Behaviour of Listeria spp. in naturally contaminated chorizo (Spanish fermented sausage)

Counts of Listeria spp. were determined during the manufacture and drying o f 21 lots of five chorizo varieties produced by three different manufacture rs. Presumptive Listeria were not isolated from any of the batches produced in a large factory (F3) using starter, sorbate and controlled ripening at high temperatures. Initial levels in factory 1 (F1), with no starter added, but controlled ripening at low temperatures, were ca 3.5 log(10) cfu/g whi le those in factory 2 (F2), with no starter added and ripening under natura l climatic conditions, were 1.17 log(10) cfu/g. Numbers of listeriae in bat ches obtained from Fl remained almost constant before decreasing by ca 0.5 log units/g in the finished product (32 days), while the levels in F2 incre ased by 1.47 log units/g after 11 days of ripening and declined further to levels above the original amount. Manufacturing procedure and smoking signi ficantly affected presumptive listeriae counts. Thirteen strains recovered from F1 batches were identified as: Listeria monocytogenes (three strains o f serovar 1/2c), Listeria innocua (eight strains of serovar 6b) and Listeri a welshimeri (two strains of serovar 6b). Listeria strains from F2 were ass igned to L. innocua and L. welshimeri. (C) 1999 Elsevier Science B.V. All r ights reserved.