Carbohydrate metabolism in cold-stored potato tubers in relation to chip processing quality

The storage of potato tubers at low temperatures (i.e., <9–10°C) initiates a process known as low temperature sweetening (LTS), which results in the conversion of starch to sugars. This phenomenon is of great importance to potato chip processors, since high levels of reducing sugars lead to undesirable nonenzymatic browning during potato chip frying operations. Previous studies of LTS in potato tubers contain limitations with respect to the scope of the study, the number of seasons of study and the sampling frequency. This study was designed to address these issues, examining the inter-relationship of the pathways of carbohydrate metabolism in order to obtain a holistic overview of sugar metabolism during LTS. The primary goals of this research were: (i) to evaluate the roles of glycolysis, anaerobic respiration, the oxidative pentose phosphate pathway (PPP) and mitochondrial respiration in the regulation of potato tuber carbohydrate metabolism during low temperature storage; and, (ii) to assess the relationship between potato chip color and a number of metabolic and compositional factors of cold-stored potato tubers, for the purpose of identifying potential indicators of chip color quality. This study represents the first known investigation of the anaerobic pathway in stored potato tubers during LTS.; Carbohydrate metabolism during 4°C storage was evaluated in four different seasons, comparing tubers of cold-tolerant (low sugar-accumulating) and cold-sensitive (high sugar-accumulating) genotypes. Parameters measured included whole tuber respiration, enzymatic activity, solids content, tissue pH, as well as concentrations of reducing sugars, sucrose, ATP, NADH, NADPH, lactate and ethanol, protein, total nitrogen, nonprotein nitrogen, ascorbic acid and chip color. The relationships between chip color and each of the metabolic and compositional factors were evaluated using correlation and multiple regression analyses.; In three of the four seasons of study (the sole exception being the moisture stressed 1998 season), the cold-tolerant tubers maintained lower levels of reducing sugars, higher levels of lactate and ethanol, and higher chip color scores relative to cold-sensitive tubers. A higher anaerobic flux in tubers of cold-tolerant genotypes may be partially responsible for a lower accumulation of reducing sugars and lighter chip color relative to cold-sensitive tubers.