Susceptibility to Pressure Flattening Correlates with Texture Analysis of Potato Tubers

The physiological disorder referred to as pressure flattening is a cause of significant economic losses in the storage of Irish potatoes (Solanum tuberosum L.) intended for use in the fresh market. As the flattened area on each tuber becomes larger in diameter or becomes more depressed the USDA quality grade, and therefore the market value of the potatoes is reduced. Experiments were conducted to identify at-harvest which potato lots within and among cultivars were likely to pressure flatten earlier or more severely. The use of an instrumented penetrometer or texture analyzer to measure peak load required for periderm deformation at harvest appears to anticipate correctly the majority of fields from which tubers are more likely to have severe pressure flattening at six months’ storage duration. At-harvest texture analysis appears to segregate varieties according to susceptibility to deformation based on cultivar specific factors that play a role in pressure flattening development during storage. The Pearson correlation coefficient (R²=0.5481) indicates that there is a correlation between tuber texture at harvest and pressure flattened area on the tuber following storage. Testing of tubers from different fields and cultivars as the potatoes are loaded into storage, may allow growers to identify and ship potatoes that are more susceptible before they develop significant pressure flattening.     

Blackspot injury of film-wrapped potatoes in relation to bruising and respiratory gases

Summary Film-wrapped potatoes were compared with non-wrapped potatoes for blackspot susceptibility. Individual ‘Russet Burbank’ potatoes wrapped in Cryovac D-955 shrink film were less susceptible than non-wrapped potatoes to internal blackspot injuries when stored at 24°C. The film wrap reduced potato weight loss (water loss) but it did not alter the rate of respiration or the endogenous oxygen or carbon dioxide levels. Thus the reduced susceptibility to blackspot could not be related to reduced oxygen levels much as would inhibit the activity of polyphenol oxidase, the enzyme responsible for the development of internal blackspot. In addition to high suscetibility to internal blackspot, the non-wrapped potatoes shrivelled at 24°C and lost their marketable appearance.     

Host Traits Influencing Severity of White Mold of Potatoes in a Rainfed Environment

Differences among cultivars of Solanum tuberosum L. in susceptibility to Sclerotinia sclerotiorum (Lib.) de Bary have been noted through observation and research. Traits hypothesized as having a potential effect upon susceptibility included, flower propensity, time to 50 % flowering, flowering duration, canopy density, oxalic acid sensitivity, and maturity. Field plots were planted using seven cultivars in which these variables were quantified and analyzed. Identification of those factors providing the greatest amount of information towards disease severity were identified using multiple linear regression, and parameter selection using Akaike’s Information Criterion. The factors of maturity (R²?=?0.77), time to 50 % flower (R²?=?0.64), and oxalic acid sensitivity (R²?=?0.57) were identified as providing the greatest predictive indices of white mold severity in potatoes.     

Field study of the relative susceptibility of eleven potato (Solanum tuberosum L.) varieties and the efficacy of two fungicides against Rhizoctonia solani attack

Rhizoctonia black scurf is an economically important disease of potatoes in Tunisia and around the world. It reduces the quality and yield of potatoes and has become an important impediment for export of potatoes, especially to Europe. The information on comparative susceptibility of potato cultivars will help the growers make informed decisions regarding the management of this disease. The eleven potato cultivars used in this study showed a range of susceptibility reactions to Rhizoctonia solani but none of these was completely resistant to the disease. The Spunta variety showed the least percentage of infection of progeny tubers by R. solani sclerotia at harvest, while the varieties Nicola, Santana, Labadia, Liseta and Tango showed a high percentage of infection of progeny tubers. Seed treatment using fungicides, presently registered in Tunisia, are not effective in controlling the disease to growers’ satisfaction. Field experiments conducted to evaluate the efficacy of two newly introduced fungicides pencycuron (Monceren^®) and azoxystrobin (Amistar^®) showed that they were effective for the control of the disease. Seed potatoes treatment and in-furrow application of azoxystrobin consistently provided superior protection in two years of experimentation.     

Determination of thiabendazole residues in potatoes using high pressure liquid chromatography

Summary This paper describes a method for the extraction, purification and quantification by high pressure liquid chromatography using fluorimetric detection, of thiabendazole residues from potatoes. Bonded silica sorbent extraction columns (diol phase) are used for sample clean up, resulting in a rapid and accurate analysis. The average recovery was 93.8%±2.1%. Levels of about 0.0004μg of TBZ, equivalent to 0.033 mg kg⁻¹ in potatoes (on fresh weight basis), were readily detected from deliberately contaminted potatoes.     

Effect of Cooking and Processing on CIPC Residue Concentrations in Potatoes and Processed Potato Products

Residue concentrations of the sprout suppressant chlorpropham (or CIPC) were determined in raw and cooked potatoes and processed potato products, 48 h after CIPC aerosol treatment and after 30 days of subsequent storage at 4 or 12 °C. In the raw (uncooked) tuber, 48 h after CIPC treatment, the CIPC residue in the peel was 4.7 mg kg^-1, while in the peeled tuber it was 0.1 mg kg^-1. Boiling resulted in a decrease in residue concentration in the peel, but no significant differences in the residue concentration of the peeled tuber were observed. Pressure cooking resulted in a significantly increased residue concentration in the peel, but no significant change in the peeled tuber, whereas microwave cooking also did not increase the residue concentration in the peel significantly compared with that in raw tubers. Also the trend towards increases in residue concentration in microwave-cooked peeled tubers was not significant. The CIPC residue concentration detected in peeled tubers was 0.4–0.7 mg kg^-1 after boiling, 0.4–1.5 mg kg^-1 after pressure cooking and 0.4–3.8 mg kg^-1 after microwave cooking. The highest values were always found for tubers stored for 30 days at 4 °C. Processed products such as crisps, French fries, dehydrated sliced potatoes and starch contained different concentrations of CIPC residue, which was also detected in the cooking water and frying oil. The highest residue concentrations detected were 0.7, 4.7, 1.3 and 0.2 mg kg^-1 in crisps, French fries, dehydrated sliced potatoes and starch, respectively. The highest CIPC residue concentration observed in raw potatoes was much lower than the maximum residue level of 10 mg kg^-1 prescribed by the European Union.     

Inactivation of trypsin inhibitors in sweet potato and taro tubers during processing

In order to understand the extent of elimination of trypsininhibitors during processing of sweet potato (Ipomoea batatas) andtaro (Colocasia esculenta) tubers, a detailed study was conductedusing tubers processed by oven drying, cooking, and microwavebaking. Between 80 and 90% trypsin inhibitor (TI) activity wasretained in sweet potato chips up to 2h at 70 ^°C. Among thefour cultivars of sweet potatoes, RS-III-2 trypsin inhibitors were more heatlabile. Heating at 100 ^°C led to rapid inactivation of TI of sweetpotatoes. Varietal differences in thermal stability were more pronouncedfor the trypsin inhibitors of taro than sweet potatoes. Taro inhibitors werealso more rapidly inactivated than sweet potato TI. Between 17 and31% TI activity was retained in cooked tuber pieces of sweet potatoes,while only 3–10% were retained in taro cultivars. Very effectiveinactivation of trypsin inhibitors of sweet potatoes and taro could beobtained through microwave baking. Flour prepared from taro was devoidof TI activity, while 5–12% TI activity was retained in the flour preparedfrom sweet potatoes. The study clearly established that among the fourtechniques used, microwave baking and flour preparation were the best methods to eliminate TI from sweet potatoes and taro.     

The incidence of decay and factors affecting bacterial soft rot of potatoes

The incidence of tuber decay in rail car shipments of potatoes from the State of Washington was determined from 1965 to 1969 inclusive. Reinspection certificates revealed that 7.9% of the rail cars of potatoes shipped during this period were rejected due to tuber defects; tuber decay accounted for 63% of these rejected cars. Percentage of rejections due to tuber decay was greater for Russet Burbank than for Norgold Russet potatoes. Temperature, moisture, and oxygen levels influenced development of bacterial soft rot in freshly harvested potatoes and in potatoes stored for 3 months at 35 F (2 C) previous to treatment. When tuber surfaces were kept dry, no soft rot developed in 11 days over ranges of 50–70 F (10–21 C) and 2–20.5% oxygen levels. Freshly harvested tubers partially immersed in water did not rot when cooled to 40 F (4.4 C) in < 24 hours and held for 8 days under either 20.5 or 4% oxygen levels; however, tubers, rotted when stored similarly but at 50 F or higher temperatures. Partially immersed tubers incubated for 1 day or longer at 70 F developed soft rot in a low oxygen (4%) when later stored for, 8 days at 40 F. When rot occurred, the amount was always greater under lower oxygen levels irrespective of storage temperature. Of various cooling methods tested in rail cars loaded with 100 lb (45.4 kg) sacks of potatoes, prechilling of tubers and icing of cars prior to loading lowered floor temperatures most rapidly. Icing cars after loading lowered floor temperatures the slowest. In a carton shipment, the temperature remained above 68 F (20 C) in cartons after 8 days in transit, even though the wall and floor temperatures had cooled to near 55 F (12.8 C) by the second day. Oxygen level surrounding, tubers in the center of car loads of 100 lb sacks of potatoes was approximately 20.5% after 8 days transit.     

Lipid composition of potatoes as affected by storage and potassium fertilization

The effects of storage treatments and potassium fertilization on the phospholipid, triglyceride and free fatty acid content of Russet Burbank potatoes were determined. Thin-layer chromatography of the lipids indicated at least 18 types of lipids were present. Eight were phospholipids which were the predominant lipid class in the potatoes. Phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid comprise the major phospholipids. A large increase in phosphatidic acid and a decrease in phosphatidylcholine were observed in potatoes stored at 5.6 C (42 F). Potatoes fertilized with 240 lbs of potassium (calculated as K₂O) had a higher content of triglycerides compared to potatoes with no fertilization. Potatoes stored at 5.6 C (42 F) exhibited a decrease in triglyceride and phospholipid content but the free fatty acids were increased. The various lipid contents of reconditioned potatoes were similar to those of freshly harvested potatoes.     

The effect of chloride fertilization on blackspot susceptibility and other quality characteristics and on yield of potato

Summary Trials were carried out in two years on a sandy loam and on a heavy clay soil with two cultivars to examine the potential of chloride fertilization as a tool to reduce blackspot susceptibility of potatoes and to investigate other effects on yield and quality. Blackspot susceptibility was significantly reduced in cv. Marijke, but not in cv. Bintje as a result of increasing doses of applied chloride from 0 to 400 kg ha1. Dry matter concentration, assessed as under-water weight, was reduced by chloride in both cultivars at the two locations. Fry colour of French fries was improved by chloride. Applying 400 kg ha⁻¹ Cl⁻ to both soil types decreased net tuber yield >35 mm of cv. Bintje but not of cv. Marijke. Chloride caused slower emergence, retarded crop development and less stems per plant on the sandy loam soil but not on the heavy clay soil.     

Rhizoctonia disease of potatoes (Rhizoctonia solani): Fungicidal efficacy and cultivar susceptibility

Rhizoctonia stem canker and black scurf is an economically important disease of potatoes in Alberta and around the world. It reduces the quality and yield of potatoes and has become an important impediment for export of seed potatoes, especially to Mexico. Seed treatment using fungicides, presently registered in Canada, are not effective in controlling the disease to growers’ satisfaction. Field experiments conducted to evaluate the efficacy of various fungicides showed that captan (Captan), iprodione (Rovral), mancozeb (Tuberseal), and fludioxonil (Maxim) provide effective control of the disease. Of these fungicides, fludioxonil consistently provided superior protection. Based on the results of this study, Maxim was registered in 2000 for control of this disease in Canada. Potato cultivars/breeding selections showed a range of susceptibility reactions toR. solani but none of these was completely resistant to the disease. The information on comparative susceptibility of potato cultivars will help the growers make informed decisions regarding the management of this disease. Of six plant species (Beta vulgaris,Brassica compestris, Hordeum vulgare, Pisum sativum,Triticum aestivum, Zea mays) most commonly used in rotation with potatoes in Alberta, none was infected by potato isolates ofR. solani. The results suggested that use of these plant species as rotation crops with potatoes in Alberta will help in reducing the development of rhizoctonia disease in potatoes.     

Gamma irradiation of potatoes: Effects on sugar content,chip color,germination, greening,and susceptibility to mold

Russet Burbank potatoes that had been stored at 40°F. for 5 months after harvest were irradiated with 5,200 and 14,000 rad of Co⁶⁰ gamma rays. In general, irradiation caused an accumulation of sugars. At 40°F., the sucrose level rose to nearly 3 times that of the control in 16 days following irradiation. Fructose and glucose showed smaller increases and the latter did not accumulate significantly in the tubers given the higher dose of gamma rays. At 70°F., the levels of sucrose and glucose in the irradiated tubers rose above those in the controls, the difference reaching a maximum in 4 days and then declining. Irradiation had no effect on loss of fructose at this temperature. Color of potato chips processed from the irradiated potatoes was in general darker than that of chips from control tubers. The storage-time pattern of color change resembled that of the reducing rather than total sugar. Fourteen thousand rad did not prevent initiation of germination in the tubers but did destroy their sprout-growth apparatus. Although the lower dosage did not prevent initiation and subsequent growth, it prevented the formation of secondary tubers, which appeared on the sprouted control tubers. Furthermore, unlike the controls, the low-dosage potatoes developed branching hair sprouts with no tendency toward apical dominance during the early stages of sprouting. The rate of greening of gamma-irradiated and illuminated tubers was significantly less than that of unirradiated illuminated controls. Evidence is presented that irradiation may increase the susceptibility of potatoes to attack by molds under some conditions.     

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.     

Effect of CIPC on Sprout Inhibition and Processing Quality of Potatoes Stored Under Traditional Storage Systems in India

Indigenous non-refrigerated methods like heaps and pits are used in India for short-term storage of potatoes (Solanum tuberosum L.) to avoid distress sale. Storing untreated potatoes generally results in high losses from sprouting, moisture loss and rotting. To reduce storage losses by inhibition of sprouting and to determine the suitability of stored potatoes for processing into crisps, a single spray application of a commercial formulation of 3-chlorophenyl carbamate (CIPC or chlorpropham) 50% a.i., (Oorja, United Phosphorus Limited, Mumbai, India) of CIPC (or chlorpropham) was tested on potatoes during storage from March to June under two traditional storage methods [heap (17–33 °C, 58–92% relative humidity (RH)) and pit (17–27 °C, 72–95% RH)] in 2 years [2005 up to 90 days of storage (DOS) and 2006 up to 105 DOS], using four cultivars and two rates of CIPC application (20 and 30 mg a.i. kg⁻¹ tubers). The two rates of application were comparably effective in reducing weight losses, sprouting and sprout growth in stored tubers, and the effect was more pronounced in pit storage than in heap storage. By contrast to untreated tubers, CIPC-treated potatoes remained turgid under the two storage methods and fetched market prices comparable to those for cold-stored (2–4 °C) potatoes after 105 days of storage. Reducing sugar concentrations in treated potatoes decreased during storage especially in 2006 when the initial reducing sugar concentration was higher than in 2005. Crisp colour improved only in 2005 after 90 DOS, but it deteriorated in 2006 during storage up to 105 DOS. Sucrose concentration increased tremendously during storage in 2 years. Only one cultivar (Kufri Chipsona-1) with low initial reducing sugar concentration and less sucrose accumulation during storage could produce acceptable colour crisps after storage in both years. The remaining three cultivars—with high initial reducing sugar concentration—were suitable for processing after storage in heap and pit in 2005, but not in 2006. Stored potatoes were safe for human consumption as the CIPC residue concentrations were far below the permissible level of 10 mg kg⁻¹ as prescribed by the European Union. Single spray application of CIPC (20 mg kg⁻¹ treatment) can effectively reduce storage losses in potatoes stored in traditional non-refrigerated methods of heap and pit and extend the storage life by 90 to 105 days.     

Antioxidants in potato

The content of compounds in potato that may act as antioxidants in the human diet is not widely appreciated. Carotenoids are present in the flesh of all potatoes. The contents mentioned in the literature range from 50 to 100 μg per 100 g fresh weight (FW) in white-fleshed varieties to 2000 μg per 100 g FW in deeply yellow to orange-fleshed cultivars. The carotenoids in potato are primarily lutein, zexanthin, and violaxanthin, all of which are xanthophylls. There is just a trace of either alpha or beta-carotene, meaning that potato is not a source of pro-vitamin A carotenes. In potatoes with total carotenoids ranging from 35 to 795 μg per 100 g FW, the lipophilic extract of potato flesh presented oxygen radical absorbance capacity (ORAC) values ranging from 4.6 to 15.3 nmoles α-tocopherol equivalents per 100 g FW. Potatoes contain phenolic compounds and the predominant one is chlorogenic acid, which constitutes about 80% of the total phenolic acids. Up to 30 μg per 100 g FW of flavonoids are present in the flesh of white-fleshed potatoes with roughly twice the amount present in red and purple-fleshed potatoes. The predominant flavonoids are catechin and epicatechin. Red and purple potatoes derive their color from anthocyanins. The skin alone may be pigmented, or the flesh may be partially or entirely pigmented. Whole unpeeled with complete pigmentation in the flesh may have up to 40 mg per 100 g FW of total anthocyanins. Red-fleshed potatoes have acylated glucosides of pelargonidin while purple potatoes have, in addition, acylated glucosides of malvidin, petunidin, peonidin, and delphinidin. The hydrophilic antioxidant activity of solidly pigmented red or purple potatoes is comparable to brussels sprouts or spinach. In red and purple potatoes with solidly pigmented flesh with levels of total anthocyanin ranging from 9 to 38 mg per 100 g FW, ORAC ranged from 7.6 and 14.2 umole per g FW of Trolox equivalents. Potato contains on average 20 mg per 100 g FW of vitamin C, which may account for up to 13 % of the total antioxidant capacity. Potatoes should be considered vegetables that may have high antioxidant capacity depending on the flesh composition.     

Response of Russet Burbank and Shepody potatoes to nitrogen fertilizer in two cropping systems

Russet Burbank and Shepody potatoes were grown with at-planting N fertilizer rates ranging from 0 to 270 kg ha^?1 during 1986 through 1989. Experiments were conducted each year following small grains and red clover. Total yields and tuber size were strongly increased by N on most sites where potatoes followed small grains. Specific gravities declined with increasing N rate. Total yields of Russet Burbank and Shepody were optimized at an average of 196 and 211 kg ha^?1 of N, respectively, following small grains. The effect of N fertilizer on yields was much less dramatic following red clover. Total yields averaged 88% of maximum with only 45 kg ha^?1 of N applied, compared to 77% of maximum for this N rate following small grains. Total yields for the two varieties were optimized at 126 and 136 kg ha^?1, respectively. U.S. #1 yields were generally not increased at N rates above 45 to 90 kg ha^?1 following red clover and tuber size was not increased at rates above 90 to 135 kg ha^?1. Based on these studies, the N fertilizer credit for red clover grown prior to potatoes can be up to 75 kg ha^?1. Maintenance of tuber quality necessitates conservative use of N fertilizer when potatoes are grown following legumes. The highest N rates tested suppressed total yields of Russet Burbank, a late-season, indeterminate variety, by approximately 9% averaged over cropping systems.     

Photoperiod,gibberellic acid,and kinetin,in potato flower differentiationin vitro

To inducein vitro floral differentiation on potato plantlets, one cm long apical explants cv. Marijke were excised and aseptically cultured in a semi-solid medium containing Murashige-Skoog salts supplemented with 0.3 mg/l indoleacetic acid; with or without one mg/l gibberellic acid (GA); 0.3, 3.0 or 30.0 mg/l Kinetin (K); 20, 40 or 60 g/l sucrose (S) and 8% agar, pH 5.7. After a five week growing period at 26–28 C with daily light PAR 35 μE/m²/sec, 14 or 24 h daylength (DL), flower buds developed with exposed sepals and an abscission zone in the peduncle. Statistical significance was found when the variation factors (GA, K, S, and DL) were analyzed individually or in combination for number and weight of floral buds. Absence of GA favored the number of buds/plant, and the interaction of continuous light with a culture medium containing 0.3 or 3.0 mg/l kinetin and 40 g/l sucrose induced the highestin vitro “yields” in number and weight of flower buds (6 per plant and up to 14 mg/bud), followed by premature abscission. In a similar experiment, to prevent such abscission, plants from five week old tissue culture were transferred to soil and maintained at 24 h DL and 26–28 C, but flower bud abortion could not be avoided. These results demonstrate the importance of manipulating exogenous factors (growth regulators, sucrose, photoperiod) to inducein vitro specific organogenesis in potatoes.     

Estimation of critical nutrient range of petiole nitrate for sprinkler-irrigated potatoes

The relationship of yield to concentration of NO₃ in petioles of potatoes (Solanum tuberosum L.) was studied as part of a comprehensive project on N use efficiency. The objective of this study was to estimate the critical nutrient range (CNR) of petiole NO₃ for Russet Burbank potatoes treated with N supplements during the season. Treatments totaled 224, 336, and 560 kg N ha^-1 for the season as NH₄NO₃ on this low N soil with one-third to one-half of the N applied at planting and the rest as periodical supplements during the season. Average yield of potatoes (74 Mt ha^-1) was highest with 336 kg N ha^-1. From this it was assumed that 224 N was optimum. Petiole NO₃ decreased through the season with linear regressions of petiole NO₃ versus time for each of three N rates accounting for variation in petiole NO₃. It was concluded that at the start of the season, the estimated CNR for petiole NO₃-N of potatoes was within the range from 9 to 13 g kg^-1. Numerically, CNR values decrease with time as the season progresses. It is concluded that until more precise calibrations are made available, the CNR approach with petiole NO₃ will be more helpful in cross checking the nutritional status of potatoes fertilized periodically with N supplements than in serving as a primary fertilizer guide.     

Influence of airflow rate on chip potato storage management

Through-the-pile ventilation is a common practice for potatoes stored in bulk. Research was initiated in 1986 to study the influence of ventilation rate on the temperature, moisture and market quality of bulk stored chip potatoes. Ventilation rates up to 168 m³ hr^?1 t^?1 were used. All ventilation rates achieved the required temperature and humidity control. Fan operation time (hours) was not reduced proportional to the increased ventilation rate. The higher ariflow resulted in proportionally less time being spent to correct pile temperature differentials. The Atlantic variety potatoes were utilized for potato chip production in all three seasons studied. Market quality after storage, measured by tuber sugar content, chip color and chip defects, was similar for all ventilation rates. For the last two storage seasons studies, the potatoes were marketed from the storage research bins at high levels of quality following 115 to 142 days of storage. Average weight losses for the airflow rates used were not statistically different. However, potato weight loss uniformity was proportional to increased ventilation rates.     

Residues of free and bound maleic hydrazide in potato tubers

Summary The method of Vadukul (1991) for determining maleic hydrazide (MH) was modified and gave recoveries of free MH of 89%±4%. The values recorded on individual tubers ranged from 2–14 mg kg⁻¹. Maleic hydrazide was evenly distributed throughout the tuber (peel, outer and inner flesh) but concentration increased slightly as tuber size increased. The concentration of free MH decreased from 7 to 3 mg kg⁻¹ over the storage period of 5 1/2 months. Acid hydrolysis released substantial amounts of MH particularly from older potatoes (13 mg kg⁻¹) compared with 6 mg kg⁻¹ from new potatoes, implying that free MH is gradually converted to a bound form with time after treatment. No evidence was found for the presence of a β-glucoside of MH.