Synthesis and sensory evaluation of conjugated linoleic acid-enriched milk.

摘要

Conjugated linoleic acid (CLA) refers to a mixture of conjugated octadecadienoic acids of predominantly ruminant origin. The main isomer in bovine milk fat is the cis-9, trans-11 18:2. Interest in CLA increased after the discovery of its health promoting properties, including potent anticarcinogenic activity. The objectives of this thesis were to evaluate dietary strategies aimed at increasing the concentration of CLA in bovine milk fat, and to evaluate the organoleptic characteristics of CLA-enriched milk.; Two feeding experiments, using a complete-randomized block design, were conducted with the aim of enriching the concentration of CLA in bovine milk. The initial study fed 28 Holstein cows for two weeks. The follow up study fed 62 Holstein cows for two months. Diets were supplemented with various combinations of safflower oil, flaxseed oil, vitamin E, and monensin. These studies showed that milk CLA concentrations could be increased by more than ten times through dietary modification.; CLA-enriched milk was processed and evaluated by a ten-person trained sensory panel and a 75-person untrained consumer panel. The trained panel found that CLA-enriched milk was not different from the control in terms of its organoleptic characteristics. Results were conflicting for consumer testing, which found one of the CLA-enriched milk samples less acceptable than control and the other CLA-enriched milk equally acceptable as control.; A final study designed as a 4 x 4 latin square, evaluated the effectiveness of post-ruminal delivery of a synthetic CLA mixture to increase milk CLA. Post-ruminal delivery of CLA, compared to tallow, safflower oil, or control, increased the concentration of CLA in milk fat but had extremely negative effects on milk production and composition. These effects, which were not observed in the initial feeding studies, were attributed to the very high content of trans-10, cis-12 in the CLA mixture. The results suggested that the extent of enrichment possible for trans-10, cis-12 CLA is limited.; The results presented in this thesis demonstrated the feasibility of producing CLA-enriched milk through dietary modification. Trained sensory evaluation demonstrated that increasing the concentration of CLA did not change the organoleptic characteristics of the milk.