Influence of different storage conditions on production of trimethylamine and microbial spoilage characteristics of mackerel products

Gradual accumulation of the fishy-odor compound trimethylamine (TMA) from bacterial reduction of trimethylamine oxide (TMAO) is one of the characteristic chemical changes attributed to fish spoilage. Changes in TMA values were correlated with sensory testing results, storage temperature, storage time, and viable bacteria counts. TMA contents were determined under different storage conditions. Headspace solid-phase micro extraction analysis with gas chromatography using flame ionization detection was used with different storage times and temperatures. Mackerel samples were inoculated with Pseudomonas fragi to monitor changes in the TMA content and pH. The TMA content increased proportionally with time during storage, and pH values and the microbiological quality were evaluated to analyze correlations with the TMA content in fish products. The TMA content increased with an increasing number of P. fragi with good linearity (R ²=0.997). Basic data are provided for developing a freshness indicator for fish spoilage.     

A halochromic indicator based on polylactic acid and anthocyanins for visual freshness monitoring of minced meat,chicken fillet,shrimp, and fish roe

Herein, a new intelligent indicator with polylactic acid (PLA)/ polyethylene glycol (PEG)/calcium bentonite (CB) blend and Malva sylvestris, as a source of anthocyanins, was developed, characterized, and used for visual freshness monitoring of a variety of proteinous foods. Anthocyanins were incorporated successfully into PLA/PEG/CB with no significant change in the chemical structure of the indicator. The hydrophilic (water contact angle of 43.9°) indicator represented visual color changes from light red (at pH 2) to green (at pH 11). Moreover, PLA/PEG/CB-Malva indicator visually distinguished (ΔE > 5) fresh, medium fresh, and spoiled shrimp and fish roe (during 6 days at 4 °C), but discriminated only fresh and spoiled minced beef and chicken fillets (during 10 days at 4 °C), which were strongly correlated with the total volatile basic nitrogen of food samples. The PLA/PEG/CB-Malva indicator has a satisfying application for monitoring the freshness of various proteinous foods.Industrial relevance textThis study showed that anthocyanins extracted from Malva Sylvestris can be used efficiently in food smart packaging. The incorporation of anthocyanins into polylactic acid has led to the production of a novel intelligent freshness indicator. The indicator revealed an appropriate response to the spoilage of different proteinous foods with the capacity to differentiate between fresh, medium fresh, and spoiled foods. This capability is an important feature in commercializing freshness indicators.     

食品新鲜度指示器的研究与发展趋势

食品新鲜度与消费者的饮食安全密切相关。新鲜度指示器可检测食品腐败所产生的释放物并产生直观的颜色变化指示食品的新鲜度,成为研究热点。这些释放物包括挥发性盐基氮、二氧化碳、硫化氢等。围绕这些释放物分别开发了盐基氮指示型、二氧化碳指示型以及硫化氢指示型指示器。本文综述了上述指示器的工作原理及研究进展,并指出加强指示新鲜度对象的特异性识别,发展天然色素显色剂型指示器,发展接触式非破坏型指示器,发展电子式智能化指示器是主要的发展趋势。随着新鲜度指示器技术不断成熟,其在新鲜食品包装领域将会得到越来越广泛的应用。     

Real time on-package freshness indicator for guavas packaging

A novel on-package color indicator has been fabricated based on bromophenol blue, and tests have been conducted to assess the freshness of guava (Psidium guajava L.). Bromophenol blue (BPB) was immobilized onto bacterial cellulose membrane via absorption method. The BPB/cellulose membrane as color indicator works based on pH decrease as the volatile organic compounds (e.g. acetic acid), produced gradually in the package headspace during developing of guava. Subsequently the color of the indicator will change from blue to green for over-ripe indication, which can be visible to the naked eye. The results showed that the color indicator could be used to determine the state of freshness of the guava at ambient condition (28–30 °C). The color change of the indicators reflects the pH of headspace of the guava packaging. Furthermore, it also in similar trends to the change of several parameters (soluble solids content, texture and sensory evaluation) that normally used to characterize the freshness of guava. Therefore, the indicator can be used for real time visual monitoring of freshness state of packaged guavas.     

Dual bacterial strains TTI for monitoring fish quality in food cold chain

Most microbial time–temperature indicators (TTIs) considered only one spoilage strain. This research compared single and dual spoilage strains-based microbial TTI for quality changes of chilled grouper fish (Epinephelus fuscoguttatus x E. lanceolatus) fillet products during distribution. The next-generation sequencing (NGS) and traditional plate count approach showed that Pseudomonas fragi and Vibrio parahaemolyticus were specific spoilage bacteria at 7 and 15°C. A dual-strain TTI response provides more accurate results than a single-strain TTI and provides an irreversible color change from yellow to reddish-brown, showing levels of fish freshness. The microbial TTI comprises fish spoilage bacteria strains with 3 log CFU/ml, a nutrient broth supplemented with 2% NaCl as a medium, and phenol red with 0.25 mg/ml as a pH indicator. Overall, this study points to the applicability of a dual-strain microbial TTI as a valuable tool for monitoring fish quality changes during cold chain break condition.     

Electronic nose system fabrication and application in large yellow croaker (<Emphasis Type="Italic">Pseudosciaena crocea</Emphasis>) fressness prediction

In this paper, an electronic nose (E-nose) system was fabricated, and its application in large yellow croaker (Pseudosciaena crocea) freshness prediction was also explored. E-nose responses to samples stored at 277 K were measured for 8 days. Freshness indexes, such as total viable counts (TVC), total volatile basic nitrogen (TVB-N) and K value, were synchronously examined by chemical examinations. Principal component analysis (PCA) and stochastic resonance (SR) were utilized for e-nose data analysis. Results suggested that PCA showed poor freshness discrimination result. SR signal-to-noise (SNR) spectrum using maximal SNR (\(Max_{SNR}\)) values quantitatively characterized freshness of all croakers. Multiple variable regression (MVR) result demonstrated that there was good linearity relationship between SR \(Max_{SNR}\) values and fish freshness indexes. Large yellow croaker freshness predicting model was developed by non-linear fitting regression on \(Max_{SNR}\) values with high accuracy and repeatability. Therefore, the method proposed in this paper provides a rapid and nondestructive methodology for freshness prediction of large yellow croakers. The predicting error of the developed model is 10 %.     

A non-destructive ammonium detection method as indicator for freshness for packed fish: Application on cod

This paper introduces a non-destructive method for monitoring headspace ammonium as an indicator for changes in the freshness status of packed fish. Electrodes in an aqueous phase in the package monitor changes in the concentration of ammonia produced in/on the packed fish and released in the headspace. The outputs of an ammonium ion-selective electrode (NH₄⁺-ISE) were compared with the volatile amines content of the fish fillets. The method was tested in triplicate with fresh cod fillets stored between −0.5 and 1.9 °C. Changes in the ammonia content of the fish could be monitored in the aqueous phase with the NH₄⁺-ISE. The changes in the NH₄⁺-ISE signal correlated with the content of volatile amines (TVB-N) in the cod fillets. This non-destructive method might be the basis for the development of an intelligent packaging for monitoring freshness of packed fish.     

Ridgetail White Prawns,Exopalaemon carinicauda,Storage Time Rapid Determination Using Electronic Nose

Ridgetail white prawns, Exopalaemon carinicauda, storage time rapid determination method based on electronic nose was investigated in this paper. Prawns were stored at 4 °C for 9 days. Each day, electronic nose responses, and total volatile basic nitrogen index were measured during the storage period. Total volatile basic nitrogen index provided a freshness standard according to China standard protocols. Signal-to-noise ratio spectrum calculated by stochastic resonance discriminates prawn samples under different storage days successfully. Prawns' storage time determination model was developed based on signal-to-noise ratio eigenvalues. Validating experiments demonstrated that this model predicted prawn storage time with an accuracy of 90 %. Prawn freshness critical value ?82.77066 was also obtained by referring to total volatile basic nitrogen index and the developed model. This method is promising in seafood freshness evaluation.     

Development of a smart packaging for the monitoring of fish spoilage

There is much interest from the fisheries industry in developing rapid methods to evaluate real-time freshness of fish and seafood products. Emphasis is on the ones that would reflect and account for the products history and their storage conditions from “harvest-to-home”. The development of a “smart packaging” that monitors the microbial breakdown products in the headspace of packaged fish is described. When fish spoils it releases a variety of basic volatile amines which are detectable with appropriate pH indicating sensors. These are prepared by entrapping within a polymer matrix a pH sensitive dye that responds, through visible color changes to the spoilage volatile compounds that contribute to a quantity known as total volatile basic nitrogen (TVB-N). Laboratory trials on fresh fish filets showed that the sensor accurately tracks the increase in amines concentration in the package headspace. The response was also found to correlate to changing microbial populations (total viable count or TVC and Pseudomonas spp.). In addition, leaching of the dye was assessed over time to assess the suitability of the sensor formulation for food packaging application.     

Analyses of Trace Crystal Violet and Leucocrystal Violet with Gold Nanospheres and Commercial Gold Nanosubstrates for Surface-Enhanced Raman Spectroscopy

Crystal violet (CV) is forbidden but still used in some aquaculture operations due to its low cost and high effectiveness against some fish diseases. Surface-enhanced Raman spectroscopy (SERS) coupled with partial least squares (PLS) regression is applied to analyze trace amounts of CV and its metabolite leucocrystal violet (LCV) in fish fillets. Two different laser sources (633 and 780 nm) and three different gold nanosubstrates (included gold nanospheres and two commercial gold substrates) were used as SERS substrates to achieve optimal analytical results. Gold nanoparticles (diameter 55.4?±?4.5 nm) as synthesized via a reduction method resulted in better sensitivity and accuracy results than the two commercial substrates. The minimum detectable concentration for CV standard solutions was 0.5 ng/mL with the use of gold nanospheres as substrate, compared to 10 and 50 ng/mL with the two commercial substrates. The R ² of actual CV concentrations versus the values predicted (cross-validation) with PLS models ranged from 0.963 to 0.989. For CV contaminated fish muscles, the minimum detectable concentration of CV was 1 ng/g, and the PLS model (n?=?64, 20 for prediction) for total CV and LCV in fish muscles was less satisfied (cross-validation R ²?=?0.889; prediction R ²?=?0.857) compared to those for standard solutions due to the interferences of nontargeted components in fish extract, but the results still indicated the possibility of applying SERS with chemometrics to determine trace amounts of CV and LCV in complex sample systems, such as fish muscles.     

食品智能包装新鲜度指示剂研究进展

作为智能包装不可缺少的一部分——新鲜度指示剂,通过指示敏感材料,与食品腐败过程中产生的特定产物发生反应,并将反应结果转换成易于消费者直接观察和判断的信号,如：颜色信号、电信号、荧光信号等,为消费者提供实时质量监控信息,本文综述了食品智能包装新鲜度指示剂的分类,包括CO₂敏感型指示剂、TVB-N敏感型指示剂、pH敏感型指示剂及其成型工艺,涵盖了食品智能包装新鲜度指示剂的应用,旨在为食品智能包装新鲜度指示剂的发展提供参考,为食品损失和污染等传统包装问题提供了潜在的解决方案,其后续发展应朝着方便、快捷、实时显示食品质量变化的方向,以减少因食品质量差和安全问题带来的健康问题,研发新型的新鲜度指示剂,有利于将智能包装技术推广至更多的包装应用中,为产品质量提供理论指导与技术支撑。     

Gloss of thermally densified alder (Alnus glutinosa Goertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) wood veneers

Thermo-mechanical densification of wood is performed to improve physical and mechanical properties of wood. During this treatment aesthetic properties of wood, including gloss, also change. Therefore, the purpose of this study was to determine the effect of short-term thermo-mechanical (STTM) densification in different wood species (alder (Alnus glutinosa Goertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.)) on their gloss changes. Commercial wood veneers were densified in a hot plate press for 4 min at temperatures of 100, 150 and 200 °C, pressures of 4, 8 and 12 MPa. Gloss was evaluated at 20°, 60° and 85° angles of incident light using PICO GLOSS 503. Gloss measurements showed an enhancement of aesthetic properties of densified wood. Findings of this study indicated that both densification temperature and pressure have a significant effect on wood gloss. Gloss values of densified wood increased with increasing densification temperature and pressure for all investigated species. Compared to non-densified wood, gloss (85°) values (across/along the grain) for alder, beech, birch and pine increased after treatment to 2109.1/2376.9, 1728.6/2311.1, 2787.5/3000, and 2591.7/1216.7 %, respectively. The greatest gloss values were recorded at 200 °C and pressure of 12 MPa for all tested angles of incident light and for all densified wood samples. Gloss changes for birch were the highest, but the glossiest surface was observed for pine among all investigated species after wood densification.     

颜色指示型智能包装监测生鲜肉新鲜度的研究进展

颜色指示型智能包装作为一种新型的包装方式,可以帮助消费者更加直观地判断生鲜肉制品新鲜程度,具有尺寸小、成本低和直观准确等优点。本文在介绍颜色指示型智能包装原理的基础上,对指示剂类型和基材进行综述,同时系统论述了其在生鲜肉新鲜度监测中应用的研究进展,指出该包装方式在实际应用中存在的局限性,并对其未来的发展进行展望,以期为颜色指示型智能包装在监测生鲜肉新鲜度中的应用和推广提供理论参考。     

三甲胺和二甲胺表征冷鲜羊肉新鲜度

三甲胺和二甲胺是冷鲜肉腐败过程中产生的典型挥发性胺,具有腐败气味,是致癌物亚硝胺的前体物质,具备表征新鲜度的潜力。为探究羊肉贮藏过程中三甲胺、二甲胺含量与新鲜度指标的变化规律,明确三甲胺或二甲胺作为潜在指标表征冷鲜羊肉新鲜度的可行性,以羊背最长肌为研究对象,研究（0.0±0.5） ℃贮藏条件下冷鲜羊肉包装及肉中三甲胺和二甲胺含量与色泽、菌落总数、总挥发性盐基氮（total volatile basic nitrogen,TVB-N）含量、硫代巴比妥酸反应物（thiobarbituric acid reactive substance,TBARs）值等新鲜度相关指标之间的相关性。结果表明：冷鲜羊肉贮藏期间色泽、菌落总数、TVB-N含量等新鲜度指标呈现上升趋势,肉新鲜度逐渐下降,在（0.0±0.5） ℃空气密封包装条件下,冷鲜羊肉货架期长达17 d;肉中及包装中三甲胺含量均与菌落总数、TVB-N含量、TBARs值呈显著正相关（P＜0.05）,相关系数分别为0.86、0.75、0.74和0.92、0.96、0.95;肉中及包装中二甲胺含量与菌落总数、TVB-N含量、TBARs值相关性稍差,相关系数分别为－0.85、－0.58、－0.60和0.90、0.74、0.65。上述结果表明,三甲胺和二甲胺均具备表征冷鲜羊肉新鲜度的潜力,而与包装中二甲胺含量相比,包装中三甲胺含量与菌落总数、TVB-N含量、TBARs值的相关系数相对较高,确证了三甲胺可以作为冷鲜羊肉在该条件下的标志性气体物质,具备表征冷鲜羊肉新鲜度的能力。     

Freshness assessment of gilthead sea bream (Sparus aurata) by machine vision based on gill and eye color changes

The fish freshness was evaluated using machine vision technique through color changes of eyes and gills of farmed and wild gilthead sea bream (Sparus aurata), being employed lightness (L^*), redness (a^*), yellowness (b^*), chroma (c^*), and total color difference (ΔE) parameters during fish ice storage. A digital color imaging system, calibrated to provide accurate CIELAB color measurements, was employed to record the visual characteristics of eyes and gills. The region of interest was automatically selected using a computer program developed in MATLAB software. L^*, b^*, and ΔE of eyes increased with storage time, while c^* decreased. The a^* parameter of fish eyes did not show clear a trend with storage time. The L^*, b^*, and ΔE of fish gills increased with storage time, but a^* and c^* decreased. Regression analysis and artificial neural networks approaches were used to correlate the eyes and gills color parameters with the time of storage and a strong correlation was found between color parameters and storage day. Gills color changes were more precise than those found for eyes in order to evaluate the fish freshness. However, the gills cover should be removed for taking the images and thus, the method is destructive and time-consuming. Therefore, the color parameters of fish eyes can be used as a green, low cost and easy method for fast and on-line assessing of fish freshness in food industry.     

猪肉新鲜度指示标签的制备及应用

基于猪肉在腐败过程中产生的挥发性含氮化合物会使包装中气体酸碱性发生变化的原理,以甲基纤维素和聚乙二醇-6000为基材,添加溴甲酚紫、溴百里酚蓝等酸碱指示剂,最终制得6 种方便、无损的新鲜度指示标签。将标签置于不同质量浓度的NH3环境中,6 种标签的颜色均发生显著变化,且随NH3质量浓度的增加而差异变化明显;将标签应用于生鲜猪肉贮存中,通过测定4 ℃条件下不同贮存时间猪肉各项腐败指标以及指示标签的颜色变化,探究其用于监测生鲜猪肉新鲜度的可行性。结果表明：初始pH值为4.24的溴甲酚紫指示标签可较好地区分出猪肉的3 个新鲜度等级;利用此标签的颜色测定数据建立偏最小二乘模型,对挥发性盐基氮含量和菌落总数进行预测的回归系数（R2）均大于0.92,通过标签颜色变化可以判断猪肉新鲜度。     

Nondestructive Prediction of Tilapia Fillet Freshness During Storage at Different Temperatures by Integrating an Electronic Nose and Tongue with Radial Basis Function Neural Networks

This study developed principal component analysis and radial basis function neural networks (PCA-RBFNNs) for predicting freshness in tilapia fillets stored at different temperatures by integrating an electronic nose and electronic tongue. Total volatile basic nitrogen (TVB-N), total aerobic counts (TAC), and K value increased at 0, 4, 7, and 10 °C, while sensory scores decreased significantly. The electronic nose and tongue acquired the volatiles and dissolved chemical compounds in the stored samples. Gas chromatography-mass spectrometry (GC-MS) verified the changes in gas species and contents in fillets stored for different periods of time at different temperatures. PCA-RBFNNs based on data fusion were developed and presented good performance for prediction of TVB-N, TAC, K value, and sensory score in tilapia fillets. The established PCA-RBFNNs based on feature variables of the electronic nose and tongue is a promising method to predict changes in the freshness of fillets stored from 0 to 10 °C in the cold chain.     

Polypropylene/Montmorillonite Nanocomposites Containing Nisin as Antimicrobial Food Packaging

Antimicrobial nanocomposites prepared with polypropylene, montmorillonite, and nisin were developed as food packaging material. Nisin was incorporated at 1, 2.5, and 5 % (w/w) and the characterization included antimicrobial, mechanical, thermal, barrier, and structural properties. Composite films inhibited the Gram-positive bacteria Listeria monocytogenes, Staphylococcus aureus, and Clostridium perfringens when tested on skimmed milk agar plates. Antimicrobial activity was released in food simulants after contact with the nanocomposites, increasing until 48 h in solutions containing the surfactant Tween 20 or acetic acid. The addition of nisin caused no significant modification in deformation at break values as compared with control films. However, results of tensile strength and Young modulus differed significantly among samples. The higher value for Young modulus was observed for films with 5 % nisin. Water vapor barrier properties were not significantly different among control and antimicrobial films, whereas oxygen permeability was higher for nanocomposites containing nisin. The nanocomposites tested had no significant differences in the melting temperature (165 to 167 °C), and the crystallization temperature ranged from 121 to 129 °C, with lower values for films containing 5 % nisin. Scanning electron microscopy showed that nanocomposites containing 1 and 2.5 % nisin present similar homogeneity to that of control films. Some film properties were affected after nisin incorporation in polypropylene/montmorillonite matrix but active antimicrobial films were obtained, showing suitable behavior as a food packaging material.     

An alternative freshness index method for modified atmosphere packaged abalone using an artificial neural network

An alternative freshness index method for abalone (Haliotis asinina) muscle packaged under atmospheric air (Air) and modified atmosphere (MA) of 40% CO₂: 30% O₂: 30% N₂ packaging conditions and stored at 2 ± 1 °C was developed. Biochemical indices covering pH, total volatile basic nitrogen (TVB-N), trimethylamine (TMA) and nucleotide degradation products, as well as instrumental texture and color of the packaged abalones, were determined. Sensory characteristics including odor, color and appearance were evaluated and then summarized into overall freshness scores (freshness index). The biochemical and instrumental analyses were then calibrated with the freshness index, using an artificial neural network algorithm. The neural network was shown to be capable of correlating biochemical and instrumental analyses with the freshness index. A useful prediction was possible, as measured by a low mean square error (MSE = 0.092) and a regression coefficient (R² = 0.98) between true and predicted data.     

The Release of Carotenoids from a Light-Protected Antioxidant Active Packaging Designed to Improve the Stability of Soybean Oil

An antioxidant active packaging was developed by coextruding two layers of high-density polyethylene (HDPE). Bags were made with the film in which the inner layer, designed to be in contact with food, contained marigold flower (Tagetes erecta) extract rich in carotenoids. The outer layer of the film was added with titanium dioxide (TiO₂) to decrease the effect of commercial lighting on the degradation of carotenoids. Four bilayer films were produced: added with TiO₂ and carotenoids, added with carotenoids, added with TiO₂, and with no additives at all (control film). Degradation of color and astaxanthin in the films was delayed by the addition of the TiO₂ when they were stored under commercial lighting at 25 °C. Bags made of these films produced an improvement on the soybean oil stability at 25 °C as a result of a synergic effect of light protection by TiO₂ and carotenoids release. This release was measured as diffusion coefficients of carotenoids from the films toward soybean oil at 10, 25, and 40 °C (2.10–19.26?×?10^?11 cm² s^?1) with activation energy of 53.66 kJ mol^?1. In conclusion, the combination of the two layers of HDPE added with TiO₂ and carotenoids introduced opacity and permitted to extend the active effect of the films in contact with soybean oil. Moreover, the effect of temperature on the diffusion of carotenoids showed that this new active packaging is able to exert its function in conditions of transport, storage, and commercialization of food.