1a. Objectives (from AD-416):
Objective 1: Enhance the human bioactive properties of resistant starch and slowly digestible starch in commercial table rice (milled, brown, and colored) while maintaining sensory texture characteristics. Sub-Objective 1.1. In this sub-objective research will characterize the sensory characteristics related to resistant starch, slowly digestible starch, and the optimization of healthy starch in cooked rice. Sub-Objective 1.2. Under this sub-objective several methods to produce high-resistant rice starch in flour will be examined in a baked food product. Resistant starch has many colonic health-promoting properties, but often does not formulate well as an ingredient in baked foods. Objective 2: Enable new commercial functional food products using whole grain rice and rice co-products. Sub-Objective 2.1. In joint research with CrispTek research in this sub-objective will focus on adding resistant starch, fiber, and protein to current low-oil absorbing frying batters utilizing rice foods and co-products. Nutritionally-enriched baked and fried foods will be developed that sustain sensory quality. Sub-Objective 2.2. Healthier rice milk beverages and improvement of rice bran soluble protein extraction for food and beverage use will be developed. Sub-Objective 2.3. The proposed research will develop and compare several methods to produce unique rice prebiotics combined with phenolics from blueberry pomace and spent green tea. The effectiveness of each prebiotic will be evaluated utilizing in vitro fermentations and a mouse model for colonic health.
1b. Approach (from AD-416):
Rice varieties vary in amylose content that lead to differences in digestibility. Cooked table rice from different varieties will be evaluated for the amount of resistant, slowly digestible, and rapidly digestible starch based on in vitro digestion times. Thermal processes and physicochemical methods will be used to produce high resistant starch content in rice flour and starch, which will be tested as ingredients in baked foods. In collaboration with CrispTek, research will focus on adding resistant starch, fiber, and protein from rice foods and co-products to current low-oil absorbing frying batters. Nutritionally-enriched baked and fried foods will be developed with sustained or enhanced sensory qualities. Rice beverages will be developed that incorporate green technologies (e.g. focusing on raw materials and enzymatic treatments that do not rely upon previous stabilization). Lastly, methods will be evaluated to produce prebiotics from rice that include thermal and physiochemical methods and encapsulation technologies.
3. Progress Report:
Several new rice varieties containing high amounts of resistant starch are being developed that need to be compared to current rice by sensory evaluation. The goal of this research is to enhance the bioactive properties of resistant starch in commercial table rice while maintaining sensory texture characteristics for human consumption. Descriptive texture attributes were developed and tested for rice containing varying amounts of resistant starch. The data analysis of the resistant/slowly digestible starch rice confirmed that the majority of the sensory variation is due to amylose content. Resistant starch positively correlates with amylose content and some texture attributes. This indicates that sensory differences in rice are partly due to the resistant, slowly digestible, and rapidly digestible starch fractions. U.S. and imported basmati and jasmine rice were evaluated for descriptive flavors and physiochemical properties. U.S. rice varieties developed for either the basmati or jasmine market all had a flavor profile and 2-acetyl-1-pyrroline (volatile chemical with “popcorn”-like flavor) levels that were similar to imported jasmine, but not as close for imported basmati rice. Although U.S. rice breeders have made significant progress in developing aromatic rice varieties that are well adapted to the U.S. production regions, there are opportunities for additional improvements in U.S. basmati rice. Scientists at the Southern Regional Research Center have developed a chemical free, green method to almost completely solubilize unstabilized freshly hulled, germinated brown rice, leading to functional rice milk beverages. This research addresses our research objective to produce a healthier rice milk beverage. The preliminary crude beverages pass sieves readily and have reduced particle sizes, which reduce processing loss and lend to rapid food grade enzyme hydrolysis. Furthermore it appears that both fibers and oils remain soluble and have almost negligible loss, as conveyed forward in the soluble matrix. Scientists at the Southern Regional Research Center have analyzed particle size distribution in controls, wet-milled, gelatinized and enzyme treated crude rice milk beverages prepared using germinated brown rice. These crude rice milk beverages prepared from brown rice have increased total phenolic contents, and scientists are in the process of analyzing the health-promoting compound gamma-aminobutyric acid (GABA) that has been linked to improved brain health. Additionally, we have produced crude rice beverages using the same green processing regime with freshly hulled, germinated purple rice. Southern Regional Research Center scientists are developing several prebiotics from rice co-products. Cyclodextrins (sugars bound together in a ring structure) have been approved as a dietary fiber in Europe and alpha-cyclodextrin has been found to lower blood sugar levels after a high starch meal. Rice starch was converted to cyclodextrins using the enzyme cyclodextrin glucanotransferase. The enymatic processing produced predominately alpha-cyclodextrin with lower levels of beta- and gamma-cylodextrins. Additionally, arabinoxylans (non-starch polysaccharides) were isolated from rice hulls using acid hydrolysis at high temperatures. Arabinoxylans have prebiotic and antioxidant properties that are beneficial to health.
1. Rice resistant starch creates healthier food batters. ARS scientists at New Orleans, Louisiana, are working to develop health-promoting fried and baked batters for chicken and fish. Resistant starch in rice is typically at low levels and requires enzymatic processing and heating/cooling steps to increase resistant starch amounts. A method was developed, which converted normal rice starch to a starch with a high resistant starch content (8-fold higher). The processed rice starch was added to rice based food batter and then evaluated. Initial studies on fried rice batters examined the effects of resistant starch on texture and the oil content. A company is interested in current ARS research utilizing rice ingredients and co-products to enhance health.
2. Red rice bran inhibits digestive enzymes. Natural foods that can block digestive enzymes are useful for treatments of diabetes by delaying digestion and delaying absorption of carbohydrates, leading to suppression of postprandial hyperglycemia. ARS scientists at New Orleans, Louisiana, working with international collaborators examined 6 red rice varieties of Oryza sativa that have been cultivated at the Africa Rice Center in the Republic of Benin. The red rice bran samples displayed in vitro ability to inhibit both alpha-amylase and alpha-glucosidase enzymes. Additional red and purple rice samples obtained from project stakeholders were also evaluated. Results indicate rice bran polyphenolics bind to and inhibit the activity of digestive enzymes. The ability of these rice varieties to inhibit digestive enzymes will provide additional health benefits of African rice and U.S. colored rice varieties.
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