Various cooking methods and the flavonoid content in onion

Area of Science:

• Food Science
• Nutritional Biochemistry

Background:

• Onions are a rich source of health-beneficial flavonoids, primarily quercetin glycosides.
• Quercetin 4'-O-beta-glucoside (Q4'G) and quercetin 3,4'-O-beta-diglucosides (Q3,4'G) are key bioactive compounds in onions.

Purpose of the Study:

• To investigate the impact of various cooking methods on the antioxidant content of onions.
• To quantify the retention of quercetin conjugates, total phenols, and ascorbic acid under different cooking conditions.

Main Methods:

• Onions were subjected to boiling, frying (with oil and butter), and microwave cooking.
• Analysis focused on quercetin glycosides, total phenolic compounds, and ascorbic acid content.

Main Results:

• Microwave cooking without water demonstrated superior retention of flavonoids and ascorbic acid.
• Boiling resulted in approximately 30% loss of quercetin glycosides, with transfer to the boiling water.
• Frying did not significantly affect flavonoid intake, but additives like glutamic acid and ferrous ions accelerated flavonoid degradation.

Conclusions:

• Cooking methods significantly influence the antioxidant profile of onions.
• Microwave cooking is recommended for preserving onion's beneficial flavonoid content.
• Understanding the effects of cooking and additives is crucial for maximizing flavonoid ingestion from dietary onions.