Effects of season and industrial processes on volatile 4-alkyl-branched chain fatty acids in sheep milk.

4-alkyl-branched-chain fatty acids (vBCFAs) are responsible for the goaty-sheepy flavour of sheep and goat milk. The levels of vBCFAs were investigated in sheep, goat and cow milk powders. The effect of season and industrial processes on the levels of vBCFAs in sheep milk was also evaluated. Sheep milk powders contained lower amounts of 4-Me-8:0 and 4-Et-8:0 (143-176 and 1.2-10.7 µg/g milk fat) than goat milk powders (335-481 and 73.1-105 µg/g milk fat), while 4-Me-9:0 was low in both sheep and goat milk powders (<8 µg/g milk fat). Odour activity values (OAVs) of sheep milk powders (17-393) were 6-fold lower than the values of goat milk powders (882-1323). Higher levels of vBCFAs were found in sheep milk produced in spring than in summer. Thermisation had little impact on vBCFAs; however, spray drying led to dramatic increases in free vBCFAs, particularly towards late lactation, which resulted in higher OAVs in sheep milk powder compared to raw milk.