Analysis of methodologies for the study of composition and biochemical carbohydrate changes in harvest and postharvest onion bulbs

Abstract

Costly investments in storage and transport of onion bulbs makes it increasingly important to identify cultivars with the best chance of long-term storage. This paper discusses our own and other researchers’ results and laboratory procedures on onion’s pungency, soluble solids, dry matter, respiration rate, carbohydrates and catabolism-related enzymes under different storage conditions. The variability in parameters such as carbohydrate composition, pungency, soluble solids and soluble uronic acid concentration in water is growth dependent, and defines the quality of onion bulbs at harvest time. During storage, these parameters can be modified by environmental conditions, presence of pathogens or termination of dormancy. Under postharvest conditions, indicators of dormancy are usually measured as percentage of either root emergence or sprouting. Biochemical and physiological parameters such as decreases in sucrose levels and increases in (1) respiration rates, (2) exo hydrolase activity, and (3) bulb-softening enzyme rates (polygalacturonase poly methyl esterase) signal the end of dormancy. However, more research is needed on environmental and chemical factors that reduce the rate of bulb sprouting.