Model studies on precursor system generating blue pigment in onion and garlic

Area of Science:

• Food chemistry
• Biochemistry
• Enzymology

Background:

• Blue-green discoloration is a common issue in mixed onion and garlic preparations.
• The exact chemical reactions responsible for this discoloration have not been fully elucidated.
• Understanding these reactions is crucial for food preservation and quality control.

Purpose of the Study:

• To investigate and identify the specific chemical reactions leading to blue-green discoloration in onion (Allium cepa L.) and garlic (Allium sativum L.) mixtures.
• To establish a model reaction system that can accurately reproduce the observed blue color.
• To determine the factors influencing the intensity and formation of the blue pigment.

Main Methods:

• Utilized a defined model reaction system.
• Included trans-(+)-S-(1-propenyl)-L-cysteine sulfoxide (1-PeCSO) from onion and S-allyl-L-cysteine sulfoxide (2-PeCSO) from garlic.
• Employed purified alliinase (EC 4.4.1.4) and glycine (or other amino acids) as key components.

Main Results:

• Successfully reproduced vivid-blue color using the defined model system.
• Identified four key reaction steps involved in pigment formation.
• Observed that crude onion alliinase yielded less pigment compared to garlic alliinase.
• Attributed the difference in pigment formation to varying amounts of thiosulfinates produced from 1-PeCSO by different alliinases.

Conclusions:

• The study successfully elucidated the chemical basis of blue-green discoloration in onion and garlic mixtures.
• The model reaction system provides a reliable method for studying and potentially preventing this food spoilage phenomenon.
• Enzyme specificity in thiosulfinate production plays a significant role in the extent of blue pigment formation.