Evolution of Strawberry Alcohol Acyltransferase Activity during Fruit Development and Storage

Abstract

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

Identification of the SAAT Gene Involved in Strawberry Flavor Biogenesis by Use of DNA Microarrays

“…SAAT gene expression is fruit specific, commencing at the white stage of fruit ripening, before any detectable formation of volatile esters in strawberry (cv Elsanta), and reaching maximal levels between turning and red stages. This result correlates with AAT activities reported for several commercial strawberry cultivars during fruit development (Perez et al, 1996). The expression pattern supports the proposition that the absence of ester formation in immature stages of fruit ripening results from a lack of ester-producing enzymes (Yamashita et al, 1977).…”

“…The K m value of SAAT for acetyl-CoA (104 M) was somewhat higher than that reported by Perez et al (1996) for a partially purified strawberry AAT (65 M) and by Harada et al (1985) for a banana AAT (50 M). The calculated K m value of SAAT for some alcohols (especially that for the best substrate, 1-octanol, or 5.7 mM) are comparable with the data for butanol (3 mM) reported by Perez et al (1996).…”

“…Esters identified by our analyses (1-butyl acetate, 1-hexyl acetate, and 1-octyl acetate) as the major volatiles emitted in the latter stages of fruit ripening were demonstrated to be genuine products of the recombinant SAAT enzyme. Perez et al (1993Perez et al ( , 1996 partially purified an AAT protein from strawberry (cv Chandler) fruits and tested AAT activity in several strawberry cultivars. The enzyme described by Perez et al showed broad substrate specificity, with a preference for the medium-chain alcohol hexanol and a lower activity with shorter chain alcohols (its activity with ethanol was 25% of that with hexanol).…”

“…We also included longer chain alcohols in our enzyme assays and found even greater activity with 1-heptanol and 1-octanol, but less with 1-nonanol and 1-decanol than with 1-hexanol. Perez et al (1996) reported only 14% activity with 3-hexen-1-ol relative to 1-hexanol; however, it is unclear whether they used the cis-or trans-isomer of 3-hexenol. The activity of the SAAT enzyme with cis-3-hexen-1-ol and with trans-3-hexen-1-ol was 46 and 14%, respectively, of that with 1-hexanol (Table 1).…”

“…BEAT has a high affinity for aromatic alcohols such as benzyl alcohol and cinnamyl alcohol. In melon, banana, and strawberry, AAT proteins have been investigated in crude fruit extracts (Harada et al, 1985;Ueda et al, 1992;Perez et al, 1993Perez et al, , 1996Olias et al, 1995). Ueda et al (1992) concluded that the alcohol moieties of the esters produced by crude strawberry fruit extracts reflected the alcohols predominantly synthesized in the fruit and that the acid moieties reflected the acyl-CoA specificity of the AAT enzyme.…”