Vegetable fermentations brined with low salt for reclaiming food waste.

Fermentation of eight vegetables was studied as an alternative for reclamation of surplus volumes. Fermentation performance was predicted by comparing the amounts of acid that could be produced from the intrinsic sugar content with that buffered by the fresh vegetable matrices prior to reaching an inhibitory pH for fermentative microbes (3.30). Native fermentations were brined with 345.0 mM sodium chloride, 40.0 mM calcium chloride, 6.0 mM potassium sorbate, and vinegar to adjust the initial pH to 4.70. High-performance liquid chromatography analysis, pH, and carbon dioxide measurements and spiral plating on selective media were employed to monitor the progress of fermentations. The average colony counts for yeast and/or molds and Enterobacteriaceae declined to undetectable levels from 3.6 ± 1.5 log CFU/ml within 7 days of fermentation. The fermentation of sugars produced lactic, acetic, succinic, and/or malic acids, and ethanol. As predicted, the fermentation of vegetables with low sugar content, such as broccoli, green leaf lettuce, and green pea proceeded to completion. The fermentation of vegetables with a moderate sugar content, such as green bell pepper, red ripened tomato, and green bean were incomplete at pH 3.1 ± 0.2. The fermentation of high sugar vegetables including sweet potato and corn were expected and observed to be incomplete. It is concluded that the intrinsic sugar content and buffer capacity of surplus vegetables are relevant parameters in obtaining complete fermentations. PRACTICAL APPLICATION: Vegetables are the second most wasted commodity in the United States and a substantial constituent of the global food waste. Development of fermentation to reclaim surplus vegetables from farms, grocery stores, and farmer's markets offers opportunities to ameliorate economic losses and environmental impact and add value to waste. The research described here suggests that a fraction of vegetables could be fermented in cover brines while others, with high sugar content, need specialized handling. Evidently, optimization of vegetable fermentation with starter cultures and added buffers represent an opportunity to stimulate complete bioconversions useful for reclaiming surplus volumes.

Impairment of cobalt-induced riboflavin biosynthesis in a Debaryomyces hansenii mutant.

Flavinogenic yeasts such as Debaryomyces hansenii overproduce riboflavin (RF) in the presence of heavy metals. Growth and RF production were compared between wild-type D. hansenii and a RF production-impaired metal-tolerant ura3 mutant in the presence of sublethal cobalt(II) concentrations. Debaryomyces hansenii (wild type) exhibits an extended lag phase with an increase in RF synthesis. Supplementation of exogenous uracil shortened the lag phase at the highest concentration of cobalt(II) used, suggesting that uracil has a possible role in metal acclimation. The D. hansenii ura3 mutant isolated by chemical mutagenesis exhibited a higher level of metal tolerance, no extended lag phase, and no marked increase in RF synthesis. Transformation of the mutant with the URA3 gene isolated from Saccharyomyces cerevisiae or D. hansenii did not restore wild-type characteristics, suggesting a second mutation that impairs RF oversynthesis. Our results demonstrate that growth, metal sensitivity, and RF biosynthesis are linked.