Review: current trends in oat protein recovery and utilization in aqueous food systems

Oat protein itself, as a substance, has extensively been studied providing information on its nutritional value, some functional properties and possible applicability in food systems. Chosen protein isolation methods and technological aspects define final composition of obtained oat protein product, its concentration, nutrition value and its functionality in food industry. Scientific data on oat protein recovery methods, typically relying on protein solubility or dry fractionation, provides an insufficient knowledge about the success in commercialization of oat protein recovery technologies and their derivatives in form of oat protein. The aim of the study was to analyse and summarize the research findings on oat protein extraction methods and functional properties of oat protein. Semi-systematic, monographic methods were used to analyse the oat protein isolation techniques, functional properties of oat protein in aqueous food systems, covering the latest information on oat protein extraction methods. Wet and dry isolation methods were demonstrated as main methods in oat protein extraction. Functional properties of oat protein, such as thermal stability, solubility, emulsification, water hydration capacity and foaming were reviewed and evaluated, identifying limitations and protein alterations which occur through the oat protein extraction process. The study provides recent trends in oat protein recovery technologies, along with an overview of current and potential oat protein utilization in food systems.

Strategies to Enhance Periplasmic Recombinant Protein Production Yields in Escherichia coli

Main reasons to produce recombinant proteins in the periplasm of E. coli rather than in its cytoplasm are to -i- enable disulfide bond formation, -ii- facilitate protein isolation, -iii- control the nature of the N-terminus of the mature protein, and -iv- minimize exposure to cytoplasmic proteases. However, hampered protein targeting, translocation and folding as well as protein instability can all negatively affect periplasmic protein production yields. Strategies to enhance periplasmic protein production yields have focused on harmonizing secretory recombinant protein production rates with the capacity of the secretory apparatus by transcriptional and translational tuning, signal peptide selection and engineering, increasing the targeting, translocation and periplasmic folding capacity of the production host, preventing proteolysis, and, finally, the natural and engineered adaptation of the production host to periplasmic protein production. Here, we discuss these strategies using notable examples as a thread.

Bioactivity Potential of Industrial Sunflower Meal Ethanol-Wash Solute Obtained as Waste from Protein Isolation Process

Industrial sunflower meal is rich in secondary metabolites, which negatively influence the quality and functional properties of respective protein isolates. To reduce their quantity, sunflower meal was subjected to a four-step treatment with 75% aqueous ethanol solution. The ethanol-wash liquids were collected, concentrated, and freeze-dried to prepare powdery sunflower meal ethanol-wash solute (SEWS). Otherwise considered waste from the main process of protein isolation, the SWES was turned into a novel product containing macrocomponents, microelements, and bioactive compounds. It was found to be rich in carbohydrates (62.14%), lipids (7.73%), and bioactive compounds such as phenols (16.38%) and flavonoids (4.41%). Gas Chromatography-Mass Spectrometry (GC–MS) analyzes revealed prevalence of sucrose (14.01%), linoleic acid (12.10%), and chlorogenic acid (85.41%) based on total ion current (TIC) of polar, nonpolar, and phenolic compounds, respectively. The SEWS was found to be rich in microelements with iron (259.02 mg/kg) and copper (109.36 mg/kg) being the highest amounts. The product contained 0.10 mg/kg selenium. Scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals increased with the increase in SEWS concentrations and reached 52.3% and 69% for 0.05% SEWS when dissolved in water and 70% ethanol, respectively. The highest hydroxyl radical scavenging activity (52.4%) was achieved at 0.1% SEWS. For all studied concentrations (0.005% to 0.1%), the SEWS exhibited a higher inhibition capacity than mannitol, which was used as a positive control. The SEWS demonstrated inhibiting properties against Gram (+) Curtobacterium flaccumfaciens PM-YT and Fusarium moniliforme ATCC 38932 fungus. The obtained results outline the SEWS as a natural product with bioactive properties that might be useful in the agriculture, food, and nutraceutical industries.

Preliminary Characterisation of Wastes Generated from the Rapeseed and Sunflower Protein Isolation Process and Their Valorisation in Delaying Oil Oxidation

Since rapeseed and sunflower meals are two of the most representative oilseed crops in the world, this study was focused on ethanol-wash solutes (EWS) obtained as wastes from the protein isolation process of rapeseed and sunflower meals. These meals have been previously valorised; however, the use of the EWS is unexplored. The present study is aimed at the characterisation of their phenolic profile, and antioxidant capacity for preventing lipid oxidation in rapeseed, sunflower, and soybean oil, which has been used as a reference oil. The sunflower EWS exhibited more total phenolic compounds (TPC) and antioxidant activity (119.39 ± 1.13 mg GA/g and 193.97 ± 9.77 mg TE/g, respectively) than the rapeseed one (103.44 ± 5.94 mg GA/g and 89.51 ± 3.17 mg TE/g). The phenolic identification showed hydroxybenzoic and protocatechuic acid in the rapeseed EWS, and pyrogallol and caffeic acid in the sunflower EWS, as the main representative phenols. Both EWS at 15% increased significantly (p < 0.05) the oxidative stability of the oils in the Rancimat equipment with values of antioxidant activity index (AAI) from 1.01 to 1.20, depending on the type of oil employed. In conclusion, the rapeseed and sunflower EWS showed great potential, and they could be used as a source of natural antioxidants within the food industry, replacing the synthetic ones, and promoting the circular economy since they are agro-food wastes.

Optimization of Protein Isolation and Label-Free Quantitative Proteomic Analysis in Four Different Tissues of Korean Ginseng

Korean ginseng is one of the most valuable medicinal plants worldwide. However, our understanding of ginseng proteomics is largely limited due to difficulties in the extraction and resolution of ginseng proteins because of the presence of natural contaminants such as polysaccharides, phenols, and glycosides. Here, we compared four different protein extraction methods, namely, TCA/acetone, TCA/acetone–MeOH/chloroform, phenol–TCA/acetone, and phenol–MeOH/chloroform methods. The TCA/acetone–MeOH/chloroform method displayed the highest extraction efficiency, and thus it was used for the comparative proteome profiling of leaf, root, shoot, and fruit by a label-free quantitative proteomics approach. This approach led to the identification of 2604 significantly modulated proteins among four tissues. We could pinpoint differential pathways and proteins associated with ginsenoside biosynthesis, including the methylerythritol 4–phosphate (MEP) pathway, the mevalonate (MVA) pathway, UDP-glycosyltransferases (UGTs), and oxidoreductases (CYP450s). The current study reports an efficient and reproducible method for the isolation of proteins from a wide range of ginseng tissues and provides a detailed organ-based proteome map and a more comprehensive view of enzymatic alterations in ginsenoside biosynthesis.

Study of Acid Whey Fouling after Protein Isolation Using Nanofiltration

In this paper, nanofiltration (NF) of acid whey after isolation of proteins was studied. Two membranes were tested: NF-99 (Alfa Laval) and DL (Osmonic Desal). Based on previous measurements that determined the highest efficiency in separating lactic acid and lactose whey, the pH was adjusted to 3. First, the most appropriate transmembrane pressure (TMP) was determined based on the highest flux measured. The TMP range was 5–25 bar for the DL membrane and 10–30 bar for the NF-99 membrane. The temperature was kept at 4 °C using a thermostat. The mechanisms of membrane fouling were investigated. The Hermia models and the modified Tansel model were applied to study the fouling mechanism and to determine which membrane would foul earlier and more severely, respectively. The most suitable TMP was determined at 20 bar. Despite the 1.4 times higher flux of the sample at DL, the fouling rate was higher when NF-99 was used. The results showed that the Tansel model is suitable for predicting the fouling time of protein-isolated whey by nanofiltration.

Does Filter Aided Sample Preparation (FASP) Provide Sufficient Method Linearity for Quantitative Plant Shotgun Proteomics?

Gel-free LC-based shotgun proteomics represents the current gold standard of proteome analysis due to its outstanding throughput, analytical resolution and reproducibility. Thereby, the efficiency of sample preparation, i.e., protein isolation, solubilization and proteolysis, directly affects the correctness and reliability of quantification, being therefore the bottle neck of shotgun proteomics. The desired performance of the sample preparation protocols can be achieved by application of detergents. However, these ultimately compromise reverse phase chromatographic separation and disrupt electrospray ionization. Filter aided sample preparation (FASP) represents an elegant approach to overcome these limitations. Although this method is comprehensively validated for cell proteomics, its applicability to plants and compatibility with plant-specific protein isolation protocols is still unknown, i.e., no data on linearity of underlying protein quantification methods for plant matrices is available. To fill this gap, we address here the potential of FASP in combination with two protein isolation protocols for quantitative analysis of pea (<i>Pisum sativum</i>) seed and <i>Arabidopsis thaliana</i> leaf proteomes by the shotgun approach. For this, in comprehensive spiking experiments with bovine serum albumin (BSA), we evaluated the linear dynamic range (LDR) of protein quantification in the presence of plant matrices. Further, we addressed the interference of two different plant matrices in quantitative experiments, accomplished with two alternative sample preparation workflows in comparison to conventional FASP-based digestion of cell lysates, considered here as a reference. Our results indicate very good applicability of FASP to quantitative plant proteomics with an only limited impact of the protein isolation technique on the methods overall performance.<br>