Study On Microwave Puffing Technology Of Rice Cracker With Wheat Bran

Wheat bran(WB)is an abundant and inexpensive by-product of wheat flour processing,that is rich in dietary fiber and bioactive compounds.However,due to its structural rigidity and coarse mouthfeel,wheat bran is mainly used as a livestock feed with low added value.Thus,there is an increasing demand for developing new ready-to-eat wheat bran-rich snack foods.In this study,the raw wheat bran(RWB)was pretreated by steam explosion(SE),and then the composition of wheat bran before and after steam explosion was determined.The effect of addition amounts of wheat bran and aging time on the quality of cracker was also investigated to provide guidance for the subsequent technological tests.Using steam-exploded wheat bran(SEWB)and rice flour as raw materials,the rice cracker with SEWB was prepared by microwave puffing technology.The sensory evaluation was conducted by fuzzy mathematics comprehensive evaluation method,and the microwave puffing process was optimized by single-factor and orthogonal experiment,using sensory score and expansion rate as target indexes.The formula of wheat bran-rice cracker product was experimentally determined and the changes of cracker qualities during storage was studied by accelerated test to predict the shelf life of the product.After steam explosion treatment,the content of soluble dietary fiber and soluble pentosan of SEWB were significantly increased compared with the raw wheat bran.The scanning electron microscopy(SEM)result showed that the morphology of SEWB was changed,and ravines and cracks appeared on the surface of their microstructures,indicating that steam explosion led to the destroy of starch granules and the destruction of dietary fiber,and thus rendered the dissolution of low-molecular weight compounds.The addition of SEWB could significantly affect the gelatinization properties of rice flour,leading to the increase of gelatinization temperature and the reduction of the viscosity of rice flour.Furthermore,the water distribution of rice cracker with SEWB was analyzed by NMR.The results showed that the content of free water increased with the increase of SEWB addition amount,while the increase of free water was not conducive to the expansion.The SEWB addition had a detrimental effect on the surface structure of cracker,resulting in the crack of product with the increase of SEWB addition amount.With the increase of aging time,the content of weakly bound water A22 increased and the water mobility in the cracker decreased.This part of water was considered as phase transition water available for expansion of cracker.The crystallinity of raw materials was improved with the increase of aging time,which is adverse to cracker expansion.The result showed that the internal structure of cracker formed a loose network after aging with an appropriate time.The optimal microwave puffing technology was as follows:the ratio of rice flour and potato starch,5:1;aging time,14 h;moisture content,9%;microwave power,1000 W;microwave time 55 s.The optimal formula of rice cracker with SEWB was as follows:74.9%of rice flour,14.98%of starch,6.00%of SEWB,2.81%of sugar,1.17%of salt,0.20%of baking soda powder.The main components of SEWB-rice cracker were as follows:86.30%of starch,3.42%of protein,8.03%of dietary fiber,1.30%of ash and 0.15%of lipid.The changes in the physicochemical properties of rice cracker with SEWB were studied under different storage temperatures(27℃ 37℃ and 47℃)at the relative humidity of 80%.The result showed that the moisture content and water activity of rice cracker with SEWB decreased continuously with the temperature increasing.The higher the temperature,the faster the descending speed of the cracker quality.The microbial index of the cracker product conformed to the requirement of China national standard.In addition,the hardness and crispness of cracker products showed a downward trend with the storage time at 37℃ and 47℃,and the product lost its brittleness taste under high temperature and high humidity.A regression equation of the correlation between shelf life and temperature was then established.Therefore,the shelf life of rice cracker with SEWB product was predicted to be 337 d at the storage temperature of 27℃.