Evaluation of bacterial fermentation and synthetic fortification as a means to enrich yogurt with conjugated linoleic acid

English: Conjugated linoleic acid has proven beneficial health properties. Approximately 18 different conjugated linoleic acid isomers exist. Two of these isomers (C18:2c9t11 and C18:2t10c12) are the most biologically active forms of conjugated linoleic acid. Results from several studies over the past few years confirmed the health benefits of conjugated linoleic acid. These benefits include anti-carcinogenic, anti-adipogenic, anti-atherogenic, anti-diabetogenic and anti-inflammatory properties. Conjugated linoleic acid consumption can also significantly decrease body fat mass without significantly altering the body weight. To reach maximum health benefits, the recommended dietary allowance for conjugated linoleic acid is in the range of 3 to 3.5 g per day. This value may vary among individuals. This is much more than the amount of conjugated linoleic acid present in dairy products, despite the fact that dairy products are the richest natural source. Approximately 45 kg of conventional milk must be consumed daily to supply enough conjugated linoleic acid for maximum health benefits. The aim of this study was therefore to increase the conjugated linoleic acid content of yogurt to levels closer to the recommended dietary allowance. The first approach was to naturally increase full cream and fat free yogurt conjugated linoleic acid levels using selected starter cultures and linoleic acid sources. Three most frequently used commercial yogurt starter cultures (YC-180, YC-X11 and ABT-5) were used. Linoleic acid and sunflower oil as were used as linoleic acid sources. Linoleic acid and sunflower oil were added to full cream yogurt and fat free yogurt to supply linoleic acid in a concentration of 1 mg/ml in the media. The full cream control yogurt had a significantly (p < 0.001) higher total CLA content than the fat free control yogurt. Fat free yogurt with linoleic acid had a slightly higher CLA content than the fat free yogurt control and fat free yogurt with sunflower oil. The highest CLA concentration in the full cream yogurt was obtained with starter culture YC-X11 and the highest CLA concentration in fat free yogurt was obtained with starter culture YC-180. Approximately 15 kg of this naturally CLA fortified yogurt however will still need to be consumed on a daily basis to achieve maximum health benefits. This is closer to the RDA than for conventional yogurt, but still not nearly sufficient. The second part of the study was therefore designed to increase CLA levels in yogurt by direct fortification with synthetic CLA (Tonalin" 60-WDP). The Tonalin" was added in four treatment levels (0 %, 1.25 %, 2 % and 5 %) and the influence of the fortification over a six-week storage period was evaluated. The total CLA per 100 g of yogurt increased with increased Tonalin" levels. The highest level of CLA that was obtained in 100 g of yogurt was with a 5 % Tonalin" inclusion level yielding approximately 2.8 g CLA. This means that a 5 % Tonalin® inclusion represents 100 % of the RDA of CLA. In other words, a consumer would receive 100 % of the CLA needed per day to achieve maximum health benefits, with the consumption of only 100 g of yogurt of this CLA fortified yogurt. Storage time had no significant (p < 0.001) influence on the total CLA content of the yogurt. Sensory evaluation on the yogurt with the four Tonalin® inclusion levels was done. The yogurt with the two lowest Tonalin'" inclusion levels (0 % and 1.25 %) obtained significantly higher scores than the yogurt with the two highest Tonalin® inclusion levels (2.5 % and 5 %). The scores for the yogurt of all four the Tonalin® inclusion levels, were between a score of 6 (like slightly) to a score of 8 (like very much), which means that not one of the yogurt batches with any treatment level of Tonalin" were disliked by the consumer panel. It was established that CLA fortification of yogurt is possible. Natural CLA production by yogurt starter cultures increased the CLA levels, but CLA levels equal to or close to the RDA were obtained with direct CLA fortification. Therefore direct fortification with synthetic CLA may be considered a more realistic approach for the development of a new functional dairy food product.