Starch preference in rats

Several experiments examined the preference of adult female rats for starch and starch-derived polysaccharides using short- and long-term two-choice tests. In Experiment 1, food-deprived rats displayed an immediate preference for powdered corn starch over powdered cellulose in 30-min/day tests. This supports the hypothesis that rats have starch (polysaccharide) taste receptors. The rats also preferred the starch powder to Polycose powder. This preference was unexpected since Polycose, being partially hydrolyzed corn starch, should be a more effective taste stimulus than corn starch. Experiment 2 revealed that nondeprived rats also preferred starch to Polycose in 30-min/day tests, but reversed their preference in 24-hr/day tests; the preference reversal was attributed to postingestive factors. Additional experiments demonstrated that rats preferred branched-chain starch (amylopectin) to unbranched starch (amylose) in both short- and long-term tests. Rats also preferred amylopectin to Polycose in short-term tests when the saccharides were in powder form, but preferred Polycose to amylopectin when the saccharides were in liquid or gel form. The preference for amylopectin powder was not due to the noncarbohydrate constituents (fatty acids, proteins, others) in the starch since rats also preferred chemically purified amylopectin to Polycose powder. Additional tests suggested that texture differences do not explain the rats' preference for starch powder over Polycose powder. Taken together, the results demonstrate that rats have a robust preference for starch but the orosensory determinants of this preference are not completely understood.