The Effect of Enzymatic Modification on Goat Milk Fat Composition and Flavour

Abstract

Goat milk has many properties that are of benefit to human health, such as tolerable to people who are allergic or suffer gastrointestinal afflictions to bovine milk, and could be are source of oligosaccharides substitutes of human milk. However, its distinct goaty odour has greatly limited its popularisation. In this study, it was found that goat milk contains higher content of short-chain fatty acid than cow milk and unique branched-chain fatty acids when compared to cow milk. These compounds impart a goaty flavour in goat milk. The major purpose of this study was to modify goat milk fat by means of lipase catalysation to generate pleasant aroma compounds. The performance of four commercial lipases (Novozyme 435, Lipozyme TL IM, Palatase 20000L and Candida Rugosa VII) were optimised and compared. The results demonstrated that the most abundant short-chain fatty acids (SCFAs) were obtained by the catalysation with Lipozyme TL IM reacting at pH 8.0, 60°C for 16 h in the hydrolysis reaction. The hydrolysed product was further subjected to esterification with the presence of ethanol. The most significant improvement was found in the ethanol/ fatty acid (E/FA) ratio 0.4 goat milk fat (GMF), where the pleasant aroma derived from esters were increased by 77.34 %, meanwhile the unpleasant odour derived from FAs were decreased by 77.5 %. Referring to the analysis of the odour activity value of each compound, the product obtained was predominated by a sweet, floral and fruity-like aroma concomitant with hints of creamy, milky and soapy odours. More importantly, 4-methyloctanoic acid responsible for the distinct goaty flavour were not detected after the modifications. The final product, with a marked improvement in the goat milk aroma, potentially enhanced the sensory profile, and could also be considered to be a non-synthetic flavourant for application in foods. During the lipase-catalysed reactions, the specificity of lipases were observed. The sn-1, 3 specific lipases had higher extent of hydrolysis than the non-specific lipases, due to the positional selection and initial lag reaction. Meanwhile, different ratios of ethanol to fatty acids also influence the catalysation. Overall, the present study developed an effective way to improve the odour profile of goat milk, filling the gap in the modification of goat milk flavour. Meanwhile, a series of factors that could manipulate lipases catalysation were optimised and presented.