Fruit respiratory climacteric

Galacturonanases in the parenchyma have been shown to be wall-bound in peach (both endo- and exo-enzymes),625 apple (exo-enzyme only),621 tomato (endo-enzyme),499 and pear (unspecified activity).641 Increases in the level of polygalacturonase activity during ripening have been demonstrated in tomato,499,642-644 avocado,615,633 peach645 date,636 cucumber,631,646 and pear,641 and, in tomato,644 avocado,615 and cucumber,631 this increase is associated with the respiratory climacteric following a transient burst of ethylene production. In the mutant rin tomato fruit, which does not ripen, this increase in galacturonanase does not occur.644... 

Aroma. Aroma Is considered to be much more complex than taste and has many dimensions (92). While the number of compounds conferring aroma In fruits and vegetables Is large, they can generally be classified as hydroxy compounds, aldehydes, ketones, acids, esters, sulphur-containing compounds, O2 heterocyclics and pyrazlnes ( 2) Several hydrolases and proteases Involved In the synthesis of fatty acid and amino acid precursors to volatiles are synthesized or activated during the respiratory climacteric (98-1001. 

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. 

---