Lipoxygenases are ubiquitous enzymes in eukaryotes. In plants, lipoxygenases are involved in the synthesis of the hormone jasmonic acid that regulates plant responses to wounding and, in addition, is an inducer of tuberization in potato. We have isolated potato lipoxygenase cDNA clones. From their deduced amino acid sequences, three distinct classes are defined (Lox1, Lox2, and Lox3). They are encoded in gene families that display organ-specific expression, lox1 being expressed mostly in tubers and roots, lox2 in leaves, and lox3 in leaves and roots. Consistent with their organ-specific expression pattern, Lox1 expressed in bacteria preferentially uses as substrate linoleic acid, abundant in membrane lipids of tubers, whereas linolenic acid, prevalent in leaves, is the preferred substrate for the other two classes of lipoxygenase. Analyses on reaction products of the enzymes expressed in bacteria reveal that Lox1 primarily produces 9- hydroperoxides. In contrast, the jasmonic acid precursor, 13-hydroperoxylinolenic acid, is the major product of the action of Lox2 and Lox3 on linolenic acid. Upon wounding, the levels of Lox2 and Lox3 transcripts rise markedly in leaves. While Lox3 mRNA accumulation peaks as early as 30 min after wounding, Lox2 shows a steady increase over a 24-h time course, suggesting different roles for these lipoxygenase isoforms in the synthesis of the plant hormone jasmonic acid.

The effect of ozone treatment on the postharvest quality of strawberry was evaluated. Strawberry fruits (Fragaria x ananassa Duch. cv. Camarosa) were stored at 2 degrees C in an atmosphere containing ozone (0.35 ppm). After 3 days at 2 degrees C, fruits were moved to 20 degrees C to mimic retail conditions (shelf life). The changes in several quality parameters such as fungal decay, color, sugar and acids distribution, and aroma were evaluated during the strawberries' shelf life. Ozone treatment was ineffective in preventing fungal decay in strawberries after 4 days at 20 degrees C. Significant differences in sugars and ascorbic acid content were found in ozone-treated strawberries. At the end of cold storage, the vitamin C content of ozonated strawberries was 3 times that of control fruits. A detrimental effect of ozone treatment on strawberry aroma was observed, with a 40% reduced emission of volatile esters in ozonated fruits.

An analytical procedure to determine major sugars and organic acids, including vitamin C, in fruits was developed using a C18 Sep-Pak cleanup process and an ion exclusion HPLC column. Dual UV monitoring and refractive index were performed for detection. To attain optimal separation and quantitation, 0.0085N H2SO4 was used as the mobile phase and the column temperature was maintained at 23 °C. This procedure was compared to others for the individual quantitation of sugars, organic acids, and vitamin C. Recovery and reproducibility of this analytical procedure were quite acceptable for strawberry and four other common fruits, allowing the analysis of all the components using a single-injection HPLC analysis in <22 min. Keywords: Simultaneous analysis; high-performance liquid chromatography; sugars; organic acids; vitamin C; strawberry; fruits

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Furaneol, mesifurane, and furaneol glucoside contents during ripening of four strawberry varieties (Oso Grande, Chandler, Tudla, and I-101) have been analyzed. Patterns of furanone contents were similar for the four varieties, amounts increasing during ripening to reach the highest values at the overripe stage. However, furaneol and derivatives differed quantitatively among varieties. The amount of furaneol shown by Oso Grande at the overripe stage is the highest so far reported (37.05 μg/g fw). The highest content in mesifurane and furaneol glucoside was found in the I-101 variety, at the overripe stage, 23.5 and 13.2 μg/g fw, respectively. Results obtained in eight different varieties, at commercial maturity stage, also showed quantitative differences. Strawberries were stored at 1 °C for 2 days to simulate refrigerated transport and then kept for 7 days at 17 °C to simulate the shelf life period. At 17 °C, the amount of mesifurane and furaneol glucoside increased more than 50% with concomitant loss of furaneol. Keywords: Strawberry; flavor; furanones

Four strawberry (Fragaria ananassa × Duch.) varieties Oso Grande, Chandler, Tudla, and I-101) were studied in relation to their alcohol acyltransferase (AAT) activity. AAT activity profile during fruit development and ripening was determined for each variety. The highest AAT activity value corresponded to Oso Grande, which is also the variety showing the earliest maximum peak of AAT activity. The effect of passive modified atmosphere (MA) storage on strawberry AAT was also studied. An increase in AAT activity was found in strawberries stored under high CO2 (>30%). This higher level of AAT activity could be attributed to a detoxifying function of AAT that might be activated to eliminate ethanol generated by fermentation. Data obtained show a good correlation between AAT activity and flavor quality in strawberries. Keywords: Strawberry; flavor; ester biogenesis; alcohol acyltransferase

The enzymes lipoxygenase and hydroperoxide lyase have been identified in strawberry (Fragariax ananassa Duch.) var. Camarosa. Their subcellular localization, substrate preference, and product specificity were determined in mature strawberry fruits. The activity of both enzymes was located mainly in the microsomal fraction. Linolenic acid was the preferred substrate for strawberry lipoxygenase, forming 13- and 9-hydroperoxides of this acid in the proportion 70:30. The strawberry hydroperoxide lyase cleaves 13-hydroperoxide of linoleic (13% relative activity) and linolenic (100% relative activity) acids to form hexanal and (3Z)-hexenal, respectively. Both enzyme activities and endogenous content of volatile aldehydes formed by sequential action of lipoxygenase-hydroperoxide lyase were evaluated during strawberry development and ripening. A sequential enzymatic pathway for the formation of green odor compounds in strawberry is proposed.