Investments – Silk Coating
Editor | On 01, May 2018
Food waste has an impact on food quality and safety, representing a loss of economic value and resources, and, a hindrance to economic development. The Food and Agriculture Organization (FAO) of the United Nations has estimated that one-third of the food produced for human consumption worldwide is annually lost or wasted along the chain that stretches from farms to postharvest treatments, processing, distribution and end-user consumption. For fruit and vegetable commodities, the FAO has estimated a 50% loss of crops throughout the food supply chain, mainly concentrated in the postharvest, distribution and end-user consumption stages and mostly due to the premature deterioration of perishable crops.
Many perishable fruit and vegetables possess in fact high metabolic activity and suffer from high possibility of microbial contamination, resulting in short shelf-life, fungal decay, colour change, and off-flavour. To date, several treatments have been explored to extend the postharvest life of fruit and vegetables (e.g. cryopreservation, exposure to synthetic chemical fungicides, modified atmosphere packaging, osmotic treatments, hypobaric and heat treatments). In this scenario, the formation of an edible coating represents an alternative route to extend crop freshness by combining extended storage periods with ease of handling. In general, food coatings should be mechanically robust matrices with hydrophobic groups to exert low permeability to oxygen and water vapours (i.e. control over fruit respiration rate and firmness retention). Biocompatibility, biodegradability, antibacterial and antifungal activities, membrane forming capacity and safety (i.e. edible and not allergenic) should also be compelling properties for an edible coating material.
To date, polysaccharides, proteins, resins, lipids and their combinations are the commonly used options for coating formulations. Polysaccharides and proteins are known to form films with good mechanical properties, but with poor permeability, while lipids and resins form brittle films with improved permeability. Among all the perishable food, strawberries are considered one of the most difficult to preserve fresh along the food supply chain and have therefore been used as a model to test the efficacy of food preservation strategies and, in particular, of edible coatings.
Silk fibroin is an extensively investigated biomaterial for its potential in textile, biomedical, photonic, and electronic applications. Silk fibroin is a structural protein, like collagen, but with a unique feature: it is produced from the extrusion of an amino-acidic suspension by a living complex organism (while collagen is produced in the extracellular space by self-assembly of cell-produced monomers). Silk fibroin properties are derived from its structure, which consists of hydrophobic blocks staggered by hydrophilic, acidic spacers. In its natural state, silk fibroin is organized in beta-sheet crystals alternated by amorphous regions, which provide strength and resilience to the protein. The multiplicities of forms in which regenerated silk fibroin can be processed at a high protein concentration and molecular weight make it attractive for several high-tech applications, as recently reported. In addition, the amino-acidic nature of silk fibroin brings a diversity of side chain chemistries that allows for the incorporation of macromolecules useful in drug delivery applications or in providing cellular instructions.
Remarkably, silk fibroin has also shown to possess features that are distinct of its regenerated form. For example, regenerated silk fibroin stabilizes heat labile molecules and compounds (e.g. enzymes and antibiotics). Silk is indeed considered a platform technology in biomaterials fabrication as its robustness and qualities bring needed assets to provide a portfolio of distinct features (e.g. nanopatterning, biochemical functionalization) for the final construct. Processing of regenerated fibroin generally involves the partial or total dehydration of a fibroin suspension (protein content of 1–15 wt%) to form films, sponges, gels, spheres (micron- to nano-sized) and foams with numerous techniques (e.g. solvent casting, freeze drying, salt leaching, sonication). The rationale beyond these fabrication processes is to manufacture a robust material that combines mechanical strength with ad-hoc biochemical properties.
The silk-fibroin research recently went public when it won the Rabobank-MIT Food & Agribusiness Innovation Prize competition for the development team at Tufts University.
The fibron—which is 99 percent water and one percent silk—is virtually undetectable, explains Jacques-Henry Grislain, CEO of Cambridge Corps, the University spin-out company now tasked with commercializing the technology. “The coating is one-tenth of thickness of hair, has no taste, and prevents oxidation and the ripening of fruit,” Grislain explains. The fibron coating acts as a protective barrier and is an alternative to current means of extending shelf life, like cold storage and 1-methylcyclopropene, which blocks the ethylene that triggers fruit to degrade.
Grislain says that while Cambridge Corps aims to make the coating a global commercial product, the team is hoping to have the greatest impact on the developing world, where food wastage is typically over 50%.
Lots of players have a stake in the food preservation story:
Coatings won’t be the ultimate winners, but the Cambridge Crops solution looks like as close to IFR as the coatings industry will ever get. Which means, if the commercialization plans go well, the refrigerator and, especially, container & packaging industries had better watch out.