Nutritional and toxicological studies on some native and modified starches.

Feeding experiments were performed in which rats were given some native or chemically modified starches as a source of carbohydrate. Rats fed on raw potato starch developed gross caecaI enlargement and some mortalities were recorded amongst these animals. Caecal distension resulted In pressure on the diaphragm and impaired respiratory function was shown to be the probable cause of death. Studies on the causal mechanisms involved in caecal enlargement suggested that the osmolality of the caecal contents was an important factor but changes in electrolyte concentrations and caecal microflora might also be involved. Some biochemical parameters in the animals showing caecal enlargement were investigated, and an elevation of the serum alkaline phosphatase and glutamic pyruvic transaminase activities were encountered in these animals. The isoenzyme patterns of serum alkaline phosphatase, studied by polyacrylamide disc electrophoresis, suggest that the elevated enzyme activity was similar to the enzyme from the liver. Raw potato starch also caused impairment of the net protein utilisation and of food efficiency when fed to young rats. Similar gastrointestinal effects to those induced by raw potato starch were not observed with any of the cereal starches: maize, wheat, sorghum, rice or the tuber cassava. Feeding to the albino rat of waxy-maize starch and three of its modified products cross-linked with phosphorus oxychloride (D. S. 0.0025, 0.006 and 0.01) or of a product highly cross-linked with sodium trimeta- phosphate (D. S. 0.06), revealed no detectable toxic effects at the dietary levels used (16% or 30%). The results of these experiments together with the results of a bacteriological investigation of the caecal flora are discussed