High-pressure treatment for shelf-life extension and quality improvement of oysters cooked in a traditional Taiwanese oyster omelet.

Whole oysters were processed using high-pressure (HP) treatment at 250 and 300 MPa for 0 to 10 min and stored at 4 degrees Celsius for up to 28 days. HP-treated oysters and untreated oysters were evaluated for lipid oxidation, growth of microorganisms, and sensory characteristics after cooking at 160 degrees Celsius for 90 s. Microbial counts after HP treatment revealed that the bacterial load was initially reduced at all pressures. HP-treated oysters had significantly higher pH and moisture (P < 0.05) relative to control (untreated) oysters during storage. HP treatment increased lipid oxidation with unpleasant odor during storage compared with the control. HP treatment decreased redness but did not significantly affect the brightness and yellowness of cooked oysters. From tests of mechanical properties, 300 MPa-treated oysters after cooking had significantly increased toughness as measured by cutting force. HP-treated oysters after cooking received higher quality scores than did the control during the storage trial. Results indicated that 300 MPa for 2 min is the optimum HP treatment that results in oysters most acceptable for oyster omelets during storage at 4 degrees Celsius, and this treatment may extend the shelf life of these oysters to 21 days.

Effect of different high pressure treatments on shucking, biochemical, physical and sensory characteristics of oysters to elaborate a traditional Taiwanese oyster omelette.

BACKGROUND: Whole oysters (Crassostrea gigas) were processed using high-pressure (HP) treatment (150-300 MPa) to determine their shucking and biochemical properties. Subsequently, HP-treated oysters were cooked at 160 degrees C for 90 s, as when preparing the oyster omelette dish, to evaluate their physical and sensory characteristics as compared to raw oysters. RESULTS: The treatments of 250 and 300 MPa for 2 min and 0 min, respectively, resulted in 100% release. The pH of HP-treated oysters increased slightly from 6.50 to 6.82, and the moisture contents of the HP-treated oysters with or without further cooking were all higher than those of the control. The brightness, yellowness and cutting strength of HP-treated oysters with further cooking changed insignificantly, while the redness decreased compared to the control. Sensory evaluation showed that oysters treated at 250 and 300 MPa oysters after cooking received higher quality scores than the control. CONCLUSIONS: HP processing at 250 and 300 MPa proved to be a good method for oyster shucking. The HP-treated oysters cooked in the oyster omelette are acceptable to consumers. Overall, the application of HP as a processing method to improve the quality and acceptability of oysters and their related products would be possible.

Effects of porcine brain hydrolysate on impairment of cognitive learning ability in amyloid ß(1-40) -infused rats.

This study assessed whether administering porcine brain hydrolysate (PBH) ameliorates the impairment of spatial cognition learning ability in amyloid ß (Aß)-infused rats. PBH was prepared using organic solvents (i.e., acetone and ethanol). Enzyme hydrolysates were derived from these PBH and the sequence of the Aß peptide for infusion was selected. The results indicated the PBH, in particular EP (porcine brain extract with ethanol and protease N), demonstrated the potentials to reduce damage of neurodegenerative disorders in vitro and in vivo. The principal findings of this study indicate that PBH has prolyl endopeptidase inhibitory activity in vitro. Moreover, administering EP to Aß(1-40)-infused rats significantly improves their performance on reference, spatial performance, and working memory tests during water maze tasks; concurrent proportional decreases are also observed in malondialdehyde levels, acetylcholinesterase (AChE) activity, and Aß accumulation levels in brain tissues. The PBH was suggested to ameliorate learning deficits associated with Alzheimer's disease by inhibition of lipid peroxidation in the brain of Aß infused rat.

Comparative study on histological structures of the vitelline membrane of hen and duck egg observed by cryo-scanning electron microscopy.

The histological structures of the vitelline membranes (VM) of hen and duck eggs were observed by cryo-scanning electron microscopy (cryo-SEM), and the chemical characteristics were also compared. The outer layer surface (OLS) of duck egg VM showed networks constructed by fibrils and sheets (0.1-5.2 microm in width), and that of hen egg presented networks formed only by sheets (2-6 microm in width). Thicker fibrils (0.5-1.5 microm in width) with different arrangement were observed on the inner layer surface (ILS) of duck egg VM as compared to those (0.3-0.7 microm in width) of hen egg VM. Upon separation, the outer surface of the outer layer (OSOL) and the inner surface of the inner layer (ISIL) of hen and duck egg VMs were quite similar to fresh VM except that the OSOL of duck egg VM showed networks constructed only by sheets. Thin fibrils interlaced above a bumpy or flat structure were observed at the exposed surface of the outer layer (ESOL) of hen and duck egg VMs. The exposed surfaces of inner layers (ESIL) of hen and duck egg VMs showed similar structures of fibrils, which joined, branched, and ran in straight lines for long distances up to 30 microm; however, the widths of the fibrils shown in ESOL and ESIL of duck egg VM were 0.1 and 0.7-1.4 microm, respectively, and were greater than those (<0.1 and 0.5-0.8 microm) of hen egg VM. The continuous membranes of both hen and duck egg VMs were still attached to the outer layers when separated. The content of protein, the major component of VM, was higher in duck egg VM (88.6%) than in hen egg VM (81.6%). Four and six major SDS-soluble protein patterns with distinct localization were observed in hen and duck egg VMs, respectively. Overall, the different histological structures of hen and duck egg VMs were suggested to be majorly attributable to the diverse protein components.

Histological structures of native and cooked yolks from duck egg observed by SEM and cryo-SEM.

A method was used to fix duck egg yolk while retaining its original sol structure to elucidate the fine structure of native yolk by using fixation with liquid nitrogen and cryo-scanning electron microscopy (cryo-SEM). Native yolk spheres showed a polyhedron shape with a diameter at approximately 50 to 100 µm and packed closely together. Furthermore, the interior microstructure of the native yolk spheres showed that a great amount of round globules ranging from 0.5 to 1.5 µm were embedded in a continuous phase with a lot of voids. After cooking, the sizes of the spheres were almost unchanged, and the continuous phase became a fibrous network structure observed by SEM with chemical fixation probably constituted of low density lipoprotein (LDL). The fine structure of the native yolk can be observed by cryo-SEM; however, the microstructure of yolk granules and plasma from cooked shell eggs can be observed by SEM with chemical fixation.