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This study aimed to establish the differences between enzymatically extracted hydrolysates and pH shifted protein isolates from whole Baltic herring and roach in terms of polypeptide patterns, functionality, sensory properties, microbial quality, yield, and composition. Alkaline extraction resulted in the highest yields, whereas the hydrolysates showed the highest protein contents. The hydrolysates showed higher protein solubility (86.0%-88.5%) than the protein isolates (5.1-14.5%) as well as the higher foam capacity for Baltic herring. However, for roach, alkaline extracted protein isolates exhibited the highest foam capacity. All hydrolysates showed poor foam stability (0-13%) while the protein isolates showed notably higher stability (30-55%). The hydrolysates showed relatively low bitterness, whereas alkaline extracted roach proteins were perceived as bitter. This study demonstrated that it was possible to produce protein isolates and hydrolysates from whole fish with good microbial quality. However, both processes need to be optimised according to the food application and fish species.

Wool fibres are subject to a variety of industrial chemical treatments prior to finishing processes. The influence of such treatments on subsequent enzymatic treatments is still poorly characterised, but its importance is paramount to achieve maximal efficiency of enzymatic action on the fibres. The effect of such treatments on wool fibre structure and their significance on the accessibility of the enzymes transglutaminase and tyrosinase to their target amino acids within wool proteins was investigated. These enzymes are of great interest due to their potential as protein cross‐linkers and their capability to covalently graft beneficial compounds onto proteins. The accessibility of target amino acids was assessed using specific peptides tagged with fluorescent probes, followed by epifluorescence or confocal microscopy. Differences in the action of the different chemical pretreatments were found, with a treatment with permonosulphuric acid resulting in the greatest level accessibility to both enzymes, followed by chlorination and plasma treatments. This was confirmed by the increase in tensile strength of treated wool observed in the enzyme‐treated yarns. This work illustrates that the accessibility of these enzymes to their target aminoacids in solid substrates such as wool is key for their action and to achieve the desired property modifications. The techniques used have the advantage of permitting the visual monitoring of the diffusion of the active enzymes through the wool fibre structure and to relate this to the extent of enzymatic reaction. Crucially, this will allow an informed choice of the best wool processing stage at which to introduce such enzyme treatments.

The aim of this work was to study the potential of tyrosinase enzymes in structural engineering of acid-induced milk protein gels. Fat free raw milk, heated milk or a sodium caseinate solution were treated with tyrosinases from Trichoderma reesei (TrTyr) and Agaricus bisporus (AbTyr) and the reference enzyme transglutaminase (TG) prior to acid-induced gelation. TrTyr treatment increased the firmness of raw milk and sodium caseinate gels, but not that of heated milk gels, even though protein cross-linking was detected in heated milk. AbTyr did not cross-link proteins in any of the studied milk protein systems. TG was superior to TrTyr in gels prepared of heated milk. In acidified heated milk and sodium caseinate, TrTyr and TG treatment resulted in a decrease of the pore size. Scanning electron microscopy revealed more extensive particle interactions in the heated milk gels with TG than with TrTyr.

Different possibilities for protein crosslinking are examined in this review, with special emphasis on enzymatic crosslinking and its impact on food structure. Among potential enzymes for protein crosslinking are transglutaminase (TG) and various oxidative enzymes. Crosslinking enzymes can be applied in cereal, dairy, meat, and fish processing to improve the texture of the product. Most of the current commercial applications are based on TG. The reaction mechanisms of the crosslinking enzymes differ, which in turn results in different technological properties.

Trametes hirsuta laccase (EC 1.10.32) alone was not able to cross-link proteins effectively unless high dosages were used. Incorporation of ferulic acid enhanced the formation of intermolecular cross-links. Cross-linking was more effective when the reaction was carried out at 45 °C rather than at room temperature. Size exclusion chromatography showed that ferulic acid monomers disappeared from the solution in the presence of laccase. Force at rupture point of the caseinate gels treated with laccase without ferulic acid was not significantly different from the control, while stronger gels were achieved when ferulic acid was present. Rheological measurements showed that laccase treatment together with ferulic acid resulted in higher G′ values than the control. Gels were analyzed with confocal laser scanning microscope. A finer network was observed when the enzyme was used together with ferulic acid. Slight proteolytic activity resulted in a negative effect on the gel firmness and microstructure when laccase was used without ferulic acid.

The effects of laccase and transglutaminase (TG) on the firmness and weight loss of cooked chicken meat homogenate gels were investigated at laboratory scale. The salt, trisodium pyrophosphate and meat contents were also used as variables. Laccase decreased firmness and increased weight loss of phosphate-free, low-meat (65%) and low-salt (1%) gels, although it modified myosin and troponin T and reacted with isolated myofibrils. By applying both low-salt (1%) and low-phosphate (0.17%) amounts, gel firmness decreased and weight loss increased (p

Effects of microbial transglutaminase (mTG), mushroom tyrosinase and an apple powder containing transglutaminase (TG) and polyphenol oxidase (PPO) on the structure of industrial pork meat homogenate were studied. Apple powder and mTG both increased the value of storage modulus (G′). Mushroom tyrosinase was not able to affect gel forming with the used dosages and treatment conditions. All the enzymes studied were able to improve gel hardness of unheated meat homogenate at 4 °C to a certain extent. In gel hardness measurements added cysteine affected positively on the apple powder—treated pork meat and negatively on mTG—and tyrosinase-treated meat. Surprisingly cysteine addition nullified also the action of mTG. Hence powdered apple pulp, a recovered co-product of an industrial process, may contain suitable enzyme activities for food protein stabilization.

Culture supernatants from strains of Melanocarpus albomyces, Myceliophthora thermophila, Chaetomium thermophilum, and Sporotrichum thermophilum were tested for their ability to release dye in neutral pH conditions from indigo-dyed cotton-containing fabric in biostoning applications. The supernatants from M. albomyces worked well in biostoning, with low backstaining. Three cellulases were purified to homogeneity from the culture medium of this species. Two of the cellulases were endoglucanases with apparent molecular masses of 20 and 50 kDa. The 20 kDa endoglucanase was a relatively heat-stable cellulase with high pH optimum. The partially purified enzyme crystallized spontaneously at pH 4.0 and 7 °C. The 50 kDa endoglucanase also had activity against 4-methylumbelliferyl-β-d-lactoside (MUL) and was active over a wide range of pH values. The third purified cellulase was the 50 kDa cellobiohydrolase with low MUL activity at acidic pH and detectable activity towards filter paper and acid swollen Solca Floc-cellulose, but no endoglucanase activity. The purified 20 kDa endoglucanase performed well in biostoning of denim fabric at neutral pH. Addition of the purified 50 kDa endoglucanase or the 50 kDa cellobiohydrolase to the 20 kDa endoglucanase decreased backstaining in biostoning.

The effects of Myceliophthora thermophila laccase are studied alone and in combina tion with the mediators violuric acid (VA) or l-hydroxybenzotriazole (HBT) on wool fibers, cystine, and tyrosine. Without a mediator, laccase is unable to oxidize wool or the amino acids. In the presence of either VA or HBT, oxygen consumption is observed, indicating oxidation of the secondary substrates of the laccase, i.e., wool, cystine, or tyrosine. The oxidation levels are low. Laccase/HBT reacts more efficiently with wool and tyrosine and laccase/VA with cystine. With the chosen enzyme dosage and mediator concentration, about 2-4% of cystine and about 1 % of tyrosine are oxidized. The slight oxidation of wool fibers is not sufficient to affect the surface chemistry or alkaline solubility of the fibers, although staining of the fibers by the oxidized mediators is significant.

A stable strain of Saccharomyces cerevisiae secreting glucoamylase (EC 3.2.1.3) with high debranching activity was constructed using recombinant DNA technology. An expression cassette without bacterial sequences, containing Hormoconis resinae glucoamylase P cDNA and the dominant selection marker MEL1 was integrated into the yeast chromosome using ARS1 homology. The glucoamylase expression level of the integrant yeast strain was increased by chemical mutagenesis. The yeast strains secreting glucoamylase were able to grow on soluble starch (5%, w/v) and ferment it to ethanol.

Publisher Summary This chapter explains that food texture plays a major role in food product quality. The rheological properties of a food are determined by the number of weak and strong physical interactions and the permanent covalent bonds, crosslinks, present in the food matrix. Covalent crosslinks make the major contribution to the firmness of food matrices. Crosslinks can be introduced to a food matrix by chemical, enzymatic, and physical means as reviewed by Munindar P. Singh (1991) and Scott N. Gerrard (2002) . Enzymatic crosslinking of food biopolymers is an attractive option owing to the specificity of enzymes and mild reaction conditions. Both food proteins and carbohydrates can be crosslinked by enzymes. Sensory perception of texture plays an important role in different types of foods. The significance of food texture has further been increased with the trend toward low fat products and “natural” additive-free products. Enzymes provide specific and natural means for tailoring food structure. By the use of enzymes, it will be possible to transform inherently available food components into functional ingredients during food processing and manufacturing. Enzymatic crosslinking in the food matrix can occur via proteins or certain carbohydrates. The type of enzyme used affects the chemistry of the crosslink formed and subsequently the structure of the biopolymer network of the food product.

The effect of laccase and transglutaminase (TG) on cross-linking, gelation, and thermal stability of salt-soluble chicken-breast myofibril proteins was investigated at pH 6. Both enzymes modified the protein pattern detected by SDS-PAGE. Identification of proteins by peptide mass mapping showed that myosin heavy chain (MHC) and troponin T were the most affected proteins. These proteins faded or disappeared as a function of the incubation time with both enzymes on SDS-PAGE. The molecular weight of actin was not, however, affected by either enzyme. The effects that the enzymes had on the gel formation of chicken-breast myofibrils were studied in 0.35 and 0.60 M NaCl solutions at 3% protein content and a constant temperature of 40 degrees C by using a small deformation viscoelastic measurement. TG substantially increased the storage modulus (G') of 3% protein in 0.35 M NaCl. Without the enzymes, gelation was insignificant in 0.35 M NaCl. The increased solubility of the proteins at 0.60 M NaCl intensified gelation with TG. G' increased 32 and 64% at dosages of 10 and 100 nkat of TG, respectively. Also, laccase increased G' of the gel in 0.60 M salt concentration. However, a high laccase dosage decreased the magnitude of G' below the control level. Differential scanning calorimetric (DSC) measurements indicated slightly reduced myosin heat stability after TG pretreatment and increased actin heat stability with both enzymes. Maximum transition temperatures did not alter with either enzyme.