Analysis On Volatile Aroma Constituent And Its Formation Characteristics Of Pears

As an important quality trait of fruit, aroma was paid more and more attention recently. Fruit aroma of different cultivars was greatly different, so the studies on aroma constituent character and biosynthesis mechanism of different pear cultivars were very important for improving fruits aroma. Fruit aroma was constituted of a great deal of volatile aroma. So constituent of volatile aroma of different cultivars were studied. On the basis, Pyrus ussuriensis cv ’Nanguoli’ and Pyrus bretschneideri cv ’Dangshansuli’ were used as materials for their obviously different aroma characters, and their volatile aroma formation characterisitics were studied. Main results were as followings:1. Volatile aroma of pears included esters, alcohols, aldehydes, ketones, hydrocarbons and others compounds, the difference of volatile aroma constituent formed the diversity of aroma characters of different cultivars. Among twelve pear cultivars in the study,’Red A’jou’,’Wujiuxiang’,’Nanguoli’ and ’Fuanjianba’were cultivars having great fruity note, ’Kuerlexiangli’was a cultivar having fruity and sweet note,’Housui’,’Aikansui’,’Zhongli 1’,’Cuiguan’ and ’Dangshansuli’ were all cultivars having light gramineous note.’Yali’ was a cultivar having light fruity note.’Xinli 7’ has similar aroma character to ’Kuerlexiangli’, but its aroma was lighter than that of ’Kuerlexiangli’.2. According to volatile aroma constituente,33 P. ussariensis cultivars could be divided into four groups by principal components analysis (PCA). The first group contained cultivars with a high concentration of esters and a low concentration of hydrocarbons, including ’Reli’,’Jinxiang’,’Hongbalixiang’,’Baibalixiang ’and’ Fuwuxiang’. The second group contained cultivars with a high concentration of hydrocarbons and a low concentration of esters, including’Qiuxiang’,’Fuanjianba’,’Longxiang1,’Guanhongxiao’, ’Shanli24’ and ’Wuxiangli’. The third group contained cultivars ’Shatangli’ and ’Manyuanxiang’, which had a high concentration of aldehydes. All the other cultivars formed the fourth group.3. Volatile aroma and correlative metabolite of P. ussuriensis cv ’Nanguoli’ and P.bretschneideri cv’Dangshansuli’fruits during development and maturity were studied, results showed that the content of volatile aroma were increased with the fruits development at the earlier stage. Near maturity, the content of volatile aroma drasticly increased, and the characteristic aroma came into being, while the development rates of fruits slowed at this stage. The content of volatile aroma of maturited ’Nanguoli’ fruits was was about ten-folds to that of’Dangshansuli’. The change characters of glucose and fructose contents were similar to that of volatile aroma during fruits development and maturity. The contents of amino acids, organic acids and polyphenols were decreased during fruit development and maturity, and the contents were lowest at maturity. LA contents were decreased in early development period, while increased at the later development stage. LeA contents of fruits decreased with the fruit development and maturity. Different change characters of LeA contents between cultivars were detected, LeA contents steadily decreased in ’Nanguoli’, while two significant decreased stages were occurred in’Dangshansuli’. There was great difference of contents of metabolite between cultivars, the contents of metabolite were higher in ’Nanguoli’ than that in ’Dangshansli’, except for amino acids. According to change character of the metabolite contents, stages of fruit inflation and maturity were considered to two active metabolic stages. Correlation of metabolite and volatile aroma elicited that volatile aroma were mainly translated from fat acids, followed by amino acids. At the early development periods of fruit, key enzymes of volatile aroma biosynthesis showed different activity and change character, but the change character of them were same at maturity. The higher activities of LOX, HPL and ADH were detected in mature fruits of ’Nanguoli’than’Dangshansuli’.4. After feeding on LA and LeA, contents of volatile esters increased in ’Dangshansuli’ and ’Nanguoli’ fruits. The contents of esters in’Dangshansuli’feeding on LA and LeA, increased 214.0 ng/g and 88.8 ng/g, which were 2.08 and 1.45 folds to control. The content of esters in ’Nanguoli’ feeding on LA and LeA, increased 440.3 ng/g and 503.3 ng/g, which were 1.66 and 1.67 folds to control. The main increased volatile aroma in’Dangshansuli’ and ’Nanguoli’ fruits feeding on hexanol was hexyl ecetate, followed by hexyl hexanate. The main increased volatile aroma in ’Dangshansuli’ and ’Nanguoli’ fruits feeding on hexanal were hexyl ecetate, acetyl hexanate and hexyl hexanate. The content of acetyl hexanate was about two-thirds of hexyl ecetate in ’Dangshansuli’, but the content of acetyl hexanate and hexyl ecetate were same in ’Nanguoli’. In a word, the content of esters in pear fruits feeding on metabolic precursors were all increased. The effects of LA and LeA on esters biosynthesis of’Nanguoli’fruits were higher than’Dangshansuli’. The effects of hexanol and hexanal on ester biosynthesis of’Dangshansuli’were higher than ’Nanguoli’.5. Content of esters, especially acetyl ester of ’Nanguoli’ fruits were enhanced by calcium treatment, however the contents of alcohols, aldehyes and hydrocarbons were scarcely affected. The increased relative content of esters endowed ’Nanguoli’ with greater fruity note. The effect of calcium treatments on volatile aroma biosynthesis in ’Dangshansuli’ was so little that the effect of calcium on flavor was not detected. The physiology of volatile aroma biosynthesis affected by calcium were researched and the results showed that the activities of p-glucosidase were activated significantly by calcium that the bound aroma of fruits hydrolyzed, then released from fruits or transformed to other volatile esters. The activity of EP in the flesh of’Dangshansuli’was significantly affected by calcium, however the volatile aroma originated from amino acids were affected little. The activities of ADH and PDC were activated and the content of aldehyde was increased in ’Nanguoli’ fruits treated by calcium. The HPL activity in ’Dangshansuli’ fruits was activated by calcium, too. The changes of enzyme activity and precursors led to increase of esters and total volatile aroma content. Contents of esters in flesh and peel of ’Nanguoli’ increased 922.8 ng/g and 2165.1 ng/g, and the total volatile aroma content increased 184.80% and 133.39%. The contents of aldehyes in ’Dangshansuli’ flesh and peel increased 33.02% and 11.35% treated by calcium.6. For ’Nanguoli’ fruits harvested at different mature stages, constitutes of volatile aroma were greatly different, especially for characteristic aroma. Eearlier harvested fruits had characteristic aroma including ethyl butyrate、2-methyl-ethyl butyrate、ethyl hexanate、 hexyl acetate、hexanal and decanal, however the normal harvested fruits had butyl acetate and 2-hexenal as characteristic aroma besides these. Normal harvest fruits had great fruity note, and the earlier harvest fruits had little grassy note beside fruity note. Effect of methyl jasmonate on volatile aroma biosynthesis of ’Nanguoli’ fruits at different harvest stages were studied by dipped in MeJA solution, results showed that ethylene production rate for normal harvested fruits were accelerated by MeJA, the content of volatile aroma increased 53.75-66.82%, and the kinds of volatile aroma increased 8-14. Esters were the main increased volatile aroma in fruits treated by MeJA, and the effect of 5mM MeJA was greater than 1mM. The ethylene production rate of earlier harvest fruits was affected little by MeJA and the content of volatile aroma was little affected, too. The results indicated that the effect of MeJA on volatile aroma biosynthesis of ’Nanguoli’ fruits was dependented on the contents of MeJA and the harvest time of fruits.