Study On Drying Method Of Soybean Dregs And Its Modification Technology

Bean dregs are the main by-products in the processing of bean products such as tofu and soy milk.Okara is a high-quality dietary fiber resource with a total dietary fiber content of more than 60%,which has broad prospects for development.The average annual wet soybean dregs produce in China is up to20 million tons.However,due to the high moisture and rich nutrient content of wet soybean dregs,it is extremely conducive for the microorganisms to grow and sire,and is likely to cause spoilage,resulting in the waste of a large amount of high-quality dietary fiber resource.Therefore,this study used wet bean dregs as raw material to study the drying method and modification process of bean dregs in order to solve the environmental pollution while reusing the resources.The main contents of this research and the conclusions obtained are as follows:（1）Study on drying process of wet bean dregs.The subject used fresh wet soybean residue as raw material to study the drying characteristics in different hot air temperatures and different microwave powers.At the same time,the drying process was respectively fitted with three kinds of agricultural products drying mathematical model.The results showed that the hot air drying best model was Wang and Singh model,the mathematical equation of drying process:MR（28）1（10）（-.00001T（10）.00033）t（10）(1.84′10^-7T-8.78′10^-6)t².The best model ofmicrowave drying was Page model,the mathematical equation of drying process:MR（28）exp[-exp（.119′10^-6P2（10）.00027P-.72784）′t^-.11′10^-6P²（10）.00007P（10）.2068].The resultsshowed that the optimum microwave-hot air combination drying process obtained through orthogonal test were first drying at 500W microwave power for12 min,and then drying at 80°C hot air temperature.Under these parameter conditions,the dry bean dregs powder color was closest to the fresh soybean dregs.（2）Optimization of extrusion process parameters of bean dregs.Using SDF content as an indicator,the process parameters of moisture content,cavity internal temperature,feed rate and screw speed on the effect of extrusion were investigated through orthogonal tests.It could be concluded that the best extrusion technology parameters of soybean dregs were as follows:the moisture content of bean dregs was 15%,the chamber temperature was 140°C,the screw speed was 30Hz,and the feeding speed was 20Hz.Under these parameter conditions,the content of SDF in the bean dregs reached 13.31%.（3）Optimization of ultramicro pulverization of soybean dregs.With dry soybean residue as raw material,taking the median particle size value and SDF content of the obtained superfine powder as indexes.Thorough the response surface test found that the best process parameters were as follows:feed amount95g,frequency of classification wheel 32Hz,grinding pressure 0.8MPa,the median particle size of soybean meal obtained in this process was 14.92μm and SDF content was 4.68%.（4）The soybean residue were compared with the original soybean dregs after three modification methods,which were expanded expansion,ultramicro pulverization and extrusion-ultramicro pulverization.It found that the powder of bean dregs after extrusion was dark yellow,and the color of the powder after the ultramicro pulverization appeared milky white.Different modification treatments had a certain effect on the nutrient content of soybean dregs,but the greatest influence one was SDF,among these theextrusion expansion was the most significant.The cation exchange capacity of the powder after modification was improved,the oil holding capacity was decreased but the solubility was increased.The results of scanning electron microscopy observation showed that the space structure of the obtained fiber of soybean dregs was damaged after modification.The ultramicro pulverization group had the smallest particle size and smooth surface.Through infrared spectrum analysis,the number of peaks and peak position in each sample were almost the same,which indicated that the basic components were not changed.From the X-ray diffraction pattern analysis,it could be concluded that the three physical modifications did not cause significant damage to the crystal structure of the bean dregs fiber.（5）The effect of adding different amounts of bean dregs ultrafine powder on flour quality,noodle cooking characteristics,dough rheological properties,and texture characteristics.It was found that with the increase of the amount of bean dregs,the color of the flour gradually become deteriorated.The peak viscosity decreased but the gelatinization temperature increased.The cooking loss rate reached the lowest value at 5%-10%.The elasticity and chewiness of cooked noodles were improved,and the hardness reached the lowest when the addition amount was 5%.The addition of bean dregs increaseed the water absorption of the dough,and the stabilization time increaseed first and then reduced,while the changed of the weakening degree was opposite.When the addition amount was 10%,the dough expansion ratio was the largest,and the elongation and the tensile curve area were the smallest.The wet gluten content of the powder did not change much when the amount of soybean residue added was less than 10%.Considering the characteristics of various aspects,the optimum addition amount of ultramicro soybean dregs powder was 7.5%.It is concluded that the best drying methods of wet soybean dregs could not only improve the drying efficiency,but also ensure the quality of dry soybean dregs.The physicochemical properties and functional properties of soybean dregs were improved through different modification processes,which could provide a theoretical basis for the development of high dietary fiber products.