Development and evaluation of an edible antimicrobial film based on yam starch and chitosan

Abstract

Edible antimicrobial films are an innovation within the biodegradable active packaging concept. They have been developed in order to reduce and/or inhibit the growth of microorganisms on the surface of foods. This study developed an edible antimicrobial film based on yam starch (Dioscorea alata) and chitosan and investigated its antimicrobial efficiency on Salmonella enteritidis. A solution of yam starch (4%) and glycerol (2%) was gelatinized in a viscoamilograph and chitosan added at concentrations of 1%, 3% and 5%. Films with and without chitosan were produced by the cast method. To evaluate the antimicrobial activity of the films, two suspensions of S. enteritidis were used in BHI medium, corresponding to counts of 2 × 108 and 1.1 × 106 CFU/ml. The suspensions (50 ml) were poured into flasks. The films were cut into 5 × 5 and 5 × 10 cm rectangles to be used at ratios of 1 : 1 (1 cm2/ml microorganism suspension) and 2 : 1 (2 cm2/ml). The film 30 µm thick on average. As a control, pure chitosan at an amount corresponding to that contained in the 3% and 5% films (5 × 10 cm) was added to flasks containing the microorganism suspension. Also, flasks containing only a suspension of S. enteritidis were used as control. The suspensions, in flasks, were kept at 37°C in a waterbath with agitation. Suspension aliquots were removed every hour for reading the optic density (OD595) and plating onto PCA medium. The results showed that chitosan has a bactericidal effect upon S. enteritidis. Films treated with chitosan at different concentrations showed similar antimicrobial efficiency, in addition to being dependent on diffusion. The chitosan-treated films caused a reduction of one to two log cycles in the number of microorganisms, whereas the pure chitosan presented a reduction of four to six log cycles compared with the control and starch film. The films showed good flexibility. Copyright © 2005 John Wiley & Sons, Ltd.