Ricardo I. Pérez-Martín

Optimization of the thermal processing of conduction-heated canned foods: Study of several objective functions

Abstract A new algorithm, ICRS/DS, for the solution of fixed terminal time optimal control problems is presented. It is based on the combination of a robust parameterization of the control function and a computationally efficient nonlinear programing algorithm of unconditional convergence. convergence. This algorithm is applied to the optimization of the thermal processing of conduction-heated canned foods, attaining for the first time optimum temperature-time profiles for different objective functions: the maximum overall retention of a nutrient, the maximum retention of a quality factor at the surface of the solid, and the minimum process time. A significant increase of quality factor retention at the surface is achieved with a variable retort temperature profile as against the optimum constant-temperature profile. In the case of process time minimization with a constraint of retention of a quality factor at the surface, the processes with a variable retort temperature show significant advantages over the traditional constant-temperature processes.

Challenges in the identification of species of canned fish

Abstract The identification of fish species becomes a problem when the usual identifying characteristics are removed on processing and only a portion of flesh is available. When the flesh is raw or cooked under normal conditions, the species is readily established by electrophoresis of the muscle proteins. The procedure cannot be used for heat-sterilised canned fish as the proteins are severely denatured. DNA is also degraded but techniques are now available for targeting and amplifying species-specific fragments. The amplified products can then be analysed by a range of techniques some of which are suitable for food control laboratories.

Fish species identification in seafood products

Abstract The opening up of international food markets has resulted in the establishment of new regulations that affect different aspects of labels, including ingredients lists. Many fish species sold around the world, especially those caught far away from the countries in which they are consumed, need to be processed on board ship, which may result in the subsequent removal of characteristics used for their classification (head, fins, internal organs). The biochemical characterization of fish species could be achieved using proteins or DNA sequences as species-specific markers. Since different seafood products undergo different processes, the method of analysis has to be chosen according to the modifications undergone by fish constituents during processing. As DNA molecules are more stable than proteins to various processes, including thermal treatment, DNA analysis appears to be a promising method for fish species identification.

Development of a sodium dodecyl sulfate-polyacrylamide gel electrophoresis reference method for the analysis and identification of fish species in raw and heat-processed samples: a collaborative study.

A collaborative study was carried out in seven European labs with the aim of achieving a sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) standard operation procedure to identify fish species in raw and cooked samples. Urea and SDS‐containing solutions were evaluated as extractants. Several preelectrophoretic operations — such as treatment with RNase/DNase, ultrafiltration and desalting — and up to ten types of gels and three SDS‐PAGE systems were considered. The SDS‐containing solution allowed a higher protein extractability than urea. Unlike urea extraction, SDS extraction seemed not to be influenced so much by the state of the sample (raw, cooked at 60oC, cooked at 85oC). Desalting, ultrafiltration or treatment with RNase/DNase did not improve the discriminatory power of the protein patterns. Commercial homogeneous 15% ExcelGels, especially when they were silver stained, yielded good results and afforded higher reproducibility, thus allowing a better matching of results among the laboratories participating in this collaborative study. Under the optimized technical conditions described above, all the fish species tested, either raw and cooked, yielded reproducible and discriminant species‐specific protein patterns.

Denaturation of fish proteins during frozen storage : role of formaldehyde

Proteins of fish muscle undergo chemical and physical changes during frozen storage which may result in, under certain conditions (i.e. long periods of storage, poor freezing practices, temperature fluctuations, etc), loss of quality, reflected mainly by an unacceptable texture as well as an undesirable flavour, odour and colour. In frozen gadoid fish species, most of these changes are caused by the production of formaldehyde in the muscle. Formaldehyde is produced, along with dimethylamine, by the enzymatic reduction of trimethylamine oxide (TMAO). Many aspects of formaldehyde production by TMAO demethylase (TMAOase) have been studied throughout the last decade. In addition, different approaches have been used to investigate the effect of formaldehyde production on protein denaturation and the associated muscle textural changes. Some insight into the reaction between protein and formaldehyde has clarified the possible mechanism of formaldehyde-mediated denaturation. However, evidence of covalent bonding between proteins and formaldehyde, to form crosslinks, has not explained fully the changes observed in fish proteins during frozen storage. The study of cold-induced denaturation of proteins might give new clues for further investigation of the problem. The implications of formaldehyde in toxicological and nutritional issues is also reviewed, as general concern about the safety of food products is a growing field in food science. Finally, different approaches have been proposed to avoid the detrimental action of formaldehyde during frozen storage of gadoid fish; they are some of the practical applications of the knowledge acquired after years of study of different workers in the field.

Fish species identification in canned tuna by PCR-SSCP: validation by a collaborative study and investigation of intra-species variability of the DNA-patterns

Analysis of single strand conformation polymorphism (SSCP) of an amplicon (123 bp) obtained by polymerase chain reaction (PCR) of the mitochondrial cytochrome b gene was used to identify the fish species in canned tuna. Single-stranded DNA (ssDNA) was separated by polyacrylamide gel electrophoresis, and visualised by silver staining. The reliability of the method was tested by a collaborative study in which eight European laboratories participated. Seven unknown samples (five from individual species and two mixtures of two tuna species) of canned tuna had to be identified by comparison with reference material. From a total of 72 cases, 65 (90.3%) were assigned correctly. Intra-species variability of SSCIP patterns was found in the case of Katsuwonus pelamis and Sarda sarda. As specimens from various fishing grounds gave two or three different patterns of ssDNA, the possibility of some variability of the DNA patterns has to be considered in SSCP analysis of these species.

Species identification of smoked and gravad fish products by sodium dodecylsulphate polyacrylamide gel electrophoresis, urea isoelectric focusing and native isoelectric focusing: a collaborative study

Abstract A collaborative study on the use of sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE), urea-isoelectric focusing (urea-IEF) and native isoelectric focusing for the identification of species of smoked salmonids, gravad salmonids and smoked eels was carried out by eight laboratories. With SDS-PAGE, minor changes took place in the profiles of the processed salmonid species making it impossible or very difficult to identify closely related species. With urea-IEF, there were fewer changes in the profiles due to processing and the system generally had greater species-discriminating power for the processed salmonids than SDS-PAGE. The profiles of the eel species as obtained on SDS-PAGE or urea-IEF were not affected by smoking. Urea-IEF had greater species-discriminating power than SDS-PAGE for the eel species. Native IEF was useful in providing supplementary identification on species difficult to identify by SDS-PAGE or by urea-IEF in the case of cold smoked products.

Species identification of cooked fish by urea isoelectric focusing and sodium dodecylsulfate polyacrylamide gel electrophoresis: a collaborative study

The suitability and reliability of urea IEF and SDS-PAGE for the identification of cooked fish flesh was tested by a collaborative study among nine laboratories. Urea IEF was performed with CleanGels as well as with ImmobilineGels, and ExcelGels were used for SDS-PAGE, enabling all three types of gels to be run in the same flat bed electrophoresis chamber. By strictly following optimised standard operation procedures (SOPs), five unknown cooked samples had to be identified with each technique using a set of 10 raw reference samples. With urea IEF, only one out of 35 identifications was incorrect, and with SDS-PAGE a similar result was obtained. It was concluded that methods, as now developed, are suitable for checking the species declaration of fishery products.

Mathematical modelling and simulation of the thermal processing of anisotropic and non-homogeneous conduction-heated canned foods: application to canned tuna

Abstract Thermal processing of conduction-heated canned foods is modelled using three approaches: (A) homogeneous isotropic, (B) homogeneous anisotropic and (C) non-homogeneous anisotropic systems. Based on these models, numerical simulations are performed, using finite differences and finite elements methods. The simulation results are validated with experimental data obtained from the sterilization of canned tuna, a rather complex system. The last approach is found to be the most appropriate, though the second can be used for practical purposes.

A comparison between conventional and fluorescence detection methods of cooking-induced damage to tuna fish lipids

ZusammenfassungLipidschäden während des Abkochens von zwei Thunfisch-Arten (Thunnus obesus undTh. thynnus) wurden untersucht. Fluorescenzmeßungen in verschiedenen Wellenlängenbereichen wurden mit anderen Methoden verglichen, die zur Bestimmung von Lipidschäden gebraucht werden. Als Ergebnis der Wärmebehandlung wurde eine Fluorescenzverschiebung zu höheren Wellenlängenmaxima offenbar; gleichzeitig zeigten die Qualitätskriterien eine verstärkte Lipidschädigung (Carbonylbildung und Bräunungsentwicklung sowie Zunahme von freien Fettsäuren). Die Fluorescenzverhältnisse zwischen 393/460 nm und 327/415 nm (Maxima) zeigten weniger Abhängigkeit von den Proben als andere Lipidschädenmessungen.AbstractThe damage to tuna fish lipids induced by cooking was investigated in theThunnus obesus andTh. thynnus varieties, using conventional and fluorescence detection methods, and the results were compared. As a consequence of thermal processing, the peaks at longer wavelengths increased, which correlated with other conventional indices of lipid damage (i.e. carbonyl compound formation, browning and increases in the free fatty acid content). A special significance was given to the fluorescence ratio between the maxima of the excitation emission data at 393/460 nm and 327/415 nm; increases in this ratio as a result of cooking were less dependent on the samples than were other conventional methods of measuring lipid damage.