9 Alex. J. Fd. Sci. & Technol. Vol. 14, No. 2, pp. 9-16, 2017 Bio-Texturisation of Soy Protein Isolate Dalia, H. Eshra Food Science and Technology Dept., Fac. of Agric., Alexandria University, El-Shatby, 21545, Alexandria, Egypt. Received: 12 September, 2017 Revised: 15 October, 2017 Accepted: 29 October, 2017 ABSTRACT The possibility of using microbial transglutaminase (MTGase, 2.3.2.13) on bio-texturising of soy protein isolate is the main object of this study. Covalent cross-linking of proteins by MTGase is easy and simple for application, safe and well controlled process than commercial methods used for protein texturisation. Two commercial preparations of MTGase were used for restructuring soy protein isolate (SPI). The investigation of the product (gel) formed was evaluated using textural profle analysis (TPA). The results indicated that using of MTGase for texturising of SPI enhance greatly most of TPA parameters. The most affected parameters were hardness, cohesiveness and gumminess. Bio- texturising of proteins is a promising tool for restructuring and modifying the structure net work of protein mol- ecules. The cross-linking reactions promoted by the action of MTGase allowing for the development and widespread use of new and improved functional properties in food industry. Keywords: Bio-texturisation, microbial transglutaminase, plant proteins, soy protein isolate, textural parameters. INTRODUCTION Proteins are one of the main food components; hence their modifcations via chemical, physical or enzymatic methods are alternative available tools for improvement and/ or development of new func- tional properties of protein-based foods (Gaspar & Góes-Favoni, 2015). Plant proteins occupy an important place in hu- man nutrition, especially in the diets of low-income earners of developing countries. Furthermore, ani- mal proteins are scarce in many countries, and veg- etable proteins have a lower price than muscle pro- teins. Besides, it is well known that meat contains cholesterol and a higher proportion of saturated fatty acids than polyunsaturated fatty acids ,which exert suppressive effects on pathogenesis of many diseases (Asgar et al., 2010). The functional properties of proteins are the physiochemical properties that affect their behav- ior in food systems, contributing to its quality and sensory or acceptability i.e., texture, appearance and favour (Gaspar & Góes-Favoni, 2015). Enzymatic texturising of protein or bio-textur- ising of protein is a promising tool for modifcation of protein molecules. The commercial enzyme, (MTGase), demonstrated its potential application in vegetable products such as soy which is little exploited in the market (Góes-Favoni & Bueno, 2014). MTGase still rarely been used in texturisa- tion of plant proteins. However, there is an increas- ing demand for vegetarian foods in many branches of the food industry (Dube et al., 2007, Piestrasik et al., 2007, Chang et al., 2011).The enzyme MTGase catalyses acyl transfer reaction forming inter-and intramolecular cross-links between amino acid res- idues of glutamine and lysine of protein molecules. The MTGase has several characteristics which cov- ering many applications in food technology. The enzyme does not alter the pH, colour or favour of food and it is active in a wide range of pH ranging from 4.0 to 9.0 (Ando et al., 1989, Cui et al., 2007). With respect to substrate specifcity, the en- zyme has a broad specifcity, so most food proteins could be cross-linked by MTGase (Nonaka et al., 1997). Besides, the enzyme is capable of incor- porating amino acids or peptides covalently into proteins, which improve nutritive value of food proteins (Yokoyama & Kikuchi, 2004).A practi- cal application of this enzyme is the formation of heat-stable and irreversible gels, which could be obtained in different substrates even at relatively low protein concentrations (Góes-Favoni & Bueno, 2014). Covalent conjugation of two or more pro- teins of different origins may also be triggered by MTGase, generating a new protein with properties