The release of methyl chloride from potato tubers

Freshly harvested Norchip and Kennebec tubers release varied amounts of methyl chloride (CH₃Cl) during suberization. Maximum rates of CH₃Cl release, ranging from 98-690 ng CH₃Cl/kg tubers/hr under laboratory and commercial conditions, were attained 2–3 days following harvest. Release rates thereafter decreased 10-40-fold by the 7th day of suberization. The period of rapid decrease in CH₃Cl release corresponds to the reported time required by cut tuber tissue to initiate resistance to water loss. Cutting of newly harvested and suberized Kennebec tubers reestablished the high release rates of CH₃Cl measured during the early stages of suberization. The enhancement of CH₃Cl release by tissue cutting was not demonstrated by two varieties stored for 10 months. Suberization differences between early and late harvested Norchip tubers were better differentiated by their respective rates of CH₃Cl release than by CO₂ generation. These preliminary findings suggest the rate of CH₃Cl release could be applied to assess harvest damage and monitor the suberization process. Methyl chloride has previously been reported as the major nonindustrial chlorocarbon in the atmosphere that is linked to a replenishable, natural source.     

Damage of potato tubers,a review

Summary Damage to potato tubers due to mechanical forces is among the most important causes of loss of quality reported throughout the world. The causes of such damage are mechanical injuries that occur primarily in association with harvesting and grading. The extent of damage is dependent on the condition of the tubers and also reflects the history of the potatoes. Although important advances have been made, there is still a considerable need for research on this subject since knowledge of the combined effects of essential physiological proceses within the cells is still lacking. The avoidance of exposure to mechanical forces constitutes the most effective protection against tuber damage.     

Phosphorus balance in potato tubers

Summary Tubers of virus-free Norland, Kennebec, Norchip, Russett Burbank, Red Pontiac, Norgold and Early Ohio potato varieties with a common environmental history were freeze-dried, and the major phosphorus-containing fractions determined. The method devised gave very reproducible values for phospholipid, nucleotide phosphorus, phytic acid phosphorus, starch phosphorus and nucleic acid phosphorus. Very little varietal differences were found as long as environmental factors were constant. The greatest variation was in inorganic phosphorus levels. There were no obvious relationships between protein level and any of the phosphorus-containing fractions.

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Zusammenfassung Unsere Arbeit über Kartoffelhybriden mit hohem Proteingehalt erforderte die Kenntnis der Interaktionen zwischen St?rke, Protein, Nukleins?ure und Nukleotiden, was wir in der Literatur nicht finden konnten. Es schien keine hinreichende Zusammenstellung über die wichtigsten phosphorhaltigen Komponenten von Kartoffelknollen zu geben, die unter bekannten Umweltbedingungen angebaut wurden. Eine Fraktionierungsmethode wurde ausgedacht, die es erm?glichte, das Total an Phospholipiden, Nukleotiden, Phytins?ure, St?rke und Nukleins?uren, das in gefriergetrocknetem Knollenpulver vorhanden ist, zu trennen und quantitativ zu bestimmen. Das Verfahren wurde an Knollen von sieben Kartoffelsorten angewendet, die unter streng vergleichbaren Umweltbedingungen angebaut wurden. Die Ergebnisse (Tabelle 1) waren-mit nur kleinen sortenbedingten Unterschieden-gut reproduzierbar und einheitlich, vorausgesetzt die Umweltbedingungen waren vergleichbar. Die Ergebnisse dienen als Vergleichswert, an dem man die Einflüsse von variierenden Ploidiestufen oder variierendem Proteinniveau in der Entwicklung von Hybriden mit hohem Proteingehalt messen kann. Die hohen St?rkegehalte stellten kein Hindernis für die Nukleins?ureausbeute unter unseren Extraktionsbedingungen dar (Tabelle 2).

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Résumé Notre étude sur les hybrides de pomme de terre, ayant une haute teneur en protéines, exigeait une connaissance des intéractions entre amidon, protéines, acides nucléiques et nucléotides, lesquelles étant introuvables dans la littérature. Aucun inventaire satisfaisant ne semble exister pour la plupart des constituants phosphorés de tubercules de pomme de terre se développant dans des conditions d'environnement connues. Une méthode de fractionnement a donc été con?ue, qui rend possible la séparation et la mesure quantitative des phospholipides, nucléotides, acide phytique, amidon et acides nucléiques totaux présents dans la poudre de tubercules lyophilisés. Le procédé a été appliqué sur sept variétés cultivées dans des conditions d'environnement comparables. Les résultats (tableau I) sont très reproductibles et uniformes, montrant peu de différences entre les variétés, en raison même des conditions de culture. Ils peuvent servir de référence pour qui veut évaluer l'effet des variations du degré de plo?die ou du taux de protéines en vue de l'obtention d'hybrides riches en protéines. Le taux élevé d'amidon ne présentait pas d'obstacle pour l'isolement des acides nucléiques, dans les conditions de notre extraction (tableau 2).

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This study was carried out while the senior author was a guest, on sabbatical leave, at the Laboratory of Plant Hardiness, Department of Horticultural Science and Landscape Architecture, University of Minnesota, St. Paul, MN 55108.     

Amylase activity in potato tubers

Summary Amylase activity in extracts of sprouted tubers was optimised at final concentrations of soluble starch in the incubation medium of 0.6–2.0 mg cm⁻³. Optimum pH was 6. The exclusion of calcium ions from extraction and incubation media did not result in reduced enzyme activity. This, together with a shift in the absorption maximum of the starch-iodine complex almost identical to that observed with pure β-amylase, indicates the predominance of β-amylase in the extracts. Over a 15-min incubation period the linearity of the response was dependent upon the volume of tuber extract included in the assay medium. Gel filtration of extracts did not influence this response.     

Lipid distribution in potato tubers

Summary To elaborate on off-flavour development in dehydrated potato granules, lipids in subcellular particles and membrane systems of the tuber were investigated. Lipid acyl-hydrolase and lipoxygenase activities were suppressed in tuber homogenates by a buffer isolation medium of pH 7.8 containing nupercaine which minimized the breakdown of phospho- and galactolipids. Phospholipid, glycolipid and neutral lipid constitutents, their fatty acid composition, and unsaturation ratios were reported for amyloplasts, cell wall, microsomes, mitochondria, peroxisomes, and plasmalemma.

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Zusammenfassung Analysen von Kartoffelknollen wurden durch lipidabbauende Enzyme, Lipidacylhydrolase (LAH) und Lipoxygenase (LOX) behindert. Die LOX-Aktivit?t in handelsüblicherzugten Kartoffeln war hoch (Tabelle 1) und konnte durch gew?hnliche Inhibitoren nicht beeinflusst werden (Tabelle 2). Die LAH-Aktivit?t, die mit Phospholipiden (PL) und Galactolipiden als Substrate hoch war, wurde durch Nupercaine in verschiedenem Ausmass unterdrückt (Tabelle 3), dessen Weglassung w?hrend der Lipidanalyse von Kartoffelmembranen und subzellularen Partikeln hohe Lipidverluste verursachen k?nnte (Tabelle 4). Lipidergebnisse für mikrosomale Pr?parate, Mitochondrien, Peroxisomen, Plasmalemmen und St?rkek?rner (Tabellen 5–9) wurden wiedergegeben: nach Isolation bei pH 7,2, wenn die LOX-Aktivit?t nicht gehemmt war (Verfahren A); in einer Puffersubstanz von pH 7,8 ohne Nupercaine, wenn wohl die Aktivit?t von LOX unterdrückt war, nicht aber jene von LAH (Verfahren B); und bei pH 7,8 mit Nupercaine, wenn die Aktivit?t beider Enzyme unterdrückt war (Verfahren C). In den meisten Analysen zeigte die Lipidzusammensetzung, wenn die Aktivit?t beider Enzyme nicht unterdrückt wurde, eine entsprechende Anreicherung von PL, Sterollipiden und freien Fetts?uren (FFA) und ihrer Abbauprodukte sowie eine Abnahme im Gehalt an Galactolipiden. Kleine Mengen von Lipiden wurden in Form von Lipidpartikeln und verbunden mit Knollenzellw?nden gefunden (Tabelle 10). Die Fetts?urezusammensetzung des Gesamtlipids und einige besondere Lipidbestandteile und ihr Nichts?ttigungsverh?ltnis (UR) wurden nur für Verfahren C berechnet. Wenn dieses Verfahren weggelassen wurde, wie dargestellt mit Hilfe der St?rkelipid-Zusammensetzung, ergab sich nicht nur ein Verlust von Membran-PL und Galactolipiden. Fast die H?lfte der zurückgebliebenen neutralen Lipidfraktion war in Form von FFA in verschiedenen Graden oxydiert (Tabelle 9). Das UR der Gesamtlipide (TL) schwankte zwischen 0,4 und 2,9. Es war niedrig in der Zellwand, h?her im Plasmalemma und am h?chsten innerhalb der Zytoplasmamembranen. Das UR nahm dann bei den Vacuolen mit St?rkek?rnern ab. Die Bedeutung der Ergebnisse für die Bestimmung der Funktion von Lipiden in einem handelsüblichen Verfahren zur Herstellung von Püreepulver wirdt diskutiert.

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Résumé La dégradation enzymatique des lipides par la lipide acyl hydrolase (LAH) et par la lipoxygénase (LOX) génait l’analyse biochimique des tubercules de pomme de terre. L’activité de la LOX était importante dans les pommes de terre cultivées pour la commercialisation (tableau 1) et n’était pas affectée par les inhibiteurs courants (tableau 2). L’activité de la LAH, qui était forte avec les phospholipides (PL) et les galactolipides, était inhibée sur différents substrats par la nuperca?ne (tableau 3); l’absence de cette dernière durant l’analyse de la membrane et des organites intracellulaires du tubercule causait de fortes pertes en lipides (tableau 4). Les résultats obtenus avec les lipides des préparations de microsomes, mitochondries, peroxysomes, plasmalemme et de grains d’ amidon (tableaux 5 à 9) sont exposés; après isolement à pH 7,2 sans inhibition de l’activité de la LOX (procédé A); dans une solution tampon à pH 7,8 sans nuperca?ne alors que l’activité de la LOX est inhibée mais non celle de la LAH (procédé B); et à pH 7,8 avec nuperca?ne et inhibition de l’activité des deux enzymes (procédé C). Dans le cas où l’activité des deux enzymes n’était pas inhibée, la composition en lipides montrait un enrichissement relatif en PL, stérols, acides gras libres (FFA) et en leurs produits de dégradation ainsi qu’une diminution de la teneur en galactolipides. Une petite quantité de lipides était retrouvée sous la forme de particules lipidiques associées aux membranes cellulaires (tableau 10). L’étude de la composition en acides gras des lipides totaux et de quelques constituants lipidiques ainsi que la mesure de leur taux d’insaturation (U.R.) ont été effectuées seulement pour le procédé C. Quand ce procédé n’était pas employé, comme l’illustre la composition en lipides de l’amidon, il y avait non seulement une perte de PL et galactolipides membranaires mais la moitié de la fraction lipidique neutre retenue se trouvait sous la forme de FFA oxydés à différents degrés (tableau 9). L’U.R. des lipides totaux (TL) variait de 0,4 à 2,9; il était bas dans les membranes cellulaires, plus élevé dans le plasmalemme et le plus haut dans les membranes cytoplasmiques. L’U.R. diminuait dans les vacuoles contenant des grains d’amidon. L’intérêt de cette découverte pour la détermination des lipides au cours de la fabrication industrielle de granules de pomme de terre est discuté.

     

A classification system for impact-related defects in potato tubers

The type of tuber bruise that occurs for a given severity of impact indicates the condition of that tuber in relation to its impact sensitivity. This article describes a system for classifying such bruises. Such information is important because sensitive tubers can be re-conditioned (e.g., temperature and/or hydration can be adjusted) to reduce risk of bruising during harvesting and handling. Each class of bruise is described, illustrated, and related to tuber condition. The literature review illustrates the inadequacies of previous bruise evaluation systems in relating bruise type to tuber condition. Growers, processors, storage operators and fresh packers can use this system to make informed decisions on adjusting modifiable factors such as temperature, hydration level, and impact velocity to reduce impact-related defects during harvesting and handling of potatoes.     

Identification of galactinol in potato tubers

Summary An oligosaccharide detected by gas chromatography of trimethylsilyl derivatives of potato extracts has been isolated and identified as galactinol, 1-0-α-D-galactopyranosyl-(1R)-myo-inositol. Galactinol was not detected in freshly harvested tubers, but 0.1% was found in cold-stored tubers. The level of this sugar decreased during reconditioning of cold-stored potatoes. A laboratory cooperatively operated by the Eastern Utilization Research and Development Division. Agricultural Research Service, United States Department of Agriculture; Minnesota Agricultural Experiment Station, North Dakota Agricultural Experiment Station; and the Red River Valley Potato Growers’ Association.     

Tensile properties of potato tubers

Mechanical properties of Kennebec and Russet Burbank potato tubers were computed from Force-elongation data on specimens cut from the tuber and tested in tension. Specimens cut from three locations in fresh and stored tubers were tested at varying strain rates at 70 F (21 C) and at 42 F (6 C). Results were analyzed for significant differences. Tests were conducted in 1964 and 1966. In spite of some differences in tuber condition and test and analysis methods, there was good agreement of results between the years. Mean values of properties for all tests were: tensile strength, 98 psi; strain at failure, 0.193 in./in.; and failure modulus (stiffness), 727 psi. Properties varied greatly with location in the tuber. The pith, in the center, is stronger and stiffer than the perimedullary zone surrounding it, and the skin-cortex exhibits different properties than either of these two. Storage affected properties at the skin and in the center much more than in the perimedullary zone. As strain rate increased, tensile strength and stiffness generally increased, and strain at failure decreased. Stiffness generally increased when temperature decreased. Effect of variety was mixed. One of the greatest problems in designing and using potato handling and processing equipment is damage to the potatoes. This lowers their market value and increases their susceptibility to disease and deterioration in storage. Various investigators, by dropping or hitting tubers experimentally or by following them through normal hanlling operations, have determined the external causes of damage to whole tubers and conditions that promote it. These experiments have yielded much needed information, but they tell little about the properties of th tubers that make them so susceptible to injury. Finney (2) and Timbers (7) have attempted to determine some of the mechanical properties of potato tubers and report them in engineering terms. This type of approach is necessary for an understanding of the behavior of potatoes in handling and processing operations. The purpose of this study is to determine mechanical properties of potato tuber tissue and report them in terms that will be usable by people who do further work in this area. Because at least some cracks in potatoes are caused by failure in tension, and because no record of tests on potato tissue in tension was found, these tests were conducted on specimens of potato tuber in tension.     

Enhanced dormancy release and emergence from potato tubers after exposure to a controlled atmosphere

The North American potato industry requires an effective and environmentally-appropriate, dormancy-release methodology. The present study examined dormancy release and subsequent sprout emergence based on a modified, controlled-atmosphere (CA) approach using such environmentallycompatible gases as nitrogen, carbon dioxide and oxygen with or without trace amounts of ethylene (50 ppm). This paper is the first published report of a semi-automated, controlled-atmosphere system for dormancy release of potato tubers. The system allows computer-controlled gas application and analysis for up to four gas mixtures simultaneously. Low oxygen concentrations (< 10%) for 10 days in the presence of 10 to 60% carbon dioxide or a high carbon dioxide (60%)/oxygen (40%) treatment caused tuber breakdown regardless of cultivar. The most effective mixtures for enhanced dormancy release and sprout emergence were 20% CO₂/40% O₂ or 60% CO₂/18-20% O₂ and their effects were further enhanced by 50 ppm C₂H₄ (ethylene). In the presence of 50 ppm C₂H₄ the 20% CO2/40% O₂ mixture was comparable to bromoethane in effectiveness. Temperature and light exposure affected subsequent Russet Burbank tuber responses to CO₂/O₂/C₂H₄ gas mixtures.     

Calcium and magnesium distribution in potato tubers

The calcium present in the potato tuber is partially extractable by water and by dilute HCl. Either of these procedures may show higher calcium content than dry-ashing. A degree of fractionation of calcium can be obtained by extraction by 1N HCl, first at room temperature and then at 70 C. Wet-ashing yielded consistently higher results for calcium than dry ashing. Analysis for calcium and magnesium in potato pith and cortex were made by wet-ashing following total sampling. The cortex of the tuber was found to contain about half of the weight but from 2/3 to 4/5 of the tuber calcium. Cortex as used here indicates the tissue exterior to the vascular ring. Magnesium was distributed evenly on a tissue weight basis. Kennebec tubers grown in three different states differed substantially in calcium content but not in magnesium content. This difference was especially pronounced in the cortex. Dividing the pith into inner and outer regions revealed that calcium levels were nearly the same throughout the pith.     

Subcellular localisation of calcium in potato tubers

Summary Deposits, believed to contain calcium, were located in different cells of the potato tuber after using an antimonate procedure. In the starch-storage parenchyma of the medulla and cortex antimonate deposits were abundant within vacuoles, on the tonoplast, and to a lesser extent in cell walls. Phloem tissues contained a high concentration of deposits, mainly within companion cells and phloem parenchyma, consistent sites of deposition being mitochondria, plastids and tonoplasts. Deposits were abundant within vacuoles of cells of the xylem parenchyma. Within vessel elements deposits were limited to the surface of secondary wall thickenings. Antimonate deposits associated with the middle lamella of xylem parenchyma were rarely found. The results are discussed in relation to previous findings for potato tubers and for higher plant cells in general.