tubers are often misshapen. Loss during peeling and preparation 

 for the kitchen is minor. After cutting tubers into thick slices, 

 the bark may be peeled off readily with a knife. The cut surface 

 of a large tuber should be exposed to dry air, which will effect 

 temporary healing. It is also possible to protect the cut surface 

 with a piece of wax paper or plastic wrap. 



Sticky proteinaceous gums exude from cut tubers, but their 

 stickiness is not related to that of cooked flesh. In addition to 

 gums, tubers exude a rich mixture of other substances, including 

 phenolic substances that may easily oxidize. The oxidation of an 

 amine catechin is believed to be responsible for the brown or 

 blackish spots found on cut surfaces. The complex browning re- 

 action requires the presence of oxygen, the catechin, and an 

 enzyme, and is avoided by the elimination or inactivation of any 

 of the three requirements. The use of cellophane or wax paper on 

 cut surfaces reduces oxidation. Varieties subject to frequent or 

 extreme oxidation are best avoided because of their unappetizing 

 appearance. 



Polyphenolic oxidation varies among cultivars but is more 

 common in old or injured tubers. The bitterness often associated 

 with oxidation appears rather to come from leucoanthocyanidin 

 content. The cut surface of some yams contains calcium oxalate 

 crystals which may sting the skin, a harmless sensation that 

 disappears in about 30 minutes. 



The yellow color of most D. cayenensis tubers is due to 

 carotenoids, including beta carotene, and numerous xanthophylls 

 and their esters. Anthocyanin coloration is not found in tubers of 

 these African species. 



The flesh of a newly cut tuber appears ricey or stringy because 

 of accumulated starch around the vascular bundles. The character- 

 istic is preserved through cooking and gives a pleasant texture 

 and appearance to the product. The actual amount of fiber in 

 the tuber is quite low, and fiber does not constitute an obstacle 

 to appearance or the palate. 



Individual varieties are seldom recognized by taste except by 

 the most acute observers. Nevertheless, there are recognizable 

 differences, and thus certain varieties are preferred for eating. 

 When cooked tuber has an acceptable appearance, it invariably is 

 also appetizing and flavorful. 



COOKING AND COOKED PRODUCTS 



The most important use of D. rotundata is as fufu, a native 

 African dish. Preparation begins by peeling and cutting tubers 

 into small pieces. They are boiled until soft, drained, and then 

 pounded in a mortar with pestle until a stiff, glutinous dough is 

 formed. The dough is molded into a ball and served. Diners remove 



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