Alkaline Protein Extraction of Oat Bran and Oat Endosperm Flour - the Effect of pH during Extraction and Precipitation
Abstract: An increased understanding of the negative impacts of animal-based proteins, on both environment and health, has led to a rise in the demand for plant-based proteins. To meet the demands, conventional crops must be efficiently utilized. One possible crop is oat which is a good source of protein, fibre, and fat, but is currently mainly used for animal feed. To better utilize the proteins in oat, they can be extracted to produce oat powders with high protein concentration. The aim of this project was to evaluate alkaline extraction for its efficacy in protein extraction from both milled oat bran and oat endosperm flour. This work also aims to provide a literature survey on oat, oat protein and its functional properties as well as protein extraction methods. The experimental set-up consisted of alkaline extraction followed by isoelectric precipitation, with focus on the effect of pH on yield, protein content and dry matter content. Two extraction pH, two precipitation pH and constant versus non-constant pH during the alkaline treatment was investigated. In addition, a differential scanning calorimetry (DSC) test was performed to analyse the proteins. Alkaline extraction resulted in high protein yields of 80-83% for oat endosperm flour and 66-70% for milled oat bran, where the range includes the results from all pH-levels tested. The protein content in the sediment extracted from oat endosperm flour and milled oat bran was 73-75% and 75-77% respectively. Precipitation pH 4.5 resulted in higher dry matter content for both raw materials, compared to pH 5.5. Constant pH during alkaline treatment did not improve protein yields, which was unexpected. However, the protein content was improved wen using constant extraction. The thermal properties analysis (DSC) of the proteins revealed higher peak denaturation temperatures for proteins precipitated at pH 5.5. This applied for both milled oat bran and oat endosperm flour. The results from this project indicate that protein extraction from oat is comparably easy, relative to other plant sources. No optimal extraction can be developed as it depends on the intended use of the proteins and would require analysis of functional properties before any definitive conclusions can be drawn. Rather, the results of this study can be used in further development of alkaline extraction of oat. The conclusions are then that the yield is mostly unaffected by the choice of pH, within the interval, and does not require constant pH to be high. Although constant pH is preferable for protein content, it is more affected by the choice of pre-treatment than it is by extraction pH. For an energy efficient process precipitating pH at 4.5 should be used to shorten the following drying process, and precipitation pH 5.5 is preferred if the proteins need to be more heat tolerant.
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