Development Of Gas Sensors Based On Silk Fibroin Fiber And Their Application In Pork Freshness Detection

Pork is the most important source of meat consumption in urban and rural residents.The freshness of pork is an important index to evaluate its quality,and is one of the biggest concerns for consumers.It is of practical significance and value to study the rapid and accurate detection of freshness of pork.Ammonia,Hydrogen sulfide and trimethylamine can be produced during storage,transportation and sales of pork,which result in a decline in pork freshness.In this study,ammonia was selected as the representative volatile gas,and the ammonia-sensitive gas sensor was studied.The information about the freshness during the pork storage was obtained through the developed sensor.The freshness levels of pork were discriminated by the data processing method.It is expected to obtain a rapid detection technique and method for freshness of pork.The main research contents of this paper are as follows:(1)The sensory evaluation and physical and chemical indicators of pork freshness.The pork was purchased in the local supermarket.All samples were taken out for its sensory evaluation and volatile salt nitrogen(TVB-N)content determination every day.According to the data obtained,all pork samples were divided into three grades,namely fresh meat,times fresh meat and rot meat.In addition,various volatile substances produced during pork storage were analyzed by Gas Chromatography-Mass Spectrometry(GC-MS).Volatile odor composition was complex,and content was constantly changing.Among them,the content of ammonia and trimethylamine would increase during storage.Both of which had similar chemical properties,and their contents increased with increasing storage time.Therefore,this study selected ammonia as a representative gas to develop the sensor for the detection of pork freshness.(2)Preparation of ammonia sensors based on fibroin fiber.PANI-TiO2/Silk composites and PANI-Ag/Silk composites were synthesized by using an in-situ polymerization method.The reaction time and the amount of TiO2 and silver nanowire were optimized.The results showed that the optimum reaction time of PANI-TiO2/Silk and PANI-Ag/Silk were 2 h and 4 h,respectively.The best dosage of TiO2 and silver nanowire were 0.025 g and 1.5 m L,respectively.In addition,these composite materials were characterized by SEM,Raman spectroscopy and EDS.It turned out that both materials had been successfully prepared.100 ?g/L NH3 was detected by the sensor of PANI-TiO2/Silk and PANI-Ag/Silk prepared under the optimized conditions.The sensitivity were 0.85 and 0.94,respectively.The response time were 20 s and 8 s,respectively.The recovery time were 280 s and 200 s,respectively.The above results showed the two sensors both had good gas sensing performance.(3)Study on the rapid detection of pork freshness based on two gas sensors.First of all,a set of pork freshness detection system was developed,and the system was divided into hardware and software in two parts.The hardware part is composed of the sensor test air way,the reaction device,the USB data acquisition card,the relay,the digital multimeter,the sensor and the computer.The software part was developed secondly based on the existing device.In the Visual Studio platform,a testing program was developed using VB programming language for the signal acquisition,recording and display.In addition,this program could also achieve the goal of real-time signal acquisition,the testing process off,as well as single-channel and multi-channel switching and other functions.Secondly,the freshness of 84 pork samples stored at 4 ? for 1 to 7 days was measured by the detection system.The resistance signals of the sensor were collected.Finally,the pork with different storage days were classified by principal component analysis(PCA)and K-Nearest Neighbor(KNN),and the corresponding discriminant models were established.Among them,the correction set and the prediction set recognition rate of the established KNN recognition model can reach 91.14% and 85.71%,respectively.The results show that the classification results according to the sensor response are consistent with TVB-N.In this study,the rapid detection of pork freshness was realized by gas sensor,and the freshness discriminant model was established by using the two kinds of sensors.The research results provided technical support for the freshness judgment and real-time monitoring of pork in actual production and life.