W. J. Weston

Chlorophyll formation in potato tubers as influenced by gamma irradiation and by chemicals

SummaryGamma ray dosages of the order of magnitude of 10 kilorads inhibit the formation of chlorophyll in illuminated potato tubers. Increasing doses to 250 kilorads, while further decreasing chlorophyll formation, did not completely suppress it. Tubers treated with the lower doses retained their residual ability to develop chlorophyll upon illumination after a period of dark storage during which the non-irradiated controls lost a significant fraction of theirs. Of the three chemicals applied to the surface of potato tubers chloroisopropyl phenyl carbamate, O-methyl threonine, and 3-amino-1 2, 4-triazole, only the last named one inhibited the development of chlorophyll. Tubers obtained from plants whose leaves had been sprayed with maleic hydrazide developed as much chlorophyll as corresponding controls. Reflectance spectra of the exposed green surface of potato tubers suggest that carotenoid synthesis may be less sensitive to gamma irradiation than is the concomitant development of chlorophyll.

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.

Separation of hexose phosphates by paper electrophoresis in borate buffers

Abstract A survey of various buffers as agents for the paper ionophoresis of hexose phosphate esters and inorganic phosphate has revealed 0.2 M borate buffer at pH 9.5 as the most suitable for separation of the phosphate compounds into four distinct groups. Variations in molarity and pH of the borate can be utilized to separate the three reducing aldohexoses not resolved by the above conditions. These procedures have been used to identify tentatively a previously unknown compound in potatoes as fructose 1-phosphate. The advantages of paper electrophoresis as well as correlation between movement and relative charge density are discussed.

Biochemical effects of gamma radiation on potato tubers

Abstract A survey of biochemical changes which follow the irradiation of potato tubers in the lower decakilorad range has revealed that the following increase above those of unirradiated controls: ( a ) sugars, especially sucrose; ( b ) inorganic phosphate; ( c ) apparent nucleic acid content of ammonium sulfate-precipitable fraction; ( d ) lactic dehydrogenase activity of soluble protein fraction; ( e ) polyphenol oxidase induced chromogenicity of freshly sliced tuber surfaces. The following were found to decrease: ( a ) the rate of sprout growth; ( b ) resistance to microbial attacks; ( c ) apparent protein content of ammonium sulfate-precipitable fraction. There was little or no consistent effect on the pH of freshly prepared crude extracts nor on the inhibition by adenosine triphosphate of the above-mentioned chromogenicity. Ascorbic acid rose immediately after irradiation but decreased to control levels within 1 day. The level of the phosphorylase with respect to controls depended upon the post-irradiation temperature. The magnitude, duration, and, in some instances, the directions of these effects were found to be dependent upon the pre- and postirradiation history of the tubers as well as on the irradiation dosage. The radiobiological basis for some of these effects is discussed. The apparent postirradiation increase in some enzyme-linked reactions has been interpreted tentatively in terms of a hypothesis involving the possible differential radiosensitivity of the mechanism for synthesis of individual enzyme proteins as compared with the sensitivity of the mechanism for their degradation.

Effect of processing variables on potato granule production

SummaryThe use of unpeeled potatoes was observed to increase product yield, darken color, and alter flavor of potato granules. Hot mash-mixing was the most successful mashing method developed for our equipment. Rapidly cooling the moist mixture immediately after mashing benefited the process. Mixing before and after tempering increased the yield of fine granules with no alteration of quality. Tempering reduced mechanical damage and improved quality of product. Precook heating and cooking procedures must be properly controlled, since they were found to affect the color, flavor, and texture of the final product. Over- or undercooking impaired product quality. The addition of sulfite was found necessary for good color control. Of the varieties used, those of higher specific gravity gave increased yield and better potato granules.

Abstracts of papers presented at Annual Meeting

HEILIGMAN, F., AND I. R. W A G N E R EFFECTS OF CHLORO-IPC ON SPROUTING AND LOSSES IN WHITE POTATOES DURING STORAGE The use of 3-Chloro-lsopropyl-N-Phenyl Carbamate (Chloro-IPC) reduced losses in white potatoes stored at 55, 72, and 85 ° F. when compared to untreated controls. The material was effective when used as a dip, as a spray, or when incorporated in water emulsion potato wax. The treatment controlled sprouting and reduced weight losses during storage. There is some evidence that the material may have some indirect effect in controlling losses caused by microbial decay. H O Y M A N , WM. G. COMPARATIVE REACTIONS OF ATTACHED AND DETACHED LEAVES TO P H Y T O P H T H O R A I N F E S T A N S Thirty potted potato selections 6 to 12 inches in height and detached leaves from them were simultaneously inoculated with zoospores from a culture of race 0. The inoculations were made in a plastic-covered chamber at 70 ° F. and 100 per cent relative humidity. The reaction of each of the 30 selections was recorded as soon as symptoms appeared and the final reading was made the eighth day following inoculation. Sporulation occurred on attached and detached leaves of 8 selections. Sporulation also occurred on the attached leaves of one selection, whereas the reaction of the detached leaf consisted of large lesions. The symptoms on both types of leaves of the 3 selections consisted of necrotic spotting. The attached leaves of 4 selections showed no symptoms, whereas the detached leaves showed definite necrotic spotting. No reaction was evident on leaves of 14 selections.