No abstract

Fruit of varieties Golden Delicious and Granny Smith, were harvested at commercial maturity in two comecutive years (1993 and 1994). The aroma components obtained were analyzed by the dynamic headspace method and quantified by gas chromatograph-mass spectrometry. In Golden Delicious the total esters represented more than 80% of the total volatile components in both years, consistent with Drawen's classification (1975). However, Granny Smith did not, since the esters made up 72 and 88% of total volatiles in the years 1993 and 1994, respectively. The aroma components are different in class and quuntity and give a characteristic sensorial perception for each type offruit and variety. In Golden Delicious, ethyl propionate and butyl acetate gave a fnrity aroma in 1993 and ethyl acetate, ethyl propionate and propyl acetate were the predominant compounds in 1994. In Granny Smith the aroma composition was slighfly different in the two years. In 1993 the aromatic profile did not show the predominance of any compound, while in 1994 it was more fruity due to the higher content of ethyl propionare and propyl acetate.

SummarySlices cut from green, unripe fruit were treated by infiltration with aqueous solutions of 2,4·dichlorophenoxyacetic acid (2,4·D) and indoleacetic acid (lAA). 2,4.D delayed but increased the size of those peaks in respiration and ethylene production which are induced by cutting; ripening was also delayed. These effects were proportional to concentrations of 2,4.D in the range 1O-L lO-3M. Higher concentrations caused injury.Ripening which may be induced by a 24·hr treatment with 10 p.p.m. ethylene is prevented or delayed in slices treated with 2,4.D. 2,4.D did not prevent a climac· teric·like rise in respiration, but the slices recovered from the effects of ethylene. This recovery is shown by a decline in respiration and ethylene production to normal pre·climacteric rates and maintenance of other green fruit characteristics. The recovery is proportional to concentration of 2,4-D in the range 1O-L lO-3M. Ripening subsequently takes place normally. The effects of lAA were similar to those of 2,4.D but less pronounced.The delay in ripening induced by 2,4.D or IAA contrasts with previous reports that treatments with these compounds by dipping or spraying usually hastened ripening of whole fruit.It is suggested that these compounds, especially 2,4-D, cause reversion of banana tissue to a more juvenile state which is less sensitive to ethylene treatment.

A cDNA clone (Banl7), encoding a protein homologous to pectate lyase, has been isolated from a cDNA library from climacteric banana fruit by means of differential screening. Northern analysis showed that Banl7 mRNA is first detected in early climacteric fruit, reaches a steady-state maximum at the climacteric peak, and declines thereafter in overripe fruit. Accumulation of the Banl7 transcript can be induced in green banana fruit by exogenous application of ethylene. This demonstrates that expression of this gene is under hormonal control, its induction being regulated by the rapid increase in ethylene production at the onset of ripening. The deduced amino acid sequence derived from the Banl7 cDNA shares significant identity with pectate lyases from pollen and plant pathogenic bacteria of the genus Erwinia. Similarity to bacterial pectate lyases that were proven to break down the pectic substances of the plant cell wall suggest that Banl7 might play a role in the loss of mesocarp firmness during fruit ripening.