Introduction
Edible coating or film is defined as a thin layer of material used for coating or wrapping food products, with the aim to extend their shelf life. Edible films are prepared separately and then applied to the food, while coatings are formed directly on the food surface (Tsironi and Taoukis, 2018). When properly formulated, both methods are considered to improve the organoleptic characteristics of packed food products. In addition, they can retard oxidation and/or delay microbial spoilage by integrating antibacterial and antioxidant agents. In order to develop edible films and coatings for food products, several materials may be used. These materials should be capable of forming a film and must be dissolved in a suitable and safe solution, that is, also compatible with the particular plasticizers, antioxidants, and/or antimicrobials. The prospective materials can be classified as hydrocolloids (e.g., polysaccharides, alginates), proteins (e.g., gelatin, casein), lipids (e.g., triglycerides, waxes), and composites (Oreopoulou and Tsironi, 2021).
Silk fibroin is an extensively investigated biomaterial for its potential in several applications, such as textile, biomedical, photonic, and electronics. Silk fibroin is a structural protein, like collagen, which has 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). The application of micrometre-thin silk fibroin membrane around the surface of strawberries and bananas has been reported as an effective management method of postharvest physiology of fruits (Marelli et al., 2016). The objective of the study was the investigation of the development of an edible food packaging material based on silk fibroin and the applicability on fresh shrimp for improving so the general freshness maintenance, as enzymatic post-mortem melanosis, commonly named black-spot (Goncalves & Oliveira, 2016).
Materials and methods
Cocoon was obtained from Bombyx Mori and used as fibroin source. Extraction of silk fibroin (SF) was performed using standard degumming processes (Marelli et al., 2016). The application of the silk fibroin based edible coating on the surface of whole, unpeeled shrimp was implemented by an immersion step, so as appropriate covering of the shrimp surface was achieved. Untreated (Control) and SF-coated samples were individually packed at aerobic conditions and stored at controlled isothermal conditions (0°C) in high-precision (±0.2°C) low-temperature incubators (Sanyo MIR 153, Sanyo Electric, Ora-Gun, Gunma, Japan). Temperature monitoring in the incubators was based on electronic, programmable miniature dataloggers. Quality evaluation was based on microbial spoilage, instrumentally measured colour and texture, enzymatic browning (polyphenol oxidase), and sensory freshness.
Results
The application of SF edible coating resulted in a significant inhibition of microbial growth and enzymatic browning of refrigerated shrimp, leading to 4-5 days shelf life extension at 0°C compared to the untreated (Control) samples with shelf life of 7 days.
Discussion and conclusion
The results of the study show the potential of SF edible coating to preserve the quality and extend the shelf life of refrigerated seafoods. Optimized production conditions were selected based on the stability of the packaged products. This novel, edible coating might serve as the basis of an eco-friendly, active food packaging system, by the addition into the film formulation of natural antimicrobial and/or antioxidant bioactive compounds.
References
Goncalves A.A., de Oliveira A.R.M. (2016). Melanosis in crustaceans_a review. LWT - Food Science and Technology, 65: 791-799. http://dx.doi.org/10.1016/j.lwt.2015.09.011
Marelli B., Brenckle M.A., Kaplan D.L., & Omenetto F.G. (2016). Silk Fibroin as Edible Coating for Perishable Food Preservation. Scientific Reports, 6: 25263
Oreopoulou V., Tsironi T. (2021). Plant Antioxidants and Antimicrobials in Edible and Non-edible Active Packaging Films. In: Ekiert H.M., Ramawat K.G., Arora J. (eds) Plant Antioxidants and Health. Reference Series in Phytochemistry. Springer, Cham. https://doi.org/10.1007/978-3-030-45299-5_29-1
Tsironi T., Taoukis P. (2018). Current practice and innovations in fish packaging. Journal of Aquatic Food Product Technology, 27: 1024-1047