Covalent Interaction between High Hydrostatic Pressure-Pretreated Rice Bran Protein Hydrolysates and Ferulic Acid: Focus on Antioxidant Activities and Emulsifying Properties

Abstract

Rice bran protein hydrolysates (RBPH) pretreated with high hydrostatic pressure (HHP) covalently interacted with ferulic acid (FA) (0.5 to 2.5 mg/mL) under alkaline conditions. The structural and functional properties of the conjugates were investigated. The results revealed that the FA binding equivalent on RBPH increased from 6.03 to 207.64 nmol/mg. FTIR spectral analysis indicated that the content of α-helix increased, whereas the contents of β-sheet, β-turn, and random coil decreased. The surface hydrophobicity (H 0 ) of RBPH increased, the fluorescence intensity decreased, and the tertiary structure changed because of covalent interactions between RBPH and FA. The emulsifying activity index of RBPH−FA (1.5 mg/mL) was 35.10% higher than that of the control, whereas FA concentrations higher than 1.5 mg/mL had a negative effect on emulsifying properties. RBPH−FA (2.5 mg/mL) exhibited the strongest antioxidant activity. This study provides a new reference for the application of RBPH−FA conjugates in food processing.

Fabrication of emulsions prepared by rice bran protein hydrolysate and ferulic acid covalent conjugate: Focus on ultrasonic emulsification

“…ζ-potential is a key indicator of the emulsion stability. Previous studies had shown that RBPH-FA conjugates can provide higher absolute ζ-potential values versus conventional proteins [ 14 ]. McClements et al [ 32 ] noted that the distribution of some specific bioactive substances on the emulsion interface increased the charge density of droplet surface.…”

“…Elias et al [ 38 ] pointed out that the oxidation of emulsion occurred mainly on the interface. RBPH-FA conjugate as an emulsifier can provide good antioxidant capacity [ 14 ], which can effectively inhibit lipid oxidation on the interface.

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“…RBPH − FA conjugates were prepared by alkali-induced covalent conjugation according to our previous research [ 14 ]. The pH of RBPH solution was adjusted to 9.0.…”

“…Ferulic acid (FA) is a major phenolic acid in paddy, which has high antioxidant, antibacterial, anti-inflammatory and hypocholesterolemic activities [ 13 ]. Our previous studies showed that the covalent conjugate of RBPH-FA had a good modification effect on RBPH and could improve its emulsifying and antioxidant properties [ 14 ]. Some studies have shown that the addition of polyphenols could change the relevant properties of the emulsion, and the polyphenols were taken to the oil droplet surface through the adsorption of protein, which has a synergistic effect with the antioxidant properties of protein, thus improving the stability of the whole system [ 7 ].…”

“…It is useful to enhance the physicochemical stability of emulsions with the molecular modified protein as emulsifier. Previous studies in our laboratory have shown that RBPH-FA conjugate has better antioxidant and emulsifying properties, and it can be used as a new type emulsifier in emulsions [ [12] , [14] ]. Although there are many studies on the functional properties of protein–polyphenol complexes, there are few reports on the application of RBPH-FA conjugate in emulsions, and the study of ultrasonic emulsification on this conjugate emulsion has not been reported.…”