 12 °C. The ACE-inhibitory activity did not decrease during ripening. The contribution of Lb. helveticus to the development of proteolysis and ACE-inhibitory peptide activities were higher than that of Lb. casei. To conclude, the use of Lb. helveticus as adjunct culture in white-brined cheese and ripening at 12 °C would be recommended to obtain white-brined cheese with high ACE-I-inhibitory peptides activity and higher levels of preoteolysis.

Effects of different fermentation parameters on quality characteristics of kefir.

The main objective of the study was to determine the effects of different fermentation parameters on kefir quality. Kefir samples were produced using kefir grains or natural kefir starter culture, and fermentation was carried out under normal or modified atmosphere (10% CO(2)) conditions. The microbiological (lactobacilli, lactococci, Lactobacillus acidophilus, Bifidobacterium spp., and yeasts), chemical (pH, lactic acid, total solids, protein, ethanol, exopolysaccharide contents), rheological, and sensory properties of kefir samples were investigated during a 21-d storage period. The use of different fermentation parameters or the choice of grain versus natural kefir starter culture did not significantly affect the content of microorganisms. Lactobacilli, lactococci, and yeast contents of kefir samples varied between 9.21 and 9.28, 9.23 and 9.29, and 4.71 and 5.53 log cfu/mL, respectively, on d 1 of storage. Contents of L. acidophilus and Bifidobacterium spp. were between 5.78 and 6.43 and between 3.19 and 6.14 log cfu/mL, respectively, during 21 d of storage. During the storage period, pH, lactic acid (%), total solids (%), protein (%), acetaldehyde, and ethanol contents of kefir samples ranged from 4.29 to 4.53, from 0.81 to 0.95%, from 7.81 to 8.21%, from 3.09 to 3.48%, from 3.8 to 23.6 mg/L, and from 76.5 to 5,147 mg/L, respectively. The exopolysaccharide contents of the samples decreased during 21 d of cold storage; the samples fermented under modified atmosphere had relatively higher exopolysaccharide contents, indicating higher potential therapeutic properties. The kefir samples exhibited non-Newtonian pseudoplastic flow behavior according to the power law model. According to the sensory results, kefir produced from natural kefir starter culture under CO(2) atmosphere had the highest overall evaluation score at d 1.

Survival of Lactobacillus acidophilus LA-5 and Bifidobacterium bifidum BB-02 in white-brined cheese.

The viability of probiotic cultures used as adjunct cultures including Bifidobacterium bifidum BB-02 and Lactobacillus acidophilus LA-5 in white-brined cheese was investigated. The microbiological and biochemical properties of cheeses were assessed throughout 90 days of storage. Two inoculum rates for probiotic starters (2.5% and 5.0%, v/v, corresponding to (1.0-1.3)x10(9) cfu/g and (2.0-2.1)x10(9) cfu/g, respectively) were compared with the control cheese. Results obtained showed that a higher inoculum rate resulted in faster proteolysis. The cheese inoculated with 5% probiotic strains had higher water-soluble nitrogen, non-protein nitrogen, proteose-peptone nitrogen and tyrosine values than the other experimental cheeses. At the end of storage, the cheese supplemented with 5% probiotic culture had a ripening coefficient of 28.3%, followed by 2.5% probiotic strains containing the sample being 24.9%, and the control being 23.6%, respectively. It was also found that the colony counts of both probiotic microorganisms declined during storage. After 90 days of storage, the number of probiotic colonies were still around the threshold for a minimum probiotic effect (10(6) cfu/g).

Effects of lactoperoxidase and hydrogen peroxide on rheological properties of yoghurt.

The effects of activation of the lactoperoxidase (LPO) system by H2O2-NaSCN and hydrogen peroxide (H2O2) on the accessibility of sulphydryl groups (SH) in skimmed milk, and on the dynamic rheological properties of the resulting yoghurt were investigated. Four different concentrations of each reagent (20-80 mg H2O2-NaSCN/kg milk and 100-400 mg H2O2/kg milk) were compared. Clear negative correlations were noted between the accessibility of SH groups and both LPO activation rate and H2O2 concentration. Also the native PAGE pattern of the heat-treated samples showed that with increase in the H2O2-NaSCN and H2O2 concentrations, the level of interaction between beta-lactoglobulin (beta-lg) and kappa-casein (kappa-CN) decreased. The complex modulus (G*) of skimmed milk yoghurts declined gradually with the decrease in the concentration of accessible SH groups accordingly. Tan delta values of yoghurt samples were found to be different from the control, but close to each other, indicating that protein interaction forces taking place in the formation of gel networks of treated yoghurts were different from the control.