pH-Drive on the Design and Properties of Legume Protein-Based Films

Abstract

Natural polymers are renewable, biodegradable materials suitable for film applications that can help extend food shelf life. Legume proteins represent promising but underexplored film-forming agents compared with animal-derived or cereal proteins. This study examined the influence of pH (7.0, 8.5, and 10.0) on the physicochemical and functional properties of films prepared from protein isolates (3% w/v) of Peruvian bean, broad bean, and lentil. Films were produced by casting with glycerol as a plasticizer and analyzed for thickness, moisture content, soluble matter, protein solubility, color, mechanical properties (puncture strength and elongation), water vapor permeability (WVP), soluble protein fractions, FTIR spectra, and thermal stability. Moisture content showed no statistically significant differences across pH levels (p > 0.05), ranging from 30.45 to 27.16%, whereas thickness, color, and solubility parameters were significantly influenced by both pH and protein source (p < 0.05). Lentil films were thinner at higher pH, while Peruvian bean and broad bean films exhibited greater thickness and yellowness under alkaline conditions. Protein solubility and soluble matter increased at higher pH (p < 0.05), particularly for Peruvian bean and broad bean films, with globulins as the predominant fraction. WVP decreased under alkaline conditions, indicating enhanced barrier properties (<0.8–1.1 g·mm/kPa·h·m2), and mechanical analyses showed improved elongation with increasing pH. FTIR and thermogravimetric results confirmed pH-dependent structural unfolding and cross-linking of proteins in alkaline conditions. Overall, alkaline pH enhanced flexibility and barrier performance in films derived from Peruvian bean and broad bean proteins, supporting their potential as sustainable materials for food packaging applications.