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.

Popular Abstract

Extraction of Protein from Oat

A growing world population combined with an increased understanding of the negative effects of animal-based proteins on the environment as well as on health, means that the demand for new and sustainable plant-based proteins is rising. To meet the interest, food companies in Sweden turn towards readily available plant-sources, such as oat, which can be locally grown in our cooler climates. But how can protein be efficiently extracted from oat, and what decides how it can be used in food products?

Oat has become more popular lately due to its nutritional benefits. Amongst other, it contains high amounts of protein compared to other cereals, but still, its main application is as feed for animals and not for human consumption. If we want to utilize oat for its full potential, one way is to separate the proteins and use them to create high-protein food products.

In this study we investigated if protein could be extracted from different oat materials, from different parts of the oat grain, with varying amounts of protein. So far, oat protein has only been produced from the high-protein oat bran, whilst the largest part of the oat grain, the endosperm, has not been used. Our results show that protein can be more easily extracted from oat than other materials such as hemp, and a protein powder with a protein content of over 70% was obtained from both the milled oat bran and the oat endosperm flour. In addition, we found that protein was easier to remove from the oat endosperm flour than from the milled oat bran. Over 80% of the protein was able to be collected from oat endosperm flour whilst the milled oat bran yielded approximately 70%.

To extract the proteins, a so-called alkaline methodology was used, in which high pH separates the proteins from the oat flours. The impact of some key parameters on the extraction process were evaluated. In particular, we found that pH did not affect the protein yields as much as previously known, and that a gentler process can be used as the material is so easy to extract from. However, pH during the purification step of the process did influence how much water the protein retains, a factor which had not been previously observed.

Finally, a review of the properties of oat proteins based on results from previous studies was summarized. These properties include amongst other how easily the protein powder is dissolved in water, how high temperature the proteins can withstand, and whether the proteins can be used to create emulsions, foams, or gels. How well a protein can do any of these things dictates the potential applications in food products. Here it was found that oat proteins unfortunately perform comparatively poor, except for having a high temperature resistance. However, the properties can be improved by using different modification methods.

In conclusion, our results indicate that oat has great potential as a plant-based protein source, which may include additional uses for this Swedish-grown grain. While more work is required to improve the properties of the resulting protein, the final product may be successfully applied in a wide range of food products.

• author: Nielsen, Bella and Rodhe, Alva
• supervisor: Jeanette Purhagen; Amanda Helstad; Christian Malmberg; Karin Arkbåge; Mats Larsson
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLTM05 20211
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering; Agriculture and Food Sciences
• keywords: Oats, Protein, Alkaline extraction, Protein extraction, Plant-based proteins, Oat protein, Oat bran, Oat endosperm, Iso-electric precipitation, Food engineering
• language: English
• id: 9054807
• date added to LUP: 2021-06-16 12:20:50
• date last changed: 2021-06-16 12:20:50