Siw Kidman

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.

Microstructure and rheological behaviour of alginate/pectin mixed gels

Abstract The synergistic interaction between alginate and pectin was systematically investigated using samples of different chemical compositions. Pectin samples with high and low degrees of esterification (DE) and amidated pectin (LA) were mixed with alginate of high and low M/G (mannuronic acid/guluronic acid) ratio. The microstructure of the gels was characterised by TEM (transmission electron microscopy) and the rheological properties by dynamic oscillatory measurements. The TEM images of the mixed gels revealed a coarse, strand-like network with pores in the range of microns, independent of the ratio and the composition of the samples. A comparison with the microstructure of a pure pectin gel showed that the pectin network was composed of thinner strands and smaller pore sizes than the mixed network. The strongest synergism was found between alginate with low M/G ratio and pectin with a high DE. These gels show the highest G ′ (storage modulus) and the fastest kinetics of gel formation. Lower G ′ and slower kinetics were found for gels based on alginate with a high M/G ratio and pectin with a low DE, or LA pectin. The nature of the pectin sample affected the network density and the strand characteristics. In contrast, no influence was found of the alginate sample. Gels based on pectin with a high DE showed a dense network composed of highly branched strands, whereas the LA-pectin based gels showed a sparse, open network, composed of long, straight strands. A relation close to 1:1 for low-G alginate and pectin with a high DE resulted in gels with the highest G ′. In contrast, for LA-pectin based gels, the highest G ′ was found for mixtures of alginate dominant ratios. For the overall network properties, the homogeneity in the microstructure decreased with alginate content, independent of the pectin sample.

Microwave heat treatment of apple before air dehydration : Effects on physical properties and microstructure

Abstract Golden delicious apple cubes were heated with microwave energy of high intensity (20 W/g), as a pre-treatment before air-dehydration at 40°C, 60°C and 80°C. After the microwave treatment extending for 0.75 up to 5 min, the cubes were finish-dried with only forced air at 2 m/s. Dehydrated and rehydrated samples were analysed with a puncture test using a texture analyser. The microstructure of the samples was studied with confocal laser scanning microscopy (CLSM). Dried apple pieces were harder and more shrunk when pre-treated with microwaves, compared to only air dehydration. Despite the shrinkage and increased firmness, the rehydration capacity of microwave “blanched” apple cubes was higher than when they were only air-dehydrated. Image analysis of the rehydrated apples showed that large voids (up to 0.5 mm in diameter) had developed, and that these increased with air temperature. Higher magnification of the images revealed cell separation and disruption of cell walls, caused by the microwave heating.

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.

Dendrimer Diffusion in κ-Carrageenan Gel Structures

The effect of the kappa-carrageenan concentration on gel microstructure and self-diffusion of polyamideamine dendrimers has been determined by transmission electron microscopy (TEM), image analysis, and nuclear magnetic resonance (NMR) diffusometry. Different salt conditions of KCl, NaCl, and mixtures thereof allowed for formation of significantly different microstructures. The kappa-carrageenan concentrations were varied between 0.25 and 3.0 w/w% for a salt mixture containing 20 mM KCl and 200 mM NaCl gels and between 0.5 and 4.0 w/w% for 250 mM NaCl gels. Furthermore, the effect of potassium ion concentration on the gel structure and the dendrimer diffusion rate was determined. The potassium ion concentration was varied between 20 mM KCl and 200 mM KCl. Two different dendrimer generations with significant difference in size were used: G2 and G6. Dendrimers were found to be sensitive probes for determination of the effect of the gel microstructure on molecular diffusion rate. A qualitative comparison between TEM micrographs, NMR diffusometry data and image analysis showed that the gel structure has a large impact on the dendrimers diffusion in kappa-carrageenan gels. It was found that diffusion was strongly influenced by the kappa-carrageenan concentration and the dendrimer generation. Small voids in the gel network gave strongly reduced diffusion. Image analysis revealed that the interfacial area between the gel network and the surrounding water phase correlated well with the dendrimer diffusion.

Ultramicroscopical Structures and Liquid Loss in Heated Cod ( Gadus morhuaL) and Salmon ( Salmo salar) Muscle

This study was performed in order to assess the effect of heating in pre- and post-rigor muscle of fed cod, wild cod and farmed salmon harvested at different times of the year. The structural changes in muscle samples pre-heated from 5 to 60°C were qualitatively evaluated using both light and transmission electron microscopy techniques. The microstructural changes are discussed in relation to the liquid loss measured by a low-speed centrifugation test. The heat-induced structural changes varied between the fish tested, reflecting different degrees of post mortemdegradation prior to heating, the muscle-pH and species-specific structural properties. The fed fish, both cod and salmon, underwent the most severe structural degradation. This reflected both the low muscle pH and the more severepost mortemdegradation observed in these fish prior to heating, compared with the wild cod. Heating caused extensive shrinkage of the myofibrils and hence, widened intermyofibrillar and extracellular spaces in both the fed cod and the salmon muscle. In the sample of wild cod muscle, the extracellular spaces were narrow and the myofibrils were closely packed. The difference in heat-induced liquid loss of the fed compared with the wild cod muscle coincides with their different structural features, as observed both by LM and TEM. The better liquid-holding properties of the salmon muscle than the cod muscle are attributed to the species-specific ultrastructural features as observed with TEM. In addition to the denser appearance of the salmon myofibres, it is suggested that both fat droplets and aggregated sarcoplasmic proteins filling the intermyofibrillar and extracellular spaces are important in preventing release of liquid upon heating.

Molecular structures obtained from mixed amylose and potato starch dispersions and their rheological behaviour

Abstract Transmission electron microscopy (TEM) and dynamic viscoelastic measurements were used to study the effects of varying the ratio of potato starch to amylose. Solubilised amylose was mixed with two different types of potato starch: one with starch in the form of swollen granules and the other in the form of a molecular dispersion. The total concentration was kept constant at 8% (w/w). When the level of added amylose was low, the shear modulus ( G∗ ) was higher for gels with swollen granules than for molecular dispersions of starch. When the level of added amylose was high, the value of G∗ was approximately the same, independent of the type of starch structure. The rheological data were evaluated by a model treating the added amylose and potato starch as phase-separated systems. The model showed that the inherent amylose of potato starch did not contribute markedly to the gel strength caused by the added amylose. Potato starch alone does not form strong gels in the time scale studied. TEM studies confirmed that the inherent and the added amylose gave rise to completely different types of structure. The added amylose had an open network structure of stiff strands. This type of structure was found in the mixed systems with added amylose and starch, but not in systems with only potato starch. Solubilised amylopectin appeared to have a droplet-like structure, often found in the form of a string of beads.