Effect of a high-temperature stress on endo-beta-mannanase and alpha and beta galactosidase activities during tomato fruit ripening

G.O. SOZZI; O. CASCONE; A.A. FRASCHINA

POSTHARVEST BIOLOGY AND TECHNOLOGY

ELSEVIER SCIENCE BV

Año: 1996 vol. 9 p. 49 - 63

0925-5214

Tomato fruit show physiological disorders when exposed to temperatures at or above 30°C.It has been suggested that the alpha and B-galactosidases (alpha and B-Ga1), as well as the endo-B-mannanase could play roles during fruit ripening. Their pattern of activities was followed in detached tomato fruit, and the degree of inhibition of the activity at high temperatures was evaluated. The potential resumption of the enzyme activity when fruits were transferred to a room-temperature environment was also studied. Mature-green fruits were incubated at: (a) 36°C for 2 days, (b) 40°C for 2 days, or (c) 40°C for 2 days + 36°C for another 2 days. After heat treatments, fruits were transferred to a 21°C dark environment. Control fruit were stored at 2l°C. In the control fruit, activity was higher for alpha-Gal than for B-Gal and revealed slightly increasing patterns toward the red-ripe stage. Endo-B-mannanase activity was not detected in mature-green tomatoes but appeared at the breaker stage and rose rapidly, reaching constant values at the red-ripe stage. The firmness and enzymatic activities of fruits initially treated at 36°C for 2 days were similar to those of the control group. Galactosidase activity decreased in tomatoes incubated at 40°C for 2 days; and in those whose heat treatment was extended another 2 days at 36°C the alpha and B-Gal reached a minimum of 1/5 and 1/25, respectively, of the initial activity on the fourth day. The activity of the endo-B-mannanase could be detected only 6 days after the fruit had been transferred to a 21°C environment and increased slowly up to 24% of that attained by the control group. alpha-Gal showed a low rate of recovery but B-Gal activity recovered after 16 days at 21°C. Results could be associated with an active role of these enzymes on the fruit softening process.