Determination of Free Fatty Acids in Breast Milk Reveals the Presence of Hydroxypalmitic and Stearic Acids.

Breast milk is a rich source of fatty acids (FAs) while being irreplaceable for the health and development of an infant. Herein, we present a fast and simple method for the direct detection and quantification of 37 free FAs (FFAs) in breast milk samples, avoiding any derivatization step, and a study on the % variation of FA contents in samples collected from the same mother within five consecutive days. The average breakdown of FAs was 60.5% saturated and 39.5% unsaturated, in which polyunsaturated FAs were 13.3% and monounsaturated FAs 26.2%. The most abundant FFA in the breast milk samples was C12:0 (18.3%), followed by C10:0 (15.0%), suggesting that further attention must be paid to the presence and role of medium-chain FAs. Among unsaturated FAs, oleic acid (C18:1 n-9) (13.3%) and linoleic acid (C18:2 n-6) (10.1%) were the most abundant. Remarkable variations of FFA contents within the five consecutive days were observed for C8:0, C10:0, C12:0, C18:1 n-9, and C18:2 n-6. The two isomers α-linolenic acid (C18:3 n-3) and γ-linolenic acid (C18:3 n-6) were quantified in all breast milk samples. The ratio of γ-linolenic acid, which most recently is important for cardiac metabolic maturation, to α-linolenic acid was found to be 1:2. Most importantly, in the present study, we explored the presence of bioactive saturated monohydroxy fatty acids (SHFAs), demonstrating for the first time the existence of distinct hydroxypalmitic and hydroxystearic acids (HPAs and HSAs, respectively) in breast milk.