Effective postharvest preservation of kiwifruit and romaine lettuce with a chitosan hydrochloride coating

Kiwifruits and romaine lettuce, among the most horticulturally-consumed fresh products, were selected to investigate how to reduce damage and losses before commercialization. The film-forming properties, physico-chemical, and morphological characteristics, as well as the antimicrobial response against Botrytis cinerea and Pectobacterium carotovorum subsp. carotovorum of chitosan hydrochloride (CH)-based coatings were investigated. The results underlined the film-forming capability of this CH that maintained its physico-chemical characteristics also after dissolution in water. Morphological investigations by FESEM (Field Emission Scanning Electron Microscopy) underlined a well-distributed and homogeneous thin coating (less than 3-5 μm) on the lettuce leaves that do not negatively affect the food product functionality, guaranteeing the normal breathing of the food. FESEM images also highlighted the good distribution of CH coating on kiwifruit peels. The in vitro antimicrobial assays showed that both the mycelial growth of Botrytis cinerea and the bacterial growth of Pectobacterium carotovorum subsp. carotovorum were totally inhibited by the presence of CH, whereas in vivo antimicrobial properties were proved for 5-7 days on lettuce and until to 20-25 days on kiwifruits, demonstrating that the proposed coating is able to contrast gray mold frequently caused by the two selected plant pathogens during postharvest phases of fruit or vegetable products.