QUANTITATIVE CHANGES IN WHOLE MYOFIBRILS AND MYOFIBRILLAR PROTEINS DURING FROZEN STORAGE OF TRUE COD

The extractability of whole myofibrils from true cod decreased more rapidly during frozen storage at −40°C than did the extractability of the component myofibrillar proteins. There was a 95% decrease in extractable myofibrils after 6 months in storage, but only a 23% decrease in extractable myofibrillar proteins.     

THE TEXTURE OF COD MUSCLE

Data on moisture, protein content and pH (after 24 h in ice post mortem) of the flesh of cod of different sizes, captured during several fishing expeditions from Aberdeen to northern fishing grounds in spring and autumn, have been examined in relation to the texture of the cooked material. It is concluded that large fish are slightly tougher than small fish, even when the pH is the same. In addition, the pH of large fish is often lower than that of small fish, so the relative toughness of large fish is enhanced. However, the size-pH relationship is clearly defined only in well-fed fish at certain times of the year. At other times, when food is scarce, the post-mortem pH of the muscle of all sizes of cod varies within wide limits, so that size no longer appears to influence the texture. Of the parameters studied, the post-mortem pH correlated best with the texture after cooking. Since fish with a high pH usually have a high water content, there was also a correlation between texture and moisture. However, the protein content seemed to exercise a negligible influence on texture, an unexpected finding considering that protein accounts for nearly all the ‘substance’ of white fish flesh after the water has been removed.     

CHANGES IN TEXTURE AND MICROSTRUCTURE OF PRESSURE-TREATED FISH MUSCLE TISSUE DURING CHILLED STORAGE

Activities of four endogenous enzymes (cathepsin C, collagenase, chymotrypsin- and trypsin-like enzymes), as well as firmness/strength and elasticity of pressurized fish tissues were monitored over 3 weeks of storage (4–7C). Results indicate that pressurization of fish muscle at 1,000 atm increased firmness whereas pressurization at 2,000 atm or 3,000 atm caused an opposite effect. Changes in tissue elasticity also showed similar trends with correlation between firmness and elasticity. During storage, pressure-inactivated enzymes were reactivated to various extents depending on level of pressurization. Scanning electron microscopy of the tissues revealed some morphological changes with pressurization. At 1,000 atm, there were no significant changes in the myofibers while pressurization at 2,000 atm and 3,000 atm resulted in breakdown of myofibers and connective tissue networks. The results indicate that pressurization may be used to enhance and maintain fresh seafood texture during storage.     

CHANGES IN MOLECULAR SPECIES COMPOSITIONS OF GLYCEROPHOSPHOLIPIDS IN THE ADDUCTOR MUSCLE OF THE GIANT EZO SCALLOP PATINOPECTEN YESSOENSIS DURING FROZEN STORAGE

Changes in lipid components, particularly glycerophospholipids, in the adducto; muscle of giant ezo scallop during storage at −20C were investigated. During storage, the contents of total lipids (TL) and polar lipids (PL) decreased, but that of nonpolar lipids increased. Thiobarbituric acid reactive substances and peroxide values of the TL increased with duration of storage. Glycerylphosphorylcholine (GPC) and glycerylphosphrylethanolamine (GPE) decomposed considerably during storage, and decreased by 50% and 15% of the initial content, while lyso-PC (LPC) and free fatty acids (FFA) increased, respectively. The percentages of polyunsaturated fatty acids (PUFAs) such as 20:5n-3 and 22:6n-3 in the TL and PL during storage decreased, however, those of the PUPAs in the NL increased. Diacylglycerylphosphorylcholine (diacyl-GPC) and diacylglycerylophosphorylethanolamine (diacyl-GPE), major components in the GPC and GPE subclasses, showed a marked decrease with duration of storage. Particularly, diacyl-GPC decreased by 68% of the initial contents of the PL. In the alkenylacyl-GPE and diacyl-GPC, the percentages of the molecular species having longer hydrocarbon chains on the sn-l positions of glycerol moieties decreased at     

EFFECT OF IN SITU FORMALDEHYDE PRODUCTION ON SOLUBILITY AND CROSS-LINKING OF PROTEINS OF MINCED RED HAKE MUSCLE DURING FROZEN STORAGE

Three forms of minced red hake muscle representing whole-mince, mince with the low molecular weight fraction removed (reconstituted-minced) and mince with low and high molecular weight soluble fractions removed (washed-minced) were stored frozen with added Fe⁺² and ascorbate (trimethylamine oxide (TMAO) was added when necessary). The production of DMA and free formaldehyde was measured as were the decreases in water-soluble and salt-soluble proteins and TMAO as a function of increasing concentrations of ascorbate. Dimethylamine (DMA) production and loss of overall protein extractability were greatest in minced muscle, followed by reconstituted-minced muscle, and least in washed-minced muscle. The minced muscle lost water-soluble proteins, however, less rapidly than the reconstituted-minced muscle. The percentage of formaldehyde that was bound was highest in the minced, next in the reconstituted-minced and least in the washed-minced muscle. This supports earlier data and indicates that formaldehyde reacts with both the small molecular weight fraction and the water-soluble proteins as well as the contractile proteins. Loss of protein extractability in all samples appeared to be heavily dependent on hydrophobic interactions. Disulfide interactions appeared to occur to some extent in the reconstituted-minced and washed-minced muscle but were a minor factor with the minced muscle samples. Surface hydrophobicity of the proteins was inversely related to their extractability. In the sample of minced muscle with the highest concentration of added ascorbate where approximately 79% of the proteins became inextractable, some 2% of the muscle proteins were covalently linked in polymers with molecular weights greater than that of the myosin heavy chains. The data indicate that cross-linking of protein components occurs as well as hydrolysis of a considerable amount of the protein.     

MODELING OF TEXTURE EVOLUTION OF CAKES DURING STORAGE

The aim of this work is to model the variation of texture parameters in cakes during staling. The evolution was studied in layer cakes (cake A) and sponge cakes (cake B). The effect of storage temperature and the addition of fiber, xanthan gum (cake A) and emulsifier (cake B) were also studied. The best model to adjust the texture parameters variation during storage in both kinds of cakes was square root x ( y = a + b * x^1/2 ), except for firmness and springiness in cakes B. Firmness and springiness were adjusted the best to the linear model. In the model, y stood for the textural parameters and x for the time. a and b were related to the initial value of the studied parameter and with its change over time respectively. In both kinds of cakes, A and B, the firmness and gumminess increased, and the cohesiveness, springiness and resilience decreased, as the storage time increased. The increase in the storage temperature and the addition of fiber minimized the firmness changes in both kinds of cakes.

PRACTICAL APPLICATIONS

This methodology simplifies the study of cake textural parameters during storage and the result interpretation. Moreover, the correlation analysis has demonstrated that the number of textural parameters of cakes to study can be reduced.     

NUTRITIONAL ESTIMATION OF CHANGES IN MINERAL CONTENT DURING FROZEN STORAGE OF WHITE ASPARAGUS

Nine essential elements (copper, iron, zinc, manganese, calcium, magnesium, sodium potassium and phosphorous) were determined in white asparagus (Asparagus officinalis, L.) by flame atomic absorption spectrophotometry in order to examine the possible variations in mineral content caused by frozen storage at ?18C for 45 and 90 days. Statistically significant differences were determined during frozen storage for all the mineral elements investigated, except for Ca, Mg, Na and P which did not exhibit any significant differences (p>0.05) and, together with Zn, showed no significant modifications under frozen storage. A diminution in Cu, Fe, Mn and K concentrations was observed during the frozen storage time. Statistically significant differences were established between thicknesses of the asparagus spear in the content of Cu, Fe, Zn, Ca, Na and K and it was seen that the thickness of the asparagus did not fit any specific model. Between portions, all the elements studied displayed statistically significant differences in their concentrations, except for Ca and K (p>0.05) and, for all the minerals elements analyzed, the highest levels were found in the apical portion of the asparagus spear, except for Na with a higher content in the basal portion. White asparagus is an adequate food source of mineral elements, except for Na, and frozen storage does not cause any great variations in the percentages of mineral RDAs (Recommended Dietary Allowances) supplied.     

ALTERATION IN LIPID OXIDATION OF CHANNEL CATFISH DURING FROZEN STORAGE IN RESPONSE TO ASCORBATE APPLICATIONS

Channel catfish were treated with ascorbate via metabolic absorption and vacuum tumbling. The fillets were subjected to varying periods (0, 1.5, 3, 4.5, and 6 months) of frozen storage at −6C. When muscle ascorbic acid levels were increased two fold by both methods, TBA-RS values were significantly lower than that of the control after 6 months of storage. Vacuum tumbled fillets with muscle ascorbic acid that increased by four fold were found to be the least stable to oxidation. The possible fate of the ascorbic acid in the fish tissue was discussed.     

EFFECTS OF CRYOPROTECTANTS IN MINIMIZING PHYSICOCHEMICAL CHANGES OF BOVINE NATURAL ACTOMYOSIN DURING FROZEN STORAGE1

Physicochemical changes in bovine natural actomyosin extracted from prerigor semimembranosus muscle were investigated during frozen storage at ?28°C as affected by the addition of cryoprotectants (5.6% Polydextrose® or 5.6% mixture (1:1) of sucrose and sorbitol). Proteins were destabilized during freezing and frozen storage as reflected by decreases in protein solubility, the visual appearance of aggregates in protein sols, decrease in intensity of flow birefringence, intrinsic viscosity and ATPase activity, and changes in size, shape, or charge of the protein (especially myosin) as evidenced by nondenaturing electrophoresis. These effects were reduced to some extent by the two cryoprotectant treatments.     

RHEOLOGICAL AND SENSORY QUALITY OF READY-TO-BAKE CHAPATTI DURING FROZEN STORAGE

The effect of prolonged frozen storage at − 18C, on the textural and sensory properties of ready-to-bake frozen chapatti (R-BFC) was evaluated. The R-BFC samples were prepared from normal- (control) and microwave-treated (18% moisture content for 80 s) wheat grains. Results showed that the extensibility of dough and maximum load for resistance increased gradually in both the samples during frozen storage; however, the increase was lesser in the treated ones. Chapattis prepared from both R-BFC samples exhibited higher hardness, cohesiveness, chewiness and lower springiness values during frozen storage. Microwave-treated R-BFC samples were rated as better retained in color, texture and overall acceptability scores as compared with control, up to 6 months of storage at − 18C. Thiamin and riboflavin contents were monitored during frozen storage and a loss of 12.0–14.5% in thiamin and 4–6% in riboflavin after 6 months of frozen storage was recorded.

PRACTICAL APPLICATIONS

During frozen storage, various physical, rheological and sensory changes occur in the food products, which determine the consumer's acceptability. The results of this study will help to establish quality of the frozen chapattis with respect to texture, color and aroma which will meet the consumer's acceptance. The protocol for the storage of frozen chapattis will help the industry to deliver the product of optimum quality.