Seasonal variations in composition, properties, and heat-induced changes in bovine milk in a seasonal calving system

Abstract

We determined seasonal variations in the composition and characteristics of bovine milk, as well as heat-induced changes in the physicochemical properties of the milk, in a typical seasonal-calving New Zealand herd over 2 full milking seasons. Fat, protein, and lactose contents varied consistently during the year in patterns similar to those of the lactation cycle. Seasonality also had significant effects on milk calcium, ionic calcium, fat globule size, buffering capacity, and ethanol stability, but not on casein micelle size. The ratio of casein to total protein did not vary significantly over the season, but late-season milk had the highest content of glycosylated κ-casein (G-κ-CN) and the lowest content of α-lactalbumin in both years. We observed significant between-year effects on protein, total calcium, ionic calcium, pH, and casein: total protein ratio, which might have resulted from different somatic cell counts in the 2 years. Compared with heating at 90°C for 6 min, UHT treatment (140°C for 5 s) induced greater dissociation of κ-casein, a similar extent of whey protein denaturation, a lower extent of whey protein-casein micelle association, and a larger increase in casein micelle size. Indeed, UHT treatment might have triggered significant dissociation of G-κ-CN, resulting in aggregation among the casein micelles and increased apparent mean casein micelle diameter. Seasonality had significant effects on the partitioning of G-κ-CN between the micelle and the serum phase, the extent of whey protein-casein micelle association under both heating conditions, and the casein micelle size of the UHT milk.

Composition, Structure, and Digestive Dynamics of Milk From Different Species—A Review

“…Protein, fat, lactose, and minerals are the four major components in all milks, irrespective of the species ( 18 ); the composition of milk within the same species varies considerably because of various factors, such as breed, stage of lactation, milking interval, type of feed, and climate ( 7 , 19 ). For example, Li et al ( 26 ) reported recently that the stage of lactation is a key factor responsible for differences in the compositional and physicochemical properties of dairy cattle milk in a seasonal calving system in New Zealand.…”

Effects of seasonal variations on the quality of set yogurt, stirred yogurt, and Greek-style yogurt

“…In each season of each year, 4 to 6 batches of yogurt were made and analyzed. Detailed information on the herd and the sampling is given in Li et al (2019).…”

“…Seasonality plays a role in altering the composition and physicochemical properties of bovine milk and subsequently affects the quality of dairy products. The effects of seasonal variation are particularly pronounced in seasonal-calving countries such as New Zealand, where most dairy cows calve at the same period of the year (Auldist et al, 1998;Li et al, 2019). A better understanding of the effects of seasonality on the properties of yogurt would allow better control of the product quality and would assist in the development of new types of fermented dairy products to meet ever-changing consumer preferences.…”

“…We analyzed and discussed the correlations between yogurt properties and seasonal milk characteristics reported in our previous work (Li et al, 2019). The standardized milk base used for making regular set yogurt and stirred yogurt was also used in our work on GDL-induced acid gelation (Li et al, 2020).…”

Genome-wide interaction analyses of milk production traits in dairy cattle

“…. The nutritional value of milk and dairy products are related to milk composition (Couvreur et al, 2006;Ortiz-Gonzalez et al, 2007;Li et al, 2019). Variation in milk yield and composition can be due to many factors, e.g., genetic differences, feeding regime, or lactation stage (Dhiman et al, 1999;Elgersma et al, 2004;Poulsen et al, 2012).…”