Causes and Remedies for Green Discoloration of Processed Garlic Puree: Effects of Storage Conditions on Ingredient Bulbs

Abstract

Storage experiments on garlic (Allium sativum L.) bulbs were conducted to elucidate the causes and prevention of green discoloration (greening) of garlic puree, a severe problem in garlic processing. Greening of the pureed bulbs increased with the accumulation of S-(E-1-propenyl)-L-cysteinesulfoxide (isoalliin), which is metabolized from N-(γ-glutamyl)-S-(E-1-propenyl)-L-cysteine (Glu-PEC) during cold storage (3°C). Greening was reduced by warm storage (> 25°C) of the cold pre-stored bulbs, with an accompanying decrease in isoalliin. Accumulated isoalliin in the garlic bulbs during cold storage was converted to 5-methyl thiomorpholine-3-carboxylic acid sulfoxide (cycloalliin) with warm storage (> 25°C). The relationship between warm storage conditions (temperature, duration) and decreases in isoalliin content were presumed to be applicable to a first order-Arrhenius equation. Two-week storage of the ingredient garlic bulbs at 40°C, after cold pre-storage at 3°C for 12 weeks, sufficiently reduced greening of the processed puree to maintain the commercial quality of the bulbs.