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 Lactobacill us sake and L. curvatus. LAB strains isolated from spoiled products of this type (liver sausage, ham and bologna sausage) were found to be sensitive t o low nisin concentrations (maximum of 1.25 mu g g(-1)). Addition of 25 mu g g(-1) nisin las 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 ef fect of three types of phosphates (used as emulsifiers) on nisin activity i n the sausages was compared. LAB growth rate was fastest in samples contain ing orthophosphate, and slowest in sausages containing diphosphate. The she lf life was also greatly extended in the latter. Fat content also affected nisin activity. Nisin activity las indicated by LAB inhibition) was greates t in samples containing 15% > 25% > 37% (wt/wt) fat. In a sausage formulati on containing 37% fat and incorporating diphosphate as emulsifier, levels o f nisin as low as 2.5 mu g g(-1) showed antibacterial effects. A nisin leve l of 6.25 mu g g(-1) totally inhibited LAB growth for over 4 weeks and 25 m u g g(-1) for 5 weeks. Spoilage control was achieved in the same sausage fo rmulation but with 25% (wt/wt) fat; 12.5 mu g g(-1) nisin prevented LAB gro wth for 5 weeks.