Studies On The Mechanism Of Ethanol Metabolism Of Harvested Kiwi Fruit

Kiwifruit(Actinidia deliciosa. cv. Bruno) is highly perishable and prone to off-flavor during storage period. In particular, alcohol odor caused by ethanol fermentation metabolism is the prevalent phenomenon for harvested Kiwifruit, which lead to the reduction of fresh food flavor, quality and commercial value. In this paper, changes in quality, ethanol metabolism, and volatile component in harvested kiwifruit ’Bruno’ were investigated during storage at different temperatures (25 ℃ and 5 ℃). The main results were as follows:(1) The firmness of kiwifruit was declined during storage time. Soluble solid content (SSC) was increased at the beginning time of storage, and then declined slightly in latter time. Ascorbic acid (AsA) content was declined during the storage. The titratable acid (TA) content was declined. The lower temperature (5 ℃) significantly maintained fruit firmness and nutrients such as AsA, reduced decay, and improved fresh colour, as compared to room temperature (25℃). Thus, the ripening process of fruit was delayed, and the quality of kiwi fruit was enhanced by lower temperature.(2) Both temperatures of 5 ℃ and 25 ℃ resulted in the accumulation of ethanol and acetaldehyde, and the enhancement of Pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) activity during storage. Also, the gene expression of PDC and ADH in kiwi fruit was enhanced. Compared to 25℃, lower temperature significantly reduced accumulation of ethanol, acetaldehyde, decreased activities and genes expression of PDC and ADH. Thus, inhibition in ethanol fermentation could effectively decrease the ethanol accumulation, and in turn benefit to the quality of fruits.(3) The amount and type of volatile compounds in kiwi fruits were enhanced during storage and ester was the major volatile components. Compared to 25 ℃, the amount and type of ester remained a stable level, and the change in ester was not great during storage at 5℃. It was found that ethanol acted as a key metabolic precursor in the formation of other volatiles, as the content of ethanol and acetaldehyde just reached a certain threshold, and then could follow-up esterification reaction. Thus, the increase of ethanol fermentation directly leads to alcohol flavor. These results suggest that besides the direct effects of ethanol, ethanol esterification products might be involved in causing off-flavor sensation in kiwi fruits.