In this study, headspace solid phase microextraction in combination with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (HS-SPME-GC × GC-TOFMS) was used to analyze the volatile compounds in whole (WM), low-fat milk (LFM) and non-fat milk (NFM). Altogether 49 volatile compounds were detected, among which methyl ketones with odd-numbered carbon chain lengths such as 2-nonanone and 2-undecanone constituted the main flavor compounds of WM. Using partial least squares discriminant analysis (PLS-DA), a model which could well differentiate among the 3 milks was developed and it was found to have good variance and cross-validation predictive ability. Nine differential key aroma compounds were identified using variable importance in the projection (VIP) > 1, P ≤ 0.05 and their contents ≥ 1% as criteria, which may be the main factors contributing to the differences in flavor profiles among the 3 milks. The heatmap from clustering analysis indicated that NFM had poor sensory performance due to the presence of off-flavor compounds (e.g., hexadecanal), whereas WM and LFM contained more aroma compounds, having a full and rich sensory aroma profile. The HS-SPME-GC × GC-TOFMS method can provide theoretical guidance for dairy flavor improvement and dairy flavoring formulation.

Escherichia coli ATCC25922 and Staphylococcus aureus ATCC25923 were used as test strains for screening of antimicrobial lactic acid bacteria from kefir grains. The fermentation supernatant of the selected isolate was processed into a freeze-dried powder. When used at a concentration greater than 6.250 mg/mL, the unpurified antimicrobial peptides had a strong bacteriostatic effect. The strain was identified as Lactobacillus casei by 16S rDNA gene sequencing. Raw whole milk was fermented by inoculating this strain at 2, 3 or 4 g/100 mL, and stored at 4 ℃ for 30 days. The pH and syneresis of fermented milk decreased with increasing inoculum size, whereas the titratable acidity, hardness, viscosity and water-holding capacity increased. The fermented milks with inoculum amounts of 3 and 4 g/100 mL did not significantly differ in sensory evaluation scores, both higher than that inoculated at 2 g/100 mL.

As increasing attention has been paid to the flavor of dairy products, research on dairy flavors will promote the rapid development of the dairy flavor industry. In this paper, we summarize recent progress in research on dairy flavors, review the main flavor compounds of some common dairy products, analyze the mechanism of off-flavor formation, and provide some solutions to this problem based on the preparation process for dairy flavors. It is expected that this review will provide new ideas for the development of flavored dairy products and dairy flavors in the future.

Set skim yogurt was supplemented with inulin as a fat replacer to improve its texture and organoleptic properties. The water-holding power, rheological properties, color and sensory evaluation of yogurt prepared from skim milk powder with added inulin were measured and compared with those of control samples (whole milk yogurt). The rheological properties and sensory evaluation of the yogurt with 3.0% inulin was similar to those of control samples, but the water-holding power was lower than that of control samples. Whey syneresis occurred in none of the yoghurt samples. It was concluded that addition of 3.0% inulin resulted in high overall acceptability and showed good potential for commercial application.