Protein Recovery from Alkaline Extracts: A Comparative Analysis of Isoelectric Precipitation and Ultrafiltration

Abstract

Proteins are one of three macro-components of a diet. An increasing demand for products that can be a complete protein source exists. The vulnerability of the current food system towards environmental impacts and the inability to keep up with the rising population has shifted the focus on valorising underutilised by-products of the food industry. The rapeseed cake (a leftover from rapeseed oil production by mechanical pressing) and spent grains (a by-product of the brewing process) are rich in proteins and a balanced amino acid profile for a complete protein product. This work used protein extraction under alkaline conditions optimal from rapeseed cake and brewers’ spent grains, respectively, and investigated the difference between the protein quantity and quality recovered using the isoelectric precipitation method and ultrafiltration combined with diafiltration.
The isoelectric precipitation method gives a good yield for rapeseed cake that has been treated with ethanol, but the purity of the proteins could be better. Ultrafiltration and diafiltration also have poor results with the same raw material. However, on the other hand, if rapeseed cake is used as is for extraction and recovery, either of the methods is good, with ultrafiltration and diafiltration providing more yield. Qualitative analysis of the results for the spent grains shows isoelectric precipitation to be ideal. However, a study with the correct methodology is needed to have conclusive results.
The choice of protein recovery method depends on the starting material used for protein extraction. Additional factors such as the intended use, further downstream processing requirements, and costs must also be considered when deciding the type of recovery process.

Popular Abstract

The Nordic Council of Ministers for Nutrition states that an adult requires ca. 0.8 - 1.5 g protein for each kg of their body weight daily, and the World Health Organization and the Food and Agriculture Organization define the daily intake requirements for the essential amino acids. As concerns about health and the environment have been on the rise in recent years, the current food system has started to show vulnerabilities. With increasing population size, production levels need to catch up. To develop a new source of healthy food that can cover all these aspects, valorising the waste/by-products of food production, often rich in proteins and other beneficial biomolecules, has been in focus. The waste from rapeseed oil production (rapeseed press cake) and the leftover grains (Brewers' spent grains) from beer production are two materials with a balanced amino acid profile to cover the daily intake requirements.
This work focuses on evaluating and comparing isoelectric precipitation and ultrafiltration combined with diafiltration as two protein recovery methods. The comparison was made based on the dry matter and protein content and the recovery yield of the final product from both methods. The proteins were extracted from the raw materials as a solution, using alkaline conditions, and then subjected to the two recovery methods. Isoelectric precipitation uses acidic pH to decrease the solubility of proteins, allowing their separation using centrifugation. On the other hand, ultrafiltration removes the solvent and concentrates the protein solution, followed by diafiltration for removing undesired impurities such as salts, minerals, etc. and improving the product purity.
The isoelectric precipitation method is ideal for recovering a high amount of protein from rapeseed cake protein extract. Still, the purity of the final product is not as good as the one made from ultrafiltration and diafiltration. When the rapeseed cake is treated with ethanol before protein extraction, the purity and content of protein in the final product are poor, irrespective of the type of recovery method used. However, if the yield is to be considered, isoelectric precipitation has the edge over ultrafiltration and diafiltration.
Due to an error in the experimental design, the spent grains could only be analysed qualitatively. The isoelectric precipitation can be considered to be ideal for the spent grains since the protein content recovered was higher. However, a study with the correct methodology is needed to have conclusive results.
The results of this work show that both methods considered here can provide good results. Still, the intended end use, the type of starting material, how it is processed, and operating costs should also be factored in when choosing the recovery method.

• author: Sharma, Anjay
• supervisor: Federico Gomez
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLTM01 20231
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Rapeseed cake, Brewers spent grains, Protein recovery, Ultrafiltration, Alkaline extraction, Food engineering
• language: English
• id: 9140482
• date added to LUP: 2023-11-15 16:25:33
• date last changed: 2023-11-15 16:25:33