Effects Of Sugar Alcohols On Dough Properties And Bread Quality

Food with high starch content such as bread suffer from some changes such as water loss,the increase in hardness of the surface,crumb chipping during storage,which have a negative effect on the textural,nutritional properties and shelf-life of bread.As a result,some kind of food improving agents,for instance,enzymes,emulsifiers and hydrocolloids are used in bread to improve the texture,slow down the retrogradation of bread.Sugar alcohols,with low calorie and a relatively low metabolic rate in vivo,are regarded as the sugar replacement for the diabetics and a kind of healthy food additives.In this research,two kinds of sugar alcohol,namely sorbitol and maltitol were used in bread making.Texture analyzer,rheometer,scanning electron microscope(SEM),low-field nuclear magnetic resonance(LF-NMR)and other instruments were used to study the effects of sorbitol and maltitol on the properties of dough and the textural properties,water-binding capacity,retrogradation properties of bread during storage.The conclusions are as followed:(1)Sorbitol and maltitol could decrease dough hardness,with a decreasing amplitude of 13.5% and 20.3%,respectively.Gumminess and chewiness of dough showed similar trends.Also,they could descend the springiness of dough from the rheological perspective.Additionally,the disulfide bond content showed a decreasing trend from 45.88±0.56 ?mol/g in control to 41.82±0.48 ?mol/g and 41.59±0.46 ?mol/g in samples with sorbitol and maltitol.The free sulfhydryl groups showed an increasing trend from 3.69±0.04 ?mol/g to 4.12±0.07 ?mol/g to 4.28±0.07 ?mol/g with the addition of sorbitol and maltitol,indicating that sugar alcohols had a retarding effect on gluten network formation.(2)Compared with the control,the fermentation rates were lower in the samples with sugar alcohols and lower hardness and chewiness were observed in these samples,with the decreasing amplitude of 50% in hardness and 47% in chewiness.Meanwhile,sugar alcohols could slow down the increasing trend of hardness and chewiness,as well as the decreasing trend of resilience during storage.The samples' hardness and chewiness during storage were fitted by Avrami Equation and the results showed that the correlation coefficients were larger than 0.95,demonstrating that the hardness and chewiness of bread could be regarded as the retrogradation parameters in the perspective of textural properties.It was observed that the addition of sugar alcohols could hinder the loss of water,the final water loss of the samples with sorbitol and maltitol were 19.75% and 20.67%,respectively,lower than the control,with 22.10% final water loss.The retrogradation degree was characterized by the content of slowly digestible starch(SDS)and the results showed that the content of SDS increased in the same sample during storage and it showed an overall 15% descending amplitude in the same storage time with the addition of sugar alcohols,which revealed that sugar alcohols could retard the retrogradation process of bread during storage.(3)LF-NMR was used to evaluate the distribution and migration of water molecules in bread during storage.Examined by CPMG pulse sequence and fitted by the corresponding program,T2 showed three different parts,namely T21,T22 and T23(T21<T22<T23),indicating that there were three kinds of water in bread during storage: the water trapped in gluten network and starch granules or combined with other macromolecule by strong interaction,defined as T21;the water connected with gluten network and starch granules by hydrogen bonds and other forces or in the tertiary structure,quaternary structure or structural domain of the macromolecule,defined as T22;the water with high mobility,namely free water,defined as T23.The changes in T21 and T23 were not obvious and T22 showed a decreasing trend approximately in the same sample during storage.T22 showed increasing trend with the addition of sugar alcohols while the regularities in T21 and T23 were not significant.The water was losing constantly and the proton signal amplitude(A2i)in each part were decreasing in the same sample during storage.Affected by the hydroxyl groups in sugar alcohols,the water loss were lower in the samples with sugar alcohols.The percentage of A21 was decreasing,A23 was increasing,while A22 didn't showed significant regularity.The water molecules migrated from the starch granules and gluten network,then became free water gradually during storage.Additionally,the total proton signal amplitude and water loss were fitted by Avrami Equation,the results were in accordance with previous results,indicating that the total proton signal amplitude and water loss could be used to describe the process of bread retrogradation.The study found that sugar alcohols could decrease the hardness and chewiness of bread,which improved the tasting properties.Also,they could retard the process of bread retrogradation.However,the addition of sugar alcohols could influence the structure of gluten network and dough fermentation,thus a longer time would be needed for dough formation and fermentation if they were used in commercial production.Therefore,the amount should be controlled when they were applied in commercial production.