Fruit climacteric stage

In mango fruit, the characteristic flavour appeared to develop only after the half-ripe stage (the climacteric stage) and the extent of flavour generation depended on the temperature conditions during storage (Gholap et al. 1986). 

The respiration rate is affected by the development stage of the fruit. A rise in respiration rate occurs with growth. This is followed by a slow decrease in respiration rate until the fruit is fully ripe. In a number of fruits ripening is associated with a renewed rise in respiration rate, which is often denoted as a climacteric rise. Maximal CO2 production occurs in the climacteric stage. De-... 

The formation of typical aromas takes place during the ripening of fruit. In bananas, for example, noticeable amounts of volatile compounds are formed only 24 h after the climacteric stage has passed. The aroma build-up is affected by external factors such as temperature and day/night variations. Bananas, with a day/night rhythm of 30 °C/20 °C, produce about 60% more volatiles than those kept at a constant temperature of 30 °C. The synthesis of aroma substances is discussed in section 5.3.2. 

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. 

The synthesis of endo-PG occurs in the ripening stage after an increase of ethylene production [21] and its appearance has been correlated with an increase in soluble pectin and softening [22]. Exo-PG is suggested to participate in the initiation of climacteric ethylene production [23]. Strawberry fruit has been accepted to be a non-climacteric fruit and ethylene... 

Figure 3 shows the hypothetical kinetics of growth, respiration and relative hormone levels in a climacteric fruit at different stages of its life cycle. Hypothetical hormone levels during development and ripening have been speculated on before (13). The rationale for this outline is based on the known influences of the various hormones on cell division,... 

These variations in behavior indicate that harvesting melons at different stages of maturity causes subsequent biochemical events involved in amino acid accumulation to follow markedly different pathways. Recent work shows that melon fhiit harvested up to ten days before commercial maturity exhibits climacteric behavior with respect to ethylene production showing that at least this aspect of ripening is not completely inhibited by premature separation from the plant(P). However, the amount of ethylene produced is dependent on maturity at harvest and fruit harvested five days prematurely generated only about half of the amount of ethylene produced by fruit harvested two days before maturity. Also the lag time required to initiate ethylene production after harvest depended on maturity and was longer for prematurely harvested fruit. Changes in the content of the phytohormone abscisic acid were also correlated with that of ethylene. However whether the different maturity related metabolic responses observed above result from the action of these or other plant hormones awaits further study. 

It is well established that 18 2 and 18 3 are the precursors of and C, aldehydes and alcohols by exogenous application of 18 2 or 18 3 and radiolabelled precursors, e.g. [93]. As for the hexyl and hexenyl esters, it is not clear if hexyl or hexenyl moieties of esters solely originate from C, aldehydes or alcohols. Incubation of apple fruits with hexanal or hexanol resulted in an increase in the formation of hexyl esters, e.g. [94], but increased levels of these esters at the ripe stage of apple fruits were much larger than the endogenous levels of aldehydes and alcohols [97]. Interestingly, methyl jasmonate application stimulated ester formation of the pre-climacteric apples, but had no effect on the ester formation of the post-climacteric fruits [17] however, it inhibited the hexyl ester formation in apples stored in a controlled atmosphere [96]. Fan et al. [17] speculated that the inhibitory effect found in the last report was owing to the toxic level of methyl jasmonate used. 

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. 

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. 

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