Volatile ester molecules are important contributors to the perception of fruit taste. Biosynthesis of volatile compounds occurs via several biochemical pathways. Ongoing studies have concentrated on alcohol acetyl transferase, the terminal step in the acetate ester synthesis pathway. Our studies on volatile biosynthesis in apples have revealed several interesting phenomena. First, the nature and amount of volatile compounds are cultivarand strain-dependent. Studies with `Delicious' show a relationship between amount of peel coloration and flavor volatile content of tissue. Second, it is possible to manipulate the preharvest growing environment to influence the content of some volatiles in the fruit. Third, generation of volatiles is closely linked to the onset of climacteric ripening. Other experiments show the response of apples to different storage conditions with regard to volatile ester synthesis. In some cultivars softening apparently provides ester precursor molecules, leading us to speculate that there are glycosidically bound intermediates that are liberated by the action of cell-wall degradation.

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Total starch and amylose (AM) concentration and a starch index (SI) were determined in 'Fuji' apple (Malus domestica Borkh.) fruit from weekly harvests in 1990 and 1991. As apples matured, SI scores increased and total starch and amylose content decreased. The percentage of AM in the total starch decreased as the apples matured. Because KI solutions interact efficiently only with AM, the SI is less reliable in representing total starch during later stages of 'Fuji' apple maturation.

Effects of jasmonates on production of aroma volatile compounds by 'Tsugaru' apples IMalus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.I at harvest, and by Delicious' apples after harvest were examined. Among volatiles classified as alcohols, esters, ketones, aldehydes, acetic acid, and a-farnesene, esters were the most prevalent compounds, followed by alcohols. Jasmonate treatment at pre-climacteric stage increased the production of esters (butyl propanoate, butyl butyrate, and propyl butyrate) and of anthocyanin. In addition, jasmonate treatment stimulated 1-aminocyclopropane-1-carboxylate oxidase 1 (ACO 1) mRNA transcript and thylene production at 3 days after treatment. This result suggests that jasmonates may influence ACC oxidase activity. The impact of jasmonate application after harvest on volatile production differed with cultivar. The combination of ethephon with jasmonates reduced volatile production by 'Delicious' compared with ethephon only. The effect of jasmonates on volatile production was related to the effect of jasmonates on internal ethylene concentration. The results show that the effect of jasmonates on aroma volatiles in apples may be mediated by ethylene. Furthermore, the effect of jasmonates on aroma volatiles may depend on the fruit development stage when treated with jasmonates.

Several strains of Fuji apples were harvested weekly from September through October in 1990 and 1991, and evaluated for maturation and quality after 1 and 7 days at 20 °C following harvest and storage in atmospheres of 0.5%, 1.0%, 2.0% O2 and air. Results showed that Fuji apples have very low ethylene production rates and little firmness loss during maturation. A change in the postharvest respiration pattern preceded the increase ethylene synthesis. Oxygen concentration during storage directly affected apple respiration rate after removal from storage. Ethylene production rates and internal ethylene concentrations indicated that the apples were still in the preclimacteric stage after 7 to 9 months storage at 0.5%, 1.0%, or 2% O2. Fuji apples develop watercore and tend to have a particular type of corebrowing during maturation on the tree, or during and after storage. The cause is unknown.