Nonclimacteric

The ripening of nonclimacteric fruits is usually considered as a process that as a whole does not require ethylene. Nevertheless, endogenous ethylene is involved at some steps of development of these fruits. In general, chlorophyll degradation in nonclimacteric fruits is believed to be ethylene stimulated, whereas the synthesis of pigments can depend on ethylene action or not. ... 

Some, but not all, fruits that are regarded as nonclimacteric are characterized by low respiratory activity.543 It should be noted that Trout and coworkers545,546 expressed doubt of the generally accepted classification of citrus fruits as nonclimacteric. Clarification of whether these and other fruits, such as fig, grape, strawberry, and pineapple, exhibit a truly nonclimacteric pattern of ripening may come from further study. 

Citrus fruits are representative of the nonclimacteric class. Following harvest, the rate of respiration of citrus slowly declines. Irradiation does not noticeably influence ripening changes in these fruits. 

Figure 1. Effect of ethylene on respiration of climacteric and nonclimacteric fruit. Ethylene causes greatest response in climacteric fruit when applied to mature fruit prior to the climacteric rise. In nonclimacteric fruit high concentrations of ethylene stimulate respiration for short time periods. This stimulation is observed at any time upon application of ethylene (3).

Several studies on irradiation of fruits and vegetables have been conducted to delay fruit ripeness, thus, their shelf life might be extended by few days to few weeks [1]. However in some horticultural crops gamma irradiation treatments initiated the climacteric ripeness sequences by inducing the preclimacteric fruits to produce stimulatory amount of ethylene [2]. Factors most likely to affect response of fruit and vegetables to irradiation may include type of fruit (climacteric or nonclimacteric), ripeness stage at expossure, dose of irradiation and post-treatment storage conditions. 

The cashew Anacardium occidentale Linn.) is a tropical tree indigenous to Brazil, which is now extensively cultivated in India and East Africa. The tree yields two edible parts the nut and the cashew apple, an edible pseudo fruit, to which the nut is attached (Figure 21.2). The peduncle is a pear-shaped nonclimacteric pseudo fruit, which can be found in three colors yellow, orange, and red. It is very juicy, fibrous, and edible, but lacks commercial value, compared to the nut. 

Nonclimacteric types, which include pineapples, oranges, strawberries, figs, grapefruit, cucumbers, cherries, cantaloupes, melons, grapes and lemons. 

It should be emphasized that nonclimacteric fruits generally ripen on the plants and contain no starch. The differing effects of ethylene on the two types of fruits are covered in Section 18.1.4.2. 

Climacteric and nonclimacteric fruits respond differently to external ethylene (Fig. 18.10). Depending on the ethylene level, the respiratory increase sets in earlier in unripe climacteric fruits, but its height is not influenced. In contrast, in nonclimacteric fruits there is an increase in respiration rate at each ripening stage which is clearly dependent on ethylene concentration. 

Ethylene increases rapidly but differently in the case of climacteric fruits. The maximum values for some fruits are given in Table 18.35. However, nonclimacteric fruits produce only a little ethylene (Table 18.35). This gaseous compound increases membrane permeability and thereby probably accelerates metabolism and fruit ripening. With mango fruits, for example, it has been demonstrated that before the climacteric stage, ethylene stimulates oxidative and hydrolytic enzymes (catalase, peroxidase and amylase) and inactivates inhibitors of these enzymes. 

Fig. 18.10. The effect of ethylene on fruit respiration, (a) climacteric, (b) nonclimacteric. Numerals on the curves ethylene in air, ppm (according to Biale, 1994)...

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