Pectin Extraction From Passion Fruit Peel By Combining Steam Explosion With Ultrasonic Treatment And Its Properties Characterization

Passion fruit(Passiflora edulis Sims)is widely distributed globally in tropical and subtropical regions,and in China mainly concentrated in Hainan,Guangxi,Yunnan,Guizhou,Fujian,and Taiwan.China's passion fruit production reached as high as 590,000tons in 2018.Pericarp accounts for more than 50%of the weight of fresh fruit and is often treated as waste during processing.The passion fruit peel is rich in pectin,so the conversion of passion fruit peel to pectin can increase the value of waste.However,traditional acid extraction methods have high energy consumption,low extraction rate,and long extraction time,leading to product quality degradation.Therefore,it is of great significance to find an extraction method with high extraction rate and efficiency.In this study,steam explosion and ultrasonic extraction were used to extract pectin from passion fruit peel,and the pectin was characterized.The main findings are as follows:1.In the process of combined steam blasting and ultrasonic extraction,the ultrasonic extraction time,steam explosion pressure and pressure time will cause a significant change in the extraction rate of pectin.Within the range of 5-25 min of ultrasound time,the pectin extraction rate from passion fruit peel increased first and then decreased,and the highest extraction rate was obtained at 15 min.In the range of steam explosion pressure of 0-1.2MPa and pressure maintenance time of 30 s-210 s,the extraction rate of pectin increases first and then decreases,and the maximum extraction rate was achieved at steam explosion pressure of 0.6 MPa and pressure maintenance time of 120 s.Therefore,the conditions of the steam explosion combined ultrasonic extraction process are:steam explosion pressure0.6 MPa and dimensional pressure 120 s,and ultrasonic extraction 15 min.2.In the combined process,steam explosion pressure and pressure maintenance time are important factors for the color and esterification degree of pectin.The conditions of steam explosion pretreatment affected the color and esterification degree of pectin.As the intensity of steam explosion increased,the browning index of pectin increased,the degree of esterification decreased,and the functional groups changed to varying degrees.3.There were obvious differences in the pectin extraction rates from different extraction processes.The extraction rate of pectin obtained by steam explosion combined with ultrasonic process was the highest(10.72%),followed by that from steam explosion extraction,which was 9.93%,and 6.52%from ultrasonic extraction.The acid extraction process had the lowest extraction rate of 5.25%.Scanning electron micrographs of peel and pectin extraction residues showed that steam explosion and ultrasound destroyed the structure of the peel cell wall,promoted the dissolution of pectin,and improved extraction rate and extraction efficiency.4.Different extraction processes have different degrees of pectin color and structure.The brightness the pectin from ultrasonic pectin and acid-extracted was significantly higher than those from steam-explosive extraction and combined process,and the color was gradually deepened.Steam explosion pretreatment promoted the dissolution of proteins and polyphenols and reduced the degree of esterification of pectin.Comparing monosaccharide composition,FTIR spectrum,DSC spectrum,XRD spectrum and ~1H NMR spectrum,it was found that there were structural differences in the pectins prepared by different extraction processes.5.Pectin from different extraction processes as an emulsifier showed better emulsifying properties at different concentrations.Emulsions with a pectin concentration of 0.5%-2.0%were prepared using pectin from different processes.Observation through digital photos,creaming index and optical microscope photos showed that the emulsion preparation prepared by using steam explosion extraction pectin with a concentration of1.0%-2.0%and the combined process pectin and the commercial pectin with a concentration of 2.0%as emulsifier showed better emulsification properties.6.The combined process pectin has better properties and functions than the acid extraction process pectin.Through comparison of foaming performance,antioxidant capacity and rheological properties of the combined process and acid-extracted pectin,it is found that the combined process pectin had better foaming capacity and higher antioxidant performance,and the rheological curve showed that the combined process pectin solution has better viscoelasticity than acid extraction.