Objective: To investigate differences in fatty acid and sn-2 fatty acid composition in colostrum, transitional and mature human milk, and in term infant formulas. Setting: Departament de Nutrició i Bromatologia, University of Barcelona, Spain and University Hospital of Granada, Spain. Subjects: One-hundred and twenty mothers and 11 available types of infant formulas for term infants. Design: We analysed the fatty acid composition of colostrum (n ¼ 40), transitional milk (n ¼ 40), mature milk (n ¼ 40) and 11 infant formulas. We also analysed the fatty acid composition at sn-2 position in colostrum (n ¼ 12), transitional milk (n ¼ 12), mature milk (n ¼ 12), and the 11 infant formulas. Results: Human milk in Spain had low saturated fatty acids, high monounsaturated fatty acids and high linolenic acid. Infant formulas and mature human milk had similar fatty acid composition. In mature milk, palmitic acid was preferentially esterified at the sn-2 position (86.25%), and oleic and linoleic acids were predominantly esterified at the sn-1,3 positions (12.22 and 22.27%, respectively, in the sn-2 position). In infant formulas, palmitic acid was preferentially esterified at the sn-1,3 positions and oleic and linoleic acids had higher percentages at the sn-2 position than they do in human milk. Conclusion: Fatty acid composition of human milk in Spain seems to reflect the Mediterranean dietary habits of mothers. Infant formulas resemble the fatty acid profile of human milk, but the distribution of fatty acids at the sn-2 position is markedly different.

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We have validated and compared two methods for the determination of fatty acid profiles in biological samples by capillary gas chromatography. Method I consisted of a previous lipid extraction and esterification of fatty acids using boron trifluoride-methanol. Method II was a direct method that combined extraction and esterification of freeze-dried samples in a single step, using acetyl chloride as the reagent. The two methods were applied to the analysis of plasma and erythrocyte samples. Both methods gave similar results in plasma, whereas in erythrocytes, the direct method gave significantly higher contents of total fatty acids. Precision and recovery rates were determined and the results were satisfactory. Detection and quantification limits showed that both methods had excellent sensitivity. It was concluded that the direct method has substantial advantages over the conventional method, such as higher values in erythrocytes, rapidity and less possibility of contamination or fatty acid losses. Therefore, it is preferable for the analysis of biological samples such as plasma and erythrocytes.

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