Structural Changes and Functional Properties of Threadfin Bream Sarcoplasmic Proteins Subjected to pH‐Shifting Treatments and Lyophilization

Abstract

Structural changes and functional properties of threadfin bream (Nemipterus sp.) sarcoplasmic proteins (TB-SP) subjected to various pH conditions (pH 3, 5, 6.3, 9, and 12) after subsequent pH readjustment to pH 7 were investigated. Fourier transform infrared spectroscopy revealed the loss of alpha-helical and beta-sheet structures of TB-SP after being subjected to pH 3 or pH 12 treatments. The extent of structural and conformational changes of TB-SP subjected to pH 3 was greater than alkaline pHs (pH 9, 12) and pH 5, respectively. The water holding capacity of lyophilized TB-SP treated at pH 3 and pH 12 increased about 6.5- and 5.4-fold, respectively, as compared to the crude counterpart. Both acid and alkaline pH treatments increased fat absorption capacity of lyophilized sample about 2-fold, but drastically decreased its solubility. The water soluble fraction of extremely acidic (pH 3-->7) and alkaline (pH 12-->7) samples exhibited higher oil binding capacity as measured by diphenylhexatriene fluorescence and emulsifying activity. A gel-like structure was formed when water-soluble fraction of crude TB-SP and those subjected to moderate pHs (pH 5, 9) at 2 mg/mL was prepared for the emulsion containing 50% oil (v/v). Functional properties of TB-SP varied, depending on the pH-adjustment process applied.

Effects of Chilling and Partial Freezing on Rigor Mortis Changes of Bighead Carp (Aristichthys nobilis) Fillets: Cathepsin Activity, Protein Degradation and Microstructure of Myofibrils

“…There existed about 9 major sarcoplasmic protein bonds with molecular weight that ranged from 14 to 97 kDa, one band had a molecular weight of approximately 14 kDa, 3 of 25 to 31 kDa, and 2 each of 31 to 43 kDa, 50, 60, and 97 kDa (Figure ). The bonds with molecular weight of 41, 39, and 36 kDa from sarcoplasmic proteins represented creatine kinase, aldolase, and glyceraldehyde‐3‐phosphate dehydrogenase, respectively (Yongsawatdigul and Hemung ). A 94 kDa band was assumed to be phosphorylase (Toyohara and others ).…”

pH-dependent characteristics of gel-like emulsion stabilized by threadfin bream sarcoplasmic proteins

“…Alizadeh-Pasdar and Li-Chan (2000) indicated that a decrease of a-helix and an increase in random coil structure of b-lactoglobulin were observed when the pH increased from pH 5 to 9. A drastic loss of a-helical and b-sheet structures of TBSP subjected to extreme alkaline at pH 12 before neutralizing back to pH 7 was previously observed (Yongsawatdigul & Hemung, 2010). It can be noticed that So PRODAN of TBSP at pH 3 was lowest although unfolding would be likely to occur.…”

“…A striking functional property of TBSP was the ability to form a gel-like emulsion containing oil volume fraction of 0.5 at concentration as low as 2 mg/mL without thermal treatment (Yongsawatdigul & Hemung, 2010). The gel-like emulsion has been previously reported in emulsion containing oil volume fraction of 0.75, which was stabilized by crayfish flour at high pH of 11.5 (Romero, Cordobes, Puppo, Cuerrero, & Bengoechea, 2008).…”

“…Krasaechol, Sanguandeekul, Duangmal, and Owusu-Apenten (2008) reported that acetylation increased emulsifying activity and foaming capacity of threadfin bream SP (TBSP). Yongsawatdigul and Hemung (2010) demonstrated that TBSP subjected to either extreme acid or alkaline conditions followed by neutralization to neutral pH exhibited conformational changes, leading to an increase in emulsifying activity and oil binding capacity of SP. However, the effect of pH on emulsifying properties of SP that are not subjected to the pH-shift process has never been examined.…”

Evaluation of pH‐treated fish sarcoplasmic proteins on rheological properties of fish myofibrillar protein mediated by microbial transglutaminase

“…However, this value was increased with the addition of pH‐treated SP samples, and addition of acid‐treated SP had higher shear stress than the alkaline‐treated SP. This study was also agreed with the study of Yongsawatdigul and Hemung (), who reported that the ability of fish SP powder to hold water could be improved by acid and alkaline treatments. In addition, an acid treatment (showing higher degree of denaturation) was more effective to hold water than that of alkaline (Yongsawatdigul & Hemung, ).…”