The application of a fermented food ingredient containing `variacin', a novel antimicrobial produced by Kocuria varians, to control the growth of Bacillus cereus in chilled dairy products T. O'Mahony 1,2 , N. Rekhif 3 , C. Cavadini 3 and G.F. Fitzgerald 1,2 1 Department of Microbiology, 2 National Food Biotechnology Centre, University College Cork, Ireland, and 3 Nestle Research Centre, Lausanne, Switzerland 396/6/00: received 5 June 2000, revised 7 August 2000 and accepted 4 October 2000 T. O'MAHONY, N. REKHIF, C. CAVADINI AND G.F. FITZGERALD. 2001. Aims: The feasibility of applying variacin, a lantibiotic produced by Kocuria varians in the form of a spray-dried fermented ingredient to control the growth of psychrotrophic Bacillus cereus strains in chilled dairy foods, was evaluated. Methods and Results: A range of chilled dairy food formulations modelling commercially- available products were fabricated, to which were added varying amounts of active ingredient. These were subsequently challenged with a B. cereus spore cocktail over a range of abuse temperatures. This work was validated by the inclusion of the fermented ingredient to commercial products. Conclusions: Results demonstrate the functionality of the bacteriocin at refrigeration abuse temperatures, and indicate the robust nature of the proteinaceous antimicrobial agent with regard to processing. Signi®cance and Impact of the Study: This study indicates the applicability of fermented food ingredients containing naturally-occurring antimicrobials as additional hurdles in food preservation. INTRODUCTION Bacillus cereus is a common soil saprophyte, ubiquitous in the environment, which frequently contaminates foods during harvesting and subsequent processing. It is routinely isolated from most pH-neutral chilled foods, including dairy products and other foods derived from milk, e.g. infant formula and milk powders (Philips and Grif®ths 1986; Wong et al. 1988; Ternstrom et al. 1993; Schraft et al. 1996). Recent research has also indicated a high incidence of B. cereus in ready-to-serve and sous-vide technology-based foods (Harmon and Kautter 1991; Turner et al. 1996). Three factors combine to make B. cereus a potential threat to food processing: (i) it's ability to form thermoduric endospores; (ii) it's capacity for growth or survival at refrigeration temperatures; and (iii) toxin production (Christiansson et al. 1989; Van Netten et al. 1989; Grif®ths 1990; Granum and Lund 1997). Therefore, the outgrowth of spores of toxigenic psychrotrophic B. cereus can pose a threat to the safe production of refrigerated minimally-processed foods. Bacteriocins are naturally-occurring, antimicrobial, ribo- sommally-synthesized peptides produced by bacteria. More than 100 have been described in lactic acid bacteria (De Vuyst and Vandamme 1994), many of which have been biochemically and genetically characterized. However, relatively few have been shown to demonstrate ef®cacy in speci®c food applications. This relatively unsuccessful transition from the laboratory to food products can be attributed mainly to the highly complex nature of food matrices, and the poorly understood interrelationship between food ingredients and bacteriocins (Jones 1974; Jung et al. 1992). This situation is further complicated by the variety of food conditions, such as pH and storage temperature, and the numerous processing treatments to which foods are subjected, e.g. heating, cooling, freeze- thawing, agitating and foaming. Correspondence to: Dr G.F. Fitzgerald, National Food Biotechnology Centre, University College Cork, Ireland. ã 2001 The Society for Applied Microbiology Journal of Applied Microbiology 2001, 90, 106±114