Study On Vacuum Freeze-drying Processing Technique And Quality Stability Of Bayberry Powder

Bayberry is the one of specialty fruits in Southern China, whose planting areaaccounted for the total planting area of98.5%in the world. Bayberry is fleshy, juicy,sweet and sour, and very popular with unique flavor and high nutritional value.Bayberry is hard to storage and transport since that it is seasonal, poor storability, easyto be perishable deterioration. Bayberry was processed into bayberry powder byvacuum freeze drying technology, and made of solid drink. This product was not onlydelicious, convenient, nutritious, also a long shelf life. This technology laid thefoundation for the research and development of the bayberry series of high-endproducts. In this study, bayberry powder was made using vacuum freeze dryingtechnology, taking full advantage of the conditions of our laboratory equipment. Thestudy content included the bayberry juice concentration processing technology(covering color protection technology, drying agent addition effects and PEFsterilization effect), vacuum freeze-drying process and the quality stability ofbayberry powder during storage. The main contents in this study were vacuumfreeze-drying process, the quality stability of bayberry powder during storage.Themain results are described as follows:1. The L₁₆(4⁵) orthogonal design research results of color protection technologyshowed that the effect on the addition of SDS on bayberry juice color stability weresignificantly higher than that of Sodium chloride and L-glutamate. When the pH=3.0and the dosage of SDS was30mg/L, the color conservation rate of bayberry juicewas highest,96.8%. The L₉(3⁴) orthogonal design research on the addition ofdesiccant showed that vacuum freeze drying rate was highest, using the maltodextrindosage of20%, the CMC dosage of0.9%or0.5%, the beta-dextrin dosage of7.5%.Under the maltodextrin dosage of30%, the CMC addition of0.9%, the productwater content was lower with good liquidity. The study on PEF sterilization effectshowed the killing effect of PEF with different treatment times on E.coli, Salmonella and other microorganisms, under the electric field strength of30kV/cm.2.Vacuum freeze-drying process contained pre-freezing and drying process. TheL₉(3⁴) orthogonal design study results of pre-freeze process showed that the freezingeffect and drying rate was enhanced effectively with the filling thickness of10mm,pre-freezing time of4hr, at a pre-freezing temperature of-35℃. The drying processinvolved three main process parameters, namely, vacuum degree, sublimation dryingtemperature and desorption drying temperature. The vacuum degree is the pressurewithin the drying cavity, which is between the pressure of material water vapor andthe cold trap vapor. The purpose is to facilitate the mass transfer of water, while thevacuum should not be too high or else the heat transfer would be affected. The freezewater in the material was evaporated by sublimation drying, in which the free water inthe material was removed. The remaining bound water in the material was removedby desorption drying. Based on orthogonal test, the parameters of drying process weredetermined to be under the vacuum degree of82Pa, at sublimation heatingtemperature of49°C, desorption heating temperature of77℃. Finally, according tothe freeze-drying process, the curves of the vacuum freeze-drying and bayberrypowder moisture content were drew. The lyophilized curve showed the processparameters setting conditions of the cold trap temperature, vacuum, sublimationheating temperature, and desorption heating temperature, along with the changes onmaterial temperature, weight and other properties. The curve of moisture contentshowed that the changes on the internal moisture of bayberry powder duringfreeze-drying process.3.The moisture content, the main nutrients (anthocyanin, reducing sugar, totalsugar, etc.) and microbial indicators of bayberry powder occurred to be changed withvarying degrees during storage. The properties of anti-caking agent indicated thatagglomeration could be avoided effectively with the addition of10.0g/Kg silicondioxide proportionally, ensuring mobility. The results of sensory evaluation with theexposure of bayberry powder to the air showed that the bayberry powder was easy tobe water absorption, sticky, oxidation and discoloration in the hot and humidenvironment. Therefore, the time of exposure to the air should be minimized.