PROCESSING AND STORAGE OF LYE-TREATED CARROTS FERMENTED BY A MIXED STARTER CULTURE

A mixed culture of Lactobacillus plantarum and Saccharomyces cerevisia e was compared with a single culture of L. plantarum as starter for th e fermentation of lye-treated carrots. Using the mixed culture, more t han 95% of glucose, fructose and malic acid was consumed after 7 days of fermentation in a brine containing 2.5% w/v NaCl and 0.7% acetic ac id, but only 54% of sucrose was degraded. The fermentation products qu antified were lactic acid, ethanol and acetic acid and carbon recovery was 88%. Using the single culture of L. plantarum, substrate consumpt ion was lower, and carbon recovery almost 100%. In uninoculated lye-tr eated carrots, heterofermentative bacteria grew, with the production o f considerable amounts of mannitol. In all cases, the stability, senso rial characteristics and carotenoid content of the packed product were studied during 9 months of storage at 30 degrees C, and two different preservation systems were compared: addition of preservatives, approx imately 500 and 1000 mg/kg of sorbic and benzoic acid, respectively, a nd pasteurization at 80 degrees C for 10 min. The pasteurized samples were microbiologically stable during the storage period, while lactic acid bacteria grew in the samples with preservatives. Storage time sig nificantly (P < 0.05) affected the texture and colour parameters (L, a, b*) of the carrots, but not the amounts of alpha- and beta-caroten e. The type of fermentation had no significant effect on texture, colo ur parameters or carotenoid content. The preservation method had no si gnificant effect on texture or carotenoid content, but did affect colo ur (parameter a). The flavour of carrots fermented by the mixed cultu re was significantly (P < 0.05) preferred to that of those fermented w ith a single culture of L. plantarum. (C) 1997 Elsevier Science B.V.