The effect of calcium and magnesium on the interaction between ß-lactoglobulin and carotenoids from sea buckthorn berries.

ß-Lactoglobulin has been shown to interact with carotenoids from sea buckthorn berries. However, previously, no studies have taken into account the effect of calcium and magnesium on the ß-lactoglobulin-carotenoids complex. This study aims to determine the effect of calcium and magnesium on the interaction between ß-lactoglobulin and carotenoids from sea buckthorn berries extract, during heating from the perspective of deepening interaction mechanisms as prerequisites for micro- and nanoencapsulation. Phase diagram, intrinsic fluorescence spectra, quenching experiments and synchronous spectra were employed to acquire information regarding the conformation of protein in the presence of calcium chloride and magnesium chloride. Intrinsic fluorescence data showed that, between 25°C and 60°C, the presence of calcium chloride in the complex favoured the movement of tryptophan residues to domains located at the protein-water interface, while magnesium chloride favoured the burial of tryptophan residues. Higher temperatures generated blue shifts regardless of which salt was present, suggesting exposure of tryptophan residues to the hydrophobic core of the protein. Extrinsic fluorescence intensity of the non-heat-treated complex with magnesium chloride was significantly higher (P < 0.01) than of the complex with calcium chloride, suggesting that 1-anilino-8-naphtalenesulphonic acid was bound to a higher proportion of the ß-lactoglobulin-carotenoids complex. Calcium chloride increased extrinsic fluorescence to a greater extent than magnesium chloride at temperatures above 70°C and was related to small structural changes induced by preheating ß-lactoglobulin.

Phytochemicals content and antioxidant properties of sea buckthorn (Hippophae rhamnoides L.) as affected by heat treatment - Quantitative spectroscopic and kinetic approaches.

The effect of thermal processing (50-100°C) on the degradation of the phytochemicals in sea buckthorn extract was investigated using chromatographic, fluorescence and FT-IR spectroscopy techniques and degradation kinetics. Heating the sea buckthorn extract resulted in structural changes that led to red- or blue-shifts in maximum emission, depending on temperature and excitation wavelengths. The attenuated total reflectance analysis of the sea buckthorn extract revealed a satisfactory thermostability of compounds at high temperatures. A fractional conversion kinetic model was used to describe the mechanism of degradation in terms of rate and activation energy. Activation energies for total carotenoids, polyphenolic, flavonoids, and antioxidant activity were 8.45±0.93kJ/mol, 2.50±0.66kJ/mol, 22.50±7.26kJ/mol and 15.22±2.75kJ/mol, respectively. The kinetic parameters evidence a higher thermal stability of carotenoids and polyphenols, suggesting higher degradation rates for flavonoids and antioxidant activity. Our results demonstrate that industrial process optimization in terms of time-temperature combinations demands product specific kinetic data.

Thermal stability of the complex formed between carotenoids from sea buckthorn (Hippophae rhamnoides L.) and bovine ß-lactoglobulin.

Sea buckthorn has gained importance as a versatile nutraceutical, due to its high nutritive value in terms of carotenoids content. ß-Lactoglobulin (ß-LG) is a natural carrier for various bioactive compounds. In this study, the effect of thermal treatment in the temperature range of 25 to 100°C for 15min on the complex formed by ß-LG and carotenoids from sea buckthorn was reported, based on fluorescence spectroscopy, molecular docking and molecular dynamics simulation results. Also, the berries extracts were analyzed for their carotenoids content. The chromatographic profile of the sea buckthorn extracts revealed the presence of zeaxanthin and ß-carotene, as major compounds. The Stern-Volmer constants and binding parameters between ß-LG and ß-carotene were estimated based on quenching experiments. When thermally treating the ß-LG-carotenoids mixtures, an increase in intrinsic and extrinsic fluorescence intensity up to 90°C was observed, together with blue-shifts in maximum emission in the lower temperature range and red-shifts at higher temperature. Based on fluorescence spectroscopy results, the unfolding of the protein molecules at high temperature was suggested. Detailed information obtained at atomic level revealed that events taking place in the complex heated at high temperature caused important changes in the ß-carotene binding site, therefore leading to a more thermodynamically stable assembly. This study can be used to understand the changes occurring at molecular level that could help food operators to design new ingredients and functional foods, and to optimize the processing methods in order to obtain healthier food products.