Submitted to: Analytical Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 11, 1995
Publication Date: N/A
Interpretive Summary: The natural process of tissue aging (senescence), water loss, and injury induced by refrigerated storage are problems that reduce quality and shorten the shelflife of fresh tomatoes and bell peppers. A critical aspect of each of these problems is a loss of integrity of two cell membranes: one that controls the flow of water and nutrients in and out of fa plant cell, and one that segregates harmful wastes and enzymes from the rest of the cell. It has recently been shown that a group of fats called cerebrosides (CBs) are often major structural components of these two membranes, and because of their unique properties CBs are thought to be involved in the injury of plant tissues caused by exposure to low temperatures or too little water. This study was conducted to determine how much and what kind of CBs are present in tomato and bell pepper tissue, and whether changes in the type and amount of CBs occur with ripening of these fruits. This information will help other plant scientists determine the importance of CBs in maintaining membrane integrity during the postharvest life of fresh fruits and vegetables. Ultimately this research will be useful in determining ways to genetically alter the pattern of CB synthesis in commodities, and to thereby reduce postharvest chilling injury and water loss.
Technical Abstract: Cerebrosides (CBs) isolated from total pericarp lipids of green and red bell pepper and tomato fruits by column and thin-layer chromatography were separated by a new C6 reverse-phase HPLC method into six or more components. HPLC profiles were similar for the two fruits and changed little with ripening. CB 1 was the major peak, CB 2 was found only in bell pepper, and CBs 4, 5 and 6 were more abundant in pepper than in tomato. Total CBs and pooled HPLC fractions were cleaved by HC1 methanolysis for analysis of fatty acid (FA), aphingoid (SP) and sugar moieties. FAs of tomato and bell pepper CBs were more than 95 percent saturated 2-hydroxy. In CBs 1 and 2, 2-hydroxy 16:0 was about 98 percent of the total FAs, whereas 2-hydroxy 22:0, 23:0, and 24:0 predominated in CBs 4, 5, and 6. SPs were derivatized to their peracetates for analysis by HPLC, GLC and GC-MS. The SPs of CB 1 and CB 2 were identified as isomers of 4,8-sphingadienine and 8-sphingenine, respectively. The SPs of CBs 4, 5, and 6 were identified as isomers of 4-hydroxy-8-sphingenine. Glucose was the only sugar in bell pepper and tomato CBs. The major CB in both fruits was tentatively identified as 1-O-B-glucosyl-N-(2'-hydroxypalmitoyl)-4-trans-8-cis-sphingadienine.