Effect Of Light On Aroma Volatiles In Peach Fruit (Prunus Persica Bastch)

As fruit has become more popular and important in daily diet in China with the development of economy, the need for assuring high quality is increasing. Volatile aroma is one of the important quality factors for peach flavor, it is determined by genetics, followed by environmental and cultural influences, especially affected by light condition. However, little work has been conducted to elucidate the influence of microclimate on peach aroma formation. Two peach cultivars, 'Hujingmilu' and 'Hakuho' (Prunus persica Batsch) were used in this study to test: (1) which degree of fruit shading is most effective in the production of aroma volatiles during maturation;(2) the effect of post-harvest light condition on the production of aroma volatiles during maturation and ripening. Results were as following;(1) Young 'Hujingmilu' peach fruits, at 50 days after full bloom (DAFB), were covered with bags made of single-, double-, and triple-layers of orange paper bag with 27.0%, 13.9% and 8.2% respectively sunlight transmission. Ethylene production, respiration rate were measured, and fruit quality was analyzed 111, 114, 117, 120 (firm-ripe stage) and 124 DAFB (full-ripe stage). Single- and triple-layer bagged fruits had higher ethylene production rates than double-layer bagged and un-bagged fruits. The skin of un-bagged fruit had higher brightness (L-value) but smaller hue angle (h~O) at the full-ripe stage compared with that of bagged fruit. Flesh firmness of un-bagged fruit was higher than that of bagged fruit until the firm-ripe stage, although triple-layer bagged fruit had higher firmness than un-bagged fruit at the full-ripe stage. Total soluble solids (TSS) in juice of single-layer bagged fruit were a little higher than that of other treated fruits, whereas titratable acidity (TA) is a little lower at the full-ripe stage. Single-layer bagged fruit showed the highest level of γ-decalactone, a maincharacteristic aroma of peach and total lactones at the firm-ripe and full-ripe stages. It was concluded that 'Hujingmilu' peach had high quality with abundant aromas when the fruits were bagged with single-layer orange paper bags at 50 DAFB. The biosynthesis of y-decalactone and other aromas may be affected by light conditions to some extent.(2) 'Hakuho' peach fruits were harvested at the immature and firm-mature stages corresponding to 7 and 3 days before the tree-ripe stage and stored at 25 °C under a light {ca 4 klx at the fruit top by an incandescent lamp) and entire dark conditions. Fruit sampling for biological and chemical analyses including ethylene production, respiration rate of fresh fruits, TSS, TA, amino acids, aroma volatiles was carried out at the start of storage, four days after (only for immaturely harvested fruit), and the end of storage. The light and dark conditions did not significantly influence the ethylene production rate when all the fruits harvested at the two stage reached full ripe stage except for a low production in the fully ripen fruit harvested at firm-mature stage and stored under the light. However, no difference was detected in fruit firmness among different treatments at the full-ripe stage. The skin anthocyanin content increased significantly during the fruits harvested at the two stages and stored under light condition. The TA content in the immaturely harvested fruit juice decreased more largely during the light storage compared with those stored in the dark. The dark storage limited the decrease of juice asparagine during the storage to some extent in the fruits harvested at the two stages. Aromatic lactones, such as Y -decalactone and Y -dodecalactone, both in skin and flesh tissues, increased more rapidly when the fruit was stored under light condition, irrespective of fruit harvest stage. From these results, we conclude that fruit storage under a light condition can improve the aroma volatiles,skin color, and promote the asparagines of 'Hakuho' peaches compared to a dark storage. Peach fruits even harvested at early stage under light storage can also produce higher quality with abundant aroma volatiles.