Amino acid analysis: determination of cysteine plus half-cystine in proteins after hydrochloric acid hydrolysis with a disulfide compound as additive

Nitrogen sources in donor human milk: True protein, nonprotein nitrogen, and amino acid profile

BACKGROUND

Devices measuring the macronutrient content of human milk are commonly used to assist with clinical decision-making. It is unknown if these devices accurately measure protein content in donor human milk (DHM). Our objective is to quantify the nitrogen sources and protein content in commercial DHM.

METHODS

The total nitrogen content (Dumas method) and nonprotein nitrogen content (Kjeldahl method) was measured in triplicate from six commercial DHM samples with protein content noted on the labels. In addition, the amino acid content was measured in 15 commercial DHM samples and protein content in each sample was calculated. The calculated protein content for each DHM sample was compared for consistency.

RESULTS

The nonprotein nitrogen content in DHM was consistently higher (0.33 ± 0.05 g/g) than previous reports, leading to overreporting of protein content on DHM labels by a median value of 0.15 g/dl (range 0.02-0.23 g/dl). Similarly, calculation of the protein content from the total nitrogen content with an assumption of 20% (grams per gram) nonprotein nitrogen consistently overrepresented the protein content as determined from the amino acid profile for DHM.

CONCLUSION

Common methods for assessing the macronutrient content of human milk may overestimate the protein content of DHM.

Comparative extraction of antioxidant proteins from whole frogs (Rana ridibunda Pollas)

The forest frog (Rana ridibunda Pollas) is a traditional medicinal source rich in active protein compounds. In order to extract these compounds, six extraction methods were employed, including freeze-thaw and stirring techniques. Three different solvents were utilized in this process: 0.15 M sodium chloride (NaCl), 0.05 M phosphate buffer (PB), and 0.05 M phosphate-buffered saline (PBS). The objective was to identify the most effective extraction method. The extraction efficiencies, protein content, structure, and physicochemical properties of the extracts were compared. Additionally, antioxidant activity and free amino acid composition were analyzed. The highest-scoring extract, denoted as M1, obtained through freeze-thaw extraction using 0.15 M NaCl, exhibited an extraction rate of 7.79 ± 0.71% and a protein content of 60.36 ± 2.12%. M1 also showed antioxidant activity against DPPH˙, ABTS+˙, and ˙OH free radicals, with IC50 values of 0.41, 0.41, and 0.39 mg mL-1, respectively. The freeze-thaw extraction method utilizing 0.15 M NaCl has been identified as effective for extracting proteins from dried forest frogs, confirming their potential as a source of antioxidant proteins for scientific research and application.

Solid Phase Peptide Carrier Conjugation

Conjugation to carrier proteins is necessary for peptides to be able to induce antibody formation when injected into animals together with a suitable adjuvant. This is usually performed by conjugation in solution followed by mixing with the adjuvant. Alternatively, the carrier may be adsorbed onto a solid support followed by activation and conjugation with the peptide by solid-phase chemistry. Different reagents can be used for conjugation through peptide functional groups (-SH, -NH2, -COOH), and various carrier proteins may be used depending on the peptides and the intended use of the antibodies. The solid phase may be an ion exchange matrix, from which the conjugate can subsequently be eluted and mixed with adjuvant. Alternatively, the adjuvant aluminum hydroxide may be used as the solid-phase matrix, whereupon the carrier is immobilized and conjugated with peptide. The resulting adjuvant-carrier-peptide complexes may then be used directly for immunization.

Mathematical optimisation of extruded mixed plant protein-based meat analogues based on amino acid compositions

Developing meat analogues of superior amino acid (AA) profiles in the food industry is a challenge as plant proteins contain less of some essential AA than animal proteins. Mathematical optimisation models such as linear/non-linear programming models were used to overcome this challenge and create high-moisture meat analogues (HMMA) with AA profiles as close as possible to chicken breast meat. The effect on the physiochemical properties and specific mechanical energy (SME) of the HMMA was investigated. The AA content of HMMA was generally lower than chicken. Strong intermolecular bonds present in the globulin fraction could hinder protein acid hydrolysis of HMMA. Plant proteins also affect the HMMA colour as certain AA forms Maillard reaction products with higher browning intensity. Lastly, different characteristics of plant proteins resulted in different SME values under the same extrusion conditions. While mathematical programming can optimise plant protein combinations, fortification is required to match the AA profile of HMMA to an animal source.

Pharmacokinetics of AXA1665, a Novel Composition of Amino Acids, in Comparison With Protein Supplement: A Single-Dose, Open-Label, Randomized Study in Healthy Subjects

We evaluated the safety and tolerability of AXA1665, a novel investigational fixed-ratio amino acid (AA) composition, the pharmacokinetics (PK) of the constituent AAs within AXA1665, and their relative bioavailability versus standard protein supplement. This study was conducted in 2 phases; in the initial phase, healthy subjects (N = 16) were randomly assigned to 4 treatment sequences (AXA1665 4.9, 9.8, and 19.6 g or 35 g protein supplement) in an open-label, single-dose, 4-way crossover study, while in the extension phase, they received single AXA1665 doses of 29.4 and 39.2 g in a sequential crossover manner. The net area under the plasma concentration-time curve (AUC) and observed time to reach maximum plasma concentration were estimated. A dose-dependent increase in plasma AUC from time 0 to the last measurable concentration (AUClast ) and maximum plasma concentration (Cmax ) was observed for all AXA1665-dosed AAs (4.9-39.2 g) except aspartic acid. AXA1665 19.6 g resulted in 1.5- to 9.5-fold higher systemic exposure to all AXA1665-dosed AAs except for aspartic acid and lysine and lower exposure to all nondosed AAs except for glutamine and alanine versus protein supplement. AXA1665 doses, up to 39.2 g, can deliver AXA1665-dosed AAs in the systemic circulation in the linear AUC range.

A fast, sensitive and fluorescent LPMO activity assay

Lytic polysaccharide monooxygenases (LPMOs) are industrially relevant enzymes that utilize a copper co-factor and an oxygen species to break down recalcitrant polysaccharides. These enzymes are secreted by microorganisms and are used in lignocellulosic refineries. As such, they are interesting from both the ecological/biological and industrial perspectives. Here we describe the development of a new fluorescence-based kinetic LPMO activity assay. The assay is based on the enzymatic production of fluorescein from its reduced counterpart. The assay can detect as little as 1 nM LPMO with optimized assay conditions. Furthermore, the reduced fluorescein substrate can also be used to identify peroxidase activity as seen by the formation of fluorescein by horseradish peroxidase. The assay was shown to work well at relatively low H2O2 and dehydroascorbate concentrations. The applicability of the assay was demonstrated.

Identification of the key off-flavor odorants for undesirable spoiled odor in thermally sterilized fermented soymilk

Spoiled odors are a problem in thermally sterilized fermented soymilk. This study aims to clarify production conditions and key odorants of spoiled odors. The sensory evaluation showed that thermal sterilization caused a decrease in the sensory intensity of yogurt and fruity odors while significantly increasing undesirable aromas including beany, acidic, cooked-beans and spoiled odors. The spoiled odors increased with increasing acidity and heating temperatures. The strongest spoiled odor was observed in fermented soymilk at titratable acidity of 5.4 g/kg, sterilized at 90 °C. Apart from common volatiles that were inherent in soymilk and generated from lactic fermentation, 2-methyltetrahydrothiophen-3-one was found for the first time in soybean foods and was found to cause the spoiled odor. 44 volatiles found in thermally sterilized fermented soymilk were jointly formed its flavor wheel. This study provides important theoretical support for solving the problem of spoiled odor restricting the popularization of plant-based fermented soymilk.

Determination of Total Amino Acids in Infant Formulas, Adult Nutritionals, Dairy, and Cereal Matrixes by UHPLC–UV: Interlaboratory Validation Study, Final Action 2018.06

Background

A method for the quantification of total amino acids (including taurine and excluding tryptophan) using ultra- HPLC separation coupled to UV detection (UHPLC–UV) was granted First Action status (AOAC 2018.06) by the AOAC INTERNATIONAL Stakeholder Program for Infant Formula and Adult Nutritionals (SPIFAN) in 2018.

Objective

An interlaboratory study was conducted to further assess method performance against the AOAC Standard Method Performance Requirements (AOAC SMPR^® 2014.013). Dairy and cereal matrixes were added to expand the scope of the method in collaboration with IDF (International Dairy Federation), ISO (International Organization for Standardization), and AACCI (American Association of Cereal Chemists International, now Cereals & Grains Association).

Methods

Sixteen different matrixes were chosen to cover the requirements of AOAC, IDF/ISO, and AACCI. Blind duplicate samples were organized into specific series to ensure that each pair was analyzed on the same day. Fifteen laboratories returned results. Data from four laboratories were considered invalid and removed from the dataset. Remaining data were assessed according to the Appendix D of the AOAC Official Methods of Analysis^SM (guidelines for collaborative study procedures).

Results

This method generally met the requirements listed in the SMPR for infant formulas and adult nutritionals, except for taurine. Method performance was comparable in dairy and cereal matrixes. Five different UHPLC instruments were used with either commercial or in-house reagents, demonstrating that the method is not limited to a single supplier.

Conclusion

This method was recommended for Final Action in infant and adult/pediatric nutritional formulas by the AOAC SPIFAN Nutrients Expert Review Panel in April 2021, with the exception of taurine. The corresponding IDF/ISO Draft International Standard (DIS) was approved by national bodies in May 2022, and comments collected during the ballot were incorporated into this manuscript.

Highlights

AOAC Official Method 2018.06 for the determination of total amino acids in infant formulas, adult nutritionals, dairy, and cereal matrixes was successfully validated in an interlaboratory study.

Determination of low molecular thiols and protein sulfhydryl groups using heterocyclic disulfides

A promising area in the analytical chemistry of thiol-containing compounds is the use of heterocyclic disulfides as analytical agents, but now only a few of them are widely used. In this paper, we evaluate the possibility of using three different heterocyclic disulfides 2,2'-dithiobis[5-phenyl-1,3,4-oxadiazole] (I), 2,2'-dithiobis[benzoxazole] (II) and 8,8'-dithiobis-quinoline (III) as analytical reagents for the low-mass aminothiols cysteine and glutathione determination. The optimal analysis conditions were found. Spectrophotometric, kinetic, CE, and HPLC methods using I, II, III for the determination of cysteine and glutathione were developed. The obtained methods are characterized by accuracy and sensitivity (detection limits in the range of 10^-5-10^-6 M) sufficient to quantify cysteine and glutathione in their physiological concentrations. Finally, the proposed disulfides were used to determine the SH-content in the bovine serum albumin (BSA). Considering a number of criteria (applicable pH range, absorption properties, susceptibility to hydrolysis) it was concluded that the proposed reagents have advantages over the commonly used ones (such as the Ellman reagent).

Inhibition of LPMOs by Fermented Persimmon Juice

Fermented persimmon juice, Kakishibu, has traditionally been used for wood and paper protection. This protective effect stems at least partially from inhibition of microbial cellulose degrading enzymes. The inhibitory effect of Kakishibu on lytic polysaccharide monooxygenases (LPMOs) and on a cocktail of cellulose hydrolases was studied, using three different cellulosic substrates. Dose dependent inhibition of LPMO activity by a commercial Kakishibu product was assessed for the well-characterized LPMO from Thermoascus aurantiacus TaAA9A, and the inhibitory effect was confirmed on five additional microbial LPMOs. The model tannin compound, tannic acid exhibited a similar inhibitory effect on TaAA9A as Kakishibu. It was further shown that both polyethylene glycol and tannase can alleviate the inhibitory effect of Kakishibu and tannic acid, indicating a likely mechanism of inhibition caused by unspecific tannin-protein interactions.

Inhibition of lytic polysaccharide monooxygenase by natural plant extracts

Lytic polysaccharide monooxygenases (LPMOs) are monocopper enzymes of industrial and biological importance. In particular, LPMOs play important roles in fungal lifestyle. No inhibitors of LPMOs have yet been reported. In this study, a diverse library of 100 plant extracts was screened for LPMO activity-modulating effects. By employing protein crystallography and LC-MS, we successfully identified a natural LPMO inhibitor. Extract screening revealed a significant LPMO inhibition by methanolic extract of Cinnamomum cassia (cinnamon), which inhibited LsAA9A LPMO from Lentinus similis in a concentration-dependent manner. With a notable exception, other microbial LPMOs from families AA9 and AA10 were also inhibited by this cinnamon extract. The polyphenol cinnamtannin B1 was identified as the inhibitory component by crystallography. Cinnamtannin B1 was bound to the surface of LsAA9A at two distinct binding sites: one close to the active site and another at a pocket on the opposite side of the protein. Independent characterization of cinnamon extract by LC-MS and subsequent activity measurements confirmed that the compound inhibiting LsAA9A was cinnamtannin B1. The results of this study show that specific natural LPMO inhibitors of plant origin exist in nature, providing the opportunity for future exploitation of such compounds within various biotechnological contexts.

Brief Research Report: Estimation of the Protein Digestibility-Corrected Amino Acid Score of Defatted Walnuts

Introduction: Walnuts are considered a good source of essential fatty acids, which is unique among tree nuts. Walnuts are also composed of about 10–15% protein, but the quality of this protein has not been evaluated. Pistachios and almonds have been evaluated for their protein content using a protein digestibility-corrected amino acid score (PDCAAS), but it is unclear how the quality of protein in walnuts relates to that in other commonly consumed tree nuts. The objective of this study was to substantiate the protein quality of walnuts by determining their PDCAAS.

Methods: A small, 10-day dietary intervention trial was conducted using male Sprague-Dawley rats (n = 8, 4 per group) with two diets: a nitrogen-free diet and a diet containing protein exclusively from defatted walnuts. Feed intake and fecal output of nitrogen were measured to estimate the true protein digestibility, and the amino acid compositions of walnuts compared to child and adult populations were used to calculate amino acid scores (AAS) and PDCAAS.

Results: The true protein digestibility score of raw walnuts was calculated to be 86.22%. Raw walnuts contained 15.6 g protein/g walnut with AAS of 0.45 and 0.63 for children aged 6 months to 3 years and 3–10 years, respectively. For each population, a PDCAAS of 39 and 46% was calculated, respectively, using a protein conversion constant of 5.30. Using a protein constant of 6.25, a PDCAAS of 39% (6 months - 3 years) or 46% (3-10 years) was calculated.

Conclusions: This is the first known assessment of the PDCAAS of walnuts. Like almonds, they appear to have a low-to-moderate score, indicating they are not a quality source of protein.

[Determination of 18 amino acids in three different kinds of milk powder by ultra performance liquid chromatography coupled with pre-column derivatization]

近年来羊奶粉和骆驼奶粉备受消费者青睐,它们具有潜在的低致敏性,因此成为牛乳不耐受人群尤其是婴幼儿的母乳替代品,其营养价值备受关注。牛奶粉、羊奶粉和骆驼奶粉中氨基酸含量的比较研究鲜有报道。利用酸水解得到游离氨基酸,选择6-氨基喹啉-N-羟基琥珀酰亚胺氨基甲酸酯(AQC)进行柱前衍生,超高效液相色谱分离并检测,外标法定量。18种氨基酸在各自线性范围内线性关系良好,相关系数(r²)大于0.999;以3倍和10倍信噪比(S/N)确定方法的检出限(LOD)和定量限(LOQ),分别为1.3~2.5 (mg/100 g)和3.9~7.5 (mg/100 g)。方法验证采用奶粉标准参考物质SRM 1849a,测定值符合其含量范围,6次测定值的相对标准偏差(RSD)为2.04%~3.65%。采用建立的方法分别对市售和网购的牛奶粉、羊奶粉和骆驼奶粉进行18种氨基酸成分和含量分析,旨在从氨基酸角度对这3种不同来源乳品进行对比。该方法快速,灵敏度高,准确可靠,适用于不同基质乳粉中18种氨基酸成分和含量的确定。

Copper binding and reactivity at the histidine brace motif: insights from mutational analysis of the Pseudomonas fluorescens copper chaperone CopC

The histidine brace (His-brace) is a copper-binding motif that is associated with both oxidative enzymes and proteinaceous copper chaperones. Here, we used biochemical and structural methods to characterize mutants of a His-brace-containing copper chaperone from Pseudomonas fluorescens (PfCopC). A total of 15 amino acid variants in primary and second-sphere residues were produced and characterized in terms of their copper binding and redox properties. PfCopC has a very high affinity for Cu(II) and also binds Cu(I). A high reorganization barrier likely prevents redox cycling and, thus, catalysis. In contrast, mutations in the conserved second-sphere Glu27 enable slow oxidation of ascorbate. The crystal structure of the variant E27A confirmed copper binding at the His-brace. Unexpectedly, Asp83 at the equatorial position was shown to be indispensable for Cu(II) binding in the His-brace of PfCopC. A PfCopC mutant that was designed to mimic the His-brace from lytic polysaccharide monooxygenase-like family X325 did not bind Cu(II), but was still able to bind Cu(I). These results highlight the importance of the proteinaceous environment around the copper His-brace for reactivity and, thus, the difference between enzyme and chaperone.

An ultra-high affinity protein-protein interface displaying sequence-robustness

Protein-protein interactions are crucial in biology and play roles in for example, the immune system, signaling pathways, and enzyme regulation. Ultra-high affinity interactions (K_d <0.1 nM) occur in these systems, however, structures and energetics behind stability of ultra-high affinity protein-protein complexes are not well understood. Regulation of the starch debranching barley limit dextrinase (LD) and its endogenous cereal type inhibitor (LDI) exemplifies an ultra-high affinity complex (K_d of 42 pM). In this study the LD-LDI complex is investigated to unveil how robust the ultra-high affinity is to LDI sequence variation at the protein-protein interface and whether alternative sequences can retain the ultra-high binding affinity. The interface of LD-LDI was engineered using computational protein redesign aiming at identifying LDI variants predicted to retain ultra-high binding affinity. These variants present a very diverse set of mutations going beyond conservative and alanine substitutions typically used to probe interfaces. Surface plasmon resonance analysis of the LDI variants revealed that high affinity of LD-LDI requires interactions of several residues at the rim of the protein interface, unlike the classical hotspot arrangement where key residues are found at the center of the interface. Notably, substitution of interface residues in LDI, including amino acids with functional groups different from the wild-type, could occur without loss of affinity. This demonstrates that ultra-high binding affinity can be conferred without hotspot residues, thus making complexes more robust to mutational drift in evolution. The present mutational analysis also demonstrates how energetic coupling can emerge between residues at large distances at the interface.

Colorimetric LPMO assay with direct implication for cellulolytic activity

BACKGROUND

Lytic polysaccharide monooxygenases (LPMOs) are important industrial enzymes known for their catalytic degradation of recalcitrant polymers such as cellulose or chitin. Their activity can be measured by lengthy HPLC methods, while high-throughput methods are less specific. A fast and specific LPMO assay would simplify screening for new or engineered LPMOs and accelerate biochemical characterization.

RESULTS

A novel LPMO activity assay was developed based on the production of the dye phenolphthalein (PHP) from its reduced counterpart (rPHP). The colour response of rPHP oxidisation catalysed by the cellulose-specific LPMO from Thermoascus aurantiacus (TaAA9A), was found to increase tenfold by adding dehydroascorbate (DHA) as a co-substrate. The assay using a combination of rPHP and DHA was tested on 12 different metallo-enzymes, but only the LPMOs catalysed this reaction. The assay was optimized for characterization of TaAA9A and showed a sensitivity of 15 nM after 30 min incubation. It followed apparent Michaelis-Menten kinetics with kcat = 0.09 s-1 and KM = 244 µM, and the assay was used to confirm stoichiometric copper-enzyme binding and enzyme unfolding at a temperature of approximately 60 °C. DHA, glutathione and fructose were found to enhance LPMO oxidation of rPHP and in the optimized assay conditions these co-substrates also enabled cellulose degradation.

CONCLUSIONS

This novel and specific LPMO assay can be carried out in a convenient microtiter plate format ready for high-throughput screening and enzyme characterization. DHA was the best co-substrate tested for oxidation of rPHP and this preference appears to be LPMO-specific. The identified co-substrates DHA and fructose are not normally considered as LPMO co-substrates but here they are shown to facilitate both oxidation of rPHP and degradation of cellulose. This is a rare example of a finding from a high-throughput assay that directly translate into enzyme activity on an insoluble substrate. The rPHP-based assay thus expands our understanding of LPMO catalysed reactions and has the potential to characterize LPMO activity in industrial settings, where usual co-substrates such as ascorbate and oxygen are depleted.

From Waste to Taste-Efficient Production of the Butter Aroma Compound Acetoin from Low-Value Dairy Side Streams Using a Natural (Nonengineered) Lactococcus lactis Dairy Isolate

Lactococcus lactis subsp. lactis biovar diacetylactis is widely used in dairy fermentations as it can form the butter aroma compounds acetoin and diacetyl from citrate in milk. Here, we explore the possibility of producing acetoin from the more abundant lactose. Starting from a dairy isolate of L. lactis biovar diacetylactis, we obtained a series of mutants with low lactate dehydrogenase (ldh) activity. One isolate, RD1M5, only had a single insertion mutation in the ldh gene compared to its parental strain as revealed by whole genome resequencing. We tested the ability of RD1M5 to produce acetoin in milk. With aeration, all the lactose could be consumed, and the only product was acetoin. In a simulated cheese fermentation, a 50% increase in acetoin concentration could be achieved. RD1M5 turned out to be an excellent cell factory for acetoin and was able to convert lactose in dairy waste into acetoin with high titer (41 g/L) and high yield (above 90% of the theoretical yield). Summing up, RD1M5 was found to be highly robust and to grow excellently in milk or dairy waste. Being natural in origin opens up for applications within dairies as well as for safe production of food-grade acetoin from low-cost substrates.

Amino Acid Profiles and Compositions of Different Cultivars of Panicum miliaceum L

Abstract

Amino acids are valuable nutrients, responsible for a variety of tasks in the human body. A favourable amino acid profile in gluten-free crops, such as millet, can thus be beneficial for human health, which is why 35 proso millet (Panicum miliaceum L.) samples, comprising 23 whole and 12 dehulled, were investigated regarding their amino acid profiles and compositions using acidic hydrolysis and ion-exchange chromatography with ninhydrin derivatization and subsequent detection with photometry. Results for amino acid compositions were compared with gluten-containing wheat and other gluten-free cereals. Furthermore, gained values were put in contrast to estimated essential amino acid requirements for adult humans. The study was able to show that cultivars of proso millet differ and that dehulling does not significantly influence the amino acid compositions. Furthermore, the results display that Panicum miliaceum L. holds more essential amino acids than other gluten-free grains and exhibits high amounts of leucine and alanine. The methionine content differs greatly between samples, which means that choosing certain cultivars is important to ensure a high content. The most abundant amino acids in proso millet grains are glutamic acid/glutamine (2.13 ± 0.34 g per 100 g), alanine (1.06 ± 0.18 g per 100 g) and leucine (1.36 ± 0.24 g per 100 g).

Graphic abstract

Phytochemical composition and nutritional value of different plant parts in two cultivated and wild purslane (Portulaca oleracea L.) genotypes

Purslane (Portulaca oleracea) is a weed naturally found in driveways, lawns, and fields and edible in many regions of Europe, Asia, the Middle East, Africa, and Australia. The purpose of this study was to compare the nutritional and phytochemical components of cultivated and wild purslane. Omega-3 contents of both purslane genotypes were comparable with 189.16 ± 25.52 mg/100 g dry weight and 188.48 ± 6.35 mg/100 g dry weight in cultivated and wild purslane leaves, respectively. Omega-6/omega-3 ratio (1:1-1:3) were low in both genotypes. However, high levels of oxalic acid were observed. Cultivated contained greater amounts of amino acids and vitamins than wild purslane. Of the 184 compounds identified in both genotypes by LC-MS/MS, including phenolic acids, organic acids, flavonoids, alkaloids, and betanin, more than 80 showed greater than two-fold abundance in the wild compared to cultivated purslane. Purslane has the potential to be cultivated as a food ingredient for nutraceutical applications.

Wheat Gluten Amino Acid Analysis by High-Performance Anion-Exchange Chromatography with Integrated Pulsed Amperometric Detection

The present chapter describes an accurate and user-friendly method for determining amino acid composition of wheat gluten proteins and their gliadin and glutenin fractions. The method consists of hydrolysis of the peptide bonds in 6.0 M hydrochloric acid (HCl) solution at 110 °C for 24 h, followed by evaporation of the acid and separation of the free amino acids by high-performance anion-exchange chromatography with integrated pulsed amperometric detection (HPAEC-IPAD). In contrast to conventional methods, the analysis requires neither pre- or post-column derivatization nor a time-consuming oxidation or derivatization step prior to hydrolysis. Correction factors account for incomplete release of Val and Ile even after hydrolysis for 24 h and for losses of Ser during evaporation. Gradient conditions including an extra eluent allow multiple sequential sample analyses without risk of Glu accumulation on the anion-exchange column which otherwise would result from high Gln levels in gluten proteins.

Characterization and safety evaluation of HPPD W336, a modified 4-hydroxyphenylpyruvate dioxygenase protein, and the impact of its expression on plant metabolism in herbicide-tolerant MST-FGØ72-2 soybean

By transgenic expression technology, a modified 4-hydroxyphenylpyruvate dioxygenase enzyme (HPPD W336) originating from Pseudomonas fluorescens is expressed in MST-FGØ72-2 soybean to confer tolerance to 4-benzoyl isoxazole and triketone type of herbicides. Characterization and safety assessment of HPPD W336 were performed. No relevant sequence homologies were found with known allergens or toxins. Although sequence identity to known toxins showed identity to HPPD proteins annotated as hemolysins, the absence of hemolytic activity of HPPD W336 was demonstrated in vitro. HPPD W336 degrades rapidly in simulated gastric fluid. The absence of toxicity and hemolytic potential of HPPD W336 was confirmed by in vivo studies. The substrate spectrum of HPPD W336 was compared with wild type HPPD proteins, demonstrating that its expression is unlikely to induce any metabolic shifts in soybean. The potential effect of expression of HPPD W336 on metabolic pathways related to tyrosine was investigated by comparing seed composition of MST-FGØ72-2 soybean with non-genetically modified varieties, demonstrating that expression of HPPD W336 does not change aromatic amino acid, homogentisate and tocochromanol levels. In conclusion, HPPD W336 was demonstrated to be as safe as other food proteins. No adverse metabolic effects were identified related to HPPD W336 expression in MST-FGØ72-2 soybean.

High-throughput analysis of amino acids in plant materials by single quadrupole mass spectrometry

BACKGROUND

The amino acid profile of plants is an important parameter in assessments of their growth potential, resource-use efficiency and/or quality as food and feed. Screening studies may involve large number of samples but the classical amino acid analysis is limited by the fact that it is very time consuming with typical chromatographic run times of 70 min or more.

RESULTS

We have here developed a high-throughput method for analysis of amino acid profiles in plant materials. The method combines classical protein hydrolysis and derivatization with fast separation by UHPLC and detection by a single quadrupole (QDa) mass spectrometer. The chromatographic run time is reduced to 10 min and the precision, accuracy and sensitivity of the method are in line with other recent methods utilizing advanced and more expensive mass spectrometers. The sensitivity of the method is at least a factor 10 better than that of methods relying on detection by fluorescence or UV. It is possible to downscale sample size to 20 mg without compromising reproducibility, which makes the method ideal for analysis of very small sample amounts.

CONCLUSION

The developed method allows high-throughput analysis of amino acid profiles in plant materials. The analysis is robust and accurate as well as compatible with both free amino acids and protein hydrolysates. The QDa detector offers high sensitivity and accuracy, while at the same time being relatively simple to operate and cheap to purchase, thus significantly reducing the overall analytical costs compared to methods based on more advanced mass spectrometers.

Enhanced efficacy of sublingual immunotherapy by liposome-mediated delivery of allergen

Immunotherapy by sublingual administration of allergens provides high patient compliance and has emerged as an alternative to subcutaneous immunotherapy for the treatment of IgE-associated allergic diseases. However, sublingual immunotherapy (SLIT) can cause adverse events. Development of allergen delivery systems enabling more efficient delivery and hence lower allergen load might reduce the adverse events. In the present study, we have investigated neutral and cationic liposomes as delivery systems of ovalbumin (OVA), as a model allergen, in an OVA-induced allergic airway inflammation model. We investigated the liposome carriers' ability to improve tolerance induction of antigens compared to the corresponding dose of free OVA. Mice were treated sublingually over 2 weeks with free or liposome encapsulated OVA followed by intraperitoneal injections and intranasal challenge. Mice sublingually treated with OVA-liposomes showed a significant reduction of airway eosinophilia and splenocyte proliferation in comparison to free OVA. A similar nonsignificant pattern was seen for OVA-specific IgE antibodies. In addition, reduced levels of interferon-γ and interleukin-5 were observed in spleen cell culture supernatants from OVA-liposome-treated mice compared to the sham-treated group. In conclusion, in vivo efficacy data showed that prophylactic SLIT with OVA-liposomes is significantly more effective in preventing allergic inflammation than the corresponding dose of free OVA.

Double-Mutated 5-Enol Pyruvylshikimate-3-phosphate Synthase Protein Expressed in MZHG0JG Corn (Zea mays L.) Has No Impact on Toxicological Safety and Nutritional Composition

MZHG0JG corn will offer growers the flexibility to alternate between herbicides with two different modes of action in their weed-management programs, helping to mitigate and manage the evolution of herbicide resistance in weed populations. The proteins conferring herbicide tolerence in MZHG0JG corn, double-mutated 5-enol pyruvylshikimate-3-phosphate synthase protein (mEPSPS) and phosphinothricin acetyltransferase (PAT), as well as the MZHG0JG corn event, have been assessed by regulatory authorities globally and have been determined to be safe for humans, animals, and the environment. In addition to the safety data available for these proteins, further studies were conducted on MZHG0JG corn to assess levels of mEPSPS as compared to previously registered genetically modified (GM) corn. The results support the conclusion of no impact on toxicological safety or nutritional composition.

The extraordinary thermal stability of EstA from S. islandicus is independent of post translational modifications

Enzymes from thermophilic and hyper-thermophilic organisms have an intrinsic high stability. Understanding the mechanisms behind their high stability will be important knowledge for the engineering of novel enzymes with high stability. Lysine methylation of proteins is prevalent in Sulfolobus, a genus of hyperthermophilic and acidophilic archaea. Both unspecific and temperature dependent lysine methylations are seen, but the significance of this post-translational modification has not been investigated. Here, we test the effect of eliminating in vivo lysine methylation on the stability of an esterase (EstA). The enzyme was purified from the native host S. islandicus as well as expressed as a recombinant protein in E. coli, a mesophilic host that does not code for any machinery for in vivo lysine methylation. We find that lysine mono methylation indeed has a positive effect on the stability of EstA, but the effect is small. The effect of the lysine methylation on protein stability is secondary to that of protein expression in E. coli, as the E. coli recombinant enzyme is compromised both on stability and activity. We conclude that these differences are not attributed to any covalent difference between the protein expressed in hyperthermophilic versus mesophilic hosts.

Growth, enzymatic glutathione peroxidase activity and biochemical status of juvenile barramundi (Lates calcarifer) fed dietary fermented soybean meal and organic selenium

Solvent-extracted soybean meal (SBM) was fermented using baker's yeast Saccharomyces cerevisae at 30 °C for 5 days. Four isonitrogenous and isocaloric diets containing 75% SBM protein, either fermented or non-fermented (SBM and FSBM), and supplemented or not with organic Se (OS) (SBMOS and FSBMOS), were fed to triplicate groups of juvenile barramundi (Lates calcarifer) (initial weight of 5 g) for 75 days. A fishmeal (FM)-based diet formulated for juvenile barramundi was used as a reference diet. The growth of fish was significantly affected by either the interaction of SBM type or by the OS level. In fish fed diets supplemented with OS (SBMOS and FSBMOS), final weight (FW), specific growth rate (SGR) and weight gain (WG) were higher in fish fed the fermented SBM (FSBMOS) than in those fed the non-fermented SBM (SBMOS). The apparent digestibility coefficient (ADC) of protein was higher in the fish fed the fermented SBM, either supplemented or unsupplemented with OS. However, there were no significant differences in the ADC of dry matter (DM) and lipids among the tested diets and in comparison to the reference diet. The haematocrit and leucocrit of fish fed the FSBMOS diet were lower than those of fish fed the FM diet. Furthermore, glutathione peroxidase (GPx) activity was significantly influenced by OS supplementation in the experimental diets; GPx activity was greater in the fish fed diets supplemented with OS. Creatinine kinase (CK) of all groups of fish was higher than the CK of those fed the reference diet. These results suggest that with a proper nutritional level, OS supplementation may act as an important factor in enzymatic GPx activity and in the haematology and blood biochemistry status of juvenile barramundi fed fermented SBM-based diets, encouraging improvement of the overall growth performance.

An Extracellular Cell-Attached Pullulanase Confers Branched α-Glucan Utilization in Human Gut Lactobacillus acidophilus

Of the few predicted extracellular glycan-active enzymes, glycoside hydrolase family 13 subfamily 14 (GH13_14) pullulanases are the most common in human gut lactobacilli. These enzymes share a unique modular organization, not observed in other bacteria, featuring a catalytic module, two starch binding modules, a domain of unknown function, and a C-terminal surface layer association protein (SLAP) domain. Here, we explore the specificity of a representative of this group of pullulanases, Lactobacillus acidophilus Pul13_14 (LaPul13_14), and its role in branched α-glucan metabolism in the well-characterized Lactobacillus acidophilus NCFM, which is widely used as a probiotic. Growth experiments with L. acidophilus NCFM on starch-derived branched substrates revealed a preference for α-glucans with short branches of about two to three glucosyl moieties over amylopectin with longer branches. Cell-attached debranching activity was measurable in the presence of α-glucans but was repressed by glucose. The debranching activity is conferred exclusively by LaPul13_14 and is abolished in a mutant strain lacking a functional LaPul13_14 gene. Hydrolysis kinetics of recombinant LaPul13_14 confirmed the preference for short-branched α-glucan oligomers consistent with the growth data. Curiously, this enzyme displayed the highest catalytic efficiency and the lowest K_m reported for a pullulanase. Inhibition kinetics revealed mixed inhibition by β-cyclodextrin, suggesting the presence of additional glucan binding sites besides the active site of the enzyme, which may contribute to the unprecedented substrate affinity. The enzyme also displays high thermostability and higher activity in the acidic pH range, reflecting adaptation to the physiologically challenging conditions in the human gut.IMPORTANCE Starch is one of the most abundant glycans in the human diet. Branched α-1,6-glucans in dietary starch and glycogen are nondegradable by human enzymes and constitute a metabolic resource for the gut microbiota. The role of health-beneficial lactobacilli prevalent in the human small intestine in starch metabolism remains unexplored in contrast to colonic bacterial residents. This study highlights the pivotal role of debranching enzymes in the breakdown of starchy branched α-glucan oligomers (α-limit dextrins) by human gut lactobacilli exemplified by Lactobacillus acidophilus NCFM, which is one of the best-characterized strains used as probiotics. Our data bring novel insight into the metabolic preference of L. acidophilus for α-glucans with short α-1,6-branches. The unprecedented affinity of the debranching enzyme that confers growth on these substrates reflects its adaptation to the nutrient-competitive gut ecological niche and constitutes a potential advantage in cross-feeding from human and bacterial dietary starch metabolism.

Ancestral Interactions of Ribosomal RNA and Ribosomal Proteins

We have proposed that the ancient ribosome increased in size during early evolution by addition of small folding-competent RNAs. In this Accretion Model, small RNAs and peptides were subsumed onto subunit surfaces, gradually encasing and freezing previously acquired components. The model predicts that appropriate rRNA fragments have inherited local autonomy of folding and local autonomy of assembly with ribosomal proteins (rProteins), and that the rProtein and rRNA are co-chaperones. To test these predictions, we investigate the rRNA interactions of rProtein uL23 and its tail, uL23^tail, which is a β-hairpin that penetrates deep into the core of the large ribosomal subunit. In the assembled ribosome, uL23^tail associates with Domain III of the rRNA and a subdomain called "DIII^core". Here using band shift assays, fluorescence Job plots, and yeast three-hybrid assays, we investigate the interactions of rProtein uL23 and its tail with Domain III and with DIII^core rRNA. We observe rRNA₁-uL23^tail₁ complexes in the absence of Mg²⁺ ions and rRNA₁-uL23^tail_n (n > 1) complexes in the presence of Mg²⁺ ions. By contrast, the intact uL23 rProtein binds in slightly anticooperative complexes of various stoichiometries. The globular and tail regions of rProtein uL23 are distinctive in their folding behaviors and the ion dependences of their association with rRNA. For the globular region of the rProtein, folding is independent of rRNA, and rRNA association is predominantly by nonelectrostatic mechanisms. For the tail region of the protein, folding requires rRNA, and association is predominantly by electrostatic mechanisms. We believe these protein capabilities could have roots in ancient evolution and could be mechanistically important in co-chaperoning the assembly of the ribosome.

Modification of Cysteine

This unit describes a number of methods for modifying cysteine residues of proteins and peptides. A general procedure for alkylation of cysteine residues in a protein of known size and composition with haloacyl reagents or N-ethylmaleimide (NEM) is presented, and alternate protocols describe similar procedures for use when the size and composition are not known and when only very small amounts of protein are available. Alkylations that introduce amino groups using bromopropylamine and N-(iodoethyl)-trifluoroacetamide are also presented. Two procedures that are often used for subsequent sequence analysis of the protein, alkylation with 4-vinylpyridine and acrylamide, are described, and a specialized procedure for 4-vinylpyridine alkylation of protein that has been adsorbed onto a sequencing membrane is also presented. Reversible modification of cysteine residues by way of sulfitolysis is described, and a protocol for oxidation with performic acid for amino acid compositional analysis is also provided. Gentle oxidation of cysteine residues to disulfides by exposure to air is described. Support protocols are included for recrystallization of iodoacetic acid, colorimetric detection of free sulfhydryls, and desalting of modified samples. © 2017 by John Wiley & Sons, Inc.

Effects of Organic Selenium Supplementation on Growth, Accumulation, Haematology and Histopathology of Juvenile Barramundi (Lates calcarifer) Fed High Soybean Meal Diets

Soybean meal (SBM) has been commonly utilised as a substitute for fishmeal (FM) in the diets of several fish species. However, little is known regarding their effects on trace element availability and thus their importance to fish. The present study employed two feeding trials to evaluate the implications of dietary selenium (Se) on the growth, accumulation, antioxidant, and histopathological responses of juvenile barramundi (Lates calcarifer). In the first trial, each of three basal diets containing 0, 15 and 43 % SBM as replacements for 0, 25 and 75 % of FM protein on an isoproteic and isocalorific basis were either supplemented or not supplemented with 2 mg kg-1 organic Se (OS). In the second trial, the potential effect of OS supplementation in a high SBM diet was investigated in a feeding trial with five experimental diets: 75 % SBM protein as replacement of FM was supplemented with 2, 3, 4, 5 or 7 mg OS kg-1. Growth was independently influenced by the SBM level and the OS supplementation level but not by their interaction. Glutathione peroxidase (GPx) activity, haematocrit, Se accumulation and muscle tissue integrity were significantly enhanced in fish fed on OS-supplemented diets. Furthermore, when high SBM was included in diets, elevated Se tended to lower the barramundi's performance. These findings suggest that dietary supplementation of OS at 2-3 g kg-1 diet is necessary when high plant protein ingredients are incorporated in the diet, in order to maintain better growth and to afford protection against oxidative stress.

Meals based on vegetable protein sources (beans and peas) are more satiating than meals based on animal protein sources (veal and pork) - a randomized cross-over meal test study

Background

Recent nutrition recommendations advocate a reduction in protein from animal sources (pork, beef) because of environmental concerns. Instead, protein from vegetable sources (beans, peas) should be increased. However, little is known about the effect of these vegetable protein sources on appetite regulation.

Objective

To examine whether meals based on vegetable protein sources (beans/peas) are comparable to meals based on animal protein sources (veal/pork) regarding meal-induced appetite sensations.

Design

In total, 43 healthy, normal-weight, young men completed this randomized, double-blind, placebo-controlled, three-way, cross-over meal test. The meals (all 3.5 MJ, 28 energy-% (E%) fat) were either high protein based on veal and pork meat, HP-Meat (19 E% protein, 53 E% carbohydrate, 6 g fiber/100 g); high protein based on legumes (beans and peas), HP-Legume (19 E% protein, 53 E% carbohydrate, 25 g fiber/100 g); or low-protein based on legumes, LP-Legume (9 E% protein, 62 E% carbohydrate, 10 g fiber/100 g). Subjective appetite sensations were recorded at baseline and every half hour using visual analog scales until the ad libitum meal 3 h after the test meal. Repeated measurements analyses and summary analyses were performed using ANCOVA (SAS).

Results

HP-Legume induced lower composite appetite score, hunger, prospective food consumption, and higher fullness compared to HP-Meat and LP-Legume (p<0.05). Furthermore, satiety was higher after HP-Legume than HP-Meat (p<0.05). When adjusting for palatability, HP-Legume still resulted in lower composite appetite scores, hunger, prospective consumption, and higher fullness compared to HP-Meat (p<0.05). Furthermore, HP-Legume induced higher fullness than LP-Legume (p<0.05). A 12% and 13% lower energy intake, respectively, was seen after HP-Legume compared to HP-Meat or LP-Legume (p<0.01).

Conclusion

Vegetable-based meals (beans/peas) influenced appetite sensations favorably compared to animal-based meals (pork/veal) with similar energy and protein content, but lower fiber content. Interestingly, a vegetable-based meal with low protein content was as satiating and palatable as an animal-based meal with high protein content.

Acetylsalicylic acid supplementation improves protein utilization efficiency while vitamin E supplementation reduces markers of the inflammatory response in weaned pigs challenged with enterotoxigenic E. coli

Background

This experiment was conducted to test the hypothesis that vitamin E (Vit E) and acetylsalicylic acid (ASA), a cyclooxygenase-2 (COX-2) inhibitor, will additively reduce the production of the immunosuppressive molecule prostaglandin E₂ (PGE₂) and hence reduce inflammatory responses in weaner pigs experimentally infected with an enterotoxigenic strain of E. coli.

Methods

The experiment was conducted in a research facility with 192 individually-housed male weaner pigs (Landrace × Large White) weighing 6.6 ± 0.04 kg (mean ± SEM). The pigs were experimentally infected with an enterotoxigenic strain of E. coli and were allocated to a 2 × 3 factorial design with the respective factors being without and with 125 ppm ASA and three levels of Vit E supplementation (50, 100 or 200 IU/kg diet, dl-α-tocopheryl acetate).

Results

Acetylsalicylic acid supplementation improved average daily gain (P < 0.05) and tended to improve feed:gain ratio (P < 0.10) during the first 14 d after weaning. Acetylsalicylic acid supplementation also improved (P < 0.001) amino acid utilization efficiency (as assessed by plasma urea level) and tended to decrease (P < 0.10) PGE₂ production in the liver without affecting small intestinal histology and tight junction protein mRNA expression in the jejunal epithelium. Vitamin E supplementation greater than 100 IU/kg diet sustained both the plasma Vit E concentration (P < 0.001) and plasma haptoglobin content (P < 0.001) after weaning. However, there was no additive effects of the combined supplementation of ASA and Vit E on performance, intestinal barrier function and inflammatory responses of weaned pigs.

Conclusions

Although ASA and vitamin E improved amino acid utilization efficiency and reduced acute inflammatory responses, ASA and vitamin E did not additively reduce production of PGE₂ and inflammatory responses in weaner pigs experimentally infected with an enterotoxigenic strain of E. coli.

A novel cell factory for efficient production of ethanol from dairy waste

BACKGROUND

Sustainable and economically feasible ways to produce ethanol or other liquid fuels are becoming increasingly relevant due to the limited supply of fossil fuels and the environmental consequences associated with their consumption. Microbial production of fuel compounds has gained a lot of attention and focus has mostly been on developing bio-processes involving non-food plant biomass feedstocks. The high cost of the enzymes needed to degrade such feedstocks into its constituent sugars as well as problems due to various inhibitors generated in pretreatment are two challenges that have to be addressed if cost-effective processes are to be established. Various industries, especially within the food sector, often have waste streams rich in carbohydrates and/or other nutrients, and these could serve as alternative feedstocks for such bio-processes. The dairy industry is a good example, where large amounts of cheese whey or various processed forms thereof are generated. Because of their nutrient-rich nature, these substrates are particularly well suited as feedstocks for microbial production.

RESULTS

We have generated a Lactococcus lactis strain which produces ethanol as its sole fermentation product from the lactose contained in residual whey permeate (RWP), by introducing lactose catabolism into a L. lactis strain CS4435 (MG1363 Δ(3) ldh, Δpta, ΔadhE, pCS4268), where the carbon flow has been directed toward ethanol instead of lactate. To achieve growth and ethanol production on RWP, we added corn steep liquor hydrolysate (CSLH) as the nitrogen source. The outcome was efficient ethanol production with a titer of 41 g/L and a yield of 70 % of the theoretical maximum using a fed-batch strategy. The combination of a low-cost medium from industrial waste streams and an efficient cell factory should make the developed process industrially interesting.

CONCLUSIONS

A process for the production of ethanol using L. lactis and a cheap renewable feedstock was developed. The results demonstrate that it is possible to achieve sustainable bioconversion of waste products from the dairy industry (RWP) and corn milling industry (CSLH) to ethanol and the process developed shows great potential for commercial realization.

Effect of increased intake of skimmed milk, casein, whey or water on body composition and leptin in overweight adolescents: a randomized trial

BACKGROUNDS

Dairy proteins may support muscle protein synthesis and improve satiety in adults. However, there are limited studies using exact measures of body composition, especially in adolescents.

OBJECTIVES

This study investigates the effect of milk proteins and water on body composition and leptin in overweight adolescents.

METHODS

Subjects (n = 193) aged 12-15 years were randomized to drink 1 L d(-1) of skimmed milk, whey, casein (all milk-based drinks 35 g protein L(-1) ) or water for 12 weeks. Twenty participants dropped out. A pre-test control group of 32 adolescents was examined 12 weeks before start of intervention. Outcomes included leptin and dual-energy X-ray absorptiometry scanning. The effects of the milk-based drinks on body composition and leptin were compared with baseline, pre-test control and water.

RESULTS

Lean mass index (LMI) increased compared to baseline (all 95% confidence intervals 0.05-0.50 kg m(-2) , all P ≤ 0.009) and the pre-test control group (0.044-0.247 kg m(-2) , P ≤ 0.002) for all four test drinks. Fat mass index (FMI) increased only for milk-based drink groups compared with baseline (0.15-0.67 kg m(-2) , P < 0.001) and also compared with water (0.029-0.255 kg m(-2) , P ≤ 0.011). For pre-test control, there was no change in FMI or LMI. Leptin increased in the casein (1.016-3.246 ng mL(-1) , P < 0.001; 0.952-3.294 ng mL(-1) , P < 0.001) and whey groups (0.135-2.273 ng mL(-1) , P = 0.027; 0.069-2.322, P = 0.038) compared with water and pre-test control group, respectively.

CONCLUSIONS

Although milk proteins increased LMI in overweight adolescents, there was a concurrent increase in FMI and leptin, whereas water only resulted in increased LMI. Thus, increased water intake may be beneficial for body composition in overweight adolescents.

A redox-dependent dimerization switch regulates activity and tolerance for reactive oxygen species of barley seed glutathione peroxidase

Monomeric and dimeric forms of recombinant barley (Hordeum vulgare subsp. vulgare) glutathione peroxidase 2 (HvGpx2) are demonstrated to display distinctly different functional properties in vitro. Monomeric HvGpx2 thus has five fold higher catalytic efficiency than the dimer towards tert-butyl hydroperoxide, but is more sensitive to inactivation by hydrogen peroxide. Treatment of the monomer with hydrogen peroxide results in dimer formation. This observed new behavior of a plant glutathione peroxidase suggests a mechanism involving a switch from a highly catalytically competent monomer to a less active, but more oxidation-resistant dimer.

Lactococcus lactis thioredoxin reductase is sensitive to light inactivation

Thioredoxin, involved in numerous redox pathways, is maintained in the dithiol state by the nicotinamide adenine dinucleotide phosphate-dependent flavoprotein thioredoxin reductase (TrxR). Here, TrxR from Lactococcus lactis is compared with the well-characterized TrxR from Escherichia coli. The two enzymes belong to the same class of low-molecular weight thioredoxin reductases and display similar kcat values (∼25 s(-1)) with their cognate thioredoxin. Remarkably, however, the L. lactis enzyme is inactivated by visible light and furthermore reduces molecular oxygen 10 times faster than E. coli TrxR. The rate of light inactivation under standardized conditions (λmax=460 nm and 4 °C) was reduced at lowered oxygen concentrations and in the presence of iodide. Inactivation was accompanied by a distinct spectral shift of the flavin adenine dinucleotide (FAD) that remained firmly bound. High-resolution mass spectrometric analysis of heat-extracted FAD from light-damaged TrxR revealed a mass increment of 13.979 Da, relative to that of unmodified FAD, corresponding to the addition of one oxygen atom and the loss of two hydrogen atoms. Tandem mass spectrometry confined the increase in mass of the isoalloxazine ring, and the extracted modified cofactor reacted with dinitrophenyl hydrazine, indicating the presence of an aldehyde. We hypothesize that a methyl group of FAD is oxidized to a formyl group. The significance of this not previously reported oxidation and the exceptionally high rate of oxygen reduction are discussed in relation to other flavin modifications and the possible occurrence of enzymes with similar properties.

Solid-Phase Peptide-Carrier Conjugation

Conjugation to carrier proteins is necessary for peptides to be able to induce antibody formation when injected into animals together with a suitable adjuvant. This is usually performed by conjugation in solution followed by mixing with the adjuvant. Alternatively, the carrier may be adsorbed onto a solid support followed by activation and conjugation with the peptide by solid-phase chemistry. Different reagents can be used for conjugation through peptide functional groups (-SH, -NH2, -COOH) and various carrier proteins may be used depending on the peptides and the intended use of the antibodies. The solid phase may be an ion-exchange matrix, from which the conjugate can subsequently be eluted and mixed with adjuvant. Alternatively, the adjuvant aluminum hydroxide may be used as the solid-phase matrix, whereupon the carrier is immobilized and conjugated with peptide. The resulting adjuvant-carrier-peptide complexes may then be used directly for immunization.

In vitro digestion of purified β-casein variants A(1), A(2), B, and I: effects on antioxidant and angiotensin-converting enzyme inhibitory capacity

Genetic polymorphisms of bovine milk proteins affect the protein profile of the milk and, hence, certain technological properties, such as casein (CN) number and cheese yield. However, reports show that such polymorphisms may also affect the health-related properties of milk. Therefore, to gain insight into their digestion pattern and bioactive potential, β-CN was purified from bovine milk originating from cows homozygous for the variants A(1), A(2), B, and I by a combination of cold storage, ultracentrifugation, and acid precipitation. The purity of the isolated β-CN was determined by HPLC, variants were verified by mass spectrometry, and molar extinction coefficients at λ=280nm were determined. β-Casein from each of the variants was subjected to in vitro digestion using pepsin and pancreatic enzymes. Antioxidant and angiotensin-converting enzyme (ACE) inhibitory capacities of the hydrolysates were assessed at 3 stages of digestion and related to that of the undigested samples. Neither molar extinction coefficients nor overall digestibility varied significantly between these 4 variants; however, clear differences in digestion pattern were indicated by gel electrophoresis. In particular, after 60min of pepsin followed by 5min of pancreatic enzyme digestion, one ≈4kDa peptide with the N-terminal sequence (106)H-K-E-M-P-F-P-K- was absent from β-CN variant B. This is likely a result of the (122)Ser to (122)Arg substitution in variant B introducing a novel trypsin cleavage site, leading to the changed digestion pattern. All investigated β-CN variants exhibited a significant increase in antioxidant capacity upon digestion, as measured by the Trolox-equivalent antioxidant capacity assay. After 60min of pepsin + 120min of pancreatic enzyme digestion, the accumulated increase in antioxidant capacity was ≈1.7-fold for the 4 β-CN variants. The ACE inhibitory capacity was also significantly increased by digestion, with the B variant reaching the highest inhibitory capacity at the end of digestion (60min of pepsin + 120min of pancreatic enzymes), possibly because of the observed alternative digestion pattern. These results demonstrate that genetic polymorphisms affect the digestion pattern and bioactivity of milk proteins. Moreover, their capacity for radical scavenging and ACE inhibition is affected by digestion.

Acid hydrolysis of wheat gluten induces formation of new epitopes but does not enhance sensitizing capacity by the oral route: a study in "gluten free" Brown Norway rats

Background

Acid hydrolyzed wheat proteins (HWPs) are used in the food and cosmetic industry as emulsifiers. Cases of severe food allergic reactions caused by HWPs have been reported. Recent data suggest that these reactions are caused by HWPs produced by acid hydrolysis.

Objectives

To examine the sensitizing capacity of gluten proteins per se when altered by acid or enzymatic hydrolysis relative to unmodified gluten in rats naïve to gluten.

Methods

High IgE-responder Brown Norway (BN) rats bred on a gluten-free diet were sensitized without the use of adjuvant to three different gluten products (unmodified, acid hydrolyzed and enzymatic hydrolyzed). Rats were sensitized by intraperitoneal (i.p.) immunization three times with 200 µg gluten protein/rat or by oral dosing for 35 days with 0.2, 2 or 20 mg gluten protein/rat/day. Sera were analyzed for specific IgG and IgE and IgG-binding capacity by ELISA. IgE functionality was measured by rat basophilic leukemia (RBL) assay.

Results

Regardless of the route of dosing, all products had sensitizing capacity. When sensitized i.p., all three gluten products induced a strong IgG1 response in all animals. Acid hydrolyzed gluten induced the highest level of specific IgE but with a low functionality. Orally all three gluten products induced specific IgG1 and IgE but with different dose-response relations. Sensitizing rats i.p. or orally with unmodified or enzymatic hydrolyzed gluten induced specific IgG1 responses with similar binding capacity which was different from that of acid hydrolyzed gluten indicating that acid hydrolysis of gluten proteins induces formation of ‘new’ epitopes.

Conclusions

In rats not tolerant to gluten acid hydrolysis of gluten enhances the sensitizing capacity by the i.p. but not by the oral route. In addition, acid hydrolysis induces formation of new epitopes. This is in contrast to the enzymatic hydrolyzed gluten having an epitope pattern similar to unmodified gluten.