Antifungal Activity of Biopolymers Made From Wheat Gluten Containing Naturally Occurring Cinnamaldehyde and Natamycin

Microbial growth has been typically overcome by direct application of an antimicrobial agent on a food surface which may result in the rapid diffusion or neutralisation of the active substance. Currently, the food industry is showing increased interest in the development of bio-based packaging materials as carriers of natural antimicrobial agents in order to reduce financial losses due to food deterioration and also to achieve demands consumers more concerned about environmental protection. Biopolymers having antimicrobial activity have generally been prepared by incorporating one type of active agent into the film with a unique mechanism of release depending on the volatility of the agent, either migration by direct contact with the food or release into the headspace of the packaging system. The combination of antimicrobial agents could lead to improved effectiveness against microorganisms by virtue of synergistic interactions that could be established between them along with the combination of the different release mechanisms.  In this study proteinaceous films obtained from wheat gluten were used as carriers for  the delivery of two naturally occurring antifungal compounds which show potential advantages for the replacement of traditional chemical preservatives: cinnamaldehyde, a volatile obtained from cinnamon essential oil, and Natamycin, a macrolide polyene produced during fermentation by Streptomyces natalensis. The antifungal activity of the films against three major postharvest decay fungi: Penicillium spp., Alternaria solani and Colletotrichum acutatum was assayed in vitro over 7 days. The release rate of the antimicrobial volatile, added to 1.5%, 3% and 5% (g/100 g protein), was evaluated in the headspace of bioassay systems by solid-phase microextraction and gas chromatography. The addition of 1.5% cinnamaldehyde to the film produced a 33% inhibition for Penicillium spp., and approximately 28% and 16% for C. acutatum and A. solani, respectively, after 7 days at 23 ºC. Greater cinnamaldehyde contents produced greater inhibitions. The effectiveness of cinnamaldehyde was different depending on the inoculated fungi, being Penicillium spp. the most sensitive. The concentration of the volatile was very reduced by the third day, and new compounds appeared due to fungal metabolism. The addition of 1% natamycin in the presence of cinnamaldehyde raised the percentage of inhibition to 73% for Penicillium spp., whilst C. acutatum and A. solani were largely unaffected. The results obtained highlight the potential for active systems of this type, comprising a renewable matrix containing naturally occurring antimicrobial substances, for the control of fungal growth especially Penicillium spp.