A study by the Institute of Agrochemistry and Food Technology (IATA) of the Spanish National Research Council (CSIC) has developed packaging materials designed to decompose in the natural environment. These biodegradable films were obtained by combining pigmented corn flour and sorghum (Sorghum bicolor) flour with marine biomass from the red algae Gelidium corneum. The results, published in Food Hydrocolloids, not only represent an innovative approach to valorizing agricultural waste and marine biomass, but the combination of both improves the rigidity and reduces the humidity sensitivity of the new packaging.

The research introduces a novel approach by using pigmented whole grain flours along with unrefined marine biomass to adjust the properties of the new packaging. The flours used are rich in starch, which interacts with the cellulose of the algae to determine the internal structure of the bioplastics. and in natural compounds such as bioactive polyphenols, which contribute to defining the color, luminosity, and UV protection of the films.

The combination of agricultural and marine byproducts was achieved through melt-compounding, an industrial polymer processing technique. This involves applying heat and mechanical energy to combine the starch from the flours and the cellulose from the algae at a molecular level, forming a homogeneous mixture. Subsequently, the final shape of the container is created through compression molding by applying heat and pressure.

Adjusting functionality without chemical modifications
The research team developed eight different formulations using the melt-compounding technique, with a 40:60 ratio of cereal flour to algae residue, respectively. After comparing the results with previous preparations without marine biomass, the researchers found that its incorporation generates a more heterogeneous internal structure and modifies the optical properties of the films: it decreases their luminosity and whiteness and increases yellow and greenish tones due to interactions between the natural pigments.

Furthermore, the presence of the marine residue increases the mechanical resistance and rigidity of the material and modifies water-related properties, such as vapor permeability, absorption, and the material's capacity to attract and retain water molecules, depending on the polyphenolic compounds present in the initial biomass. During storage, these effects are accentuated, partly due to starch retrogradation, a physicochemical process by which the molecules reorganize, forming firmer structures.

The research, led by IATA-CSIC, is the first study to use pigmented whole grain flours and unrefined marine biomass in a combined and complementary manner. “This approach leverages the natural interactions between pigments, polysaccharides, and proteins to adjust the functionality of the films without resorting to chemical modifications, and uses undervalued marine waste as sustainable and low-cost reinforcements that improve the material's strength, modulate water sensitivity, and provide UV protection,” explains Amparo López, an IATA researcher who led the study.

Similarly, María José Fabra, co-author of the article and a member of IATA-CSIC, maintains that this valorization strategy “promotes a circular bioeconomy and introduces a new paradigm in the design of functional biopolymer films, based on the use of alternative raw materials and minimally processed, pigment-rich marine waste.”

“The different compositions of each flour and the incorporation of the marine waste influence various properties of the freshly made and stored films, with implications for their potential applications in food packaging,” she adds.

Improved Functionality of Compounds

The study shows that the improved properties are not solely due to physical reinforcement, but also to molecular compatibility between cereal starches, cellulose present in marine biomass, and the native phenolic compounds in flours. The integration of seaweed residue significantly influences the molecular organization of starch-based matrices, promoting the formation of cohesive networks.

The researchers point out that “these synergistic interactions explain the observed increase in stiffness and tensile strength, the reduction in elongation, and the change in surface polarity.”

“Our results demonstrate a chemically synergistic pathway for valorizing agricultural and marine waste in biodegradable packaging materials, improving both the material's performance and its sustainability within the circular bioeconomy.”

FOOD HYDROCOLLOIDS