Azorean bovine milk conjugated linoleic acid. Effect of green pasture diet, storage and processing temperature

Abstract

Conjugated linoleic acids (CLA) that are isomeric forms of the cis-9,cis-12 linoleic acid have sparked considerable interest in the scientific community due to their reported beneficial health properties. The objective of this study was the quantification of the CLA in commercial Azo- rean bovine milk and comparison with CLA in Portuguese mainland milk, and evaluation of the effect of storage and the processing temperature on the CLA content in milk. The relative average of CLA (cis-9,trans-11 isomer) content in Azorean (S. Miguel Island-Portugal) and Portuguese mainland milks represents 1.33 ± 0.09% and 0.79 ± 0.07% of total fatty acid methyl esters (tFAME), respectively. The cis-9,trans-11-CLA isomer variation in Azorean ultrapasteurized (UHT) milk, throughout the year, ranged from 1.16 ± 0.09% to 1.46 ± 0.09% and reflects the bovine pasture-fed diet (fresh grass) during all seasons and the mild winter in the Azores Islands. The CLA content of Azorean milk is a little higher than that published in the literature for New Zealand (1.20% of tFAME). The effect of the processing temperature on the CLA level shows a decrease in the cis- 9,trans-11-CLA isomer content from 1.56 ± 0.05 (raw milk) to 1.40 ± 0.04 and 1.26 ± 0.04 (% to tFAME) in different pasteurized and UHT-treated milks, respectively. The effect of storage time on the CLA content of commercial UHT milk, kept refrigerated at 6-7 oC for two months, shows a loss of 1.2%, which is negligible compared with the processing temperature effect. Azorean milk is natu- rally rich in CLA, and according to recently published literature, has a wide array of health benefits and may be useful in the prevention of some degenerative diseases. milk / fatty acid / conjugated linoleic acid / gas chromatography