517 Heat Treatments and Controlled Atmospheres Maintain Quality and Reduce the Inner Leaf Extension or “Telescoping” of Minimally Processed Green Onions

Abstract

Minimal processing of green onions (Allium cepa × A. fistulosum) involves trimming and removing damaged leaves, cutting of roots, and removal of the compressed stem. If the stem tissue is completely removed with the roots, the white inner leaf bases may extend, or “telescope,” during storage. Storage at 0 °C greatly retards extension growth, but storage at 5 °C results in unacceptable extension rates. To maintain high quality and to extend the shelf life of intact and minimally processed green onions, the potential benefits of heat treatments and controlled atmosphere storage were evaluated. Atmospheres of 0.1% to 0.2% O2 or 0.1% to 0.2% O2 containing 7.5% to 9.0% CO2 at 5 °C were the CA conditions that best maintained visual appearance and prolonged shelf life to more than 2 weeks in both intact and cut onions. No CA treatment completely controlled “telescoping” at 5 °C. Several heat treatment combinations (52.5 and 55 °C water for 4 and 2 min, respectively) of the white inner leaf bases were effective in controlling “telescoping” of cut green onions stored at 5 °C. The effective heat treatments resulted in higher average respiration rates during 12 days, but did not affect the visual quality or shelf life of the cut green onions. Total soluble sugars decreased in intact or cut green onions, but concentrations were maintained in heat -treated onions. Thiosulfinate concentrations did not vary importantly during 14 days at 5 °C, except for a reduction in heat-treated onions not stored under CA.