Some morphological features accompanying the aerobic photodegradation of whole Potato starch

Peat and Whelan¹ have already described the chemical changes occurring during the aerobic photodegradation of amylose and amylopectin when dispersed in water. More recently, Whelan and Baker² have extended these investigations to commercial whole starches in the dry state (note: such starches still contain 15-20 per cent of bound water). During the aerobic degradation of whole starches, morphological changes were observed which promised to throw some light upon the gross and fine structural organisation of the raw starch granule. When potato starch irradiated in ultra-violet light of 3660 A. was mounted in a non-aqueous medium such as anisole (refractive index 1.51), microscopic examination showed that the majority of the granules still retained their birefringence. If examined at room temperature, in water, iodine solution or other aqueous reagents, the granules swelled almost immediately and lost their birefringence. These changes were accompanied by the separation of clearly defined surface membranes and by solubilization of the contents of the granule, which diffused slowly into the surrounding medium. Swelling appeared to be due in part to osmosis, since a proportion of the granules burst, leaving the peripheral membrane as a shrunken residue in which a clear rent, through which the solubilized contents had escaped, was always demonstrable. Also, on irrigation with ethanol, the process was reversed and the swollen granules contracted.