Shenglan Zhao

Optimization of production conditions for antioxidant peptides from walnut protein meal using solid-state fermentation

Solid-state fermentation (SSF) of walnut protein meal (WPM) by Bacillus subtilis was optimized for the maximum degree of hydrolysis (DH) and reducing power (RP) using response surface methodology (RSM). Optimum fermentation conditions were fermentation time of 82.01 h, inoculum concentration of 10.40, and water content of 1.50 mL/g. Optimized values were 41.80% and 0.78 for DH and RP, respectively. Walnut peptides (WP) were ultrafiltration membrane fractionated. The WPs-II (molecular weight <5 kDa) fraction showed the highest RP value. WPs-II showed good DPPH free radical scavenging and Fe2+ chelating activities, higher than for GSH (l-glutathione reduced) at the same concentration. Amino acid composition analysis of WPs-II showed that Asp, Glu, and Arg were the major amino acids playing important roles in the antioxidant activity. WPs is an efficient antioxidant suitable for use as a food additive and as a pharmaceutical agent.

STUDY ON THE INTERACTION BETWEEN THEASINESIN AND BOVINE SERUM ALBUMIN BY FLUORESCENCE METHOD

Theasinesin (TS), a polymer of epigallocatechin gallate, is the main active component of tea polyphenols. Several studies indicate that tea polyphenols have extensive pharmacology activity. However, there is little research about the transportation and metabolism of tea polyphenols in vivo. Serum albumin is a most important protein serving as a depot protein and as a transport protein for many drugs and other bioactive small molecules. This study observed the interaction between TS and bovine serum albumin (BSA) by fluorescence and absorption spectroscopy. The results showed that both static and dynamic quenching occurred in the fluorescence quenching of BSA by TS. The binding sites number is 1.1845 and the binding sites may close to the tyrosine residues. The thermodynamic parameters ΔH°, ΔG°, ΔS° at temperatures 310 K were calculated 1.7 KJ, −35.4 KJ, and 0.12 KJ. The negative sign of free energy (ΔG°) means that the interaction process is spontaneous. The positive enthalpy (ΔH°) and entropy (ΔS°) values of the interaction of TS and BSA indicate that the binding is mainly entropy-driven and the enthalpy is unfavorable for it, the hydrophobic forces playing a major role in the reaction. A distance of 4.037 nm was found between donor (BSA) and acceptor (TS), obtained according to the Főrster theory of non-radiation energy transfer, which indicates that the energy transfer from BSA to TS occurs with high probability. The results of synchronous fluorescence spectra and UV–vis absorption spectra showed that the peptide strands of BSA molecules extended more and the hydrophobicity decreased with the addition of TS.

Optimization of simultaneous microwave/ultrasonic-assisted extraction of phenolic compounds from walnut flour using response surface methodology

Abstract Context: Walnut is a traditional food as well as a traditional medicine recorded in the Chinese Pharmacopoeia; however, the large amounts of walnut flour (WF) generated in walnut oil production have not been well utilized. Objective: This study maximized the total polyphenolic yield (TPY) from the walnut flour (WF) by optimizing simultaneous ultrasound/microwave-assisted hydroalcoholic extraction (SUMAE). Materials and methods: Response surface methodology was used to optimize the processing parameters for the TPY, including microwave power (20–140 W), ultrasonic power (75–525 W), extraction temperature (25–55 °C), and time (0.5–9.5 min). The polyphenol components were analysed by LC–MS. Results: A second-order polynomial model satisfactorily fit the experimental TPY data (R2 = 0.9932, P < 0.0001 and Radj2    = 0.9868). The optimized quick extraction conditions were microwave power 294.38 W, ultrasonic power 93.5 W, temperature 43.38 °C and time 4.33 min, with a maximum TPY of 34.91 mg GAE/g, which was a rapid extraction. The major phenolic components in the WF extracts were glansreginin A, ellagic acid, and gallic acid with peak areas of 22.15%, 14.99% and 10.96%, respectively, which might be used as functional components for health food, cosmetics and medicines. Discussion and conclusion: The results indicated that walnut flour, a waste product from the oil industry, was a rich source of polyphenolic compounds and thus could be used as a high-value functional food ingredient.

Investigation of the Interaction Between Gallic Acid and α-Amylase by Spectroscopy

Gallic acid is one of the important polyphenols in plants and it inhibits α-amylase. The interaction between gallic acid and α-amylase was investigated by fluorescence quenching spectroscopy, UV-vis spectroscopy, synchronous spectroscopy, and the three-dimensional fluorescence spectroscopy under mimic physiological conditions. The result of the emission quenching at different temperatures revealed that there are static quenching of intrinsic fluorescence of α-amylase induced by gallic acid and a complex of gallic acid-α-amylase was formed. The results obtained from the evaluation of three-dimensional fluorescence spectra, UV-vis spectra, and synchronous spectra suggested that the association between gallic acid and α-amylase did change the molecular conformation of α-amylase. Gallic acid can enter the primary substrate-binding pocket and alter the microenvironment around tryptophan and tyrosine residues.