Preparation Of Porous Starch By Bioextrusion Combined With Enzymolysis And Its Application In Microencapsulation Of Sweet Orange Oil

Porous starch is a novel modified starch with excellent adsorption capacity and slow-release effect,which has wide applications in food,medicine and other fields.Enzymolysis method is the most widely used method for the preparation of porous starch,but there are still some problems such as long time consuming,uneven starch pore formation,etc.,which need to be further improved.Bioextrusion is a technology which introduces exogenous enzymes into the extrusion process,which shows high efficiency,environmentally protection and continuous production.At present,this technology has been widely used in the fields of saccharification,fermentation and so on.Based on the characteristics of green and high efficiency of bioextrusion,we took bioextrusion as a pretreatment technology of activated starch,and combined the traditional enzymolysis method,a new technology of preparing porous starch with bioextrusion pretreatment and enzymolysis method was established,and its application potential of preparing sweet orange oil powder was explored in order to provide theoretical basis and explore for developing porous starch materials with better pore structure and adsorption performance.Firstly,the effects of the combination of bioextrusion and enzymolysis on corn starch were investigated through its microstructural and physicochemical properties.Scanning electron microscopy showed dense pores were produced on the surface of bioextruded starch,and pores on the surface of bioextruded starch followed by enzymolysis was more uniform.Polarizing light microscope showed good internal structure and granule completeness of bioextruded starch followed by enzymolysis.The results of fourier transform infrared spectroscopy,X-ray diffraction and differential scanning calorimetry showed that the crystallinity?12.87%?,short-range order and gelatinization temperature?73.33°C?of bioextruded starch followed by enzymolysis were higher than those of native starch followed by enzymolysis.The low-temperature nitrogen adsorption experiment showed that the specific surface area?2.52 m²/g?,the total pore volume(4.53×10^-3 cm³/g)and the average pore size?7.36 nm?of bioextruded starch followed by enzymolysis was significantly increased.The results of the degree of hydrolysis exhibited that bioextrusion could improve the enzymolysis efficiency of starch in the enzyme reactor.In the adsorption experiments of oil,water and methylene blue,the adsorption capacity of bioextruded starch followed by enzymolysis increased significantly?oil absorption rate 63.29%,water absorption rate162.61%,methylene blue absorption rate 6.04%?.These results showed that bioextrusion pretreatment could improve the pore structure and adsorption capacity of porous starch,which was an effective method to prepare porous starch.Secondly,the oil absorption rate of porous starch was used as an investigation index to study the influence of the bioextrusion-enzymolysis parameters on the oil absorption rate.Through the Placket-Burman Design test,the factors that significantly affect the oil absorption rate of porous starch were the addition amount of medium temperature?-amylase,moisture content of material,addition amount of glucoamylase,and enzymolysis time.The maximum response area of the factors was determined by the steepest climbing test,and the best process parameters were obtained by Box Benhnken Design test:moisture content of material?36%?,addition amount of medium temperature?-amylase?0.52%,14.97 U/g of dry base starch?,bioextrusion temperature?70°C?,screw speed?120 r/min?,p H 5.0,temperature of enzymolysis 50°C,enzymolysis time 7.7 h,addition amount of glucoamylase?1.73%,1417.15 U/g of dry starch?,starch concentration?25%?.Under this condition,the oil absorption rate reached 68.83%,which was 14.97%higher than that of the porous starch with enzymolysis only.Finally,the storage and physicochemical properties of the sweet orange oil microencapsulation prepared by porous starch were analyzed.The images of laser scanning confocal microscope displayed that the sweet orange oil was well adsorbed into the porous structure of porous starch granule.The storage experiment showed that the release curve fitted well with Avrami's equation,compared with the sweet orange oil microencapsulation by spray drying,the sweet orange oil microencapsulation by porous starch had higher stability under different temperatures,air and light conditions.The physical properties experiments showed that sweet orange oil microencapsulation by porous starch had better fluidity?36.02°?,lower bulk density?0.68 g/cm³?and higher moisture absorption rate?27.66%?.The results of thermogravimetric analysis indicated that sweet orange oil adsorbed by porous starch could be retained at less than 150°C,and the upper retention temperature was higher than that of sweet orange oil microencapsulation by spray drying.The aroma compounds were analyzed by gas chromatography-mass spectrometry,the results revealed that comparing to the sweet orange oil microencapsulation by spray drying,sweet orange oil microencapsulation by porous starch could better retain the aroma compounds of the sweet orange oil,and the retention rate of the key aroma component?d-limonene?was 77.10%.In summary,through the study on the preparation of porous starch by bioextrusion-enzymolysis,it is considered that bioextrusion is an effective pretreatment method for the preparation of porous starch.The prepared porous starch has good porous structure and adsorption capacity,and can be used as the excellent wall material of microencapsulation for sweet orange oil.This study can provide information and theoretical support for the preparation of porous starch and its application in the microencapsulating of sweet orange oil.