Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/7/2004
Publication Date: 8/15/2004
Citation: Klotz, K.L., Finger, F.L. 2004. Impact of temperature, length of storage and postharvest disease on sucrose catabolism in sugarbeet. Postharvest Biology and Technology. 34:1-9. Interpretive Summary: Identification of the enzymes that contribute to sucrose loss during sugarbeet root storage is essential for understanding the underlying causes of postharvest sucrose loss. Although several studies have examined the role of sucrose cleaving enzymes during storage, no consensus exists about the relative contribution of individual enzymes to postharvest losses. Because differences in storage temperature, length of storage, and the presence of storage pathogens may have contributed to the discrepant results from earlier studies, the impact of these three factors on sugarbeet root postharvest sucrose catabolism was determined. The activities of sucrose cleaving enzymes, sucrose concentration, and invert sugar concentration were determined in healthy roots after varying lengths in storage at three temperatures, and in roots exhibiting severe storage rot symptoms. Regardless of storage temperature, length in storage or disease state, few changes in the activities of sucrose cleaving enzymes were observed. Sucrose synthase was the predominant sucrose cleaving activity under all storage conditions investigated. In rotted roots, an increase in acid invertase activity was observed, but this increase in activity was due to acid invertases from the pathogen responsible for the rot. These results suggest that sucrose synthase has a central role in the sucrose loss incurred during storage of sugarbeet roots.
Technical Abstract: Sucrose catabolism during postharvest storage of sugarbeet (Beta vulgaris L.) root has been the subject of several studies, yet no consensus exists about the contribution of individual sucrolytic activities to postharvest sucrose loss. Because differences in storage temperature, length of storage, and the presence of storage pathogens may have contributed to the discrepant results from earlier studies, the impact of these three factors on sugarbeet root postharvest sucrose catabolism was determined. Sucrolytic activities and soluble carbohydrate concentrations were measured in roots exhibiting no pathological symptoms during storage at 6, 12 and 21o C, and in roots exhibiting severe rotting symptoms due to infection by Penicillium spp. and Botrytis cinerea at 6o C. Sucrose synthase was the predominant sucrolytic activity throughout storage, regardless of storage temperature, length of storage, or pathogenesis, and accounted for more than 90% of the total soluble sucrolytic activity present in roots. In disease free roots, no significant change in sucrose synthase activity, soluble acid invertase activity, insoluble acid invertase activity, glucose concentration or fructose concentration occurred in roots stored at 6 or 12o C, although an increase in sucrose synthase activity and fructose concentration was observed in roots stored at 21o C. Alkaline invertase activity was impacted by the length of storage and exhibited a transient decline in activity at all storage temperatures. In roots with severe rot, insoluble acid invertase activity declined, sucrose synthase and alkaline invertase activities were unchanged, and soluble acid invertase increased seven-fold. The increase in soluble acid invertase activity was primarily due to the presence of fungal acid invertase isoforms. These results indicate that sugarbeet sucrolytic activities change little during storage, regardless of storage temperature, length of storage, and pathogenesis, and suggest that sucrose synthase, as the predominant sucrolytic activity in stored roots, is central to postharvest sucrose catabolism in sugarbeet roots.