Effect of dehydration methods on the nutritional composition of onion and garlic

Abstract

Allium cepa (onion) and Allium sativum (garlic) are important spices with notable nutritional and medicinal properties. However, their high perishability causes post-harvest losses and seasonal scarcity. This study explored preservation techniques to extend shelf life while retaining nutritional quality. Fresh bulbs were procured from Wadata market, Makurdi, Nigeria and taxonomically authenticated. It was then taken to the laboratory for preparation and analysis. Forty bulbs each of onion and garlic were sliced and divided into four parts. One part was meshed and stored in airtight containers as fresh samples; others were processed via sun drying, freeze drying, and microwave irradiation. Samples were subjected to proximate, mineral, vitamin, and amino acid analyses. Fresh onion and garlic had high moisture contents (85.47±0.55 % and 66.82±0.10 %), while dried samples ranged from 7.73±0.01 % to 18.80±0.25 %, supporting microbiological stability. As moisture decreased, ash, fat, protein, fibre, and carbohydrate levels increased. Mineral content remained stable, though potassium in onion rose from 16.99±0.01 mg/100 g (fresh) to 163.37±0.00 mg/100 g (freeze-dried). Vitamins A, B₁, and B₂ were consistently low. Vitamin C declined, especially in microwave-dried garlic (1.25±0.01 to 0.04±0.00 mg/100 g). Amino acid levels increased with drying; microwave-treated garlic had high lysine (5.83±0.01 mg/100 g). Freeze drying proved most effective, best preserving nutrients and bioactivity in onion and garlic.