Development of a new, continuous, inline, Aqua-gas drying system and its application to drying perilla leaves while retaining the functional components and antioxidant activities

Abstract

We tested a continuous inline food-drying system that consists of a conveyor belt passing through three chambers containing Aqua-gas^® (AQG), superheated steam (SHS) in the near-anaerobic state, and cooling nitrogen or carbon dioxide gas. Common viable and coliform bacteria were sterilized by the AQG, SHS, AQG→SHS, and steaming treatments. The SHS, AQG→SHS, hot air (HA) drying, and steaming→HA drying treatments each produced dried perilla leaves with a final wet weight-based water content of <10 %. Most of the treatments preserved the α-linolenic acid content. The rosmarinic acid content was greatly increased by SHS and AQG→SHS treatment but greatly decreased by HA drying treatment. The AQG treatment produced significantly higher antioxidant activity, which was greatly increased by the SHS and AQG→SHS treatments due to the increase in the total soluble polyphenol content by the blanching effect, but the activity was greatly decreased by HA drying treatment. Radical-scavenging activity was well correlated with the total soluble polyphenol content. This prototype continuous inline AQG drying system both retains functional components and enables more efficient processing.