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

[摘要] English: Conjugated linoleic acid has proven beneficial health properties. Approximately 18 differentconjugated linoleic acid isomers exist. Two of these isomers (C18:2c9t11 andC18:2t10c12) are the most biologically active forms of conjugated linoleic acid. Resultsfrom several studies over the past few years confirmed the health benefits of conjugatedlinoleic acid. These benefits include anti-carcinogenic, anti-adipogenic, anti-atherogenic,anti-diabetogenic and anti-inflammatory properties. Conjugated linoleic acid consumptioncan also significantly decrease body fat mass without significantly altering the body weight.To reach maximum health benefits, the recommended dietary allowance for conjugatedlinoleic 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 ofconventional milk must be consumed daily to supply enough conjugated linoleic acid formaximum health benefits. The aim of this study was therefore to increase the conjugatedlinoleic 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 conjugatedlinoleic acid levels using selected starter cultures and linoleic acid sources. Three mostfrequently used commercial yogurt starter cultures (YC-180, YC-X11 and ABT-5) wereused. Linoleic acid and sunflower oil as were used as linoleic acid sources. Linoleic acidand sunflower oil were added to full cream yogurt and fat free yogurt to supply linoleic acidin 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 withlinoleic acid had a slightly higher CLA content than the fat free yogurt control and fat freeyogurt with sunflower oil. The highest CLA concentration in the full cream yogurt wasobtained with starter culture YC-X11 and the highest CLA concentration in fat free yogurtwas obtained with starter culture YC-180. Approximately 15 kg of this naturally CLAfortified yogurt however will still need to be consumed on a daily basis to achievemaximum health benefits. This is closer to the RDA than for conventional yogurt, but stillnot nearly sufficient.The second part of the study was therefore designed to increase CLA levels in yogurt bydirect fortification with synthetic CLA (Tonalin 60-WDP). The Tonalin was added in fourtreatment levels (0 %, 1.25 %, 2 % and 5 %) and the influence of the fortification over asix-week storage period was evaluated. The total CLA per 100 g of yogurt increased withincreased Tonalin levels. The highest level of CLA that was obtained in 100 g of yogurtwas with a 5 % Tonalin inclusion level yielding approximately 2.8 g CLA. This means thata 5 % Tonalin® inclusion represents 100 % of the RDA of CLA. In other words, a consumerwould receive 100 % of the CLA needed per day to achieve maximum health benefits, withthe consumption of only 100 g of yogurt of this CLA fortified yogurt. Storage time had nosignificant (p < 0.001) influence on the total CLA content of the yogurt. Sensory evaluationon the yogurt with the four Tonalin® inclusion levels was done. The yogurt with the twolowest Tonalin' inclusion levels (0 % and 1.25 %) obtained significantly higher scores thanthe yogurt with the two highest Tonalin® inclusion levels (2.5 % and 5 %). The scores forthe 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 anytreatment level of Tonalin were disliked by the consumer panel.It was established that CLA fortification of yogurt is possible. Natural CLA production byyogurt starter cultures increased the CLA levels, but CLA levels equal to or close to theRDA were obtained with direct CLA fortification. Therefore direct fortification with syntheticCLA may be considered a more realistic approach for the development of a new functionaldairy food product.

[发布机构] University of the Free State