Reduced Protein Solubility Research Articles

Exploring the Impact of Solid-State Fermentation on Fava Bean Flour: A Comparative Study of Aspergillus oryzae and Rhizopus oligosporus.

Fava bean (Vicia faba L.) is a protein-rich pulse with high nutritional value, but its functional and sensory characteristics limit its application in foods. Solid-state fermentation (SSF) can modify the composition of plant proteins, modulate its functionality, and enhance the sensory aspects. In this study, fava bean flour (FB) was fermented with Aspergillus oryzae and Rhizopus oligosporus to produce FBA and FBR, respectively, ingredients with distinct nutritional, functional, and aroma characteristics. The protein content increased by 20% in FBA and 8% in FBR, while fat levels rose more significantly in FBR (+40%). The overall content of fermentable oligo-, di-, mono-saccharides, and polyols (FODMAPs) decreased by 47% (FBA) and 57% (FBR), although polyol production by A. oryzae was observed. SSF improved the nutritional profile of FBA and FBR, with a notable increase in the concentration of essential amino acids observed, and a reduction in most antinutrients, with the exception of trypsin inhibitors. SSF resulted in the formation of aggregates, which increased the particle size and reduced protein solubility. Emulsions prepared with the fermented ingredients separated faster, and the foaming capacity of both FBA and FBR was decreased, but an increase in water-holding capacity was observed. SSF resulted in the production of predominantly savoury-associated aroma compounds, with compounds characteristic of metallic and mouldy aromas reduced. These results indicate the potential of SSF to transform FB with enhanced nutritional value and improved sensory and functional properties.

PH-induced conformational changes of lupin protein-pectin mixtures and its effect on air-water interfacial properties and foaming functionality

Lupin protein isolate (LPI) has high nutritional value and good foaming properties around neutral pH; however, its functionality becomes poor at acidic pH, due to reduced protein solubility. The addition of pectin to LPI can increase its solubility at acidic pH and hence improve protein functionality. Here, we investigated the air-water interfacial and foaming properties of LPI-pectin (1:1) mixtures at pH 3.5–7.0. We used interfacial shear and dilatational rheology, characterized the air-water interfacial microstructure with AFM of Langmuir-Blodgett films, and linked the results to the foaming properties of the LPI-pectin mixtures. Based on the phase diagram, LPI and pectin formed co-soluble mixtures at pH 6.0 and 7.0, while LPI-pectin electrostatic complexes were formed at pH 3.5 and 4.0. In the co-soluble mixtures, proteins diffused faster towards the air-water interface than the electrostatic complexes, due to smaller particle sizes of the proteins. Their air-water interfaces showed distinct differences with respect to microstructure and mechanical properties. The interfaces stabilized by co-soluble mixtures were dominated by protein aggregates, leading to weaker interfaces in response to shear and dilatational deformation, while the complexes formed thicker and denser polymeric air-water interfaces that were stiffer and more solid-like. As a result, the complex-stabilized foams were more stable than those stabilized with co-soluble mixtures. Findings from this study indicate that soluble LPI-pectin complexes formed at pH 3.5 and 4.0 were more efficient in improving interfacial and foaming properties of LPI than the co-soluble mixtures at pH 6.0 and 7.0, which can be used to tailor the properties of acid aerated products stabilized by LPI.

Predicting the effects of mutations on protein solubility using graph convolution network and protein language model representation.

Solubility is one of the most important properties of protein. Protein solubility can be greatly changed by single amino acid mutations and the reduced protein solubility could lead to diseases. Since experimental methods to determine solubility are time-consuming and expensive, in-silico methods have been developed to predict the protein solubility changes caused by mutations mostly through protein evolution information. However, these methods are slow since it takes long time to obtain evolution information through multiple sequence alignment. In addition, these methods are of low performance because they do not fully utilize protein 3D structures due to a lack of experimental structures for most proteins. Here, we proposed a sequence-based method DeepMutSol to predict solubility change from residual mutations based on the Graph Convolutional Neural Network (GCN), where the protein graph was initiated according to predicted protein structure from Alphafold2, and the nodes (residues) were represented by protein language embeddings. To circumvent the small data of solubility changes, we further pretrained the model over absolute protein solubility. DeepMutSol was shown to outperform state-of-the-art methods in benchmark tests. In addition, we applied the method to clinically relevant genes from the ClinVar database and the predicted solubility changes were shown able to separate pathogenic mutations. All of the data sets and the source code are available at https://github.com/biomed-AI/DeepMutSol.

Protein structural changes in lentil flour during soaking/germination and thermal treatments: Indication of nutritional and functional properties

Functional characteristics of lentil's protein have a significant impact on texture of developed food products and are an important consideration for ingredient manufacturers in food industries. Soaking/germination and thermal treatments are well-known methods in modifying these characteristics by altering protein structure. Therefore, in this study, the combination of these methods at two heat intensity categories, above and below protein denaturation, was utilized to examine modification of the structural, nutritional, and functional properties of processed lentil flours. The results showed that processing of lentil seeds impacted their protein secondary structure from ordered to disordered structures, by decreasing β-sheet and α-helix and increasing intermolecular β aggregates and random coil conformation. In terms of nutritional value, the applied processing improved lentil flours by higher protein content after germination and enhanced protein digestibility after thermal processing. Generally, protein solubility was negatively affected by thermal conditions, with microwave-infrared drying having the most significant impact on reducing protein solubility. Mostly, the processing did not noticeably affect the emulsifying activity and oil binding capacity, while it significantly reduced emulsifying stability at high-temperature methods. The findings suggests that germination-thermal processing combination enhances nutritional/functional properties of lentil flours and provides opportunities for their incorporation into value-added food product formulations.

Ensiling and thermic treatment effects on ruminal carbohydrate fermentation and post-ruminal crude protein concentration in partial-crop peas and faba beans

This study was conducted to examine effects of ensiling, toasting or ensiling plus toasting in partial-crop field peas and faba beans harvested each with 375 g dry matter/kg (Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie (BBCH) scale 79 and 81, respectively) on gas production and post-ruminal crude protein (PRCP) concentration byin vitro incubation in ruminal fluid batch-cultures. The silages made from partial-crop field peas and faba beans (Rostock Model Silages) had a pH of 4.3 and 4.6, respectively, and were not typically lactic acid dominated. The silages remained stable after opening for 100 h (peas) and 168 h (faba beans). Toasting was simulated in a drying oven at 160 °C for 60 min. Post-incubation pH and gas accumulation profiles were little affected by treatment. Ensiling did not alter effective PRCP. Toasting and ensiling plus toasting increased effective PRCP up to 25 and 20%-points in peas and up to 35 and 11%-points in faba beans, respectively. Ensiling increased non-protein nitrogen and soluble protein concentration, whilst toasting decreased soluble protein. Significant correlations existed between protein fraction B3 (neutral detergent-insoluble protein) and effective PRCP (r≥0.84;P<0.05) and fraction C (acid detergent-insoluble protein) and effective PRCP (r≥0.79;P<0.05). Ensiling and toasting both decreased arginine and lysine levels. It was concluded that partial-crop peas and faba beans with BBCH 79 and 81, respectively, can provide readily available nutrients and high-quality fibre in the residual plant. However, preserving by ensiling required balance between the reduction of non-protein nitrogen and fermentability characteristics. Toasting reduced protein solubility and increased PRCP, but it was not clear if PRCP was usable for ruminants or was partially bound into Maillard polymers.

Alkali-Induced Phenolic Acid Oxidation Enhanced Gelation of Ginkgo Seed Protein.

The effect of alkali-induced oxidation of three phenolic acids, namely gallic acid, epigallocatechin gallate, and tannic acid, on the structure and gelation of ginkgo seed protein isolate (GSPI) was investigated. A mixture of 12% (w/v) GSPI and different concentrations of alkali-treated phenolic acids (0, 0.06, 0.24, and 0.48% w/w) were heated at 90 °C, pH 6.0, for 30 min to form composite gels. The phenolic treatment decreased the hydrophobicity of the GSPI sol while enhancing their rheological properties. Despite a reduced protein solubility, water holding capacity, stiffness, and viscoelasticity of the gels were improved by the treatments. Among them, the modification effect of 0.24% (w/v) EGCG was the most prominent. Through the analysis of microstructure and composition, it was found to be due to the covalent addition, disulfide bond formation, etc., between the quinone derivatives of phenolic acids and the side chains of nucleophilic amino acids. Phenolic acid modification of GSPI may be a potential ingredient strategy in its processing.

Investigating starch and protein structure alterations of the processed lentil by microwave-assisted infrared thermal treatment and their correlation with the modified properties

Microwave-assisted infrared is an emerging green technology that can be used in the thermal processing of lentils to modify their functional and nutritional properties as high-value plant-based protein ingredients. The study employed this technology to heat lentil seeds tempered to three higher moisture contents to produce modified flours. The influence of thermal process conditions on the starch structure was evaluated by reducing the degree of order through gelatinization, and the protein structure was assessed through denaturation, which led to the decline in the ordered structure of protein, β-band and α-helix, and the rise in the aggregated intermolecular structure, β-I, and unordered structure, random coil. Results showed that seeds tempered to the highest moisture content, 50%, and processed in higher thermal intensities, by the rise in microwave power and infrared combinations, experienced a higher degree of starch gelatinization and protein denaturation, improving the water holding capacity while reducing protein solubility. Particle size distributions and scanning electron microscopy analyses illustrated that thermal treatment eased the milling process in breaking down coarse particles. The modification process was also an effective way to improve nutritional properties by increasing in vitro starch and protein digestibility.

Physicochemical and microstructural mechanisms for quality changes in lightly salted tilapia (Oreochromis niloticus) fillets during frozen storage.

Frozen tilapia fillet has become a leading aquatic product. High drip loss, dry and fibrous mouthfeel, and an unappealing appearance are its main problems. It was hypothesized that light salting could improve the quality, and that the preparation conditions would affect the storage stability of frozen tilapia fillets. The quality changes of lightly salted tilapia fillets were evaluated during frozen storage, and the underlying mechanisms were studied from the physicochemicaland microstructural perspectives. Though the salt content was 1.5% in all samples,the amount of ice crystals in frozen tissues decreased with the descending water content and freezing point (P < 0.05). No intracellular voids were observed in the samples prepared under proper salting conditions, and the myofibers were plump and smooth after freezing-thawing, which contributed to the high water-holding capacity of lightly salted fillets. After 28 days,the water-binding capacity of the salted groups was 14.69%-18.62% higher than that of their unsalted counterparts (P < 0.05). The reduced protein solubility in the salted fillets was likely to have occurred because the solubilized and unfolded proteins interacted more easily during frozen storage. The oxidation degree of myofibrillar proteins was also affected by salting condition, and the fillets with less oxidized sulfhydryl groups maintained high springiness after 28 days of frozen storage. The salting condition of 9% NaCl solution for 1h was recommended for the preparation of lightly salted fillets from freshwater fish, taking into account quality, processing efficiency, and storage stability. The enhanced water-holding capacity and texture of lightly salted tilapia fillets were attributed to modified physicochemical and microstructural properties. These results could provide a scientific basis for the processing and storage of high-quality, frozen, lightly salted fillets from freshwater fish. © 2022 Society of Chemical Industry.

The Fate of IgE Epitopes and Coeliac Toxic Motifs during Simulated Gastrointestinal Digestion of Pizza Base.

Understanding how food processing may modify allergen bioaccessibility and the evolution of immunologically active peptides in the gastrointestinal tract is essential if knowledge-based approaches to reducing the allergenicity of food are to be realised. A soy-enriched wheat-based pizza base was subjected to in vitro oral–gastro–duodenal digestion and resulting digests analysed using a combination of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry (MS). The digestion profile of pizza base resembled that of bread crust where higher temperatures during baking reduced protein solubility but still resulted in the generation of a complex mixture of peptides. MS profiling showed numerous peptides carrying IgE epitopes, and coeliac toxic motifs were in excess of 20–30 residues long and were only released after either 120 min of gastric digestion or a combination of gastric and duodenal digestion. In silico prediction tools showed an overestimated number of cleavage sites identified experimentally, with low levels of atypical peptic and chymotryptic cleavage sites identified particularly at glutamine residues. These data suggest that such alternative pepsin cleavage sites may play a role in digestion of glutamine-rich cereal foods. They also contribute to efforts to provide benchmarks for mapping in vitro digestion products of novel proteins which form part of the allergenicity risk assessment.

Effects of Different Heat Processing on Molecular Weight and Allergenicity Profile of White Shrimp (Litopenaeus vannamei) and Mud Crab (Scylla serrata) from Indonesian Waters

Shrimp and crab are fishery products with high nutritional value, especially as protein sources. However, they belong to the crustacean group known to cause many allergies in Southeast Asian countries. Not only affecting the nutritional composition, processing also has the potential in reducing the allergenicity of a food ingredient. This study aims to analyze the effects of various heat processing on nutrient composition, soluble protein content, protein molecular weight profile, and allergenicity of white shrimp and mud crab. The processing was carried out by boiling, frying, and autoclaving. Changes in macronutrient content were determined using proximate analysis. Soluble protein content was analyzed using the Bradford method, while molecular weight and allergenicity profiles were analyzed using SDS-PAGE electrophoresis and ELISA techniques. Results showed that processing treatment could significantly reduce protein solubility. SDS-PAGE profile showed that heating shrimp and crab using autoclave at 121.1 oC and pressure of 0.2 MPa for 10 min was able to remove protein bands of 35-38 kDa, which were suspected as the allergen bands. However, boiling (100 oC for 10 min) and deep frying in palm oil (160 oC for 10 min) treatments of the samples gave stronger 35-38 kDa bands intensity than the unprocessed sample. Autoclaving was able to significantly reduce IgE reactivity to shrimp extract better than the boiling and frying process. In contrast, IgE reactivity of crab extract was increased by heat processing especially frying. Thus, autoclaving can be used in the white shrimp processing to produce hypoallergenic food.

Microstructure change in whole egg protein aggregates upon freezing: Effects of freezing time and sucrose addition

Protein is not stable under freezing conditions, which may lead to changes in protein aggregates. In this study, liquid whole egg samples were frozen and thawed. The structural changes in the whole egg aggregates were then analyzed. After analyzing samples using tunable resistance pulse sensing, it was found that the number of protein aggregate samples increased nearly six-fold after freezing and thawing. The addition of sucrose reduced the enhancement of particle number. The surface characteristics of whole egg protein aggregates varied during the freezing process. By adding sucrose to the whole egg sample, the variation in aggregate surface characteristics was weakened. The same samples were also investigated using a small-angle X-ray scattering device. The results showed that the inner structure of whole egg protein aggregates became less packed during the freezing process. However, changes in protein aggregates caused by freezing were prevented by the addition of sucrose. In conclusion, freezing unfolded whole egg proteins and reduced protein solubility, which further increased the number of protein aggregates and changed the structure of the aggregates. Sucrose could be a cryoprotectant and inhibit the influence of freezing on whole egg protein aggregates. • Aggregate formation upon freezing of the whole egg solution was investigated. • It found that the particle number concentration increased during the freezing process. • The aggregates became less packed during the freezing process. • It was confirmed that the addition of sucrose reduced the degree of structural change of aggregate during freezing.

Sensory profile, functional properties and molecular weight distribution of fermented pea protein isolate

Pea protein isolate (PPI, from Pisum sativum L.) was fermented with six different lactic acid bacteria strains for 24 ​h and 48 ​h. The fermented samples were analyzed regarding their retronasal aroma and taste, their protein solubility, emulsifying and foaming capacity. Changes in the molecular weight distribution were analyzed to monitor potential effects of fermentation on the main allergenic protein fractions of PPI. After 24-h fermentation, PPI's characteristic aroma attributes and bitter taste decreased for all fermented PPI. However, after 48-h fermentation, cheesy aroma, and acid and salty tastes were increased. The PPI fermented with L. plantarum showed the most neutral taste and the panel's highest preference; instead, fermentation with L. fermentum led to a fecal aroma and was the least preferred. The protein solubility and emulsifying capacity decreased after PPI fermentation, while foaming capacity remained constant in comparison to the untreated PPI. The electrophoretic results showed a reduction in the intensity of the allergenic protein fractions; however, these changes might be attributed to the reduced protein solubility rather than to a high proteolytic effect of the strains. Fermentation of PPI for 24 ​h and 48 ​h might not be a suitable method for the production of highly functional pea proteins. Further modification methods have to be investigated in the future.

H2O2-induced cataract as a model of age-related cataract: Lessons learned from overexpressing the proteasome activator PA28αβ in mouse eye lens

Cataract, the world-leading cause of blindness, is formed when crystallin aggregates cloud the eye lens. We overexpressed PA28αβ, a proteasome activator with properties protective against aggregation and oxidative stress, and examined whether they are less prone to develop cataract arisen from aging and/or hydrogen peroxide (H2O2) treatment. Another objective of this work was to compare the H2O2-induced cataracts of mouse lenses ex vivo to cataracts formed upon aging in mice.As part of an aging study of F2 hybrid C57BL/6NxBALB/c mice, ocular lenses of mature adult (7 months), middle-aged (15 months), and old (22 months of age) PA28αOE mice and their wildtype littermates (n = 22–44 lenses per group) were dissected and evaluated with regard to their cataractous state. In parallel, ocular lenses from 3 to 4 months old PA28αOE and wildtype C57BL/6 N littermates were treated with 100 μM H2O2 every 24 h for 7 days, with progression of cataract and physical appearance monitored daily. Lenses from both studies were also subjected to analysis of oxidative protein damage (carbonylation) and protein solubility.We found that overexpression of PA28αβ had no effect on neither age-related nor H2O2-induced cataract and conclude that overexpression of PA28αβ does not protect mice from developing cataract. The inefficiency of PA28αβ against cataract could be due to its anti-aggregation activity being already excessively present in the eye lens, exerted by crystallins. Crystallins are likely also constituting the 20–25 kDa proteins that were the dominant carbonyl targets in the eye lens irrespective of cataractous state.Assessment of H2O2-induced cataract in relation to age-related cataract demonstrated that high molecular weight protein carbonylation correlates to cataract both in vivo and ex vivo, while reduced protein solubility is more pronounced in age-related cataract. Furthermore, this work highlights vast dissimilarities in the physical manifestations of cataract upon aging and H2O2 ex vivo treatment. Age-related cataract initiation can take various forms, as a vague general blurriness or as a barely visible demarcated opacity, while H2O2-induced cataractogenesis seems to follow a specific scheme. In mice, this scheme begins with relatively opaque peripheral areas emerging that clear up later on as the lenses start to display a hat-like appearance. This transformation takes place synchronous to swelling of the eye lens, and is likely a result of osmotic disturbances causing a phase separation between the viscous lens cortex and the more solid fibers of the lens nucleus.

Effect of pulsed light on microbial inactivation, sensory properties and protein structure of fresh ricotta cheese

Ricotta cheese was subjected to PL treatments at increasing fluence (1.3, 3.1, 7.5, 15.0 J/cm2) and stored at 4 °C. Just treated samples presented microbial counts (Pseudomonas spp., Enterobacteriaceae, yeasts) lower than those of the untreated one. PL at 1.3 and 3.1 J/cm2 allowed delaying microbial spoilage during storage but higher fluences favoured microbial growth and off-odour formation, probably due to the surface nature of PL technology. The penetration depth of the UV-C fraction of PL resulted of only 1.5 mm, hindering microbial inactivation at the core and promoting local modification of ricotta cheese constituents. FTIR, SDS-PAGE and DLS analysis demonstrated that PL induced the formation of small protein particles, able to interact with lipids and carbohydrates, and rearrange into larger aggregates. Aggregation reduced protein solubility and occurred following exposure of hydrophobic protein groups, enhancement in S–S bonding and changes in α-helix and β-sheets structures. Proteins photoreaction was confirmed by the formation of melanoidins and carbonyls.

Impact of cold plasma processing on major peanut allergens

Cold plasma is emerging as a novel food processing technology, with demonstrated efficacies for microbial inactivation and residual chemical dissipation of food products. Given the technology’s multimodal action it has the potential to reduce allergens in foods, however data on the efficacy and mechanisms of action are sparse. This study investigates the efficacy of cold plasma on major peanut allergens (Ara h 1 and Ara h 2). For this purpose, dry, whole peanut (WP) and defatted peanut flour (DPF) were subjected to an atmospheric air discharge using a pin to plate cold plasma reactor for different treatment durations. With increases in plasma exposure, SDS-PAGE analysis revealed reduced protein solubility of the major peanut allergens. Alterations in allergenicity and structure of Ara h 1 and Ara h 2 were examined using ELISA and circular dichroism (CD) spectroscopy. Competitive ELISA with proteins purified from plasma treated WP or DPF revealed reduced antigenicity for both Ara h 1 and Ara h 2. The highest reduction in antigenicity was 65% for Ara h 1 and 66% Ara h 2 when purified from DPF. Results from CD spectroscopy analysis of purified proteins strongly suggests the reduction in antigenicity is due to modifications in the secondary structure of the allergens induced by plasma reactive species. Cold plasma is effective at reducing peanut protein solubility and causes changes in allergen structure leading to reduced antigenicity.

Storage stability of soy protein isolate powders containing soluble protein aggregates formed at varying pH.

Soy protein is wildly used in food industry due to its high nutritional value and good functionalities. However, the poor storage stability of commercial soy protein products has puzzled both the producers and the users for a long time. The current study assessed the changes in protein solubility, aggregation, oxidation, and conformation of soy protein isolate (SPI) with various soluble aggregates formed at different pH values (pH 5–8) during storage. During storage, SPI samples showed a reduced protein solubility (p < .05), an increased protein oxidation (p < .05), and an attenuated conformational enthalpy (∆H). SPI with a higher pH produced more disulfide‐mediated aggregates at the expense of sulfhydryl groups and experienced greater losses of protein tertiary structure and a faster reduction in solubility. Yet, all samples nearly shared similar rising trend during 8‐week storage, which indicated the production of protein carbonyls was insensitive to pH. Soluble aggregates present in fresh SPI samples appeared to induce instability of SPI during storage. These findings suggested SPI prepared at pH 6 was in favor of its storage stability, and soluble aggregates presented in fresh samples should be paid more attention for further study of storage stability kinetics.

Solubility of proteins.

Solubility is a fundamental protein property that has important connotations for therapeutics and use in diagnosis. Solubility of many proteins is low and affect heterologous overexpression of proteins, formulation of products and their stability. Two processes are related to soluble and solid phase relations. Solubility refers to the process where proteins have correctly folded structure, whereas aggregation is related to the formation of fibrils, oligomers or amorphous particles. Both processes are related to some diseases. Amyloid fibril formation is one of the characteristic features in several neurodegenerative diseases, but it is related to many other diseases, including cancers. Severe complex V deficiency and cataract are examples of diseases due to reduced protein solubility. Methods and approaches are described for prediction of protein solubility and aggregation, as well as predictions of consequences of amino acid substitutions. Finally, protein engineering solutions are discussed. Protein solubility can be increased, although such alterations are relatively rare and can lead to trade-off with some other properties. The aggregation prediction methods mainly aim to detect aggregation-prone sequence patches and then making them more soluble. The solubility predictors utilize a wide spectrum of features.

Diverse proteins aggregate in mild cognitive impairment and Alzheimer\u2019s disease brain

BackgroundAll cells accumulate insoluble protein aggregates throughout their lifespan. While many studies have characterized the canonical disease-associated protein aggregates, such as those associated with amyloid plaques, additional, undefined proteins aggregate in the brain and may be directly associated with disease and lifespan.MethodsA proteomics approach was used to identify a large subset of insoluble proteins in the mild cognitively impaired (MCI) and Alzheimer’s disease (AD) human brain. Cortical samples from control, MCI, and AD patients were separated into detergent-soluble and detergent-insoluble fractions, and high-resolution LC/MS/MS technology was used to determine which proteins became more insoluble in the disease state. Bioinformatics analyses were used to determine if the alteration of protein aggregation between AD and control patients was associated with any specific biological process. Western blots were used to validate the proteomics data and to assess the levels of secondary protein modifications in MCI and AD.ResultsThere was a stage-dependent increase in detergent-insoluble proteins, with more extreme changes occurring in the AD cohort. Glycolysis was the most significantly overrepresented gene ontology biological process associated with the alteration of protein aggregation between AD and control patients. It was further shown that many low molecular weight proteins that were enriched in the AD brain were also highly aggregated, migrating on SDS-PAGE far above their predicted molecular masses. Glucose-6-phosphate isomerase, ubiquitin carboxyl-terminal hydrolase isoenzyme L1 (UCHL1/PARK5), and the DNA damage repair enzyme KU70 were among the top insoluble proteins identified by proteomics and validated by Western blot to be increased in the insoluble fractions of both MCI and AD brain samples.ConclusionsDiverse proteins became more detergent-insoluble in the brains of both MCI and AD patients compared to age-matched controls, suggesting that multiple proteins aggregate in these diseases, likely posing a direct toxic insult to neurons. Furthermore, detergent-insoluble proteins included those with important biological activities for critical cellular processes such as energetics, proteolysis, and DNA damage repair. Thus, reduced protein solubility likely promotes aggregation and limits functionality, reducing the efficiency of multiple aspects of cell physiology. Pharmaceutical interventions that increase autophagy may provide a useful therapeutic treatment to combat protein aggregation.

Digestibility, antioxidative activity and stability of plant protein-rich products after processing and formulation with polyphenol-rich juices: kale and kale–strawberry as a model

Protein–polyphenol interactions can possibly be affected by processing and modifying the product stability, the digestive fate and stability during shelf-life of proteins and polyphenols. In this study, the combined effects of the addition of a polyphenol-rich matrix (strawberry) and the preservation technology (thermal, PEF, HPP) on kale juice (K), as model for a protein-rich vegetable juice, on the techno-functional and antioxidant properties were investigated before and during in vitro digestion. While the different processing did not affect the protein and physical stability of kale juice, combination with strawberry (KS) strongly reduced protein solubility and physical stability, likely due to the protein–polyphenol interactions in a processing-dependent manner. Kale proteins were easily digestible with full digestion within 30 min gastric phase. During digestion, the antioxidant capacity of K and KS increased, likely indicative of the release of soluble, antioxidative compounds, yet it was not significantly influenced by different preservation treatments.

Strategies for Improving the Protein Yield in pH-Shift Processing of Ulva lactuca Linnaeus: Effects of Ulvan Lyases, pH-Exposure Time, and Temperature

Globally, there is a need for novel vegetarian protein sources. We recently showed that the pH-shift process, using alkaline protein solubilization followed by isoelectric precipitation, is an efficient way to produce extracts with high protein concentrations from Ulva lactuca (>50% on a dry matter basis). However, the total protein yield was low, and to improve this, the effects of adding ulvan lyase, preincubating the seaweed homogenate at pH 8.5 and using different protein extraction temperatures (8 °C, RT and 40 °C), were evaluated in this study. Addition of ulvan lyase reduced protein solubility but increased the precipitation. Incubation at pH 8.5, without ulvan lyase added, significantly increased both protein solubility and precipitation at 8 °C and RT. Temperature per se had no effect on protein solubility, while protein precipitation increased with decreasing temperature. Highest protein yield (29%) was achieved when keeping the process at 8 °C with a preincubation step at pH 8.5 for 1 h. By these process modifications, the yield was 3.2 times higher than achieved by the control process (9.2%).