Effect of pH-shifting on the gel forming characteristics of salt-ground meat from walleye pollack

ABSTRACT:   In order to elucidate the mechanism of the changes in gel forming characteristics of fish meat by pH-lowering, the gelation-temperature curve and the gelation-moisture content curve were examined using the acidified walleye pollack surimi or neutralized one after acidification. In the gelation-temperature curve, the gel strength was highest at 30°C and lowest at approximately 50–60°C, irrespective of pH shifting. The gel strength at 30°C and 80°C decreased with the decrease in pH value. The neutralization of acidified surimi improved the gel strength, but it was considerably lower than the original gel strength. The gel strength at 50–60°C was not affected by pH lowering. The gel strength at 80°C could not be revived to the original by pH readjustment, either in the presence or in the absence of EDTA. These results suggest that irreversible changes of meat protein take place under the low pH, and the oxidation ability of sulfhydryl (SH) groups of protein molecule is not affected by pH-shifting.     

Antihypertensive effect of Narezushi, a fermented mackerel product, on spontaneously hypertensive rats

ABSTRACT:   During the fermentation of mackerel to narezushi , the concentration of peptides required to inhibit 50% of the ACE activity in the assay media (IC₅₀), as an index of the angiotensin  I-converting enzyme (ACE) inhibitory activity, was remarkably decreased with a rapid increase in peptide contents. Systolic blood pressure (SBP) in spontaneously hypertensive rats (SHR) decreased between 2 and 4 h after the single oral administration of greater than 10 mg peptide/kg narezushi extract, and recovered to the initial level by 8 h thereafter. The SBP decreased at seven successive daily doses of 10 mg/kg of narezushi extract and then recovered to the initial level 5 days after stopping a total of 10 daily administrations. The extract was administered to five-week-old SHR rats for 70 days and SBP decreased 21 days after starting and continued for 28 days after the end of administration. The peptide-rich fraction from narezushi extract had a powerful antihypertensive effect, whereas the other fraction had a similar, but weak effect.     

Expression analysis of the type I keratin protein keratin 33A in goat coat hair

The coat of a goat, like that of many mammalian species, consists of an outer coat of coarse hairs and an under coat of fine, downy hairs. The coarse guard hairs are produced by primary follicles and the finer cashmere hairs by secondary follicles. We previously reported that hair keratins are components of cashmere hair, and proteomic analysis revealed that their expression is elevated in winter coat hair. To determine detailed characterization, we have cloned keratin 33A gene, a major highly expressed keratin in winter, and then analyzed the expression of goat hair coat. By Western analysis, we detected that keratin 33A protein is expressed only in hair coat among the various goat tissues. Moreover, the expression level in winter has increased in cashmere high‐producing Korean native breed, whereas the expression levels between summer and winter had not changed in cashmere low‐producing Saanen. In addition, by immunohistochemistry we determined that keratin 33A is localized in the major cortex portion of cashmere fiber. These results confirm that keratin 33A is a structural protein of goat cashmere hair fiber.     

Permeability of the fish intestinal membrane to bulky chemicals

The ability to predict the environmental behavior of chemicals precisely is important for realizing more rational regulation. In this study, the bioaccumulation of nine chemicals of different molecular weights absorbed via the intestinal tract was evaluated in fish using the everted gut sac method. The amounts of chemicals that passed through the intestinal membrane after a 24-hr exposure were significantly decreased for chemicals with MW≥548 and D_{max min}≥15.8 Å (or D_{max aver}≥17.2 Å). These thresholds are consistent with those previously proposed in terms of MW (>800) and molecular size (D_{max min}>15.6 Å or D_{max aver}>17.1 Å) for the limit of permeable chemicals through the gill membrane. The results show that the same MW and D_max criteria can be used to predict low bioaccumulation through both the gill membrane and the intestinal tract. These findings are helpful in reducing the need to conduct animal tests in environmental safety studies.     

Contribution of the polymerization of protein by disulfide bonding to increased gel strength of walleye pollack surimi gel with preheating time

ABSTRACT: To clarify the contribution of polymerization of myosin heavy chain (MHC) by disulfide bonding to increased gel strength of cooked gel via preheating, the pastes of walleye pollack surimi (SS and C grades) were preheated at 25°C and 40°C for a variety of hours prior to heating at 80°C for 20 min. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) patterns of cooked gels were analyzed with and without reducing the samples, which were solubilized in 8 M urea–2% SDS solution. The formation of polymers by disulfide bonding in cooked gels was almost constant in each of the SS and C grade surimi gels despite the period of preheating. Therefore, it was suggested that polymerization by disulfide bonding occurred during cooking at 80°C and not during preheating.     

Inhibiting effect of polymerization and degradation of myosin heavy chain during preheating at 30°C and 50°C on the gel-forming ability of walleye pollack surimi

ABSTRACT: To confirm the contribution of polymerization and degradation of myosin heavy chain (MHC) during preheating to the gel-forming ability of fish meat paste, walleye pollack surimi paste was preheated at 30°C and 50°C prior to heating at 80°C in the presence of various inhibitors. At 30°C, ethyleneglycol bis(2-aminoethyl ether) -N,N,N ', N '-tetraacetic acid (EGTA) and ethylenediaminetetraacitic acid (EDTA) inhibited gel formation as well as the polymerization of MHC, whereas dithiothreitol (DTT) and leupeptin promoted gel formation, which was accompanied by the enhancement of MHC polymerization and decreased MHC degradation, respectively. At 50°C, leupeptin inhibited MHC degradation and improved gel strength, whereas EGTA, EDTA and DTT had no effect on MHC polymerization and degradation and did not affect gel formation. The results demonstrate that the gel strength of cooked gel (80°C) is not affected by preheating at 30°C and 50°C and does not inhibit polymerization and degradation. Results suggest that the gel strength of cooked gel is dependent on the polymerization and degradation of MHC during preheating.     

A simple method for selection of cumulus-oocyte complexes from bovine ovaries by sedimentation with percoll

Selection of bovine cumulus-oocyte complexes (COCs) for in vitro embryo production (IVP) is generally based on the morphological characteristics of the cumulus cells surrounding the oocytes and the ooplasm under microscopic observation. The purpose of this study was to examine a simple method for selection of COCs by sedimentation with Percoll solutions. COCs were aspirated from ovaries derived from a local slaughterhouse, and the COCs were classified by the morphology of their cumulus cell layers, as follows: Class A, compact and thick; Class B, compact but thin; Class C, partially denuded and thin; and Class D, denuded. Percoll solutions were prepared by diluting Percoll to 7.5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5 and 30% solutions, respectively. COCs were placed on the surface of the Percoll solution for 3 min, and the precipitated COCs were transferred to stepwise high density solution. The percentage of Percoll solution just before buoyancy was considered to the specific sedimentary value of the COC and oocyte. The mean sedimentary value of Class A COCs was higher than those of the other classes (P<0.01). The mean sedimentary values of denuded oocytes from Classes A and B were higher than those from Classes C and D (P<0.01). Our results show that sedimentation of COCs and denuded oocytes was generally related to the morphological quality of the COCs, although the sedimentary values ranged widely for one class of COCs and oocytes. The Percoll method can be used for simple selection of COCs.     

Utility of 5-aminolaevulinic acid fluorescence-guided endoscopic biopsy for malignant mesothelioma in a cat and dog

Malignant mesothelioma (MM) is uncommon in cats and dogs and can be challenging to diagnose. Adequate tissue sampling is required for superior diagnostic accuracy. Protoporphyrin IX, a metabolite of 5-aminolaevulinic acid (5-ALA), is a photosensitiser for photodynamic diagnosis (PDD). To the best of our knowledge, no study has reported the use of 5-ALA-PDD to detect MM in veterinary medicine. The present study describes the use of 5-ALA-PDD for MM diagnosis in a cat and dog, as well as the effectiveness of intracavitary chemotherapy. We evaluated the use of PDD with 5-ALA hydrochloride (5-ALA-PDD) in two cases of MM. A 12-year-old cat presented with a 1-month history of respiratory distress, and a 9-year-old dog presented with a 3-month history of mild abdominal distention. We endoscopically biopsied lesions in both the cases using 5-ALA-PDD. Histopathological examination revealed mesothelioma, and immunohistochemical staining was positive for calretinin. Both patients were treated with carboplatin. The cat died of respiratory failure. Although, the dog's condition improved 21 days after the first chemotherapeutic drug administration, the dog died on day 684 owing to cardiac-related issues. 5-ALA-PDD is thus, safe and feasible for the diagnosis of MM in veterinary medicine.     

Oleosome-Associated Protein of the Oleaginous Diatom Fistulifera solaris Contains an Endoplasmic Reticulum-Targeting Signal Sequence

Microalgae tend to accumulate lipids as an energy storage material in the specific organelle, oleosomes. Current studies have demonstrated that lipids derived from microalgal oleosomes are a promising source of biofuels, while the oleosome formation mechanism has not been fully elucidated. Oleosome-associated proteins have been identified from several microalgae to elucidate the fundamental mechanisms of oleosome formation, although understanding their functions is still in infancy. Recently, we discovered a diatom-oleosome-associated-protein 1 (DOAP1) from the oleaginous diatom, Fistulifera solaris JPCC DA0580. The DOAP1 sequence implied that this protein might be transported into the endoplasmic reticulum (ER) due to the signal sequence. To ensure this, we fused the signal sequence to green fluorescence protein. The fusion protein distributed around the chloroplast as like a meshwork membrane structure, indicating the ER localization. This result suggests that DOAP1 could firstly localize at the ER, then move to the oleosomes. This study also demonstrated that the DOAP1 signal sequence allowed recombinant proteins to be specifically expressed in the ER of the oleaginous diatom. It would be a useful technique for engineering the lipid synthesis pathways existing in the ER, and finally controlling the biofuel quality.