CHANGES IN CELL WALL GALACTOSYL AND SOLUBLE GALACTOSE CONTENT IN TOMATO FRUIT STORED IN LOW OXYGEN ATMOSPHERE

Authors: KIM, JONGKEE - CHUNGANG UNIVERSITY; SOLOMOS, THEO - UNIVERSITY OF MARYLAND; Gross, Kenneth

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Fruit softening leads to increased susceptibility of fruit to fungal decay as well as decreased quality and storage life. Decreased quality can make fresh fruits and vegetables more susceptible to growth of microorganisms and therefore more likely to have food safety-related problems. In order to limit the roughly 25 percent loss of all fruits and vegetables that occur in the U.S. due to this postharvest deterioration and in order to help maintain a safe food supply, we have studied the biochemical mechanisms involved in the fruit softening process in an effort to modify plants genetically so that they produce fruit that resist the softening process. The present study has shown that some of the processes involved in fruit softening are under a different control that other general ethylene-related fruit ripening processes. This is important because it will help us to determine how the genes that code for enzyme(s) which break down the cell wall are regulated. The cell wall is a sugar envelope surrounding each fruit cell, and it's breakdown during ripening leads to a loss of structural integrity and thus fruit firmness. This information will be used by us and other scientists in an attempt to limit the expression of the gene(s) coding for these enzymes during ripening, to slow cell wall degradation and fruit softening.

Technical Abstract: Mature green tomato fruit were stored in atmospheres of low oxygen (3.05 kPa; 3 percent) or air (control) at 20 degrees C. Their subsequent ripening behavior was compared in an effort to evaluate the temporal relationship among ethylene production, respiration, cell wall galactosyl residue loss and the increase in free galactose that occurs during ripening. An increase in ethylene evolution and respiration, red color development, and loss in fruit firmness were delayed in fruit held in low oxygen compared to control fruit held in air which showed normal ripening-related changes. Both the ripening-related decrease in cell wall galactosyl residues and the increase in soluble galactose were suppressed for 9 days in fruit held in low oxygen. However, after 9 days storage, these processes did commence and changed significantly by 13 days of storage. These results either suggest that only relatively low baseline levels of ethylene were necessary for it to exert its effect on these cell wall-related fruit ripening processes to occur or that the cell wall-related changes observed were ethylene-independent. It is clear that the levels of ethylene generally produced during the respiratory climacteric are not necessary to begin the processes associated with cell wall modification, such as the large net loss of galactosyl residues from the wall during tomato fruit ripening.