Active coatings based on oxidized chitin nanocrystals and silk fibroins for the control of anthracnose in 'Hass' avocados

Postharvest avocado losses are mainly due to anthracnose disease caused by Colletotrichum gloeosporioides. Chemical fungicides are effective, but their negative effects on health and the environment have led to the search for sustainable alternatives such as biopolymer-based coatings and natural compounds. Therefore, chitin nanocrystals (NCChit) were extracted using a sustainable deep eutectic solvent (DES) and chemically modified into oxidized chitin nanocrystals (O-NCChit) or deacetylated chitin nanocrystals (D-NCChit) to modulate and increase the charge surface density and the dispersibility of the crystals. The modified NCChits were dispersed with silk fibroins (SF), essential oil (EO), melatonin (MT) and/or phenylalanine (Phe) to elaborate active coatings. Antioxidant and antifungal in vitro analyses showed that the O-NCChit/SF-based coating had the best performance. In addition, in vivo tests were carried out through the artificial inoculation of C. gloeosporioides on coated avocados. O-NCChit/SF/MT-based coatings reduced the severity of anthracnose by 45 %, the same effect as the chemical fungicide (Prochloraz®). Moreover, avocado quality parameters during cold storage and the shelf-life period were also evaluated, where nonsignificant differences were observed. Therefore, this study demonstrates the great potential of O-NCChit and SF in combination with active compounds for the control of anthracnose in 'Hass' avocados.

Characterization of Bombyx mori and Antheraea pernyi silk fibroins and their blends as potential biomaterials

Fibroin proteins isolated from the cocoons of certain silk-producing insects have been widely investigated as biomaterials for tissue engineering applications. In this study, fibroins were isolated from cocoons of domesticated Bombyx mori (BM) and wild Antheraea pernyi (AP) silkworms following a degumming process. The object of this study was to obtain an assessment on certain properties of these fibroins in order that a concept might be had regarding the feasibility of using their blends as biomaterials. Membranes, 10–20 μm thick, which are water-insoluble, flexible and transparent, were prepared from pure fibroins and from their blends, and subjected to water vapor annealing in vacuum, with the aim of providing materials sufficiently strong for manipulation. The resulting materials were characterized by electrophoretic analysis and infrared spectrometry. The tensile properties of the membranes were measured and correlated with the results of infrared analysis. At low concentrations of any of the two fibroins, the mechanical characteristics of the membranes appeared to be adequate for surgical manipulation, as the modulus and strength surpassed those of BM silk fibroin alone. It was noticed that high concentrations of AP silk fibroin led to a significant reduction in the elasticity of membranes.