Volatile 4-alkyl-branched chain fatty acids in New Zealand sheep milk

Abstract

Sheep milk provides a good alternative source to cow milk since it contains higher total solids and major nutrients. However, the characteristic goaty-sheepy flavour of sheep milk and milk products is less acceptable by some customers. It has been suggested that volatile branched chain fatty acids (vBCFAs), mainly 4-methyloctanoic acid (4-Me-8:0), 4-ethyloctanoic acid (4-Et-8:0), and 4-methylnonanoic acid (4-Me-9:0), are responsible for this typical flavour in sheep and goat milk. The goal of this study was to investigate how vBCFA levels: A) differ between sheep, goat and cow milk; B) vary during the milking season and C) are affected by processing (thermisation and spray drying). Results: A) Sheep milk contains less than half the amount of 4-Me-8:0 and 7-10 fold lower amount of 4-Et-8:0 than goat milk. 4-Me-9:0 is low in both sheep and goat milk. Cow milk has 5-6 fold lower amount of 4-Me-8:0 compared to sheep milk. In addition, odour activity values (OAVs) of sheep milk are 6 fold lower than those of goat milk due to the significant higher free vBCFAs concentrations in goat milk. B) The levels of vBCFAs in sheep milk differed significantly throughout the season with higher levels in spring. C) Thermisation of sheep milk did not affect the levels of vBCFAs, however, spray drying led to release of free vBCFAs particularly towards late lactation which resulted in more than twice of OAVs in milk powder compared to raw milk. These findings provide new insights for processing control and product innovation to develop flavoursome sheep milk products and support the growth of New Zealand sheep milk industry