Continuous Nisin Z Production from Cheese Whey by Luffa-Immobilized Lactococcus lactis

Abstract

Nisin is a bacteriocin produced by Lactococcus lactis. Antibacterial activities of nisin against a wide range of foodborne microorganisms result in its application as a natural preservative in food industries. Nisin synthesis is often inhibited due to the accumulation of some microbial metabolites such as lactic acid. The goals of this study are (1) immobilization of L. lactis subsp. lactis (PTCC 1336) cells in the Luffa cylindrica sponge through the adsorption with a polycationic arms of polyethyleneimine to overcome the inhibition, (2) investigation of the luffa-immobilized cells in a fluidized bed reactor, and (3) using cheese whey as a cheap carbon source of the process at a continuous mode. L. lactis was successfully immobilized on luffa because the size of the interconnecting holes in the matrix is considerably larger than the bacterial dimensions, and its high specific surface area (11.99 m² g⁻¹) provides enough surface for the cell’s attachment. Immobilized cells showed reasonable stability (immobilization efficiency = 86%) against washout during 30 days of the operation. The dilution rate and temperature as the influential operational factors were studied and the best dilution rate (0.091 hours⁻¹) at 30°C yielded a nisin titer activity of about 5260 AU mL⁻¹ with nisin productivity (R _P) 4.78 × 10⁺⁵ AU L⁻¹ h⁻¹ and nisin-to-lactose yield (Y _P) of 1.32 × 10⁺⁵AU g_Lactose ⁻¹. The analyses on the isolated nisin revealed the production of nisin Z with a half-maximal effective concentration (EC₅₀ = 65 mg L⁻¹) against M. luteus (Gram-positive bacteria).