carotenoids 



Factors influencing Carotenoid Production in Ripening Fruit 



Naturally most of the work which has been reported has been 

 carried out on the economically important tomato. Fruit formed under 

 growing conditions unfavourable to fruit production contain more 

 lycopene than do well-developed fruit. This variation is not a function 

 of the size of the fruit nor is it caused by the formation of other caro- 

 tenoids at the expense of lycopene. ^ <> * In general, fruit gathered 

 unripe continue to produce carotenoids, but vine ripened tomatoes 

 always contain more than do fruit ripened in storage. 2 o s, 2 o e Stored 

 tomatoes can synthesize up to 1200 [xg. of carotenoids per day. 2**' 



(i) Oxygen 



Oxygen is needed for the ripening process, for artificial ripening in 

 an atmosphere of ethylene or carbon dioxide prevents the expected 

 increase in the carotenoid content of tomatoes, paprika, ^^"^^ Physalis 

 alkekengi ^ ' ^ and Tatnus communis. ^ " '^ Similarly oranges fail to 

 synthesize carotenoids in an atmosphere of ethylene and in the case of 

 limes, lemons and grapes ripened in ethylene, there is in fact a slight 

 loss during maturation. ^ » ^ 



(ii) Light 



The well-known domestic habit of ripening tomatoes in dark cup- 

 boards and drawers indicates that light is not essential for carotenoid 

 synthesis during maturation. Information concerning the precise 

 role of light is however scanty and occasionally contradictory. The 

 observation that with commercial strains of tomatoes, fruit matured on 

 the vine in the dark (by bagging the fruit) contain less carotenoids than 

 do those grown normally in the light, 2 », 2 1 indicates that a photo- 

 chemical factor is concerned in carotenogenesis. However, an in- 

 creased synthesis apparently occurs in the dark in the case of albino 

 (Clark's albino) and golden (Ruby Gold) tomatoes and Elberta peaches, 

 Humbolt nectarines and Royal apricots. This may be a true varietal 

 and species difference but other uncontrolled factors such as tem- 

 perature may have been operating. A separation of photo- and thermo- 

 chemical effects is difficult to achieve, and, as will be seen later, the 

 thermal factor is of major importance in carotenoid synthesis. A 

 further factor which has not yet been adequately explored is the pro- 

 bability that there is an optimum light intensity for synthesis, and that 

 the optimum value may vary for each carotenoid component ; for 

 example, on ripening tomatoes in '* normal " sunlight lycopene 

 proceeds at a greater rate than does [i-carotene synthesis, ^ ^ 2 but [^ 

 " strong " light the former is slowed down and the latter speeded 



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