Yoghurt has the strong flavour produced by adding Cheddar cheese into the milk and cold storage process before the fermentation. The flavour analysis of yoghurt was investigated by e-nose, e-tongue and gas chromatography-mass spectrometry (GC-MS). Yoghurt samples with adding Cheddar cheese or whole milk powder showed significant differences in their e-nose flavour profiles, but their e-tongue flavour profiles were roughly similar. Besides, neither e-nose nor e-tongue could accurately distinguish the yoghurt samples which were subjected to cold storage process before the homogenization or not. Among the detected volatile compounds, pentanal and dimethyl trisulfide were the most highly correlated with the cold storage process, and pentanal, ethyl butanoate, methanethiol, dimethyl disulfide and dimethyl trisulfide discriminated yoghurt samples adding Cheddar cheese or whole milk powder. This study showed the potential of adding Cheddar cheese in the yoghurt production to accelerate the flavour formation and increase the flavour compounds.

The aim of this study was to investigate the influence of proteolytic pork hydrolysate (PPH) on yoghurt production by Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Fresh lean pork was cut into pieces and mixed with deionized water and dealt with protease, then the resulting PPH was added to milk to investigate the effects of PPH on yoghurt production. The fermentation time, the viable cell counts, the flavor, free amino acids compounds, and sensory evaluation of yoghurt were evaluated. These results showed that PPH significantly stimulated the growth and acidification of the both bacterial strains. When the content of PPH reached 5% (w/w), the increased acidifying rate occurred, which the fermentation time was one hour less than that of the control, a time saving of up to 20% compared with the control. The viable cell counts, the total free amino acids, and the scores of taste, flavor and overall acceptability in PPH-supplemented yoghurt were higher than the control. Furthermore, the contents of some characteristic flavor compounds including acids, alcohols, aldehydes, ketones and esters were richer than the control. We concluded that the constituents of PPH such as small peptide, vitamins, and minerals together to play the stimulatory roles and result in beneficial effect for the yoghurt starter cultures growth.