title: Effect of storage temperature, duration and drying technique on the major volatile organic compounds in mango ginger (Curcuma amada Roxb.)
Creators: name: Radha, Bindukala
Publisher: name: University of Reading
Year: 2022

description: Curcuma amada Roxb. is an important member of the Zingiberaceae family and is commonly known as mango ginger due to its resemblance to ginger and the green mango like aroma of the rhizome. The biochemical profile of mango ginger is characterised by a number of volatiles that have application in the food and pharmaceutical industries. However, due to the niche nature of where mango ginger is cultivated, commercial production and extraction of these volatiles have not been the subject of research. There is also insufficient literature on the effect of post-harvest processing techniques on the sensory attributes of mango ginger. As a result, harvested mango ginger rhizomes are often transported and stored alongside other major agricultural produce, without a clear understanding of the optimum storage temperature and duration required for the rhizomes. This study focuses on the changes in the content and composition of volatile organic compounds (VOCs) in mango ginger when subjected to different storage temperatures and durations. Additionally, the study also explores the effect of two commercially followed drying techniques on the biochemical profile. SPME-GCMS analysis of the change in chemical profile was also complemented by sensory analysis as part of this study. The first phase of this study was aimed at improving the current practice prevalent among wholesalers and retailers, of storing mango ginger rhizomes for a short period without undergoing any commercial post-harvest treatments. The intention of the second phase was to determine whether commercial post-harvest treatments such as drying followed by long term storage were feasible options for mango ginger, with a view to explore new avenues on commercial use of the dried powder. This is the first report that analyses the combined effects of drying techniques and storage duration on the organoleptic properties of mango ginger rhizomes. To this purpose, this study explored the effect of three storage temperatures (8 °C, 15 °C and 22 °C) across three storage durations (1, 15 and 29 days) during its first phase. The analysis was extended to its second phase by utilising two drying techniques (hot air drying and freeze drying) and storing the rhizomes for three different storage durations (1, 2 and 3 months). The study concluded that monoterpenes make up a significant proportion of the VOCs in mango ginger, which provide the signature aroma and flavour characteristics. In terms of relative abundance, the major terpenes were identified as myrcene, β-(E)-ocimene, β-pinene, eucalyptol, epoxy myrcene and α-pinene. Other compounds like alcohols, aldehydes, ketones, and esters make up the rest of the VOC composition and are responsible for imparting fresh, floral, and spicy notes. SPME-GCMS and sensory analysis in phase 1 confirmed that storage duration had a more significant impact on the VOC profile than storage temperature. The highest relative abundance of terpenes was identified in samples stored at 15 °C for 15 days. Principal Component Analysis (PCA) also aligned with these findings by displaying a strong positive correlation between the flavour and aroma characteristics of green mango and mild turmeric for these samples. Phase 2 concluded that the combined effect of both drying technique and storage duration was able to significantly impact the biochemical profile. Significant variations in relative abundance values were seen in different chemical groups, along with the formation of new compounds like alkanes and alkenes, and the total absence of alcohols, when compared to that of fresh rhizomes. These trends can be attributed to the formation of secondary metabolites produced by the plant in response to stress induced by mechanical injury during peeling and slicing, followed by Maillard and Strecker reactions that occur when the samples were exposed to drying. Sensory analysis in phase 2 confirmed that samples that were hot air dried and then stored for up to two months were able to retain most of the aroma and flavour attributes of fresh rhizomes. PCA also aligned with these findings by displaying a strong correlation between green mango and mild turmeric aroma and flavour compounds in these samples. This study opens up other avenues of research, such as the use of gas chromatography – olfactory analysis, to determine the aroma of individual chemical groups and identify the most dominant odour active compounds present in mango ginger. Other methods like vacuum drying need to be explored to optimise conditions such as temperature, drying time and pressure to achieve an end product with desirable organoleptic properties and shelf-life for commercial use of the essential oils in the food and pharmaceutical industry. The results could then be combined with sensory and consumer trials to determine the acceptance of the flavour and aroma attributes of mango ginger by the end user.