Lecithin associated off-aromas in fermented milk

Soy, rice and hydrogenated soy lecithins were added to milk with lactic acid fermentation to characterize and elucidate formation of volatile off-aromas. Sensory panelists detected off-aromas in fermented milk containing unmodified soy or rice lecithin. Instrumental aroma analysis revealed that off-flavor compounds included (E,E)-2,4-nonadienal and (E,Z)- and (E,E)-2,4-decadienal. Formation of 2,4-decadienals occurred within the first 4 h of lactic acid fermentation and reached maximum levels within 14 h of incubation. Enzymatic assays confirmed that washed cells of Lactococcus produced H₂O₂. Hydrogenated soy lecithin was suitable to use in cultured dairy products, but use of other soy or rice lecithin resulted in off-flavor formation due to oxidation of polyunsaturated fatty acids.