Tombul hazelnut (Corylus avellana L.) peptides with DPP-IV inhibitory activity: In vitro and in silico studies

Peptides with biological and technofunctional properties produced by bromelain hydrolysis of proteins from different sources: A review

Bromelains are cysteine peptidases with endopeptidase action (a subfamily of papains), obtained from different parts of vegetable belonging to the Bromeliaceae family. They have some intrinsic medical activity, but this review is focused on their application (individually or mixed with other proteases) to produce bioactive peptides. When compared to other proteases, perhaps due to the fact that they are commercialized as an extract containing several proteases, the hydrolysates produced by this enzyme tends to have higher bioactivities than other common proteases. The peptides and the intensity of their final properties depend on the substrate protein and reaction conditions, being the degree of hydrolysis a determining parameter (but not always positive or negative). The produced peptides may have diverse activities such as antioxidant, antitumoral, antihypertensive or antimicrobial ones, among others or they may be utilized to improve the organoleptic properties of foods and feeds. Evolution of the use of this enzyme in this application is proposed to be based on a more intense direct application of Bromeliaceae extract, without the cost associated to enzyme purification, and the use of immobilized biocatalysts of the enzyme by simplifying the enzyme recovery and reuse, and also making the sequential hydrolysis using diverse proteases possible.

Isolation, virtual screening, action mechanisms, chelation with zinc ions, and stability of ACE-inhibitory peptides from ginkgo seed globulin

Ginkgo seed has potential applications in the prevention and treatment of hypertension, but its application in food is limited. Thus, ginkgo seed globulin was hydrolyzed using dual enzymes (Alcalase and thermolysin). After gel column separation, reverse-phase high-performance liquid chromatographic purification, and ESI-MS/MS analysis, five oligopeptides containing fewer than 12 amino acid residues were obtained. Among them, the heptapeptide Glu-Ala-Ser-Pro-Lys-Pro-Val (EASPKPV) offered relatively high capacities to inhibit ACE (IC50: 87.66 μmol L-1) and bind with zinc ions (5.35 ± 0.32 mg g-1). Moreover, EASPKPV showed competitive inhibitory kinetics against ACE. Fourier-transform infrared spectroscopy analysis evidenced that the amino group and carboxyl group of EASPKPV could both provide binding sites for zinc ions. EASPKPV can restrain ACE in the following ways: (i) competitively linking with five key residues (Gln281, Ala354, Glu376, Lys511, and Tyr523) in the S1 and S2 pockets of ACE by short hydrogen bonds; (ii) binding to thirteen active residues of ACE via hydrophobic interactions; and (iii) binding with residue His383 or the zinc ion of zinc tetrahedral coordination. Additionally, simulated gastrointestinal digestion did not show any remarkable efficacy on the capacities of EASPKPV to restrain ACE and bind with zinc ions. These results indicate that ginkgo peptides may be used for antihypertension.

Preparation, identification, and inhibitory mechanism of dipeptidyl peptidase IV inhibitory peptides from goat milk whey protein

This study explores potential hypoglycemic mechanisms by preparing and identifying novel dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from goat milk (GM) whey protein. Papain was used to hydrolyze the GM whey protein. After purification by ultrafiltration, the Sephadex column, and preparative RP-HPLC, the peptide inhibited DPP-IV, α-glucosidase, and α-amylase with IC50 of 0.34, 0.37, and 0.72 mg/mL, respectively. To further explore the inhibitory mechanism of peptides on DPP-IV, SPPEFLR, LDADGSY, YPVEPFT, and FNPTY were identified and synthesized for the first time, with IC50 values of 56.22, 52.16, 175.7, and 62.32 µM, respectively. Molecular docking and dynamics results show that SPPEFLR, LDADGSY, and FNPTY bind more tightly to the active pocket of DPP-IV, which was consistent with the in vitro activity. Furthermore, the first three N-terminals of SPPEFLR and FNPTY peptides exhibit proline characteristics and competitively inhibit DPP-IV. Notably, the first N-terminal leucine of LDADGSY may play a key role in inhibiting DPP-IV.

Combined Neutrase-Alcalase Protein Hydrolysates from Hazelnut Meal, a Potential Functional Food Ingredient

Consumers' interest in functional foods has significantly increased in the past few years. Hazelnut meal, the main valuable byproduct of the hazelnut oil industry, is a rich source of proteins and bioactive peptides and thus has great potential to become a valuable functional ingredient. In this study, hazelnut protein hydrolysates obtained by a single or combined hydrolysis by Alcalase and Neutrase were mainly characterized for their physicochemical properties (SDS-PAGE, particle size distribution, Fourier-transform infrared (FTIR) spectroscopy, molecular weight distribution, etc.) and potential antiobesity effect (Free fatty acid (FFA) release inhibition), antioxidant activity (DPPH and ABTS methods), and emulsifying properties. The impact of a microfluidization pretreatment was also investigated. The combination of Alcalase with Neutrase permitted the highest degree of hydrolysis (DH; 15.57 ± 0.0%) of hazelnut protein isolate, which resulted in hydrolysates with the highest amount of low-molecular-weight peptides, as indicated by size exclusion chromatography (SEC) and SDS-PAGE. There was a positive correlation between the DH and the inhibition of FFA release by pancreatic lipase (PL), with a significant positive effect of microfluidization when followed by Alcalase hydrolysis. Microfluidization enhanced the emulsifying activity index (EAI) of protein isolates and hydrolysates. Low hydrolysis by Neutrase had the best effect on the EAI (84.32 ± 1.43 (NH) and 88.04 ± 2.22 m²/g (MFNH)), while a negative correlation between the emulsifying stability index (ESI) and the DH was observed. Again, the combined Alcalase-Neutrase hydrolysates displayed the highest radical scavenging activities (96.63 ± 1.06% DPPH and 98.31 ± 0.46% ABTS). FTIR results showed that the application of microfluidization caused the unfolding of the protein structure. The individual or combined application of the Alcalase and Neutrase enzymes caused a switch from the β-sheet organization of the proteins to α-helix structures. In conclusion, hazelnut meal may be a good source of bioactive and functional peptides. The control of its enzymatic hydrolysis, together with an appropriate pretreatment such as microfluidization, may be crucial to achieve the best suitable activity.

Sequence alterations affect the antidiabetic attributes of hazelnut peptide fractions during the industrial manufacture and simulated digestion of hazelnut paste

Press cakes are by-products of cold press oil manufacture and are characterized by significant protein concentrations. Our group has previously demonstrated potential bioactive attributes of hazelnut protein hydrolysates including their antidiabetic activities. Here, an effort was made to utilize DPP-IV (Dipeptidyl peptidase-IV)-inhibitory hazelnut peptides in industrial food manufacture. Hazelnut protein isolates (approx. 95% protein) were obtained via an alkali extraction-isoelectric precipitation method. Papain, bromelain and pepsin were used in the enzymatic hydrolysis and hydrolysates were fractionated via Fast Protein Liquid Chromatography. As a general observation, although fractionation lead to dilution of the samples, fractions were observed to be more bioactive than the total hydrolysates. In vitro antidiabetic activities of the fractions were tested and 3 antidiabetic fractions were added to hazelnut paste. Afterwards simulated gastrointestinal digestion and antidiabetic activity assays were performed. DPP-IV inhibition was the major antidiabetic mechanism in the fractions and digested paste, while some fractions were characterized by comparable IC50 values as the positive controls. Alpha-glucosidase inhibition was limited by digestion trials, whereas alpha-amylase inhibition was only slight in the digested paste (< %6). In silico analyses predicted partial degradation of the peptides, whereas the interactions between DPP-IV or alpha-glucosidase and hazelnut peptides were predicted to be significant (p < 0.05). Consequently hazelnut press cakes were regarded as a potential source of antidiabetic peptides that can be used in industrial manufacture of functional foods, while food processing conditions or gastrointestinal digestion could largely affect peptide bioactivity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05601-2.

Interactions between Hazelnut (Corylus avellana L.) Protein and Phenolics and In Vitro Gastrointestinal Digestibility

In this study, we investigated the formation of protein–phenolic complexes from dephenolized hazelnut meal protein isolates (dHPI) and hazelnut skin phenolic extracts (HSE) and their effects on the bioaccessibility of both hazelnut proteins and phenolics. The dHPI–HSE complexes were of considerable size and were dependent on HSE concentration due to aggregation. Although catechin was the main component of HSE, it did not cause aggregation, except for a slight rise in particle size. According to fluorescence quenching, the hazelnut protein–phenolic extract complex had a linear Stern–Volmer plot expressing static quenching between 0–0.5 mM concentration; the interaction was mainly dependent on hydrogen bonding and van der Waals forces (ΔH < 0 and ΔS < 0), and the reaction was spontaneous (ΔG < 0). According to Fourier transform infrared (FTIR) spectroscopy results, higher phenolic extract concentration caused an increase in irregular structures in hazelnut protein, while the lowest catechin and phenolic concentration altered the regular structure. Skin extracts did not alter the digestibility of dephenolized proteins, but dephenolization reduced the degree of hydrolysis by pancreatin. The formation of the protein–phenolic complex had a beneficial effect on the bioaccessibility of hazelnut skin phenols, predominantly those on the galloylated form of the catechins, such as gallocatechin gallate and epigallocatechin gallate. Thus, the bioaccessibility and antioxidant activity analysis results showed that protein–phenolic complexes obtained from hazelnut meal and skin may promote the transition of phenolic compounds from the gastrointestinal tract without degradation.