| As a novel nonthermal processing technology, dense phase carbon dioxide (DPCD)could effectively inactivate microorganisms and enzymes when applied both meat andaquatic products. As well as heat treatment, DPCD could also result in the damage ofmuscle tissue, and cause the structure and conformation of protein, enzyme and other largebiological molecules change. In order to explore the mechanism of muscle damage andprotein denaturation induced by DPCD, and make DPCD technology realize industrializedproduction. In this paper, the effects on muscle qualities, sarcoplasmic and myofibrillarproteins denaturation of Litopenaeus vannamei by DPCD treatment were investigated. Andfeasibility of preparing protein gel induced by dense phase carbon dioxide (DPCD) wasexplored. Main contents and conclusions were shown as belows:(1) The effects of treatment pressure (5~25MPa), temperature (35~55℃) andexposure time (10~50min) of DPCD treatment on the muscle qualities of Litopenaeusvannamei were investigated. The results showed that DPCD had no significant effect(p>0.05) on muscle pH and springiness; weight loss, hardness and color (L*、a*and b*value) increased significantly (p<0.05) with exposure time, temperature and pressureincreasing; and water holding capacity (WHC), proximate composition decreasedsignificantly (p<0.05). With the treatment intensity of DPCD increasing, higher rates oftransformation of myofibrillar and sarcoplasmic protein to insoluble protein resulted in asignificant decrease in sarcoplasmic, myofibrillar proteins fractions (p<0.05), accompaniedby a significant increase in the muscle stroma protein fraction and protein loss (p<0.05).The results of LF-NMR analysis showd that peeled shrimps had four kinds of watermobility, the degree of freedom of bound water increased and the degree of freedom ofimmobilised water and free water decreased with exposure time, temperature and pressureincreasing. And the content of bound water and free water increased significantly (p<0.05),immobilised water content decreased significantly (p<0.05).(2) The effects of treatment pressure (5~30MPa), temperature (35~60℃) andexposure time (10~60min) of DPCD treatment on the sarcoplasmic proteins and activityof metabolic enzymes from Litopenaeus vannamei were investigated. The results showedthat ten active enzymes (alkaline phosphatase, esterase, esterase lipase and acidphosphatase et al) were detected in sarcoplasmic protein using an API ZYM enzyme assay kit. The activity of ten enzymes decreased with exposure pressure, temperature or timeincreasing. And the effect of DPCD on the enzymes depends on type of enzymes. Theresults of SDS-PAGE and Native-PAGE showed that DPCD treatment could make allsarcoplasmic protein denaturation and aggregation when DPCD treatment conditions werehigh enough, leading to the decrease of protein solubility. But the decline rates of differentprotein solubility were different, big molecular proteins were more easily affected by highdensity CO2than small molecule protein. Comparaed with heat treatment, enzymeinactivation effect and the protein denaturation degree induced by DPCD were moreserious at same temperature.(3) The effects of treatment pressure (5~30MPa), temperature (35~60℃) andexposure time (10~60min) of DPCD treatment on the physicochemical properties andsecondary structure of myofibrillar proteins from Litopenaeus vannamei were investigated.The results showed that myofibrillar protein solubility, sulfhydryl content, Ca2+-ATPaseactivity increased sharply (p<0.05) at the beginning of the rise in treatment pressure,temperature and time. While the surface hydrophobicity increased significantly (p<0.05).The results of SDS-PAGE showed that DPCD treatment could make myofibrillar proteindenaturation and aggregation, and lead to the decrease of protein solubility. FTIR analysisshowed that α-helix and random coil could drastically change to β-sheet and β-turn afterdifferent DPCD treatment conditions (5MPa,45℃,30min;35℃,15MPa,30min;10min,15MPa,45℃), comparaed with untreated protein. But the change became slightlywith the treatment intensity of DPCD continue to rise. Comparaed with heat treatment, theeffect of DPCD treatment on physicochemical properties and secondary structure ofmyofibrillar proteins were more serious at same temperature.(4) The effects of treatment pressure (5~30MPa), temperature (50~70℃) andexposure time (10-50min) on gel properties and proximate composition of shrimp surimifrom Litopenaeus vannamei were studied. The results showed that DPCD could induceshrimp surimi to form protein gel. The pressure, exposure time and temperature hadsignificant effect on gel properties. Gel properties of shrimp surimi induced by DPCD werebetter under conditions of20or25MPa,60℃,30min. Compared with the gel induced byheat (80℃,30min), the gel induced by DPCD had higher gel strength and water holdingcapacity, and retained more nutrient components (p<0.05). The denser and morehomogenous networks was also observed in shrimp surimi gel induced by DPCD. |
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