EFFECTS OF PRETREATMENT AND DRYING METHODS ON THE BIOACTIVE COMPONENTS IN GINGER (Zingiber officinale) RHIZOME POWDER

Abstract

The aim of this study was to identify the effect of drying methods and pretreatments on the quality of ginger powder. Ginger underwent two types of pretreatments: blanching in boiling water for 1 min, and sulfitation in a 0.15% potassium metabisulfite (KMS) for 5 min and for the control sample, ginger rhizomes were immersed in clean water for 5 min. After pre treatment, ginger slices were sun dried, solar dried, and cabinet dried at 50˚C, 55˚C, and 60˚C till the moisture content reached 10%. All samples were ground into fine powder, and their physical and chemical properties were examined. The preferred pretreatment and drying methods were obtained by analyzing different factors, i.e., oleoresin, essential oil content, total phenolic content (TPC), antioxidant activity, and physical properties such as bulk density, true density, porosity, and solubility. Based on the physical properties, bulk density, true density, and solubility were 0.360±0.010, 1.043±0.076, and 0.685±0.019, respectively, and were found to be significantly higher (P<0.05) in powder that was blanched and sun dried. Solubility was inversely related to temperature. Statistical analysis showed a significant difference (P<0.05) at the 5% level across all physical properties tested. Sun drying combined with KMS treatment was the most effective method for retaining total phenolic content, oleoresin, and essential oils, resulting in essential oil content of 3.78%, oleoresin of 8.25%, TPC of 21.20 mg GAE/g dry matter, and antioxidant activity of 75.57%. Conversely, cabinet drying at 55°C with KMS treatment proved effective for preserving antioxidant content. Most of the samples were significantly different (P<0.05) to each other at 5% significance level. Hence, this study highlighted that pretreating ginger rhizomes before drying could help to retain bioactive components.