Select Committee on GRAS Substances (SCOGS) Opinion: Hydroxypropyl Starch
- SCOGS-Report Number: 115*
- Type Of Conclusion: 3
- ID Code: 9049-76-7
- Year: 1979
- 21 CFR Section:
Incomplete digestibility of hydroxypropyl starch was demonstrated by the isolation of hydroxypropyl maltose in feces of rats fed this modified starch. This residue increased as the degree of hydroxypropylation of the starch was increased. Other experiments in which labeled hydroxypropyl starch was fed indicated that over 90 percent of the hydroxypropyl groups were excreted in the feces. Thus high degrees of substitution as permitted by the present specifications for hydroxypropylated food starches may reduce the digestibility and caloric value of the starch significantly. Usage of starches of high hydroxypropyl content as compared to a more completely digestible starch could result in a significant reduction of caloric value of the food. It is suggested that a limit be placed on the content of hydroxypropyl groups introduced into a hydroxypropylated modified starch.
Hematological findings were normal and no pathological changes were observed in the major organs in 90-day rat feeding studies of starch containing 1.53 percent hydroxypropyl groups. Weight gains were consistently but not significantly lower than controls at dietary levels of 12 g per kg and above, and diarrhea was observed at 35 g per kg. In a similar study with an oxidized hydroxypropyl starch containing 14.9 percent hydroxypropyl groups, no pathological findings were reported. However, growth rate and food efficiency were reduced at dietary levels of 8 and 20 g per kg and the depress ion in growth rate was significant at the higher dietary level. Diarrhea also occurred at the 20 g per kg level. Because this starch was both oxidized (i. e. carboxyl and carbonyl groups introduced) and hydroxypropylated, the growth depression and diarrhea cannot be attributed solely to either treatment.
In the hydroxypropylation of starch by treatment with propylene oxide, propylene chlorohydrin may be formed by reaction with chloride ions that may be present. Short-term (22-week) experiments in which propylene chlorohydrin were administered to rats by gavage showed no hematological or histopathologic changes in treated animals at dose levels of 75 mg per kg, the highest dose level at which histological examination of rats was made. However, the liver-body weight ratio was increased at the 25 mg per kg dose level for males and at the 75 mg per kg dose levels for both sexes. Propylene chlorohydrin was mutagenic to Salmonella typhimurium TA 1530 but not for TA 1538 when tested in agar containing 1.1 mg propylene chlorohydrin per plate. Present specifications for hydroxypropyl starches permit 5 ppm of residual propylene chlorohydrin in the product. Long-term rat feeding experiments with hydroxypropyl distarch glycerol etherified by treatment of starch with 5 percent propylene oxide showed no increase in tumors as compared to control animals. Three generation reproduction and lactation studies with the same hydroxypropylated starch revealed no adverse effects. No increase in neoplastic lesions was observed in long-term studies with mice fed hydroxypropyl distarch phosphate at a level providing about 350 µg propylene chlorohydrin per kg body weight. This is four orders of magnitude greater than per capita human exposure assuming that hydroxypropylated starches are the only modified starches used in processed foods. Although no adverse effects have been observed which have been attributed to residual propylene chlorohydrin, the Select Committee suggests that the limits on this residue be reduced to the lowest level consistent with feasible manufacturing practice, and that long-term animal feeding studies be undertaken with graded levels of propylene chlorohydrin to clarify whether the mutagenic activity observed in a bacterial system is an indication of potential for similar activity in animals. This modified starch is not currently used in infant foods.
In view of the foregoing considerations, the Select Committee concludes that:
While no evidence in the available information on hydroxypropyl starch and oxidized hydroxypropyl starch demonstrates a hazard to the public when they are used at levels that are now current and in the manner now practiced, uncertainties exist requiring that additional studies should be conducted.