Developing innovative marker systems for garlic post-harvest quality assessment

Work presented here furthers current understanding of the postharvest biology of garlic and identifies volatile organic compounds (VOCs) as markers of quality for culinary and biotechnological uses of garlic. Quality markers were developed for gauging storage time, storage temperature, harvest year, cold stress, incidence of disease and alliinase activity. This work also furthers understanding of interspecific and interseasonal variance in postharvest quality traits of garlic. Significant headway was made in translating the VOC quality markers into techniques for industrial application. Chapter 3 focusses on a single garlic cultivar and discovered improved maintenance of alliinase activity in ambient storage, compared to the industry standard of -2 °C but also found that alliinase activity loss did not correlate with alliinase gene expression. The water content of cloves was stable over time and weight loss in garlic occurred at a 1:2 ratio of DW to FW. VOC profiles varied significantly between storage time and temperature; compounds were identified as putative markers for storage conditions. Chapter 4 explores the interseasonal and interspecific variation in quality and alliinase activity throughout storage, and whether VOC based quality assessment is reliable across years and cultivars. A complex relationship was identified, with quality traits of cultivars changing differently according to season, time and temperature of storage. VOC marker systems correlated with alliinase activity, disease rate and discriminated between seasons. Chapter 5 applies the findings from lab work to the industry. A new thermal desorption sampling method allows passive sampling of VOCs from warehouse air and was trialled over a 6 month period in industry. Cold stress did not affect alliinase activity, v but caused significant changes to quality parameters and the VOC profile. Finally, a pulsed flame photometric detector was trialled as an alternative tool for VOC assessment