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

Effect of high pressure processing on the microstructure, myofibrillar protein oxidation, and volatile compounds of sauce lamb tripe

In this study, sauce lamb tripe was used as the research object. High pressure processing (HPP) was carried out at 100, 250, and 400 MPa, with holding times of 5, 10, 15, 20, and 25 min at 25 °C, respectively. The effects of HPP on the microstructure and volatile compound content of sauce lamb tripe and the properties of myofibrillar protein were studied. The degree of protein oxidation was most significant at 400 MPa for 25 min. The secondary structure of myofibrillar protein became unstable and the microstructure of the sauce lamb tripe became loose at 400 MPa. The retention of hydrocarbons, aldehydes, alcohols, and ketones was maximum at 250 MPa for 15 min, and the flavor-contributing compound (3-Hydroxy-2-butanone) was also retained by 11.9% on ketones at 250 MPa for 15 min. The results showed that myofibrillar protein was appropriately oxidized; the sauce lamb tripe had better microstructure and several representative volatile compounds after HPP. Therefore, better processing conditions for sauce lamb tripe were 250 MPa for 15 min.

Changes to the tropomyosin structure alter the angiotensin-converting enzyme inhibitory activity and texture profiles of eel balls under high hydrostatic pressure

Changes in the structure of tropomyosin (TM) altered the texture profiles of eel balls and the inhibitory activity of the angiotensin-converting enzyme (ACE). The secondary and tertiary structure of TM was determined after high hydrostatic pressure (HHP) treatment. The correlation between the spatial structure of TM and the texture profiles of eel balls was developed and discussed. The β-sheet was converted to a β-turn and a random coil when treated at HHP (200-400 MPa), meanwhile the α-helix unfolded and was converted into a β-sheet, β-turn and a random coil with treatment at 500 and 600 MPa. The surface hydrophobicity (H0) was increased and the sulfhydryl (SH) content decreased with an increase in the pressure. The results indicated that the texture profiles of eel balls showed a negative relationship with the α-helix, β-sheet and SH content. The texture profiles of eel balls were greatly enhanced after treatment at 500 and 600 MPa, leading to the improved surface network of the eel ball products. The ACE inhibitory activity of TM after HHP treatment exhibited a positive relationship with the β-sheet content in the protein. The ACE inhibitory activity was preserved under 600 MPa.

Impact of High Hydrostatic Pressure on the Shelling Efficacy, Physicochemical Properties, and Microstructure of Fresh Razor Clam (Sinonovacula constricta)

The effects of high hydrostatic pressure (HHP) treatments (200, 300, and 400 MPa for 1, 3, 5 and 10 min) on the shelling efficacy (the rate of shelling, the rate of integrity and yield of razor clam meat) and the physicochemical (drip loss, water-holding capacity, pH, conductivity, lipid oxidation, Ca²⁺ -ATPase activity, myofibrillar protein content), microbiological (total viable counts) and microstructural properties of fresh razor clam (Sinonovacula constricta) were investigated. HHP treatments significantly (P < 0.05) increased shelling efficiency, water-holding capacity, pH, conductivity, and lipid oxidation, and HHP-treated razor clam showed lower levels of microorganisms and drip loss than untreated razor clam. Levels of thiobarbituric acid reacting substances (TBA) in HHP-treated razor clam were greatly increased (up to 0.93 ± 0.09 mg MDA/kg at 400 MPa for 10 min) which was caused by the formation of hydroperoxides during HHP treatment. All HHP treatments were found to have adverse effects on the activity of Ca²⁺ -ATPase and the content of myofibrillar protein (MP), which might be due to the substantial damage to the tertiary structure of proteins at high pressure. Moreover, scanning electron microscopy (SEM) revealed the compaction of the muscle fibers and a decrease in the extracellular space with increasing pressure and holding time. This phenomenon was mainly correlated with the compaction of muscle fibers and denaturation, aggregation, and gelation of muscle protein triggered by high pressure. In general, HHP could be applied as a safe and effective nonthermal technology to produce high-quality shelled razor clam.

PRACTICAL APPLICATION

High hydrostatic pressure (HHP) is now well known as a nonthermal processing technology and becoming increasingly acknowledged. However, it has not been widely applied to shell seafood due to its uncertain influence on its quality and shelling property. This study could provide valuable information regarding the shelling efficacy, physicochemical properties, and microstructure of razor clam treated by HHP. And it demonstrated that HHP showed a positive impact on quality of razor clam treated by HHP.

Extension of shelf life of chilled hake (Merluccius capensis) by high pressure/Prolongación de la vida útil de merluza (Merluccius capensis) sometida a altas presiones conservada en refrigeración

Vacuum packed hake muscle subjected to 400 MPa (three 5-min cycles) at 7 °C proved to be more stable at chilled temperatures (2-3 °C), and sensorially acceptable, until 43 days of storage in comparison with the nine days for the non-pressurized hake. The lot pressurized at 400 MPa had the appearance of cooked muscle. The microbial load was initially reduced by two log units by pressurization at 400 MPa. Trimethylamine nitrogen (TMA-N) values were also very low. Pressurization had no effect on dimethylamine nitrogen (DMA-N) production. The lot pressurized at 400 MPa showed slower increase in drip loss from day 15 of storage. In the lot subjected to 200 MPa (three 5-min cycles) at 7 °C, which retained the appearance of raw fish, microorganisms were one log unit lower than in the non-pressurized sample and TMA-N was lower. In conclusion, the chilled shelf life was prolonged by about one week in the lot pressurized at 200 MPa and about two weeks in the lot pressurized at 400 MPa.

Behavior of Octopus Muscle (Octopus vulgaris) under a Process of Pressure-Time-Temperature Combinations

Octopus muscle ( Octopus vulgaris) of different sex was treated for various different simultaneous combinations of pressure (0.1 or 450 MPa), time (15 or 30 min) and temperature (7, 40, 75 or 100 °C). The sex of specimens was not a significant factor. High pressure was effective in reducing the microbial load and the intense autolytic activity in the octopus muscle. Pressurization time was found to be a significant factor for hardness, but neither hardness nor the exudates were reduced by pressurizing at 450 MPa. Progressive raising of the temperature increased the drip loss, while hardness was reduced only at high temperatures. Increasing temperature produced ultrastructural changes relating to softening, but nevertheless, the ultrastructural changes observed after pressurization did not correspond with modifications in shear strength.

Evaluation of quality characteristics of chicken meat emulsion/nuggets prepared by using different equipment

Chicken meat emulsions prepared using food processor (FP), an indigenous meat cutter (MC) and bowl chopper (BC) were evaluated for physicochemical, texture and electron microscopic studies (SEM). Product yield, emulsion stability, hydration properties and gel strength (N) were significantly (P < 0.05) higher in BC. Total fluid release (TFR), water release (WR) and fat release (FR) was lowest in BC. Significantly (P < 0.05) higher lightness (L) in BC and redness (a) in FP emulsion were observed. Higher firmness, gumminess, chewiness and cohesiveness were observed in BC emulsion. SEM studies revealed a dense and compact protein matrix characteristic of heat induced protein gels. All micrographs showed structures that are compatible with fat globules, muscle fiber, meat protein matrix and heat induced gel/protein matrix. Sensory evaluation showed no significant difference between three treatments for colour, flavour, texture and acceptability scores. Thus, food processor and indigenously developed meat cutter found suitable for producing a stable chicken meat emulsion required for indigenous meat products.

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.

Extension of the shelf life of prawns (Penaeus japonicus) by vacuum packaging and high-pressure treatment

The present study has investigated the application of high pressures (200 and 400 MPa) in chilled prawn tails, both conventionally stored (air) and vacuum packaged. Vacuum packaging and high-pressure treatment did extend the shelf life of the prawn samples, although it did affect muscle color very slightly, giving it a whiter appearance. The viable shelf life of 1 week for the air-stored samples was extended to 21 days in the vacuum-packed samples, 28 days in the samples treated at 200 MPa, and 35 days in the samples pressurized at 400 MPa. Vacuum packaging checked the onset of blackening, whereas high-pressure treatment aggravated the problem. From a microbiological point of view, batches conventionally stored reached about 6 log CFU/g or even higher at 14 days. Similar figures were reached in total number of bacteria in vacuum-packed samples and in pressurized at 200-MPa samples at 21 days. When samples were pressurized at 400 MPa, total numbers of bacteria were below 5.5 log CFU/g at 35 days of storage. Consequently, a combination of vacuum packaging and high-pressure treatment would appear to be beneficial in prolonging freshness and preventing spotting.