Effect of Various Inhibitors on the Growth of Lactic Acid Bacteria in a Model Grape Juice System.

Various compounds were tested to determine whether they would substitute for SO2 as inhibitors of strains of Leuconostoc oenos when inoculated into a model fruit beverage containing 5°C Brix Concord grape and 0.1% yeast extract. The following additives and their maximal concentrations exhibited varying degrees of inhibitory activity: fumaric acid, 1.5 mg/ml; sorbic acid, 300 µg/ml; decanoic acid, 20 µg/ml; nisin, 100 IU/ml; and carbon dioxide, 2.8 volumes. Effectiveness of the inhibitors was enhanced by the presence of 8 to 10% ethanol, and was inversely related to the size of the inoculum.

Stability of Sauerkraut Packaged in Plastic Bags 1.

Commercially processed sauerkraut, packaged in plastic bags, was evaluated for product stability following storage at 2, 20, 32 C. When stored at 2 C in the presence of benzoic acid and potassium metabisulfite, the product was stable for more than 8 months, whereas at 20 and 32 C the shelf life was reduced to 20 and 13 weeks, respectively. The reductions in shelf life were due to development of excessive discoloration (browning) and objectionable flavor formation. These defects appear to be caused by chemical rather than microbiological actions. In addition to serving as effective anti-microbial agents, the chemical preservatives (presumably sulfur dioxide) showed protective effects in retarding losses of naturally-occurring ascorbic acid found in sauerkraut. Under similar temperatures of storage, fresh sauerkraut containing no chemical additives had shelf life values of 22, 1.5, and 0.75 weeks, respectively. When stored at 32 and 20 C, the major defects (swollen or broken bags) were attributed to the actions of yeasts. Storage at 2 C markedly arrested and reduced viable yeasts counts, thereby extending the shelf life of the bagged product.

Induction of Red Color Formation in Cabbage Juice by Lactobacillus brevis and Its Relationship to Pink Sauerkraut.

Membrane-filtered cabbage juice, when fermented by Lactobacillus brevis under conditions of controlled pH, frequently produced a water-soluble red pigment. The pigment, presumably responsible for imparting a highly objectionable discoloration to sauerkraut, was formed during the post logarithmic phase of growth. Color development is pH dependent (5.2 to 6.3) and can be suppressed by chemical reductants or anaerobic conditions of growth. The compound responsible for discoloration was purified and partially characterized.

Growth stimulants in plant extracts for Leuconostoc citrovorum.

The growth of Leuconostoc citrovorum ML 34, an isolate associated with the malo-lactic fermentation of wine, was stimulated in part by grape, orange, cabbage, and tomato juices. The stimulatory activity of tomato serum was associated with the carbohydrate fraction. Further purification of the fraction showed that fructose was the factor responsible for initiating growth. In addition to fructose, the organism required CO(2) for establishing growth. Saturated CO(2) atmosphere and catalytic amounts of fructose served as substitutes for plant extracts in a complex glucose medium.

Fermentation patterns of poorly fermenting cabbage hybrids.

Thirteen varieties of cabbage, including five commonly used commercial varieties and eight newly developed hybrids, were analyzed for their ability to undergo lactic acid fermentations. The rates of fermentation, total quantities of acids produced, and chemical analyses indicate that 11 of the 13 selections could support adequate fermentation at any of the three stages of maturation. However, two varieties G27 x G51 (105) and G60 x W-1 (106), harvested during the earlier phases of the 1967 and 1968 growing seasons, failed to undergo proper fermentations and consistently resulted in producing putrid products. These hybrids when harvested at the late stage of maturation were capable of producing total titratable acidities comparable to the acceptable varieties. However the resulting sauerkrauts were judged to be of poor quality. The inability of these varieties to support adequate fermentations may be due to growth inhibitory substances or the lack of inherent maturation-dependent growth factor(s) essential for the growth of lactic acid bacteria.

Growth Response of Lactobacillus brevis to Aeration and Organic Catalysts.

Under stationary and anaerobic conditions, greater cell yields of Lactobacillus brevis were obtained from autoclaved than from filter-sterilized glucose media. Fructose, tentatively identified as a product generated by the heating process, served as an excellent catalyst for inducing growth. The addition of micromolar quantities of pentoses or potential pentose precursors to the filter-sterilized medium was equally effective in stimulating growth. These organic catalysts were not essential for growth under aerobic conditions. Upon agitation, similar cell yields were obtained from the autoclaved and filter-sterilized media. The micromolar quantities of lactic acid produced per micromole of carbohydrate fermented appeared to be similar under aerobic and static conditions of incubation. The final concentration of acetic acid increased as the result of agitation. This increase in volatile acidity was accompanied by a significant decrease in ethyl alcohol production. The cell yield was increased nearly 50% under aerobic conditions.