Study On The Quality Improvement For Hard Biscuit Processed By Enzymes

Hard biscuits occupy an important share in the bakery products and have great potential for development.Sodium metabisulfite(SMS)and Cysteine hydrochloride(CYS)was widely used in the production of hard biscuit as chemical modifiers.However,the health problem of SMS and the high costs of CYS greatly limit their promotion in the production of hard biscuits.In contrast,the enzymes with less dosage,and display no side effects for healthy,thus possessing significant advantages.Base on the fact that few enzymes were applied into the production of hard biscuit and less mechanism was studied on the quality improvement,the effects of various enzymes on the quality improvements of hard biscuits and relevant mechanism were studied for providing theoretical basis for the application and promotion of enzymes.The sensory evaluation and physical properties were analyzed among hard biscuit added respectively with SMS,CYS,Papain(PAP),Bromelain(BRP),Neutral protease(NEP)and other three kinds of commercial biscuits.The evaluation method of biscuit texture and the parameters of good hard biscuits were confirmed using the correlation analysis between sensory evaluation and physical results.The results showed that there were extremely significant correlations between hardness,crispness,and crunch measured by the texture analyzer and the sensory scores of taste(p<0.01).The texture parameters of the group with excellent taste scores in the sensory evaluation were taken as references to confirm the texture parameters of the fine quality hard biscuits with good guality:hardness:600~100 g;crunch:1200~400 g·s;crispy:17.0~25.0.In the above range,hard biscuits with smaller hardness,less crispness,and more crunch owned more uniform structure and better the taste.The effect of different proteases(PAP,NEP,BRP)and xylanase(PEM,VEN)with varying rations on the quality improvement of the hard biscuits was investigated by exploring the changes of stacking height,specific volume,color and texture compared with those of hard biscuits with SMS and CYS.The results showed that both protease and xylanase could increase the the specific volume,improve the texture and optimize the taste of biscuits.The effect of PAP was better than other two proteases for the quality improvement in the same dosages.With the addition of 350 mg/kg PAP,the stacking height of biscuit was 2.58 cm,the specific volume was 2.18 cm~3/g,the hardness of biscuit was 132 g,the crunch of biscuit was626 g·s,and the crispy of biscuit was 19.7 respectively,which was also superior to the hard biscuit added with SMS and CYS.Between two kinds of xylanase,biscuits added with PEM had better quality compared with biscuits treated by VEN.With the addition of 1100 mg/kg PEM,the stack height of biscuit was 2.42 cm,the specific volume of biscuit was 1.90 cm~3/g,and the hardness of biscuit was 500 g,the crunch of biscuit was 594 g·s,the crispy of biscuit was 22.2.In addition,the combined effect of protease and xylanase on the quality of biscuits was also studied through adding PAP and PEM into the biscuits in different proportions.The result showed that there was no obvious synergistic effect on the optimization of stacking height and specific volume.While the crunch and crispy of the hard biscuits were greatly improved.The crunch of biscuits added with 200 mg/kg PAP and 800 mg/kg PEM was 469g·s,which decreased by 71.03%compared to the control group,and decreased by 40.54%compared to the dosage of 200 mg/kg PAP group.The Crispy of compound biscuit was 23.6,which increased by 45.23%compared with the control and increased by 20.44%compared to the group added with 200 mg/kg PAP respectively.The mechanism of effects of enzymes on hard biscuit quality improvement was studied on the dough rheological properties,flour SRC value,dough’s moisture distribution,dough’s microstructure and wheat starch gelatinization properties.As the results showed,the addition of proteases reduced the elasticity and water holding capacity of the dough.The amount of damaged starch was increased,while the parameters of RVA was all reduced.The microstructure of dough was more loosen and the structure of gluten was weaker by adding PAP.The analysis of molecular weight distribution on the gluten protein suggested that the enzymatic hydrolysis of peptide bonds by proteases reduced the amount of glutenin macromolecule polymer(GMP)in the dough and weakened the gluten structure,while SMS and CYS attenuated the gluten through destroying the disulfide bonds between gladins and gluten,which did not change the GMP content significantly.There are essential differences between these two methods for weakening gluten in the dough.The addition of xylanase also influenced the aggregation behavior of GMP.Meanwhile,the degradation of GMP in the gluten was observed in the biscuit with combined addition of xylanase and protease.The conclusion was also proved by adding GMP in the biscuit making,which led to the significant decrease of specific volume and deterioration of texture in hard biscuit.