Solubility, stability and blood pressure lowering-properties of fresh and cured beef proteins

Abstract

This study aimed to investigate the solubility, stability, and blood pressure lowering-properties of fresh and cured beef product (pastirma) proteins. The changes in solubility, oxidation, molecular weights, and surface hydrophobicity of muscle proteins were investigated. Antihypertensive activities of peptic hydrolysates from fresh meat (FM) and pastirma (PS) were also determined using an angiotensin-converting enzyme (ACE) assay. Pastirma showed a higher solubility of sarcoplasmic and myofibrillar protein (3.59 and 6.10mg/ml) than in fresh meat (2.71 and 5.35/ml). Data suggests that the salt-curing process of beef increases the solubility of both sarcoplasmic and myofibrillar proteins. The high solubility in PS proteins referred to the spontaneous proteolyses occurred during the course of the process, which results in a remarkable protein denaturation phenomenon. Data illustrates that SH and free S groups (477 and 413µmol/g) in fresh beef were higher than those in pastirma (116 and 56µmol/g) samples meaning that a protein oxidation-reduction reaction has occurred during the course of processing. Salt as a pro-oxidant in pastirma might have broken the disulfide bridges of the native proteins allowing reactive oxygen species to react in-depth with the hydrophobic amino, which perhaps results in producing thiol and sulfonic-related compounds. Proteins surface hydrophobicity was a 2-fold increase in PS due to protein denaturation meaning that more hydrophobic amino acids were liberated during the course of processing. The SDS-PAGE gel images distinguish the number of changes occurred on protein structure. Myosin heavy chain protein (200kDa), β–galactosidase (117kDa) and glutamic dehydrogenase (55kDa) were present in fresh meat but they have become vanished in the cured beef. The salt-curing process and cemen treatment during the course of manufacturing highly contributed to the inexistence of those proteins. ACE inhibition ratios in FM and PS samples were 85.55 and 77.24%. The antihypertensive activities (IC50) of fresh beef and pastirma were 1.13 and 0.92 mg/ml (p< 0.05), respectively. Hydrolysates in pastirma showed a higher antihypertensive activity than in fresh beef. Data of this article suggests that solubility of pastirma protein was increased but the stability decreased, however, pastirma may contain a potential number of constituents that could be utilized in the area of functional food and nutraceuticals