| Total Viable-bacteria Count（TVC）is an indicator of food safety microorganisms,which is mainly used to evaluate food cleanliness and reflect whether food meets health requirements in the production process.Once the food with the total viable count exceeding the standard is eaten by healthy people,it is likely to cause vomiting,diarrhea and other symptoms,and even intestinal diseases such as dysentery,which endangers human health and safety.Therefore,it is necessary to take appropriate means and methods to count the total number of viable colonies in food timely and accurately,so as to achieve the detection purpose of microbial limit index for food.At present,the detection methods of microbial colony count are divided into two categories,traditional TVC detection and new TVC detection methods at home and abroad in recent years.Traditional TVC detection methods include plate colony counting method and TTC medium method.However,these methods are time-consu ming and laborious due to their cumbersome operation,vulnerability to pollution and large subjective error.Therefore,in recent years,in order to overcome the shortco mings of the above detection methods,many novel sensing technologies and counting methods have emerged in China and abroad,such as ATP fluorescence,PCR detection technology,growth metabolism and so on.However,these methods have the disadvantages of low detection limit,invasive detection and high detection cost.Therefore,seeking a non-invasive,simple,accurate and automated microbial colony count detection is the mainstream.As one of the products of microbial growth and metabolism,CO2 can quickly reflect the growth of microorganisms in real time.Currently,the detection scheme based on CO2has been applied to the measurement of microbial growth curve.Tunable diode laser absorption spectroscopy（TDLAS）as a sensitive,selective,fast response time,real-time online,non-invasive,simple structure of trace gas detection technology has been successfully applied in air pollution component detection,medical diagnosis,chemical reaction process and other fields.The main purpose of this study is to combine most probable number（MPN）counting method with TDLAS technology to propose a non-invasive,low cost,simple structure and accurate method for the detection of total bacterial count.The overall arrangement of the paper:（1）The basic theory of maximum probable number（MPN）counting method in national standard（GB4789.2-2016）is introduced,and the confidence interval of MPN counting method is analyzed.In the case of the same MPN value,with the increase of single gradient tube number,the narrower the confidence interval,the smaller the error;（2）The basic principle of TDLAS was discussed,and the measurement performance of TDLAS technology was analyzed.The detection limit of the system was 72.55 ppm,and the threshold value of TDLAS technology to deter mine the negative/positive culture flask（0.58 V）was deter mined.（3）Through the combination of MPN counting method and TDLAS technology,the verification and performance analysis of MPN-TDLAS method are carried out.The measurement results have a good linear relationship.The linearity of the measurement results of 3,4,5 and 6 tube methods under the single dilution gradient is more than 0.97.The feasibility of MPN-TDLAS method is verified experimentally,and the parallel comparison with the national standard plate counting method is carried out.The results show that the consistency between MPN-TDLAS method and the national standard plate counting method is 0.99,indicating that the two methods have good correlation.（4）MPN-TDLAS method was used to detect the total number of colonies in the quality control samples of Jinhua Institute of Food and Drug Testing.The detection results were evaluated by Z-score.The detection results of MPN-TDLAS method were all in the satisfactory region,and most of them were smaller than the Z value of the national standard plate method,indicating that the MPN-TDLAS method was more reliable and satisfactory than the national standard plate counting method on the whole.The experimental results showed that MPN-TDLAS method could be well applied to the detection of total bacterial count.In summary,the goal of this paper is to apply MPN-TDLAS method to the field of food detection,and can achieve today’s existing technical level,which paves the way for future prototype research and application research.Finally,the full text is summarized,and the future work is prospected. |
