342: Low Temperature Induced Hemp Protein Gels as Encapsulation Wall Materials: Effects of Crosslinkers, Pre-Treatment, and Protein Extraction Techniques

Introduction

Hemp protein, derived from byproducts, is gaining attention as a sustainable ingredient with the potential for encapsulating bioactive compounds in functional foods and nutraceuticals. However, conventional gelation at high temperatures is unsuitable for heat-sensitive compounds, necessitating low-temperature gelation using physical treatments and crosslinking agents. The objective of this research is to develop hemp protein gels at 40°C by optimizing citric acid (CA) crosslinker concentration and sonication time while evaluating the gelling properties of three hemp proteins (ALK, SALT, DES) extracted using alkaline, divalent-salt, and deep eutectic solvent methods.

Methods

Hemp protein (ALK, SALT, DES) was extracted and hydrated at 20% concentration overnight. Briefly, protein dispersions were sonicated for 0, 5, or 10 minutes, and then citric acid (CA) was added at varying concentrations (0, 0.1, 0.3, or 0.5 mmol/g protein). After adjusting pH to 4 and homogenization, the solution was heated at 40°C for 1 hour, cooled, and stored at 4°C. Gel strength, viscoelastic properties, oral tribology, thermal stability, structure, and interactions were analyzed. General linear regression with a two-way ANOVA model was used to optimize CA concentration and sonication time, considering gel strength as the response. For the characterization data, one-way ANOVA with Tukey's test was used for means comparison.

Results

DES-based gels showed a significant interaction (p < 0.05) between CA concentration and sonication time on gel strength. The highest gel strength (746.9 ± 25.4 g) occurred at 0.03 mmol/g CA and 5 minutes sonication, while control gels had the lowest (198.4 ± 23.4 g). FTIR analysis confirmed CA-induced crosslinking through peak shifts at ~3300 cm⁻¹, 1630 cm⁻¹, and 1530 cm⁻¹ (H-bonds, amide-I, and amide-II). Protein secondary structures remained unchanged by sonication, but improved gel strength suggests sonication exfoliated proteins, enhancing crosslinking. Under optimized conditions, SALT-based (440.9 g) and ALK-based gels (301.0 g) exhibited lower gel strength than DES-based gels, as confirmed by rheological analysis showing differing viscoelastic properties.

Significance

Fabricating gels at low pH and temperature is challenging but crucial for developing novel functional foods from heat-sensitive bioactives to promote human health. Sonication and CA crosslinking offer promising solutions for this process using DES-extracted hemp protein.

Authors: Thilini Dissanayake, Manpreet Kaur, Ben Kew, and Nandika Bandara