Identification of bitter peptides in whey protein hydrolysate

Comparison of prediction models for soy protein isolate hydrolysates bitterness built using sensory, spectrofluorometric and chromatographic data from varying enzymes and degree of hydrolysis

The bitterness of soy protein isolate hydrolysates prepared using five proteases at varying degree of hydrolysis (DH) and its relation to physicochemical properties, i.e., surface hydrophobicity (H0), relative hydrophobicity (RH), and molecular weight (MW), were studied and developed for predictive modelling using machine learning. Bitter scores were collected from sensory analysis and assigned as the target, while the physicochemical properties were assigned as the features. The modelling involved data pre-processing with local outlier factor; model development with support vector machine, linear regression, adaptive boosting, and K-nearest neighbors algorithms; and performance evaluation by 10-fold stratified cross-validation. The results indicated that alcalase hydrolysates were the most bitter, followed by protamex, flavorzyme, papain, and bromelain. Distinctive correlation results were found among the physicochemical properties, influenced by the disparity of each protease. Among the features, the combination of RH-MW fitted various classification models and resulted in the best prediction performance.

Enzymatic debittering of cheese flavoring and bitterness characterization of peptide mixture using sensory and peptidomics approach

Peptides in cheese flavoring produced through proteolysis plus fermentation generated bitterness. Bitterness of individual peptide can be quantified using quantitative structure-activity relationship, where molecular mass (M), hydrophobicity, residues, C-terminal hydrophobic amino acids (C-HAAs), and N-terminal basic ones (N-BAAs) are crucial. However, their accumulative influence on the overall bitterness of peptide mixture remains unknown. This study delved into extensive proteolysis to debitter and to correlate the multi-influencing factors of peptides and the collective bitterness. As hydrolysis increased from 7.5 % to 28.0 %, bitterness reduced from 5.0 to 0.3-2.7 scores, contingent on proteases used, in which FU was optimal. The overall bitterness cannot be predicted through the summation of individual peptide bitterness, which depended on M (0.5-3 kDa) and 5-23 residues, followed by N-BAAs and C-HAAs. Analysis of enzymatic cleavage sites and substrate characteristics revealed, to more effectively debitter bovine milk protein hydrolysates, proteases specifically cleaving Pro, Leu, Phe, and Val were desired.

Two-dimensional liquid chromatography with reversed phase in both dimensions: A review

Two-dimensional liquid chromatography (2D-LC), and in particular comprehensive two-dimensional liquid chromatography (LC×LC), offers increased peak capacity, resolution and selectivity compared to one-dimensional liquid chromatography. It is commonly accepted that the technique produces the best results when the separation mechanisms in the two dimensions are completely orthogonal; however, the use of similar separation mechanisms in both dimensions has been gaining popularity as it helps avoid difficulties related to mobile phase incompatibility and poor column efficiency. The remarkable advantages of using reversed phase in both dimensions (RPLC×RPLC) over other separation mechanisms made it a promising technique in the separation of complex samples. This review discusses some physical and practical considerations in method development for 2D-LC involving the use of RP in both dimensions. In addition, an extensive overview is presented of different applications that relied on RPLC×RPLC and 2D-LC with reversed phase column combinations to separate components of complex samples in different fields including food analysis, natural product analysis, environmental analysis, proteomics, lipidomics and metabolomics.

Physicochemical and Sensory Characterization of Whey Protein-Enriched Semihard Cheese

In view of potential future changes of German food legislation with regard to cheese product quality parameters, this study aimed to evaluate the quality of whey protein-enriched semihard cheese (WPEC). Model WPEC was produced in a pilot plant and on an industrial scale by adding defined amounts of high-heat (HH) milk to the cheese milk and comprehensively analyzed during cheese processing. The dry matter, total protein, pure protein, fat, and sodium chloride content of six-week ripened cheese samples were not significantly different (p < 0.05) when the technologically necessary heating of the curd was adapted to the amount of HH milk. However, the ripening, firmness, and melting behavior of WPEC was different compared to cheese without HH milk. During ripening, no formation of whey protein peptides was observed, but differences in the amount of some bitter peptides deriving from the casein fraction were found. Sensory data suggested a slightly more bitter taste perception by the panelists for the WPEC. Further technological adjustments are recommended to obtain marketable WPEC.

Bitter Peptides in Fermented Soybean Foods - A Review

Fermented soybean foods with a long history are popular worldwide because of rich nutrition. However, many traditional fermented soybean foods have unacceptable bitterness, which mostly comes from the bitter peptides produced from the hydrolysis of soybean proteins. In this review, the bitter peptides in fermented soybean foods is briefly reviewed. The structural properties of bitter receptors and bitter peptides were reviewed. Bitterness is perceived through the binding between bitter compounds and specific sites of bitter receptors (25 hTAS2Rs), which further activate the downstream signal pathway mediated by G-protein. And it converts chemical signals into electrical signals, and transmit them to the brain. In addition, the influencing factors of bitter peptides in fermented soybean foods were summarized. The bitterness of fermented soybean foods primarily results from the raw materials, microbial metabolism during fermentation, unique techniques, and interactions of various flavor compounds. Moreover, the structure-bitterness relationship of bitter peptides was also discussed in this review. The bitterness degree of the bitter peptide is related to the polypeptide hydrophobicity, amino acids in the peptide, peptide molecular weight and polypeptide spatial structure. Studying the bitter peptides and their bitter characteristics in fermented soybean foods is beneficial for improving the sensory quality of fermented soybean foods and prompting more consumers accept them.

Red Quinoa Hydrolysates with Antioxidant Properties Improve Cardiovascular Health in Spontaneously Hypertensive Rats

In recent years, quinoa has been postulated as an emerging crop for the production of functional foods. Quinoa has been used to obtain plant protein hydrolysates with in vitro biological activity. The aim of the present study was to evaluate the beneficial effect of red quinoa hydrolysate (QrH) on oxidative stress and cardiovascular health in an in vivo experimental model of hypertension (HTN) in the spontaneously hypertensive rat (SHR). The oral administration of QrH at 1000 mg/kg/day (QrHH) showed a significant reduction in SBP from baseline (-9.8 ± 4.5 mm Hg; p < 0.05) in SHR. The mechanical stimulation thresholds did not change during the study QrH groups, whereas in the case of SHR control and SHR vitamin C, a significant reduction was observed (p < 0.05). The SHR QrHH exhibited higher antioxidant capacity in the kidney than the other experimental groups (p < 0.05). The SHR QrHH group showed an increase in reduced glutathione levels in the liver compared to the SHR control group (p < 0.05). In relation to lipid peroxidation, SHR QrHH exhibited a significant decrease in plasma, kidney and heart malondialdehyde (MDA) values compared to the SHR control group (p < 0.05). The results obtained revealed the in vivo antioxidant effect of QrH and its ability to ameliorate HTN and its associated complications.

Food matrix design can influence the antimicrobial activity in the food systems: A narrative review

Antimicrobial agents are safe preservatives having the ability to protect foods from microbial spoilage and extend their shelf life. Many factors, including antimicrobials' chemical features, storage environments, delivery methods, and diffusion in foods, can affect their antimicrobial activities. The physical-chemical characteristics of the food itself play an important role in determining the efficacy of antimicrobial agents in foods; however the mechanisms behind it have not been fully explored. This review provides new insights and comprehensive knowledge regarding the impacts of the food matrix, including the food components and food (micro)structures, on the activities of antimicrobial agents. Studies of the last 10 years regarding the influences of the food structure on the effects of antimicrobial agents against the microorganisms' growth were summarized. The mechanisms underpinning the loss of the antimicrobial agents' activity in foods are proposed. Finally, some strategies/technologies to improve the protection of antimicrobial agents in specific food categories are discussed.

Identification of a Bitter Peptide Contributing to the Off-Flavor Attributes of Pea Protein Isolates

The aversive bitter taste of pea protein ingredients limits product acceptability. Compounds contributing to the bitter perception of pea protein isolates were investigated. Off-line multi-dimensional sensory-guided preparative liquid chromatography fractionation of a 10% aqueous PPI solution revealed one main bitter compound that was identified by Fourier transform ion cyclotron resonance mass spectrometry and de novo tandem mass spectrometry (MS/MS) sequencing as the 37 amino acid peptide PA1b from pea albumin and further confirmed by synthesis. Quantitative MS/MS analysis reported that the concentration of the bitter peptide was 129.3 mg/L, which was above the determined bitter sensory threshold value of 3.8 mg/L and in agreement with the perceived bitter taste of the sample.

Analysis of Volatile Organic Compounds in Milk during Heat Treatment Based on E-Nose, E-Tongue and HS-SPME-GC-MS

Volatile organic compounds (VOCs) make up milk flavor and are essential attributes for consumers to evaluate milk quality. In order to investigate the influence of heat treatment on the VOCs of milk, electronic nose (E-nose), electronic tongue (E-tongue) and headspace solid-phase microextraction (HS-SPME)-gas chromatography-mass spectrometry (GC-MS) technology were used to evaluate the changes in VOCs in milk during 65 °C heat treatment and 135 °C heat treatment. The E-nose revealed differences in the overall flavor of milk, and the overall flavor performance of milk after heat treatment at 65 °C for 30 min is similar to that of raw milk, which can maximize the preservation of the original taste of milk. However, both were significantly different to the 135 °C-treated milk. The E-tongue results showed that the different processing techniques significantly affected taste presentation. In terms of taste performance, the sweetness of raw milk was more prominent, the saltiness of milk treated at 65 °C was more prominent, and the bitterness of milk treated at 135 °C was more prominent. The results of HS-SPME-GC-MS showed that a total of 43 VOCs were identified in the three types of milk-5 aldehydes, 8 alcohols, 4 ketones, 3 esters, 13 acids, 8 hydrocarbons, 1 nitrogenous compound, and 1 phenol. The amount of acid compounds was dramatically reduced as the heat treatment temperature rose, while ketones, esters, and hydrocarbons were encouraged to accumulate instead. Furfural, 2-heptanone, 2-undecanone, 2-furanmethanol, pentanoic acid ethyl ester, 5-octanolide, and 4,7-dimethyl-undecane can be used as the characteristic VOCs of milk treated at 135 °C. Our study provides new evidence for differences in VOCs produced during milk processing and insights into quality control during milk production.

Bitter-RF: A random forest machine model for recognizing bitter peptides

Introduction

Bitter peptides are short peptides with potential medical applications. The huge potential behind its bitter taste remains to be tapped. To better explore the value of bitter peptides in practice, we need a more effective classification method for identifying bitter peptides.

Methods

In this study, we developed a Random forest (RF)-based model, called Bitter-RF, using sequence information of the bitter peptide. Bitter-RF covers more comprehensive and extensive information by integrating 10 features extracted from the bitter peptides and achieves better results than the latest generation model on independent validation set.

Results

The proposed model can improve the accurate classification of bitter peptides (AUROC = 0.98 on independent set test) and enrich the practical application of RF method in protein classification tasks which has not been used to build a prediction model for bitter peptides.

Discussion

We hope the Bitter-RF could provide more conveniences to scholars for bitter peptide research.

From bitter to delicious: properties and uses of microbial aminopeptidases

Protein hydrolysates are easily digested and utilized by humans and animals, and are less likely to cause allergies. Protein hydrolysis caused by endopeptidases often leads to the exposure of hydrophobic amino acids at the ends of peptides, which consequently causes bitter taste. Microbial aminopeptidases remove the exposed hydrophobic amino acids at the ends of aminopeptides, which improves taste, allowing for easier production. This processe is attacking significant attention from industry and laboratories. Aminopeptidases selectively hydrolyze peptide bonds from the N-terminal of proteins or peptides to produce free amino acids. Aminopeptidases can be classified into leucine, lysine, methionine and proline aminopeptidases by hydrolyzed N-terminal residues; metallo-, serine- and cysteine- aminopeptidases by the reaction mechanisms; dipeptide and triphoptide enzymes by the released number of amino acid residues at the end of hydrolyzed peptides; or acidic, neutral and basic aminopeptidases by their optimal hydrolysis pH. Commercial aminopeptidases are generally produced by microbial fermentation, and are mainly applied in the debittering of protein hydrolysates, the deep hydrolysis of protein, and the production of condiments, cheese, and bioactive peptides, as well as for disease detection in the medical industry.

An overview of bitter compounds in foodstuffs: Classifications, evaluation methods for sensory contribution, separation and identification techniques, and mechanism of bitter taste transduction

The bitter taste is generally considered an undesirable sensory attribute. However, bitter-tasting compounds can significantly affect the overall flavor of many foods and beverages and endow them with various beneficial effects on human health. To better understand the relationship between chemical structure and bitterness, this paper has summarized the bitter compounds in foodstuffs and classified them based on the basic skeletons. Only those bitter compounds that are confirmed by human sensory evaluation have been included in this paper. To develop food products that satisfy consumer preferences, correctly ranking the key bitter compounds in foodstuffs according to their contributions to the overall bitterness intensity is the precondition. Generally, three methods were applied to screen out the key bitter compounds in foods and beverages and evaluate their sensory contributions, including dose-over-threshold factors, taste dilution analysis, and spectrum descriptive analysis method. This paper has discussed in detail the mechanisms and applications of these three methods. Typical procedures for separating and identifying the main bitter compounds in foodstuffs have also been summarized. Additionally, the activation of human bitter taste receptors (TAS2Rs) and the mechanisms of bitter taste transduction are outlined. Ultimately, a conclusion has been drawn to highlight the current problems and propose potential directions for further research.

E-nose, E-tongue Combined with GC-IMS to Analyze the Influence of Key Additives during Processing on the Flavor of Infant Formula

In order to analyze the influence of key additives during processing on the flavor of infant formula, the headspace-gas chromatography-ion mobility spectrometry, electronic tongue, and electronic nose techniques were used to evaluate flavor during the processing of stage 1 infant formula milk powder (0-6 months), including the analysis of seven critical additives. A total of 41 volatile compounds were identified, involving 12 aldehydes, 11 ketones, 9 esters, 4 olefins, 2 alcohols, 2 furans, and 1 acid. The electronic nose metal oxide sensor W5S had the highest response, followed by W1S and W2S, illustrating that these three sensors had great effects on distinguishing samples. The response results of the electronic tongue showed that the three sensory attributes of bitter, salty, and umami, as well as the richness of aftertaste, were more prominent, which contributed significantly to evaluating the taste profile and distinguishing among samples. Raw milk is an essential control point in the flavor formation process of stage 1 infant formula milk powder. Demineralized whey powder is the primary source of potential off-flavor components in hydrolyzed milk protein infant formula. This study revealed the quality characteristics and flavor differences of key additives in the production process of stage 1 infant formula milk powder, which could provide theoretical guidance for the quality control and sensory improvement of the industrialized production of infant formula.

Enzymatic hydrolysis of lentil protein concentrate for modification of physicochemical and techno-functional properties

The effects of hydrolysis by commercial food-grade proteases on the physicochemical and techno-functional properties of lentil protein concentrate were investigated. Lentil protein concentrate was hydrolysed with Alcalase, Novozym 11028 or Flavourzyme, and a control was prepared without enzyme addition under the same conditions. Differences in specificity between the three proteases were evident in the electrophoretic protein profile, reversed-phase HPLC peptide profile, and free amino acid composition. Alcalase and Novozym were capable of extensively degrading all the major protein fractions. Alcalase or Novozym treatment resulted in considerably higher solubility under acidic conditions compared to the control. Flavourzyme treatment resulted in moderately improved solubility in the acidic range, but slightly lower solubility at pH 7. Alcalase treatment resulted in slightly larger particle size and slightly higher viscosity. The foaming properties of the protein concentrate were not significantly affected by hydrolysis. Increased solubility in acidic conditions with hydrolysis could broaden the range of food and beverage applications for lentil protein concentrate.

Review on the release mechanism and debittering technology of bitter peptides from protein hydrolysates

Recent scientific evidence indicates that protein hydrolysates contain bioactive peptides that have potential benefits for human health. However, the bitter-tasting hydrophobic peptides in protein hydrolysates negatively affect the sensory quality of resulting products and limit their utilization in food and pharmaceutical industries. The approaches to reduce, mask, and remove bitter taste from protein hydrolysates have been extensively reported. This review paper focuses on the advances in the knowledge regarding the structure-bitterness relationship of peptides, the release mechanism of bitter peptides, and the debittering methods for protein hydrolysates. Bitter tastes generating with enzymatic hydrolysis of protein is influenced by the type, concentration, and bitter taste threshold of bitterness peptides. A "bell-shaped curve" is used to describe the relationship between the bitterness intensity of the hydrolysates and the degree of hydrolysis. The bitter receptor perceives bitter potencies of bitter peptides by the hydrophobicity recognition zone. The intensity of bitterness is influenced by hydrophobic and electronic properties of amino acids and the critical spatial structure of peptides. Compared to physicochemical debittering (i.e., selective separation, masking of bitter taste, encapsulation, Maillard reaction, and encapsulation) and other biological debittering (i.e., enzymatic hydrolysis, enzymatic deamidation, plastein reaction), enzymatic hydrolysis is a promising debittering approach as it combines protein hydrolyzation and debittering into a one-step process, but more work should be done to advance the knowledge on debittering mechanism of enzymatic hydrolysis and screening of suitable proteases. Further study can focus on combining physicochemical and biological approaches to achieve high debittering efficiency and produce high-quality products.

Enzymatic hydrolysates of soy protein promote the physicochemical stability of mulberry anthocyanin extracts in food processing

Soy protein papain hydrolysate (SPAH) and soy protein pepsin hydrolysate (SPEH) were used as protective agents for mulberry anthocyanin extracts (MAEs) to inhibit its color fading and enhance the anthocyanin stability at pH 6.3. Both SPAH and SPEH showed a significant protective effect on total anthocyanins in MAEs solutions. 1.0 mg/mL of SPEH presented the best protective effect on MAEs by increasing its half-life from 1.8 to 5.7 days. SPAH/SPEH-cyaniding-3-O-glucoside (C3G) interactions were investigated at pH 6.3 by fluorescence, Fourier-transform infrared spectroscopy (FT-IR), and Circular Dichroism (CD). Their association was mainly driven by hydrophobic interactions, and SPEH showed a higher binding affinity for C3G than SPAH, with a KA value of 2.62 × 105 M-1 at 300 K. The second structures of SPAH and SPEH were altered by C3G, with a decrease in the β-sheets and an increase in the turns and random coils.

Bioactive Peptides: From Basic Research to Clinical Trials and Commercialization

Chronic diseases, including metabolic diseases, have become a worldwide public health issue. Research regarding the use of bioactive peptides or protein hydrolysates derived from food, as the diet-based strategies for the prevention and mitigation of chronic diseases, has increased exponentially in the past decades. Numerous in vitro and in vivo studies report the efficacy and safety of food-derived bioactive peptides and protein hydrolysates as antihypertensive, anti-inflammatory, antidiabetic, and antioxidant agents. However, despite promising preclinical results, an inadequate understanding of their mechanisms of action and pharmacokinetics restrict their clinical translation. Commercialization of bioactive peptides can be further hindered due to scarce information regarding their efficacy, safety, bitter taste, as well as the lack of a cost-effective method of production. This review provides an overview of the current clinical evidence and challenges to commercial applications of food-derived bioactive peptides and protein hydrolysates for the prevention and alleviation of chronic diseases.

Alternatives to Cow’s Milk-Based Infant Formulas in the Prevention and Management of Cow’s Milk Allergy

Cow’s milk-based infant formulas are the most common substitute to mother’s milk in infancy when breastfeeding is impossible or insufficient, as cow’s milk is a globally available source of mammalian proteins with high nutritional value. However, cow’s milk allergy (CMA) is the most prevalent type of food allergy among infants, affecting up to 3.8% of small children. Hypoallergenic infant formulas based on hydrolysed cow’s milk proteins are commercially available for the management of CMA. Yet, there is a growing demand for more options for infant feeding, both in general but especially for the prevention and management of CMA. Milk from other mammalian sources than the cow, such as goat, sheep, camel, donkey, and horse, has received some attention in the last decade due to the different protein composition profile and protein amino acid sequences, resulting in a potentially low cross-reactivity with cow’s milk proteins. Recently, proteins from plant sources, such as potato, lentil, chickpeas, quinoa, in addition to soy and rice, have gained increased interest due to their climate friendly and vegan status as well as potential lower allergenicity. In this review, we provide an overview of current and potential future infant formulas and their relevance in CMA prevention and management.

Current findings support the potential use of bioactive peptides in enhancing zinc absorption in humans

More than two billion people around the world are affected by zinc deficiency, mainly due to the inadequate intake and absorption of zinc. Based on recent research findings, the bioactive peptides could potentially be used to combat zinc deficiency particularly due to their Zinc chelating ability. The main aim of this review was to present current findings, supporting the potential use of bioactive peptides based on their ability to enhance zinc absorption. In-vivo, in-vitro, and ex-vivo studies have demonstrated that zinc chelating peptides can enhance the retention, transportation, and absorption of zinc. Comparative studies on zinc bioavailability from protein hydrolysates and zinc salts have demonstrated that the protein hydrolysates-zinc complexes are more bioavailable than the zinc salts. Data from the structure-function relationship of zinc chelating peptides suggest that the zinc chelating capacities of peptides increase in the following order; the position of zinc chelator > zinc chelator strength > abundance of zinc chelators > net charge > molecular weight. In addition, the transport mechanism of peptide-zinc complex is hypothesized, and the potential use of bioactive peptides based on their safety and taste and limitations to their commercialization are also discussed.

Enthalpy-entropy compensation in calcium binding to acid-base forms of glycine tyrosine dipeptides from hydrolysis of α-lactalbumin

Calcium binding to peptides formed by hydrolysis of whey proteins during digestion is important for calcium uptake in the intestines and affects the antioxidant function of the peptides. For the two dipeptides, Gly-Tyr and Tyr-Gly, potential hydrolysis products of α-lactalbumin, calcium binding to the three forms of each dipeptide in acid-base equilibrium at intestinal pH was determined electrochemically and compared to binding to tyrosine for aqueous 0.16 M NaCl for 5 < pH < 9 at 15 °C, 25 °C, and 37 °C. At milk pH at 25 °C, binding of calcium to the zwitterion of GlyTyr dominates, with an association constant K_ass2 = 22 M^-1 with ΔH⁰ = -46 kJ·mol^-1, while binding to the mononegative TyrGly dominates for TyrGly with K_ass3 = 32 M^-1 and ΔH⁰ = -38 kJ·mol^-1. At intestinal conditions, pH = 7 and 37 °C, binding of calcium has similar affinity for GlyTyr and TyrGly, while at higher pH and lower temperature, GlyTyr binds stronger. Density Functional Theory calculations confirmed a stronger binding to the zwitterion of GlyTyr than of TyrGly and an increasing affinity with increasing pH for both. Calcium binding to the acid/base forms of the dipeptides is at neutral pH strongly exothermic with ΔH⁰ becoming less negative at higher pH, and a linear enthalpy-entropy compensation (r² = 0.99) results in comparable binding important for calcium bioavailability along the changing distribution among acid-base forms. Calcium binding decreases radical scavenging rate and antioxidative activity of both dipeptides.

Sensory evaluation, chemical structures, and threshold concentrations of bitter-tasting compounds in common foodstuffs derived from plants and maillard reaction: A review

The bitterness of foodstuffs is often associated with toxicity, which negatively influences product acceptability. However, bitter compounds have many benefits, and a slight bitter taste is sometimes favored. In this review, we summarize the methods used to isolate and evaluate the taste of bitter compounds in different foods. The chemical structures and threshold concentrations of these compounds are also recapped. Although the structures and thresholds of many bitter compounds have been confirmed, further studies are needed to develop detailed bitter-masking strategies and establish the relation between functional groups (hetero-cyclic substituents and bonding types) and taste quality. Furthermore, a comprehensive bitterness database and chemometric data must be provided in order to quickly assess the bitterness of unfamiliar products.

A proteomics approach to characterizing limited hydrolysis of whey protein concentrate

Whey Protein Concentrate was hydrolyzed by trypsin and Protease M, a novel endo/exopeptidase mix from Aspergillus oryzae. Protein peptide profiling demonstrated that Protease M preferentially hydrolyzedα-lactalbumin (α-la), while trypsin targeted β-lactoglobulin (β-lg). Peptide fractions were analyzed by liquid chromatography coupled with tandem mass-spectrometry to characterize differences in enzyme specificity, peptide hydrophobicity, and bioactivity, using bioinformatics tools. While trypsin cleaved at the C-terminal end of lysine and arginine, Protease M contributed to pepsin-like endopeptidase activity coupled with carboxyl, amino, and leucine exopeptidase activity, resulting in relatively more hydrophilic peptides compared to those released by trypsin hydrolysis. While trypsin and Protease M had varying specificity, 9 bioactive peptides were common among the hydrolysates, which was attributed to the exopeptidase activity of Protease M. The proteomics coupled with bioinformatics approach provided fundamental knowledge needed to optimize whey protein hydrolysis in a direct and efficient manner for targeted applications.

Principal Component Analysis from Mass Spectrometry Data Combined to a Sensory Evaluation as a Suitable Method for Assessing Bitterness of Enzymatic Hydrolysates Produced from Micellar Casein Proteins

Enzymatic hydrolysis of food proteins generally changes the techno-functional, nutritional, and organoleptic properties of hydrolyzed proteins. As a result, protein hydrolysates have an important interest in the food industries. However, they tend to be characterized by a bitter taste and some off-flavors, which limit their use in the food industry. These tastes and aromas come from peptides, amino acids, and volatile compounds generated during hydrolysis. In this article, sixteen more or less bitter enzymatic hydrolysates produced from a milk protein liquid fraction enriched in micellar caseins using commercially available, food-grade proteases were subjected to a sensory analysis using a trained and validated sensory panel combined to a peptidomics approach based on the peptide characterization by reverse-phase high-performance liquid chromatography, high-resolution mass spectrometry, and bioinformatics software. The comparison between the sensory characteristics and the principal components of the principal component analysis (PCA) of mass spectrometry data reveals that peptidomics constitutes a convenient, valuable, fast, and economic intermediate method to evaluating the bitterness of enzymatic hydrolysates, as a trained sensory panel can do it.

An alternative for proteinase K-heat-sensitive protease from fungus Onygena corvina for biotechnology: cloning, engineering, expression, characterization and special application for protein sequencing

Background

A neutral, heat-sensitive serine protease (NHSSP) originating from the feather-degrading fungus Onygena corvina (O. corvina) was described and defined as an alkaline serine protease of the subtilisin type S8 family, exhibiting an enzymatic activity at neutral pH. Generally, broad specificity proteases, such as proteinase K or trypsin, have found numerous applications in research and biotechnology.

Results

We report the cloning and expression in the yeast PichiaPink™ system, as well as purification, and characterization of the NHSSP. Recombinant, His₆-tagged NHSSP was efficiently expressed from an optimized, synthetic gene and purified using a simple protocol based on ammonium sulfate fractionation and hydrophobic interaction chromatography. The enzyme shows atypical C-terminal processing, the coded preproprotein undergoes signal peptide removal and maturation through the clipping of a propeptide section and 10 amino acids (aa) from the C-terminus, including the His₆-tag. The deletion variant has been constructed, devoid of the C-terminal ORF segment, thus eliminating the need for C-terminal processing. Both NHSSP variants exhibit very similar enzymatic characteristics. The purified enzymes were characterized to determine the optimal proteolytic conditions. We revealed that the mature NHSSP is reproducibly active over a wide pH range from neutral to mild acidic (pH of 5.0 to 8.5), with an optimum at pH 6.8, and at temperatures of 15 to 50 °C with an optimum at 38–42 °C. Interestingly, we demonstrated that the protease can be fully deactivated by a moderate increase in temperature of about 15 °C from the optimum to over 50 °C. The protease was partially sensitive to serine protease inhibitors, and not inhibited by chelating or reducing agents and detergents. SDS induced autolysis of NHSSP, which points to a high stimulation of its proteolytic activity.

Conclusions

The NHSSP was produced as a recombinant protein with high efficiency. Compared to proteinase K, the most common serine protease used, NHSSP shows an approx. twofold higher specific activity. Protein sequencing can be a valuable technical application for the protease. The protein coverage is significantly higher in comparison to trypsin and reaches about 84–100% for β-lactoglobulin (BLG), antibody (mAb) light and heavy chains. Furthermore, the option to perform digestions at neutral to slightly acidic pH-values down to pH 5.0 avoids modification of peptides, e.g. due to deamidation.

Role of sweeteners on temporality and bar hardening of protein bars

Protein bars are one product that meet consumer demands for a low-carbohydrate, high-protein food. With such a large market for protein bars, producers need to find the correct texture and sweetness levels to satisfy consumers while still delivering a high-protein, low-carbohydrate bar. In the bar industry, bar hardening is a major concern, and currently the effects of non-nutritive sweeteners on bar hardening is unknown. Due to the negative implications of bar hardening, it is important to investigate the sweetener-protein relationship with bar hardening. The objective of this study was to characterize the effects of sweetener and protein source on flavor, texture, and shelf life of high-protein, low-carbohydrate bars. The iso-sweet concentration of sweeteners (sucralose, sucrose, monk fruit, stevia, and fructose) in pea protein (PP), milk protein (MP) and whey protein isolate (WPI) bars were established using magnitude estimation scaling and 2-alternative forced-choice testing. Descriptive analysis and temporal check-all-that-apply methods were then applied to determine flavor and temporal differences between the protein bars. Finally, an accelerated shelf life study was completed to understand how sweetener and protein types affect the shelf life of protein bars. The 15 protein bars formulated at iso-sweet concentration were all stored at 35°C and 55% humidity for 35 d, and measurements were taken every 7 d, beginning at d 1 (d 1, 7, 14, 21, 28, and 35). Bars made with MP required significantly less sweetener, compared with PP and WPI, to reach equal sweetness. Bars sweetened with stevia or monk fruit had distinct bitter and metallic tastes, and sucralose had a low metallic taste. Bars made with WPI were the most cohesive, and PP and WPI bars were more bitter and metallic compared with MP bars. Bars made with WPI and fructose were initially the hardest, but after d 14 they scored at parity with PP sucrose. There were no significant differences among bars in terms of hardness by d 21. Bars made with WPI were consistently denser at all time points than bars made with PP or MP. Bars made with PP were the driest and least cohesive and had the fastest rate of breakdown in the study. Non-nutritive sweeteners did not have a negative effect on bar hardness in low-carbohydrate, high-protein bars. Findings from this study can be applied to commercially produced protein bars for naturally sweetened bars with different protein types without negative effects on protein bar texture.

Bitterness of fish protein hydrolysate and its debittering prospects

Fish processing by-products often generated as discard can enzymatically be processed into a product known as fish protein hydrolysates (FPH). FPH is a good source of amino acid and peptides with bioactivities. FPH can be added to foods to improve nutritive values and bioactivities. However, bitterness in FPH, associated with hydrophobicity, degree of hydrolysis, molecular weight, proline residues, type of enzymes, and amino acid sequences has limited its uses in foods. Thus, FPH is used in foods at low levels. Numerous procedures such as extraction with alcohol, activated carbon treatment, Maillard reaction, cyclodextrin, chromatographic separation, and enzymatic hydrolysis with exopeptidase and plastein reaction have been explored to remove the bitterness of FPH. These methods can lower bitterness and improve its taste. However, changes in structure and loss of some peptides may occur. FPH with less or no bitterness can therefore be used at higher levels to alleviate nutrition deficiencies in foods. PRACTICAL APPLICATIONS: Fish protein hydrolysate (FPH) is a nutritive ingredient, which can be produced from fish processing by-products. However, bitterness in FPH has limited its potential use as a nutritive ingredient. As a result, it is incorporated into foods at low levels. Nevertheless, application of several reported debittering processes could assist to solve the problem of bitterness in FPH. The debittering can improve sensory property of FPH, thus widening its utilization.

Relationship between enzyme, peptides, amino acids, ion composition, and bitterness of the hydrolysates of Alaska pollock frame

Alaska pollock frame is a kind of byproduct that was rich in protein, amino acids, and mineral elements. However, the unfavorite bitterness may probably be produced in enzymatic processes. In this study, the bitterness accounted from the hydrolysates prepared by neutral proteases, alkaline proteases, papain, flavourzyme, and animal proteases, was investigated. The hydrolysis conditions, amino acids composition, metal ion composition, molecular weight distribution, and peptide composition of the hydrolysates were detected to figure out the relationship between bitterness and compositions of the hydrolysates. The hydrolysate digested by alkaline protease has the highest bitterness intensity, and that amino acids composition, peptide composition, and molecular weight distribution had a significant influence on the bitterness degree. Hydrophobic amino acids and alkaline amino acids, such as leucine, isoleucine, lysine, and so on are likely to contribute to the bitterness and molecular weight distribution of peptides that affect bitterness is mainly lower than 3,000 Da. PRACTICAL APPLICATIONS: Fish bones would produce a bitter taste when reusing them by hydrolysis. Bitterness is one of unfavorable flavor as to consumers. The results of this study are of great significance for the further utilization of Alaska pollock frame. For products obtained from the hydrolysate of Alaska pollock frame, such as condiments and health care product the results of this study provide the processing technology of the lowest bitter hydrolysate, which can effectively improve the flavor and acceptability of the products.

Sensoproteomics: A New Approach for the Identification of Taste-Active Peptides in Fermented Foods

Aiming at the identification of the key bitter peptides in fermented foods, a new approach, coined "sensoproteomics", was developed and applied to fresh cheese samples differing in bitter taste intensity. By means of MPLC fractionation of the water-soluble cheese extracts in combination with taste dilution analysis, complex fractions with intense bitter taste were located and then screened by UPLC-MS/MS for the entire repertoire of ∼1600 candidate peptides, extracted from a literature meta-analysis on dairy products, by using a total of 120 selected reaction monitoring methods computed in silico. A total of 340 out of the 1600 peptides were found in the cheese samples, among which 17 peptides were identified as candidate bitter peptides by considering only peptides that were located in the bitter-tasting MPLC fractions (signal-to-noise ratio: ≥10) with a fold-change of ≥3 when comparing the less bitter to the more bitter cheese sample and that were validated by comparison with the synthetic reference peptides. While EIVPNS[phos]VEQK (α_s1-CN_70-78) and INTIASGEPT (κ-CN_122-131) did not exhibit any bitter taste up to 2000 μmol/L, 15 of the 17 target peptides showed bitter taste thresholds ranging from 30 (ARHPHPHLSFM, κ-CN_96-106) to 690 μmol/L (IQKEDVPS, α_s1-CN_81-88). Finally, quantitative peptide analysis followed by calculation of dose-overthreshold factors revealed a primary contribution of MAPKHKEMPFPKYPVEPF (β-CN_102-119) and ARHPHPHLSFM (κ-CN_96-106) to the perceived bitter taste of the fresh cheese samples. Finally, the evolution of the bitter peptides throughout two different fresh cheese manufacturing processes was quantitatively recorded.

Natural Preservatives for Extending the Shelf-Life of Seafood: A Revisit

Consumer demand for minimally processed seafood that retains its sensory and nutritional properties after handling and storage is increasing. Nevertheless, quality loss in seafood occurs immediately after death, during processing and storage, and is associated with enzymatic, microbiological, and chemical reactions. To maintain the quality, several synthetic additives (preservatives) are promising for preventing the changes in texture and color, development of unpleasant flavor and rancid odor, and loss of nutrients of seafood during storage at low temperature. However, the use of these preservatives has been linked to potential health hazards. In this regard, natural preservatives with excellent antioxidant and antimicrobial properties have been extensively searched and implemented as safe alternatives in seafood processing, with the sole purpose of extending shelf-life. Natural preservatives commonly used include plants extracts, chitosan and chitooligosaccharide, bacteriocins, bioactive peptides, and essential oils, among others. This review provides updated information about the production, mode of action, applications, and limitations of these natural preservatives in seafood preservation.

Peptidomic screening of bitter and nonbitter casein hydrolysate fractions for insulinogenic peptides

Sodium caseinate hydrolysates (NaCaH) contain biologically active peptides that can positively influence human health. However, their intense bitterness hinders their inclusion in food products. To our knowledge, no studies have investigated whether a correlation between bitterness and bioactivity exists in NaCaH, so it is not yet known what effect selective removal of bitterness has on NaCaH bioactivity. A deeper understanding of the physicochemical characteristics affecting both bitterness and bioactivity is therefore needed. The aim of this study was to use in silico analysis to elucidate the relationship between bitterness and bioactivity of the insulinogenic NaCaH. The NaCaH fractions were generated by membrane filtration and flash chromatography and were subsequently evaluated for bitterness by a sensory panel. In this present study, peptidomic and bioinformatic processing of these NaCaH fractions allowed for the identification of insulinogenic peptides as well as other literature-identified peptides in each of the fractions. The results showed that the most bitter fraction contained the highest abundance of insulinogenic peptides, whereas another bitter fraction contained the highest abundance of other literature-identified bioactive peptides exhibiting angiotensin-converting enzyme-inhibition activity. Although some bioactive peptides were identified in the least bitter fractions, the abundance of these peptides was very low. These observations show a correlation between bitter taste and bioactivity, highlighting potential complications in removing bitterness while maintaining bioactivity. However, as the most bitter fraction contained the highest abundance of insulinogenic peptides, there is potential for using a lower dose of this enriched bioactive fraction to exert health benefits. The second most bitter fraction contained a very low abundance of insulinogenic peptides and other bioactive peptides. Therefore, removal of this fraction could reduce the NaCaH product's bitterness without significantly altering overall bioactive potential.

Appetite-Inducing Effects of Homoeriodictyol: Two Randomized, Cross-Over Interventions

SCOPE

Anorexia of aging, characterized by a decrease in appetite and/or food intake, is a major risk factor of under-nutrition and adverse health outcomes in elderly people. Recent in vitro evidence suggests homoeriodictyol (HED), a naturally occurring, bitter-masking flavanone, as a promising agent to increase appetite and food intake.

METHODS AND RESULTS

In two cross-over intervention trials, 30 mg NaHED, either solely (n = 10, Study I) or in combination with a 75 g glucose load (n = 17, study II) were administered to healthy adult subjects. Ratings of hunger were assessed at fasting and either 30 min (Study I) or 120 min (Study II) post intervention. Ad libitum energy intake from a standardized breakfast and plasma changes in hunger-/satiety-associated hormones PYY, GLP-1, ghrelin and serotonin were determined after blood drawings. Effects were more pronounced when NaHED was administered in combination with 75 g glucose since ad libitum energy (+ 9.52 ± 4.60%) and protein (+ 7.08 ± 7.97%) intake as well as plasma ΔAUC ghrelin values increased in study II solely, whereas plasma serotonin concentrations decreased after both interventions.

CONCLUSIONS

NaHED demonstrated appetizing effects in healthy adults when administered with a glucose load. Long-term intervention studies are warranted to verify these effects in compromised subjects.

Screening for proteolytically active lactic acid bacteria and bioactivity of peptide hydrolysates obtained with selected strains

In a screening for proteolytically active lactic acid bacteria, three strains, Lactobacillus delbrueckii ssp. lactis 92202, Lactobacillus helveticus 92201, and Lactobacillus delbrueckii ssp. bulgaricus 92059, showed the highest activities following growth in milk. All three strains degraded α- and β-casein, but did not hydrolyse κ-casein. HPLC analysis of skim milk fermentation revealed increasing amounts of peptides after 5 and 10 h with Lb. d. ssp. bulgaricus 92059. Hydrolysates obtained with Lb. d. ssp. lactis 92202 and Lb. d. ssp. bulgaricus 92059 revealed the highest angiotensin-converting enzyme-inhibitory effect. The effect was dose dependent. Almost no effect (<10%) was seen for Lb. helveticus 92201. For Lb. d. ssp. bulgaricus 92059, maximal inhibition of approx. 65% was reached after 25 h of fermentation. In an in vitro assay measuring potential immunomodulation, hydrolysates of the three strains yielded anti-inflammatory activities in the presence of TNF-α. However, the effects were more pronounced at lower hydrolysate concentrations. In the absence of TNF-α, slight pro-inflammatory effects were observed. The hydrolysate of Lb. d. ssp. bulgaricus 92059, when purified by means of solid-phase extraction, exhibited pro-inflammatory activity. Sour whey containing Lb. d. ssp. bulgaricus 92059 cells showed pro-inflammatory activity while cell-free sour whey was clearly anti-inflammatory. In the purified hydrolysate, 20 different α- and β-casein (CN)-derived peptides could be identified by LC-MS. Most peptides originated from the central and C-terminal regions of β-casein. Peptide length was between 9 (β-CN(f 59-67)) and 22 amino acids (β-CN(f 117-138)).

Validation of a paper-disk approach to facilitate the sensory evaluation of bitterness in dairy protein hydrolysates from a newly developed food-grade fractionation system

Casein-hydrolysates (NaCaH) are desirable functional ingredients, but their bitterness impedes usage in foods. This study sought to validate a paper-disk approach to help evaluate bitterness in NaCaHs and to develop a food-grade approach to separate a NaCaH into distinct fractions, which could be evaluated by a sensory panel. Membrane filtration generated <0.2-μm and <3-kDa permeates. Further fractionation of the <3-kDa permeate by flash-chromatography generated four fractions using ethanol (EtOH) concentrations of 5, 10, 30 and 50%. As some fractions were poorly soluble in water, the fractions were resolubilzed in EtOH and impregnated into paper-disks for sensory evaluation. Bitterness differences observed in the membrane fractions using this sensory evaluation approach reflected those observed for the same fractions presented as a liquid. The flash-chromatography fractions increased in bitterness with an increase in hydrophobicity, except for the 50% EtOH fraction which had little bitterness. Amino acid analysis of the fractions showed enrichment of different essential amino acids in both the bitter and less bitter fractions.

Practical Applications

The developed food-grade fractionation system, allowed for a simple and reasonably scaled approach to separating a NaCaH, into physicochemically different fractions that could be evaluated by a sensory panel. The method of sensory evaluation used in this study, in which NaCaH samples are impregnated into paper-disks, provided potential solutions for issues such as sample insolubility and limited quantities of sample. As the impregnated paper-disk samples were dehydrated, their long storage life could also be suitable for sensory evaluations distributed by mail for large consumer studies. The research, in this study, allowed for a greater understanding of the physicochemical basis for bitterness in this NaCaH. As some essential amino acids were enriched in the less bitter fractions, selective removal of bitter fractions could allow for the incorporation of the less bitter NaCaH fractions into food products for added nutritional value, without negatively impacting sensory properties. There is potential for this approach to be applied to other food ingredients with undesirable tastes, such as polyphenols.

Cheese Whey Catalytic Conversion for Obtaining a Bioactive Hydrolysate With Reduced Antigenicity

Bioinformatics was used to design a procedure for industrial enzymatic proteolysis of cheese whey. The specificity rules for commercial enzymes were applied to in silico proteolysis of cheese whey proteins. The pattern of antigens was considered, along with molecular descriptors of bitter taste, antioxidant capacity, and anti-hypertensive activity. The main objective was to obtain hydrolysates with reduced antigenicity and satisfactory sensory properties; an additional goal was to characterize their bioactivity profiles. Protamex/Alcalase mixtures were first used as multienzyme compositions to obtain non-bitter cheese whey hydrolysates. The multifactor optimization performed for degree of hydrolysis, free amino acid content, and residual antigenicity has revealed the optimal Protamex/Alcalase ratio of 3.5:0.5 and the optimal hydrolysis duration of 90 min. The hydrolysate obtained using Protamex/Alcalase 3.5:0.5 mixture had a double antioxidant capacity and a 15 times lower ACE-I inhibition concentration IC50 compared to cheese whey concentrate, and an 11 times lower β-LG residual antigenicity.

Food protein-originating peptides as tastants - Physiological, technological, sensory, and bioinformatic approaches

Taste is one of the factors based on which the organism makes the selection of what to ingest. It also protects humans from ingesting toxic compounds and is one of the main attributes when thinking about food quality. Five basic taste sensations are recognized by humans: bitter, salty, sour, sweet, and umami. The taste of foods is affected by some molecules of some specific chemical nature. One of them are peptides derived from food proteins. Although they are not the major natural compounds originating from food sources that are responsible for the taste, they are in the area of scientific research due to the specific composition of amino acids which are well-known for their sensory properties. Literature data implicate that sweet, bitter, and umami are the tastes attributable to peptides. Moreover, the bitter peptide tastants are the dominant among the other tastes. Additionally, other biological activities like, e.g., inhibiting enzymes that regulate the body functions and acting as preventive food agents of civilization diseases, are also associated with the taste of peptides. The advance in information technologies has contributed to the elaboration of internet archives (databases) as well as in silico tools for the analysis of biological compounds. It also concerns peptides - namely taste carriers originating from foods. Thus, our paper provides a summary of knowledge about peptides as tastants with special attention paid to the following aspects: a) basis of taste perception, b) taste peptides detected in food protein sequences with special emphasis put on the role of bitter peptides, c) peptides that may enhance/suppress the taste of foods, d) databases as well as bioinformatic approaches suitable to study the taste of peptides, e) taste-taste interactions, f) basis of sensory analysis in the evaluation of the taste of molecules, including peptides, and g) the methodology applied to reduce/eliminate the undesired taste of peptides. The list of taste peptides serving some biological functions is presented in the Supplement file. The information provided includes database resources, whereas peptide sequences are given with InChiKeys, which is aimed at facilitating the Google® search. Our collection of data regarding taste peptides may be supportive for the scientists working with the set of peptide data in the context of structure-function activity of peptides.

Spermidine Derivatives in Lulo (Solanum quitoense Lam.) Fruit: Sensory (Taste) versus Biofunctional (ACE-Inhibition) Properties

The bitterness in lulo (Solanum quitoense Lam.) fruit is increased during processing (juicing or drying). To identify the bitter-active compounds, the ethanolic fruit pulp extract was subjected to RP-18 solid-phase extraction, and then sensory-guided fractionated by HPLC. Two spermidine derivatives, N(1),N(4),N(8)-tris(dihydrocaffeoyl)spermidine and N(1),N(8)-bis(dihydrocaffeoyl)spermidine, were isolated and their structures confirmed by analysis of their HPLC-ESI/MS and (1)H and (13)C NMR data. The N(1),N(4),N(8)-tris(dihydrocaffeoyl)spermidine was synthesized and used as an authentic sample to unequivocally confirm the structure of this compound and to quantitate it in both fresh and dried fruit. In silico analyses demonstrated that spermidine derivatives identified in lulo pulp exhibited a strong ACE-I (angiotensin I-converting enzyme) inhibitory activity. Subsequently, these results were confirmed by in vitro analyses and showed the potential use of lulo fruit pulp as an ingredient of functional foods related to the prevention of blood hypertension.

Changes in the enzyme-induced release of bitter peptides from wheat gluten hydrolysates

Extraction of wheat gluten hydrolysates prepared using Proteax with isobutyl alcohol has opened a new avenue for exploring the release characteristics of bitter peptides.

Emerging trends in nutraceutical applications of whey protein and its derivatives

The looming food insecurity demands the utilization of nutrient-rich residues from food industries as value-added products. Whey, a dairy industry waste has been characterized to be excellent nourishment with an array of bioactive components. Whey protein comprises 20 % of total milk protein and it is rich in branched and essential amino acids, functional peptides, antioxidants and immunoglobulins. It confers benefits against a wide range of metabolic diseases such as cardiovascular complications, hypertension, obesity, diabetes, cancer and phenylketonuria. The protein has been validated to boost recovery from resistance exercise-injuries, stimulate gut physiology and protect skin against detrimental radiations. Apart from health invigoration, whey protein has proved its suitability as fat replacer and emulsifier. Further, its edible and antimicrobial packaging potential renders its highly desirable in food as well as pharmaceutical sectors. Considering the enormous nutraceutical worth of whey protein, this review emphasizes on its established and emerging biological roles. Present and future scopes in food processing and dietary supplement formulation are discussed. Associated hurdles are identified and how technical advancement might augment its applications are explored. This review is expected to provide valuable insight on whey protein-fortified functional foods, associated technical hurdles and scopes of improvement.