Towards the design of hypolipidaemic peptides: Deoxycholate binding affinity of hydrophobic peptide aggregates of casein plastein

Antioxidant Properties and Prediction of Bioactive Peptides Produced from Flixweed (sophia, Descurainis sophia L.) and Camelina (Camelina sativa (L.) Crantz) Seed Meal: Integrated In Vitro and In Silico Studies

Flixweed (sophia) seed meal and camelina, both by-products of oil processing, were employed to generate protein hydrolysates by applying Flavourzyme and Alcalase. This study aimed to integrate in vitro and in silico methods to analyze sophia and camelina protein hydrolysates for releasing potent antioxidative, dipeptidyl peptidase IV (DPP IV) inhibitors and angiotensin-converting enzyme (ACE) inhibitory peptides. In vitro methods were used to investigate the antioxidant potential of sophia/camelina protein hydrolysates. Bioinformatics techniques, including Peptideranker, BIOPEP, Toxinpred, AlgPred, and SwissADME, were employed to obtain the identification of bioactive peptides produced during the hydrolysis process. Protein hydrolysates produced from sophia and camelina seed meal exhibited higher ABTS and DPPH radical scavenging activities Ithan their protein isolates. Among the produced protein hydrolysates, Alcalase-treated samples showed the highest oxygen radical absorbance capacity and hydroxyl radical scavenging activity. In addition, sophia/camelina hydrolysates prevented hydroxyl and peroxyl radical-induced DNA scission and LDL cholesterol oxidation. In silico proteolysis was conducted on Alcalase-treated samples, and resultant peptides showed potential DPP IV and ACE-inhibitory activities. Identified peptides were further assessed for their toxicity and medicinal properties. Results indicate that all digestive-resistant peptides were non-toxic and had desirable drug-like properties. The findings of this study suggest that sophia/camelina protein hydrolysates are promising candidates for functional foods, nutraceuticals, and natural therapeutics.

An updated review on food-derived bioactive peptides: Focus on the regulatory requirements, safety, and bioavailability

Food-derived bioactive peptides (BAPs) are recently utilized as functional food raw materials owing to their potential health benefits. Although there is a huge amount of scientific research about BAPs' identification, purification, characterization, and physiological functions, and subsequently, many BAPs have been marketed, there is a paucity of review on the regulatory requirements, bioavailability, and safety of BAPs. Thus, this review focuses on the toxic peptides that could arise from their primary proteins throughout protein extraction, protein pretreatment, and BAPs' formulation. Also, the influences of BAPs' length and administration dosage on safety are summarized. Lastly, the challenges and possibilities in BAPs' bioavailability and regulatory requirements in different countries were also presented. Results revealed that the human studies of BAPs are essential for approvals as healthy food and to prevent the consumers from misinformation and false promises. The BAPs that escape the gastrointestinal tract epithelium and move to the stomach are considered good peptides and get circulated into the blood using different pathways. In addition, the hydrophobicity, net charge, molecular size, length, amino acids composition/sequences, and structural characteristics of BAPs are critical for bioavailability, and appropriate food-grade carriers can enhance it. The abovementioned features are also vital to optimize the solubility, water holding capacity, emulsifying ability, and foaming property of BAPs in food products. In the case of safety, the possible allergenic and toxic peptides often exhibit physiological functions and could be produced during the hydrolysis of food proteins. It was also noted that the production of iso-peptides bonds and undesirable Maillard reaction might occur during protein extraction, sample pretreatments, and peptide synthesis.

Anti-Salmonella Activity and Peptidomic Profiling of Peptide Fractions Produced from Sturgeon Fish Skin Collagen (Huso huso) Using Commercial Enzymes

This study investigated peptide fractions from fish skin collagen for antibacterial activity against Escherichia coli and Salmonella strains. The collagen was hydrolyzed with six commercial proteases, including trypsin, Alcalase, Neutrase, Flavourzyme, pepsin and papain. Hydrolyzed samples obtained with trypsin and Alcalase had the largest number of small peptides (molecular weight <10 kDa), while the hydrolysate produced with papain showed the lowest degree of hydrolysis and highest number of large peptides. Four hydrolysates were found to inhibit the growth of the Gram-negative bacteria, with papain hydrolysate showing the best activity against E. coli, and Neutrase and papain hydrolysates showing the best activity against S. abony; hydrolysates produced with trypsin and pepsin did not show detectable antibacterial activity. After acetone fractionation of the latter hydrolysates, the peptide fractions demonstrated enhanced dose-dependent inhibition of the growth (colony-forming units) of four Salmonella strains, including S. abony (NCTC 6017), S. typhimurium (ATCC 13311), S. typhimurium (ATCC 14028) and S. chol (ATCC 10708). Shotgun peptidomics analysis of the acetone fractions of Neutrase and papain hydrolysates resulted in the identification of 71 and 103 peptides, respectively, with chain lengths of 6–22 and 6–24, respectively. This work provided an array of peptide sequences from fish skin collagen for pharmacophore identification, structure–activity relationship studies, and further investigation as food-based antibacterial agents against pathogenic microorganisms.

Antioxidant potential and physicochemical properties of protein hydrolysates from body parts of North Atlantic sea cucumber (Cucumaria frondosa)

Abstract

Protein hydrolysates were prepared from North Atlantic sea cucumber (Cucumaria frondosa) body wall (BW), and processing by-product flower (FL) and internal organs (IN). Sea cucumber proteins from these three tissues were hydrolysed with selected endopeptidases and exopeptidases. The enzymes used were Alcalase (A), and Corolase (C) as endopeptidases and Flavourzyme (F) with both endo- and exopeptidase functions. These were employed individually or in combination under controlled conditions. The hydrolysates so prepared were subsequently analysed for their antioxidant potential and functionalities in food systems for the first time. Hydrolysates treated with the combination of A and F exhibited the highest radical scavenging activity against DPPH and ABTS radicals. The highest metal chelation activity was observed for samples hydrolysed with the combination of enzymes (C + F and A + F). All treatments inhibited beta-carotene bleaching in an oil-in-water emulsion and TBARS production in a meat model system. In addition, sea cucumber protein hydrolysates were more than 75% soluble over a pH range of 2–12. Hydrolysed proteins were also effective in enhancing water holding capacity in a meat model system compared to their untreated counterparts. The amino acids of sea cucumber protein hydrolysates had desirable profiles with glutamic acid as the predominant component in samples analysed. These findings demonstrate the desirable functionalities of hydrolysates from North Atlantic sea cucumber and their potential for use as functional food ingredients.

Graphical abstract

Plastein from hydrolysates of porcine hemoglobin and meat using Alcalase and papain

Plastein is defined as a protease-induced peptide aggregate and has been explored for over a century. This study investigated the effects of Alcalase and papain on plastein formation in protein hydrolysates of porcine hemoglobin and meat by measuring turbidity, particle size distribution, free amino groups and chemical interactions, as well as identifying the soluble peptides remaining in solution by LC-MS/MS. The results showed that Alcalase induced more peptide aggregation than papain in terms of increases in turbidity and particle size. Porcine hemoglobin was better than meat in inducing plastein formation in a short reaction time. Besides, covalent bonds involving peptide bonds and disulfide bonds were not crucial in the plastein reaction, instead a high proportion of hydrophobic interactions dominated the plastein. Not all peptides of both hydrolysates took part in plastein formation, and the regions of sequence that were prone to aggregation were visualized by Peptigram.

Biochemical and structural characterization of sturgeon fish skin collagen (Huso huso)

The potential use of sturgeon fish skin waste (Huso huso), an Iranian major sturgeon species, as a rich source for collagen extraction was evaluated. Yields of ASC and PSC obtained by acidic and enzymatic extractions were 9.98% and 9.08% (based on wet weight), respectively. SDS-PAGE profiles of both collagens led to classification of the proteins as type I with two different α chains (α₁ and α₂ ). Scanning electron microscopy (SEM) of the collagen sponges indicated dense sheet-like film linked by random-coiled filaments. Glycine was the most predominant amino acid, and the imino acids contents were 21.14% and 21.58% for ASC and PSC, respectively. Fourier-transform infrared spectra (FTIR) confirmed that pepsin digestion did not disrupt PSC triple helical structure. Denaturation and melting temperatures of ASC and PSC were 29.34°C, 92.03°C, and 29.89°C, 88.93°C, respectively. Thus, the sturgeon fish skin waste could serve as an alternative collagenous source for biomedical materials, food, and pharmaceutical applications. PRACTICAL APPLICATIONS: Beluga (Huso huso) is one of the most important sturgeon fish on the Caspian Sea and aquaculture industries. With the exception of the meat and caviar, wastes generated after their processing are usually discarded. Skin and cartilage of sturgeon fish are the by-products of the processing, and they are often discarded as waste or used for low-value purposes, although they are a good source for production of collagen-based biomaterials. Collagen type I is the most abundant collagen in the skin and this work reports the sturgeon fish skin as an important collagen resource with potential for use in the food, biomedical, and cosmetic industries.

Bioinformatics of edible yellow mealworm (Tenebrio molitor) proteome reveal the cuticular proteins as promising precursors of dipeptidyl peptidase-IV inhibitors

Bioinformatics was applied for strategic processing of yellow mealworm (Tenebrio molitor) proteins to produce dipeptidyl peptidase (DPP)-IV inhibiting peptides. In silico analysis of 384 mealworm proteins revealed structural proteins as better precursors of DPP-IV inhibiting peptides, compared with other protein types, after pepsin and papain hydrolysis. This was associated with the higher hydropathicity and amounts of residues associated with DPP-IV inhibition in the structural (cuticular) proteins. In silico, the peptides were mostly released with pepsin than papain. Cuticular (CP) and non-cuticular proteins (NC) were extracted from yellow mealworm and hydrolyzed with pepsin and papain in vitro to validate the virtual findings. CP hydrolysate with papain inhibited DPP-IV the most compared to CP hydrolysate with pepsin, whereas NC hydrolysates were mostly inactive. CP had higher hydrophobic-hydrophilic amino acid ratios and contents of the activity-associated residues than NC. The findings demonstrate the application of bioinformatics in processing proteins for bioactive peptide production. PRACTICAL APPLICATIONS: The discovery of bioactive peptides from food proteins is typically based on the classic approach involving working with a small number of protein-protease combinations in vitro. For the first time, this study reported the application of in silico tools in comprehensively studying hundreds of proteins from yellow mealworm (an edible insect) as sources of DPP-IV inhibitors, followed by in vitro processing and validation guided by the results obtained in silico. The advantage of this approach is that it allows for analysis of several protein-protease combinations (with multiple datasets of structural, functional, and bioactivity parameters) in a short time. This work is relevant in advancing research on emerging or alternative proteins as well as structure-informed food protein processing. The bioinformatics approach can be adapted for strategic processing of proteins in the food industry prior to making major resource investments.

Enzymatic release of dipeptidyl peptidase-4 inhibitors (gliptins) from pigeon pea (Cajanus cajan) nutrient reservoir proteins: In silico and in vitro assessments

In silico and in vitro parameters were used to assess the potential of pigeon pea (Cajanus cajan) nutrient reservoir proteins as sources of dipeptidyl peptidase (DPP)-4 inhibitors. In silico, 40 pigeon pea proteins evaluated had 46% of amino acids associated with DPP-4 inhibition. After virtual hydrolysis, pepsin had the highest frequency of release and bioactivity of released DPP-4 inhibiting peptides, compared to papain and thermolysin. In vitro, thermolysin released the most active DPP-4 inhibitors. The protein hydrolysates contained similar amino acids but different particle sizes. Thus, the bioactivity patterns are attributable to the different nature and behavior of proteins/peptides under actual and virtual conditions. Using eight physicochemical variables, a random forest model with moderate prediction accuracy was developed for predicting DPP-4 inhibitory activity of papain hydrolysates. The findings demonstrate that proteins from pigeon pea are precursors of DPP-4 inhibitors, with potential use in formulating functional food for managing type 2 diabetes. PRACTICAL APPLICATIONS: The emerging use of in silico simulations to predict bioactivity of peptides can provide a framework to direct further wet lab assessments. This pattern can enhance focusing on factors relevant to the bioactive properties of interest. However, there is still limited evidence to confirm the reliability and accuracy of this tool. This study therefore provides insight into the practical use of in silico simulations to predict bioactivity of food peptides by assessing the factors relevant to the enzymatic release of dipeptidyl peptidase-4 inhibitors from pigeon pea seed storage proteins and validating the findings with wet lab assessment. This work also provides important information that can enhance the utilization of pigeon pea, which is an orphan crop, in developing functional food products for managing type 2 diabetes mellitus in developing countries.

In Vitro Antithrombotic and Hypocholesterolemic Activities of Milk Fermented with Specific Strains of Lactococcus lactis

Milk fermented with specific lactic acid bacteria (LAB) was reported to be a rich source of metabolites, such as peptides with different biological activities that may have a positive effect on cardiovascular health. Thus, in this study, the antithrombotic and hypocholesterolemic activities of fermented milk with specific strains of Lactococcus lactis were investigated before and after exposure to a simulated gastrointestinal digestion (SGD) model. The inhibition of thrombin-induced fibrin polymerization (IC₅₀ peptide concentration necessary to inhibit thrombin activity by 50%), anticoagulant activity, inhibition of micellar solubility of cholesterol and bile acid binding capacity of water soluble fractions (WSF) <3 kDa from fermented milk were evaluated. Results indicated that the WSF from fermented milk with Lc-572 showed antithrombotic (IC₅₀ = 0.049 mg/mL) and hypocholesterolemic (55% inhibition of micellar solubility of cholesterol and 27% bile acid binding capacity) activities. Meanwhile, fermented milk with Lc-571 showed mainly antithrombotic activity (IC₅₀ = 0.045 mg/mL). On the other hand, fermented milk with Lc-600 presented mainly hypocholesterolemic activity (31.4% inhibition of micellar solubility of and 70% bile acid binding capacity). Moreover, biological activities were not lost after simulated gastrointestinal digestion conditions. Thus, fermented milk with these specific L. lactis strains show potential for the development of functional foods.

Plastein reaction enhanced bile-acid binding capacity of soybean protein hydrolysates and whey protein hydrolysates

Plastein reaction is a modification reaction that can improve the functional properties of protein hydrolysate. The product of the reaction is a thixotropic aggregation of peptides. This study investigated the formation condition of soybean-whey plastein and bile acid binding capacity of plastein. Soy protein and whey protein were hydrolyzed by pepsin. The mixture (1:1, w/w) of two hydrolysates was modified by pepsin again. After the reaction, the decrease in free amino groups and the turbidity of the modified hydrolysate were measured to obtain appropriate reaction condition. Results showed that the concentration of hydrolysates 40% (w/v), enzyme ratio of 2.0 KU/g protein, pH 5.0, 37 °C, reaction time of 3.0 h respectively, were showed maximum changes in protein hydrolysates. Tricine SDS-PAGE analysis under denaturing conditions revealed that whey protein was more sensitive to pepsin and yielded different polypeptides (PPs) of molecular weight ranged from 3.5-17 kDa. However, a high molecular weight PP was completely hydrolyzed while PPs of 14.2-26 kDa were partially digested after pepsin treatment. Native page analysis further revealed the presence of a high-molecular weight PP in crude and purified plastein product. The bile acid binding capacity was improved by the plastein reaction. The amount of binding sodium deoxycholate, sodium taurocholate, and sodium cholate were 0.75, 2.0 and 1.87 μmol/100 mg respectively.