Methods to Evaluate Fish Freshness in Research and Industry PDF

Review Methods to evaluate fish...

Review Methods to evaluate fish Knowledge of the various descriptors of properties freshness in research and that are encounteredin fish immediately after harvest or catch must be known as well as of the changesin prop- erties that take place over time2.This information can be gained by performing controlled storage experiments industry that extend from the time of harvest until spoilage. Freshness,loss of freshnessand spoilage can thus be monitored; once the dynamics and the rate of the vari- ous changes that occur have been measured, the next G. blafsdbttir, E. Martinsdbttir, step is to try to develop a model. The future aim is to use a model to determine when a samplewas harvested J. Oehlenschbger, P. Dalgaard, B. Jensen, or predict the remaining shelf life of an unknown sample.To achieve this aim, it is useful to combine sev- I. Undeland, I.M. Mackie, G. Henehan, eral measurementsobtained by different methodologies and correlate the findings with sensory assessments, J. Nielsen and H. Nilsen which are currently the most used method to evaluate fish freshness. Sensoryevaluation of fish freshness Current work in a European concerted action project ‘Evaluation Sensory evaluation is defined as the scientific disci- of Fish Freshness’ (AIR3 CT94-2283) focuses on harmonizing pline used to evoke, measure, analyse and interpret characteristics of food as perceived by the sensesof research activities in the area of fish freshness evaluation in sight, smell, taste, touch and hearing. Sensory testscan leading fish laboratories in Europe (see Box 1). The overall be divided into three groups: discriminative tests, which aim of the concerted action project is to validate methods for indicate whether there is a difference between samples; the assessment of fish freshness and to discuss the freshness descriptive tests; and affective tests’. Discriminative and criteria for fish commercialized within the European Union. descriptive tests are objective analytical tests in which a trained panel is used. Affective tests are subjective con- The project’s participants are working in subgroups studying sumer teststhat are basedon a measureof preference or sensory analysis, microbiology, volatile compounds, proteins, acceptance.The choice of method dependson the pur- lipids, adenosine triphosphate and physical measurements pose of the application of the sensory evaluation and with respect to fish freshness evaluation. In this article, the whether it is used in product development, quality con- trol, consumerstudiesor research.The most commonly different subgroups have summarized changes that occur in used descriptive tests are structured scaling for quality fish and methods to evaluate fish freshness as a first step to- assessmentand profiling for a detailed description of wards the definition of criteria for fish freshness. one or more attributes. Characteristicsensorychangesoccur in the appearance, odour, taste and texture of fish when they deteriorated.In Freshnessmakes a major contribution to the quality of Europe, the most commonly used method for the quality fish or fishery products. For all kinds of products, fresh- assessmentof raw fish in the inspection service and in ness is essential for the quality of the final product. the fishing industry is the EuropeanUnion scheme’.This Figure 1 depicts the relationship between quality and schemedoes not take into account differences between freshness,focusing on the different characteristics of speciesbecauseonly generalparametersare used.Alterna- freshnessas approached by the different subgroupsof tive scaling methods such as the quality index method the project. Freshnesscan be explained to some extent (QIM) have been suggestedh,‘,where the descriptions of by someobjective sensory, (bio)chemical, microbial and the individual gradesare precise, objective, independent physical parameters’,and can therefore be defined as an and primary rather than a cluster of terms. The QIM is objective attribute. basedon the significant sensoryparametersfor raw fish. The scoresfor all of the characteristics are then addedto give an overall sensoryscore,the so-calledquality index, G. blafsdbttir (corresponding author) and E. Martinsdbttir are at the which can alsobe used to predict storagelife. In the fish Icelandic Fisheries Laboratories, Skfilagata 4, 101 Reykjavik, Iceland (fax: industry, the grading of raw fillets alsooccurs. However, +354-5620740; e-mail: [email protected]). J. Oehlenschbger is at the Federal it is morecommon to cook fillets before carrying out sen- Research Center for Fisheries, Palmaille 9, D-22767 Hamburg, Germany. sory evaluation, and the Torry scheme”is the most com- P. Dalgaard, B. Jensen and J. Nielsen are at the Danish lnstltute for Fisheries monly usedscale for the freshnessevaluation of cooked Research, DTU Building 221, DK-2800 Lyngby, Denmark. I. Undeland is al fish, both in the fish industry and in researchlaboratories SIK, PO Box 5401, S-402 29 Ctiteborg, Sweden. I.M. Mackie is at the Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen. UK A62 9SB. throughout Europe. G. Henehan is at the Dublin Institute of Technology, Cathal Brugha Street, In the fish industry, a few highly specializedtrained as- Dublin 1, Ireland. H. Nilsen is at the Fiskeriforskning, PO Box 2511, N-9005 sessorsusually evaluate the freshnessof fishx. Guidelines Tromso, Norway. for the sensoryevaluation of fish and shellfishin inspection 258 Copwght 01997. Elsever Science Ltd. All r,ghts reserved. 0924.2244/97/$17.00 Trends in Food Science & Technology August 1997 [Vol. 81 PII: 50924-2244197)01049-2  BOX1. institutes participating in the concerted action project ‘Evaluation of Fish Freshness’ and principal scientists (contact persons) Denmark J.V. McLaughlin University of Dublin Trinity College, Dublin jette Nielsen Fax: +353-l-6793545 Danish Institute for Fisheries Research, Copenhagen E-mail: [email protected] Norway Faroe Island Nils K. SSrensen DAnial K. Christiansen Norwegian institute of Fisheries and Aquaculture, TromsG Food and Environmental Institute, Thorshavn E-mail: [email protected] E-mail: [email protected] Portugal Finland Paul0 Vaz-Pires Tapani Hattula ES6 - Escola Superior de Biotechnologia, Port0 VTT Biotechnology and Food Research, Helsinki E-mail: vazpiresBesb.ucp.pt E-mail: [email protected] Maria L. Nunes France IPIMAR - lnstituto de lnvestigacao das Pescas e do Mar (Research Institute for Fisheries and Sea), Lisbon ]&I Fleurence E-mail: [email protected] or Fax: +351-l-3015948 IFREMER - French Research Institute for the Exploitation of the Sea, Nantes E-mail: [email protected] Javier Borderias Germany Ins&to del Frio, Madrid J&g Oehienschlager E-mail: [email protected] Federal Research Center for Fisheries, Hamburg Fax: +49-403-8905262 Sweden lngrid Undeland Greece SIK -The Swedish Institute for Food Research, CGteborg George-John E. Nychas E-mail: [email protected] Agricultural University of Athens, Athens E-mail: [email protected] The Netherlands Iceland Joop B. Luten RIVO-DLO - Netherlands Institute for Fisheries Research, Cudrun blafsdbttir or Emilia Martinsdbttir IJmuiden Icelandic Fisheries Laboratories, Reykjavik E-mail: [email protected] E-mail: [email protected] or [email protected] Ireland UK Marlene Proctor Ian Mackie Dublin Institute of Technology, Dublin Rowett Research Institute, Aberdeen E-mail: [email protected] Fax: +44-l 224-716629 and regulation services9are currently under discussion Microbial methods by the Codex Committee on Fish and Fishery Products. The activity of microorganismsis the main factor lim- The future aim is to usetrained panelsto evaluate raw iting the shelf life of fresh fish. An estimationof the total materials and products, asa part of the quality assurance viable counts (TVC) is usedas an acceptability index in programme performed by fish processing companies. standards,guidelinesand specifications. The objective of The sensory evaluation of food hasbeen describedwith the collaborative work of this subgroup is to study the the establishment of quality control programmes in application of microbial methods for the evaluation of mind’“. In research laboratories, it is common to have the freshnessof fish from different countries and stored trained panels with proven skills, complete sensory under different conditions of temperature (0-1O’C) and evaluation facilities and computerized data sampling. atmosphere(air, vacuum or modified-atmospherepack- Some of the food research laboratories studying the aging). The remaining shelf life is used as a definition quality of fish have received an accreditation for their of fish freshness. sensory evaluation methods (e.g. VTT, Finland) based Newly caught fish contain a diversemicroflora. TVC of on the EN 45001 and the ISO/IEC Guide 25l’. The IS0 102-106cfu/gare usualon whole fish and cut fillets. Dur- standards describe both the selection and training of ing chill storage,psychrotolerant microorganismsare se- panellists. lected; thus, differential counting of thesemicroorganisms Trends in Food Science & Technology August 1997 [Vol. 81 259  from -0.85 to -0.99 were reported both for aerobically stored and packed fresh fish15,1h. Photobacterium phosphoreum was identified as the SSO in some modified- atmosphere packed (MAP) fish. This microorganism can be specifically de- tected using a conductance technique”, and a good correlation was found be- tween this SSO and the remaining shelf life of MAP cod fillets. Clearly, microbial methods can pro- vide useful measures of fish freshness; however, the most promising results have been achieved with relatively slow detection methods such as plate count and other growth techniques that involve a period of incubation. Therefore, the development of practical techniques for the concentration and separation of microorganisms from fresh fish will be important in improving the response time, sensitivity and specificity of both the classical and new rapid methods. At the point of sensory rejection, the TVC of fish products are typically vow, appearan lo’-10xcfu/g. Nevertheless, standards, guidelines and specifications often use much lower TVC as indices of accept- ability. In a recent European study by consumers, fish was assumed ‘not to be in a good enough condition to be stored for long’ when TVC were lO’cfu/g Fig. 1 (Ref. 18). Microbial criteria based on Relationship between quality and freshness. Quality is a function of freshness; freshness is essential for low TVC such as 106cfu/g are problem- quality but it is not a priori a quality factor. The upper ‘quality’ circle comprises the factors atic to use because a correlation between that contribute to quality, and the lower ‘freshness’ circle details the various approaches used to TVC and the remaining shelf life is as- evaluate fish freshness. The K value is defined as the ratio of the sum of inosine and hypoxanthine sumed but generally not known. There- fore, it has been suggested that microbial concentrations to the total concentration of adenosine triphosphate (ATP) metabolites. methods for the evaluation of fish fresh- TMA, trimethylamine; TVB, total volatile bases. ness are developed together with math- ematical models that express the effects was suggested as a measure of fish quality in early studies. of storage conditions such as temperature and atmos- More recently, the bacterium Shewanella putrefaciens, phere on the correlation between microbial numbers and which produces hydrogen sulphide, was determined as the remaining shelf life. Thus, rapid microbial methods could specific spoilage organism (SSO) of some chilled fresh be useful not only at the time of analysis but also later fish. This microorganism can be enumerated in iron- on during storage of the fish. containing agar, and correlation coefficients as high as -0.97 were achieved when comparing log numbers of S. Volatile compounds as indicators of freshness and putrefaciens with the remaining shelf life of aerobically spoilage stored fish, as determined by sensory evaluation. Owing Odour is one of the most important parameters used to to the selection of microorganisms in chilled fish, the evaluate fish freshness. Measurements of characteristic correlation between SSO and freshness is usually higher volatile compounds can be used to monitor the freshness or than between TVC and freshness’2-15. spoilage stage of fish. The volatile compounds contribut- Most marine fish spoilage bacteria reduce trimethyl- ing to fish odour can be divided into three groups based on amine oxide to trimethylamine (TMA), and this reduc- their origin, as illustrated in Fig. 2. Various compounds tion is used as the basis for several rapid, automated have been suggested as indicators of spoilage. Classical conductance assays. The time required to detect changes chemical methods for the analysis of total volatile bases in conductance showed good correlation with the fresh- and TMA (trimethylamine) have been used for the de- ness of various fish species, and correlation coefficients termination of fish freshness in the industry’. 260 Trends in Food Science & Technology August 1997 [Vol. 81  Headspace methods for the analysis I of volatile compounds involve the col- lection and concentration of the vola- tiles for subsequent chromatographic separation to identify and quantify the separated compounds. Extremely vola- tile, low molecular weight compounds can be analysed by static headspace methods19. More efficient, dynamic planty, cucumber- and headspace methods are necessary for mushroom-like odours collecting and concentrating less-volatile compoundszO such as those contribut- ing to ‘fresh fish’ and ‘oxidized’ odours. Higher-boiling compounds require even more efficient isolation methods such as solvent extraction with organic sol- vents or supercritical carbon dioxide”. Other approaches are simultaneous dis- tillation and extraction in the gas phase” Fig. 2 or high-vacuum distillation2’. Once the Categorization of fish odours and the volatile compounds that contribute to the characteristic odour of volatiles have been trapped, they are fresh, spoiled and oxidized fish. TMA, trimethylamine. transferred by thermal desorption or solvent extraction to a chromatograph for separation and identified by appropriate detectors. activity. However, in the caseof the myofibrillar proteins, Although instruments with a high degree of auto- the cytoskeletal proteins (ar-actinin and cl-connectin) mation are available for the trapping and chromatography undergo proteolysis. The Z-disc region of the myofibril steps, the complexity, cost, and lengthiness of volatile appears to be destroyed by the action of proteases, analysis methods make them suitable only for special- releasing a-actinin. It has also been shown that (Y- ized research and analytical laboratories. connectin, an extremely high molecular weight protein The rapid assessment of volatile compounds in food that runs longitudinally along the myofibril, is broken using arrays of gas sensors, so-called electronic noses, is down to @connectin by proteolysisz8.However, changes of increasing interest2”, and an instrument with electro- have not been reported in the major contractile proteins chemical gas sensors has been developed for the rapid de- myosin and actin. The collagen proteins are relatively tection of fish freshnes@. A validation of an electronic minor components of muscle and, despite conflicting nose designed to detect spoilage in minced beef showed evidence, it is generally agreed that some degree of that its reproducibility, repeatability and discriminative breakdown by collagenasestakes placez9. power need to be improvedz6. However, assessment of the It can be concluded that, in the main, the proteins of quality of salmon (Salmo salar) and whiting (Merlangius muscleare largely unaffected during postmortemstorage, merlangus) using an electronic nosehasshown that sam- and that the softening of muscle is due not to the break- plescan be classifiedinto three sensorycategories,namely down of myofibrils but to proteolytic digestion of minor good, acceptable and not acceptable (J. Luten and cell componentsthat link the major structural units to- P. Scheerman,pers.commun.;M. EtienneandJ. Fleurence, gether’OT3’. These changescan be observed by light and unpublished). electron microscopy and can be measuredto some ex- For the future development of rapid gas sensortech- tent by texturometers. There are, however, difficulties as- niquesfor fish freshnessapplication,it will be necessaryto sociatedwith the use of texturometers on whole muscle define standardmethodsbasedon gassensorsand to vali- becauseof the inherent nature of muscletissues.Changes date their usagefor detecting the characteristic volatile in the size of proteins can be determinedby electrophor- compoundsthat areindicative of the freshnessstageof fish. etic and chromatographic techniques, but these tech- niques are not suitable for industrial use. Similarly, the The effects of postmortem storage of fish on proteins isolation of proteins involves lengthy extraction and frac- After water, which accountsfor -80% (w/w), proteins tionation procedures, which are only suitable for a re- are the major constituents (15-20%) of fish flesh. The search laboratory. However, once isolated, collagens, proteins found in muscle can be broadly categorized as: for example, can be characterized using relatively sim- water-soluble or sarcoplasmicproteins; contractile pro- ple techniques to determine their solubility properties teins (e.g. myosin and actin), which are extractable in and thermal denaturation temperatures. solutions of relatively high ionic strength, and proteins To date, there are no rapid methods for determining that are insoluble in solutions of either high or low ionic changesin muscle proteins during postmortem storage; strength (collagens)“. furthermore, until it is possible to detect the releaseof On postmortem storage, the sarcoplasmic proteins proteolytic enzymes in muscle tissue, there is little undergo no change in either composition or enzymatic prospect of the emergenceof methods that are suitable Trends in Food Science & Technology August 1997 [Vol. 81 261  for industry. However, instrumental methods of measur- ATP as a chemical indicator of freshness ing texture show more promise (see ‘Physical measure- A chemical index of fish freshness is appealing be- ments’, below). cause it is quantifiable, objective and lends itself to automation. ATP alone cannot be used because it is so Measurements of lipid oxidation in fish rapidly converted to IMP. Concentrations of its inter- The highly unsaturated lipids of fish easily become oxi- mediate degradation products rise and fall, making them dized, resulting in alterations in smell, taste, texture, colour unreliable indexes of freshness. As a result, attention and nutritional value. Oxidation starts immediately after has focused on inosine and hypoxanthine, the terminal catch, but becomes particularly important for shelf life catabolites of ATP. Inosine accumulates in some species only at temperatures cO”C~~, when oxidation rather than of fish whereas hypoxanthine accumulates in others as microbial activity becomes the major spoilage factor. terminal catabolites”. The initiation of lipid oxidation arises from various In the literature, the extent of ATP degradation is ex- early postmortem changes in fish tissues. These changes, pressed as the K value, which is defined as the ratio of which disturb the natural balance between antioxidants and the sum of inosine and hypoxanthine concentrations to pro-oxidants, include the accumulation of active oxygen the total concentration of ATP metabolites. A fresh fish species, the activation of haemoproteins, an increase in will have a low K value. There is abundant evidence in free iron and the consumption of antioxidants”. the literature to suggest that the K value is a reliable indi- Once initiated, the extent of lipid oxidation can be cator of freshness that is applicable for frozen fish, smoked followed using either the reactants or the products. fish and fish stored under modified atmospheres39,4”. Measurements of oxygen consumption can be moni- A shortcoming of the K value as a freshness index tored with an oxygen electrode34, whereas the loss of is its dependence on a variety of variables”‘. It varies fatty acids and antioxidants can be measured using gas between species owing to differences in rates of ATP chromatography (GC) and high-performance liquid degradation. It also varies with postmortem time and chromatography (HPLC)35. The peroxide value is the temperature storage conditions, handling conditions42 most common measure of lipid hydroperoxides, also and method of ki1143.Thus, a profile of K value versus called primary lipid oxidation products. Other methods time must be established for each species and its spe- are HPLC in combination with, for example, chemi- cific handling and storage conditions before K-value luminescence detection36 or, if conjugated double bonds measurements can be used to evaluate freshness. are present, simple spectrophotometry37. The primary products easily break down into secondary products, K-value measurement such as aldehydes and ketones. The volatile nature of Following acid extraction and neutralization, metab- these compounds makes them suitable for both GC and olites are separated by ion-exchange chromatography or sensory analysis. Aldehydes can also be measured us- HPLC and quantified by their absorbance. Although ing several calorimetric methods, such as the method other methods have used enzymatic assays and biosen- that determines the anisidin value, or the widely used sors3y, it is generally agreed that the HPLC method is thiobarbituric-acid-reactive substances (TBARS) test3’. the most reliable. Tertiary products, arising from interactions between oxi- The use of ATP metabolites as freshness indexes is a dizing lipids and nitrogen-containing compounds, can research technique that is not widely used in industry be followed using fluorescence spectroscopy or, in later owing to the time and expense involved in the measure- stages, by visual assessment or colorimetry38. ments. The future development of this approach requires All of these techniques are used in research, but only cheap, reliable and rapid methods for ATP catabolite a few of them are routinely applied in the fish industry, measurement. because they are time-consuming and require expensive laboratory equipment and trained personnel. To monitor Physical measurements the progression of lipid oxidation, it is important to use Physical changes in fish that result in the decline of more than one method, especially when comparing dif- freshness are mainly related to structure and colour. ferent types of fish products. Otherwise, the instability Texture measurements can be used to determine struc- of the various oxidation products makes the results tural changes. The instruments used are texturometers difficult to interpret and extremely misleading. fitted with a wide variety of accessories for the different types of analyses. The texture of whole fish muscle is ATP as a freshness indicator in fish difficult to measure because it lacks a uniform structure, Following death, ATP is rapidly degraded to inosine making the preparation of samples of standard size diffi- monophosphate (IMP) by endogenous enzymes (auto- cult. This has led to a variety of sample preparation pro- lysis). The further degradation of IMP to inosine and cedures and hence variable results and applications for hypoxanthine is much slower, and is catalysed mainly the different methods, Comparisons of texture measure- by endogenous IMP phosphohydrolase and inosine ribo- ments of fish with sensory analysis have shown good hydrolase, with a contribution from bacterial enzymes correlation in some cases44.45. as storage time increases. The degradation of ATP was Another means of assessing the structure of fresh fish found to parallel the perceived loss of freshness of fish is microstructural characterization of the fish muscle. as determined by trained analysts”. Different techniques are available: macroscopy [low 262 Trends in Food Science & Technology August 1997 [Vol. 81  Box 2. Conclusions and future aims for fish freshness evaluation. Sensory evaluation is currently the most important method for freshness (2-10 times) magnification], light microscopy, confocal evaluation in the fish sector. The trend is to standardize sensory evaluation laser scanning microscopy, scanning electron micros- by improving the methodologies and training of panels to make sensory copy and transmission electron microscopy. Structural evaluation an objective measurement. changes to fish collagen during the postmortem period l The development of microbial methods for evaluation of fish freshness and their effects on further processing have been de- together with mathematical models expressing the effects of storage condi- scribed by Bremner 46. Weakening of the pericellular con- tions (temperature and atmosphere) on the growth of relevant spoilage nective tissue has been shown to be one of the reasons microorganisms has been suggested. for postmortem tenderization of fish muscle”‘. Postmortem l The rapid assessment of volatile compounds in fish using gas sensors to changes to the microstructure of cod and salmon also af- determine freshness is of increasing interest. fect the liquid-holding capacity4*. To date, there are no rapid methods to determine changes in muscle Changes in fish freshness can also be determined by l proteins during postmortem storage. measuring the electrical properties of the fish muscle. Three different instruments are available to measure the l Most of the techniques that have been described to monitor lipid oxidation change in electrical properties: the Torrymeter (Distell are suitable only for research purposes, and few are routinely applied in the Industries Ltd, Fauldhouse, West Lothian, UK), the fish industry. To monitor the progression of lipid oxidation, it is important to Fishtester VI (IT) (Intellectron International Electronics, use more than one method, especially when comparing various types of fish products. Hamburg, Germany) and the RT-Freshness Grader (RT Rafagnataekni, Reykjavik, Iceland), which all show good l The use of ATP (adenosine triphosphate) metabolites as freshness indexes is correlation with sensory scores of fish freshness, when a research technique that is not widely used in industry. The future trend used within their applicable range of operation49,5k52. is the development of rapid techniques for the measurement of ATP These meters cannot be used with thawed fish or fish metabolites. that have been stored in chilled seawater, and their use l The following physical measurements provide information on parameters for fillets is limited to a few days; water-ice with a high that are related to fish freshness. However, none of these methods is suffi- salt content and mechanically damaged fish cause erro- cient to determine unambiguously whether a fish is fresh. neous results. The advantage of electrical testers is their - It is likely that time-temperature indicators will gradually be introduced immediate response and their suitability for field use into the wholesale and retail food chain, starting with temperature-sensitrve, and for use by personnel without previous experience. high-value foods such as fish. Changes in fresh fish can be related to changes in - Texture measurements of fish have been compared with sensory analvsis, colour measurements. Instrumental colour measurements and some studies have shown good correlation. are becoming important in quality control in the food in- dustry. Advanced technologies have simplified the per- - Changes in the microstructure of fish muscle have been related to the post- mortem tenderization and liquid-holding capacity of fish muscle. formance of these methods5’. Recently, the effects of icing and storage temperatures on salmon quality attrib- - Changes in the freshness of fish can bemonitored by measuring the electrical utes, and the postmortem changes in colour of carp and properties of fish muscle. The advantage of electrical testers is their immedi- trout were studieds”*‘j. However, there is a need for the ate response and their suitability for field use and for use by personnel with- standardization of instrumental colour measurements. out previous experience. During the past few years, spectroscopic methods have - Changes in colour measurements can be related to changes in fresh fish. gained importance in the evaluation of food quality pa- - Spectroscopic methods have recently gained importance in the evaluation rameters. The advantages of spectroscopic methods are of food quality parameters. their ability to provide rapid analysis and simultaneous ~.- evaluation of several parameters, and their potential for on-line or at-line use. These techniques have also been foods to indicate the time-temperature history of the introduced into seafood analysis. Fluorescence spectra food. The time-temperature history is recorded by using can be used to indicate whether a fish has been frozen, some biological, physical or chemical process that de- and the intensity of the fluorescence from fish muscle pends on time and temperature. The temperature record decreases with storage time on ice5h. Nagashima et al.“’ can be usedto develop appropriate modelsof the effects reported the use of absorbancespectroscopy in the UV- of bacterial or enzymatic spoilage on shelf life58,59. It is visible range to determine the freshnessof yellowfin likely that ITIs will gradually be introduced into the tuna. Although spectroscopic methods have so far not wholesaleand retail food chain, starting with temperature- proven sufficient to characterize fully the properties of sensitive, high-value foods such asfish. fresh fish, developments in instrumentation and the Although there are many different physical measure- techniquesusedto evaluate spectral data are likely to fa- ments that provide information on parametersrelated to cilitate the collection of more information on the charac- fish freshness,asdiscussedabove, none of thesemethods teristics of fish. An example of this is the preliminary is able to determine unambiguously whether a fish is researchperformed at Fiskeriforskning in Norway, which fresh or not. indicates that the application of near-infrared spectros- copy may reveal information on the storagetime of fresh Future aimsfor fish freshnessevaluation fish. The overall conclusions and future trends for the Time-temperature indicators (TITS) are devices or methods of fish freshness evaluation that have been materials that can be attached to, or incorporated into, reviewed in this article are summarized in Box 2. The Trends in Food Science & Technology August 1997 [Vol. 81 263  future aim is to combine different standard methods that 16 Gibson, D.M. and Ogden, I.D. (1987) ‘Estimating the Shelf Life of Packed Fish’ use rapid measurement techniques with a mathematical in Seafood Quality Determination (Kramer, D.E. and Liston. J., eds). pp. 437-451, Elsevier model to predict the freshness, number of days posthar- 17 Dalgaard. P., Mejlholm, 0. and HUSS, H.H. (1996) ‘Conductance Method for vest or remaining shelf life of an unknown fish sample. Quantitative Determinatron of Photobacterium phosphoreum in Fish Products’ Such a model could complement sensory analysis for in I. Appl. Bacferiol 81, 5764 fish freshness evaluation in the near future. However, 18 Anon. (1995) Parallel Food Testing in the European Union: Fish, International Consumers Research &Testing Limited, London, UK more research is needed; this should include controlled 19 Mile, C. and Crosch, L\‘. !I 995) ‘Detection of Odor Defects rn Boiled Cod and storage experiments of different species of fish, to Trout by Gas Chromatography Olfactometry of Headspace Samples’ rn obtain valid parameters for use in mathematical models. /. Agric. Food Chem. 43,459-t62 20 Refsgaard, H.H.F., Brockhoff, P.M. and Jensen, B. 11996) ‘Sensory and Chemical Changes of Salmon Durrng Frozen Storage’ in FfavourScience. Contributing coauthors Recent Developments [Taylor, A.]. and Mottram, D.S.. eds), pp. 344-347, This review article is a collaborative work of the Royal Society of Chemrstry, Cambridge, UK participants of the concerted action project ‘Evaluation 21 Snyder, J.M. and King, J.W. (1994) ‘Analysrs of Volatile Compounds From Supercritical Extracted Soybeans by Headspace Gas Chromatography and of Fish Freshness’ (AIR3 CT94-2283) funded by the Thermal Desorption oi a Polymer Adsorbent’ in /. SC;. food Agric. AIR programme of the European Union. Special thanks 64,257-263 are due to the following, who have contributed to 22 Chung. H.Y. and Cadwallader, K.R. (1994) ‘Aroma Extract Dilution Analysrs of Blue Crab Claw Meat Volatiles’ in I. Agric. FoodChem. the preparation of this manuscript: J. Luten, M. Etienne, 42,2867-2870 K. Randell, M. Proctor, P. Nesvadba, R. Schubring, 23 Mile, C. and Crosch, W. 11996) ‘Changes in the Odorants of Boiled Salmon K. Heia, J. Borderias, K. Nilsson and B. Jorgensen. and Cod as Affected by the Storage of the Raw Material’ in 1. Agnc. Food Chem. 44, 236662371 24 Mielle, P. (1996) “‘Electronrc Noses”: Towards the Objective Instrumental References Characterization of Food Aroma’, in Trends Food Sci. Technol. 1 Howgate, P. 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(19941 ‘Shelf Life oi Iced-stored Redfish, Sebastes marinus and Impact of Temperature Abuse on Meat and Poultry Products’ in / Food and S. menteila’ m Inf. /. Food SC;. Technol. 29, 303-313 Sai 15(31,201-227 Any suggestions? Trends in Food Science & Technology is now the 3rd most highly cited journal in the field of food science (SC//ournal Citation Reports@ 1996). Although articles published in TIFS are usually specially invited, we welcome ideas from readers for articles on new and developing areas. A brief synopsis of the proposal should be sent to the Editor, who can provide detailed information on manuscript preparation. Reviews focus on promising areas of food research that are advancing rapidly, or are in need of re-review in the light of recent advances or changing priorities within the food industry. Features are similar in style to reviews, highlighting specific topics of broad appeal to the food science community. 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