Effect of high hydrostatic pressure on the steady-state kinetics of tryptic hydrolysis of β-lactoglobulin

A Response Surface Methodology (RSM) Approach for Optimizing the Attenuation of Human IgE-Reactivity to β-Lactoglobulin (β-Lg) by Hydrostatic High Pressure Processing

The response surface methodology (RSM) and central composite design (CCD) technique were used to optimize the three key process parameters (i.e., pressure, temperature and holding time) of the high-hydrostatic-pressure (HHP) processing either standalone or combined with moderate thermal processing to modulate molecular structures of β-lactoglobulin (β-Lg) and α-lactalbumin (α-La) with reduced human IgE-reactivity. The RSM model derived for HHP-induced molecular changes of β-Lg determined immunochemically showed that temperature (temp), pressure (p²) and the interaction between temperature and time (t) had statistically significant effects (p < 0.05). The optimal condition defined as minimum (β-Lg specific) IgG-binding derived from the model was 505 MPa at 56 °C with a holding time of 102 min (R² of 0.81 and p-value of 0.01). The validation carried at the optimal condition and its surrounding region showed that the model to be underestimating the β-Lg structure modification. The molecular change of β-Lg was directly correlated with HHP-induced dimerization in this study, which followed a quadratic equation. The β-Lg dimers also resulted in the undetectable human IgE-binding.

Co nanoparticles decorated with N-doped carbon nanotubes as high-efficiency catalysts with intrinsic oxidase-like property for colorimetric sensing

Artificial nanozymes are designed for pursuing the functions of splendid catalytic efficiency and prominent selectivity of natural enzymes, meanwhile obtaining higher stability than that of natural enzymes. This emerging technology shows widespread application in the crossing field between nanotechnology and biomedicine. In this work, we employed a universal approach to fabricate a Co@N-CNTs hybrid nanocomposite as an oxidase mimic, in which fine Co nanoparticles were wrapped in N-doped carbon nanotubes, stacking on a hollow dodecahedron carbon skeleton. The synergistic effects of nanostructure engineering, N-doping and carbon coating, as well as the derived interfacial effect contribute to the glorious oxidase-like activity, stability and reusability. It can catalytically oxidize the colorless substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue oxidation product (ox-TMB). As a result, a colorimetric technique with excellent selectivity and sensitivity for detecting ascorbic acid (AA) with naked eyes was established, in view of specific inhibitory effects towards oxidation of TMB. Under optimal detection conditions, this method exhibits a good linearity ranging from 0.1 to 160 μM with a low limit of detection (LOD) of 0.076 μM. For practical applications, Co@N-CNTs hybrid catalyst as a mimic oxidase was used for the determination of AA in human serum, which yielded satisfactory results. This work may serve as a new research thought to guide the design of high-performance nanozymes and establish a sensing platform for the detection of AA.

In this work, we designed a Co@N-CNTs hybrid nanocomposite as an oxidase mimic for the colorimetric detection of ascorbic acid with the naked eye.

High hydrostatic pressure-assisted enzymatic hydrolysis improved protein digestion of flaxseed protein isolate and generation of peptides with antioxidant activity

Exploration of innovative high hydrostatic pressure (HHP)-assisted enzymatic hydrolysis of plant based food proteins may help improve peptide yield and bioactivity of hydrolysates. In this study, we performed enzymatic hydrolysis of flaxseed proteins using trypsin under HHP (100 and 300 MPa for 5 and 10 min) to evaluate the effect of presurization on protein denaturation, degree of hydrolysis (DH), and peptide profile and bioactivity of hydrolysate. Spectrofluorimetric analyses showed that 300 MPa induced the maximum destablization of flaxseed protein structures. The same pressure level drastically improved the DH by 1.7 times as compared to that of control. Applying HHP did not modify the peptide profiles of flaxseed protein hydrolysates but their concentrations increased with severity of treatment. Similarly, peptide molecular weight distributions were affected by pressurization parameters, increasing mainly the relative abundance of 500-1500 Da peptides. Finally, pressurization at 300 MPa for 5 and 10 min improved the antioxidant activity of flaxseed protein hydrolysates by 39 and 55%, respectively, compared to the control.

Hydrolysis under high hydrostatic pressure as a means to reduce the binding of beta-lactoglobulin to immunoglobulin E from human sera

Cows' milk allergy is the most frequent food allergy in children, and beta-lactoglobulin (beta-Lg) is a major allergen. Milk-based hypoallergenic ingredients are manufactured by enzymatic hydrolysis, a process that could be improved by the application of high-pressure treatments. This study showed that the treatment of beta-Lg dissolved in buffer with chymotrypsin and trypsin under high pressure for relatively short times accelerated proteolysis by leading to a rapid removal of the intact protein. The rapid proteolysis of the beta-Lg substrate under pressure led to the production, in 20 min, of hydrolysates with lower immunoglobulin (Ig) G binding than those produced in 8 h (chymotrypsin) or 48 h (trypsin) at atmospheric pressure. However, those hydrolysates retained some residual IgE-binding properties that could be traced to the preferential release, during the initial stages of proteolysis, of peptides containing IgE epitopes, such as (Val-41-Lys-60), (Leu-149-Ile-162), and (Ser-21-Arg-40). The formation of these fragments was favored when proteolysis was conducted under high pressure due to the preferential hydrolysis of Arg-40 and Arg-148 by trypsin, and Tyr-42 and Leu-149 by chymotrypsin, all located at the dimer interface of beta-Lg or very close to it. Although our results do not support that trypsin and chymotrypsin under high pressure selectively address the allergenic regions of beta-Lg, it is possible to select the conditions that quickly produce hydrolysates with reduced potential allergenicity that could be used in hypoallergenic foods.

Peptic and Tryptic Hydrolysis of Native and Heated Whey Protein to Reduce Its Antigenicity

This study examined the effects of enzymes on the production and antigenicity of native and heated whey protein concentrate (WPC) hydrolysates. Native and heated (10 min at 100 degrees C) WPC (2% protein solution) were incubated at 50 degrees C for 30, 60, 90, and 120 min with 0.1, 0.5, and 1% pepsin and then with 0.1, 0.5, and 1% trypsin on a protein-equivalent basis. A greater degree of hydrolysis was achieved and greater nonprotein nitrogen concentrations were obtained in heated WPC than in native WPC at all incubation times. Hydrolysis of WPC was increased with an increasing level of enzymes and higher incubation times. The highest hydrolysis (25.23%) was observed in heated WPC incubated with 1% pepsin and then with 1% trypsin for 120 min. High molecular weight bands, such as BSA, were completely eliminated from sodium dodecyl sulfate-PAGE of both native and heated WPC hydrolysates produced with pepsin for the 30-min incubation. The alpha-lactalbumin in native WPC was slightly degraded when incubated with 0.1% pepsin and then with 0.1% trypsin; however, it was almost completely hydrolyzed within 60 min of incubation with 0.5% pepsin and then with 0.5% trypsin. Incubation of native WPC with 1% pepsin and then with 1% trypsin for 30 min completely removed the BSA and alpha-lactalbumin. The beta-lactoglobulin in native WPC was not affected by the pepsin and trypsin treatments. The beta-lactoglobulin in heated WPC was partially hydrolyzed by the 0.1 and 0.5% pepsin and trypsin treatments and was completely degraded by the 1% pepsin and trypsin treatment. Antigenicity reversibly mimicked the hydrolysis of WPC and the removal of beta-lactoglobulin from hydrolysates. Antigenicity in heated and native WPC was reduced with an increasing level of enzymes. A low antigenic response was observed in heated WPC compared with native WPC. The lowest antigenicity was observed when heated WPC was incubated with 1% pepsin and then with 1% trypsin. These results suggested that incubation of heated WPC with 1% pepsin and then with 1% trypsin was the most effective for producing low-antigenic hydrolysates by WPC hydrolysis and obtaining low molecular weight small peptides. Further research is warranted to identify the low molecular weight small peptides in the WPC hydrolysates produced by pepsin and trypsin, which may enhance the use of whey.

Functional Improvement of Milk Whey Proteins Induced by High Hydrostatic Pressure

High pressure is emerging as a new processing technology that produces particular changes in the molecular structure of proteins and thus gives rise to new properties inaccessible via conventional methods of protein modification. This review deals with the main effects of high hydrostatic pressure on the physicochemical characteristics of milk whey proteins and how modifications in their structural properties contribute to functionality. In this paper the mechanism underlying pressure-induced changes in ss-lactoglobulin, a-lactabumin, and bovine serum albumin is explained, and related to functional properties such as gel-forming ability, emulsifying activity, or foaming capacity. The possibility of using high pressures to favor chemical reactions of proteins with other food components, such as carbohydrates, to produce novel molecules with new food uses is also considered.

Changes in chymotrypsin hydrolysis of beta-lactoglobulin A induced by high hydrostatic pressure

Beta-lactoglobulin (beta-Lg) was subjected to high pressures up to 400 MPa and proteolysis with chymotrypsin. The hydrolysates were analyzed by SDS-PAGE and RP-HPLC, and the fragments obtained were identified by ESI-MS/MS. The results obtained showed that beta-Lg was hydrolyzed by chymotrypsin in a "progressive proteolysis" manner at either atmospheric or high pressure. Proteolysis during or after high-pressure treatment showed longer and more hydrophobic peptides than proteolysis at atmospheric pressure. Chymotrypsin showed a behavior similar to that of trypsin, with some differences, probably related to the orientation of the target residues specific for each enzyme. The similarities between proteolytic fragments produced by the two enzymes support that proteolysis enhancement under high pressure depends on the substrate changes rather than the enzyme. High pressure seemed to accelerate the first steps of proteolysis, probably through dimer dissociation, while leaving portions of the molecule more resistant to the enzyme.