Ripening and the control of flavour, texture and shelf-life

By regulating the activity of enzymes involved in fruit ripening, such as cell wall-degrading enzyme polygalacturonase, or ethylene biosynthesis, it is possible to control or delay fruit softening allowing the fruit to stay longer on the plant for greater flavour and texture development, and improving its shelflife. Both antisense technology and over-expression of metabolising enzymes have been used, for example, in tomato (Smith et al. 1988a). Several strategies have been developed to control ethylene production in plant tissues, including:

• antisense 1–amino-cyclopropane-1–carboxylic acid (ACC, precursor of ethylene) synthase (Oeller et al. 1991)
• ACC oxidase (Hamilton et al. 1990)
• reduction of ACC by over-expressing in plants the alien gene of Pseudomonas sp, ACC deaminase, which converts it to α-ketobutyrate (Klee et al. 1991)
• lowering the substrate for ACC synthase by over-expressing the S-adenosyl methionine hydrolase (SAMase) gene (Mathews et al. 1995a)

Among fruit crops, ripening-controlled strawberry, banana, and pineapple are expected to be on the market in a few years. Work has been done on gene expression during fruit development and ripening for fruit crops such as peach (Trainotti et al. 1997), avocado (McGravey et al. 1990), grape (Robinson et al. 1997; Tattersal et al. 1997), sweet orange (Alonso et al. 1995) and strawberry (Wilkinson et al. 1995). In addition there have been studies of gene transfer in apple by using inhibition of ethylene and polygalacturonase biosynthesis (Table 3.2).