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Postharvest Biology and Technology 34 (2004) 1–9

Impact of temperature, length of storage and postharvest disease on sucrose catabolism in sugarbeet
Karen L. Klotz a,∗ , Fernando L. Finger b
a

USDA-ARS, Northern Crop Science Laboratory, P.O. Box 5677, University Station, Fargo, ND 58105-5677, USA b Departamento de Fitotecnia, Universidade Federal de Viçosa, 36571-000 Viçosa, MG, BrazilReceived 10 December 2003

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 the major sucrolytic activities to postharvest sucrose loss. Because differences in storage temperature, length of storage, and the presence of storage pathogens may have contributed to thediscrepant 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 21 ◦ C and in roots exhibiting severe rotting symptoms due to infection by Penicillium spp. and Botrytiscinerea during storage at 6 ◦ 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, or insoluble acidinvertase activity occurred in roots stored at 6 or 12 ◦ C, although an increase in sucrose synthase activity was observed in roots stored at 21 ◦ C. Alkaline invertase activity was impacted by the length of storage and exhibited a transient decline in activity at all storage temperatures. Glucose and fructose concentrations generally increased as a function of time in storage at 6, 12, and 21 ◦ C. Inroots 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, regardlessof 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. © 2004 Elsevier B.V. All rights reserved.
Keywords: Acid invertase; Alkaline invertase; Beta vulgaris; Postharvest storage; Storage rot; Sucrose synthase; Sugarbeet

1. IntroductionSugarbeet (Beta vulgaris L.) roots after harvest are stored in large outdoor piles prior to processing in
∗ Corresponding author. Tel.: +1 701 239 1356; fax: +1 701 239 1349. E-mail address: klotzk@fargo.ars.usda.gov (K.L. Klotz).

the northern United States, Canada, northern Europe, and Russia. Roots may be stored up to 200 days, during which a substantial loss of sucrose and an increase inglucose and fructose occur. Metabolism of sucrose to provide substrates for respiration and the healing of wounds incurred during harvest and piling is the primary cause of postharvest sucrose loss (Wyse and Dexter, 1971; Wyse, 1973). Further sucrose loss

0925-5214/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2004.05.016

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K.L. Klotz, F.L.Finger / Postharvest Biology and Technology 34 (2004) 1–9

occurs due to the enzymatic conversion of sucrose to its monosaccharides, glucose and fructose (Wyse and Dexter, 1971; Berghall et al., 1997). Storage rots, caused primarily by the pathogenic fungi, Penicillium claviforme Bainier, Phoma betae Frank, and Botrytis cinerea Pers. ex Fr., also contribute to sucrose degradation and invert sugar...