Relationship of long-term storage and raffinose metabolism in sugarbeet

Authors: FINGER, FERNANDO - Universidade Federal De Vicosa; LAFTA, ABBAS - North Dakota State University; KHAN, MOHAMED - North Dakota State University; Fugate, Karen

Submitted to: International Commission for Sugar Technology
Publication Type: Abstract Only
Publication Acceptance Date: 1/15/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: In the Red River Valley of the USA, sugarbeets are stored in ventilated piles or sheds for up to 250 d. Roots are stored for 100 – 140 d at cold, nonfreezing temperatures, then frozen for the remainder of the storage period. Prior to freezing, root metabolism induces changes in the concentration of raffinose, a naturally occurring non-sucrose sugar in sugarbeet. Raffinose concentrations are small relative to sucrose, but the compound significantly increases processing inefficiencies by slowing the rate of sucrose crystallization and causing crystals to elongate which hinders their separation from molasses. In this work, taproots were evaluated for changes in the expression of genes involved in raffinose metabolism during storage for 120 d at 12 and 5 °C. Raffinose concentration increased during storage, but only in roots stored at 5 °C. Increases in raffinose content in 5 °C storage were evident after 12 d with maximal elevation occurring at 40 d. At the same time, galactinol, a substrate in the synthesis of raffinose that is believed to be rate-limiting, showed a sharp increase in concentration at the beginning of storage, with peak concentrations occurring between 12 and 40 d. The most significant change in raffinose-related gene expression was a 20-fold increase in a raffinose synthase gene that occurred after 12 d storage at 5 °C. Two a-galactosidase genes, responsible for the hydrolysis of raffinose to sucrose, were strongly downregulated during storage regardless of storage temperature.