Effective use of nisin to control lactic acid bacterial spoilage in vacuum-packed bologna-type sausage

Lactic acid bacteria (LAB) commonly cause spoilage in minimal heat-treated vacuum-packed cured delicatessen meats. Predominant species are Lactobacillus sake and L. curvatus. LAB strains isolated from spoiled products of this type (liver sausage, ham and bologna sausage) were found to be sensitive to low nisin concentrations (maximum of 1.25 microgram g(-1)). Addition of 25 microgram g(-1) nisin (as Nisaplin) inhibited the growth of LAB spoilage organisms inoculated into vacuum-packed pasteurized bologna-type sausages stored at 8 degrees C. Control sausages became spoiled (>10(8) LAB CFU g(-1)) by day 7, whereas sausages containing nisin remained unspoiled for >50 days. The effect of three types of phosphates (used as emulsifiers) on nisin activity in the sausages was compared. LAB growth rate was fastest in samples containing orthophosphate, and slowest in sausages containing diphosphate. The shelf life was also greatly extended in the latter. Fat content also affected nisin activity. Nisin activity (as indicated by LAB inhibition) was greatest in samples containing 15% > 25% > 37% (wt/wt) fat. In a sausage formulation containing 37% fat and incorporating diphosphate as emulsifier, levels of nisin as low as 2.5 microgram g(-1) showed antibacterial effects. A nisin level of 6.25 microgram g(-1) totally inhibited LAB growth for over 4 weeks and 25 microgram g(-1) for 5 weeks. Spoilage control was achieved in the same sausage formulation but with 25% (wt/wt) fat; 12.5 microgram g(-1) nisin prevented LAB growth for 5 weeks.