| Dairy is a special food that is very easy to deteriorate.During the process from production to drinking,the quality of dairy products will be lost due to many factors such as biology,chemistry and physics,resulting in the decline of freshness and even deterioration.Generally,consumers judge whether dairy products are edible through sensory experience or static label data(production date and expiry date,etc.).However,these methods cannot obtain real-time and accurate freshness of dairy products in actual environments.In this paper,paper-based percolation chips and components were designed and prepared to detect the real-time quality of dairy products after opening.A detection method for determining the quality of dairy products using changes in electrical and optical signals were proposed,and the performance of paper-based seepage chips was analyzed.The real-time quality of dairy products was characterized by measuring the dielectric parameters of dairy products using designed and prepared paper-based seepage chips and components;In terms of optical signals,by observing the sequence change process and morphology change of dairy products with different degrees of deterioration after reaction with NaCl solution,the mechanism of dairy deterioration process was deeply studied,which provided a new idea for the quality and safety detection of dairy products.The main research results are as follows:(1)Paper-based seepage chips were designed to detect changes in electrical and optical signals during the spoilage process of dairy products.The design of paper-based seepage chip for electrical detection includes the design of seepage channels and paper-based seepage chip and components.The seepage channel is a hydrophilic and hydrophobic single channel pattern,which allows liquid samples to flow in a specific single channel area on paper-based seepage chip.The paper-based seepage chip components used for electrical detection include linear electrode-paper-based seepage chip and plane electrode-paper-based seepage chip.Linear electrode-paper-based seepage chip refers to a kind of conductive circuit designed in the seepage channel of paperbased percolation chip to make the liquid sample form a loop when entering the chip,so as to measure the electrical signal of the liquid sample.Planar electrode-paper-based seepage chip is to fix two pieces of ITO conductive glass on the clamp as the base sensing material,place paper-based seepage chip in the middle,and connect LCR digital bridge to measure the capacitance between the two plates.The paper-based seepage chip used for optical detection fixes the liquid sample in the detection area and completes optical detection in the fixed area.(2)Paper-based seepage chips and components were prepared for measuring the dielectric parameters of dairy products and detecting dairy optical signals,and their functionality was tested.Preparation and construction were completed based on the design of different chips and components.The ink jet printing method was used to draw the seepage channels of various paper-based seepage chips on the paper base with capillary force,The linear electrode-paper-based percolation chip was packaged using a dispensing machine to draw the circuit of the wire chip.Functional tests were carried out on the two chips and components,including the study of the paper-based material performance of the paper-based percolation chip,seepage channel size,structure selection of the paper-based seepage chip used to detect the dielectric parameters of dairy samples,liquid filling volume and testing time.(3)The electrical properties of dairy products during spoilage were tested using a paper-based percolation chip,and the changes in dielectric parameters and spoilage mechanism throughout the spoilage process were analyzed.The dielectric parameters of the entire process of dairy spoilage(0-50 hours after opening)were measured by paper-based seepage chip and device for optical detection of dairy products,and the trend of changes in dielectric parameters during the entire process of dairy spoilage was analyzed.Research has found that the dielectric parameters of the entire process of dairy spoilage exhibit a fluctuation of "3 V" with changes in dairy quality.pH composite electrode was used to measure the pH value of dairy spoilage process,and the relationship model between dielectric parameter and pH value in the whole process of dairy spoilage was established.During the process of milk spoilage,the change of pH value was monotonic decreasing,and in this process,the milk has had multiple quality change processes,and the measurement of dielectric parameters was non monotonicity at different stages,which can obtain more accurate measurement results.It was determined that the pH value alone could not accurately characterize the freshness of fresh milk,and the capacitance was more sensitive to the change of quality of dairy.(4)The optical properties of dairy products during the spoilage process were tested using a paper-based percolation chip,and the spoilage mechanism of dairy products was analyzed.Inorganic compound was used to characterize organic crystallization,and inorganic compound NaCl solution was introduced,optical microscopy was used to observe the microscopic structure of dairy products after reaction with NaCl solution in the whole process of metamorphism.It was found that dairy products at different fresh stages showed different and unique morphological characteristics after reaction with NaCl solution.Based on the correlation analysis between the change of crystallization behavior and the change of dielectric parameters,it was found that the periodic changes of the two were consistent.Based on the change law of the two,it was proposed to divide the total dairy spoilage process(0-50 h)into four stages:very fresh,fresh,beginning to deteriorate and spoilage.By means of scanning electron microscope(SEM),the crystal morphologies generated by the interaction between dairy and inorganic matter at four stages were studied,and the metamorphic mechanism of dairy products was studied. |
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