pH-dependent protein–alginate interactions shape gel structure, protein release and in vitro digestion.

Description

Title: pH-dependent protein–alginate interactions: physicochemical, structural, and digestion data Description: This dataset contains raw and processed experimental data supporting the article “pH-dependent protein–alginate interactions shape gel structure, protein release and in vitro digestion”. It provides a complete record of how pH modulates the interactions between sodium alginate and plant proteins (soy protein isolate, SPI; hemp protein isolate, HPI; and pea protein isolate, PPI), and how these interactions influence bead formation, entrapment efficiency, and gastrointestinal stability. Contents: Protein solubility data: Solubility (%) of SPI, HPI, and PPI measured across pH 2–7. Zeta potential data: Apparent surface charge (mV) of proteins and alginate across pH 2–7, showing charge inversion near isoelectric points. FTIR spectral data: Absorbance values in the amide I and II regions (1600–1700 cm⁻¹), highlighting conformational changes and protein–alginate interactions at pH 4 and 7. Bead morphology: Diameter and sphericity factor of alginate–protein beads produced at pH 4 and 7, with confocal microscopy images showing protein and alginate distribution. Entrapment efficiency (EE): Protein retention capacity of alginate–protein beads, including maximum EE values. Protein release kinetics: Protein release profiles during simulated gastrointestinal digestion (oral, gastric, intestinal phases) following the INFOGEST protocol. Peptide size distribution: High-performance size exclusion chromatography (SEC) data showing generation of bioaccessible peptides smaller than 300 Da. Methodology: Data were generated using standardized protocols: Pierce™ BCA Protein Assay for solubility and release quantification, Zetasizer Nano ZS for zeta potential, ATR-FTIR spectroscopy for molecular interactions, bead production via external gelation with CaCl₂, confocal laser scanning microscopy for bead structure, and the INFOGEST static in vitro digestion protocol for protein release and proteolysis. SEC analysis was performed to determine peptide size distribution. Potential Use: This dataset provides a comprehensive view of pH-dependent protein–alginate interactions, offering valuable insights for researchers in food science, encapsulation technologies, and biopolymer chemistry. It is particularly relevant for the development of plant protein-based delivery systems and controlled-release applications. Keywords: protein–alginate interactions, solubility, zeta potential, FTIR, hydrogel beads, entrapment efficiency, in vitro digestion, peptide bioaccessibility, soy protein isolate, hemp protein isolate, pea protein isolate.

Steps to reproduce

The dataset was obtained through physicochemical, structural, and digestion experiments designed to evaluate pH-dependent interactions between sodium alginate and plant proteins (soy protein isolate, SPI; hemp protein isolate, HPI; and pea protein isolate, PPI). Protein Solubility Assay: Protein isolates (1% w/v) were dissolved in distilled water and adjusted to pH 2–7 using 1 M HCl or NaOH. Samples were centrifuged (10,000×g, 20 min), and soluble fractions were quantified using the Pierce™ BCA Protein Assay Kit. Absorbance was measured at 562 nm with a spectrophotometer, and solubility (%) was calculated relative to total protein concentration. Zeta Potential Measurements: Protein and alginate solutions (0.1% w/v) were prepared at different pH values. After centrifugation (8,000×g, 20 min), supernatants were analysed using a Zetasizer Nano ZS (Malvern Instruments, UK) to determine apparent surface charge (mV). FTIR Spectroscopy: Protein–alginate mixtures (1:1 v/v, 0.1% w/v each) were freeze-dried and analysed using ATR-FTIR spectroscopy (PerkinElmer Spectrum One). Spectra were collected over 4000–600 cm⁻¹, baseline-corrected, and vector-normalized. Difference spectra were generated to identify molecular interactions in the amide I and II regions, highlighting conformational changes at pH 4 and 7. Bead Production and Morphology: Alginate–protein mixtures (2% w/v each) were adjusted to pH 4 or 7 and extruded into 250 mM CaCl₂ baths to form hydrogel beads via external gelation. Bead diameter and sphericity factor were determined using ImageJ software from digital micrographs. Confocal laser scanning microscopy (CLSM) was used to visualize protein and alginate distribution after fluorescent staining, providing structural insights into bead formation. Entrapment efficiency (EE): Beads were dissolved in 3% sodium citrate, and protein content was quantified using the BCA assay. EE (%) was calculated as the ratio of encapsulated protein to total protein in the initial mixture. In vitro digestion and protein release: Beads were subjected to the standardized INFOGEST static digestion protocol, including oral, gastric, and intestinal phases. Protein release was quantified using the BCA assay at each stage, generating release profiles that reflect pH-dependent stability and gastrointestinal behaviour. Peptide size distribution: Bioaccessible fractions were analysed by high-performance size exclusion chromatography using a TSKgel G2000SWxl column. Elution profiles were compared against molecular weight standards to determine peptide size distribution. Together, these protocols integrate biochemical assays, spectroscopy, particle characterization, microscopy, and digestion modelling to provide a reproducible workflow. The combination of standardized assays (BCA, INFOGEST), advanced instrumentation (Zetasizer Nano ZS, ATR-FTIR, CLSM, SEC), and open-source software (ImageJ) ensures methodological transparency and reproducibility.

Institutions

• Universidad de La Frontera

  Araucanía, Temuco
• Teagasc - The Irish Agriculture and Food Development Authority

  Leinster, Carlow

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