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

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.