Study On Quality And Retrogradation Improvement Of Chestnut Powder Under Different Drying Treatments

Fresh chestnuts have high moisture content.They are prone to mold and mildew during storage and transportation.Therefore,it is necessary to moderately process fresh chestnuts to maintain their better quality characteristics.Powdering after drying is a common food processing method.Radio frequency-vacuum drying(RFVD)and airimpingement jet drying(AJID)are new drying technologies that have emerged in recent years,and have good application prospects.Retrogradation can lead to shorter shelf life and reduce nutritional value of starch-based products.It was found that chestnut shells contain a variety of active ingredients such as phenolic compounds,which have the potential to delay retrogradation.Therefore,adding ethanolic extract of chestnut shell may be a new strategy to improve retrogradation.Based on the above research background,the raw and cooked chestnut power were prepared from fresh chestnuts and cured chestnuts by four drying methods: hot air drying(HAD),vacuum freeze drying(VFD),radio frequency-vacuum drying(RFVD)and airimpingement jet drying(AJID).The aim of this study was to investigate the effects of curing treatment and different drying methods on the quality characteristics,microstructure and starch functional properties of chestnut powder.Subsequently,ethanolic extract of chestnut shells(EECS)were added to chestnut power,and the effect of EECS on retrogradation characteristics of chestnut power was investigated,in order to provide a theoretical basis for the preparation of chestnut power and the development of its starch-based products,and to provide new ideas for improving the retrogradation of chestnut power.The main findings are as follows:(1)The effect of different drying methods combined with curing treatment on the quality characteristics and microstructure of chestnut powder was studied.The results showed that the chestnut powder prepared by HAD had higher fat content,but poor color and quality and uneven distribution of powder particles;The raw and cooked chestnut powder prepared by VFD has the lowest moisture content(3.01%,4.29%),and is resistant to storage.The powder has the highest starch content,the greatest brightness and whiter color,and the raw powder particles are irregular large lamellae structure.Although the chestnut powder prepared by AJID and RFVD has poor color,the reducing sugar content is higher,the free phenol content is significantly higher than that of the HAD product,and the microstructure retention is better.After curing treatment,the water-holding capacity and bulk density of cooked chestnut powder prepared by different drying methods increased,but the content of free phenol and the L* value of brightness decreased.(2)The chestnut powder prepared by different drying methods combined with curing treatment was made into a paste system,and its functional properties(solubility,swelling degree,freeze-thaw stability,transparency),gelatinization properties,thermal properties,rheological properties,coagulation properties were compared.The differences in colloidal texture properties and in vitro digestion properties showed that the raw and cooked chestnut powder prepared by VFD had the highest solubility and the best freezethaw stability,but curing treatment reduced the solubility,freeze-thaw stability and transparency of chestnut powder.The gelatinization temperature of raw and cooked chestnut powder prepared by VFD was significantly lower than that of the other three drying methods(P<0.05).The raw and cooked chestnut powder paste systems prepared by different drying methods have shear-thinning properties,showing a weak gel rheological dynamic system,and the curing treatment also improves the dynamic viscoelasticity,hardness and viscosity of the gel system of chestnut powder paste system.The raw chestnut powder granules prepared by different drying methods have a firmer crystal structure and thus are more resistant to digestion.(3)The retrogradation inhibition effect of EECS with different additions on chestnut power prepared by different drying methods was different,which might be related to the content of amylose and amylopectin in chestnut power.When the addition amount of EECS was 5.0%,the retrogradation inhibition effect on the chestnut powder prepared by HAD was better,and when the addition amount of EECS was 7.5%,the retrogradation inhibition effect on the chestnut powder prepared by VFD,RFVD and AJID was better.There was shear-thinning in the compound paste of chestnut powder/ethanolic extract of chestnut shell.The results of differential scanning calorimetry and X-ray diffraction analysis showed that the addition of EECS significantly reduced the melting enthalpy of the compound system.Scanning electron microscope characterization showed that the aged chestnut powder samples formed a looser matrix and reduced continuous lamellar structure during storage after the addition of EECS.EECS may have a certain inhibitory effect on the retrogradation of chestnut powder.