Temperature,cyanide, and oxygen effects on the respiration,chip color,sugars, and organic acids of stored tubers

The possibility that sugar accumulation of potatoes stored at low temperatures may be linked to activation of cyanide-resistant respiration (CRR) was investigated. After a lag period of several days, continuous HCN treatment stimulated CO₂ production of tubers stored in 20% O₂. At 1°C in 20% O₂, HCN treatment increased respiration over that effected by low temperature treatment. After several weeks of treatment, cyanide-stimulated CO₂ production was greater at 1°C than at 10°C. Sucrose and malate levels of HCN treated tubers were sometimes higher than those of the 10°C control tubers, but they were always lower than those of the 1°C control tubers. This indicated that CRR alone could not account for the sugar increases at 1°C. Storage in 2% O₂ blocked the increase in CO₂ production and changes in constituents associated with HCN treatments in 20% O₂. HCN treatment had no significant effect on chip color. The level of CRR was measured in freshly cut slices from Monona, Norchip, and Kennebec tubers previously stored at 10°, 5°, or 1°C for several months. Slices from tubers previously stored at 1°C had increased CRR, but there was no difference in CRR between the 5°C and 10°C treatments. Sugars accumulated at 5°C, again indicating that sugar accumulation in potatoes stored at low temperatures was at least partially independent of the activation of CRR.     

The effect of storage factors on membrane permeability and sugar content of potatoes and decay byErwinia carotovora var.atroseptica andFusarium roseum var.Sambucinum

Russet Burbank and WC230-14 potato tubers were stored at 0 C (32 F) and 5 C (41 F) in air, air plus 4% CO₂ and air plus 8% CO₂ for a 175 day storage period. Four times during this period, tubers were removed and inoculated withErwinia carotovora var.atroseptica (van Hall) Dye orFusarium roseum var.sambucinum (L. K.) Sn. and H. and stored at 17 C (62.6 F). Tuber samples were also reconditioned for two weeks at 17C(62.6 F) and then inoculated. Tubers were evaluated for rate of membrane permeability, free glucose, free fructose, and sucrose content and the rate of tuber decay by the two pathogens. Relative to 5 C (41 F), 0 C (32 F) storage increased sugar content, membrane permeability and the rate of tuber breakdown. Increasing CO₂ during storage at 0 C (32 F) and 5 C (41 F) increased each of the above parameters. Reconditioning tended to alleviate the adverse effects of 0 C (32 F) storage and increasing CO₂ levels, but varietal differences existed. A significant and high correlation was obtained between the rate ofErwinia decay, membrane permeability, and sucrose content of the tubers.     

Potato tuber sugar content during development and storage (10°C): possible predictors of storage potential and the role of sucrose in storage hexose accumulation

Summary Reducing sugar and sucrose contents of potato tubers (Solanum tuberosum L.) from six cultivars were monitored both during the growing season and after a four months storage period at 10°C. Significant correlations were found between tuber sugar contents (sucrose, reducing and total) measured at harvest and the reducing sugar content after storage. Similarly, in five of the six cultivars, the sucrose loss and the corresponding reducing sugar gain during storage were significantly correlated.     

Small tuber studies of sugar accumulation in potatoes

Small potato tubers, less than 1 cm in diameter, responded in a manner typical of larger tubers and accumulated sucrose and reducing sugars during storage at 1°C. Prolonged soaking (50% submerged) was used as a method for introducing metabolic inhibitors into intact, small tubers. Judging from the effects on respiration, cycloheximide was absorbed within 25 h. Cycloheximide treatment inhibited the sucrose and reducing sugar accumulation associated with storage at 1°C     

A study of methods of incorporation and source of14C on distribution of radioactivity in potato plants

Russet Burbank potato plants grown in the greenhouse were given¹⁴C as¹⁴CO₂ and as uniformly labelled sucrose. Labelled sucrose was applied; (1) by injection into the main stem, (2) injection with a hypodermic needle into the debladed petiole and (3) uptake of labelled sucrose kept in a vial fastened to the main stem using thread as a wick. Plants harvested 6 hours later were analyzed for radioactivity in the foliage, roots, and tubers. The greatest proportion of radioactivity was found in the foliage. Tubers were analyzed for radioactivity in the basic (amino acids), acidic (organic acids and sugar phosphates), neutral (sugars) and alcohol insoluble solid (starch) fractions. Most of the radioactivity was found in the sugar component of the chemical fraction. Plants treated with¹⁴⁷CO₂ had a higher percentage of radioactivity in the acidic and starch fractions than plants treated with sucrose. Sucrose applied by petiole injection not only showed higher total incorporation but also exhibited more translocation of labelled material into the tubers than the other methods.     

Increase in phosphorylase activity during cold-induced sugar accumulation in potato tubers

Summary The accumulation of reducing sugars, sucrose and hexose phosphates in cv. Bintje and genotype KW77-2916 during storage at 2, 4, or 8°C was studied in relation to several catalytic activities. Bintje tubers accumulated sugars during storage at 2 or 4°C, whereas KW77-2916 showed reduced cold-sweetening at 2°C. The increase in glucose 6-phosphate and sucrose occurred concurrently and preceded the increase in reducing sugar concentration. Phosphorylase activity showed a strong interaction with temperature, storage duration and sugar accumulation in both genotypes. Invertase activity increased in Bintje concomitantly with the increase in reducing sugars, but this effect was less obvious in KW77-2916. The activities of other glycolytic and Krebs cycle enzymes showed no obvious correlation with sugar accumulation. It is suggested that the increase in phosphorylase activity acts as a triggering event in the sweetening of potato tubers during cold storage.     

The effect of oxygen and carbon dioxide concentrations on bacterial soft rot of potatoes. I. King Edward potatoes inoculated withErwinia carotovora var.atroseptica

Summary MatureKing Edward potatoes were wounded, inoculated withErwinia carotovora var.atroseptica and stored at +10°C and 100% r.h. in controlled concentrations of oxygen and carbon dioxide for up to 18 days. After incubation in air or in 5% O₂ in N₂ rots were brown, dry and restricted; more extensive, soft spreading rots were produced in potatoes stored in 5% O₂+16% CO₂, in 1% O₂+20% CO₂, in 1% O₂ and in N₂, the most extensive rots occurring in the anaerobic conditions. In addition toE. carotovora var.atroseptica, pectolytic clostridia could also be recovered from the spreading rots. The experiments demonstrate the extent to which the concentration of oxygen and carbon dioxide in the environment may effect the sensitivity of tubers to bacterial attack.     

A mechanism for low temperature induced sugar accumulation in stored potato tubers: The potential role of the alternative pathway and invertase

The accumulation of reducing sugars in stored potato tubers is of significant commercial importance because of its effect on processing quality. The process by which the accumulation of sugars occurs involves the interaction of many metabolic pathways and is yet to be fully described. Low temperature conditions result in an accumulation of ATP in potato tissue. Published evidence suggests that low temperature activation of the alternative pathway (cyanide resistant respiration) leads to decreased ATP levels and simultaneous increases in sucrose concentrations. This sucrose becomes the substrate for vacuolar acid invertase resulting in the accumulation of reducing sugars. Inhibition of the alternative pathway results in decreased sugar accumulation thereby minimizing the sucrose available to the acid invertase and the subsequent reducing sugar accumulation. Control of the alternative pathway on its own, or in combination with acid invertase activity, may provide insight into the phenomenon of low temperature sweetening in stored potato tubers.     

The influence of storage on the physiology and productivity of Kennebec seed potatoes

Kennebec seed potatoes were stored in various atmospheres of O₂ and CO₂ at 32 and 41 F (0 and 5 C). Samples were removed every 6 weeks for measurement of bud and parenchyma tissue respiration, rate of ion loss from tissue sections and reducing sugar content. Potatoes remaining at the end of the storage period were warmed, cut and planted immediately in a randomized complete block design for yield evaluation. Intact tuber respiratory rates were higher at 32 F than 41 F. Increasing CO₂ increased respiratory rates and decreasing O₂ decreased respiratory rates at both temperatures. Decreasing O₂ concentration significantly decreased reducing sugar at both 32 and 41 F. Increasing CO₂ significantly increased reducing sugar at 41 F but not at 32 F. Kennebec potatoes did not tolerate added CO₂ at 32 F but did survive 4% CO₂ at 41 F. Reducing oxygen decreased the tolerance to CO₂. The onset of carbon dioxide injury was not clearly evident from changes in bud and parenchyma tissue respiration or in loss of electrolytes from cut tissue sections. However, CO₂ accelerated tuber breakdown by unidentifiedFusarium Spp. No significant differences in yield were observed between treatments that survived the storage period.     

The relationship between common scab severity and reducing sugar contents in the peel of potato tubers

Summary Total sugar, reducing sugar, glucose, fructose, and sucrose of scabbed (Streptomyces scabies) and scab-free harvested tubers of several potato cultivars were analysed in four portions (pell and tube flesh separtely, from basal and apical halves), and also in small whole growing tubers. The peel of scabby harvested tubes had higher reducing sugar (glucose and fructose) contents than that of corresponding scab-free tubers. The sugar contents in the flesh and in small growing tubers did not show significant difference beween the scabbed and scab-free state. Tubers of scab-susceptible cultivars had more scab and a higher reducing sugar content than those of resistant cultivars. The results indicate that the contents of reducing sugar (glucose and fructose) in tuber peel are positively correlated with scab severity.     

An investigation into the factors influencing sugar levels in UK grown potatoes (cv. Record)

Summary Reducing sugar and sucrose content of potato tubers (cv. Record) grown in Tayside (northern United Kingdom (UK)) and Lincolnshire (southern UK) were monitored during the 1984 growing season and after two months storage at 10°C. Neither latitude nor agronomic factors were shown to affect sugar content. Significant correlations were found between the post storage reducing sugar content and the sugar contents measured at harvest. Regression analyses indicated that in immature tubers sucrose breakdown was responsible for reducing sugar accumulation during storage.     

Possible involvement of fructose 1,6-bisphosphatase in cold-induced sweetening of potato tubers

Summary In measuring fructose 1,6-bisphosphatase (EC 3.1.3.11; FBPase) in potato tubers, we used anti PFP antibodies to ensure that the assay was specific for FBPase and that PPi:fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90: PFP) did not contribute to the production of fructose 6-phosphate (Fru-6-P). The involvement of cytosolic FBPase in cold sweetening was determined by monitoring enzyme activity during storage ofSolanum tuberosum cv. Erntestolz tubers at 2 or 8°C. In contrast to the rapid increase in sucrose and reducing sugars, the specific activity of FBPase showed no change and PFP rose slightly during storage at 2°C. Sugar concentrations and enzyme activities remained virtually unchanged during storage at 8°C. These data allow the interconversion of fructose 1.6-bisphosphate (Fru-1,6-P₂) to Fru-6-P and vice versa by FBPase and PFP, respectively, in potato tubers, but do not support a causal relationship between coarse metabolic control of FBPase and cold-induced sweetening.     

Influence of moisture stress during growth on14CO2 fixation and translocation inSolanum tuberosum L.

Moisture stressing of potato plants resulted in reduced¹⁴CO₂ fixation and translocation of labelled photosynthates from leaves to tubers. A majority of the label was recovered in the sugar fraction of both leaves and tubers. The amount of labelled¹⁴C recovered in the organic acid fraction of tubers of normally irrigated plants was significantly higher than in tubers which had been moisture stressed. In the other fractions, the differences were not significantly different. Injection of uniformly labelled sucrose into the basal portion of attached tubers of stressed and non-stressed plants showed greater translocation of labelled carbon by tubers of stressed plants from basal to the apical portion and also into the stems as compared to non-stressed plants.     

The immediate effect of gamma irradiation upon the sugar content of potatoes previously stored at 2, 4.5, 6, 10 and 15.5°C

Summary The sugar content of samples of potatoes, cv. Majestic, was varied by storage for 4 weeks at 2, 4.5, 6, 10 and 15.5°C, before irradiation with 10 krad. With initial sucrose contents of 0.14–0.37% FW (tubers from 4.5–15.5°C) the marked temporary increase in sucrose, as reported previously, was observed, reaching a maximum after 3–7 days before falling rapidly to a level rather higher than in non-irradiated tubers. Tubers from 2°C, with 1.4% sucrose, showed an immediate drop in this after irradiation, succeeded within 3 days by a rise to values not significantly different from the controls. Irradiation caused a significant increase in reducing sugar content, for a period of up to 7 days in sweetened tubers, but for 21 days or more in unsweetened tubers. Previous storage at the different temperatures had some permanent residual effect upon the sugar content of the controls during subsequent storage for up to 90 days at 10°C.     

The effect of controlled atmosphere storage at 4°C on crisp colour and on sprout growth,rotting and weight loss of potato tubers

Summary After three weeks curing at 10°C, potato tubers cv. Record were stored at 4°C under different controlled atmospheres (CA) for six months to study the effect on crisp fry colour, sprout growth and rotting. Combinations of low levels of CO₂ (0.7–1.8%) and low levels of O₂ (2.1–3.9%) gave a significantly lighter crisp colour, low sprout growth and fewer rotted tubers compared with 0.9% CO₂ and 21.0% O₂. Tubers stored in these conditions. showed a significantly higher weight loss and shrinkage after reconditioning. High CO₂: low O₂ combinations during storage completely inhibited sprout growth and caused the darkest crisp colour, but after reconditioning tubers gave the same level of sprouting and crisps as light as the other CA combinations. Furthermore these combinations, especially CO₂ at 10 or 15%, increased the onset of rotting. Also our results showed that at low concentrations of CO₂ (0.7–1.6%), and low O₂ (2–2.4%) there was an increase in tuber rotting.     

Impact of Stolbur Phytoplasmas on Potato Tuber Texture and Sugar Content of Selected Potato Cultivars

Potato stolbur is a phytoplasmal disease that seriously affects yield and tuber quality in South Eastern Europe, Russia and the Mediterranean areas. In 2007 and 2008, field experiments were carried out to determine stolbur resistance of processing potato cultivars at Sannicolau Mare (Romania) by determining consistency and concentration of reducing sugars (fructose and glucose), sucrose and phytoplasmas in potato tubers. In both years, non-symptomatic potato tubers showed sucrose levels in the range of 3,000 mg kg⁻¹ fresh weight (FW). In contrast, sucrose concentrations were up to 11,820 mg kg⁻¹ FW in 2007 and 19,560 mg kg⁻¹ FW in 2008 in tubers showing severe symptoms. These high values severely affect suitability of tubers for processing as sucrose serves as substrate for the formation of reducing sugars that are the limiting factor in fried potato production for Maillard-related discolouration. The cultivars examined differed considerably in susceptibility to stolbur disease. Whereas cvs. ‘Courage’ and ‘Lady Rosetta’ showed high numbers of diseased tubers and high sucrose concentrations, ‘Lady Claire’ had a lower incidence of symptomatic tubers and lower sucrose concentrations. However, fully resistant cultivars were not observed. Across all cultivars examined, phytoplasmal concentration was significantly higher in symptomatic tubers than in non-symptomatic ones.     

Effect of controlled atmosphere,temperature and cultivar on sprouting and processing quality of stored potatoes

Summary Three crisping potato cultivars, Record, Saturna and Hermes, were stored at 5 or 10°C in gas mixtures of either 0.5% CO₂ and 21.0% O₂ (control) or 9.4, 6.4, 3.6 or 0.4% CO₂ all combined with 3.6% O₂. There was almost complete sprout inhibition, low weight loss and maintenance of a healthy skin for all cultivars stored in 9.4% CO₂ with 3.6% O₂ at 5°C for 25 weeks. When tubers from this treatment were stored for a further 20 weeks in air at 5°C the skin remained healthy and they did not sprout. The fry colour of crisps made from these potatoes was darker than the industry standard but when they were reconditioned, tubers of cv. Saturna produced crisps of an acceptable fry colour while crisps from the other two cultivars remained too dark. Reducing sugar levels were related to fry colour both after storage and after reconditioning. The other gas combinations and the controls did not have the same effect on sprouting and none of the controlled atmosphere treatments controlled sprouting at 10°C.     

Factors influencing the soft-rotting of potato tubers by bacteria

Summary The production of extensive soft rot in potato tubers which were wounded, inoculated withErwinia carotovora var.atroseptica and stored inc. 100% RH at 20° was greatly increased by replacing air in containers with N₂. Accumulation of CO₂ due to tuber respiration did not significantly affect the production of rots in these conditions. When tubers were inoculated with sterile water in place of theErwinia and held under anaerobic conditions, spreading soft rots were also produced andClostridia, but not soft rotErwinia, were isolated from the rotted tissue. Some of theseClostridia were shown to be capable of breaking down potato tissue, and may be a significant cause of potato soft rots developing in store.     

Preconditioning and storage of chemically immature Russet Burbank and Shepody potatoes

Russet Burbank and Shepody potatoes of different chemical maturities (i.e. varying sucrose concentrations) at harvest were preconditioned by holding at 15 C for various durations to lower the concentration of reducing sugars to levels acceptable for processing as french fries out of 8 C storage. In chemically immature tubers (i.e. those harvested with a high sucrose), sucrose declined after harvest and stabilized in storage regardless of the preconditioning period. However, there was a temporary small increase in sucrose after harvest in more chemically mature tubers. The concentrations of the reducing sugars glucose and fructose were low at harvest, usually < 1.0 mg g^?1, but increased rapidly during the first 30 to 45 d of storage in tubers with more than 2.0 mg g^?1 sucrose at harvest. Preconditioning for up to 70 d at 15 C either limited the increase in reducing sugars or lowered them more rapidly during storage than when preconditioned for only 14 d. Fresh weight loss of Russet Burbank and Shepody was greater in physically and chemically immature tubers compared to more mature tubers. Extended preconditioning of Russet Burbank and Shepody resulted in minimal additional weight loss.