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.

To expound on the correlation between the microorganism communities and the formation of off-odour in Xuanwei ham, the microorganism communities and volatile compounds were investigated in the biceps femoris (BF) and semimembranosus (SM) of Xuanwei ham with different quality grades (normal ham and spoiled ham). The single molecule real-time sequencing showed that differential bacteria and fungi were more varied in normal hams than in spoiled hams. Headspace solid-phase microextraction–gas chromatography (HS-SPME-GC-MS) results indicated that aldehydes and alcohols were significantly higher in spoiled hams than those in normal hams (p < 0.05). The off-odour of spoiled hams was dominated by ichthyic, malodourous, sweaty, putrid, sour, and unpleasant odours produced by compounds such as trimethylamine (SM: 13.05 μg/kg), hexanal (BF: 206.46 μg/kg), octanal (BF: 59.52 μg/kg), methanethiol (SM: 12.85 μg/kg), and valeric acid (BF: 15.08 μg/kg), which are positively correlated with Bacillus cereus, Bacillus subtilis, Bacillus licheniformis, Pseudomonas sp., Aspergillus ruber, and Moraxella osloensis. Furthermore, the physicochemical property and quality characteristics results showed that high moisture (BF: 56.32 g/100 g), pH (BF: 6.63), thiobarbituric acid reactive substances (TBARS) (SM: 1.98 MDA/kg), and low NaCl content (SM: 6.31%) were also responsible for the spoilage of hams with off-odour. This study provided a deep insight into the off-odour of Xuanwei ham from the perspective of microorganism communities and a theoretical basis for improving the flavour and overall quality of Xuanwei hams.

Fermented milk is the daily products facing many challenges, including natural flavor, good texture, and more health. In this study, the Leuconostoc mesenteroides and Saccharomyces cerevisiae were employed as the auxiliary fermenters to solve the challenge. After the fermentation, both cow fermented milk and yak fermented milk showing comprehensive fruit flavors, and the GC-MS/MS demonstrated that the generation of 19 kinds of volatile compounds including ester, ketone, aldehyde, and acid are major contributor and mainly provide fruit, flowers, and coconut flavor. Such as isoamyl acetate and ethyl caprylate, increased by 164.20 ± 8.04 µg/kg and 115.53 ± 13.49 µg/kg in ME after the addition of auxiliary fermenters. Meanwhile, the concentration of off-volatile compounds decreased or degradation by the fermentation with auxiliary fermenters, such as 3-methyl-2-butenal (roasted flavor). At the same time, the fermented milk participated with the auxiliary fermenters improve the texture, especially in firmness increasement by 1.28% and 27.7% for ME and YE, respectively. The result of scanning electron microscope also proofed that protein network was thicker with smaller gaps and larger clusters fermented by auxiliary than that of the control. The milk fermented participated with auxiliary increase the water holding capacity by 73.33% and 98.47% for ME and YE, respectively. And the total acceptance than that of the control.