Biodegradable active packaging based on controlled release of volatile natural antimicrobials from cyclodextrins
PER V. NIELSEN
Center for Process Biotechnology, BioCentrum-DTU,
Technical University of Denmark, DK-2800 Lyngby,
Controlled release of volatile antimicrobials from packaging films into the packaging atmosphere is a promising new tool for controlling microbial spoilage of food. This active packaging (AP) technology is especially interesting for products where Modified Atmosphere Packaging (MAP) and oxygen scavengers cannot ensure product safety and a sufficient shelf life.
The objective of this multidisciplinary project was to develop new types of antimicrobial biobased packaging material based on polylactate (PLA) for cheese. This includes selection of appropriate antimicrobial compound and inclusion of these into the nanosize cyclodextrins, CD, which can be integrated into the packaging material to control release of the active component. Focus was put on antimicrobial compounds that have been proven to have strong effect as volatiles (thymol, from thyme; citral from lemon and AITC from mustard [1,2]). The potential new preservative in the cheese environment, imazalil, was also included.
All antimicrobial compounds were tested both by the direct method and the indirect method on all relevant cheese spoilage fungi (Penicillium commune, P. roqueforti, P. nalgiovense, P. verrucosum, P. casifulvum, P. camenberti, Debaromyces hansenii, Kluvariomyces marxinanus). In the direct method up to 100 ml or mg of all compounds where spread on the surface of cheese medium with aw 0.96 corresponding to the amount that can be incorporated in to a 100 mm thick film (10% w/w). The fungi were inoculated on top in 3 point. In the indirect method oils, CD/CD-complex, and finished films was added in the bottom of a 220-ml glass jar. Circular cheese pieces Ø3.8 cm diameter were placed on a watch glass inside the jar. 10 ml of the spore suspensions was spotted on the cheese slice. The jar was closed tightly.
Citral and thymol generally had very little inhibitory effect in the doses tested. Imazalil were effective in direct contact, but had only limited effect in the indirect system, due to it limited volatility. AITC were effective both in direct and indirect contact. Not all fungi were equally affected by these compounds. P. nalgiovense was generally more resistant than the other fungi tested while the most important cheese spoilage fungi P. commune was the most sensitive.
The type of CD and the processing conditions had a strong effect on the antimicrobial effect of the final film. Measurements of release rate of the different CD-complexes and films at different temperatures and relative humidities (50 and 96%) on a GC with a static headspace sampler showed very good correlation between release and antimicrobial effect.
Based on data on release of AITC from the different film types and antimicrobial test on real cheese packs, it was concluded that an addition of 10% AITC CD to PLA are sufficient to obtain the needed antimicrobial effect in a normal package size (300 cm2). Optimization of the manufacturing process will reduce the required film area, thickness and price. This shows that this project successfully has applied this completely new concept of incorporating preservatives in CDs into a biopackaging.
Acknowledgements
This research was carried out as a part of the "Biopack" project: Proactive Biobased Cheese Packaging (QLK5-CT-2000-00799), funded by the European Commission. The research does not necessarily reflect the Commission's views and in no way anticipates their future policy in this area. We thank all the participants for their co-operation and enthusiasm.
Reference:
[1] Nielsen, P.V. and Rios, R. 2000. International Journal of Food Microbiology. 60:219-229.
[2] Suhr, K.I. and Nielsen, P.V. 2003. Journal of Applied Microbiology 94 (4), 665-674