Mesa Redonda: Discusao Raúl Bueno; Rodolfo A. Franconi; Francisco Caetano Lopes Jr ...
Revista de crítica literaria latinoamericana,
01/1994, Letnik:
20, Številka:
40
Journal Article
ABSTRACT
The aim of this work was to study the role of cell wall and ethylene related enzymes to papaya fruit firmness. Irradiation treatment was used as an imposed stress to cause changes in ...firmness. Physiologically mature papaya fruits were irradiated (500 Gy) and allowed to ripen at 22C and 90% RH. Polygalacturo‐nase (PG), pectinmethylesterase (PME), βgalactosidase, cellulose and 1‐aminocyclopropane‐1‐carboxylate oxidase (ACC‐oxidase) activities were followed during ripening and correlated to changes in firmness, skin and pulp color, respiration and ethylene production. The firmness of irradiated fruits was retained at least 2 days longer than in normal fruits and also had a slower rate of softening. Total soluble solids (d̀Brix), cellulase activity and ethylene production were not altered by irradiation treatment. The activity patterns of PG, PME and β‐galactosidase were related to pulp softening and affected by irradiation. ACC‐oxidase activity was influenced by irradiation treatment, but its changes were not temporally related to those in firmness. It was concluded that irradiation had no direct effect on firmness but it acted by altering the ripening induced synthesis of cell wall enzymes, mainly PME.
Banana pulp, irrespective of the degree of ripening, contained soluble and cell wall-bound forms of acid α-glucosidases (SAAG and BAAG). BAAG was released with a neutral buffer containing 0.2-2 M ...NaCI after extracting of SAAG with a salt-free buffer. From the same bunch of ripe yellow bananas, SAAG and BAAG were purified at 732-fold and 264-fold, respectively, using ConASepharose and Sephadex G-150 gel column chromatographies. The molecular weights of SAAG and BAAG were 70, 000 and 90, 000, respectively, by gel filtration. These enzymes were typical maltases that required maltose (G2) and malto-oligosaccharides (G3-G7) as substrates, but not isomaltose, treharose, sucrose, pullulan, glycogen, or soluble starch. The Vmax/Km ratios (apparent hydrolytic efficiencies) of SAAG and BAAG toward G5-G7 were 89-112 and 14-52%, respectively, with the ratio toward maltose being 100%. As for ripe yellow banana where cell wall or amy loplastic membrane has not been maintained, it is speculated that BAAG could access starch and its hydrolytic products and would share in starch degradation in collaboration with amylases and SAAG.
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