Effect of ultra-high pressure and heating treatment on fatty acid composition of goat milk

Abstract: Goat milk has more nutrition advantages compared with bovine milk, and its fat contains a large number of fatty acids, some of which are very important for human health such as anti-carcinogenesis, anti-atherosclerosis and strengthening immunity. In addition, the specific flavor of goat milk is mainly influenced by free fatty acid of short-chain, such as octanoic acid (C8:0) and decanoic acid (C10:0). Therefore, the purpose of this paper was to study the effects of ultra-high pressure and heating treatment on fatty acid compositions in goat milk from Laoshan dairy goat. The samples were treated under the ultra-high pressure conditions of 100, 200, 300 and 400 MPa and heating treatment of 65℃ every 30 min, 75℃ every 15 min, and 90℃ every min. Then, composition of fatty acid was analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that with the treatment of ultra-high pressure and heating processing, the content of short-chain fatty acid (SCFA) and saturated fatty acid (SFA) increased, while unsaturated fatty acid (USFA) decreased, and there were no significant differences under ultra-high pressure processing, but significant differences were observed under the treatment of heating (P<0.01, P<0.01 and P<0.001). Under the heating treatment of 90℃ every min, SCFA increased to the highest, which was 64.91% (P<0.05) higher than the raw milk, respectively, while the content of USFA decreased to the minimum under the treatment of boiling, which was 35.85% (P<0.01) lower than raw milk. For the SCFA, with the treatment of ultra-high pressure, the differences of caproic acid (C6:0), C8:0 and C10:0 were not significant, however, the significant increase (P<0.01) occurred in C10:0 after heating. For the SFA, significant differences were observed in lauric acid (C12:0), myristic acid (C14:0) and stearic acid (C18:0) under various pressure conditions (P<0.01, P<0.01 and P<0.05), while there was no significant difference for C16:0. The contents of C12:0, C14:0 and palm acid (C16:0) increased with ultra-high pressure treatment and up to the maximum at 300, 200 and 100 MPa respectively, which were enhanced by 179%, 54%, and 26% respectively (P<0.05, P<0.05, P>0.05) compared with raw milk. However, the content of C18:0 decreased with the treatment of ultra-high pressure, and it was the lowest at 200 MPa, which decreased by 65% compared with raw milk (P<0.05). The contents of C12:0, C14:0 and C16:0 were increased with heating treatment and up to the maximum under the boiling condition, which were enhanced by 91%, 74% and 21% respectively (P<0.05) compared with raw milk. For USFA, there was no significant difference in oleic acid (C18:1) with the treatment of ultra-high pressure, but the changes of linoleic acid (C18:2) and flax acid (C18:3) were significant (P<0.01 and P<0.05). The contents of C18:1, C18:2 and C18:3 all decreased with the treatment of ultra-high pressure, and under 300 MPa the contents reached the minimum and reduced by 27%, 60% and 58% respectively compared with raw milk (P>0.05, P<0.05 and P<0.05). The contents of C18:1, C18:2 and C18:3 all decreased with the treatment of heating (P<0.001, P<0.05 and P<0.001), and under the treatment of boiling the contents were the minimum, which were reduced by 33%, 66% and 64% respectively compared with raw milk (P<0.01, P<0.05 and P<0.01). The results of this study reveal that the effect of ultra-high pressure on fatty acids in goat milk is slighter, and it is helpful for the applications of ultra-high pressure technology and heat treatment in the dairy and provides theoretical basis for the development of goat milk resource.