Vegetable fermentations brined with low salt for reclaiming food waste

Abstract

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.

Keywords: fermentation; food waste; reclaim; vegetable.