MICROMANIPULATIVE STUDIES ON GELATINIZED STARCH GRANULES

Gelatinized starch granules are generally considered to be comprised of sacs or outer membranes of starchy material enclosing a more or less fluid colloidal starch dispersion [see reviews by RADLEY (10)] and KERR (6). NXGEI, (9) and MEYER (8) considered the membrane to be precxistent in the native, ungelatinized granule. ALSBERG (1) and BADENHUIZEN (2, 3) on the other hand, concluded that the membrane is formed as an artifact by the swelling and coalescence of the more resistant lamellae. Experimental results reported by HESS and RABINowITscH (5) and further aiscussed by ROBERTS (11) indicate that, however it may be formed, the outer membrane of the gelatinized granule is tough and can be punctured by a needle, releasing a fluid colloidal suspension with which the sac is filled. During the course of an investigation at this Laboratory of the factors affecting starch paste viscosity, micromanipulative studies were made of the degree to which gelatinized granules of corn, potato, tapioca, and glutinous corn starch could be stretched. Several hundred granules of each kind of starch were observed, each granule being stretched until broken. The main purpose of the study was to determine whether length of paste might be correlated with ability of the individual unbroken granules to stretch. (A long paste has a small yield value and low mobility.) Information was also obtained on the degree to which starch granules could be stretched after pasting at different temperatures and for different lengths of time. Some effects of chemical pretreatment of starch granules upon their subsequent ability to stretch were also noted. The starches used in these experiments included commercial tapioca starch, laboratory-processed glutinous corn starch, and both commercial and laboratory-processed corn and potato starches. Nitrogen and ash contents of these starches, determined as described by MACMASTEMS and HnIBERT (7), are given in table I. The laboratory-processed samples of corn starches were prepared by the method described by Cox, MACMASTERs, and HiLBERT (4).