Sequential hydrolysis of commercial casein hydrolysate by immobilized trypsin and thermolysin to produce bioactive phosphopeptides

Measuring the oral bioavailability of protein hydrolysates derived from food sources: A critical review of current bioassays

BACKGROUND

Food proteins are a source of hydrolysates with potentially useful biological attributes. Bioactive peptides from food-derived proteins are released from hydrolysates using exogenous industrial processes or endogenous intestinal enzymes. Current in vitro permeability assays have limitations in predicting the oral bioavailability (BA) of bioactive peptides in humans. There are also difficulties in relating the low blood levels of food-derived bioactive peptides detected in preclinical in vivo models to pharmacodynamic read-outs relevant for humans.

SCOPE AND APPROACH

In this review, we describe in vitro assays of digestion, permeation, and metabolism as indirect predictors of the potential oral BA of hydrolysates and their constituent bioactive peptides. We discuss the relationship between industrial hydrolysis processes and the oral BA of hydrolysates and their peptide by-products.

KEY FINDINGS

Hydrolysates are challenging for analytical detection methods due to capacity for enzymatic generation of peptides with novel sequences and also new modifications of these peptides during digestion. Mass spectrometry and peptidomics can improve the capacity to detect individual peptides released from complex hydrolysates in biological milieu.

Effect of Tris Buffer in the Intensity of the Multipoint Covalent Immobilization of Enzymes in Glyoxyl-Agarose Beads

Tris is an extensively used buffer that presents a primary amine group on its structure. In the present work trypsin, chymotrypsin and penicillin G acylase (PGA) were immobilized/stabilized on glyoxyl agarose in presence of different concentrations of Tris (from 0 to 20 mM). The effects of the presence of Tris during immobilization were studied analyzing the thermal stability of the obtained immobilized biocatalysts. The results indicate a reduction of the enzyme stability when immobilized in the presence of Tris. This effect can be observed in inactivations carried out at pH 5, 7, and 9 with all the enzymes assayed. The reduction of enzyme stability increased with the Tris concentration. Another interesting result is that the stability reduction was more noticeable for immobilized PGA than in the other immobilized enzymes, the biocatalysts prepared in presence of 20 mM Tris lost totally the activity at pH 7 just after 1 h of inactivation, while the reference at this time still kept around 61 % of the residual activity. These differences are most likely due to the homogeneous distribution of the Lys groups in PGA compared to trypsin and chymotrypsin (where almost 50% of Lys group are in a small percentage of the protein surface). The results suggest that Tris could be affecting the multipoint covalent immobilization in two different ways, on one hand, reducing the number of available glyoxyl groups of the support during immobilization, and on the other hand, generating some steric hindrances that difficult the formation of covalent bonds.

Effect of amine length in the interference of the multipoint covalent immobilization of enzymes on glyoxyl agarose beads

Trypsin, chymotrypsin, penicillin G acylase and ficin extract have been stabilized by immobilization on glyoxyl agarose, adding different aliphatic compounds bearing a primary amine group during the immobilization: ethyl amine, butyl amine, hexyl amine (at concentrations ranging from 0 to 20 mM) and octyl amine (from 0 to 10 mM) to analyze their effects on the immobilized enzyme stability. As expected, the presence of amines reduced the intensity of the enzyme-support multipoint covalent attachment, and therefore the enzyme stability. However, it is clear that this effect is higher using octyl amine for all enzymes (in some cases the enzyme immobilized in the presence of 10 mM octyl amine was almost inactivated while the reference kept over 50 % of the initial activity). This way, it seems that the most important effect of the presence of aminated compounds came from the generation of steric hindrances to the enzyme/support multi-reaction promoted by the ammines that are interacting with the aldehyde groups. In some instances, just 1 mM of aminated compounds is enough to greatly decrease enzyme stability. The results suggested that, if the composition of the enzyme extract is unknown, to eliminate small aminated compounds may be necessary to maximize the enzyme-support reaction.

Effect of Concentrated Salts Solutions on the Stability of Immobilized Enzymes: Influence of Inactivation Conditions and Immobilization Protocol

This paper aims to investigate the effects of some salts (NaCl, (NH₄)₂SO₄ and Na₂SO₄) at pH 5.0, 7.0 and 9.0 on the stability of 13 different immobilized enzymes: five lipases, three proteases, two glycosidases, and one laccase, penicillin G acylase and catalase. The enzymes were immobilized to prevent their aggregation. Lipases were immobilized via interfacial activation on octyl agarose or on glutaraldehyde-amino agarose beads, proteases on glyoxyl agarose or glutaraldehyde-amino agarose beads. The use of high concentrations of salts usually has some effects on enzyme stability, but the intensity and nature of these effects depends on the inactivation pH, nature and concentration of the salt, enzyme and immobilization protocol. The same salt can be a stabilizing or a destabilizing agent for a specific enzyme depending on its concentration, inactivation pH and immobilization protocol. Using lipases, (NH₄)₂SO₄ generally permits the highest stabilities (although this is not a universal rule), but using the other enzymes this salt is in many instances a destabilizing agent. At pH 9.0, it is more likely to find a salt destabilizing effect than at pH 7.0. Results confirm the difficulty of foreseeing the effect of high concentrations of salts in a specific immobilized enzyme.

Immobilization of thermolysin enzyme on dendronized silica supports. Evaluation of its feasibility on multiple protein hydrolysis cycles

This work evaluates different dendrimer-silica supports for the immobilization of enzymes by multipoint covalent binding. Thermolysin was immobilized on two dendrimers (PAMAM and carbosilane) with two different generations (zero (G0) and first (G1)). Results were compared with a control, a silica support functionalized with a monofunctional molecule. Dendrimers increased the number of available sites to bind the enzyme. Despite the enzyme was immobilized on all supports, G0 dendrimers immobilized a 30% more enzyme than G1. Thermolysin immobilized on G0 dendrimer supports showed the highest activity and could be employed in three consecutive hydrolysis cycles. Optimal immobilization time was 1 h while optimal protein loading was 25 mg enzyme/100 mg support. Enzyme activity was promoted when using 5 mg of immobilized enzyme at 750 rpm, 60 °C, and 2 h of hydrolysis. Under these conditions, the activity of thermolysin increased up to the 78% of the free enzyme activity. Kinetics of the hydrolysis reaction using the immobilized thermolysin was also studied and compared with the obtained using the free thermolysin. The addition of ZnCl₂ and NaCl during the immobilization procedure increased thermolysin activity in the second (22% more) and in the third (14% more) hydrolysis clycles.

Exploring the antioxidant effects of peptides from almond proteins using PAni-Ag-GONC conjugated trypsin by improving enzyme stability & applications

Functionalized graphene oxide nano-sheets (PAni-Ag-GONC) were prepared and employed as carrier for covalent immobilization of trypsin. This low cost setting, which involves loading of high amount of enzyme on the matrix, displayed significantly enhanced thermo-stability and pH resistance. The nano-composite (NC) bound trypsin preserved 90% of activity whereas native trypsin retained only 44% of activity after 60 days of storage at a temperature of 4°C. Immobilized trypsin conserved 80.5% of activity even after its ten repeated uses. Almond protein hydrolysates prepared by native and conjugated enzyme was investigated for antioxidant activities and found that peptides resulted from NC bound trypsin displayed increase in radical scavenging activity (i.e. around 30% and 37% scavenging activity observed, respectively by native and NC bound trypsin from same concentration of peptides). This strategy provides a new approach for production of potential biopeptides which may be incorporated in drugs and functional food industries applying PAni-Ag-GONC based biocatalysis. CHEMICAL COMPOUNDS: Trichloroacetic acid (PubChem CID: 6421); Tris (hydroxymethyl)aminomethane (PubChem CID: 6503); Glycine (PubChem CID: 750); and 2,2'-diphenyl-1-picrylhydrazyl (PubChem CID: 74358); Nα- Benzoyl-DL-arginine 4-nitroanilide hydrochloride (PubChem CID: 2724371); Ammonium sulphate (PubChem CID: 6097028).

Enhancing bioactive peptide release and identification using targeted enzymatic hydrolysis of milk proteins

Milk proteins have been extensively studied for their ability to yield a range of bioactive peptides following enzymatic hydrolysis/digestion. However, many hurdles still exist regarding the widespread utilization of milk protein-derived bioactive peptides as health enhancing agents for humans. These mostly arise from the fact that most milk protein-derived bioactive peptides are not highly potent. In addition, they may be degraded during gastrointestinal digestion and/or have a low intestinal permeability. The targeted release of bioactive peptides during the enzymatic hydrolysis of milk proteins may allow the generation of particularly potent bioactive hydrolysates and peptides. Therefore, the development of milk protein hydrolysates capable of improving human health requires, in the first instance, optimized targeted release of specific bioactive peptides. The targeted hydrolysis of milk proteins has been aided by a range of in silico tools. These include peptide cutters and predictive modeling linking bioactivity to peptide structure [i.e., molecular docking, quantitative structure activity relationship (QSAR)], or hydrolysis parameters [design of experiments (DOE)]. Different targeted enzymatic release strategies employed during the generation of milk protein hydrolysates are reviewed herein and their limitations are outlined. In addition, specific examples are provided to demonstrate how in silico tools may help in the identification and discovery of potent milk protein-derived peptides. It is anticipated that the development of novel strategies employing a range of in silico tools may help in the generation of milk protein hydrolysates containing potent and bioavailable peptides, which in turn may be used to validate their health promoting effects in humans. Graphical abstract The targeted enzymatic hydrolysis of milk proteins may allow the generation of highly potent and bioavailable bioactive peptides.