Protective effect of porcine plasma protein hydrolysates on the gelation of porcine myofibrillar protein exposed to a hydroxyl radical-generating system

https://doi.org/10.1016/j.ijbiomac.2017.09.036Get rights and content

Highlights

  • Addition of PPPH to MP reduced the loss in gel strength and WHC induced by HRGS.

  • LF-NMR results indicated that the addition of PPPH improved protein hydration.

  • PPPH promoted the formation of a more smooth and homogeneous MP gel network.

  • PPPH effectively retarded oxidation-induced MP gel deterioration.

Abstract

This study investigated the effect of different concentrations of porcine plasma protein hydrolysates (PPPH) on the gelation of porcine myofibrillar protein (MP) exposed to a hydroxyl radical-generating system (HRGS). Compared to non-oxidized MP, the oxidative modification led to a decreased penetration force and water holding capacity (WHC) (P < 0.05). Meanwhile, addition of PPPH (1.5 mg/mL) reduced the loss of MP gel strength and WHC induced by HRGS (P < 0.05). Low-field nuclear magnetic resonance results suggested that the addition of PPPH facilitated the hydration of the protein. The results concerning molecular forces revealed that hydrophobic interactions, hydrogen bonds, and disulphide bonds are the primary forces in gel formation. Non-reducing electrophoresis indicated that the addition of PPPH reduced protein loss and aggregation. The addition of PPPH promoted the formation of a more smooth and homogeneous gel network. Our results demonstrated that PPPH effectively retarded oxidation-induced MP gel deterioration and could be used as an antioxidant in meat products.

Introduction

The properties of comminuted meat products, such as a desirable texture and water-binding capacity, are based on the heat-induced gelling and rheological behaviour of the proteins. Salt-soluble myofibrillar protein (MP) plays a remarkable role in imparting these properties to meat products [1]. Meat proteins are susceptible to oxidation, especially during meat processing and storage, and protein oxidation negatively affects the MP gelling. Protein oxidation is initiated by reactive oxygen species (ROS), especially free radicals, and is characterized by conformational changes, reduced solubility, aggregation, and a general loss of functional properties [2]. Tunhun et al. [3] reported that the oxidation of fish protein during washing decreased its ability to dimerize and form a gel. Huang et al. [4] reported that protein oxidation reduces the gelling capacity of porcine MP, which contributes most to the loss of texture in dumpling meat fillings. More importantly, Wang et al. [5] reported that, at high malondialdehyde oxidative concentrations (25–50 mM), the gelling quality of MP in silver carp was weakened, probably because of the formation of excessive covalent bonds. However, Lu et al. [6] proved that mild protein oxidation caused by frozen storage or treatment with 0.1 mM H2O2 promotes bighead carp MP gel formation.

Of various antioxidative strategies, the most effective approach to inhibiting protein oxidation is the application of antioxidants [7]. Protein hydrolysates prepared with different kinds of enzymes are increasingly used as natural antioxidants in the food industry and provide many health benefits, which have been mainly attributed to the bioactive peptides in them. Porcine plasma protein hydrolysates (PPPH), hydrolysed with alcalase for 5 h, show strong radical-scavenging, Cu2+-chelation and reducing power abilities [8]. In rats, PPPH has strong antioxidant activity in protecting the liver against CCl4-induced oxidative damage [9]. Li et al. [10] reported that a combination of zein hydrolysates and sage extract exhibits a significant synergism against oxidation in liposomes. Li et al. [11] studied the effect of combined whey protein isolate hydrolysates and cryoprotectants on inhibiting the loss of quality in common carp (Cyprinus carpio) surimi during freezing. Their results showed that treatments with combined protein hydrolysates and cryoprotectants decrease the extent of protein oxidation and limit protein structural changes.

Although there have been studies on the inhibition of MP oxidation with protein hydrolysates, few studies have studied the influence of protein hydrolysates on the gelling of oxidized MP. The aim of this study was to study the influence of different concentrations of PPPH on the gelling properties, including gel penetration force, water holding capacity (WHC), and microstructure and surface morphology of porcine MP under controlled oxidizing conditions created with a hydroxyl radical-generating system (HRGS). Moreover, a possible protective mechanism was proposed by analysing molecular forces in the gel, water distribution and data from sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE).

Section snippets

Materials

Porcine plasma protein, purchased from Beidahuang Meat Corporation (Harbin, Heilongjiang, China), contained 85% protein as determined by the Kjeldahl method of standard procedures (AOAC, 2000). Pork longissimus muscle (1 d post mortem) was obtained from a local commercial store (Harbin, Heilongjiang, China). The samples were kept on ice and transported to the laboratory and used on the same day. Piperazine-N,N bis, and Piperazine-1,4-bis(2-ethanesulfonic acid) (PIPES) was purchased from Sigma

Gel strength and water-holding capacity

The gel strength of MP and OxiMP samples with or without PPPH was evaluated using penetration testing and the results are shown in Fig. 1A. The penetration force of the OxiMP gel significantly decreased by 37.25% (P < 0.05) compared with the control MP gel. This decrease may primarily be due to intense protein carbonylation induced by protein oxidation, and therefore weakened MP gelling capacities [23]. Xiong et al. [24] reported that higher concentrations of H2O2 weaken the strength of the gel.

Conclusions

The protective effect of PPPH on gelation of MP exposed to an HRGS was investigated in this study. The results demonstrate that PPPH reduced the loss of MP gel strength and WHC induced by an HRGS. LF-NMR analysis revealed that weak hydration of MP induced by oxidation could be improved by the addition of PPPH. SDS-PAGE patterns proved that PPPH reduced protein aggregation. PPPH also reduced the damage to the gel microstructure and improved the gel texture. Therefore, the addition of PPPH in the

Acknowledgements

This study was supported by the National Natural Science Foundation of China (Grant No. 31671788), the Young Innovative Talents Training Plan of General Institutes of Higher Education in Heilongjiang Province (Grant No. UNPYSCT-2016006) and the Programme for Academic Backbone of Northeast Agricultural University (Grant No. 16XG18).

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