Abstract
Lactic acid fermented fruit and vegetables are normally obtained following a natural spontaneous fermentation in which no starter cultures are added. It could be expected that a suitable starter culture would help standardise production. Several lactic acid bacteria were selected for a series of physiological studies, in a defined medium (MRS broth) and in carrot juices, under varying conditions of growth temperature, salt concentration and carbohydrate source. Based on these, the homofermenter Lactobacillus pentosus and the heterofermenter Leuconostoc mesenteroides were tested as potential starters, in single and mixed cultures, for the fermentation of carrots (Daucus carota), as a novel fermentable substrate, and cabbage (Brassica oleracea) into sauerkraut. Fermentations were performed in the presence of the natural microflora. Sugar catabolism and acid production were monitored through H.P.L.C.. In the fermentation of carrots Leuconostoc mesenteroides played a major role, with no homofermenters present. For sauerkraut, the mixed starter culture composed of Leuconostoc mesenteroides and Lactobacillus pentosus gave the closest resemblance to the product normally obtained following a natural commercial fermentation. The inclusion of the heterofermenter provided the required acid balance for correct product flavour and aroma by enhancing production of acetic acid. Acetate is also a better antimicrobial than lactate. A shorter fermentation time was also obtained, reducing the time from 3-4 weeks in the natural fermentation to only 7 days with the use of the mixed starter. When reduced salt concentrations were tried, 1% NaCl (w/w) resembled the spontaneous fermentation more closely, in regard to microbial sequence, pH and total acidity. Different ratios of the two lactic acid bacteria in combination were tried, the best being that in which L, mesenteroides and L. pentosus were initially present in the same proportions. Survival of Listeria monocytogenes in fermenting sauerkraut was shorter when starter cultures were used, but no difference was detectable between mixed and single cultures.