TROPICAL YAMS AND THEIR POTENTIAL, PART 3 31 



Table 3. — Tuber composition of five D. alata varieties^ 



[Percent of whole-tuber weight] 

 Substance Variety — 



Water 77.60 



Starch 15.60 



Mucilage or protein 2.10 



Cellulose 1.10 



Sugar (^) 



Minerals 96 



Fats 23 



Not determined 2.41 



1 From Wildeman {31). 

 - Not given. 



group the varieties contain less 

 starch than usually reported; it is 

 not uncommon to find tubers with 

 28 percent starch. Little carbohy- 

 drate occurs as sugars. The amount 

 of cellulose is low; in fact, very 

 few tubers contain enough cellu- 

 lose to present a fibrous appear- 

 ance. Fats are negligible. Vitamin 

 C in useful quantities has been re- 

 ported. Minerals are not important 

 components. 



Starches, which make up 13 to 

 32 percent of the tuber, are rela- 

 tively difficult to extract from D. 

 alata. During peeling and cutting, 

 the equipment is likely to become 

 clogged with released water-sol- 

 uble gums, which must be dis- 

 persed with large amounts of 

 water. Once the gums are dis- 

 persed the larger particles of 

 starch settle to the bottom of the 

 container in about 24 hours. The 

 starch must then be resuspended 

 in water two or three times and 

 allowed to settle. The resulting 

 starch cake can then be dried. 



65.95 



67.12 



72.42 



76.15 



19.50 



23.87 



17.71 



19.34 



5.68 



1.36 



6.87 



1.31 



7.50 



3.15 



2.53 



.65 



1.19 



.50 



1.00 



(2) 



(2) 



(^) 



(^) 



.73 



.18 



.11 



.04 



.16 





3.89 



.43 



1.66 



Starch prepared in this fashion 

 contains few other materials, but 

 can be expected to have 13 to 18 

 percent moisture and 1 to 4 per- 

 cent protein. 



The particles of D. alata starches 

 are mostly large and pyramidal in 

 shape. One point of the pyramid 

 represents the small grain on the 

 side of which successive layers of 

 starch are deposited. The mature 

 grains vary from 1 to 7 micro- 

 meters in diameter, although much 

 larger grains have been reported, 

 making the grain considerably 

 larger than that of cassava, a 

 major source of industrial starch. 

 The large size might make D. alata 

 starch difficult to digest, especially 

 when uncooked. 



The amylose content of D. alata 

 starches ranges from 19 to 20 per- 

 cent, somewhat higher than that 

 of D. esculenta, but not significant- 

 ly different from that of cassava. 

 The viscosity of D. alata starches 

 has been reported to be moderate, 

 although there is much variation 



