Influence of the inoculum level of Lactobacillus parabuchneri in vat milk and of the cheese-making conditions on histamine formation during ripening

Histamine formation by four histaminogenic Lactobacillus parabuchneri strains in experimental cheeses was investigated. Firstly, Raclette cheeses were manufactured from pasteurised milk inoculated with different levels of selected L. parabuchneri strains ranging from 10(1) to 10(4) cfu mL(-1). Secondly, cheeses were produced using four different curd cooking conditions (20 min at temperatures of 44-56 degrees C) to study survival of L. parabuchneri strains. The growth of L. parabuchneri during cheese ripening and the formation of biogenic amines was monitored using a species-specific qPCR assay and HPLC, respectively. The spoilage threshold in cheese milk was very low, at about 10(1)-10(2) cfu mL(-1). Up to 992 mg of histamine kg(-1) was accumulated in the cheeses within 180 days. L. parabuchneri proved to be a rather heat tolerant species; however, heating at 56 degrees C for 20 min proved to be sufficient to inactivate L. parabuchneri and thus to prevent histamine formation. (C) 2020 The Authors. Published by Elsevier Ltd.