بررسي اثر EPS ميكروبي خمير ترش بر خواص رئولوژيك خمير نان مسطح

چكيده انگليسي :

148 Effect of Microbial EPS of Sourdough on Rheological Characteristics of Flat Bread Dough Behnaz Nasiri Esfahani b nasiriesfahani@ag iut ac ir March 13 2011 Department of Food Science and Technology Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Mahmood Sheikh Zeinoddin zeinodin@cc iut ac ir Mahdi Kadivar kadivar@cc iut ac ir Abstract Sourdough fermentation as a dough leavening agant is one of the oldest examples of application of food biotechnology in food production Due to the rising interest by consumers in natural healthy foods with better taste sourdough bread has received increased demand in recent years Sourdough is known to be used to improve flavor of the wheat bread but it could also affect structure of bread dough Leavening is the main functional property of sourdough which gives a better texture to bread Lactic acid bacteria LAB produce numerous different metabolites such as organic acids enzymes and exopolysaccharides EPS in sourdough with positive impact on bread quality In addition to probiotic property the produced EPS in sourdough has the potential to be used as an alternative to rather expensive hydrocolloides used in bread to improve its quality The objective of this study was to evaluate effect of EPS produced by LAB in sourdough on rheology of the flat bread doughs from Isfahan region For this purpose microbial flora and EPS content of a few sourdough samples were first studied and the best sample was chosen for the next stage of the study The microbial population of the chosen sourdough was first stabilized by a series daily backslopping processes Bread doughs were then produced using different percentage of the stabilized sourdough 5 10 15 and 20 The rheological properties of the dough samples were determined using farinographic and extensographic tests Farinograms were performed according to International Association for Cereal Science and Technology standard method 115 1 at a mixing speed of 63 2 rpm For the samples containing sourdough this standard method was modified by the addition of sourdough which was premixed with the flour at the beginning of the mixing perior to the addition of water To separate possible effects of acids and salt from that of EPS on rheological behavior of the dough samples control samples were produced using lactic and acetic acid to reach pH 4 37 5 51 of respective doughs containing different sourdough percentage The standard method of farinographic test was modified by the addition of table salt and acids which were solubilized in part of the total water at the beginning of the mixing period The results showed that in general EPS in sourdough could neutralize negative effects of acids and salts on dough structure thus positively improve the dough structure EPS increased water holding capacity of dough from 54 90 in control dough with no adding acids and sourdough to 56 15 in dough containing 20 sourdough where acid and salt alone decreased water holding capacity from 54 90 in control dough with no adding acids and sourdough to 48 55 in control sample respective dough containing 20 sourdough EPS neutralized the reducing effect of acids and salt on the mixing time and resistance and at the same time improved both the degree of softening and farinographic quality number of dough samples In addition results indicated that EPS has played a balancing impact on increasing resistance to extention reducing energy extensibility and E R ratios of the dough samples during 135 min time of dough developments Key words Sourdough Microbial Exopolysaccharides Rheological properties of flat bread dough Farinograph test Extensograph test

نصيري اصفهاني، بهناز

بررسي اثر EPS ميكروبي خمير ترش بر خواص رئولوژيك خمير نان مسطح

اگزوپلي ساكاريدهاي ميكروبي , آزمون فارينوگراف , آزمون اكستنسوگراف