Ásbjörn Jónsson

Shrimp processing assessed by low field nuclear magnetic resonance, near infrared spectroscopy, and physicochemical measurements--the effect of polyphosphate content and length of prebrining on shrimp muscle.

The effect of using polyphosphates during prebrining and the effect of prebrining time of cold water shrimp (Pandalus borealis) was studied with low field nuclear magnetic resonance (LF-NMR) transverse relaxation time measurements (benchtop and unilateral) and near infrared (NIR) spectroscopy with the aim of improving shrimp processing. Strong calibrations were obtained for moisture content and water-holding capacity (WHC) using the NIR technique. Multivariate analysis indicated significant correlations between benchtop NMR parameters and moisture content and WHC, as measured with physicochemical methods and NIR spectroscopy. Significant correlations were also observed between NMR parameters and muscle pH, protein content, and phosphate content. The study showed that LF-NMR contribute to improved understanding of the shrimp brining process and to improved process control on-line or at-line, especially in combination with NIR measurements. However, optimization of the unilateral device is necessary.

Influence of smoking and packaging methods on lipid stability and microbial quality of Capelin (Mallotus villosus) and Sardine (Sardinella gibossa).

Lipid and microbial quality of smoked capelin (two groups differing in lipid content) and sardine was studied, with the aim of introducing capelin in the smoked sardine markets. Lipid hydrolysis (phospholipid and free fatty acids) and oxidation index (hydroperoxides and thiobarbituric acid-reactive substances), fatty acid composition, and total viable count were measured in raw and packaged smoked fish during chilled storage (day 2, 10, 16, 22, 28). Lipid hydrolysis was more pronounced in low lipid capelin, whereas accelerated lipid oxidation occurred in high lipid capelin. Muscle lipid was less stable in sardine than capelin. Essential polyunsaturated fatty acids (eicosapentaenoic acid and docosahexaenoic acid) constituted 12% of fatty acids in capelin and 19% in sardine. Vacuum packaging as well as hot smoking retarded bacterial growth, recording counts of ≤log 5 CFU/g compared to ≥log 7CFU/g in cold smoked air packaged. Smoked low lipid capelin was considered an alternative for introduction in smoked sardine markets.

The effects of pre-salting methods on salt and water distribution of heavily salted cod, as analyzed by 1H and 23Na MRI, 23Na NMR, low-field NMR and physicochemical analysis

The effect of different pre-salting methods (brine injection with salt with/without polyphosphates, brining and pickling) on the water and salt distribution in dry salted Atlantic cod (Gadus morhua) fillets was studied with proton and sodium NMR and MRI methods, supported by physicochemical analysis of salt and water content as well as water holding capacity. The study indicated that double head brine injection with salt and phosphates lead to the least heterogeneous water distribution, while pickle salting had the least heterogeneous salt distribution. Fillets from all treatments contained spots with unsaturated brine, increasing the risk of microbial denaturation of the fillets during storage. Since a homogeneous water and salt distribution was not achieved with the studied pre-salting methods, further optimizations of the salting process, including the pre-salting and dry salting steps, must be made in the future.

Effects of Different Temperatures on Storage Quality of Heavily Salted Cod (Gadus morhua)

The aim of this study was to compare the effects of different storage temperatures (+2°C, -4°C, -12°C, -18°C and -24°C) and time (0, 1, 3 and 6 weeks) on the quality of heavily salted cod. The color, water content, water holding capacity (WHC), cooking yield, total volatile basic nitrogen (TVB-N) and trimethylamine (TMA) of the samples were determined. Results showed that the whiteness of the salted cod decreased slightly, whereas the yellow/orange color increased during the storage period. The WHC and cooking yield increased and were inversely related to water content. The TVB-N value increased slightly, whilst a lightly decrease in TMA value was observed. Storage at -4°C and lower temperatures had a detrimental influence on the color of the product which is the main quality criterion for salted cod. Therefore, it is not suitable to store the product at -4°C or lower temperatures.

The Effects of Short‐Time Temperature Abuse on the Microbial and Sensory Quality of Chilled Saithe (Pollachius virens) Fillets

Chilled fish products are highly perishable with a limited shelf life (10 to 14 d). For this reason, the control of the cold chain for fish is essential. This study´s objective was to investigate the effects of short-time temperature abuse during processing on spoilage of chilled saithe (Pollachius virens) fillets. Analysis of microbial growth, freshness grades, and sensory score by Quality Index method, as well as pH, were carried out during a 10-d storage period at 2 ± 2 °C. Before storage, the fillets were kept at 16 °C for 0, 1, and 2 h. The results showed that spoilage of the fillets was accelerated with longer holding time at 16 °C. The 1- and 2-h holding before packing and storage caused a 22% (2 d) and 44% (4 d) loss of shelf life, respectively, compared to fillets that were packed immediately after processing. These findings indicate how bottlenecks and delays during processing may result in loss of microbial and sensory quality of chilled fish products. PRACTICAL APPLICATION The observations show the importance of maintaining a low temperature in fish, even for a short period such as during processing. Any delays, such as due to buffering or mechanical failure, may accelerate spoilage of chilled products during subsequent storage. This effect is even more pronounced when products are packed in bulk volumes as the cooling rate is much slower than the piece-by-piece cooling rate.

Near infrared spectroscopy for seafood process optimisation and monitoring–A shrimp case study

12 Introduction F ish and seafood are complex materials and the quality of seafood is influenced from both ante-mortem and post-mortem factors. Raw material characteristics are crucial factors with regard to final product quality. These characteristics not only vary with species but also with season, place of catch, the catching technique and general handling during processing. As a general rule, quality that is lost in a value chain cannot be regained and good handling and processing procedures through the whole value chain from catch to consumer are therefore essential to ensure good quality in a finished product. Quality preservation, therefore, calls for increased monitoring of the most essential quality parameters. Standard laboratory methods for the determination of physicochemical properties of seafood are not only complex, time-consuming and expensive, but are also generally destructive of the sample and may require the use of dangerous or corrosive solvents to isolate the compound of interest. Rapid, non-destructive measuring methods would therefore be an advantage for in-line, on-line or at-line monitoring to assess the quality of seafood during processing. Near infrared (NIR) spectroscopy is an optimal method for quality monitoring of several physicochemical properties of fish and seafood, since NIR absorption is dependent on the physical, chemical, structural and biological properties of a molecule and its environment. NIR spectroscopy has, in combination with multivariate chemometrics, proven to be an excellent tool for the quantitative determination of all four major food constituents of seafood—water, protein, fat and carbohydrate—and has also shown high correlations with important sensory attributes, fish freshness and ice fraction of glaze in superchilled salmon, to mention just a few applications. The properties of water are here of special importance, since it is the most abundant component in muscle food and its content and properties influence the quality of seafood with regard to texture, sensory attributes and shelf-life. The production of cold water shrimp (Pandalus borealis) is complex and therefore represents a challenging process in which to assess the application of NIR spectroscopy as a quality monitoring method. This process includes steps in which muscle structure is affected by both chemical, physical and mechanical treatment, involving salt and phosphate addition during pre-brining, cooking, mechanical peeling, brining, freezing and glazing. This article therefore deals with the application of NIR spectroscopy for monitoring processing of cold water shrimp, with a focus on its water properties and retention.