Evaluation of the use of malic acid decarboxylase-deficient starter culture in NaCl-free cucumber fermentations to reduce bloater incidence.

Abstract

Accumulation of carbon dioxide (CO2 ) in cucumber fermentations is known to cause hollow cavities inside whole fruits or bloaters, conducive to economic losses for the pickling industry. This study focused on evaluating the use of a malic acid decarboxylase (MDC)-deficient starter culture to minimize CO2 production and the resulting bloater index in sodium chloride-free cucumber fermentations brined with CaCl2 . Attempts to isolate autochthonous MDC-deficient starter cultures from commercial fermentations, using the MD medium for screening, were unsuccessful. The utilization of allochthonous MDC-deficient starter cultures resulted in incomplete utilization of sugars and delayed fermentations. Acidified fermentations were considered, to suppress the indigenous microbiota and favour proliferation of the allochthonous MDC-deficient Lactobacillus plantarum starter cultures. Inoculation of acidified fermentations with L. plantarum alone or in combination with Lactobacillus brevis minimally improved the conversion of sugars. However, inoculation of the pure allochthonous MDC-deficient starter culture to 107 CFU per ml in acidified fermentations resulted in a reduced bloater index as compared to wild fermentations and those inoculated with the mixed starter culture. Although use of an allochthonous MDC-deficient starter culture reduces bloater index in acidified cucumber fermentations brined with CaCl2 , an incomplete conversion of sugars is observed. Economical losses due to the incidence of bloaters in commercial cucumber fermentations brined with CaCl2 may be reduced utilizing a starter culture to high cell density.