G. B. Nadkarni

The involvement of phenolics and phytoalexins in resistance of potato to soft rot

SummaryPhenolics, for example chlorogenic, caffeic and ferulic acid, and phytoalexins, such as rishitin and phytuberin, were identified in potato tubers cv. Kufri Chandramukhi. The tissue of healthy tubers contained no detectable phytoalexins but did contain phenolics. The levels of these compounds were correlated with soft rot development. The rotting tissue either was free of these groups of compounds or had low concentrations. The wound periderm formed as a result of recovery from injury and infection contained high levels of the compounds. Much higher concentrations were detected at lower storage temperatures when oxygen supply was adequate. Antibacterial properties of the phenolics identified were tested againstErwinia carotovora which was inhibited by chlorogenic, caffeic and ferulic acids. The three phenolics were more effective together, in proportions in which they occurred in wound periderm, than individually. It was observed that none of these phenolics could inhibit pectolytic enzymes ofE. carotovora.

Coimmobilization of D-amino acid oxidase and catalase by entrapment ofTrigonopsis variabilis in radiation polymerised Polyacrylamide beads

Trigonopsis variabilis induced for D-amino acid oxidase and catalase was immobilized by entrapment in Polyacrylamide beads obtained by radiation polymerisation. Permeabilization of the cells was found to be essential for optimal activity of the enzymes in free cells. However, the process of entrapment itself was found to eliminate the permeability barrier of cells immobilized in Polyacrylamide. The two enzymes exhibited a differential response on Polyacrylamide entrapment. Thus, D-amino acid oxidase activity was stabilized to heat inactivation whereas catalase in the same cells showed a destabilization on entrapment in Polyacrylamide. The coimmobilized enzyme preparation showed an operational half life of 7–9 days after which the D-amino acid oxidase activity remained stable at a value 35–40% of that of the initial activity for a study period of 3 weeks. Coimmobilization of MnO2 was not effective in enhancing the operational life of the enzyme preparation.

Inhibition of aflatoxin-producing fungi by ethyl acetate extracts from gamma-irradiated potatoes

SummaryEthyl acetate extracts prepared from potatoes exposed to a sprout-inhibiting dose (10 krad) of gamma-irradiation were tested for inhibitory activity towardsAspergillus flavus andA. parasiticus. The treatment did not adversely affect the naturally occurring compounds which inhibit growth of these aflatoxin-producing fungi and which were still evident 4 weeks after irradiation following storage at 15°C.

Activity of radiation degradation products of vitamins A and E to haemolyse erythrocyte

Exposure of vitamin A acetate in freely dissolved state to γ-radiationin vitro caused a dose dependent degradation accompanied by the formation of new products. The radiation degradation products were separated by chromatography using step gradient elution. The parent molecule, vitamin A acetate, induced negligible haemolysis of erythrocytes. In contrast, the polar products formed by irradiation were found to be potent haemolysing agents. A highly polar product, eluted with methanol revealed maximum haemolytic activity. Acetylation of these products resulted in loss of their haemolytic properties. Similarly, vitamin E acetate, a known stabilizer of the biomembranes, after irradiation yielded products which caused haemolysis of erythrocytes. It was demonstrated that irradiation introduces hydroxyl groups which impart haemolytic properties to the radiation degradation products of vitamin A