M.A. Thesis:

Effect of protease and Lipase enzymes on dough rheological properties and quality of bagutte bread

Bread is the oldest food produced by human. The share of bread in the household consumption basket of the Iranian families, is very important because most people in Iran are providing most of their daily needs for energy from this product. Considering the importance of this commodity and the big losses in its production and also considering the necessity to achieve better quality, more attention must be paid to this strategic product. Therefore, offering any solution for systematicically improving the current situation can be useful. The improving additives will increase the quality of bread and increase its lifetime. The enzymes are one of the improving agents that are widely being used to improve the quality of breads and their use is expanding day by day. Nowadays, to improve the rheological properties of dough and increase the bread quality we can benefit of the unique synergistic effect of some enzymes. For example, we can use the synergistic effects of some enzymes that influence the cross-linking of gluten along with degrading enzymes of gluten and polysaccharide in the production of bread. In this study, protease enzymes in 1.5 and 2.5 g (P1, P2) and lipase in the 0.5 and 2.5 gr (L2, L1) are used per 100 kg of flour and their individual and combinated effects on the rheological properties of the dough was studied. Experimental results by the mixolab showed that for 0.5 g Lipase enzyme the maximum torque to break the protein mollecular system as well as the highest degree of softening was observed for this enzyme. Also the increases in the amount of starch gelatinisation, increase in the consolidation of the gel already formed, increasing in the amount of starch retrogradation, lowest rate of water absorption, maximum dough development time, biggest time of resistance for the dough and the highest falling value, was found by adding the lipase timar were seen. Also about the elasticity of the dough, by adding 0.5 gr lipase, and then the mix of 2.5 protease and 2.5 lipase (LP3) and 2.5 lipase and protease 1.5 (LP4) the highest level of elasticity has been seen and in comparison with the control sample the difference was significant and the lowest elasticity was belonging to the Timar control sample (A) and then lipase 2.5 g (L2) and protease 1.5 (P2) and 2.5 g (P1) and the enzyme mixture of 0.5 g lipaseand and 2.5g protease (LP1) and 0.5g lipase and 1.5g protease (LP2), respectively. Also by adding protease anzyme the starch gelatinisation has decreased, the consolidation of the gel already formed has decreased, the amount of starch retrogradation decreased, highest rate of water absorption, smallest time of resistance for the dough and the lowest falling value, anfd the development time of dough in a mixture of 2.5 protease and 2.5 lipase (LP3) were observed. Considering the fact that Timar has 0.5gr lipase and 2.5gr per 100 kg of flour, the best results in terms of reheological properties were obtained. Thus, a dose of 0.5 gr and 2.5 gr Lipase was used and the quality of the breads produced was evaluated. According to staling tests including the sensory tests and the densitometry, it was finally concluded that the bread prepared from 0.5 g lipase per 100 kg flour on the fifth day to maintain showed the highest quality of sensory and degree of rigidity and longer time of resistance against staling.

Keywords: lipase, protease, bread, French bread, dough rheological properties,staling