Lisa O. Knowles

Temperature-induced changes in potato processing quality during storage are modulated by tuber maturity

Knowledge of how potato (Solatium tuberosum L.) cultivars respond to non-conventional storage temperature regimes may expand options for managing immature, overmature, or otherwise stressed potatoes. Here we demonstrate that temperature-dependent changes in the processing quality of tubers are modulated by tuber maturity. ‘Russet Burbank’ (RB), ‘Ranger Russet’ (RR), and ‘Umatilla Russet’ (UR) tubers from early- and late- planted crops (grown for 163 d and 133 d, respectively) were conditioned for a month at 4.5, 6.7, or 9 C, and subsequently stored at 4.5, 6.7 or 9 C (nine temperature regimes) for an additional 182 d before reconditioning at 16 C. Fry color darkened as conditioning temperature (CT) decreased from 9 to 4.5 C, and tubers were most sensitive to low temperatures for loss of processing quality during the initial conditioning period following wound-healing. Conditioning at higher temperatures increased the tolerance of tubers to lower subsequent holding temperatures (HT) later in the storage season. The processing quality of chronologically older (early planting) RR and UR tubers was inferior to the younger tubers (late planting), resulting in fewer CT/HT combinations for managing the former. Regardless of maturity, RR tubers maintained processing quality for up to 230 d when conditioned and stored at higher temperatures; however, tubers from the late planting had a greater tolerance of lower temperatures than those from the early planting. Although reconditioning improved the processing quality for all cultivars and thus expanded the CT/HT management options, the responsiveness of cold-sweetened UR tubers to reconditioning attenuated over the 230 d storage period, reflecting earlier onset of irreversible senescent sweetening in this cultivar. Chronologically younger tubers of the most dominant processing cultivars in the Pacific Northwest stored better than tubers produced over a prolonged growing season. Collectively, these studies suggest strategies to manage tubers of differing maturity to best preserve processing quality during storage.ResumenEl saber de cómo los cultivares de papa (Solanum tuberosum L.) responden a regímenes de temperatura no convencional de almacenamiento puede aumentar las opciones para el manejo de papas inmaduras, sobre maduras o estresadas. Aquí demostramos que los cambios temperatura-dependiente de la calidad del producto son regulados por la madurez del tubérculo. Los tubérculos de ‘Russet Burbank’ (RB), ‘Ranger Russet’ (RR) y ‘Umatilla Russet’ (UR) de cultivos sembrados temprano y tardíamente (crecidos por 163 y 133 días, respectivamente) fueron acondicionados por un mes a 4.5, 6.7 y 9 C y luego almacenados por 182 días adicionales a 4.5, 6.7 o a 9 C (nueve regímenes de temperatura) antes de reacondicionarlos a 16 C. E1 color de la fritura se oscureció a medida que la temperatura de acondicionamiento (CT) disminuyó de 9 a 4.5 C y los tubérculos fueron más sensibles a las temperaturas bajas para pérdida de su calidad de procesamiento durante el periodo inicial de acondicionamiento, después de la cicatrización de las heridas. El acondicionamiento a temperaturas más altas incrementó la tolerancia de los tubérculos a mantenimiento posterior a temperaturas mas bajas (HT) hacia el final del período de almacenaje. La calidad de procesamiento de los tubérculos más viejos (siembra temprana) de RR y UR fue inferior a la de tubérculos más jóvenes (siembra tardía) resultando en pocas combinaciones CT/HT de mane jo para los primeros. Prescindiendo de la madurez, los tubérculos de RR mantuvieron la calidad de procesamiento hasta 230 días cuando se acondicionaron y almacenaron a temperaturas más altas; sin embargo, los tubérculos de siembra tardía tuvieron mayor tolerancia a temperaturas bajas que aquellos de siembra temprana. Aunque el acondicionamiento mejoró la calidad de procesamiento de todos los cultivares y por lo tanto amplió las opciones de manejo CT/HT, la respuesta de los tubérculos de UR endulzados por frío al acondicionamiento se atenuó después de 230 días de almacenamiento, reflejando una temprana aparición de dulzor senescente irreversible en este cultivar. Tubérculos cronológicamente más jóvenes de los cultivares prominentes en el Pacífico noroccidental se almacenaron mejor que los tubérculos de permanencia prolongada en el campo. Colectivamente, estos estudios sugieren estrategias de manejo de tubérculos de diferente estado de madurez para preservar mejor su calidad de procesamiento durante el almacenamiento.

Phosphorus status affects postharvest respiration, membrane permeability and lipid chemistry of European seedless cucumber fruit (Cucumis sativus L.)

Fruit of European seedless cucumber were grown in a greenhouse under low and high phosphorus (P) fertilization regimes. Tissue P concentration of fruit (number one grade) from low-P plants was, on average, 45% of that of fruit from high-P plants. Fruit P status affected membrane lipid chemistry and fruit respiration after harvest. Mesocarp tissue of low-P fruit had a lower concentration of phospholipids, lower level of unsaturation in various pools of fatty acids, and a greater rate of electrolyte leakage than that of high-P fruit. On average, respiration of low-P fruit was 21% higher than that of high-P fruit over a 16-day postharvest interval at 23°C. Moreover, low-P fruit experienced a climacteric in respiration that began about 40 h after harvest, reached a maximum at 72 h, and declined to preclimacteric levels by 90 h. The difference in respiration rate between low- and high-P fruit was as high as 57% during the climacteric. The respiratory climacteric was unique to the low-P fruit and was not associated with an increase in fruit ethylene concentration or ripening. Phosphorus nutrition can thus alter the postharvest physiology of cucumber fruit by affecting membrane lipid chemistry, membrane integrity and respiratory metabolism.

Lipid biochemistry of echinochloa crus-galli during anaerobic germination

Abstract Seven day old seedlings of Echinochloa crus-galli var. oryzicola (Vasing) had a higher total lipid content when germinated under N 2 than in air, although ungerminated seeds contained more lipid than either seedling. The triacylglycerol pool was not depleted under anaerobiosis as it was in air and only air-grown seedlings showed a net increase in free fatty acids and polar lipids. Concentrations of most of the individual acids of the total fatty acid profile declined during germination in air and in the free acid and polar lipid fractions of these seedlings the relative proportion of polyunsaturated fatty acids increased. Compared to air-grown seedlings, ungerminated seeds and N 2 -grown seedlings had a similar qualitative and quantitative lipid composition. Our results show that mobilization of storage lipids was apparently severely inhibited under anoxia. The importance of lipid metabolism to the germination and growth of Echinochloa during anoxia is discussed in terms of maintaining membrane integrity and serving (indirectly) to reoxidize pyridine nucleotides.

Toxicity and Metabolism of Exogenous α,β-Unsaturated Carbonyls in Potato (Solanum tuberosum L.) Tubers

A group of aliphatic α,β-unsaturated carbonyl compounds was evaluated for their utility as inhibitors of sprout growth in stored potato tubers (Solanum tuberosum L.). Nondormant tubers were treated with vapors of six 8-10-carbon compounds of this chemistry. Subsequent sprout growth at 16 °C (95% relative humidity) over ca. 3 months in storage was suppressed by all compounds in a concentration-dependent manner. The volatile metabolites produced by sprout and associated tuber tissues following treatment with 3-octen-2-one, 3-nonen-2-one, and 3-decen-2-one were the corresponding alkyl ketones and alkyl secondary alcohols. In contrast, (E)-2-octenal, (E)-2-nonenal, and (E)-2-decenal were metabolized by two pathways: (1) parent compound to the corresponding alkyl aldehyde and then to the alkyl primary alcohol and (2) parent compound to the alkenyl primary alcohol. Residues of 3-nonen-2-one and (E)-2-nonenal and their metabolites were analyzed in whole tubers over a 28 day post-treatment period. The concentrations of the parent ketone and aldehyde declined rapidly following application, and the most persistent metabolites were 2-nonanol and (E)-2-nonen-1-ol, respectively. The sequence of reactions leading from the α,β-unsaturated carbonyls to the alcohols was determined by application of each of the 9-carbon compounds individually to tubers. In long-term efficacy studies, a single application of (E)-2-nonenal and 3-nonen-2-one to nondormant tubers terminated sprout growth and prevented regrowth for 2-3 months. A second application suppressed sprouting for at least 4-5 additional months. This efficacy, combined with rapid metabolism and low residue levels, makes the 8-10-carbon α,β-unsaturated ketones and aldehydes worth consideration for use as sprout inhibitors.

1,4-Dimethylnaphthalene treatment of seed potatoes affects tuber size distribution

Abstract1,4-DMN is a relatively new sprout inhibitor for use on maincrop and seed potatoes. Despite its registration as a “dormancy enhancer” for seed, relatively little is known about its effects on plant establishment and productivity. The main objective of this study was to evaluate the effects of 1,4-DMN on the productivity of seed potatoes. ‘Umatilla Russet’ (UR), ‘Ranger Russet’ (RR), and ‘Russet Burbank’ (RB) seed tubers were stored at 4, 7, and 9 C over three seasons to create 80-, 554- and 642-degree-day seed, and 1,4-DMN was applied to maintain dormancy several times during each season. 1,4-DMN residue levels at the end of storage were lower in seed aged at higher temperatures. Multiple applications of 1,4-DMN at higher-than-label rates were necessary to effectively inhibit sprouting of seed of all cultivars stored above 4 C. In field trials, depending on cultivar and year, 1,4-DMN either delayed plant emergence slightly or had no effect. 1,4-DMN increased stem numbers from RB and UR seed, but not from RR seed. 1,4-DMN reduced total tuber yields by 3.2 to 5.6 t ha−1 (5% to 9%), and U.S. No. 1 tuber yields by 4.8 to 7.8 t ha−1 (8% to 15%) in all cultivars, regardless of seed tuber age. 1,4-DMN also reduced the average tuber weight for all three cultivars and shifted the size distribution from larger (> 284 g) to smaller tubers. 1,4-DMN reduced the respective yields of > 397-g, 340-to 397-g, and 284-to 340-g tubers by 43%, 19%, and 18% for RR seed, 31%, 14%, and 11% for RB seed, and 40%, 47%, and 27% for UR seed. Conversely, depending on cultivar, yields of smaller tubers (≤170 g) were 11% to 38% higher from 1,4-DMN-treated seed. The shift in tuber size distribution for RR was accompanied by a 1,4-DMN-induced increase in tuber number per plant and per hectare. However, no such effects on tuber set occurred in RB and UR. Moreover, in most cases, the 1,4-DMN effects on yield and tuber size distribution were independent of seed age. Since the 1,4-DMN-induced shifts in tuber size distribution were greater than the reductions in total and U.S. No. 1 yields, 1,4-DMN may be a suitable treatment to reduce average tuber size and increase yield and uniformity of specific size classes of tubers to more closely match market requirements.ResumenEl 1,4-DMN (Dimetil naftaleno) es un inhibidor de brotes de papa relativamente nuevo que se usa tanto para cultivos comerciales como para cultivos de semilla. A pesar de su registro como estimulante de dormancia de semilla, se sabe muy poco sobre sus efectos en el establecimiento del plantel y su productividad. El objetivo principal de este estudio fue de evaluar los efectos del 1,4-DMN sobre la productividad de los tubérculos semilla. Tubérculos de ‘Umatilla Russet’ (UR), ‘Ranger Russet’ (RR) y ‘Russet Burbano’ (RB) se almacenaron a 4, 7 y 9 C durante tres campanas agrícolas para producir 80-, 554-y 642-grados-día de semilla y se aplicó 1,4-DMN varias veces durante cada campaña para mantener la dormancia de la semilla. Los niveles de residuo del 1,4-DMN al final del período de almacenamiento fueron más bajos en las semillas envejecidas a temperaturas mayores. A temperaturas de almacenamiento por encima de los 4 C se necesitan niveles mayores a los recomendados y aplicaciones múltiplas de 1,4-DMN para inhibir efectivamente el brotamiento de las semillas en todos los cultivares. En pruebas de campo, dependiendo del cultivar y del año, el 1,4-DMN, retardó ligeramente o no tuvo efecto en la emergencia de la planta, aumentó el número de tallos por semilla de RB y UR, pero no en RR. El 1,4-DMN redujo los rendimientos de 3.2 a 5.6 t/ha−1 (5 a 9%) en todos los cultivares, sin tener en cuenta la edad del tubérculo semilla. El 1,4-DMN también redujo los rendimientos en el peso promedio del tubérculo en los tres cultivares y cambió la distribución de tamaño de los tubérculos grandes (284 g) a tubérculos más pequenos. Redujo los respectivos rendimientos de tubérculos > 397 g, 340–397 g y tubérculos de 284–340 g por 43%, 19% y 18% para la semilla de RR, 31%, 14% y 11% para la semilla de RB y 40% 47% y 27% para la semilla UR. Contrariamente, dependiendo del cultivar, los rendimientos de tubérculos más pequeños (170 g) fueron de 11 a 38% mayores que en la semilla tratada con 1,4-DMN. El cambio en la distribución de tamaño en RR aumentó el número de tubérculos por planta y por hectárea inducida por el 1,4-DMN. Sin embargo, no sucedió lo mismo en RB y UR. Más aún en la mayoría de los casos, los efectos del 1,4-DMN sobre el rendimiento y distribución del tamaño del tubérculo fueron independientes de la edad de la semilla. Desde que los cambio inducidos por el 1,4-DMN en la distribución del tamaño del tubérculo fueron mayores que la reducción en el total de tubérculos US-1, el 1,4-DMN puede ser un tratamiento adecuado para reducir el promedio del tamaño del tubérculo y puede aumentar el rendimiento y la uniformidad en el tamaño específico de las clases de tubérculos para que estén de acuerdo con los requerimientos del mercado.

Impact of Agronomic and Storage Practices on Acrylamide in Processed Potatoes

Acrylamide is a probable carcinogen found in processed potato products. The compound is formed at elevated temperatures by the Maillard reaction from two primary precursors - reducing sugars (fructose and glucose) and asparagine. Significant advances have been made in reducing acrylamide formation by selecting varieties with low precursor concentrations through conventional breeding or genetic modification techniques. However, acrylamide in many of the traditional varieties processed for fries or chips is sometimes found at elevated levels. Both agronomic and storage practices can significantly influence glucose, fructose, and asparagine concentrations and therefore the potential to form acrylamide during processing. This summary of a symposium presentation given at the 99th Annual Potato Association of American Meeting is to provide a general overview of previous studies that have examined the effects of agronomic factors such as nutrient and water management and storage factors such as temperature and duration on acrylamide precursors and/or acrylamide in processed potato products. A better understanding of how these factors affect acrylamide precursors is a first step in minimizing acrylamide formation during processing and improving the quality of processed potato products.ResumenAcrilamida es un posible carcinogénico encontrado en productos de papa procesada. El compuesto se forma a temperaturas elevadas mediante la reacción de Maillard de dos precursores primarios: azúcares reductores (fructosa y glucosa) y asparagina. Se han hecho avances significativos en reducir la formación de acrilamida con la selección de variedades con bajas concentraciones del precursor a través de mejoramiento convencional o técnicas de modificación genética. No obstante, algunas veces se encuentra la acrilamida a niveles elevados en muchas de las variedades tradicionales procesadas para fritura. Tanto las prácticas agronómicas como las de almacenamiento pueden influenciar significativamente las concentraciones de glucosa, fructosa y asparagina, y en consecuencia el potencial para formar acrilamida durante el procesamiento. Este resumen de la presentación del simposio efectuado durante la 99 Reunión Anual de la asociación Americana de la Papa, es para proporcionar una visión general de estudios previos que han examinado los efectos de los factores agronómicos, tales como el manejo de nutrientes y agua, y factores de almacenamiento como la temperatura y la duración de los precursores de la acrilamida en los productos de papa procesada. Un mejor entendimiento de cómo estos factores afectan a los precursores de la acrilamida, es un primer paso en la minimización de la formación de acrilamida durante el procesamiento y en el mejoramiento de la calidad de los productos de la papa procesada.

Zebra chip disease enhances respiration and oxidative stress of potato tubers (Solanum tuberosum L.)

AbstractMain conclusionThe physiological phenotype of potato tubers afflicted by zebra chip disease is characterized by increased oxidative stress metabolism and upregulation of systems for its mitigation. Starch catabolism and extensive buildup of reducing sugars render potatoes infected with zebra chip (ZC) pathogen (Candidatus Liberibacter solanacearum) unsuitable for fresh market and processing into chips/fries. Here we show that the disease inflicts considerable oxidative stress, which likely constitutes a substantial sink for metabolic energy, resulting in increased respiration rate of afflicted tubers. In contrast to healthy tubers, tissue from diseased tubers had greater ability to reduce 2,3,5-triphenyl-tetrazolium chloride to formazan, indicating enhanced dehydrogenase activity, probable disease-induced changes in cellular redox potential, and increased respiratory activity. The respiration rate of diseased tubers (cv. Atlantic) was 2.4-fold higher than healthy tubers and this correlated with increased activities of glucose-6-phosphate and 6-phosphogluconate dehydrogenases, key enzymes responsible for synthesis of cytosolic reducing equivalents. Wound-induced NADPH oxidase activity was greater for ZC than healthy tubers, but the resulting superoxide was rapidly catabolized by higher superoxide dismutase activity in ZC tubers. Peroxidase, catalase, glutathione reductase and ascorbate free radical reductase activities were also higher in diseased tubers, as was malondialdehyde, a biomarker of peroxidative damage and oxidative stress. Upregulation of the glutathione–ascorbate pathway is a direct response to (and indicator of) oxidative stress, which consumes reducing equivalents (NADPH) to catabolize reactive oxygen species and maintain cellular redox homeostasis. ZC disease substantially altered the oxidative metabolism of tubers, resulting in a physiological phenotype defined by metabolic changes directed toward mitigating oxidative stress. Paradoxically, the increased respiration rate of ZC tubers, which fuels the metabolic pathways responsible for attenuating oxidative stress, likely also contributes to oxidative stress.