The accelerated freeze-drying of potatoes

Summary During the past few years a new method of freeze-drying foodstuffs has been developed in Britain which is applicable to a very wide range of commodities. It can be used for the production of potatoes in the form of strips 12.5·12.5 mm sections which, after soaking in hot water for about 5 minutes, can be fried to give potato “chips”. In the dehydration process the trimmed potatoes are cut into strips of these cross section dimensions, washed free of surface starch, scalded in steam for 4 minutes, frozen, and freeze-dried by a development of the Vacuum Contact Plate technique. A freeze-dried meat and vegetable stew, incorporating potato, has also been developed, as well as an excellent mashed potato.

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Zusammenfassung In den letzten Jahren wurde in Grossbritannien eine neue Methode der Trocknung von Lebensmitteln mit dem Gefrierverfahren eingeführt, welche man bei sehr vielen Konsumwaren anwenden kann. Das Verfahren kann für die Zurichtung von Kartoffelst?bchen im Querschnitt von 12.5·12.5 mm angewandt werden, aus welchen man nach 5 minütigem Einweichen in heisses Wasser als Kartoffelchips, d.h. Pommes frites, backen kann. Im Laufe des Dehydrationsprozesses werden die zugerichteten Kartoffeln in St?behen mit obigem Diameter geschnitten, die anhaftende St?rke abgewaschen, die St?behen 4 Minuten lang ged?mpft, gefroren und mit dem “Vacuum Contact Plate”-Verfahren der Gefriertrocknung unterzogen. Mit dem Gefrier-Trocknungsverfahren hat man auch ein Gericht aus Fleisch und Gemüse mit Kartoffeln hergestellt, sowie ein ausgezeichnetes Kartoffelpürree.

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Résumé Ces dernières années, une nouvelle méthode de séchage par le gel de produits alimentaires a été mise au point en Grande-Bretagne. Cette méthode peut être utilisée pour les articles les plus divers, par exemple pour la production de pommes de terre sous forme de bátonnets d'une section de 12.5·12.5 mm qui, après avoir trempé dans de l'eau bouillante pendant 5 minutes environ, peuvent être frits pour former des pommes de terre frites. Dans le processus de déshydratation, les pommes de terre préparées sont coupées en bátonnets des dimensions indiquées, leur surface est débarrassée de la fécule par lavage, puis les bátonnets sont traités à la vapeur pendant 4 minutes, gelés et séchés par le gel selon un nouveau procédé de la Vacuum Contact Plate technique. On a également mis au point la production d'un repas déshydraté composé de viande, de légumes et de pommes de terre, ainsi que celle d'une excellente purée de pommes de terre.

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Paper read to the Section “Utilization” at the 1st Triennial Conference of the European Association for Potato Research, Brunswick-V?lkenrode, on 14th September, 1960.     

Leaching of solutes and sloughing of potato tuber tissue

Thin slices of tissue from low (1.075–1.078 and high (1.092–1.094) specific gravity tubers were soaked in distilled water (100g/250ml) for 0, 1, 2, 3, 4, and 6 hours. Following the soak periods, the soak water and remaining tissues were separated and analyzed. Analyses of the soak water included pH, electrical conductivity, total solids, K, P and citric acid. The tissue analyses included total ash, alkalinity of ash, Ca, Mg, total N and phytate P. Other tissue samples were soaked the same periods of time and used to evaluate the amount of sloughing that occurred during cooking. All constituents studied diffused into the water during the soak periods. The greatest loss from the slices occurred in the first 2 to 3 hours and were similar for both specific gravity groups. After 6 hours the average amounts of material in the soak water were: total solids — 23%, P — 68%, phytate P —55%, K — 71%, total ash — 62%, total nitrogen — 56%, Ca — 35% and Mg —50%. Citric acid diffused into the soak water during the first 3 hours and the amount in the water then decreased. This apparent change may be due to metabolism of the acid. The sloughing of tissue decreased with the length of the soak period. The decrease in sloughing was highly correlated (P<1 %) with the length of the soak period, increases in electrical conductivity of the soak water, and with the leaching of all constituents measured.     

The cause of deep-pitted scab of potatoes

By use of a tyrosine-casinate-nitrate medium,Streptomyces atroolivaceous, S. cinerochromogenes, S. corchorusii, S. diastatochromogenes, S. lydicus, S. malachiticus, and three unidentifiedStreptomyces spp. were isolated from deep-pitted scab lesions on potato cultivars Green Mountain, Red Pontiac, Russet Burbank, and Saco. Over 90% of the deep-pitted lesions contained one or more of theseStreptomyces spp., butS. scabies the cause of shallow scab was not isolated. Isolates ofStreptomyces spp. were also consistently isolated from aseptically excised non-necrotic tissue near the edge of lesions. TheseStreptomyces spp. appeared to be the primary colonizers of this tissue. Alternaria spp.,Fusarium spp.,Penicillium spp.,Rhizopus spp.,Trichoderma spp., and several unidentified non-sporulating fungi as well asBacillus spp.,Pseudomonas spp., andMicrococcus spp. were isolated from deep-pitted scab lesions. Fungal and bacterial isolates varied from one scab lesion to another and except for anAlternaria sp., were not pathogenic. Most of theStreptomyces spp. isolates used to infest heat pasteurized field soil caused deep and/or shallow scab on tubers of the potato cultivar Kennebec in greenhouse and outdoor plantings. Re-isolations from resulting scab lesions yieldedStreptomyces spp. similar in morphology to those used as inoculum. We concluded that a number ofStreptomyces spp. probably includingS. scabies (ATCC 3352 = S.griseus) may cause deep and shallow scab.     

The storage of true seeds of potatoes

Summary Seeds stored in sealed glass tubes and kept at 5°C have retained their viability for 15 years. The advantages of seed storage for maintaining potato collections are discussed.     

The profitability of continuous potatoes versus rotations including potatoes and other cash crops: I

In a continuing experiment, at two locations in Ontario, continuous Norchip and Kennebec potatoes are being compared for profitability with rotations including potatoes followed by malting barley or grain corn or soybeans. At the end of the first seven-year cycle Kennebec may have started to decline in yield in continuous production, but continuous potatoes remains the most profitable cropping sequence.     

The effect of storage conditions on chemical content of raw potatoes and texture of cooked potatoes

Summary Texture of boiled potato tubers (cv. Beate) was studied over several months of storage at either 4 or 8 °C, in relation to dry matter content, non-starch polysaccharides (NSP), methyl groups, glucose, starch and amylose. The dry matter content decreased significantly during storage at 4 °C, but increased at 8 °C due to evaporation. The insoluble NSP contained rhamnose, galactose, arabinose, xylose, mannose, fucose and glucose; the first three sugars decreased significantly after the first 7 weeks of storage. Fracturability and percent compression before break increased during storage at 8 °C, particularly percent compression after 15 weeks. The change in fracturability could partly be explained (R²=43.4%) by the content of the NSP and the increase in percent compression by dry matter (R²=91.8%). Changes in texture during storage at 4 °C, however, were not striking, and could not be explained by changes in the potato components that were analysed.