Influence of pasture-based feeding systems on fatty acids, organic acids and volatile organic flavour compounds in yoghurt

Graduate Student Literature Review: Network of flavor compounds formation and influence factors in yogurt

Yogurt is popular as a natural and healthy food, but its flavor greatly affects acceptability by consumers. Flavor compounds of yogurt is generally produced by the metabolism of lactose, protein and fat, and the resulting flavors include carbonyls, acids, esters and alcohols, etc. Each flavor compounds could individually provide the corresponding flavor, or it can be combined with other compounds to form a new flavor. The flavor network was formed among the metabolites of milk components, and acetaldehyde, as the central compounds, played a role in connecting the whole network. The flavor compounds can be affected by many factors, such as the use of different raw milks, ways of homogenization, sterilization, fermentation, post ripening, storage condition and packaging materials, etc., which can affect the overall flavor of yogurt. This paper provides an overview of the volatile flavor compounds in yogurt, the pathways of production of the main flavor compounds during yogurt fermentation, and the factors that influence the flavor of yogurt including type of raw milk, processing, and storage. It also tries to provide theoretical guidance for the product of yogurt in ideal flavor, but further research is needed to provide a more comprehensive description of the flavor system of yogurt.

Effect of Cephalosporin Antibiotics on the Activity of Yoghurt Cultures

The presence of antibiotics in milk is a significant problem affecting the technological safety of dairy products. The aim of the study was to determine the sensitivity of yoghurt cultures to residual levels of selected cephalosporin antibiotics (cephalexin, cefoperazone, cefquinome, cefazolin, and ceftiofur). Five yoghurt cultures were selected containing strains of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Artificially fortified milk samples (whole pasteurized milk; 85 °C; 3−5 s) with cephalosporins at a concentration of the maximum residue limit were used to evaluate the sensitivity of the yoghurt cultures by monitoring the pH, titratable acidity, and the concentration of selected organic acids (lactic, pyruvic, citric, acetic, orotic, oxalic, formic, uric, and succinic acids) at the end of fermentation (43 °C; 4−5.5 h; pH ≤ 4.6). The titratable acidity was determined by the Soxhlet−Henkel method and the organic acid concentration was monitored by reversed-phase HPLC. Ceftiofur had the greatest effect on the yoghurt culture activity, with a statistically highly significant effect (p < 0.05) on the pH, titratable acidity, and the content of lactic, pyruvic, and acetic acids in all cultures. Other cephalosporins also showed an inhibitory effect on yoghurt metabolism as seen by the evaluation of the lactic and pyruvic acid concentrations.

Biofuel by-product can replace partially corn in supplement for Angus × Nellore heifers: productive performance and meat characteristics

The aim of this is study was to test the hypothesis that corn can be partially replaced by crude glycerin (at a level of 50%) without affecting performance, ingestive behavior, ruminal parameters, meat composition, and fatty acids profile on the meat of heifers. Sixty-four intact plus four rumen cannulated Angus × Nellore heifers (359.0 ± 12.15 kg BW) were used. The cannulated animals received the same diets as the intact ones to determine the ruminal N-NH3 concentration, pH, and chewing activity weekly. All heifers were maintained in Brachiaria brizantha pasture and supplemented with a concentrate containing corn, soybean meal, urea, premixed minerals, and glycerin partially replacing corn. A completely randomized experimental design was used, with two treatments (corn ground or glycerin + corn ground). The inclusion of crude glycerin (high fat) decreased nutrients intake and ruminal N-NH3 concentration in the rumen but increased lipid intake. Inclusion of glycerin had no effect (P > 0.05) on ruminal pH, daily gain, performance, time spent eating, rumination, idling, or water intake. The moisture, ash, and protein contents of meat were not affected (P > 0.05) by crude glycerin intake. Crude glycerin increased saturated fatty acids (C14:0, C16:0, and C18:0) and decreased unsaturated fatty acids (C18:2n6c and C20:1) in meat. Despite the reduction in nutrient intake, we recommend crude glycerin to replace corn in concentrate because glycerin did not impair the performance, meat composition, and ruminal pH. Therefore, crude glycerin is a by-product that can partially replace corn in diets efficiently.

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.

Fatty acid profiles of milk and Minas frescal cheese from lactating grazed cows supplemented with peanut cake

Milk and Minas frescal cheese were evaluated from crossbred Holstein × Gir cows that were fed diets enriched with 0, 33, 66 and 100% inclusion levels of palm kernel cake in a concentrated supplement in replace of soybean meal. Eight crossbred lactating cows were distributed (four animals × four treatments × four periods) in the experimental design of double 4 × 4 Latin squares. The capric (C : 10, P = 0·0270), undecylic (C : 11, P = 0·0134), and lauric (C : 12, P = 0·0342) saturated fatty acid concentrations and CLA (C18 : 2c9t11, P = 0·0164) of the milk fat decreased linearly with an increasing percentage of peanut cake in the diet. The increased peanut cake content (100%) in the diet was associated with a linear decrease in C : 10 (P = 0·0447), C : 12 (P = 0·0002), mirystic (C : 14, P < 0·0001) and palmitic (C : 16, P < 0·0001) saturated fatty acid concentrations and an increase in arachidic, lignoceric, palmitoleic and elaidic acid levels in the Minas frescal cheese fat made from the milk. Both the milk and the Minas frescal cheese showed a linear decrease in the concentration of monosaturated fatty acids (P < 0·0001), atherogenicity index, and thrombogenicity index (P < 0·05), while the hypocholesterolaemic: hypercholesterolaemic and omega 6: omega 3 (P > 0·05) ratios were not influenced by the different peanut cake levels. The inclusion of up to 100% peanut cake as a substitution for soybean meal in the concentrate of grazing lactating cows resulted in changes in the nutritional quality of their milk products, as indicated by the increase in polyunsaturated fatty acids and the decrease of saturated fatty acids (lauric, myristic, and palmitic).