Valorization of sorghum distillers dried grains with solubles (DDGS) as functional films using combination of suitable pretreatment with electrospinning and solvent-casting film manufacturing technologies

Abstract

Growing environmental concerns related to petroleum-based plastics have increased interest in developing sustainable and biodegradable packaging materials derived from renewable resources. Distillers’ dried grains with solubles (DDGS), a major by-product of grain fermentation in bioethanol production, represent a promising feedstock for biodegradable film manufacturing due to their high protein and fiber content. Sorghum-derived DDGS, in particular, offers additional advantages because sorghum is a drought-tolerant and widely cultivated crop with strong potential for sustainable agricultural systems. Valorization of DDGS into value-added packaging materials therefore supports both waste reduction and circular bioeconomy strategies. The first objective of this thesis was to develop biodegradable films from sorghum DDGS using solvent casting and to evaluate the influence of chemical pretreatment, mechanical processing, and lipid removal on film performance. DDGS samples were subjected to four solvent pretreatments including water, hydrochloric acid (HCl), sodium hydroxide (NaOH), and sodium hydroxide combined with ethanol (NaOH+EtOH), together with two ball milling cycles (1x and 3x) under both defatted and non-defatted conditions. The resulting films were characterized for physicochemical, surface, and mechanical properties including color difference ([Delta]E), thickness, moisture content, contact angle, total phenolic content (TPC), elongation, normalized toughness and structural properties using FTIR analysis. Results demonstrated that solvent pretreatment significantly influenced several film properties, particularly color, surface wettability, and mechanical behavior (p < 0.05). Alkaline pretreatments generally enhanced phenolic extraction and surface hydrophobicity, while mechanical milling improved particle dispersion within the film matrix. Application studies using fresh-cut apples as a model food system showed that DDGS-based coatings maintained stable microbial counts during storage and slowed browning kinetics. The second objective of this thesis was to develop functional nanofibrous biodegradable films using coaxial electrospinning and DDGS-derived bioactive extracts. Core–shell nanofibers were produced using pullulan or micellar casein as shell polymers and emulsified active ingredients including thymol and DDGS extracts as the core phase. Emulsions were stabilized using Tween 20 or lecithin and processed through a coaxial electrospinning system to generate nanofibrous mats. The electrospun films were characterized for physicochemical, structural, and mechanical properties including color, thickness, moisture content, tensile behavior, and FTIR spectra. Results showed that polymer type and emulsifier significantly influenced film performance (p < 0.05). Pullulan-based films exhibited improved mechanical strength and lower moisture content compared to micellar casein films. Incorporation of DDGS extracts did not significantly affect color or thickness, (p > 0.05), but influenced moisture content and deformation behavior of the nanofibers (p < 0.05). In addition, selected electrospun films reduced browning kinetics of fresh-cut apples compared to uncoated samples. Overall, this research demonstrates that sorghum DDGS can be successfully valorized into functional biodegradable films through both conventional solvent casting and advanced electrospinning technologies. The findings highlight the importance of pretreatment strategies and formulation parameters in tailoring film properties and demonstrate the potential of DDGS-derived materials for sustainable food packaging applications.