Enzymolysis kinetics and activities of ACE inhibitory peptides from wheat germ protein prepared with SFP ultrasound-assisted processing
Introduction
Wheat germ, a by-product of wheat industrial processing, is a potential plant-based protein resource because of its high protein content (30%) [1]. Reported research indicates that angiotensin converting enzyme (ACE) inhibitory peptides from wheat germ, prepared with traditional enzymolysis, have high activities [2], [3]. They are thus good and safe food-based functional peptides. However, traditional enzymolysis has many disadvantages, such as long enzymolysis time, low utilization rate of the enzyme, and low conversion rate of the substrate. This is mainly due to (1) low contact frequency caused by uneven stirring, (2) decreased enzyme activity, and (3) aggregation and deposition of protein during enzymolysis. Therefore, researchers have been studying different processing methods to improve the utilization rate of enzyme and conversion rate of substrate as well as reduce the enzymolysis time. The ultrasound-assisted technology has been widely applied in solving the disadvantages of traditional enzymolysis [4], [5], [6]. Some researchers have reported that ultrasound treatment can improve enzymatic hydrolysis [7], [8], [9], [10], [11]. The mechanism of ultrasound treatment is attributed to mechanical, cavitation, and thermal efficacies, which can result in enhanced mass transfer, increased contact frequency between substrate and enzyme, enzyme configuration change, etc., [12], [13], [14], [15]. However, no research has been reported on the process conditions and kinetics of sweep frequency and pulsed (SFP) ultrasound-assisted enzymolysis for producing ACE inhibitory peptides from wheat germ protein. Angiotensin converting enzyme is an important endogenous enzyme, which can result in a blood pressure increase in the human body. Thus, all peptides that inhibit ACE are named ACE inhibitory peptides and are evaluated in vitro by a crucial indicator of ACE inhibitory activity.
The objectives of this research were to (1) study the effects of SFP ultrasound on the enzymolysis processes under different times and substrate concentrations, and (2) determine the conversion rate of protein, ACE inhibitory activity of peptide and kinetic parameters of SFP ultrasound-assisted enzymolysis, and compare them to traditional enzymolysis. The conversion rate of protein and ACE inhibitory activity of peptide were used to evaluate the feasibility of SFP ultrasound-assisted enzymolysis, which can provide the theoretical basis and technological support for further research in functional peptides production.
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Materials and reagents
Defatted wheat germ was obtained from An-yang Mantianxue Food Manufacturing Co., Ltd. (Henan, China). Alcalase with the activity of 1.325 × 105 U/g and recommended temperature of 50 °C and pH value 8.0 and was purchased from Novozymes Co., Ltd. (Shanghai, China). Angiotensin converting enzyme (ACE) was extracted from the pig lung according to the reported method [16], which had the activity of 0.1 U/mL. N-Hippuryl-His-Leu hydrate (HHL, No. H1635) was purchased from Sigma–Aldrich Co. (Shanghai,
Effect of SFP ultrasound on enzymolysis process
Fig. 1(a) and (b) shows the enzymolysis processes of wheat germ protein in traditional and SFP ultrasound-assisted enzymolysis at different substrate concentrations during an enzymolysis time of 120 min. It can be seen that the hydrolyzed protein concentrations in traditional enzymolysis increased almost linearly within the first 15 min of enzymolysis, and then slowed down to stabilization in the 20th min for low substrate concentrations (⩽3.0 g/L) and the rate of increase slowed down for high
Conclusions
SFP ultrasound-assisted enzymolysis significantly increased the enzymolysis efficiencies and activities of ACE inhibitory peptide at different substrate concentrations and enzymolysis times. By considering the activity of ACE inhibitory peptide and operation cost, the recommended conditions of SFP ultrasound-assisted enzymolysis are an enzymolysis time of 120 min and substrate concentration of 24.0 g/L, which gave the conversion rate of the protein and ACE inhibitory activity of the peptide as
Acknowledgements
The authors wish to extend our appreciation for the supports provided by the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions, Senior Professional Research Start-up Fund of Jiangsu University (10JDG121), Postdoctoral Funds of Jiangsu Province (1101039C), and for the National Natural Science Foundation of China (31071502).
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