Seasonal Variations in the Composition and Physicochemical Characteristics of Sheep and Goat Milks

Abstract

There has been growing consumer interest in sheep and goat milk products as alternatives to cow milk products. The physicochemical characteristics of milk vary not only between ruminant species, but also during different seasons; they determine the nutritional quality and processing properties of the milk. In this study, we characterized sheep and goat milks from New Zealand over the seasons for their composition (macronutrients, macro- and micro-minerals, fatty acids, and proteins) and physicochemical properties (e.g., ionic calcium, fat globule size, casein micelle size, viscosity, and melting behavior of milk fat). Heat-induced (95 °C for 5 min) protein interactions and changes in the physical properties of the milks were also investigated. The compositional and structural features of sheep and goat milks were identified and compared with those reported for cow milk. Seasonal variations in the milk characteristics were more pronounced for sheep milk than goat milk and were probably affected by the production systems. Sheep milk, particularly in the late season, had the largest heat-induced increases in casein micelle size and viscosity, probably arising from the greater casein–whey protein and casein–casein interactions during heat treatment. This study provides comprehensive information on the properties of sheep and goat milks and highlights the interaction effects between species, season, and processing.

Characteristics of Red Deer (Cervus elaphus) Milk: Lactational Changes in Composition and Processing Impacts on Structural and Gelation Properties

“…The impacts of lactation on different compositions of the red deer milk, including proximate composition (total solids, fat, protein, lactose, and casein), mineral composition (calcium, magnesium, potassium, sodium, phosphorus, chloride, copper, iodine, selenium, and zinc), protein composition, and fatty acid composition were analyzed using methods described in Li et al [ 19 ].…”

“…The fatty acid composition of the deer milk was analyzed using gas chromatography with flame ionization detection (Shimadzu Nexis GC-2030, Shimadzu, Kyoto, Japan) on a Restek Rx 2330 column (105 m × 0.25 mm ID, 0.20 μm film thickness) as described in Li et al [ 19 ].…”

“…The SDS-PAGE gel was scanned using the Gel Doc XR+ system and analyzed for band staining intensity using Image Lab 5.2.1 software (Bio-Rad Laboratories, Hercules, CA, USA). The deer skim milk was also analyzed for protein composition using an HPLC method previously applied to other ruminant milks, as described by Li et al [ 19 ]. To verify whey protein peaks in the chromatogram, whey proteins were separated using acid precipitation (to pH 4.6), as modified from Vasbinder and De Kruif [ 21 ].…”

“…The physicochemical properties of raw deer milk were characterized as described previously [ 14 , 19 ]. The fat globule size was determined using a Malvern MasterSizer 2000 (Malvern Instruments Ltd., Malvern, UK) after chemically dissociating the casein micelles using a solution containing 50 mM EDTA and 2% (wt/wt) SDS.…”

“…In this work, we studied the compositions (macronutrients, minerals, fatty acids, and proteins) of New Zealand red deer milk throughout the lactation cycle and characterized the physicochemical features and gelation properties (acid- and rennet-induced) of differently processed deer milks. Similar methods had been used for previous studies on bovine, ovine, and caprine milks produced in New Zealand [ 14 , 19 ], allowing identification of the similarities and differences in ruminant milk characteristics and enabling optimized applications.…”