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Research is presented concerning the molecular changes which result from the action of transglutaminase in foods. The comparison of proteins extracted from croissant and bread dough treated with transglutaminase and proteins not treated is discussed.

A study was conducted to examine the influence of using transglutaminase on effects related to oxidizing improvers and intensive mixing in breadmaking. Three standard doughs were utilized as experimental controls while a miniature extensigraph method was used to carry out dough strength measurements. Results indicated that transglutaminase minimized work input and enhanced the water absorption of dough.

Research into pastry and croissants containing transglutaminase.

Byline: M. Garvey, S.L. Gras, S. Meehan, S.J. Meade, J.A. Carver, J.A. Gerrard Self assembling protein nanofibres have great potential within the nanotechnology industry. To realise this potential, nanofibres need to be manufactured on a commercial scale. To date, amyloid fibrils, a form of protein nanofibre with desirable bionanotechnological properties, have only been produced using expensive and time-costly, small-scale methods. This paper describes the production of protein nanofibres from semi-pure and crude mixtures of bovine crystallin proteins, currently a waste product in the meat industry. These nanofibres displayed amyloid fibril characteristics. Moreover, distinct fibre morphologies were observed dependent upon the formation conditions adopted. This research shows that amyloid fibrils can be inexpensively produced from crude crystallin protein mixtures, making them a potential industrial source for protein nanofibres.

The aims of this paper are (1) to probe the relationship between molecular structure and protein cross-linking ability for a range of small molecules; (2) to establish whether this relationship holds within a food matrix; and (3) to test the impact of Maillard cross-linking on food functionality, particularly texture, in wheat- and soy-based food systems. A variety of molecules were obtained, either commercially or via organic synthesis. Cross-linking ability was tested using our standard model system, employing ribonuclease A and analyzing the results by SDS-PAGE. Molecules of varying reactivity were tested in wheat- and soy-based products, and the changes in functionality were correlated with changes in protein cross-linking. No simple relationship was found between molecular structure and ability to cross-link ribonuclease. Only the most reactive reagents were able to cross-link within the food matrix. Nevertheless, a low degree of cross-linking was shown to have significant consequences on the properties of wheat- and soy-based foods, suggesting that the Maillard reaction may represent a means to control food texture. [ABSTRACT FROM AUTHOR]

The Maillard reaction influences not only the colour and flavour of foods, but also their texture. One of the mechanisms by which this occurs is via protein crosslinking. In the preceding paper, the capacities formaldehyde, glyceraldehyde and glutaraldehyde to crosslink wheat proteins were compared in vitro and in situ. All three molecules crosslinked wheat proteins in vitro, but only glutaraldehyde crosslinked the proteins when added to wheat flour dough. Here the effects of this crosslinking on dough, bread and croissants are reported. The effect of glutaraldehyde on the dough properties was marked. Upon baking, addition of glutaraldehyde was shown to alter crumb strength and texture of bread, but had no perceivable effect on croissants. A comparison to previous results, comparing enzymatic crosslinking, suggests that crosslinking of specific wheat proteins can be correlated with particular properties of cereal foods. This suggests that the Maillard reaction may be harnessed by food processors to manipulate the texture of foods. [Copyright &y& Elsevier]

As part of a study of the effects of the Maillard reaction on food texture, we have established, in the preceding paper, the capacities of formaldehyde, glyceraldehyde and glutaraldehyde to crosslink a model protein. In this paper, we validate our model study using wheat proteins, both in vitro and in situ. All three molecules were found to crosslink all fractions of wheat proteins (albumins and globulins, gliadins, SDS-soluble glutenins and SDS-insoluble glutenins) in vitro, with glutaraldehyde being the most reactive. Of the four fractions of wheat proteins, gliadins proved the least susceptible to Maillard crosslinking. Crosslinking was accompanied by a loss of lysine residues in all cases. In situ, only glutaraldehyde underwent protein crosslinking, and the reaction was specific to the albumin and globulin fraction. In the following paper, we explore the effects that this specific crosslinking of albumins and globulins in dough has on the texture of bread and croissants. [Copyright &y& Elsevier]

Abstract: Protein crosslinking via the Maillard reaction has been shown to alter the functional properties of several food proteins, but the potential to use this chemistry to alter the functional performance of cocoa proteins has yet to be fully explored. This study investigated the potential of employing cocoa protein crosslinking during processing. Cocoa protein solutions were extracted from dried cocoa beans and the resulting cocoa protein solutions were treated with 2–300mM glutaraldehyde and methylglyoxal, which established model compounds for Maillard crosslinking chemistry. SDS–PAGE analysis showed remarkably few crosslinks of the cocoa protein solutions, although lysine and particularly arginine availability were both reduced during the incubations. These results suggest that cocoa proteins are not greatly susceptible to intermolecular cross-linking via Maillard chemistry, perhaps due to non-cross-linking modifications to the arginine residues, and/or to interference from high levels of polyphenols in the cocoa bean. [Copyright &y& Elsevier]

Abstract: In this paper, we explore the use of Maillard cross-linking agents (formaldehyde, glyceraldehyde and glutaraldehyde) in tofu, to probe the relationship between cross-linking of soy proteins and tofu texture. 1–2mM glutaraldehyde treatment resulted in an acceptable product with altered microstructure. At 2mM glutaraldehyde, the fracture force was increased if the reagent was added before soymilk boiling, but decreased if it was added after boiling, when more cross-linking was observed due to the denaturation of the proteins. The fracture forces and microstructures are hard to rationalise in terms of cross-linking, suggesting that other factors, such as non-cross-linking protein glycation, may be responsible for the observed changes. Taken together with the results reported in the previous paper, these findings suggest that protein cross-linking agents may change the functional properties of tofu via non-cross-linking modifications of the sidechains of the amino acid residues, changing their isoelectric point and their gelation properties. [Copyright &y& Elsevier]

Abstract: The enzyme transglutaminase was investigated for its cross-linking effect on the soy proteins of tofu. In vitro incubations confirmed that soy proteins are excellent substrates for transglutaminase, especially when denatured. The macroscopic effects resulting from the addition of transglutaminase were compared to changes at the microstructural and molecular level. Treatment produced a firmer tofu, with a significantly increased fracture force. Examination by SEM showed a change in the matrix structure, with transglutaminase resulting in a finer-stranded, uniform network that accounted for the increase in fracture force. At the molecular level, little, if any, cross-linking occurred within the tofu matrix in situ. This suggests that the change in functional properties afforded by addition of transglutaminase to tofu is due to a side reaction of the enzyme, for example hydrolysis of glutamine residues, rather than its cross-linking activity. These ideas are further explored in the accompanying paper. [Copyright &y& Elsevier]

The crosslinking of wheat flour proteins results in significant improvements in the functional properties of baked products. In this research, the enzyme glucose oxidase was investigated for its crosslinking effect on the dough proteins of bread and croissants. The macroscopic effects resulting from the addition of glucose oxidase to the dough formulation were compared to changes seen at the molecular level in individual protein fractions. Treatment with glucose oxidase produced slight improvements in crumb properties but no increase in product volume. At the molecular level, crosslinking occurred mainly in the water-soluble (albumin and globulin) fraction and was demonstrated to involve both disulfide and non-disulfide linkages. The SDS-soluble and -insoluble glutenins, which make up much of the gluten network, were crosslinked to a much lesser extent, with mainly non-disulfide linkages. These findings corroborate our theories on the relationship of wheat protein crosslinking and functional properties. Specifically, we conclude that (i) crosslinking of albumin and globulin proteins enhances crumb properties and (ii) changes in croissant volume require crosslinking of the glutenin fraction of wheat proteins. [Copyright &y& Elsevier]

In this study we have surveyed the betaine content of a wide range of foods commonly found in the western diet. Glycine betaine, proline betaine (stachydrine), trigonelline and dimethylsulfoniopropionate (DMSP) were the only betaines to be found at ⩾150 μg/g. Glycine betaine was primarily found in shellfish, flour, and some vegetables, such as beetroot, spinach and silverbeet. Proline betaine was found in citrus fruit and alfalfa sprouts, while trigonelline was found in coffee, chick peas, lentils and rolled oats. Significant DMSP was only found in some shellfish. Different sources of individual foods showed variation in betaine content, and the way in which individual foods were cooked affected betaine content, with boiling causing the highest loss of betaine. [Copyright &y& Elsevier]