Hot Air And Infrared Drying Characteristics And Quality Evaluation Of Bitter Melon Slice

Bitter melon(Momordica charantia L.)is a plant of Cucurbitaceae.It is not only a crop with high economic value,but also a traditional Chinese medicinal herb with excellent medicinal value.It is rich in protein,vitamins,carotene and other nutrients.It also has saponins and other active substances.Bitter melon is mainly distributed in tropical,subtropical and temperate regions.It has a long history of planting in China,with large planting area and high yield.Our country has always attached great importance to the processing industry of agricultural products.At present,in the field of agricultural products processing,it focus on the extraction of nutrient functional ingredients in fruits and vegetables such as bitter melon,and the development of processed foods of homology of medicine and food and health care products.The development of bitter melon industry has broad prospects but it is started late,and there are few studies on the deep processing technology of bitter gourd.The moisture content of freshly harvested bitter gourd is as high as 95%,it is highly susceptible to environmental temperature and humidity and other factors during storage and transportation,causing spoilage,resulting in serious loss of nutrients and active substances and reducing economic benefits.Therefore,in addition to fresh food,bitter melon should be dried in a short period of time.The traditional method of open sun drying has not been able to meet large-scale production and requires mechanized drying methods to be put into production.Hot air drying is the most widely used drying method.Infrared drying is a relatively new,efficient and clean drying method.In this paper,the characteristics of hot air and infrared drying of bitter melon slices were studied.The variation of effective moisture diffusivity of bitter melon slice under different drying conditions was studied,and the activation energy of hot air drying and infrared drying of bitter melon slice was obtained.Based on the orthogonal experiment,the optimal drying process of bitter melon slices of hot air drying and infrared drying was obtained by taking the effective moisture diffusivity,retention rate of Vc content,total color difference and total saponin content as evaluation indexes,and the quality of bitter melon slices by hot air drying and infrared drying was compared briefly.At the same time,the basic theory of bitter melon drying was deeply studied,and the mathematical models of bitter melon slice hot air drying and infrared drying were established.Based on artificial neural network,the moisture ratio model of bitter melon hot air drying and infrared drying was established,and the real-time prediction of moisture ratio in bitter melon drying process was realized.The main conclusions of this study are as follows:Firstly,the hot air drying process of bitter melon slice was during the falling rate drying stage,and there was no obvious constant drying stage.Under different hot air drying conditions,the effective moisture diffusivity of bitter melon slice increased first and then decreased with the decrease of dry basis moisture content.Slice thickness is the most important factor affecting the effective diffusion coefficient,followed by hot air temperature and air speed.Page model is the best mathematical model to describe the drying characteristics of bitter melon slices.Hot air temperature,slice thickness and air speed have significant effects on the comprehensive quality of bitter melon.Hot air temperature had the highest level of influence on the comprehensive quality during hot-air drying of bitter melon slice,and it was followed by air speed and slice thickness,the confidence levels of each factor were 99.6%,98.1% and 96.5% respectively.The optimal combination of hot air drying of bitter melon slices is hot air temperature of 55oC,slice thickness of 9mm,hot air speed of 1.2m/s.The activation energy of bitter melon slice with thickness of 3mm,6mm and 9m was 22.651 kJ/mol,26.850 kJ/mol and 29.964 kJ/mol under hot air speed of 0.9m/s.Secondly,the infrared drying process of bitter melon slice was also during the falling rate drying stage,and there was no obvious constant drying stage.Under different infrared drying conditions,the effective moisture diffusivity of bitter melon slice increased first and then decreased with the decrease of dry basis moisture content.Modified Page model is most suitable for describing the infrared drying characteristics of bitter melon slice,and has strong applicability to the infrared drying of bitter melon slice.Infrared temperature,slice thickness and radiation distance have significant effects on the comprehensive quality of bitter melon slice.Infrared temperature had the highest level of influence on the comprehensive quality during infrared drying of bitter melon slice,and it was followed by slice thickness and radiation distance,the confidence levels of each factor were 99.2%,98.9% and 98.8% respectively.The optimal combination of infrared drying of bitter melon slices is infrared temperature of 55oC,radiation distance of 145 mm and slice thickness of 3mm.The activation energy of bitter melon slice with thickness of 3mm,6mm and 9mm was 39.421kJ/mol,38.244 kJ/mol and 39.375 kJ/mol under infrared distance of 145 mm.Then,the total color difference of bitter melon slices after infrared drying was obviously smaller than total color difference of hot air drying samples,the color of bitter melon slice after infrared drying was better compared with color of hot air drying samples;the total saponins content of bitter melon slice after infrared drying was close to that of hot air drying samples.The comprehensive quality of bitter melon slice after infrared drying meets the production requirements,and the production of bitter melon by infrared drying is of great siginificance for popularization.Finally,based on BP neural network,the moisture ratio prediction models of hot air drying and infrared drying of bitter melon slices were established.BP neural network moisture ratio model can effectively predict the change of moisture ratio during the hot air drying and infrared drying of bitter melon slices,and has good generalization ability.Under the experimental conditions of hot air temperature of 55oC,air speed of 0.9m/s and slice thickness of 7mm,the determinant coefficient between the predicted value of Page model and the experimental value is 0.9448 and the average relative error is 23.47%;while the determinant coefficient between the predicted value of BP neural network and the experimental value is 0.9975 and the average relative error is 7.73%,which is lower than the average relative error predicted by Page model.Under the experimental conditions of infrared temperature of 55oC,radiation distance of 145 mm and slice thickness of 7mm,the determinant coefficient between the predicted value of Modified Page model and the experimental value is 0.9746 and the average relative error is 15.46%;while the determinant coefficient of BP network is 0.9988 and the average relative error is 3.73%.In hot air drying and infrared drying of bitter melon slices,the correlation degree of predicting moisture ratio by BP neural network model is higher than that by traditional mathematical model,and the relative error of predicting moisture ratio by BP neural network model is lower than that by traditional mathematical model.The moisture ratio model based on BP neural network is more advantageous in predicting the moisture change during the drying process of bitter melon slices.