IMMUNOHISTOCHEMICAL LOCALIZATION OF PHENOLOXIDASE IN HEPTOPANCREAS, MUSCLE AND EPIDERMIS OF GRASS SHRIMP (PENAEUS MONODON F.)

The in vivo sites of melanogenesis in grass shrimps (black tiger shrimp, Penaeus monodon F.), unirradiated and irradiated (5 kGy), was investigated by determining the location of phenoloxidase in heptopancreas, muscle and epidermis using an immunocytochemical technique with electron microscopy. Specific labelling by gold-IgG complex particles was observed over the microvillar border, apical surface and endoplasmic reticula in hepatopancreas, sarcoplasmic reticula in muscle and chromatophores in epidermis. These results suggest that phenoloxidase is synthesized in R-cells of heptopancreas, or chromatophores in epidermis and transferred to muscle. There was no difference in the location of phenoloxidase in shrimp tissues that were nonirradiated and irradiated. Consequently, R-cells in heptopancreas and chromatophores in the epidermis were considered to be important in studying melanogenesis in shrimps.     

IDENTIFICATION OF PROTEOGLYCANS IN BOVINE M. SEMIMEMBRANOSUS BY IMMUNOHISTOCHEMICAL METHODS

The distribution pattern of proteoglycans in the extracellular matrix of M. semimembranosus from young bulls was studied in frozen tissue sections by immunohistochemical methods. The small proteoglycan, decorin, was found widely distributed in both perimysial and endomysial layers. Another member of the same proteoglycan family, fibromodulin, could only be seen associated with the fiber bundles of the perimysium. Furthermore, aggrecan-like proteoglycans were detected mainly in the perimysium with a different staining pattern than decorin and fibromodulin. A basement membrane type heparan sulfate proteoglycan was present only in the endomysium, with particularly strong staining in the junctions of endomysial layers between neighboring myofibers. The distribution of proteoglycans in the peri- and endomysium of striated muscle tissue influences the organization of the collagen fibrils and, therefore, the texture and strength of muscle matrix. Proteoglycans should be considered a component of muscle influencing meat tenderness.     

BREAKDOWN OF LARGE PROTEOGLYCANS IN BOVINE INTRAMUSCULAR CONNECTNE TISSUE EARLY POSTMORTEM

In the present study, a decomposition of intramuscular connective tissue in beef early postmortem was demonstrated by comparing samples from M. longissimus dorsi (LO) collected immediately after slaughter and after 24 h and 48 h storage by histological and biochemical methods. The histological study showed a widening of the endomysial sheaths after storage. For fiactionation of proteoglycans, extraction in 4M guanidine-HCl added protease inhibitors, CsCl, gradient ultracentrifugation and gel chromatography were used. Gel chromatography demonstrated that the proteoglycan preparation was broken into fragments of lower molecular weight. Cellulose acetate electrophoresis and dot blot analysis identified the components involved as hyaluronic acid (HA) and a large proteoglycan (PGL) immunologically related to aggrecan from sclera. SDS polyacrylamide gel electrophoresis (SDS-PAGE) confirmed depolymerization of the high molecular weight components, and a large component of molecular weight above 220 KDa with glycosaminoglycan (GAG) staining properties was not visible in the gel after storage.     

GLYCOLYTIC POTENTIAL IN SEMIMEMBRANOSUS MUSCLE OF ITALIAN LARGE WHITE PIGS

The objective of this study was to determine the distribution of glycolytic potential (GP) and its relationships with meat pH and the estimated breeding values (EBVs) of some traits in Italian Large White pigs. GP was determined on samples taken from the semimembranosus muscle at 120 min postmortem. Values of GP were normally distributed around a mean value of µmol/g 103.5  ±  23.0. Increasing GP was associated with decreasing pH at 2 and 24 h postmortem. A nonlinear relationship was found between GP and pH_u. GP also showed no relationship with the EBVs of daily gain and feed : gain ratio and a weak relationship with EBVs of carcass traits such as backfat thickness and lean cut weight. The positive but weak correlation between GP and EBV of ham weight loss during the first salting period may suggest a potential risk of using meat with high GP in dry-cured ham production.

PRACTICAL APPLICATIONS

Glycolytic potential is considered to be a determinant parameter for pork quality, especially when the meat is going to be processed. A better knowledge of its variation and its relationship with other valuable traits in vivo and postmortem is important in a breed such as the Italian Large White, largely used in the production of heavy pigs destined to produce meat for seasoned products. Data reported here on the variation of GP could suggest to breeder association the need to control this parameter in selection programs irrespectively to the presence of the RN^- negative allele, as the relationship of GP with processing losses could hinder dry-cured ham producers.     

CHANGES IN THE LOW MOLECULAR WEIGHT NITROGENOUS COMPOUNDS OF EXCISED BOVINE MUSCLE

Investigations were completed to determine whether any differences could be detected in the low molecular weight nitrogenous compounds of excised bovine muscle at O-time or that held at 4° C for 12 days. No differences were noted between the electrophoretic patterns of the soluble proteins of the 0 and 12day samples either before or after gel filtration on Sephadex G-25 columns. However, gel electrophoretic patterns indicated that one band consisted of low molecular weight non-protein compounds. Absorbance data (280 and 260 nm) of the soluble proteins separated by gel filtration indicated that the 12day sample contained a slightly higher level of low molecular weight nonprotein nitrogenous compounds than did the O-day sample. Results of nitrogen determinations of the gel-filtered extracts also supported this finding. Data of ultraviolet scanning of gel-ftltered extracts showed that the low molecular weight nitrogenous compounds had a greater absorbancy at 260 than at 280 nm. Results of two-dimensional paper chromatography-high voltage electrophoresis did not reveal the presence of polypeptides in either the O- or 12day samples.     

ETHANOL ACCUMULATIONS IN MUSCLE TISSUE AS A CHEMICAL INDICATOR OF FISH SPOILAGE

Ethanol concentration was shown to accumulate in post mortem muscle tissue of marine fish as storage time increased. Concentration of the alcohol was determined using a rapid, enzymatic procedure. A study was conducted under commercially simulated storage conditions comparing the effectiveness of ethanol in monitoring fish spoilage to three more common quality tests. The ethanol method mas shown to be as effective as established organoleptic, chemical, and biological testing procedures when following fish flesh degradation.     

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.