Abstract
Ginger (Zingiber officinale Roscoe) rhizomes are mostly used as spice and medicine due to their high aroma intensity and medicinal bioactive compounds. However, the volatile compounds of ginger, partly responsible for its aroma and medicinal properties, can be affected by the pretreatment, drying method, and extraction processes employed. The objective of this study was to assess the effects of pretreatment and drying on the volatile compounds of yellow ginger variety at nine months of maturation. The effect of potassium metabisulfite (KMBS) and blanching pretreatment and drying on the volatile compounds of ginger using head space solid-phase microextraction with GCMS/MS identification (HS-SPME/GCMS/MS) was investigated. KMBS of concentrations 0.0 (control), 0.1, 0.15, 0.2, and 1.0% and blanching at 50°C and 100°C were used for pretreatment and dried in a tent-like concrete solar (CSD) dryer and open-sun drying (OSD). The different concentrations of KMBS-treated fresh ginger rhizomes did not result in any particular pattern for volatile compound composition identification. However, the top five compounds were mostly sesquiterpenes. The 0.15% KMBS-treated CSD emerged as the best pretreatment for retaining α-zingiberene, β-cubebene, α-farnesene, and geranial. The presence of β-cedrene, β-carene, and dihydro-α-curcumene makes this study unique. The 0.15% KMBS pretreatment and CSD drying can be adopted as an affordable alternative to preserve ginger.
Highlights
Ginger (Zingiber officinale Roscoe) is a rhizome of the aromatic Zingiberaceae family mainly used as a spice [1]
Drying of Fresh Washed Sliced Ginger. e remaining sliced ginger of each pretreatment was divided into two parts: one part was dried in the concrete solar dryer (CSD) (Figure 1) and the other part was dried in the open sun (OSD) for five days. e temperatures and humidity ranged 29.0–52.50°C; 27–91.5% RH, and 28.0–55.5°C; 29.5–90.5% RH for the CSD and open-sun drying (OSD), respectively, using a digital temperature-humidity data longer (HOBO pro v2 digital logger (Model U23-001, USA) (Appendix 1). e dried sliced ginger was further analysed for volatile compounds composition using HS-Solid-phase microextraction (SPME)/Gas Chromatography-Mass Spectrometry (GCMS)
Results and Discussion e major volatile compounds identified are presented in Tables 1–3 and the Head space solid-phase microextraction (HS-SPME)/GCMS chromatograms in Appendix 2. e fresh control retained dihydroα-curcumene (99.78%), which is quite different compared to the compounds retained in the KMBS-pretreated fresh ginger rhizomes
Summary
Ginger (Zingiber officinale Roscoe) is a rhizome of the aromatic Zingiberaceae family mainly used as a spice [1] It possesses strong pungent [2] and unique flavour components which are dominated by α-zingiberene, α-curcumene, α-farnesene, β-sesquiphellandrene, β-bisabolene, geranial, and neral or Citral [3]. A pretreatment method that has frequently been used for agricultural produce including ginger without heat application is the use of dilute potassium metabisulfite (KMBS). Washing in dilute potassium metabisulfite has the additional advantage of reducing the microbial load as well as increasing the antioxidant activity of the product. It partly preserves the ginger flavour compounds [10]
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