ARS | Publication request: Shelf life and microbial profile of peeled onions

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: February 12, 2013
Publication Date: N/A

Technical Abstract: The increased usage of peeled onions over the past ten years by food service operations and fast-food restaurants has been plagued by black mold decay during cold-chain storage. This study examined the epiphytic microbiological distribution on onions and what effects various processing steps have on these populations and how they might affect the shelf-life of peeled onions. Yellow onion bulbs were aseptically separated into top, root, dry scales, and consecutive fresh-scale layers from outside to inside. Tissues from each segment were stomached and enumerated via spread plating for total aerobic bacteria, yeasts and molds. The effect of onion peeling, cutting, and washing sequences on microbial counts and shelf-life of peeled onions during cold storage were also investigated. Results indicate that spores of black mold are primarily located in the top portion, followed by roots and outside dry scales of the onions. This same distribution was also seen in total aerobic bacteria, yeasts and other mold counts. A processing sequence of peeling, cutting, and then washing with 200 ppm chlorine solution significantly reduced all residual microbiological populations and the development of black mold decay during storage. Peeled onions processed according to this optimized sequence were stored at 5 °C for 35 days with no evidence of black mold decay, resulting in acceptable product quality. This study provides cost-effective solutions for the industry to improve the quality and shelf life of peeled onions.