| High pressure processing(HPP) is an emerging technology that can affect protein conformations and lead to protein denaturation, aggregation or gelation, therefore modifying the functional properties of food protein. Effects of HPP are subject to the pressure condition, the protein system and amino acids. L-Arginine, as the most common solvent additive, has been used to solubilize protein in low ionic strength solutions. However, only the livestock and poultry meat, as the protein supplement, is considered, but the aquatic product is ignored. Thus, myosin from tilapia white meat was selected as research object in this study. Changes in the solubility and conformation of tilapia myosin subjected to HPP were firstly investigated. And the discussed influence factors were the applied pressure level, holding time and temperature, pH, ionic strength and L-arginine. Then, the gelation properties and rheological behaviors of high-concentration myosin treated by L-arginine and HPP were also analyzed. The aims of this work were to provide technical support and theoretical guidance for high pressure processing in the food industrial production, and to promote the value-added utilization of aquatic protein resources and development of new protein resources. The main results were as follows:1. One myosin heavy chain at 200 kDa and four light chains at 25.7, 21.2, 17.0, 16.0 kDa were observed on SDS-PAGE gel. And the purity of myosin was 94%. At 200-600 MPa(10 min), the turbidity and surface hydrophobicity(ANS-S0) of myosin significantly increased(p<0.05) and α-helical content decreased, but the solubility not obviously decreased(p>0.05). However, changes in the solubility and conformation of myosin were also not obvious at 200-600 MPa(20-60 min)(p>0.05). Moreover, the turbidity and ANS-S0 of myosin at 45 oC increased and the solubility decreased significantly(p<0.05), compared with 4 oC and 25 oC.2. The shape of pH-solubility line of myosin was “U” and the solubility of myosin at isoelectric point was minimal. At neutral and extreme alkaline pHs(pH 11.0 and 12.0), there were no differences between 300 and 600 MPa and no pressure(10 min). While at extreme acidic pHs(pH 2.0 and 2.5), increase in the turbidity was observed(p<0.05), especially at 600 MPa(10 min), and the solubility of myosin at pH 2.0 and 2.5 were significantly decreased from 84.2%, 81.5% to 20.6%, 2.7%, respectively. In the pH range of experiment, the ANS-S0 value, β-sheet and β-turn content of myosin pressurized increased, but the α-helix content decreased. Moreover, SDS-PAGE profile analysis showed that myosin tended to denaturation and aggregation at acid pHs, but myosin might unfold and expose sulfhydryl groups to form aggregation by disulfide bonds at neutral and extreme alkaline pHs.3. Myosin was insoluble in lower ionic strength solutions(1-150 mmol/L KCl), so the turbidity was higher and the solubility was lower. Moerover, at 100-300 MPa(10 min), the turbidity greatly increased and the solubility significantly decreased(p<0.05), especially at 300 MPa, the solubility of myosin at 150 mmol/L KCl was decreased from 70% to 17%. While, myosin was well soluble in higher ionic strength solutions(200-600 mmol/L KCl). And there were no obvious changes in the solubility and turbidity of myosin at 100-300 MPa(10 min). The ANS-S0 value of myosin increased obviously with increasing pressure, especially at 300 MPa(p<0.05), but α-helical content decreased obviously. Besides, ANS-S0 also significantly incresed with increasing ionic strength.4. Myosin, at low(1 mmol/L KCl) and physiological ionic strength(150 mmol/L KCl), was significantly solubilized by L-arginine(10 mmol/L)(p<0.05). In a low ionic strength solution, the solubility of myosin with L-arginine decreased at 200-300 MPa(10 min)(p<0.05). In a physiological ionic strength solution, the turbidity and ANS-S0 of myosin with L-arginine increased significantly at 300 MPa(10 min), but α-helix content and solubility decreased(p<0.05). In a high ionic strength solution, ANS-S0 of myosin regardless of L-arginine increased at 100-300 MPa(10 min)(p<0.05), but the α-helix content and solubility not changed significantly.5. Effects of L-arginine and HPP on the gelation properties and rheological behaviors of myosin(17.0 mg/m L) were obvious. The dynamic elastic modulus(G’) of heat-induced gel of myosin changed with increasing temperature(20-90 oC, 1 oC/min). Without L-arginine, the beginning elastic modulus(G’) of myosin at low and physiological ionic strength significantly increased at 200 MPa(10 min), and the elastic modulus(G’) at 75 oC and above also distinctly increased at high ionic strength(p<0.05). With L-arginine, the G’ value of myosin at a low ionic strength significantly decreased at 100-200 MPa(10 min), but the G’ value at 75 oC and above increased significantly at physiological and high ionic strength(p<0.05). Furthermore, the contributions of chemical interactions to myosin gels are subject to the ionic strength. In a low ionic strength solution, the main chemical interactions were disulfide bonds, hydrophobic interactions and non-disulfide bonds. At physiological and high ionic strength, the main chemical interactions were disulfide bonds and non-disulfide bonds, respectively. Without L-arginine, hydrophobic interactions and disulfide bonds decreased at a low ionic strength and at 200 MPa(10 min), but non-disulfide bonds increased, besides, ionic bonds and hydrogen bonds decreased at a high ionic strength(p<0.05). With L-arginine, hydrophobic interactions, disulfide bonds and non-disulfide bonds decreased at a low ionic strength and at 100-200 MPa(10 min), while at a high ionic strength, hydrophobic interactions decreased, but hydrogen bonds increased(p<0.05). |
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