Location: Plant Polymer Research
Title: Effect of okra-extract on wheat, corn, and rice starches properties Authors
Submitted to: Journal of Food Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 31, 2011
Publication Date: N/A
Interpretive Summary: The objective of this work was to determine the effect of okra extract on starch properties and bread quality. Okra extract is a product from okra pods and is used as a source of soluble fiber. Bread made from okra extract is expected to have high protein, additional soluble fiber and low carbohydrates. Among other health benefits, soluble fiber has been proven to lower elevated cholesterol. To deliver 0.75 g per bread serving, the minimum required by the FDA in order to make a health claim, at least 10% of okra soluble-fiber containing products, such as bread, should be consumed. This is a two step project. The first step was to study the effect of okra-extract on starch properties. The second will be to develop new bread formulations containing high soluble fiber extracted from okra pods. In this project we added up to 15% okra soluble fiber to different starches. Okra extracts were found to alter starch properties significantly. Lower starch retrogradation and gel firmness were observed in the presence of okra extract. This effect is expected to improve bread formulations, which require increasing the protein content of the formulation using vital gluten. This project benefits the overall public health and increases the profitability of the oats industry. This project may also help to increase the sales of wheat grown in North Dakota.
Technical Abstract: Seedless okra pods were extracted with 0.05M NaOH. The extract was centrifuged and the supernatant and the precipitate were freeze-dried. Wheat, corn and rice starch blends were prepared by replacing 0, 5, 190, and 15% of the starch with dried supernatant (DSP) or dried precipitate (DPP). The effect of DSP and DPP on starch properties was determined by rapid visco-analysis (RVA), gel texture analysis, and dynamic rheology. The presence of DSP significantly (p= 0.05) reduced the peak temperature of starch compared to 100% starch. The DPP containing samples exhibited significantly higher peak temperature due to the presence of more cellulose. Similar effect was observed on the setback of all starches. Starch-gel firmness was significantly reduced by DSP. Although corn starch showed the highest gel firmness value, it had the highest drop in firmness, whereas wheat starch showed a linear reduction in firmness compared to corn starch. The reduction in gel firmness is due to two factors, the replacement of starch and the action of the DSP. The reduction in gel firmness was found to be 39% for 15% starch replacement. All test frequencies showed that starches exhibited G’ higher than G”. The elastic moduli (G’) of wheat starch reached a plateau about 1360 Pa, while the phase shifts were in the range of 5o - 17o. Corn starch showed slightly weaker viscoelastic solid properties compared to wheat starch with a G’-plateau around 1120 Pa and phase shifts range between 5o and 16o, while rice starch was the weakest. The presence of 15% DSP reduced the G’ of both wheat and corn starch by 50%, while DPP effect was the higher G’. All starches exhibited shear thinning behavior, where the viscosity of wheat and corn starches was lower than 10Pa-s at 100 s-1 shearing rate.