A comparative study of the effect of peeling and drying on phytochemical and proximate composition of ginger varieties in Nepal

The handling and processing of ginger are done by farmers in Nepal by following primitive practices that result in poor and unhygienically processed ginger of low quality. Due to little information on the quality and compositional aspects of ginger and its value-added product (essential oil), there is a need to improve traditional methods of processing and drying for a better quality of ginger and its product. This study aimed to assess the effects of peeling and drying conditions on two local ginger varieties in Nepal. A three-factor Completely Randomized Design (CRD) experiment was laid out at Ginger Research Program, Kapurkot, Salyan, Nepal. Three treatment factors were variety (Bose ginger and Nase ginger varieties), peeling (peeled and unpeeled ginger), and drying methods (direct sun drying and oven drying). After drying ginger rhizomes, the dry recovery percentage was calculated and the dried ginger rhizomes were ground to powder and subjected to laboratory analysis, where essential oil content and proximate composition of ginger powder were evaluated. Then, the extracted essential oil was subjected to GC-MS (Gas Chromatography and Mass Spectrometry) analysis to know the chemical composition of essential oil. The result obtained showed that unpeeled oven-dried gingers retained higher essential oil content (2 %). The moisture content of oven-dried peeled ginger was reduced to 10.49 % which is within the standard of 7-12 % acceptable to the international market unlike that of direct-sun drying which could only attain about 17% moisture content in the study area. Likewise higher dry recovery percentage (22.25%) was observed in unpeeled sun-dried gingers. Ether extract (5.05 %) and crude fiber (5.05 %) were higher in the Nase variety whereas nitrogen-free extract (75.51 %) was more efficient in Bose variety. From the GC-MS analysis of ginger oil, α-Zingiberene (16.61-21 %) was found to be a major chemical constituent of ginger essential oil followed by (E, E)-α-farnesene (8.68-10.99 %) and β-Sesquiphellandrene (8.26-10.23 %). The use of an oven to dry unpeeled ginger will improve the retention of essential oil; However, peeling of ginger showed reduced fiber content in the ginger.