Rabbit bone gelatin edible films: impact of glycerol concentration on properties and application in soybean oil packaging

Abstract

Rabbit bone, a by-product of rabbit meat processing, remains underutilized and is often discarded as waste. However, its high collagen content makes it a promising alternative source of gelatin for developing biodegradable edible films as replacements for plastic packaging. This study investigated the effect of varying glycerol concentrations (RG20:20%, RG30:30%, and RG40:40%) on the physicochemical, mechanical, barrier, optical, and thermal properties of rabbit bone gelatin-based films and evaluated their potential application in soybean oil packaging. A bovine gelatin film with 30% glycerol served as the control. Increasing glycerol concentrations led to higher moisture content (9.96–19.16%), thickness (0.087–0.109 mm), solubility (31.77–50.84%), water vapor permeability (WVP) (0.63 to 2.43 × 10⁻⁹ g m⁻¹ Pa⁻¹ s⁻¹), and elongation at break (99.29–163.11%). However, it reduced the opacity value (2.13 to 1.62), tensile strength (7.34 to 3.00), and melting temperature (178.46 to 149.34 °C). Among the formulations, the RG20 film exhibited superior tensile strength and barrier, thermal, and optical properties, confirming the functional promise of rabbit bone gelatin for edible film development. The RG20 film was selected for further testing and compared with LDPE packaging. On day 9, the peroxide value of soybean oil exhibited a more rapid increase in LDPE (13.12 meq O₂ kg⁻¹) than in RG20 (6.57 meq O₂ kg⁻¹). However, the RG20 film was less effective in inhibiting the increase in the anisidine value (12.15) compared to LDPE (6.5) in early storage periods. Free fatty acid levels remained relatively stable in both treatments, indicating minimal hydrolytic degradation. These findings suggest that RG films have potential use as biodegradable alternatives for soybean oil packaging.