Effects of freezing on composition and fatty acid profiles of sheep milk and cheese

Abstract

A study was conducted with sheep milk to determine the effects of freezing temperature and freezing time on milk composition, cheese yield and composition and fatty acid profile of milk and cheese. Bulk tank samples of sheep milk were collected for 4 consecutive weeks and stored at −15 or −25 °C for 1–6 months. Milk samples frozen at the two different temperatures were thawed monthly at 22 °C and milk was used for cheese making. Results showed freezing temperature and freezing time had no effect on concentration of milk total solids, protein, casein, non-protein N, true protein and lactose contents, however, milk fat percentage decreased ( P < 0.05) progressively during the 6 months freezing period with less changes ( P < 0.05) observed at −25 °C than at −15 °C. Freezing at either temperature for more than 2 months reduced ( P < 0.05) actual cheese yield with lowest ( P < 0.05) yield observed at 6 months of storage, however, 37% moisture adjusted cheese yield and cheese fat and protein percentages were not affected by freezing treatments. Fatty acid composition of thawed milk and fatty acid profile of cheeses were not affected by freezing temperature and freezing time. It was concluded that freezing sheep milk at −15 and −25 °C for up to 6 months had only minor effects on milk and cheese composition. Despite the fact that freezing reduced actual cheese yield, adjusted cheese yield was similar for all freezing treatments. Freezing had no effect on milk or cheese fatty acid concentrations. Under the conditions of this study, good quality cheese can be produced from ovine milk frozen at −15 and −25 °C for up to 6 months without influencing cheese yield or composition.