Rapid measurement of fish freshness indices by an amperometric flow-injection system with a 16-way switching valve and immobilized enzyme reactors

A novel flow-injection system is proposed for the rapid measurement of the fish freshness indices K₁ and K₂: K₁=[([HxR+[Hx])×100/([IMP]+[HxR]+[Hx])] and K₂=[[Hx]×100/([HxR]+[Hx])], where [IMP], [HxR] and [Hx] are inosine-5′-monophosphate, inosine and hypoxanthine concentrations, respectively. For the estimation of index K₁, 5′-nucleotidase immobilized reactor and nucleoside phosphorylase (NP)/xanthine oxidase (XO) coimmobilized reactor were incorporated in series in the flow-injection line made up by a 16-way switching valve with two sample loops. For the estimation of index K₂, NP and XO immobilized reactors were also incorporated in the similar flow-line. Two sample portions passed through the flow-line with different residence times so that two peaks were obtained. The first and second peaks obtained in the K₁-determining system corresponded to the total of HxR and Hx and the total of Hx, HxR and IMP, respectively. Similarly, the first and second peaks obtained in the K₂-determining system corresponded to Hx and the total of Hx and HxR, respectively. Therefore, the indices K₁ and K₂ can be estimated by

where i₁ and i₂ present the peak current of the first and second peaks, respectively, and f the ratio of the peak currents of the first and second peaks for a Hx standard solution. A sea bream was selected as a model fish and it was stored at 4 °C after death. A good correlation was found between the index K₁ and the storage time over a period of 400 h, with a correlation coefficient of 0.992, but no correlation between the index K₂ and the storage time. The measurements could be performed at a rate of 22 samples per hour with satisfactory precision (0.6–1.2% R.S.D.), without calibration for each species, accurate weighing of fish meat and any interferences in fish meat.     

Internet of Things: The Optimal Generation Rates under Preemption Strategy in a Multi-Source Queuing System

With the rapid development and wide application of the Internet of Things (IoT), how to provide timely and fresh information for strategic analysis and decision-making has become a key issue. Recent studies have shown that preemption strategies are of great importance to the improvement of information freshness. In view of this, we focus on the multi-source preemptive queuing model and investigate how to control the generation rate of each source to achieve the optimal overall information freshness. Specifically, we consider two typical preemption strategies: self-preemption strategy and global-preemption strategy. Noting that the urgency requirements of the systems on the data of each source are different, we propose the weighted average age of information (AoI) to characterize the overall information freshness of the system. For the self-preemption strategy, we prove that the optimal generation rate allocation is a convex problem and present an efficient algorithm to find the optimal solution. Additionally, we also derive a closed-form approximate optimal solution under light load cases to meet the demands for rapid deployment. For the global-preemption strategy, we directly derive the closed-form optimal solution of the corresponding problem. By comparing the optimized weighted average AoIs, the performance achieved by the global-preemption system was better than that achieved by the self-preemption system in terms of the overall timeliness. The numerical analysis verified the correctness of the theoretical analysis and that the proposed approximate solution had high accuracy not only under light load cases but also under other cases.     

A Novel Flow Injection Optical Fiber Biosensor for Hypoxanthine Based on Luminol Electrochemiluminescence

IntroductionIn the food industry,the determination of hy-poxanthine in fish meatcan be regarded as a simplemethod for evaluating fish freshness.When a fishis caught and killed,the breakdown of adenosine-5 - triphosphate( ATP) in the fish meat results inthe release of adenosine- 5 - diphosphate ( ADP) ,and further degradation products are adenosine- 5 -monophosphate( AMP) ,inosine- 5 - monophosphate( IMP) ,inosine( Hx R) ,hypoxanthine( Hx) ,xan-thine( X) and uric acid( UA) . It has be…     

Development of a volatile amine sensor for the monitoring of fish spoilage

A sensor with potential for the development of a “chemical barcode” for real-time monitoring of fish freshness is described. This on-package sensor contains a pH sensitive dye, bromocresol green, that responds through visible colour change to basic volatile spoilage compounds, such as trimethylamine (TMA), ammonia (NH₃) and dimethylamine (DMA) collectively known as Total Volatile Basic Nitrogen (TVB-N). The sensor characteristics were studied as well as its response with standard ammonia gas. Trials on cod and under-utilised species have verified that the sensor response correlates with bacterial growth patterns in fish samples thus enabling the “real-time” monitoring of spoilage in various fish species. The sensor response can be interrogated with a simple, inexpensive reflectance colorimeter that we have developed based on two light emitting diodes (LEDs) and a photodetector.     

零售商风险规避条件下基于期权契约的生鲜农产品供应链协调研究

民以食为天,随着生活水平的不断提高,生鲜农产品在消费结构中的重要性越来越突出,本文将期权思想引入生鲜农产品供应链运作当中,针对由一个零售商和一个供应商组成的二级生鲜农产品供应链,结合生鲜农产品的自然属性,考虑在途损耗对产品数量的影响以及保鲜投入对产品新鲜度的影响,运用CVaR模型研究了零售商的风险规避程度对供应链决策的影响以及期权契约协调机制。研究表明,期权机制可实现风险在供需双方之间共担,可解决随机需求下生鲜农产品供应链的协调问题并合理分配整体利润;仅当零售商的风险规避程度较低时系统协调和帕累托改进才能同时达成。     

高均匀度LED植物光源的设计

针对现有植物灯均匀度差的问题,通过在R（红）、G（绿）、B（蓝）三色LED芯片上加装导光管和光纤透镜,实现了高均匀度的出光效果,通过调节导光管和光纤的尺寸获得了达90%的混色、光谱以及光量子通量密度（PPFD）的均匀性。进一步对光源的热学性能进行表征发现光纤透镜的增加有利于减少光源正面的热量,并且基于光量子学照明参数对该灯的均匀度进行评价,并进一步提出有效光能利用率来更加科学的表征光源性能。结果表明,混色均匀性与PPFD均匀性可达90%,有效光能利用率可达到43%。进一步将该灯用于鲜切玫瑰花保鲜,并通过脉冲宽度调制技术（PWM）实现了光谱的动态可调,通过对玫瑰花鲜重日失重率以及抗氧化物质如黄酮素等物质含量变化的测量,探究鲜切玫瑰花保鲜的最佳光照条件。实验结果表明,最有利于鲜切玫瑰保鲜的光质条件和光照周期为R+G、6 h/24 h。     

An Improved Residual Network for Pork Freshness Detection Using Near-Infrared Spectroscopy

Effective and rapid assessment of pork freshness is significant for monitoring pork quality. However, a traditional sensory evaluation method is subjective and physicochemical analysis is time-consuming. In this study, the near-infrared spectroscopy (NIRS) technique, a fast and non-destructive analysis method, is employed to determine pork freshness. Considering that commonly used statistical modeling methods require preprocessing data for satisfactory performance, this paper presents a one-dimensional squeeze-and-excitation residual network (1D-SE-ResNet) to construct the complex relationship between pork freshness and NIRS. The developed model enhances the one-dimensional residual network (1D-ResNet) with squeeze-and-excitation (SE) blocks. As a deep learning model, the proposed method is capable of extracting features from the input spectra automatically and can be used as an end-to-end model to simplify the modeling process. A comparison between the proposed method and five popular classification models indicates that the 1D-SE-ResNet achieves the best performance, with a classification accuracy of 93.72%. The research demonstrates that the NIRS analysis technique based on deep learning provides a promising tool for pork freshness detection and therefore is helpful for ensuring food safety.     

纳米TiO2的制备及对三甲胺气体的敏感性能

用硬脂酸凝胶法制备纳米TiO₂材料,并用XRD、TEM、IR对纳米晶的晶型、晶粒大小及形貌进行表征；用XPS分析不同晶型的纳米TiO₂表面吸附氧的情况，发现锐钛矿型纳米TiO₂比金红石型纳米TiO₂有较多的表面吸附氧. 检测了不同晶型纳米TiO₂对三甲胺（TMA）气体的敏感性能.结果表明锐钛矿型纳米TiO₂对TMA有较高的灵敏度. 对敏感性能的机理进行了讨论.     

A sensitive xanthine oxidase electrode with silk net for estimating fish freshness

An enzyme biosensor was constructed using a plate platinum electrode and immobilized xanthine oxidase (XOD).Only a very small quantity of enzyme was chemically immobilized on a special silk net.Hydrogen peroxide released during the enzymatic reaction was detected by the electrode at+0.65 V (vs.Ag/AgCl).The electrode was very sensitive to hypoxanthine and its detection limit was 1×10-7 mol/L.When it was applied to the determination of fish freshness,the results agreed well with those obtained by traditional methods-determination of total volatile basic nitrogen (TVB-N) and microbial count.A range for estimating the freshness of river fish was suggested.     

Nondestructive egg freshness assessment from the equatorial and blunt region based on visible near infrared spectroscopy

This research was to study which orientation was better for freshness prediction of the white-shelled eggs using visible near infrared spectroscopy. The transmission spectra were acquired in the equatorial region and at the blunt end of the eggs. After each spectral measurement, the Haugh unit, yolk index, and albumen pH as the freshness parameters were simultaneously measured using traditional destructive methods. Pretreatment methods containing Savitzky-Golay smoothing, multiplicative scatter correction, the standard normal variate, the first derivative and the second derivative were used. A partial least squares regression was developed to predict the Haugh unit, yolk index, and albumen pH. The best correlation coefficients of prediction were obtained from the equatorial region, and were 0.881, 0.855, and 0.888 for the Haugh unit, yolk index and albumen pH, respectively. And root mean square errors in the prediction set were 7.720, 0.034, and 0.147 for the Haugh unit, yolk index and albumen pH, respectively. The results illustrated that the equatorial region showed better ability than the blunt end to predict freshness of the white-shelled eggs.