苹果果实香气产生过程中氨基酸和脂肪酸含量及一些相关酶活性的变化

Changes in Amino Acid and Fatty Acid Contents as well as Acitivity of Some Related Enzymes in Apple Fruit During Aroma Production

研究了苹果果实成熟期间香气和乙烯的产生动态,以及游离氨基酸、游离脂肪酸含量和脂氧合酶(LOX)、醇-酰基转移酶(AAT)活性的变化。结果表明,果实香气物质是随着乙烯释放的增加而产生和增加的。在此过程中,异亮氨酸大量积累。游离脂肪酸在果实香气很少时呈增加趋势;随着香气产生的增多而迅速下降;乙烯高峰过后又有增加。脂氧合酶活性随着果实成熟而提高,其活性在乙烯释放达到高峰时达到最大值,之后迅速下降。醇-酰基转移酶活性在果实开始产生香气时迅速增加,之后保持较高活性。

Aroma volatiles from apple （Malus domestica Borkh. var. Starkrimson） fruit at different stages of maturity were collected by solid adsorbent-Tenax-GC and determined by thermodesorption and GC-MS. Production of propyl acetate, butyl acetate, ethyl 2-methylbutanoate and total ester volatiles and changes in concentration of the precursors of aroma biosynthsis- free amino acids and fatty acids and activities of lipoxygenases （LOX） and alcohol acetyltransferase （AAT） in apple fruits during ripening were studied. The results showed that propyl acetate and total esters were very low when the endogenous ethylene formation of the fruit was very low. At the stage of the increase in ethylene production, the rate of formation of propyl acetate and total esters increased. Butyl acetate appeared at the beginning of ethylene rise and increased thereafter. Ethyl 2-methylbutanoate was produced at the beginning of climacteric stage and then increased sharply （Fig. 1）. These facts suggest that the aroma production is closely related to ethylene production. Among the 14 free amino acids detected in fruit, isoleucine which is considered to be the biosynthetic precursor of some branched chain esters showed a great increase during fruit ripening while the others decreased or remained stable （Table 1）. The accumulation of isoleucine suggested that isoleucine supply in fruit may not limit the biosynthesis of esters with branched chain alkyl groups. Concentrations of free fatty acids such as palmitic, linolenic, oleic, linoleic, stearic acids increased before the increase of aroma production, decreased with the increase of aroma production and showed an increase at postclimacteric stages （Fig.2）. LOX activity increased at climacteric stages and declined rapidly thereafter. AAT activity increased sharply at the early stage of fruit maturity when the aroma was very low and remained at a stable high level during fruit ripening （Fig.3） indicating that the AAT activity is not the limiting factor for aroma formation in apple fruit.