Effect of postharvest drying on physicochemical properties, volatile yield, composition, and sensory attributes of Alpinia zerumbet (shell ginger) rhizome

Abstract

Alpinia zerumbet or shell ginger, an essential oil-bearing rhizomatous native herb of Southeast Asia belongs to the family Zingiberaceae. The rhizome has high culinary value and is profusely used as a spice, food additive, in cosmetics and others. The current study was conducted to investigate the effect of six postharvest drying treatments (shade, sun, freeze, microwave, and oven drying at a temperature of 40 °C and 60 °C) on physicochemical properties, volatile yield and compositions, and sensory attributes of shell ginger. In contrast to other drying methods, freeze drying showed better water activity, rehydration capacity and retained the usual color and micro-structure of sliced rhizomes. FTIR analysis of dried rhizome powders revealed the corresponding banding for C-O-C stretching, CC stretching, CH2 asymmetric stretching and free phenolic OH stretching respectively. The maximum yield of essential oil was obtained in freeze drying (0.028%), followed by fresh rhizomes (0.02%), and the minimum yield was recorded in microwave drying (0.003%). The GC-MS analysis of rhizome oil reported 4-terpineol (31.89–46.85%), eucalyptol (14.28–23.74%), γ-terpinene (2.19–6.67%), fenchyl acetate (5.01–11.21%), o-cymene (2.99–14.92%), and β-pinene (2.18–5.05%) as the principal volatile constituents which were significantly affected by the six drying methods. Spicy and camphoraceous aroma were dominant in fresh and dried rhizome essential oil accessions with traces of pine and lemon odor. The fresh rhizome oil negatively affected the germination rate and inhibited the shoot and root length of wheatgrass seeds with IC50 values of 882.55, 87.79 and 72.2 µg/mL respectively showing its mild phytotoxic potential. These findings demonstrated the freeze drying as the most efficient postharvest technique to preserve the natural qualities of shell ginger and laid down a basic experimental framework for further value addition and industrial feasibility.