Suppression of the vacuolar invertase gene delays senescent sweetening in chipping potatoes

Authors: WIBERLY-BRADFORD, AMY - University Of Wisconsin; Bethke, Paul

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2017
Publication Date: 6/9/2017
Publication URL: http://handle.nal.usda.gov/10113/5863238
Citation: Wiberly-Bradford, A.E., Bethke, P.C. 2017. Suppression of the vacuolar invertase gene delays senescent sweetening in chipping potatoes. Journal of the Science of Food and Agriculture. 98(1):354-360. https://doi.org/10.1002/jsfa.8478.

Interpretive Summary: Consumers and potato chip processors require potato tubers that produce attractive products. At later times in storage, potatoes accumulate elevated amounts of the sugars sucrose, glucose and fructose as a result of a biological process referred to as senescent sweetening. These sugars cause dark-colored blemishes on potato chips. The enzyme vacuolar invertase converts sucrose to glucose and fructose, and vacuolar invertase is hypothesized to play a role in senescent sweetening. To test this hypothesis, senescent sweetening was quantified in multiple lines of potato in which vacuolar invertase activity had been reduced using molecular tools. Chip darkening from senescent sweetening was delayed by about four weeks for tubers with reduced vacuolar invertase. The frequency of dark chips increased as potato glucose plus fructose content increased. It is likely that vacuolar invertase contributes to glucose and fructose accumulation during senescent sweetening and to the production of potato chips with unattractive blemishes. Decreasing potato tuber invertase increased the storage period of the chip potato crop, and this benefits potato growers who store chipping potatoes and chip processors who need a source of high quality potatoes throughout the year.

Technical Abstract: Background: Potato chip processors require potato tubers that meet quality specifications for fried chip color, and color depends largely upon tuber sugar contents. At later times in storage, potatoes accumulate sucrose, glucose and fructose. This developmental process, senescent sweetening, manifests as a blush of color near the center of the fried chip, becomes more severe with time, and limits the storage period. Vacuolar invertase (VInv) converts sucrose to glucose and fructose and VInv is hypothesized to play a role in senescent sweetening. To test this hypothesis, senescent sweetening was quantified in multiple lines of potato with reduced VInv expression. Results: Chip darkening from senescent sweetening was delayed by about four weeks for tubers with reduced VInv expression. A strong positive correlation between frequency of dark chips and tuber hexose content was observed. Tubers with reduced VInv expression had lower hexose/sucrose ratios than controls. Conclusion: VInv activity contributes to reducing sugar accumulation during senescent sweetening. Sucrose breakdown during frying may contribute to chip darkening for tubers with low hexose contents. Suppressing VInv expression increases the storage period of the chip potato crop, and this is an important consideration as potatoes with reduced Vinv expression are entering commercial production in the U.S.