14B-32

O. SURIYAPHAN, M. A. Drake, and K. R. Cadwallader. Dept. Food Science, Mississippi State University, Box 9805, Mississippi State, MS 39762-9805

Lipid oxidation is one of the primary causes of deterioration in food products. Soy lecithin is widely accepted as a favorable label-friendly ingredient due to the functional food concept. To be used as a functional additive in fermented dairy products, soy lecithin must be stable under acidic conditions and to other by-products of lactic fermentation.

The aim of the present study was to determine the effect of different lactic starter cultures and soy lecithin content on lipid oxidation in fermented milk systems with soy lecithin.

Culture effects were determined by inoculating sterile milk containing 2 % soy lecithin with Lactococcus lactic ssp. lactis, Lactococcus lactis ssp. cremoris, Streptococcus thermophilus, Lactobacillus helveticus, or Lactobacillus delbrueckii ssp bulgaricus (10⁶ CFU/mL). In a subsequent experiment, culture concentration (10², 10⁶ CFU) and lecithin concentration (0.2, 1, 1.5, 2 %) were combined in milk in a factorial design. After inoculation, milks were incubated for 24 hr prior to chemical, microbiological, sensory evaluation, and aroma analysis.

Gas chromatography-mass spectrometry (GC-MS) revealed that (E,E)-2,4-nonadienal, (E,Z)-2,4-decadienal and (E,E)-2,4-decadienal were lipid oxidation products and were produced in fermented milks containing soy lecithin but not in control fermented milks. Sensory analysis confirmed GC-MS results. Fermentation by all lactic acid bacteria promoted lipid oxidation of soy lecithin as determined by chemical and sensory evaluation (P<0.05). Lipid oxidation products increased with lactic culture and soy lecithin concentration.

These results indicate that care should be taken when applying soy lecithin to fermented dairy foods and that the application of lactic acid bacteria as an antimicrobial to refrigerated foods may lead to off-flavors associated with cell membrane lipid oxidation.