Drying techniques affect the quality and essential oil composition of Ghanaian ginger (Zingiber officinale Roscoe)

Abstract

This work aimed to determine the effects of five drying methods on the quality and essential oil composition of Ghanaian ginger. To this end, slices of fresh ginger rhizomes were dried using the following dryers; relative humidity convective (RHC) dryer, freeze (F) dryer, infrared (IR) dryer, microwave (MC) dryer and pulsed vacuum (PV) dryer. The antioxidant activities, total phenolic content (TPC), sensory characteristics and moisture content of the dried slices were assessed. The effects of the various drying techniques on the chemical composition of the essential oil components were determined using gas chromatography-mass spectrometry (GC–MS). With respect to the sensory attributes of the various dried ginger samples, the RHC-dried samples attained the highest scores for aroma, flavor and general acceptability while the F-dried samples scored the highest marks for appearance (i.e., colour). The RHC-dried samples had the lowest moisture content (5.45 %) followed by the F-dried (6.36 %), IR-dried (8.06 %), MC-dried (9.15 %) and PV-dried (10.07 %) samples. The F-dried samples retained the highest TPC (110.36 mg Gallic acid equivalent (GAE)/g db) and exhibited the highest antioxidant activities as evidenced by the outcomes of 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and ferric reducing antioxidant power capacity (FRAP) tests. The chemical profiles of the essential oil extracted from the various dried ginger samples were distinct and unique. The essential oil obtained from the F-dried samples was observed to have the highest compounds (24). The number of compounds identified in the oil extracted from the other dried samples were : RHC drying, 23; IR drying, 16; MC drying, 15; PV drying, 3. In general, the samples subjected to F and RHC drying gave the best outcomes for all the quality parameters assessed and are therefore recommended for large-scale industrial application.