starch present. The grain size is large for any root and tuber and 

 many times larger than the average starch grain of D. esculenta. 



The amylose content of the starch is about 20 to 26 percent, 

 similar to that in D. alata, cassava, and several other roots and 

 tubers, but much higher than that in D. esculenta. D, rotundata 

 starches produce a gel that is highly viscous (necessary for fufu 

 production) but low in tensile strength. Pasting temperature is 

 about 76° C, low compared to other yam species. 



No special uses of D. rotundata and D. cayenensis starches 

 have been found, and in fact the starch is seldom extracted. 



The few analyses made so far show the protein content of 

 both species to be about 4 to 8 percent, somewhat lower than that 

 of D. alata and D. esculenta (table 5). The amino acid spectrum 

 of the protein is fair. Lysine content tends to be high, and sulfur- 

 containing amino acids low, as compared with the FAO reference 

 protein. Tryptophan content (not measured in the cultivars listed 

 in table 5) is low, from 10 to 30 percent of the FAO standard. 



The vitamin C content of D. rotundata and D. cayenensis is 

 sufficient to make these species fair sources, but is slightly higher 

 in D. rotundata (6.5-11.6 mg/100 g) than in D. cayenensis 

 (4.5-8.2 mg/100 g), according to Coursey (8). On the other hand, 

 provitamin A (beta carotene) occurs only in the yellow forms, 

 mixed with other carotenoids (19), 



Not enough work has been done on the nutritive composition 

 of the African species. During the process of selection or the 



Table 5. — Essential amino acids and total protein in D. rotundata 

 and D. cayenensis cultivars compared with FAO reference 

 protein 



[Grams amino acid per 100 grams protein] 



Protein reference 



component nroteini 'Negro' 'Guinea Blanco' 'Saint Prix' 'Akandu' 



Amino acids : 



Valine 4.2 4.6 4.6 4.8 5.1 



Isoleucine 4.2 4.2 4.2 4.3 4.0 



Leucine 4.8 7.6 7.7 8.0 7.4 



Threonine 2.8 3.9 4.3 3.9 4.3 



Methionine 2.2 1.5 1.9 1.4 1.4 



Crystine 2.0 .1 .7 .0 .4 



Phenylalanine •• 2.8 6.1 6.3 6.2 4.8 



Tyrosine 2.8 2.8 3.2 3.0 2.0 



Lysine 4.2 5.4 5.5 5.6 4.7 



Total proteins ... 5.1 6.7 7.5 5.6 



1 FAO Nutritional Studies 24 {11). 

 - Grams per 100 grams of yam tuber. 



33 



