Gas chromatography-mass spectrometry profiling of fatty acids in breast milk from nursing mothers in Bungoma County, Kenya

Abstract

Human breast milk is universally recognized as the optimal food for term infants. Fatty acids play important roles in biological systems and the newborn’s fatty acid requirements are wholly met by the mothers’ breast milk. Although there have been many studies on fatty acid composition of human milk from Western countries and Africa, there is little information about that in the Kenyan population. This study was conducted to characterize and analyze quantitatively the fatty acid profile of breast milk at 2 stages of lactation from nursing mothers in Bungoma County, Kenya. Breast milk samples were obtained at the fourth and ninth month postpartum from nursing mothers who were participating in a Cohort for Vitamin A (COVA) study. The samples were collected by manual expression and stored at –20 0C until analysis. The fat was extracted from milk and methylated using the Association of Official Analytical Chemists International (AOAC) Official methods. The separation, identification and quantification of the fatty acid methyl esters was performed by gas chromatography coupled with mass spectrometry (GC-MS). Fatty acids were identified based on retention times and mass spectral data. These were compared with corresponding standards and a library of known mass spectra. The results showed that the major fatty acids of breast milk fat at the 4th month of lactation were oleic acid (66.6%), followed by linoleic acid (51.3%) and palmitoleic acid (28.9%). However, at the 9th month, the major component was linoleic acid (58.1%), followed by oleic acid (30.9%) and stearic acid (23.1%). The caprylic acid content was the least (˂ 4%) among the fatty acids in both stages of lactation. The fatty acid composition was expressed as weight percentage of all fatty acids detected with C8–C18 chain length. More than 80% of the total fatty acids were composed of C18:1n-9 (oleic acid) and C18:2n-6 (linoleic acid). The percentage average of the total saturated fatty acids at 4 months (16.62%) was significantly lower (p ˂ 0.05) than the average percent of the total unsaturated FAs (48.93%). Similarly, at the 9th month the percentage average of the total saturated fatty acids (15.18%) was significantly lower (p ˂ 0.05) than the average percent of the total unsaturated FAs (31.05%). The fatty acid composition was significantly different between the two lactation/ nursing periods. This study has shown that breast milk fat is an excellent source of the essential fatty acid omega-6 (linoleic acid) for infants in Bungoma County.