Lactic acid bacteria (LAB) are industrially important bacteria that are widely used in the fermented food industry, especially in the manufacture of yogurt. Characteristic flavors are produced by LAB during fermentation and storage that affect the quality and acceptability of fermented milk products. In this study, the volatile compounds in milk fermented by Streptococcus thermophilus IMAU80842 alone, Lactobacillus delbrueckii ssp. bulgaricus IMAU20401 alone, or both species together were identified using solid-phase microextraction methods coupled with gas chromatography-mass spectrometry. A total of 53, 43, and 32 volatile compounds were identified in milk fermented by S. thermophilus alone, L. delbrueckii ssp. bulgaricus alone, or both species together, respectively. The presence of some important flavor compounds was confirmed: acetic acid, acetaldehyde, acetoin, 2,3-butanedione, ethanol, and 1-heptanol. Our results demonstrate that the composition of the volatile compounds in fermented milk depends on the species of LAB used and whether they are used alone or in combination. This is important for the selection of appropriate starter cultures for the production of different types of fermented milk product with particular flavors.

Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus are key factors in the fermentation process and the final quality of dairy products worldwide. This study was performed to investigate the effects of the proportions of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus isolated from traditionally fermented dairy products in China and Mongolia on the profile of volatile compounds produced in samples. Six proportional combinations (1:1, 1:10, 1:50, 1:100, 1:1000, and 1:10,000) of L. delbrueckii subsp. bulgaricus IMAU20401 to S. thermophilus ND03 were considered, and the volatiles were identified and quantified by solid-phase microextraction and gas chromatography–mass spectrometry (SPME-GC-MS) against an internal standard. In total, 89 volatile flavor compounds, consisting of aldehydes, ketones, acids, alcohols, esters, and aromatic hydrocarbons, were identified. Among these, some key flavor volatile compounds were identified, including acetaldehyde, 3-methylbutanal, acetoin, 2-heptanone, acetic acid, butanoic acid, and 3-methyl-1-butanol. The of L. delbrueckii subsp. bulgaricus IMAU20401 to S. thermophilus ND03 influenced the type and concentration of volatiles produced. In particular, aldehydes and ketones were present at higher concentrations in the 1:1000 treatment combination than in the other combinations. Our findings emphasize the importance of selecting the appropriate proportions of L. delbrueckii subsp. bulgaricus and S. thermophilus for the starter culture in determining the final profile of volatiles and the overall flavor of dairy products.

Angiotensin I-converting enzyme (ACE) inhibitory activities in untreated koumiss and koumiss digested with ACE, pepsin, trypsinase, and chymotrypsin were compared and analyzed. Four novel ACE inhibitory peptides (P(I), P(K), P(M), and P(P)) were purified using ultrafiltration and high performance liquid chromatography (HPLC). The classification study showed that these 4 peptides were of the true inhibitor type. The amino acid sequences of these peptides are YQDPRLGPTGELDPATQPIVAVHNPVIV, PKDLREN, LLLAHLL, and NHRNRMMDHVH, respectively. Their individual IC(50) (50% inhibitory concentration) values were as follows: 14.53+/-0.21microM, 9.82+/-0.37microM, 5.19+/-0.18microM, and 13.42+/-0.17microM. From sequence analysis, we determined that P(I) was part of beta-casein in mare's milk. The 3 peptides P(K), P(M), and P(P) did not correspond with any known milk protein. The results suggest that koumiss is rich in ACE inhibitory peptides, and the ACE inhibitors in koumiss are of the pro-drug type or a mixture of the pro-drug type and the true inhibitor type. These results may provide evidence about the beneficial effects of koumiss, especially on cardiovascular health.

The lactic acid bacterium Streptococcus thermophilus is a major starter culture for the production of dairy products. In this study, the physiochemical characteristics of milk fermented by the MGA45-4 isolate of S. thermophilus were analyzed. Our data indicate that milk fermented using S. thermophilus MGA45-4 maintained a high viable cell count (8.86 log10 colony-forming units/mL), and a relatively high pH (4.4), viscosity (834.33 mPa·s), and water holding capacity (40.85%) during 14 days of storage. By analyzing the volatile compound profile using solid-phase microextraction and gas chromatography/mass spectrometry, we identified 73 volatile compounds in the fermented milk product, including five carboxylic acids, 21 aldehydes, 13 ketones, 16 alcohols, five esters, and 13 aromatic carbohydrates. According to the odor activity values, 11 of these volatile compounds were found to play a key role in producing the characteristic flavor of fermented milk, particularly octanal, nonanal, hexanal, 2,3-butanedione, and 1-octen-3-ol, which had the highest odor activity values among all compounds analyzed. These findings thus provide more insights in the chemical/molecular characteristics of milk fermented using S. thermophilus, which may provide a basis for improving dairy product flavor/odor during the process of fermentation and storage.

It is well known that consumers are keen to try fermented milk products with different flavors and starter cultures are important in determining the resulting fermented dairy products. Here, we present the phenome of 227 Lactococcus lactis subsp. lactis isolates from traditionally fermented dairy products and the selection of potential starter strains. Large-scale phenotyping revealed significant technological diversity in fermentation characteristics amongst the isolates including variation in fermentation time, viscosity, water holding capacity (WHC) and free amino nitrogen (FAN) production. The 16 isolates with the best fermentation characteristics were compared, in a sensory evaluation, with the commercial starter Chr. Hansen R-704 as excellent fermentation characteristics to identify potential starter isolates and find the isolate which can product good flavors. From these, and from solid phase micro extraction (SPME) – gas chromatography (GC)-mass spectrometry (MS) analysis, we identified IMAU11823 and IMAU11919 as producing 3-methyl butanal and 3-methyl-2-butanone which contribute to the malt aroma. This study expands the characterization of L. lactis subsp. lactis phenotypic dataset and technological diversity and identified isolates with potential culture starter in the fermentation industry.

Probiotics have been characterized as useful for maintaining the balance of host gut flora and conferring health effects, but few studies have focused on their potential for delaying aging in the host. Here we show thatLacticaseibacillus rhamnosusProbio-M9 (Probio-M9), a healthy breast milk probiotic, enhances the locomotor ability and slows the decline in muscle function of the model organismCaenorhabditis elegans. Live Probio-M9 significantly extends the lifespan ofC. elegansin a dietary restriction-independent manner. By screening various aging-related mutants ofC. elegans, we find that Probio-M9 extends lifespan via p38 cascade anddaf-2signaling pathways, independent ondaf-16but dependent onskn-1. Probio-M9 protects and repairs damaged mitochondria by activating mitochondrial unfolded protein response. The significant increase of amino acids, sphingolipid, galactose and fatty acids in bacterial metabolites might be involved in extending the lifespan ofC. elegans. We reveal that Probio-M9 as a dietary supplementation had the potential to delay aging inC. elegansand also provide new methods and insights for further analyzing probiotics in improving host health and delaying the occurrence of age-related chronic diseases.