Co-assembly of nisin and zein in microfluidics for enhanced antilisterial activity in Queso Fresco

Nisin-loaded zein microcapsules were prepared in a microfluidic chip using an internal phase separation method. The release profiles of nisin from the microcapsules were modified by varying nisin loading and flow rate during the microfluidic process. Rapid release of nisin was achieved with low flow rate in dispersed phase (0.2 ml/h) and high loading (9.67-12.64 mu g/mg) of nisin in the microcapsule, while slow release of nisin was achieved with high flow rate in dispersed phase (0.3 ml/h) and low loading of nisin (5.94 mu g/mg) in the microcapsule. When tested in fresh cheese, all treatments with the nisin loaded zein microcapsules achieved overall lower viable Listeria cell counts relative to the treatment with free nisin, notably at early cheese storage. After 3 days of cold storage, the microcapsules with high flow rate and low nisin load reduced the initial viable population of L. monocytogenes by approximately 1 Log CFU/g, and the high nisin load capsules exhibited a reduction of approximately 0.5 Log CFU/g of the pathogen. Although subsequent regrowth of L. monocytogenes was observed after 7 days of cold storage for all the encapsulated nisin treatments, the high flow rate and low load microcapsules maintained the greatest difference in L. monocytogenes counts, approximately 2 Log CFU/g, compared to the untreated cheese. The cheese with the high flow rate and high load microcapsules was least effective on controlling L monocytogenes. Nano-FTIR spectrum suggested that the distribution of nisin in the zein microcapsule was homogeneous, which indicates that a co-assembly of zein and nisin occurred during the internal phase separation process.