A four-year study of a number of compositional parameters of potato tubers during low-temperature storage was conducted to examine the compositional differences between cold-tolerant (low sugar-accumulating) and cold-sensitive (high sugar-accumulating) tubers in relation to potato chip processing quality. Compositional parameters analyzed included sucrose, reducing sugars, nitrogen, protein, ascorbic acid, and dry matter content. Pearson correlation analysis of the data illustrated that chip color was most closely correlated with reducing sugar concentration. Multiple regression analysis revealed that the relative contribution of each parameter to chip color varied greatly among the cultivars and selections evaluated and from season to season. This analysis demonstrates that the quantitative relationships between the measured compositional parameters and chip color were not sufficient to provide a general predictive index of chip color quality for tubers processed directly from low-temperature storage.
Following exposure to low temperatures (i.e. < 9–10°C), tubers of potato (Solanum tuberosum) undergo a phenomenon known as low‐temperature sweetening (LTS), which results in the conversion of starch to sugars. LTS in stored potato tubers was evaluated by monitoring glycolysis, the oxidative pentose phosphate pathway, anaerobic respiration and mitochondrial respiration, in order to obtain an overview of the regulation of sugar metabolism during LTS. Carbohydrate metabolism during 4°C storage was evaluated in four different storage seasons, comparing tubers of cold‐tolerant (low sugar‐accumulating) clones (ND 860‐2, V 0056‐1 and Wis 1355‐1) and cold‐sensitive (high sugar‐accumulating) cultivars (Novachip and Monona). Parameters measured included whole tuber respiration, concentrations of sucrose, reducing sugars, ATP, NADH, NADPH, lactate and ethanol, as well as tissue pH. In three of the four seasons of study, the cold‐tolerant tubers maintained lower levels of reducing sugars, and higher levels of lactate and ethanol, 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 relative to cold‐sensitive tubers. This study represents the first known report on the role of the anaerobic pathway during LTS in potato tubers.
Following exposure to low temperatures (i.e., <10 °C), potato tubers undergo low-temperature sweetening (LTS), the conversion of starch to sugars. This phenomenon is of great importance to potato chip processors because high levels of reducing sugars lead to undesirable nonenzymatic browning during potato chip frying operations. The purpose of this study was to elucidate the biochemical differences in carbohydrate metabolism between a tolerant (ND 860-2) and a sensitive (Novachip) cultivar during 4 °C storage. On chilling, there was an increase in the levels of sucrose, fructose, and glucose in both cultivars, with levels being at least 2-fold higher in the sensitive cultivar. Increased levels of ATP and NADH, along with a higher respiratory rate observed in the tolerant tubers, collectively indicate a higher metabolic rate in the LTS-tolerant cultivar. ATP- and pyrophosphate-dependent phosphofructokinase activity was similar in both cultivars. Higher levels of ethanol and lactate were also observed in ND 860-2, suggesting a greater flux of sugars via anaerobic respiration. No significant differences were observed in enzymatic activities in the oxidative pentose phosphate pathway (PPP) or in levels of NADPH, thereby suggesting that the PPP does not play a role in conferring LTS tolerance. Therefore, we propose that LTS-tolerant potatoes may maintain low tissue sugar concentrations via an overall increased metabolism, rather than differing in one specific metabolic step. This increased metabolic rate does not appear to be due to greater enzyme expression (i.e., coarse control) but, rather, to a greater overall flux of carbohydrates through glycolysis and respiration.
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