12 



BULLETIN 53, HAWAII EXPERIMENT STATION 



The above data on viscosity and gelling strength bring out a num- 

 ber of important differences among the starches. The concentra- 

 tions necessary to cause any appreciable increase in viscosity were 

 1.5 per cent of arrowroot, 2 per cent of tree fern, and 3 per cent of 

 cornstarch. Above 3 per cent the curve for cornstarch shows a very 

 sharp increase. A 1-gram increment causes an increase in viscosity 

 of 1 to 6, whereas a like increment of tree fern and arrowroot over 

 the concentrations of 2 and 3 per cent, respectively, causes increases 

 of 1 to 3. As the concentration increases, the tree fern and corn- 

 starch curves practically coincide. The arrowroot curve, although 



*55 



SO 



0 4.0 

 \ 



3.0 



\ 



k 









































































Y 































rA 



































A, 







222 





















7 



























































































































































































5- 

































Fig. 2.- 



O J O & 7 9 // J<3 /& /7 /P 2/ 23 25 27 29 31 

 ///&CO&/7~y (Af/A/C/T£:$) AT 80°C. 



—Comparison of the viscosity of tree-fern starch and other commercial starches. 



showing greater viscosity than that of the tree fern, is of the same 

 general nature. 



The gelling strengths of the three starches were in the opposite 

 order of their viscosities. A cornstarch solution with a viscosity of 

 8.75 formed a stiff gel when cooled, while a tree-fern solution re 

 quired a viscosity of 27 to form a gel. A 4 per cent arrowroot solu 

 tion required from three to four hours to pass through the visco- 

 simeter, and yet a 5.25 per cent solution was necessary to form a gel 



The physical qualities and appearance of the three are likewise 

 distinct, Cornstarch forms a tender, clean-cutting, definite hydro- 



i 



