Processing Induced Changes in Food Proteins: Amyloid Formation during Boiling of Hen Egg White.

Amyloid fibrils (AFs) are highly ordered protein nanofibers composed of cross ß-structure that occur in nature, but that also accumulate in age-related diseases. Amyloid propensity is a generic property of proteins revealed by conditions that destabilize the native state, suggesting that food processing conditions may promote AF formation. This had only been shown for foie gras, but not in common foodstuffs. We here extracted a dense network of fibrillar proteins from commonly consumed boiled hen egg white (EW) using chemical and/or enzymatic treatments. Conversion of EW proteins into AFs during boiling was demonstrated by thioflavin T fluorescence, Congo red staining, and X-ray fiber diffraction measurements. Our data show that cooking converts approximately 1-3% of the protein in EW into AFs, suggesting that they are a common component of the human diet.

Wheat Seed Proteins: Factors Influencing Their Content, Composition, and Technological Properties, and Strategies to Reduce Adverse Reactions.

Wheat is the primary source of nutrition for many, especially those living in developing countries, and wheat proteins are among the most widely consumed dietary proteins in the world. However, concerns about disorders related to the consumption of wheat and/or wheat gluten proteins have increased sharply in the last 20 years. This review focuses on wheat gluten proteins and amylase trypsin inhibitors, which are considered to be responsible for eliciting most of the intestinal and extraintestinal symptoms experienced by susceptible individuals. Although several approaches have been proposed to reduce the exposure to gluten or immunogenic peptides resulting from its digestion, none have proven sufficiently effective for general use in coeliac-safe diets. Potential approaches to manipulate the content, composition, and technological properties of wheat proteins are therefore discussed, as well as the effects of using gluten isolates in various food systems. Finally, some aspects of the use of gluten-free commodities are discussed.

Proteins of Amaranth (Amaranthus spp.), Buckwheat (Fagopyrum spp.), and Quinoa (Chenopodium spp.): A Food Science and Technology Perspective.

There is currently much interest in the use of pseudocereals for developing nutritious food products. Amaranth, buckwheat, and quinoa are the 3 major pseudocereals in terms of world production. They contain high levels of starch, proteins, dietary fiber, minerals, vitamins, and other bioactives. Their proteins have well-balanced amino acid compositions, are more sustainable than those from animal sources, and can be consumed by patients suffering from celiac disease. While pseudocereal proteins mainly consist of albumins and globulins, the predominant cereal proteins are prolamins and glutelins. We here discuss the structural properties, denaturation and aggregation behaviors, and solubility, as well as the foaming, emulsifying, and gelling properties of amaranth, buckwheat, and quinoa proteins. In addition, the technological impact of incorporating amaranth, buckwheat, and quinoa in bread, pasta, noodles, and cookies and strategies to affect the functionality of pseudocereal flour proteins are discussed. Literature concerning pseudocereal proteins is often inconsistent and contradictory, particularly in the methods used to obtain globulins and glutelins. Also, most studies on protein denaturation and techno-functional properties have focused on isolates obtained by alkaline extraction and subsequent isoelectric precipitation at acidic pH, even if the outcome of such studies is not necessarily relevant for understanding the role of the native proteins in food processing. Finally, even though establishing in-depth structure-function relationships seems challenging, it would undoubtedly be of major help in the design of tailor-made pseudocereal foods.

Investigation of starch functionality and digestibility in white wheat bread produced from a recipe containing added maltogenic amylase or amylomaltase.

In the crumb of fresh white wheat bread, starch is fully gelatinized. Its molecular and three-dimensional structure are major factors limiting the rate of its digestion. The aim of this study was to in situ modify starch during bread making with starch-modifying enzymes (maltogenic amylase and amylomaltase) and to investigate the impact thereof on bread characteristics, starch retrogradation and digestibility. Maltogenic amylase treatment increased the relative content of short amylopectin chains (degree of polymerization ≤ 8). This resulted in lower starch retrogradation and crumb firmness upon storage, and reduced extent (up to 18%) of in vitro starch digestion for fresh and stored breads. Amylomaltase only modestly shortened amylose chains and had no measurable impact on amylopectin structure. Modification with this enzyme led to slower bread crumb firming but did not influence starch digestibility.

Use of Amylomaltase to Steer the Functional and Nutritional Properties of Wheat Starch.

The fine molecular structure of starch governs its functionality and digestibility, and enzymatic approaches can be utilized to tailor its properties. The aim of this study was to investigate the in situ modification of starch by amylomaltase (AMM) from Thermus thermophilus in model starch systems subjected to hydrothermal treatments under standardized conditions and the relationship between molecular structure, rheological properties and in vitro digestibility. When low dosages of AMM were added to a wheat starch suspension prior to submitting it to a temperature-time profile in a Rapid Visco Analyzer, the increased peak viscosity observed was attributed to partial depolymerization of amylose, which facilitated starch swelling and viscosity development. At higher dosages, the effect was smaller. The low cold paste viscosity as a result of the activity of AMM reflected substantial amylose depolymerization. At the same time, amylopectin chains were substantially elongated. The longer amylopectin chains were positively correlated (R2 = 0.96) with the melting enthalpies of retrograded starches, which, in turn, were negatively correlated with the extent (R2 = 0.92) and rate (R2 = 0.79) of in vitro digestion. It was concluded that AMM has the potential to be used to deliver novel starch functionalities and enhance its nutritional properties.

Heating Wheat Gluten Promotes the Formation of Amyloid-like Fibrils.

Amyloid fibrils (AFs) are highly ordered nanofibers composed of proteins rich in ß-sheet structures. In this study, the impact of heating conditions relevant in food processing on AF formation of wheat gluten (WG) was investigated. Unheated and heated WG samples were treated with proteinase K and trypsin to solubilize the nonfibrillated protein, while protein fibrils were extracted with 0.05 M sodium phosphate buffer (pH 7.0) from the undissolved fraction obtained by the same enzymatic treatment. Conditions (i.e., heating at 78° for 22 h) resembling those in slow cooking induced the formation of straight fibrils (ca. 700 nm in length), whereas boiling WG for at least 15 min resulted in longer straight fibrils (ca. 1-2 µm in length). The latter showed the typical green birefringence of AFs when stained with Congo red. Their X-ray fiber diffraction patterns showed the typical reflection (4.7 Å) for inter-ß-strand spacing. These results combined with those of Fourier transform infrared and thioflavin T spectroscopy measurements validated the identification of ß-rich amyloid-like fibrils (ALFs) in dispersions of boiled WG. Boiling for at least 15 min converted approximately 0.1-0.5% of WG proteins into ALFs, suggesting that they can be present in heat-treated WG-containing food products and that food-relevant heating conditions have the potential to induce protein fibrillation.

Hydrothermal Treatments Cause Wheat Gluten-Derived Peptides to Form Amyloid-like Fibrils.

Formation of amyloid fibrils (i.e., protein structures containing a compact core of ordered ß-sheet structures) from food proteins can improve their techno-functional properties. Wheat gluten is the most consumed cereal protein by humans and extensively present in food and feed systems. Hydrolysis of wheat gluten increases the solubility of its proteins and brings new opportunities for value creation. In this study, the formation of amyloid-like fibrils (ALFs) from wheat gluten peptides (WGPs) under food relevant processing conditions was investigated. Different hydrothermal treatments were tested to maximize the formation of straight ALFs from WGPs. Thioflavin T (ThT) fluorescence measurements and transmission electron microscopy (TEM) were performed to study the extent of fibrillation and the morphology of the fibrils, respectively. First, the formation of fibrils by heating solutions of tryptic WGPs [degrees of hydrolysis 2.0% (DH 2) or 6.0% (DH 6)] was optimized using a response surface design. WGP solutions were incubated at different pH values, times, and temperatures. DH 6 WGPs had a higher propensity for fibrillation than did DH 2 WGPs. Heating DH 6 WGPs at 2.0% (w/v) for 38 h at 85 °C and pH 7.0 resulted in optimal fibrillation. Second, trypsin, chymotrypsin, thermolysin, papain, and proteinase K were used to produce different DH 6 WGPs. After enzyme inactivation and subsequent heating at optimal fibrillation conditions, chymotrypsin and proteinase K DH 6 WGPs produced small worm-like fibrils, whereas fibrils prepared from trypsin DH 6 WGPs were long and straight. The surface hydrophobicity of the peptides was key for fibrillation. Third, peptides from the wheat gluten components gliadin and glutenin fractions formed smaller and worm-like fibrils than did WGPs. Thus, the peptides of both gluten protein fractions jointly contribute to gluten fibrillation.

The Impact of Hydro-Priming and Osmo-Priming on Seedling Characteristics, Plant Hormone Concentrations, Activity of Selected Hydrolytic Enzymes, and Cell Wall and Phytate Hydrolysis in Sprouted Wheat (Triticum aestivum L.).

Priming improves the seed germination rate and grain yield. Before this work was executed, little, if any, research has been reported on priming wheat for improving its nutritional properties. The impact of hydro-priming and osmo-priming using solutions with different water potentials on selected hydrolytic enzyme activities and their breakdown of starch, cell wall materials, and phytates during subsequent sprouting was studied here. A higher germination rate in the early growth stage of seedlings was found for hydro-primed or osmo-primed (-0.3, -0.6 MPa) grains. Hydro-primed sprouted grains had the longest radicles and coleoptiles and the highest hydrolytic enzyme activities. The latter lead to a 90% increase in reducing sugar, a 20% increase in water-extractable arabinoxylan, and an 8% decrease in phytate contents after 5 days of sprouting. This study thus offers opportunities for optimizing agricultural practice. The presence of different plant hormones and their concentrations are generally not affected by priming. However, the plant hormone concentrations in grains primed at -1.2 MPa and subsequently sprouted were lower than those in all other samples under study. The induction of too high osmotic stresses in these grains leads to disruption of the sprouting processes. Finally, it was for the first time found, based on the known biosynthesis pathways of wheat, that gibberellic acid (GA)20-oxidase in (primed) sprouted wheat is more active than GA3-oxidase and much more active than GA13-oxidase.

Assignments of proton populations in dough and bread using NMR relaxometry of starch, gluten, and flour model systems.

Starch-water, gluten-water, and flour-water model systems as well as straight-dough bread were investigated with (1)H NMR relaxometry using free induction decay and Carr-Purcell-Meiboom-Gill pulse sequences. Depending on the degree of interaction between polymers and water, different proton populations could be distinguished. The starch protons in the starch-water model gain mobility owing to amylopectin crystal melting, granule swelling, and amylose leaching, whereas water protons lose mobility due to increased interaction with starch polymers. Heating of the gluten-water sample induces no pronounced changes in proton distributions. Heating changes the proton distributions of the flour-water and starch-water models in a similar way, implying that the changes are primarily attributable to starch gelatinization. Proton distributions of the heated flour-water model system and those of fresh bread crumb are very similar. This allows identifying the different proton populations in bread on the basis of the results from the model systems.