Effect of Solar Drying and Vinegar Pretreatment on the Antioxidant Properties and Bioactive Compounds of Sliced Ginger

A comparison of concrete solar dryer (CSD) to stainless steel solar dryer (SSSD) in terms of the effect of drying and 10% vinegar pretreatment on antioxidant activities of ginger rhizome using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity method, Ferric Reducing Antioxidant Power (FRAP) Assay, and total antioxidant methods was investigated. The effect of the two solar dryers and open-sun drying (OSD) on bioactive compound composition of the 10% vinegar pretreated sliced ginger using ethanol and aqueous extracts with GCMS/MS identification was also evaluated. The antioxidant activities of ethanol and aqueous extract of the 10% vinegar pretreated ginger using FRAP, DPPH, and total antioxidant methods were all higher than that of the dried samples, with CSD having the highest antioxidant activities among the dried methods. Drying reduced the main bioactive compound, which is gingerol, from 47.97% in the fresh sample to 32.49% in the OSD sample. The CSD sample demonstrated close likeness to the fresh sample with regard to retaining the highest gingerol and alpha-zingiberene. Hence, CSD can be adopted for commercial processing of ginger to reduce postharvest losses of the crop.