Enzymatic treatment forms resistant starch from rice.

Rice flour and starch are becoming popular ingredients since they are hypoallergenic, low in fat and neutral in flavor. Commercial rice grain contains 87% carbohydrates, 7% to 8% protein, and a small amount of fat and dietary fiber. Unfortunately, many of us are not consuming enough fruits and vegetables to meet the daily requirements for dietary fiber: 28 grams to 35 grams.

Enzymatically treating rice starch and flour could facilitate the development of resistant starch. Resistant starch is a functional food ingredient that offers an increased nutritive value and dietary fiber content. The objective of researchers at Louisiana State University was to determine if gelatinization and storage with pullulanase would affect the formation of resistant starch at 37 C.

In their research, the scientists gelatinized samples, refrigerated them at 3 C overnight and then incubated them for 24 hours at 37 C. Other samples were not gelatinized and then incubated for 24 hours at 37 C. A third group of samples was gelatinized and incubated for 24 hours at -37 C, and then refrigerated with the pullulanase enzyme at 3 C for two days.

The scientists created a rice starch-to-water ratio of 1:20. They added 10 ml of pullulanase to the sample at near-neutral pH at 37 C. Centrifugation separated the rice starch from the enzyme and water. The samples were freeze-dried. Analysis was conducted by differential scanning calorimetry.

The investigators found that there was no gelatinization peak in the first group of samples mentioned above. Gelatinization for the second group began at 67 C, peaked at 73 C and ended at 85 C. Another peak in the second and third groups of samples began at 87 C. They peaked at 100 C and topped off at 112 C. These peaks could belong to lipid-amylose complexes. The peaks for lipid-amylose complexes was larger in the treated samples than in the untreated rice starch.

The third group of samples experienced a second peak beginning at 112 C. This group peaked at 117 C and ended at 124 C. The second peak at 117 C may be related to resistant starch that developed during enzymatic processing. If enzymatic treatments are effective in producing resistant starch, they could be used to facilitate the production of functional ingredients. Further research is necessary to determine the stability of resistant starch.

Further information. Joan King, Department of Food Science, Louisiana State University, 104B Food Science Building. Baton Rouge, LA 70803; phone: [phone]; fax: [phone]; email: [e-mail].