Study On The Technic Of Super Heated Steam Pufifng Dried Tomato And Its Physicochemical Qualities

Super heated steam puffing drying technology was a kind of new fruits andvegetables processing technologys,which was began to be studied in the NineteenSeventies and Eighties at abroad, but in China the theory and application study of thistechnology was at the starting stage. In this paper, tomato as raw materials, the effectfactors for the puffing were analyzed and the puffing technic was optimized, andsuper heated steam puffing dried tomato’s physicochemical characteristics were alsostudied, aiming to supply theory and technology for producing super heated steampuffing dried tomato.This paper comprised four parts, every part in this paper were as follows:Screening out better pre-treatment for tomato super heated steam puffing; choosingthe initial drying condition and building initial drying mathematic model; analyzingthe effect parameters for technique, optimizing the technological parameters andobtaining the later drying condition; studying on super heated steam puffing driedtomato’s physicochemical characteristics. The main conclusions could be summarizedas follows:1. With the effect analysis and comparison of blanching, NaCl solution osmotictreatment, different kinds of sugar solution osmotic treatment and glycerol solutionosmotic treatment on tomato super heated steam puffing, the best pre-treatment wasscreened out, the technique for tomato pre-treatment was in3%glycerol solution foran hour at room temeperature.2. Tomatoes was initial dried in hot air at different temperature after3%glycerol solution osmotic treatment, taking initial drying speed, tomato’s color andthe effect on tomato super heated steam puffing into consideration,70℃was chosento be the initial drying condition for tomato super heated steam puffing. Meanwhile,Water losing characteristics of tomato at different temperature was studied, then thetomato initial drying mathematic model at any time was built, the fitted equation was:MR=exp (-kt~n), k=0.027308exp (-556.6565/T), n=22.7352-0.1310T+0.0002T~2（333.15K≤T≤363.15K）3. The effect technique parameters were determined by mono-parameterexperiment, the results were as follows: tomato shape of square (10mm×10mm×6mm),puffing pressure difference of0.25MPa, and water content after initial drying of25%,puffing temperature of115℃, detention time of40s. 4. On the basis of mono-parameter experiment, quadratic general rotationdesign experiment was used to optimize the technological parameters, the regressionequations about the relationships between the effect factors (water content after initialdrying, puffing temperature, detention time) and evaluation indexes(bulk density,rehydration rate and comprehensive score) were obtained. Optimizing the regressionmodel of comprehensive score, the optimum tomato super heated steam puffingconditions were obtained: water content after initial drying of23.9%, puffingtemperature of117.6℃, detention time of37s.5. Though the comparison of later drying speed and the changes of color, bulkdensity, rehydration rate of puffing dried tomato, as well as the comparison of dryingefficiency between hot air drying and super heated steam puffing drying, resultsshowed70℃was befitting in later drying; Super heated steam puffing tomato hadstable structure and smaller contraction after later drying, it could better keep itsoriginal volume; tomato after the treatment of super heated steam puffing drying has afaster drying velocity, which could decrease34.4%drying time than hot air drying.6. Super heated steam puffing drying tomato’s physicochemical characteristicswere also systematically studied, main contents including its color, main nutrients,microstructure, texture and rehydration characteristic. The results showed that superheated steam puffing dried tomato had bright color, tomato color value（Tc value）reduced, but its tomato color value had no significant difference with initial dryingtomato,puffing dried tomato could better keep its color; the contents of reducingsugar,total sugar, protein, crude fiber increased a little, while the content of total acidshad decreased, it tasted better; puffing dried tomato has a full volume and a poroushoneycomb microstructure; Meanwhile, it also had a higher rehydration rate than hotair dried tomato when the rehydration temperature was higher at the same rehydrationtime; after6min rehydration at the temperature of85℃, the tomato had moderatehardness and mucosity, maximal elasticity and chewiness value, as well as the highestsensory evaluation score.