HAWAIIAN TREE FEKN AS A SOURCE OF STARCH 



13 



geh while the other two starches form what may be termed plastic 

 gels, or simply emulsions having a very high viscosity. The former 

 gel is greatly affected by changes in temperature, concentration, 

 and agitation, whereas the latter are relatively little affected. In 

 appearance, cornstarch gel is opaque, while the tree fern and arrow- 

 root gels are translucent. 



USES 



Tree-fern starch has beeji put on the market both as a laundry 

 starch and as a food. It is claimed that only half the concentration 

 necessary for cornstarch is required for tree-fern starch for laundry 

 purposes. Reference to Figure 2 bears out this claim to some extent, 

 since a 2 per cent solution of tree-fern starch has a viscosity equal 

 to 3 per cent of cornstarch, which is about the usual concentration 

 used for laundering. 



Since the physical properties of tree-fern starch are similar to 

 those of the arrowroot, the former is being advocated as a substitute 

 for the latter for invalids and infants. Although Figure 2 shows- 

 it to have less strength than arrowroot starch has, its cost is only 

 slightly more than cornstarch and only a small fraction of that of 

 arrowroot. 



In Hawaii, tree-fern starch is largely used as a mixture with poi. r 

 The starch is simply cooked with water and added to the poi. The 

 cost of the poi is materially reduced by adding the starch to it, its 

 flavor is said to be improved, and the rate of fermentation desirably 

 retarded. These claims are substantiated by the fact that practi- 

 cally all Hawaiian institutions using poi now incorporate tree-fern 

 starch with it. 



As a food substitute for cornstarch, tree-fern starch is not gener- 

 ally popular. Figure 2 shows that at a concentration of 4.25 per 

 cent, which is about the concentration necessary to produce a corn- 

 starch pudding, tree-fern starch has practically the same strength. 

 As previously noted, however, it is, like arrowroot starch, son e- 

 what sticky and tenacious in comparison with cornstarch, which is 

 tender, and clean-cutting. 



In an experiment made to determine the digestibility of various 

 raw starches, Langworthy and Deuel 8 found that 93.4 per cent of 

 raw tree-fern starch was assimilated by the human system. The} 7 

 also found that tests of samples of the feces gave no distinct blue 

 color with iodin, which would seem to indicate that " the proportion 

 of undigested starch was very small." 



Although no digestion tests have been conducted with the cooked 

 starch, it is thought that its digestibility is rather high, due to its 

 large granules and its exceptionally easy conversion into soluble 

 starch. 



> STARCH MAKING FROM THE TREE FERN 



If the trunk of any of the different species of tree fern is cut 

 crosswise, it will be found to contain a central starch core of 3 to 10 

 inches in diameter. Inclosing this core is a very hard, inner bark 



7 Poi, which forms an important part of the native diet, is made from taro, which for 

 the purpose is peeled, cooked, mashed, pounded,, and then allowed to ferment slightly. 



8 Jour. Biol. Chem., 52 (1922), No. 1, p. 259. Digestibility of raw rice, arrowroot, 

 canna, cassava, taro, tree-fern, and potato starches. 



