effect of guar gum and amylase enzymes on quality part baked frozen barbari bread

introduction: bread stales and unfortunately it is a certainty and causes significant product waste all over the world.staling results in loss of important sensory parameters of bread, like flavor and texture, and it is a consequence of a group of several physical–chemical changes occurring during bread storage that lead mainly to an increase of crumb firmness and loss of freshness (gray and bemiller 2003). at 21th century freezing technology introduced to bakery industry in order to increase bread shelf life, access fresh bread with a minimum need for equipment and skilled personal at any time.the current trend in the baking industry is to use frozen dough to manufacture quality products because it can be quickly transformed into fresh baked product. however, the use of frozen dough has certain disadvantages such as its variable performance and loss of stability over long-term frozen storage (ribotta and le bail 2007). research has shown that ice crystallization and recrystallization causes physical damage to the gluten network, leading to changes in the rheological properties of the frozen dough. water available for freezing forms ice crystals that injure yeast cells (mazur 1968). gums trap free water and control moisture migration.furthermore, ward and andon (1993) mentioned that gums such as carboxymethyl cellulose, carrageenan, gum arabic, and locust bean gum may be used to alleviate the problems associated with frozen dough. numerous studies report that enzymes play key roles in bread making such as increasing loaf volume, producing finer crumb cells, and extending shelf-life. amylase improved frozen dough bread quality; the enzyme allowed us to obtain breads from frozen dough with high specific volume and low crumb firmness(ribotta and le bail 2007). therefore, the aim of this work was to study the effect of guar gum and alpha amylase on frozen dough and the influence of them on the minimization of the damage caused by frozen storage. materials and methods: wheat flour sample (cvs, pishgam) with 10.52% moisture, 10.8% proteins ,79% ash, 26.7% wet gluten, was obtained from silo no.3, mashhad, iran. bread recipes also contained active dry yeast (razavi co., mashhad, iran), vegetable oil( ladan co. behshahr, iran), salt and sugar (local market). amylase enzyme (25 klu/g) and guar gum afforded from novozyme and rodhia co respectively. the bread formula used for barbari bread consisted of flour (100 parts), compressed yeast (2 parts), salts (2 parts), sugars (1parts), vegetable oil (1 part) and water (based on water absorption at 500 bu). guar and amylase replaced in bread formulation at two levels (0.4 and 0.8%), and (0.05. 0.07 %) respectively. bread was part baked in an electric oven with an incorporated proofing chamber (zuccihelli, forni, hal, italy) at 210˚c for 7 min to obtain texture structure before starting coloring reaction. barbari bread sample were packaged in polyethylene bags and frozen in a blast freezer. after storage at -18°c for 15 day, pbf bread was thawed at room temperature for 10 min and rebaked at 260°c for 8 min. the fresh bread baked at 230 °c for 15 mines (ba´rcenas and rosell, 2007). specific volume , porosity, texture evaluation, image analysis (l*a*b*) and sensory evaluation of bread were measured using aacc methods (2000). results were reported as the average of three replications (all treatments were evaluated in three batches). the data obtained were statistically treated by a complete randomized design (factorial) analysis while the means were compared by the duncan’s test at a significance level of 5%, in both cases using spss statistical software (version 17). result and discussion: the results showed that frozen storage had significant effects on the specific volume, moisture content, crumb hardness, sensory properties and bread color. addition of gum and enzyme to bread recipe improved bread quality, alone and in combination. the presence of guar and amylase removing the negative effects of process conditions. addition of guar at 0.4% improved specific volume, textural properties, color, sensory score and decrease bread firmness. also using of amylase in 0.07%,increased bread quality. when guar used in combination with amylase, the synergistic effect was observed. the best result, obtained with 0.4% guar and 0.07% amylase. conclution: in summary, the result of this study has shown that textural and sensory properties of part baked frozen bread were poor. addition of guar gum increased specific volume and sensory score of bread. guar in 0.4% concentration in comination with amylase in 0.07%, were more effective and it could introduce as a improver for part baked frozen bread.