Luis J. Pérez Córdoba1*, Elisabete M. C. Alexandre1, Paulo J. Sobral1

An important problem to produce active films using essential oils is it poor dispersion into film-forming solutions (FFS). This behavior may be minimized applying nanoemulsions, which allow a better dispersion of hydrophobic active compounds into biopolymer matrix. This study aimed to improve physical, antioxidant and antimicrobial properties of gelatin-based films enriched with nanoemulsioned cinnamaldehyde (C) and -tocopherol (T).

MATERIAL AND METHODS

CONCLUSION

RESULTS AND DISCUSSION

Developed gelatin-based films activated with nanoemulsioned C and T presented suitable physical properties along with strong antioxidant activity, indicating their potential use as active and biodegradable packaging material for food preservation.

1 Department of Food Engineering, FZEA, University of São Paulo, 13635-900 Pirassununga/SP, Brazil. *mail: luchop283@usp.br

FFSs were prepared with 5g gelatin/100g FFS, 30g glycerol/100g gelatin, and enriched with oil-in-water nanoemulsions containing 2.5gC+1.25gT or 5gC+2.5gT/100g gelatin.

Active gelatin-based films were prepared by casting method. Film thickness was kept constant in 80 m and after films were further

characterized and tested (Fig. 1).

Acknowledgement: To the São Paulo Research Foundation FAPESP for the PhD fellowship (13/14324-2) of the first author. Work of the CEPID-FoRC (13/07914-8)

Table 1. Mechanical properties of gelatin-based films containing oil-in-water nanoemulsion with different concentration (2.5gC+1.25gT or 5gC+2.5gT/100g gelatin)

The a* values decreased, while b* values increased (p<0.05) as a function of active compounds concentration (Table 2). No effect was observed for Luminosity (L*). Nanoemulsions reduced the film gloss (p<0.05) as compared with the pure gelatin film, in 5.6% and 35.8% for C2.5:T1.25 and C5:T2.5 ratios, respectively.

Table 2. Color parameters and gloss of gelatin-based films containing oil-in-water nanoemulsion with different concentration (2.5gC+1.25gT or 5gC+2.5gT/100g gelatin)INTRODUCTION

Gelatin-based films with nanoemulsioned C and T not showed antimicrobial activity against S. aureus and P. aureaginosa (Fig. 3) But, it presented excellent antioxidant activities in respect to pure gelatin films (Table 3).

Films microstructure (SEM and AFM)

Color and Gloss parameters

Antimicrobial and Antioxidant activity

The SEM images (Fig. 2) showed a homogeneous distribution of oil droplets into the polymer matrix. The cross-section and AFM analysis showed that films enriched with nanoemulsioned C and T had a marked increase on average and root mean square roughness in respect to pure gelatin film.

P. aeruginosaS. aureus

Pure gelatin C2.5:T1.25 ratio C5:T2.5 ratio

Active gelatin-based films

Physical properties

Mechanical properties (ASTM standard method 882, 2001)

Color and Gloss

SEM and AFM

Antioxidant activity Antimicrobial activity

DPPH assay (Brand-Williams et al., 1995)

Agar disc diffusion method (NCCLS, 1997)

Table 3. Antioxidant activity (Inhibition percentage (%) of radical DPPH)

Gelatin pure film 1.8 0.1

C2.5:T1.25 11.4 0.7

C5:T2.5 26.8 1.0

Concentration ratio TS (MPa) EB (%) EM (MPa) 0 (Pure gelatin film) 33.23 4.6a 47.43 7.0a 473.05 35.2a

C2.5:T1.25 29.75 4.3a 58.22 9.3b 412.32 53.0b

C5:T2.5 25.03 2.8b 74.29 5.5c 318.52 30.5c

Concentration ratio Color parameters Gloss (°) L* a* b* Angle (60 °)

0 (Pure gelatin film) 91.18 0.1a -1.03 0.2a 3.49 0.5a 147.45 6.9a C2.5:T1.25 91.67 0.3a -2.64 0.3 b 7.22 0.9b 139.11 3.9b C5:T2.5 91.31 0.1a -3.29 0.2c 8.60 0.8c 94.61 7.0c

Figure 1. Physical, antioxidant and antimicrobial analysis of active gelatin-based films

Figure 2. SEM and AFM images of active gelatin-based films

Figure 3. Antimicrobial activity

Films produced with nanoemulsioned active compounds presented lower tensile strength (TS), lower elastic modulus (EM) and higher elongation at break (EB) (p<0.05) as compared to pure gelatin films (Table 1).

Mechanical properties

PHYSICAL, ANTIOXIDANT AND ANTIMICROBIAL PROPERTIES OF

GELATIN-BASED FILMS ENRICHED WITH NANOEMULSIONED CINNAMALDEHYDE AND

-TOCOPHEROL