Controlled Release of Nisin from Biopolymer Films

Nisin is a bacteriocin approved as a food preservative. In food systems, nisin loses its antimicrobial activity over time because it binds to proteins, fats, etc. This problem can be alleviated by controlling the overall release rate of nisin into foods. This research was undertaken to evaluate various biopolymer-based films for use in controlled-release of nisin into aqueous food systems. The objectives of this study were to investigate various biopolymers – locust bean gum (LBG), xanthan gum (XG), carrageenans (CA), alginates (AL), hydroxypropylmethyl cellulose (HPMC) and corn zein (CZ) – for nisin release, and to study their antimicrobial activity by the agar diffusion method. XG and LBG films quickly dissolved on the agar surface without producing a distinguishable inhibition zone. Similarly, kappa and iota CG films did not produce any inhibition zone. Blended films made with kappa CA and HPMC exhibited measureable nisin release and the inhibition zone increased with increasing HPMC concentration in the film. AL and CZ film formed clear inhibition zones. For AL films, the inhibition zone decreased with increasing crosslinking time and % CaCl2; while the zone size increased with higher % guluronic acid. The amount of nisin released from CZ films was quantified using a high performance liquid chromatographic (HPLC) technique, and a Weibull model was fitted to the data. Nisin release decreased as the concentration of corn zein in the film matrix increased. Films made with HPMC, AL and CZ showed promise for developing controlled release applications with nisin in aqueous food systems.