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.

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.

In this study, a low-fat Cheddar cheese was developed using polymerized whey protein (PWP) as a fat replacer and Lactobacillus helveticus as an auxiliary culture, and the effects of PWP on the physicochemical properties of cheese were studied. Results showed that addition of PWP and Lactobacillus helveticus increased the contents of moisture, protein, free amino acids and volatile compounds and lactic acid bacterial population, and markedly improved sensory characteristics and acceptance of cheese. Addition of PWP reduced the fat ripening period, and increased pH 4.6-soluble nitrogen (SN) fraction by 9.45% and 12 g/100 mL trichloracetic acid (TCA)-SN fraction by 11.74% after ripening. Cheese yield was not affected by adding PWP or the auxiliary culture. All the data indicated that polymerized whey protein can be used as a promising fat replacer for developing low-fat Cheddar cheese with good texture and sensory properties.

The purpose of this study was to investigate the effects of geographical origin, dairy animal species and fermentation on the contents of mineral elements (calcium, iron and zinc), vitamin A and vitamin E in milk from minor dairy species (horse, camel and yak). In total, 86 samples of fresh and fermented milk were collected in main pastoral areas of Xinjiang, Inner Mongolia, Qinghai and Gansu in western China. The contents of mineral elements and vitamins in these samples were determined and by inductively coupled plasma mass spectrometry (ICP-MS) and high performance liquid chromatography (HPLC), respectively. The results showed that: 1) There was no significant difference in the contents of calcium, iron and zinc in fresh horse milk between Xinjiang and Inner Mongolia (P > 0.05), whereas there was a significant difference in the contents of calcium and iron in fresh camel milk between the two pastoral areas, as well as in the contents of iron and zinc in fresh yak milk between Gansu and Qinghai (P < 0.05); the contents of vitamins A and E were higher in fresh camel milk from Xinjiang than Inner Mongolia, as well as in fresh yak milk from Qinghai than Gansu (P < 0.05). 2) There were significant differences in calcium, iron and zinc contents among dairy animal species with significantly higher levels for each element being observed in yak milk than in camel milk and horse milk (P < 0.05); likewise, significant inter-species differences in the contents of vitamin A and E in milk were found (P < 0.05); the contents of both vitamins were slightly higher in horse milk from Inner Mongolia than Xinjiang (P > 0.05). 3) Fermentation had no significant effect on mineral element contents in milk. The content of vitamin E in fermented horse milk was significantly higher than in fresh horse milk (P < 0.05), and the contents of vitamins A and E in fresh milk from the other species decreased in varying degrees after fermentation.

Because of its gelling, thickening and stabilizing properties, marine polysaccharide can be used as stabilizer for stirred yogurt. In this study, the effects of carrageenan, sodium alginate, instant and ordinary agar on properties of stirred yoghurt were studied. The indexes observed were viscosity, acidity, fermentation state and flavor. In comparison, instant agar could improve the viscosity of yogurt, increase shear resistance, improve mouthfeel and enhance flavor, and decrease whey syneresis. The product with instant agar demonstrated smooth mouthfeel, a suitable viscosity, and extended shelf life. The stirred yogurt had the best taste when instant agar was added at 0.15%.

Yoghurt was made by fermentation of reconstructed milk mixed with Puerariae radix pulp. The optimization of four fermentation conditions (Puerariae radix pulp concentration, inoclum amount, fermentation time and temperature) for the improved sensory quality and flavonoid content of products was carried out using a combination of single factor and orthogonal array designs. The optimal fermentation conditions were 14%, 2.5%, 4.5 h and 41 ℃ for Puerariae radix pulp concentration, inoclum amount, fermentation time and temperature, respectively. The obtained product contained 1.71 mg/mL flavonoids.