The aim of the present study was to produce lactoferrin (L) and chitosan (C) nanoparticles by ionic crosslinking with TPP and thereby increase the antimicrobial activity of biopolymers. The nanoparticles were synthesized in different proportions of biopolymers and TPP and characterized regarding their size, zeta potential, morphology, chemical interactions, structural characteristics and antibacterial activity. They were also applied as coatings on strawberries with the aim of increasing fruit shelf-life. Circular dichroism spectra revealed that the addition of TPP altered the secondary structure of lactoferrin. The nanoparticles 3.5L:5.5C:1TPP and 4.5L:4.5C:1TPP showed higher zeta potential values and lower hydrodynamic diameters (+39.30 mV, 81.87 nm and + 33.07 mV, 97.67 nm, respectively) and intense bacteriostatic action against S. aureus (0.0370 mg/ml and 0.0463 mg/ml, respectively).The minimum inhibitory concentration of these nanoparticles was three times lower than those of pure biopolymers. When applied to strawberries coating, the nanoparticles delayed the ripening and degradation of the fruit. These results con rm that it is possible to intensify the antimicrobial properties of lactoferrin and chitosan through ionic crosslinking with TPP and, thus, expand their use as natural food preservatives.

Chitosan (CS) nanoparticles were formed by two different methodologies: ionic (with sodium tripolyphosphate -TPP) and chemical (with genipin -GN) cross-linking. CS-TPP and CS-GN nanoparticles showed positive zeta potential (+46.24 and +62.86 mV, respectively) and sizes ranging from 83.70 to 835.91 nm, respectively. Ionic cross-linking (with TPP) resulted in particles smaller than those formed by chemical cross-linking (with GN). The in vitro antibacterial activity revealed an efficient inhibitory effect, especially regarding CS-TPP. In situ, antibacterial and antioxidant studies were carried out on O/W emulsions. The mesophilic and psychrotrophic counts, peroxide value and quantification of conjugated dienes and trienes during time revealed that nanoparticles tend to improve the microbiological and oxidative stability of emulsions. These findings underline the direct relationship between the reduction of particle size and the increase in biopolymer functional properties and expand the possibilities of CS application as a natural preservative of emulsified systems.

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