Date of Award
Doctor of Philosophy
Food Science and Human Nutrition
Conjugated linoleic acid (CLA) is present primarily in dairy products with many positive nutritional benefits. The predominant CLA isomers, cis-9, trans-11 CLA and trans-10, cis-12 CLA, function as an anticarcinogen and body fat reducer, respectively. Other health benefits include roles as an immune system modulator, anti-atherosclerosis and antidiabetic agent. Linoleic acid isomerase activity in probiotic bacteria contributes to CLA formation. Free linoleic acid is the primary substrate for linoleic acid isomerase and the biohydrogenation pathway of rumen bacteria. There is strong interest to increase the content of CLA in yogurt and other cultured dairy products using probiotic bacteria and unique processing methods.;The objectives of this study were to (1) evaluate the ability of probiotic bacteria to convert linoleic acid (as the free or esterified fatty acid) to CLA in model systems characteristic of yogurt; and (2) develop yogurts with enhanced CLA content and acceptable quality attributes using probiotic bacteria with CLA-producing activity with and without conventional yogurt cultures (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus, 1:1).;The 11 probiotic bacteria evaluated were able to produce CLA from linoleic acid in the model system containing hydrolyzed soy oil (1%) emulsified in milk, but not in model systems of unhydrolyzed soy oil (1%) emulsified in milk or 1% fat milk. The propionibacteria demonstrated the greatest increase in CLA content compared to other lactic acid bacteria in model system.;A yogurt processed with yogurt cultures in conjunction with probiotic bacteria resulted in the greatest formation of the CLA and similar acidity, texture and flavor as the control yogurt. The combination of Lactobacillus rhamnosus with yogurt cultures produced a yogurt with the highest content of CLA and acceptable quality characteristics. The CLA formation, microbial counts, and quality attributes were stable over a 14-day storage time at 4°C. The inoculation concentration of L. rhamnosus and yogurt cultures did not have significant effect on CLA content and texture, but affected acidity and volatile flavor compounds of yogurts.;These findings indicate that probiotic dairy foods with enhanced CLA content and acceptable quality attributes can be effectively developed. The research results would help the food industry produce a more nutritional product for consumers.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Xu, Sa, "Effect of probiotic bacteria on the conjugated linoleic acid (CLA) content and quality of yogurt " (2004). Retrospective Theses and Dissertations. 1208.