Effects of onion bulb processing conditions on drying characteristics, physicochemical and functional properties profile of onion (Allium cepa L.) powder

Abstract

Onion (Allium cepa L.) is one of the most perishable consuming vegetable in the world as an aromatic seasoning and for its health promoting bioactive compounds. However, drying and blanching are two essential thermal treatments in vegetables processing which lead to considerable changes in their properties. This study investigated the effects of temperature (70, 80, and 90 °C), time (2, 4, 6, and 8 hr), and blanching (100 °C for 5 min) followed by drying at 70 °C for 8 hr on the drying kinetics, physicochemical (Ash and total polyphenol content, pH, and titratable acidity), and functional (water solubility index and particle size) properties of onion powder, as well as compared to local market powders. The variety violet of Galmi was used. The results revealed that the moisture content of non-blanching powder was below 13 ± 0.76 g/100 g with pH under 4. In addition, total polyphenol contents were higher than 512 ± 15.06 mg GAE/100 g DM. These powder showed a small particle size (under 400 µm) and high solubility (≤81.36 ± 2.3 g/100 g DM). Blanching did not affect the powders quality. Local market powders showed a lowest total polyphenol content (386.60 ± 10.02 mg GAE/100 g DM) with large particles (≤800 µm) and a lowest solubility (65.33 ± 1.62 g/100 g DM). Drying at 80 °C for 8 hr without blanching emerge as the best compromise drying conditions resulting in optimal physico-chemical and functional properties (10.8 ± 0.8 g/100 g, 846.6 ±15.09 mg GAE/100 g DM and 88.12 ± 2.31 g/100 g DM of moisture content, total polyphenol content, and water solubility index, respectively. These findings can contribute to reduce postharvest losses in onion and to stimulate the industrialization of onion enriched-powder production in Africa. PRACTICAL APPLICATION: This study provides critical information on onion properties profile during its transformation, on which processor might build on its decision to make an appropriate choice of processing parameters and tools for producing health promoting onion powder meeting modern consumer requirements. In this study, oven-drying at 80 °C for 8 hr without blanching might be the suitable condition to deliver innovative onion powder tailored specifically to functional ingredients of many food formulations.

Keywords: Allium cepa L; functional properties; onion; physicochemical properties; processing conditions; total polyphenols.