Study Of Heat-mediated Waxy Flour And Its Functionality In Dough And Bread Systems

In this paper, the combination of two heat treatment temperature (100°C,120°C) andfour heat treatment time (15min,60min,90min,120min) was applied and the changes ofthe properties of heat-mediated waxy flour as well as its application in dough and breadsystems as a new functional ingredient were investigated. Also, the effect of lipase onheat-treated waxy bread and its staling properties were studied.The pasting properties of waxy flour under heat treatment at100°C and120°C for15min,60min,90min and120min respectively were analyzed by RVA. The results showedthat in neutral condition (pH7.0), the pasting parameters (peak viscosity, hot paste viscosity)were higher than the control. Higher final viscosity contributed to non-cohesive texture.Under100°C thermal processing condition, the setback decreased gradually. For100°C/120min sample, the setback decreased by8.32%, suggesting better viscosity stability. However120°C showed negative effect on viscosity stability with increased setback.DSC results showed that both Toand Tpincreased with longer treatment time. For100°C/120min and120°C/120min group, Toincreased by6.08%and7.73%, suggestingmore energy was required for starch to gelatinize, indicating that chemical bond of starchgranule was strengthened. The gelatinization temperature range was narrowed after heattreatment, suggesting better homogeneity. Higher gelatinization temperature of heat-treatedwaxy flour may help improve shrinkage in bread crumb. Retrogradation enthalphy ΔH ofheat-treated waxy flour decreased to a certain extent then decreased.The content of free thiol group and glutenin marco polymer of30%heat-mediatedsamples were analyzed. The results indicated that the initial thio l group for heat-mediatedsamples was lower and decreased dramatically during dough development. For waxy wheatflour treated after120min at100°C and120°C, GMP content increased11.88%and12.25%respectively and showed a positive correlation with thermal processing time. Both resultssuggested that heat treatment may induce more thiol and disulfide interaction, which maypromote the formation of GMP content, contributing to a better gluten matrix.According to Dynamic Rheometry results, elastic modulus G′increased and viscousmodulus G″decreased for dough incorporating with30%heat-treated waxy flour. F3Rheofermentometer results indicated that maximum height of dough (Hm) increased by15.36%,17.05%and7.49%for100°C/90min,100°C/120min and120°C/90minheat-treated samples. Under the same thermal processing time,100°C heating temperature isbetter than120°C in increasing Hmand gas retention ability.The specific volume of bread with waxy flour treated for90min under100°C and120°C was4.87mL/g and4.73mL/g, increased by14.32%and11.03%compared to thecontrol. Image analysis showed that more and higher density crumb cells were generated forheat-treated waxy bread and less post baking collapse was observed. For100°C/120minbread samples, the hardness, gumminess and chewiness were lowered by35.17%,32.1%and34.3%, which may change the fact that the substitution of higher amounts of waxy four maygenerate sticky crumb texture with lower sensory evaluation. However, the lightness of allheat-treated samples was lowered. Using40%and50%heat-treated waxy flour (100°C/90min and120°C/90min) as afunctional ingredient, we studied the effect of different amount of lipase on the properties ofwaxy dough incorporated with heat-treated waxy flour. The results showed that lipase (10mg/kg and30mg/kg) enhanced the gluten strength and dough stability as well as the lightnessof bread crumb. During7-day storage, the harness of waxy bread containing lipase (over10mg/kg) was much lower than the control group. Higher the amount of lipase was, the lowerhardness for bread was maintained during7-day storage. The soluble starch for waxy breadcontaining lipase was higher than the control and showed a positive correlation with theamount of lipase. For bread with50mg/kg lipase, the anti-staling effect was most obvious.Sensory evaluation showed that30mg/kg lipase was optimal.