In recent years, the baking industry has undergone very important changes in its productive processes. Some of the major changes have been brought about by an increasing mechanization in its processing unit operations (Schmidhuber and Shetty, 2005). This fact has contributed to increasing the demand for strong wheat flours, yielding dough with high tolerance to handling and mixing, and able to remain stable during fermentation. Functional properties of flours greatly depend on the gluten proteins. On the other hand, the quality of gluten is dependent on diverse factors such as wheat variety and growing conditions. For this reason, the capacity of some countries to produce high-quality flours is limited. In this context, the treatment of flour with functional additives is considered. Chemical improvers have been used for decades in bread making as a method of adjusting the variations in flour properties and baking conditions. Nowadays, the baking industry is deeply involved in research for alternatives to chemical compounds because of their potential hazards. The enzymatic treatment of wheat flours is an interesting alternative to create changes in the structure of the dough and in consequence, for improving functional properties of flours. They are generally recognized as safe and do not remain active in the final product after baking. Therefore, enzymes do not have to appear on the label, which is an additional commercial advantage. The intentional inclusion of enzymes in bread formulas dates back to more than one century .Today, a wide range of enzymes produced especially for bread-making is available for bakers. A variety of aims may be pursued by enzyme addition, for example, to achieve a partial gluten hydrolysis for improving machinability, to obtain enough sugars for fermentation by means of starch hydrolysis, to attain a certain amount of lipid peroxidation for dough strengthening, or to reduce retrogradation and crumb firming through gelatinised starch hydrolysis. Gluten cross-linking enzymes play an important role in current baking processes. Through different biochemical mechanisms (the oxidative coupling of thiol groups, the cross-link of tyrosine residues due to the action of intermediate reactive compounds such as hydrogen peroxide, the acyl-transfer reaction between amino acid residues), these enzymes promote the formation of covalent bonds between polypeptide chains within a protein or between different proteins, improving functional behaviour of dough during the bread-making process. Transglutaminase (TG) (EC 18.104.22.168) is a transfer enzyme that is able to yield inter- and intramolecular ?-N-(?-glutamyl)lysine cross-links. Its addition causes structural changes in gluten proteins, being high molecular weight (HMW) glutenin subunits the most affected protein fraction. TG may also lead to the formation of disulfide bridges by oxidation due to the proximity of sulfur containing amino acids. Because of these effects, TG has been widely used to improve wheat dough functionality and bread quality. The possibility of using this enzyme to reduce some of the detrimental effects of frozen storage of puff pastry and croissants, as well as to solve the damage promoted by the insect attack of wheat has been proposed. The results obtained with wheat flour have been also assumed to other cereals, allowing an improvement in the viscoelastic properties of the rice dough and therefore in the ability of rice flour to retain the carbon dioxide produced during proofing. Recently, the possibility that TG in wheat-based baked products may generate the epitope associated with the coeliac response has been suggested, although there is no experimental evidence to support this postulate. Glucose oxidase (EC 22.214.171.124) (GO) is an oxidative enzyme that catalyses the oxidation of ?-d-glucose to ?- d-gluconolactona and hydrogen peroxide. Disulfide bond interchange and the gelation of pentosans promoted by hydrogen peroxide action are the most widespread theories to explain the strengthening effect of the GO. Furthermore, it has been related with the formation of non-disulfide covalent intermolecular bonds in the gluten proteins by GO treatment, either among glutenins or between albumins and globulins. GO modifies the functional properties of dough, increasing its tenacity and elasticity. It is revealed even an increase in the elastic and viscous moduli of rice flour dough. As a result of such changes in dough behavior, GO showed positive effects on bread quality, yielding improved specific volume, bread texture and crumb grain. Through a similar oxidative mechanism, hexose oxidase (EC 126.96.36.199) (HO) has been also suggested as an efficient bread improver. When this enzyme is added to dough model systems, it induces the formation of disulfide bridges between proteins and the gelation of pentosans, increasing dough strength and bread volume. HO was found to be more effective than GO because of its ability for using several monosaccharides and oligosaccharides as substrates and its higher affinity for glucose. Since Si proposed laccase (LAC) (EC 188.8.131.52) as dough and bread improver as a result of its oxidant effect on dough constituents, numerous studies have been developed to analyse the effects and applications of this oxidoreductase. LAC is a type of polyphenol oxidase able to gel water soluble arabinoxylans by coupling feruloyl esters of adjacent chains into dehydrodimers. The probable development of a protein–arabinoxylan network by LAC action has been hypothesized. Even it has concluded that gluten and arabinoxylans form two distinct networks, it is proposed a mechanism by which tyrosine-containing proteins cross-link with arabinoxylans. Because of the simultaneous arabinoxylans gelation and oxidative action, LAC addition significantly improves gluten quality and leads to changes in the rheological properties of dough, slightly diminishing dough extensibility, increasing dough consistency, reducing time to maximum consistency and accelerating dough breakdown during mixing. Improvement in the quality of bread elaborated with LAC has been also reported. The functional properties of bread dough greatly depend on the proteins forming the gluten network. Strengthening enzymes affect different protein fractions (glutenins, gliadins, albumins or globulins) depending on their particular action mechanism. The type of protein being cross-linked appears to be more important than the cross-linking agent or type of cross-link formed and it is highly correlated with the character of qualitative changes in the final product. Thus, while HMW glutenin subunits are correlated with several macroscopic properties of dough and baked products (such as strength of gluten network and volume), the albumins and globulins play an important role in textural and crumb grain properties. For this reason, association of different gluten modifying enzymes could be an excellent option to improve overall quality of baked products. Besides the gluten network, another secondary crosslinks among minor compounds of flour such as arabinoxylans and pentosans can be promoted. The combined use the aforementioned enzymes with non-starch polysaccharide degrading enzymes could induce synergistic effects on dough behavior or product quality. Combinations of hemicellulase/GO/?-amylase, TG/amylase/hemicellulase and TG/pentosanase/?- amylase have been reported as bread quality enhancers. Amylolytic enzymes have been also proposed as active contributors towards fresh bread quality and staling behavior during storage. The objective of this study is to analyze the individual and synergistic effects of wheat germ oil currently used in increasing the nutritional value of the products in bread-making industries.
All Research Proposal
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