Location: Food Science Research
2012 Annual Report
Acidified cucumbers are imported in cover brine solutions containing 2.5 to 3.0% acetic acid, added as vinegar, and 4% sodium chloride, added as table salt. Preservatives such as sodium metabisulfite are also added to achieve preservation during transit, which may take up to 2 months. A significant portion of the processing cost is attributed to the addition of high concentrations of acetic acid and sodium chloride. Once in solution, sodium metabisulfite serves as the precursor for sulfite, which acts as the preservative or antimicrobial compound. It has been observed that sulfite concentrations in acidified cucumber cover brine solutions decrease during transit to the United States (US), indicating the presence of some sort of chemical reactivity. The reduction of sulfite concentrations during transit provides an opportunity for the proliferation of multiple yeast species in the imported goods, causing bloating of the cardboard containers upon arrival to the US and thus, rejection of the product and losses for the international producers.
Regulatory agencies in the US are implementing stricter standards for acidified cucumber processors. In particular, processors in the US are currently challenged with the reduction of chloride levels in the waste waters so that environmental pollution due to industrial activities is minimized. Thus, acquisition of acidified cucumbers containing high sodium chloride concentrations (4%) represents a problem considering that the local processing of such product generates millions of gallons of high chloride waste waters every year. The acetic acid content in the imported acidified cucumbers also generates a relatively high biological oxygen demand in the waste waters, translating into a need for a more robust water treatment system, which increases production costs.
A solution for the challenges associated with the importation of acidified cucumbers to the US includes the brining of the fresh fruits with 100 mM calcium chloride as opposed to 1M sodium chloride, 1% (150 mM) acetic acid instead of 2.5% to 3% and natural preservatives such as fumaric acid, plant derived extracts and lauric arginate at pH 3.5. ARS scientists showed that cover brine formulations containing 20 mM fumaric acid to inhibit the lactic acid bacteria and 2 mM allyl isothiocyanate or 3.8 mM cinnamaldehyde to control the yeasts population are effective at the laboratory scale. The sodium chloride free treatments have been effective against the natural microbiota from the fruits and inoculated acid resistant Lactobacillus plantarum and spoilage yeasts, such as Zygosaccharomyces globiformis and Z. bailii. Combinations of the plant derived extracts in reduced concentrations as compared to those listed above have been determined to exert a synergistic effect in achieving acidified cucumber preservation.
The evaluation of the proposed low acid and salt formulations at the commercial scale requires an integrated effort between researchers and local and international processors. ARS scientists have been collaborating with processors to test the low salt and acid treatments at a semi-commercial scale with successful outcomes. The second stage of this project will include the testing of selected treatments at the commercial scale in the International processing environment. This second stage will be initiated at the end of August 2012.