Études récentes sur les teneurs en acide ruménique dans la matière grasse laitière en France

Abstract

Rumenic acid (RA), cis-9, trans-11 18:2, is the main conjugated linoleic acid (CLA) produced in milk fat. Updating the food composition tables was needed to determine RA levels in French milkfat in order to evaluate AR intake by French population. In a preliminary study, we analysed 54 butters from local producers in 7 different French regions, at different periods of the year. The average RA levels in butter were 0.45g RA/100g butter in winter, 0.58 in spring, and 0.80 in summer, showing seasonal variations. Regional variations of RA levels in butters were also observed from different producing areas in France. Butters from mountain regions, and butters from Normandy, a prairie country, showed the highest annual average RA levels and the largest magnitudes of variations from winter to summer. To complete these data, a second study was held throughout a year on several dairy products. During twelve months, 3 samples were monthly collected: milk, cream produced from this milk, butter processed from this cream, in 5 French dairy industries which collected local milks. Annual averages of rumenic acid levels were 0.59g RA/100g milkfat in milk (rsd = 0.219, n = 54), 0.62g RA/100g milkfat in cream (rsd = 0.223, n = 57), and 0.60g AR/100 g milkfat in butter egion to region from 0.48 to 0.69g RA/100g milkfat (annual averages of the poorest and the richest region). No significant differences in rumenic acid content were observed between milk, cream, and butter samples from a same origin (same spot, same time). Results suggest that several parameters influence the rumenic acid production by cows, such parameters including feeding, farm strategy, breed,⋯, and vary from region to region. However, no rumenic acid variations were noticed during butter making (skimming of milk, cream ripening) and churning does not seem to modify the RA contents of milkfat.