Study On Dynamic Characteristics Of Hot Air Drying Of Cut Apricot Meat With Different Pretreatment

Xinjiang is an important region for the development of apricot industry.At present,the processing methods are still mainly natural drying and hot air drying.There are some problems,such as low drying efficiency,uncontrollable drying parameters and poor product quality,which seriously limits the development of dried apricot industry.Taking Saimaiti fresh cut apricot as raw material,this paper uses different pretreatment combined with hot air drying to explore the drying characteristics,establish corresponding models and study relevant quality indexes.Firstly,the best conditions for inhibiting browning endogenous enzymes are selected,then hot air drying at different temperatures is carried out under these conditions,and the water state and spatial distribution in the drying process are studied with the help of low field NMR and imaging technology.Finally,through detection,The quality changes of cut apricot during drying at different temperatures were studied.The main conclusions are as follows:（1）Four pretreatment methods were used to inactivate apricot fruits.The inactivation rate of browning endogenous enzymes was more than 90%.The results showed that the hot water blanching temperature was100℃and the blanching time was 90 s;The steam blanching temperature is 100℃and the blanching time is 90 s;Under microwave treatment,the power is set at 50%（about 350 W）and the time is 5 min;Under sulfur treatment,the sulfur leaching concentration is 2 g/L and the time is 2 h.（2）There are two main stages in the hot air drying process of the four pretreated cut apricot fruits,which are acceleration deceleration stage and no obvious constant speed drying stage.The combination of microwave treatment and sulfur treatment with hot air drying can reduce the drying time.The D_effof cut apricot increased with the increase of temperature,and its range was 5.9637×10^-7m²/s-1.3530×10^-6m²/s,the average value of Ea is 22.62 KJ/mol.（3）The hot air drying model of sliced apricots treated with hot water,steam blanching and microwave can be described by Wang and Singh model MR=a+bt+ct².The hot air drying model of sliced apricots treated with sulfur can be described by Page model MR=exp（-ktⁿ）.After regression fitting,the equations are as follows:under hot water blanching MR=(0.1961+0.034785T-3.555×10^-4T²)+(-0.5307+0.022865T-2.615×10^-4T²)t+(0.0139-6.2×10^-4T+7×10^-6T²)t²;under steam blanching MR=(-0.376+0.05256T-4.78×10^-4T²)+(-0.2039+7.57×10^-3T-9.3×10^-5T²)t+(8.3×10^-3-3.5×10^-3T+4×10^-6T²)t²;under microwave treatment MR=(0.4527+0.018945T-1.455×10^-4T²)+(-0.1561+6.08×10^-3T-8.2×10^-5T²)t+(6.3×10^-3-2.85×10^-4T+3.5×10^-6T²)t²;under sulfur treatment MR=exp[-(0.736-0.028975T+2.875×10^-4T²)t^{（7.3449-0.323705T+0.0042245T2）}].After the model fitting is verified,R²is 0.9929（hot water blanching）,0.9955（steam blanching）,0.9942（microwave treatment）and 0.9967（sulfur treatment）respectively,and the fitting degree of the model is good.（4）Based on the low field NMR technology to explore the internal water migration changes of materials,it is found that at different temperatures,the T₂relaxation curve changes of cut apricot in the drying process are all with the extension of time,T₂shows a decreasing trend as a whole,and the transverse relaxation times T₂₁,T₂₂and T₂₃gradually migrate to the left.In terms of peak area,A_totaland A₂₃decreased significantly,and the apex of each peak gradually moved to the left;A₂₁and A₂₂decreased first and then increased at lower temperatures（40℃and 50℃）.Compared with blanching treatment,microwave treatme-nt and sulfur leaching treatment have uniform water distribution and complete loss of free water content.（5）From the sensory score,the overall trend of four pretreatment after hot air drying is sulfur treatment>microwave treatment>steam blanching>hot water blanching;From the color difference value,the overall trend is steam blanching>hot water blanching>microwave treatment>sulfur treatment.Reducing sugar can be effectively accumulated during drying.Higher temperature（60℃）is conducive to slow down the decline of titratable acid content of dried apricot and accelerate the decomposition of original pectin.The shear force and hardness at this temperature are generally higher than those at other temperatures at the same time.Compared with natural air drying,four pretreatment methods combined with hot air drying can slow down the degradation of original pectin.Compared with blanching,microwave treatment and sulfur treatment combined with hot air drying can effectively accumulate the content of reducing sugar in the drying process,but sulfur treatment can increase the shear force and hardness of products.