Study On Processing And Storage Of Low-fat Carrot Chips

In recent years, people have drawn more attention to the vacuum frying featured the excellent qualities and extensive adaptability to material. The chips made of vacuum fried vegetables and fruits were developed rapidly because of their natural color, crispness and crude components. However, because of the complexity at vacuum frying mechanism, its developments mainly rely on practice time after time, thus there are some defects in higher fat content and poorer qualities. The objective of this paper was to study the role of fat absorption and quality change, analyze its heat and mass transfer and investigate its storage stability.In order to reduce the fat content, improve qualities and the drying rate, different pretreatments during vacuum frying were studied based on the theories of enzyme activity, antioxidation, cell structure and drying rate etc. using carrot as test material. The mechanism of fat absorption was analyzed. The results showed that the fat absorption were not only affected by the initial moisture content but also was related to the size and distribution of voids left by moisture evaporation.Frying and defatting parameters will affect the fat content and the quality of food during frying. Scholars put forward different opinions. A three-factor, five-levels Response Surface Methodology (RSM) based on the single-factor experiment, was chosen to evaluate independent variables affecting the moisture content, fat content and breaking force. The independent variables selected for this study were frying temperature, vacuum degree and frying time. The results showed the optimum frying conditions were: vacuum frying temperature of 100℃-110℃, vacuum degree of 0.080-0.090Mpa and frying time of 15-20min. Whereas the optimum defatting conditions were: vacuum degree of 0.090Mpa, rotation speed of 300 r/min, defatting time of 5 min and the defatting rate was related to the frying time.At present, there are two kinds of technology featured higher fat content to produce crisps at home and abroad. In this paper, a new method of vacuum frying combined with osmotic dehydration and air drying was proposed. Mass transfer was quantitatively investigated during dehydration of carrot over a range of concentration and temperature of osmotic solution. Effective diffusion coefficients of water were estimated using the solution of Fick's unsteady state second law. The diffusion coefficients of water has been correlated with the concentration and temperature of the osmotic solution in addition to a parameter indicating the interaction between these two variables by an equation similar to that of Arrhenium relation. The frying kinetic models of vacuum frying combined with the osmotic dehydration and air drying were developed and the model coefficients were determined.The foundational characteristics were also studies during vacuum frying, including a firstorder kinetic equation was used to analyze the moisture and fat content and found the empirical equation of moisture, fat content and drying rate as a function of frying time. The micro-structure was studied at different frying time using lights and scanning electron microscopy, fat distribution was also studied by stained Oil Sudan Black. The mechanism of fat absorption was further analyzed and it has been established that fat absorption was related to the moisture evaporation, the fat distribution relies on the original moisture content of the material. An one-dimensional heat transfer model was developed to obtain the convective heat transfer coefficient during vacuum frying. A quasi-steady state analysis and simplified method were developed to predict the center temperature during vacuum frying. A good agreement between experimental and predicted data was obtained. A first order kinetic equation combined with series of empirical models was used to predict the moisture and fat content as a function of thickness, frying temperature and vacuum pressure.Water activity combined with the glass transition temperature, a new method to predict storage stability of dried food, could be used to determine, predict the food's shelf lives. The adsorption isotherms of carrot chips were determined. The data were fitted to six models at three temperatures. Sorption characteristics, based on the GAB model were analyzed and the monolayer moisture content, AHC and AH^ were determined. Through the non-linear regression the result showed the Gordon-Taylor equation could predict well the moisture plasticization effect and the model coefficients were determined. A combination of water sorption and Gordon-Taylor equation of carrot chips was analyzed, the critical water content and the critical water activity at which the glass transition occurs were obtained at a determined storage temperature. The changes of carrot chip's quality at different storage conditions during 6 months were investigated and included moisture, fat content, water activity, texture value, P -carotene content, aerobic acid, color value and acid value. The reaction rate was studied and the activation energy of 48.9 kJ/mol was determined based on the acid value. The estimated shelf-lives of carrot chips defined by degradation time of acid value at different storage conditions were determined. The results showed the monolayer moisture content is not a moisture content that assures quality preservation during storage of carrot chips, its quality doesn't significantly change only with the monolayer, but more relies on the water plasticization effect and storage temperature.