(Carbelac Isolac) and Danisco Beaminster Ltd (Beaminster, U.K.) for supplying Nisin NP. Citric. Malic. Lactic .... Journal of Food Science. 66(7):1006-1011.
Edible films with bioactive characteristics against Listeria monocytogenes C.M.B.S. Pintado1,2, I. Sousa1 and M.A.S.S. Ferreira1 (1) Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, 1349-017, Lisboa, Portugal. (2) Escola Superior Agrária, Instituto Politécnico de Castelo Branco, Quinta da Senhora de Mércoles, Apartado 119, 6001-909 Castelo Branco, Portugal.
INTRODUCTION
RESULTS AND DISCUSSION
Post-processing contamination with Listeria monocytogenes on food surfaces is a reality and this pathogen is frequently isolated from cheese (1).
To wrap cheese produced from raw ewe milk, a by-product of cheese manufacturing, whey protein isolate, was utilized as a biopolymer with added glycerol as plasticizer, to produce transparent and flexible edible films with bioactive antilisteric activity. Different organic acids (citric, malic, formic, acetic and lactic) were used to set pH at 3.000.30. These acids
Preliminary studies with WPI-G fluids and films made at 1.5 and 3.0 % of several organic acids were tested. Results of
visual analysis, antimicrobial activity, tensile strength, % elongation, puncture strength, viscosity and viscoelasticity were obtained to characterized and select the best performing film to be used in a subsequent assay with nisin. The films made with formic acid (1.5 and 3.0%) and citric acid (1.5%) did not show any halo of inhibition and presented brittleness. The films made with 3% malic, lactic or citric acid (with pH values of 2.76, 2.92 and 2.90, respectively) demonstrated higher inhibitory effect than 1.5%, and were selected for evaluation of their anti-listerial activity, with and without nisin, compared with 3% HCl 2N (pH 3.29) as a pH control.
were investigated with respect to rheological and antimicrobial properties,
Effect of nisin (50IU/ml) 0 IU/ml
with and without nisin. 95% CI Halo of inhibition (mm)
50 IU/ml
MATERIALS AND METHODS Whey protein isolate (WPI, 7% w/v, Carbery)
4,00
2,00
Dissolved in distilled water and stirred
Glycerol (G, 3% w/v)
0,00
Incorporation of organic acids (1.5 and 3.0% w/v) and 3%HCl 2N (control) and stirred
Hydrochloric
Figure 1 – Representative picture of inhibition zones of WPI-G films incorporated with acids (3%) with and without nisin (50 IU/ml).
Lactic Malic Type of acid ( 3% w/v)
Citric
Figure 2 – Average values for the inhibitory zones with 95% confidence intervals.
Data demonstrated that the nisin+organic acid combinations, incorporated into WPI-G films, are effective in inhibiting L. monocytogenes growth, showing a synergistic or an additive antimicrobial effect. The best average of halos of inhibition was
4.00±0.92 mm using malic acid + nisin (Fig.2). Antimicrobial activity of films with malic, lactic and
citric acids with nisin were significantly different (p
