Study On Microwave Roasting Process Of Arabica Coffee And Analysis Of Its Physical And Chemical Index

Due to the advantages of rapid heating,energy saving and environmental protection,microwave heating technology has been attracting the attention of researchers at home and abroad in recent years,but it has not been involved in coffee roasting applications.Based on the current situation of coffee industry in Yunnan,this study proposes microwave heating technology to achieve coffee roasting,Yunnan Arabica coffee as test object,optimize the microwave roasting process parameters through various experiments,and microwave roast coffee on the basis of optimization process.The physical and chemical indicators of beans were systematically studied and analyzed.Taking the bulk density and roasting color value of coffee beans as the evaluation index,microwave power density,roasting time,drum rotation speed and wind speed as the influencing factors,the trends and causes of the effect of microwave-roasted coffee beans related indicators on the influencing factors were analyzed by single factor experiment;The roasting process was optimized by orthogonal test with 4 factors and 4 levels.The results show that the primary and secondary factors affecting microwave roasting are microwave power density,roasting time,wind speed,and roller speed.The optimal process parameters for microwave roasting are microwave power density 8W/g,roasting time 12 min,roller speed 75r/min.The wind speed is 1.5m/s.The verification result of the best process parameters is coffee bean bulk density 0.286g/mL,roasting color value 32.1,roasting degree is deep,and the test results have better chroma,puffing degree and uniformity,as well as avoiding the partial burnt black and quality loss phenomenon,has better roasting result than the previous roasting result of other parameters,verifying the rationality of the process parameters,and eliminating the preheating time than the traditional electric roasting,the same roasting time can reach more roasting amount,as well as reduces the energy consumption and time of roasting and improves the roasting efficiency.On the basis of the optimization process,the physical and chemical indicators of microwave roasted coffee beans were systematically studied and analyzed.Firstly,with the rupture force as the index,microwave roasted coffee beans under different baking degrees were tested by compression.The regression model between coffee bean rupture force and roasting chromaticity value and bulk density was established by SPSS software.The variation law of rupture force is also studied.The results show that the model has a fitting coefficient of R2=0.988,and the coefficients of the equation all reach extremely significant(<0.01)level.According to the roasting chromaticity value and bulk density of coffee beans,the rupture force value can be reasonably analyzed and predicted,in order to ensure the quality requirements of coffee bean products in many aspects in transportation,storage and grinding.Secondly,the antioxidant properties of microwave roasted coffee beans under different roasting degrees such as raw beans,light roasting,medium roasting and deep roasting,were analyzed.The antioxidant activity of coffee was determined by an in vitro antioxidant system such as DPPH radical scavenging activity and iron ion reducing ability,and the corresponding VC equivalent of its antioxidant capacity was obtained.The results show that the DPPH free radical scavenging rate can still be maintained between 87% and 89% during the light roasting and deep roasting,and the iron ion reducing ability can also be maintained at the VC equivalent level of 0.05 ~0.10mg/mL.DPPH free radical scavenging activity and iron ion reducing ability,so that microwave roasting can better retain the antioxidant properties of coffee beans.Furthermore,the content of active components such as chlorogenic acid,caffeine,fenugreek base and caffeic acid in coffee beans under the roasting degree of raw beans,light roasting,medium roasting and deep roasting is further subjected to high performance liquid chromatography(HPLC).The measurement method is used to analyze the change rule of the active ingredient in microwave roasting by multi-dimensional data such as the content value of the active ingredient,the damage rate,the contribution rate,and the coefficient of variation.The results show that he results showed that during the microwave roasting process,except for the content of caffeic acid,which was reduced from 4.71 mg/100 g to close to 0,the active components such as chlorogenic acid,caffeine and fenugreek with antioxidant properties can be well preserved,their content was retained at 76.71~1119.81 mg/100 g,1102.11~1042.49 mg/100 g,and 586.14~965.99 mg/100 g,and the content decreased with the deepening of roasting.In the deep roasting,the total relative content of the active ingredients retained by the microwave-baked beans was 2.67% higher than that of the electric baking beans,the relative content of the coffee bitter flavor flavoring substances such as chlorogenic acid and fenugreek in the microwave-roasted beans was 1.15% and 3.89%,higher than that of the electric-roaster beans,while the caffeic acid content is degraded to very low,which is caused by microwave coffee The electric roasted coffee has a bitter taste and no obvious acidic flavor;In addition to the four main active ingredients,the HPLC spectrum shows other peak shape response values during microwave roasting,indicating that there are other new compounds occurred in the process that are yet to be studied.