Ueli Bütikofer

CLA isomers in milk fat from cows fed diets with high levels of unsaturated fatty acids

The concentrations of CLA isomers were determined by Ag+-HPLC in the milk fat of cows fed a control diet consisting of hay ad libitum and 15 kg of fodder beets or this diet supplemented with oilseeds containing either high levels of oleic acid (rapeseed), linoleic acid (sunflower seed), or α-linolenic acid (linseed). Highly significant (P≤0.001) correlations were found between the daily intakes of oleic acid and the concentration of the CLA isomer trans-7,cis-9 in milk fat; of linoleic acid and the CLA isomers trans-10,trans-12, trans-9,trans-11, trans-8,trans-10, trans-7,trans-9, trans-10,cis-12, cis-9,trans-11, trans-8,cis-10, and trans-7,cis-9; and of α-linolenic acid and the CLA isomers trans-12,trans-14, trans-11,trans-13, cis,trans/trans,cis-12,14, trans-11,cis-13, and cis-11,trans-13. CLA concentrations were also determined in the milk fat of cows grazing in the lowlands (600–650 m), the mountains (900–1210 m), and the highlands (1275–2120 m). The concentrations of many isomers were highest in milk fat from the highlands, but only three CLA isomers (cis-9,trans-11, trans-11,cis-13, and trans-8,cis-10) showed a nearly linear increase with elevation. Therefore, these three CLA isomers, and particularly the CLA isomer trans-11,cis-13, the second-most important CLA in milk fat from cows grazing at the three altitudes, could be useful indicators of milk products of Alpine origin.

Benzoic acid as a natural compound in cultured dairy products and cheese

Abstract This review deals with the ‘state of the art’ of benzoic acid in cultured dairy products and cheese. During fermentation, benzoic acid is produced from hippuric acid, a component of milk naturally present at concentrations of up to 50 mg/kg. In smearripened cheese, however, higher benzoic acid concentrations have often been measured on the surface or even inside such cheeses. A second metabolic pathway has been proposed: during ripening, an additional quantity of benzoic acid originates from phenylalanine degradation, with β-phenyl-propionic (hydrocinnamic) acid and cinnamic acid as intermediate products. Acetophenone is a by-product of this breakdown, which essentially occurs in the rind and the smear. The presence of these intermediate products and their concentration gradient, the concentration of benzoic acid and its formation during cheese ripening, and the simultaneous production of ammonia resulting from deamination support the validity of this second metabolic pathway. A third way could he the auto-oxidation of benzaldehyde, produced by certain strains of lactic acid bacteria. In addition to the transformation of hippuric acid, these two sources (phenylalanine degradation, auto-oxidation of benzaldehyde) supply benzoic acid in cheese.