Application of the broad-spectrum bacteriocin enterocin AS-48 to inhibit Bacillus coagulans in canned fruit and vegetable foods R. Lucas a ,M a J. Grande a , H. Abriouel a , M. Maqueda b , N. Ben Omar a , E. Valdivia b,c , M. Martı ´nez-Can ˜ amero a , A. Ga ´lvez a, * a  Area de Microbiologı ´a, Departamento de Ciencias de la Salud, Facultad de Ciencias Experimentales, Universidad de Jae ´n, Campus Las Lagunillas s/n, 23071 Jae ´n, Spain b Departamento de Microbiologı ´a, Fac. Ciencias, Universidad de Granada, 18071 Granada, Spain c Instituto de Biotecnologı ´a, Universidad de Granada, 18071 Granada, Spain Received 7 July 2005; accepted 20 May 2006 Abstract The enterococcal bacteriocin (enterocin) AS-48 is a broad-spectrum cyclic peptide. Enterocin AS-48 was tested against Bacillus coag- ulans in three vegetable canned foods: tomato paste (pH 4.64), syrup from canned peaches (pH 3.97), and juice from canned pineapple (pH 3.65). When vegetative cells of B. coagulans CECT (Spanish Type Culture Collection) 12 were inoculated in tomato paste supplemented with 6 lg/ml AS-48 and stored at different temperatures, viable cell counts were reduced by approximately 2.37 (4 °C), 4.3 (22 °C) and 3.0 (37 °C) log units within 24 h storage. After 15-days storage, no viable cells were detected in any sample. Strain B. coagulans CECT 561 showed a poor survival in tomato paste, but surviving cells were also killed by AS-48. The bacteriocin was also very active against B. coag- ulans CECT 12 vegetative cells in juice from canned pineapple stored at 22 °C, and slightly less active in syrup from canned peaches. In food samples supplemented with 1.5% lactic acid, enterocin AS-48 (6 lg/ml) rapidly reduced viable counts of vegetative cells below detec- tion limits within 24 h storage. Addition of glucose and sucrose (10% and 20%) significantly increased bacteriocin activity against vege- tative cells of B. coagulans CECT 12. Enterocin AS-48 had no significant effect on B. coagulans CECT 12 spores. However, the combined application of AS-48 and heat (80–95 °C for 5 min) significantly increased the effect of thermal treatments on spores. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Bacillus coagulans; Canned vegetables; Flat sour; Biopreservation; Enterocin AS-48 1. Introduction Food canning has been one classical way to provide a continuous supply of food independently of the seasonal availability of raw materials. Acidification and thermal treatment are two widely used methods in preservation of canned foods. However, several types of bacteria can toler- ate these adverse conditions and proliferate in foods causing spoilage. Endospore-forming bacteria are a common prob- lem in the food industry both because they are frequently found in many raw materials and because endospores require more intense treatments for inactivation than vege- tative cells. This results in higher processing costs and less preserved product quality. Survival of bacterial endospores during food processing is of special significance in canned foods, and other additional hurdles such as acidification are often required in order to ameliorate endospore outgrowth and food spoilage. Bacillus coagulans is a slightly acidophilic and thermotolerant spoilage bacterium of con- siderable concern during the processing of acid and acidi- fied foods. This bacterium may cause ‘‘flat-sour’’ spoilage, due to the production of lactic acid without gas formation. Spores of B. coagulans are able to germinate and grow at pH values as low as 4, and are of significance in vegetable foods (Brackett, 2001) and in canned fruits, especially in tomato products, with a pH of 4.1–5.0. For this reason, B. coagulans is the microorganism most frequently isolated 0278-6915/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.fct.2006.05.019 * Corresponding author. Tel.: +34 953 212160; fax: +34 953 21 29 43. E-mail address: agalvez@ujaen.es (A. Ga ´lvez). www.elsevier.com/locate/foodchemtox Food and Chemical Toxicology 44 (2006) 1774–1781