Study On Formation Mechanism And Process Optimization Of Texture And Quality Of Microwave Puffing Raspberry Snacks

Raspberry is a small berry with unique flavor and rich nutrition.However,raspberry berries have high moisture content and are easy to rot,which is not conducive to storage and transportation.Microwave puffing technology is used to make raspberry snacks,which not only retains the nutritional value of raspberry and prolongs the shelf life,but also enriches the diversity of raspberry products.However,the mechanism of microwave puffing raspberry chips is unclear,the process is complex and the quality is not easy to control.It seriously affects the application and popularization of microwave puffing technology in berry processing industry.In order to obtain microwave puffed raspberry snacks with strong applicability.The texture formation and quality change mechanism of microwave puffing raspberry snacks were studied by means of numerical simulation and bench test.The quality optimization model of microwave puffing raspberry snacks was proposed.Firstly,the texture formation of raspberry snacks during microwave puffing was studied by bench test in microwave workstation.The characteristics of temperature,moisture distribution and volume change of raspberry chips during microwave puffing were simulated and analyzed to reveal the mechanism of microwave puffing of raspberry chips.Secondly,according to the formation law of texture characteristics of microwave puffing chips,taking the turning point of Young’s modulus change rate as the critical point,different microwave power input modes are proposed to puffed berry snacks in order to ensure the nutritional value of snacks.Finally,according to the effect of microwave power input mode on the quality of raspberry snacks.With moderate hardness and crispness as the texture quality goal,the continuous microwave puffing process parameters of raspberry snacks were optimized.The main research contents and conclusions are as follows.(1)The formation mechanism of texture and quality of microwave expanded raspberry chips was studied.In the process of microwave puffing berry chips,the microwave heating rate significantly affected the pore formation of raspberry chips and determined the formation of texture quality.The increase of heating rate caused the formation of porous structure and the increase of overall volume of raspberry chips;Then,the elasticity,resilience and cohesion of chips are reduced,while the porosity,expansion rate and hardness are increased.By optimizing the microwave puffing parameters,the heating rate of raspberry chips was controlled to improve the texture and quality of raspberry snacks.(2)Based on electromagnetic temperature moisture solid mechanics,a multi physical field coupling model of microwave berry chips were constructed,and the simulation strategy of thermal puffing of raspberry chips in microwave workstation was proposed.The laws of temperature,moisture distribution and volume expansion during the puffing process were analyzed.In the initial stage,the chips absorbed microwave energy,stored heat and increased temperature,and the changes of moisture content and volume were small;In the puffing stage,the temperature distribution is high in the center and low on the surface.The moisture distribution is opposite to the temperature.The water evaporation forms enough steam pressure to drive the volume expansion of berry chips;In the later stage of puffing,the microwave absorption capacity and heat conversion capacity of raspberry chips are weakened,the water evaporation capacity and steam capacity are reduced,the puffing power is reduced,and the expansion degree is weaker than that in the early stage,but the volume deformation of chips gradually tends to be stable,and a loose porous structure is formed in raspberry snacks.In the volume expansion stage,the center of the chip is high temperature,the corresponding moisture content is low,and the moisture content of the outer surface is higher than that of the inner surface.In the expansion stage of microwave expanded berry chips,the volume expansion degree of chips is the largest,forming the texture state of snacks(hardness,brittleness,etc.).(3)On the premise of ensuring the texture quality of raspberry snacks,in order to ensure the overall quality of color and nutrition of raspberry snacks,based on the turning point of the change rate of Young’s modulus of raspberry snacks,a mode of microwave variable power puffing of raspberry snacks was proposed,and the effects of different microwave intensities on the puffing characteristics(color,volume,temperature uniformity and moisture uniformity)and nutritional components(anthocyanin and ascorbic acid)of raspberry snacks were explored.Before the turning point,use the microwave intensity of 10.0 W/g(microwave puffing for 2.5 min),and after the turning point,apply five microwave intensity(2.5,5.0,7.5,10.0,12.5 W/g)input modes.The experimental results show that the temperature uniformity and water uniformity of raspberry snacks are high when microwave power is variable and microwave intensity is lower than 10.0 W/g(5.0,7.5 W/g)after the turning point.The temperature uniformity and water uniformity of snacks are high.Water evaporation and steam form the driving force of volume expansion,form loose porous structure and no burnt paste.The color of raspberry snacks is close to that of the raspberry chips,which improves the nutrient retention rate of raspberry snacks.According to the changes of turning point of Young’s modulus of raspberry snacks,the puffing mode of two-stage variable intensity microwave input is adopted,which not only ensures the texture quality of raspberry snacks,but also improves the appearance quality and nutritional value.(4)The central combined experimental method was employed to investigate the effects of microwave intensity,puffing time,air velocity and microwave mode on temperature,moisture content,snack hardness and crispness.The results show that the quality of raspberry snacks can be significantly affected by the input of microwave energy in different microwave modes under microwave puffing.In the early stage of microwave puffing,high microwave intensity and high air velocity can quickly achieve volume expansion and hard surface of raspberry snacks to obtain highquality raspberry snacks.The optimal process parameters are developed as microwave intensity of9.5 W/g,puffing time of 3 min,air velocity of 1 m/s,and microwave mode of D(assignment of power distribution at 5,3,2,1,1 k W).The verification test validates the high consistency of response index of the simulation and test results.The research results provide a theoretical and technical basis for microwave high-efficiency and quality-preserving processing of raspberry snacks.