Open Access
Chacko, Jino
Graduate Program:
Food Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
February 29, 2008
Committee Members:
  • Dr John D Floros, Thesis Advisor
  • Ramaswamy C Anantheswaran, Thesis Advisor
  • Nisin
  • Nisaplin
  • Controlled release
  • Food packaging
  • pseudo-Fickian
Nisin is a bacteriocin that is permitted to be used in food as a natural food preservative and is approved ‗generally recognized as safe‘ (GRAS) by both Food & Drug Administration (FDA) and World Health Organization (WHO). Nisin is commercially available as Nisaplin®. Pure nisin has an activity of 40 x 106 IU/g and Nisaplin® has an activity of 1 x 106 IU/g. In some food systems, especially meat, it has been observed that nisin loses its activity over time because it binds to protein, fat etc. Several researchers have reported that the direct addition of antimicrobials to food leads to a loss of activity. However, this loss can be prevented to a great extent by controlled release of antimicrobials to food. This work was undertaken to develop a biopolymer-based film for the controlled release of nisin into food systems for inhibiting pathogenic organisms. The first phase of the research identified potential biopolymers for the film matrix and evaluated their stability in an aqueous system. In the second phase, nisin was entrapped within seven biopolymer-based films and the antimicrobial activity of the films was evaluated by the agar diffusion method using Micrococcus luteus. The third phase of the research consisted of modeling the nisin release kinetics via a mechanistic diffusion model, as well as an empirical Weibull model. These models were validated by experiments in the final phase. In the final experiments with corn zein, nisin release was quantified using a high performance liquid chromatographic (HPLC) technique. Using the agar diffusion method, it was found that xanthan films and locust bean films collapsed or dissolved on the agar surface without producing a distinguishable iv inhibition zone. Kappa and iota carrageenan films did not collapse on the agar surface, but failed to inhibit M. luteus. It was hypothesized that nisin was not released from kappa and iota carrageenan due to the physical entrapment of nisin in the gel network. Blended films made with kappa and non-gelling lamda carrageenan exhibited inhibition against M. luteus. The amount of nisin released in the agar diffusion method increased as the concentration of lamda carrageenan in the film increased. Blended films made with kappa carrageenan and hydroxypropylmethyl cellulose (HPMC) also exhibited nisin release. Nisin release increased as the concentration of HPMC in the film increased. Corn zein films containing Nisaplin® formed clear inhibition zones using the agar diffusion method. The nisin released from these films into citrate buffer was further quantified using a HPLC technique. The profile of released nisin demonstrated that as the corn zein concentration in the film increased, nisin release decreased. The diffusivity of nisin decreased from 38 x 10-11 to 8 x 10-11 cm2/s (a fourfold decrease), as the corn zein concentration in the film increased from 4 to 10% (w/v). This observation may be attributed to increased tortuosity in the film. Other researchers also have reported that the release of active compounds from a matrix decreases as the biopolymer concentration increases. Mathematical analysis of the early portion of the nisin release profile indicated that nisin release from corn zein films exhibits a pseudo-Fickian behavior. An empirical Weibull model was developed and tested. It demonstrated excellent prediction (R2 > 0.95), power, and described the kinetics of nisin release well. Corn zein films can be used to develop a matrix for controlled release of nisin in food system, thereby maintaining a constant microbial inhibitory effect. Also, release can v be controlled by varying the concentration of biopolymer in the matrix. Corn zein films can be used as coating within a package or as an edible coating for the product for controlled release of antimicrobials and other active compounds. Since corn zein is hydrophobic, it can also be successfully used for delivery of active compounds within aqueous food systems such as beverages, meat and other high moisture foods.