Seasonal Changes in the Chemical Composition of Commingled Goat Milk

Abstract

Production of goat milk cheese in North America has been growing rapidly during the past several years. However, information on chemical composition and its seasonal variation of year-round bulk-collected goat milk is limited. The objective of this study was to analyze the chemical composition of commercial goat milk shipments for an entire year to provide fundamental information for cheese making and milk cheese yielding potential and pricing. Samples were collected weekly from bulk milk shipments to a commercial cheese company over 12 mo, beginning in April, 1996, and analyzed for contents (%) of total solids (TS), fat (F), lactose, crude protein, casein, nonprotein nitrogen (NPN), ash, minerals, and specific gravity (G). Chemical composition of the goat milk varied widely during the year. The contents of fat and TS decreased over the first 20 wk from 3.6 and 12.7% to 3.0 and 11.3%, respectively, and then increased to peak values of 13.4 and 4.4% in January. Crude protein and casein contents also decreased over the first 20 wk, from 3.5 and 2.7% to 3.2 and 2.3%, respectively, before increasing gradually to 3.8 and 2.9% in February. The concentration of lactose seemed to decrease below mean levels during August and January. Ash content declined during the first 20 wk from 0.82 to 0.78%, and then increased sharply to 0.90% by wk 36 before decreasing sharply again toward the end of the study. Calcium content decreased steadily from about 0.16 to 0.14% by wk 20, before increasing to 0.16% by around wk 40. It was found that TS content could be estimated using the equation: TS = 0.13 G + 1.41 F + 4.28 (r 2 = 0.94, P < 0.01). (