Fat is one of the most important nutrients in milk; however, unsaturated fatty acids in milk, especially polyunsaturated fatty acids, are prone to oxidation. As transparent packaging has been increasingly applied by milk producers, the light-induced oxidation of milk fat has become one of the most important causes of the quality deterioration and rancidity of milk, which is detrimental to the flavor of milk. Furthermore, the oxidation products pose a huge threat to human health. This article reviews the mechanism, the main influence factors and the evaluation methods of milk fat photooxidation, which will provide a theoretical basis for evaluating and inhibiting photooxidation in milk, ensuring the quality of milk, and guiding the production, packaging and marketing of milk.

A comparative analysis of fatty acid contents between ultra-high temperature (UHT) milk and reconstituted milk was carried out using 1H nuclear magnetic resonance (1H NMR) spectroscopy. The results showed that the relative contents of linolenic acid, linoleic acid, oleic acid and saturated fatty acid in UHT milk and reconstituted milk were (0.98 ± 0.11)% and (0.90 ± 0.04)%, (1.15 ± 0.36)% and (1.11 ± 0.36)%, (27.30 ± 0.56)% and (26.78 ± 0.78)%, and (43.26 ± 1.56)% and (43.81 ± 2.34)%, respectively. Orthogonal partial least squares discriminant (OPLS-DA) analysis and independent sample t test were performed on the 1H NMR spectrum peaks and fatty acid contents of the two milks. It was found that the relative content of linolenic acid was significantly different (P < 0.05) between the two milks. Nutritional assessment showed that UHT milk was more suitable than reconstituted milk for people with hyperlipidemia and/or high cholesterol, while the nutritional value of other fatty acids was similar between both milks.

Response surface methodology based on Box-Behnken design was employed to optimize the fermentation conditions of juice of “Milpa Alta” cactus stems (Opuntia ficus-indica Mill.) added with skimmed milk powder for producing fermented milk beverage. The optimal fermentation parameters were determined as follows: the concentrations of cactus stem juice, sucrose and starter culture (Lactobacillus bulgaricus:Streptococcus thermophilus = 1:1) were 15.3%, 9.4% and 0.16%, respectively; the fermentation was proceeded at 42 ℃ for 6.8 h. The acidity value of fermented beverage produced under these conditions was 93.2 °T, and it had a distinctive flavor and abundant nutrients.

The fermentation conditions for producing a fermented dairy beverage from skim milk added with the polysaccharide extract from Dendrobium officinale were optimized in the present study. Beverage with the best flavor was obtained when skim milk added with 50% Dendrobium officinale polysaccharide and sugar at levels of 10% and 7% (by mass), respectively was fermented at 42 ℃ for 6 h after inoculation with the starter culture (Lactobacillus bulgaricus:Streptococcus thermophilus = 1: 1) at a level of 0.10%.

To investigate the effect of dietary nano selenium (Se) on the level of Se in cow’s milk, ten healthy Holstein dairy cows were divided into two groups of 5 animals each, i.e., control and test groups. The control group was fed a basal diet and the test group was additionally given 15 g of dietary nano selenium each day for each cow. The results indicated that despite having no significant effect on the contents of milk fat, protein and lactose (P > 0.05), dietary nano selenium significantly increased the level of Se concentration compared with (P < 0.05). The concentration of milk Se was increased gradually with prolonged dietary supplementation, reaching 29.4 μg/L on day 30 compared to only 16.6 μg/L for the control group (P < 0.05). From these results it can be concluded that dietary supplementation with nano-Se could increase the concentration of Se in milk.

In this study, the production of polysaccharides by kefir grains during milk fermentation was optimized with respect to the amount of nutrients added to the fermentation medium (sterilized milk) employing one-factor-at-a-time and orthogonal array design methods. The results showed that the optimal carbon sources added to sterilized milk were 3% maltose, 4% sucrose and 4% glucose, resulting in a maximum yield of polysaccharides of 1.92 g/L, the optimal nitrogen sources were 0.2% yeast extract, 1% peptone and 0.004% L-tyrosine, resulting in a maximum yield of polysaccharides of 2.07 g/L, and the optimal inorganic salts were 0.4% KH2PO4, 0.08% MgSO4·7H2O, 0.02% CaCO3 and 0.25% NaCl, resulting in a maximum yield of polysaccharides of 2.01 g/L.

A gas chromatography method with hydrogen flame ionization detection was proposed to analyze the fatty acid composition of infant milk powder by temperature-programmed heating. Samples were hydrolyzed with hydrochloric acid and extracted with ether-ethanol-petroleum ether (1:1:1, V/V) for lipids. The extracted lipids were reacted with potassium hydroxide in methanol prior to being analyzed by gas chromatography. The method showed good figures of merit. The average recoveries for mixed standards of seven fatty acids in infant formulas for three different age groups spiked at three levels were 86.4%– 103.9%, and the precision of the method was 0.91%–3.82% (RSD, n=6). In addition, this method exhibited a high sensitivity and a limit of detection of 0.1 mg/100 g. Compared with the national standard method, it required more simple and rapid sample pretreatment and easier operation while providing excellent reproducibility, thus being suitable for primary laboratories.