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This study aimed to turn classically brittle zein films into flexible antimicrobial ones by the use of lactic (LA), malic (MA) and tartaric acids (TA). The most effective plasticizer was LA (400% elongation at break [EB] at 4%), while MA (189% EB at 4.5%) and TA (68% EB at 5%) showed moderate and limited plasticizing effects, respectively.The LA-and MA-loaded films maintained their flexibility during 30-day storage at 4 C or 25 C. Fourier transform infrared (FTIR) analysis suggested that the plasticization of LA and MA could be related to secondary structural changes in zein such as increased α-helix and random coils (mainly by MA) and spaced/modified intermolecular (only by LA) and intramolecular (mainly by MA) β-sheets. Atomic force and scanning electron microscopy showed that LA and MA gave more homogenous and smoother films than TA. Films with LA showed the highest water vapour permeability followed by those of control, MA-and TA-loaded films. Films with 3%-4% LA or MA formed clear zones on Listeria innocua and Klebsiella pneumonia, but only films with LA formed clear zones on Escherichia coli. All OA-loaded films gave unclear zones on Staphylococcus aureus in disc-diffusion tests, but this bacterium was inactivated rapidly in antimicrobial tests based on surface inoculation tests. LA is the best OA to develop flexible antimicrobial films from zein, an industrial by-product that films could not have been utilized as a widespread packaging material due to their brittleness.

Summary The objective of this study was to employ pectin‐based antimicrobial coatings for inhibition of Listeria on surfaces of whole webbed‐rind melons that cause frequent outbreaks of listeriosis. For this purpose, emulsion‐based coatings were developed using citrus pectin (CPEC) or pectin extracted from processing wastes of sun‐dried figs (FPEC) and eugenol (EUG). The emulsions of FPEC and CPEC with EUG (droplet size range: 1.99–11.22 µm) were highly stable for minimum 10 days at 10 °C. The FPEC‐EUG films showed higher flexibility and degree of wettability than CPEC‐EUG films. In contrast, CPEC‐EUG films had a higher gas barrier performance against oxygen at 50% relative humidity than FPEC‐EUG films. The zone inhibition tests showed that FPEC‐EUG films are more effective against Listeria innocua than CPEC‐EUG films. However, FPEC and CPEC coatings with 2% EUG caused 2.2 and 2.7 decimal inactivation of Listeria on Galia melons within 1 week, respectively. The pectin coatings with EUG could reduce the risk of listeriosis from webbed‐rind melons.

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