Food Science and
Technology - 93



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Project Leader and Principal UC Investigators

Norman F. Haard, professor, Department of Food Science & Technology, UC Davis

Nora Dimes, staff research associate

Maria Izquerdo-Pulido, visiting scientist

Dr. Houde Han, visiting scientist

Ms. Jessie Hung, M.Sc. graduate student

Scientists in the UC Davis Department of Food Science and Technology continued their studies of rice-derived compounds that retard the breakdown of animal protein. These compounds are known as proteinase inhibitors. Ultimately, this work may lead to an entirely new market for California rice.

Rice Bran Chart.jpg (62546 bytes)Surimi is a processed seafood that consumers may recognize as the main component of "artificial" crabmeat. Certain underutilized fish species such as Pacific Hake and Arrowtooth Flounder can be used by seafood processors as surimi. However, substances known as "proteinase inhibitors" need to be added to prevent protein breakdown and excessive softening. Rice contains a number of these inhibitors - most notably "oryzacystafin." The food scientists have been in the process of analyzing what these inhibitors are, how frequently they occur in different rice varieties, and how well they inhibit the decay of fish protein. Researchers also analyzed extracts of rice straw for their ability to inhibit protein degradation and concluded that other chemicals were at work. Oryzacystatin is a protein, as are most plant proteinase inhibitors. The inhibitory activity in rice straw was not due to proteins but was caused by less specific agents, probably phenolic compounds. This finding prompted the food scientists to cease any further work on rice straw.

In addition to oryzacystatin, other proteinase inhibitors exist in rice. Researchers examined 11 widely grown varieties and found relatively high levels of one inhibitor, chymotrypsin, in M-103 and another, trypsin in L-203, L-202, M-103 and Calmochi. The trypsin inhibitor was found concentrated mostly in the bran, while a subtilisin inhibitor was distributed in both bran and endosperrn.

Scientists also examined the pH and thermal stability of proteinase inhibitors from rice. In work to evaluate best methods of recovering oryzacystafin from rice, researchers determined that the inhibitor is salt soluble, mostly recovered by one step extraction and best recovered from presoaked bran. They also found that gains in oryzacystatin purity from a heat treatment are not offset by loss in yield.

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