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Research Project: Improved Processes for the Preservation and Utilization of Vegetables, Including Cucumber, Sweetpotato, Cabbage, and Peppers to Produce Safe, High Quality Products with Reduced Energy Use and Waste

Location: Food Science Research

Title: Viability of commercial cucumber fermentation without nitrogen or air purging

item ZHAI, YAWEN - North Carolina State University
item Perez Diaz, Ilenys
item DIAZ, JOSCELIN - North Carolina State University

Submitted to: Trends in Food Science and Technology
Publication Type: Literature Review
Publication Acceptance Date: 5/19/2018
Publication Date: 11/1/2018
Citation: Zhai, Y., Perez Diaz, I.M., Diaz, J.T. 2018. Viability of commercial cucumber fermentation without nitrogen or air purging. Trends in Food Science and Technology. 81:185-192.

Interpretive Summary: Formation of hollow cavities or bloaters in fermented cucumbers is a defect causing significant economic losses for the pickling industry. Substantial research resources have been invested over the last eight decades to understand the mechanistic origin and identify effective strategies to minimize bloating defect. This mini-review aims at describing such efforts in a centralize document to generate ideas an insights in how to further develop knowledge and strategies to reduce the defect in the new and environmentally friendly NaCl-free cucumber fermentations. It is understood that elimination of oxygen and adequate control of the natural microbial load in fresh cucumbers are critical elements in eradicating fermented cucumber bloating. The document presented here is to be submitted for publication to a peer reviewed journal and use as a training module for a vegetable fermentation workshop been developed by the USDA-ARS Food Science Research Unit.

Technical Abstract: Background: Bloated cucumber defect, resulting from the accumulation of the biologically produced carbon dioxide in the fruit, reduces yield and economic gains for the pickling industry worldwide. It was the aim of this review to identify commonalities among effective strategies to reduce bloater defect and determine the theoretical viability of commercial cucumber fermentations without bloater defect and/or purging. Scope and approach: This article summarizes the known causes of fermented cucumber bloating defect, including sources of carbon dioxide, and the strategies developed to mitigate the production of the carbonic gas such as controlled fermentation, inoculation of selected starter cultures, cover brine acidification and reformulation and the application of air or nitrogen purging. Key findings and conclusions: It was understood that microbial activity during fermentation, cucumber tissue respiration, as well as the pressure in the fruits and fermentation tanks, ambient temperature and cover brine composition, impact the levels of dissolved carbon dioxide in the system. Although the biological conversion of oxygen to carbon dioxide reduces the cucumbers internal gas pressure, the dissipation of the gas from the tissue is reduced by brining. Once the gas accumulates in the cucumber tissue in concentrations high enough to displace it, the irreversible formation of hollow cavities or bloaters occurs. Residual carbon dioxide is produced by acid-preserved cucumbers, presumably by tissue respiration, which results in the absence of bloating. Thus, microbial activity seems to contribute most of the carbon dioxide needed for cucumbers to bloat. It is speculated that colonization of the internal cucumber tissue by indigenous microbes, in particular aerobic gram-negative bacteria, results in the localized production of carbon dioxide causing bloating defect early in the fermentation. It is concluded that effective manipulation of the microbiota, reduction of dissolved oxygen levels and the use of adequately selected starter cultures may enable cucumber fermentations of acceptable quality without purging.