Far-infrared Baking Process Control And Quality Optimization Of Oolong Tea

Far infrared technology has been used more and more in tea production because of its good heating quality,energy saving,efficiency and other advantages.However,at present,the understanding of baking quality still remains in the subjective perception and experience of tea farmers.On this basis,a set of far-infrared tea baking test platform based on electronic nose was established,and the influence of baking temperature,baking time and other factors on the internal and external sensory quality of tea was experimentally studied.On this basis,electronic nose technology was used to rapidly identify tea under different roasting temperature and roasting time.By measuring tea odor and studying its change mechanism,the baking temperature control strategy was designed to achieve the goal of reoptimization of tea baking quality.The main work includes the following:(1)A far-infrared tea baking test system based on electronic nose technology was established.The far-infrared baking device adopts PC control to sustainably adjust energy and temperature;The temperature detection part uses thermocouple to monitor the temperature in the baking cage in real time.In the odor detection part,the electronic nose is used to collect the odor of tea in real time.PC control part online to complete temperature monitoring,feedback control and data preservation.The error of system constant temperature control is within ±1 ℃,and the control delay is short.(2)The effects of different baking temperature(85 ℃～135 ℃)and baking time(0～6 h)on tea’s intrinsic quality,sensory quality and intrinsic taste substance were studied,and the relationship between characteristic sensor and intrinsic taste substance was established.The results showed that the content of key taste substances changed regularly or remained stable,and the higher the baking temperature was,the longer the baking time was,the faster the consumption rate of tea polyphenols,catechins,amino acids and soluble sugars was,the lower the content was.When baking temperature and baking time are moderate,the phenol-ammonia ratio increases and amino acids are retained,and the aroma and taste of the tea will be better.There is a certain correlation between sensory quality and inner taste substance.(3)Using principal component analysis,linear discriminant analysis and intelligent algorithms to establish mathematical models for the rapid and accurate determination and identification of tea at different baking stages.The results showed that the electronic nose sensor could classify tea leaves with different degrees of roasting well,and the established RF model had the best effect,the accuracy of correction set reached 100%,and the accuracy of verification set reached 98.44%.The contents of total volatile substances and aroma substances detected by GC-MS in the baking process increased first and then decreased,and the contents of aroma substances and characteristic substances in tea increased sharply in the later baking period.In addition,PLSR analysis models demonstrated a close association between electronic nose sensors and volatile substances.(4)The fuzzy control strategy of baking temperature based on electronic nose technology is designed to realize self-regulation of temperature in the process of far-infrared baking.Research shows that baking time T can be used as the dividing line of baking period.When0≤t<120,it is the early stage of baking;when 120≤t<240,it is the middle stage of baking;when 240≤t≤360,it is the late stage of baking.In order to be easy to control,the baking stage adopts constant temperature baking.In the middle stage of baking,R7 and R9 values were used as input temperature control to enhance the baking aroma,reduce heterodorous flavor and rapidly consume the content of tea polyphenols.In the later baking period,R6 and R9 values were used as input temperature control to ensure the formation of characteristic aroma,flavor substance and fragrance maintenance.Under the fuzzy control scheme,tea polyphenol content was 12.87%,catechin content was 62.93 mg/g,amino acid content was 2.66%,phenol-ammonia ratio was 4.84,soluble sugar content was 1.44%,theanine content was2.42%,and the final sensory score was 91.40,which improved the intrinsic quality and sensory quality.