Redhaven peaches treated with gibberellic acid (GA, 100 ppm) and ethephon (75 and 150 ppm) 21 and 46 days after full bloom were evaluated for enzymatic browning in the ripe fruit. Treated fruit had less browning than untreated fruit, and fruit treated 46 days after bloom had less browning than fruit treated 21 days after bloom. Fruit pH and fresh weight were affected by treatment, but o-diphenol content and polyphenoloxidase (PPO) activity were not. Forward stepwise multiple regression on browning showed that 81% of the variation in browning was explained by differences in treatment, treatment application date, o-diphenol content, PPO activity, and fresh weight.
Twenty-one polyphenolic compounds from Redhaven peaches were separated by two-dimentional thin layer chromatography. Eight were oxidized by PPO, and were tentatively identified as four chlorogenic acid isomers, three leucoanthocyanidins, and catechin. No differences in qualitative distributions of phenolic compounds were observed in peaches receiving the different treatments.
Polyacrylamide disc gel electrophoresis of peach PPO preparations showed the presence of up to eleven isozymes with activity toward catechol. The isozymes had different substrate specificities and were present in different amounts. PPO from peaches treated 21 days after bloom appeared to have a catechol reactive isozyme not present in untreated peaches or peaches treated 46 days after bloom. One PPO isozyme from peaches treated 46 days after bloom with 150 ppm ethephon appeared to have decreased substrate specificity toward pyrogallol.
Crude PPO preparations from untreated fruit and fruit receiving the 46-day treatments oxidized o-dihydroxyphenolic compounds only. The relative activities of the PPO preparations with these compounds varied with treatment. The same PPO preparations exhibited two pH optima; pH 4.4 and 6.2 for untreated and GA treated peaches (46-day treatment), and pH 4.4 and 6.6 for peaches treated with ethephon (75 or 150 ppm, 46-day treatment). PPO from the treated peaches had a lower proportion of total activity at pH 4.4 than PPO from untreated peaches. The Michaelis constant for PPO from untreated peaches was 9.1 x 10⁻³M. / Land and Food Systems, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/20889 |
| Date | January 1978 |
| Creators | Paulson, Allan Thomas |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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