Ragni Ofstad

Liquid Loss as Effected by Post mortem Ultrastructural Changes in Fish Muscle: Cod (Gadus morhua L and Salmon Salmo salar

This study was performed in order to assess the effect of early post mortem structural changes in the muscle upon the liquid-holding capacity of wild cod, net-pen-fed cod (fed cod) and farmed salmon. The liquid-holding capacity was measured by a low speed centrifugation test. Transmission electron microscopy was used to discover ultrastructural changes both in the connective tissue and in the myofibrils. Differential scanning calorimetric thermograms of the muscle proteins were recorded to elucidate whether fundamental differences did exist between the proteins of the raw material tested. Multivariate statistics were used to explicate the main tendencies of variations in the thermograms. The salmon muscle possessed much better liquid-holding properties than the cod muscle, and wild cod better than fed cod regardless of the storage time. Both fed cod and farmed salmon, underwent the most severe structural alterations, probably caused by the low muscle pH values. The higher liquid-holding capacity of the salmon muscle was related to species specific structural features and better stability of the muscle proteins. The myofibrils of the salmon muscle were denser and intra- and extracellular spaces were filled by fat and a granulated material. The differences in thermograms of muscle from wild and fed cod were largely explained by the variations in pH. The severe liquid loss of fed cod is due to a low pH induced denaturation and shrinkage of the myofibrils. Post mortem degradation of the endomysial layer and the sarcolemma may have further facilitated the release of liquid.

Seasonal variations in chemical and sensory characteristics of farmed and wild Atlantic halibut (Hippoglossus hippoglossus)

Abstract Quality characteristics of farmed and wild halibut from the period of May to December were investigated by measuring liquid-holding capacity, muscle pH, fatty acid (FA) composition and by a quantitative descriptive sensory analysis. The liquid-holding capacity of farmed halibut muscle varied throughout the season. A significant increase in liquid loss was observed in July and August, indicating that the quality is lower in these months. The liquid loss (LL) increased with decreasing pH at pH lower than 6.3, whereas at higher pH, the LL was independent of pH. In the farmed halibut, the average muscle pH 6.14 varied from 5.90 to 6.64. Average muscle pH in the wild halibut (6.41) varied from 6.33 to 6.49. The fat content in the wild halibut muscle was

Water and salt distribution in Atlantic salmon (Salmo salar) studied by low-field 1H NMR, 1H and 23Na MRI and light microscopy: effects of raw material quality and brine salting.

The effect of different Atlantic salmon raw materials (prerigor, postrigor and frozen/thawed) on water mobility and salt uptake after brine salting was investigated by using LF 1H NMR T2 relaxation,1H and 23Na MRI and light microscopy. Distributed exponential analysis of the T2 relaxation data revealed two main water pools in all raw materials, T21 and T22, with relaxation times in the range of 20-100 ms and 100-300 ms, respectively. Raw material differences were reflected in the T2 relaxation data. Light microscopy demonstrated structural differences between unsalted and salted raw materials. For prerigor fillets, salting induced a decrease in T21 population coupled with a more open microstructure compared to unsalted fillets, whereas for frozen/thawed fillets, an increase in T21 population coupled with salt-induced swelling of myofibers was observed. The result implies that the T21 population was directly affected by the density of the muscle myofiber lattice. MR imaging revealed significant differences in salt uptake between raw materials, prerigor salted fillets gained least salt (1.3-1.6% NaCl), whereas the frozen/thawed fillets gained most salt (2.7-2.9% NaCl), and obtained the most even salt distribution due to the more open microstructure. This study demonstrates the advantage of LF NMR T2 relaxation and 1H and 23Na MRI as effective tools for understanding of the relationship between the microstructure of fish muscle, its water mobility and its salt uptake.

Noncontact salt and fat distributional analysis in salted and smoked salmon fillets using X-ray computed tomography and NIR interactance imaging.

To be able to monitor the salting process of cold smoked salmon, a nondestructive imaging technique for salt analysis is required. This experiment showed that X-ray computed tomography (CT) can be used for nondestructive distributional analysis of NaCl in salmon fillets during salting, salt equilibration, and smoking. The combination of three X-ray voltages (80, 110, and 130 kV) gave the best CT calibrations for NaCl, with a prediction error (root mean square error of cross-validation, RMSECV) of 0.40% NaCl and a correlation (R) of 0.92 between predicted values and reference values. Adding fat predictions based on NIR interactance imaging further improved the NaCl prediction performance, giving RMSECV = 0.34% NaCl and R = 0.95. It was also found that NIR interactance imaging alone was able to predict NaCl contents locally in salted salmon fillets with RMSECV = 0.56% and R = 0.86.

Revealing Covariance Structures in Fourier Transform Infrared and Raman Microspectroscopy Spectra: A Study on Pork Muscle Fiber Tissue Subjected to Different Processing Parameters

The aim of this study was to investigate the correlation patterns between Fourier transform infrared (FT-IR) and Raman microspectroscopic data obtained from pork muscle tissue, which helped to improve the interpretation and band assignment of the observed spectral features. The pork muscle tissue was subjected to different processing factors, including aging, salting, and heat treatment, in order to induce the necessary degree of variation of the spectra. For comparing the information gained from the two spectroscopic techniques with respect to the experimental design, multiblock principal component analysis (MPCA) was utilized for data analysis. The results showed that both FT-IR and Raman spectra were mostly affected by heat treatment, followed by the variation in salt content. Furthermore, it could be observed that IR amide I, II, and III band components appear to be effected to a different degree by brine-salting and heating. FT-IR bands assigned to specific protein secondary structures could be related to different Raman C–C stretching bands. The Raman C–C skeletal stretching bands at 1031, 1061, and 1081 cm−1 are related to the IR bands indicative of aggregated β-structures, while the Raman bands at 901 cm−1 and 934 cm−1 showed a strong correlation with IR bands assigned to α-helical structures. At the same time, the IR band at 1610 cm−1, which formerly was assigned to tyrosine in spectra originating from pork muscle, did not show a correlation to the strong tyrosine doublet at 827 and 852 cm−1 found in Raman spectra, leading to the conclusion that the IR band at 1610 cm−1 found in pork muscle tissue is not originating from tyrosine.

Post-mortem structural characteristics and water-holding capacity in Atlantic halibut muscle

Structural characteristics of seven farmed and wild Atlantic halibut muscle (5 days post mortem) were individually studied, in relation to the pH and water-holding capacity (WHC) of the muscle. Both light- and electron-microscopic techniques were used to qualitatively investigate structural attributes that influence WHC. Farmed and wild halibut with different muscle pH and similar WHC were compared as well as farmed samples having similar pH but different WHC and vice versa. Both farmed and wild halibut exhibited the same structural alterations post mortem but they appeared more pronounced in the farmed fish. Small, new fibres were seen more often in the farmed fish than in the wild fish muscle. Common structural characteristics that could be related to decreased WHC were detachment of sarcolemma, gaps in the extracellular matrix, increased intermyofibrillar space and transverse shrinkage of the cells. It was not evident whether disruptions of the myofilaments influenced the WHC or not. The results indicated, however, that low pH in combination with pronounced structural degradation influenced the WHC more than low pH in combination with minor structural degradation.

Liquid-holding capacity and structural changes in comminuted salmon (Salmo salar) muscle as influenced by pH, salt and temperature

The loss of liquid in salmon muscle comminuted with salt was studied as a function of pH and heating temperature. A factorial experiment was designed to compare the effects of; the raw material, NaCl concentration, pH, degree of comminution and heating temperature in order to evaluate both main effects and interaction effects. The liquid-holding capacity was measured by a low speed centrifugation net test. The changes in microstructure in the samples were investigated by light microscopy using fat- and protein-staining techniques. The heating temperature, pH, NaCl concentration, variation of raw material and degree of comminution influenced liquid loss according to a second-order interaction linear model. The interaction effect between low pH, low salt concentration and high temperature was strongest. Addition of salt extracted the myofibrillar proteins and resulted in a homogeneous protein matrix with few intact fibres and uniformly dispersed fat droplets. Liquid loss was closely related to the microstructure of the comminutions. When heated above 30 °C, enlarged pores and gaps, some of them forming channels, occurred in the protein matrix. In comminutions prepared with a low salt concentration and/or a low pH the more frequent presence of pores and gaps enhanced the liquid loss.

Effects of carbon dioxide on yield, texture and microstructure of cooked ground beef.

The objective of the study was to find the effects of CO(2) gas on cooking loss, instrumental hardness and microstructural changes of ground beef heated to 70-83 °C. In two experiments, ground beef was stored for 4 days in 60% CO(2)/39.6% N(2)/0.4% CO and vacuum (1), or in 100% CO(2), 50% CO(2)/50% N(2), 20% CO(2)/80% N(2), 100% N(2) and vacuum (2). In an additional experiment, slices of beef semimembransosus muscles were stored for 10 days in 100% CO(2), 100% N(2) and vacuum. Cooking loss of ground beef patties was higher of all CO(2) treatments than non-CO(2) treatments (p<0.05). Storage of raw ground beef in CO(2) caused a concentration dependent decrease in raw meat pH of up to 0.12 units in 100% CO(2). In the beef slices, small CO(2) related fissures and pores were formed in the cooked meat. These changes in pH and microstructure probably contributed to the elevated cooking loss. The hardness of cooked ground beef was not affected by CO(2) exposure (p>0.05). Because CO(2) in concentrations of 20-100% is commonly used in industrial packaging processes for retail meat and meat trimmings, a reduction in cooking yield of 1-3% may have sensory and economic implications.

Monitoring Protein Structural Changes and Hydration in Bovine Meat Tissue Due to Salt Substitutes by Fourier Transform Infrared (FTIR) Microspectroscopy

The objective of this study was to investigate the influence of NaCl and two salt substitutes, MgSO4 and KCl, in different concentrations (1.5, 6.0, and 9.0%) on meat proteins by using Fourier transform infrared (FTIR) microspectroscopy. Hydration properties and secondary structural properties of proteins were investigated by studying the amide I, amide II, and water regions (3500-3000 cm(-1)) in FTIR spectra. By applying multivariate analysis (PCA and PLSR), differences between samples according to salt concentration and salt type were found and correlated to spectral bands. The most distinctive differences related to salt type were obtained by using the water region. It was found that samples salted with MgSO4 exhibited hydration and subsequent denaturation of proteins at lower concentrations than those salted with NaCl. Samples salted with KCl brines showed less denaturation even at the 9.0% concentration. The FTIR results were further supported by water-binding capacity (WBC) measurements.

Analyzing Designed Experiments with Multiple Responses

Abstract This paper is an overview of a unified framework for analyzing designed experiments with univariate or multivariate responses. Both categorical and continuous design variables are considered. To handle unbalanced data, we introduce the so-called Type II* sums of squares. This means that the results are independent of the scale chosen for continuous design variables. Furthermore, it does not matter whether two-level variables are coded as categorical or continuous. Overall testing of all responses is done by 50-50 MANOVA, which handles several highly correlated responses. Univariate p-values for each response are adjusted by using rotation testing. To illustrate multivariate effects, mean values and mean predictions are illustrated in a principal component score plot or directly as curves. For the unbalanced cases, we introduce a new variant of adjusted means, which are independent to the coding of two-level variables. The methodology is exemplified by case studies from cheese and fish pudding production.