Original article Probiotic lactic acid bacteria from Kung-Som: isolation, screening, inhibition of pathogenic bacteria Noraphat Hwanhlem, 1 Nisit Watthanasakphuban, 1 Siriporn Riebroy, 2 Soottawat Benjakul, 3 Aran H-Kittikun 1 & Suppasil Maneerat 1 * 1 Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand 2 Department of Home Economics, Faculty of Agriculture, Kasetsart University, Bangkok 10900, Thailand 3 Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand (Received 16 April 2009; Accepted in revised form 14 December 2009) Summary Lactic acid bacteria (LAB) were isolated from Kung-Som at various fermentation periods. Only ten strains, named D2SM22, D6SM3, D6SM24, D6SM26, D8SM21, D10SM5, D10SM11, D10SM16, D10SM20 and D16SM26 showed a survival rate of more than 50% under the simulated gastric juice. After being subjected to simulated gastric juice, four strains (D6SM3, D8SM21, D10SM16 and D10SM20) showed a survival rate of more than 50% in simulated small intestinal juices. Growth of strain D6SM3, D8SM21 and D10SM16 under micro-aerobic and anaerobic conditions was not different. Tested pathogenic strains (Escherichia coli, Staphylococcus aureus, Bacillus cereus, Vibrio parahaemolyticus and Salmonella sp.) were inhibited by probiotic LAB. However, none of strains could produce bacteriocins. All strains were identified as Lactobacillus plantarum. No differences in pH, acidity, LAB count and liking scores between Kung-Som produced with starter culture and conventional method were observed (P > 0.01). Keywords Fermented shrimp, lactic acid bacteria, Lactobacillus plantarum, pathogenic bacteria, probiotic. Introduction Fermentations have been used traditionally to preserve foods due to the inhibitory effect toward many micro- organisms. Lactic acid bacteria (LAB) have been reported to be the predominant microorganisms in fermented foods (Nout, 1994). Inhibitory effect of lactic acid depends on species and load of pathogenic bacteria, sanitation process as well as number of LAB in fermented foods. According to Caplice & Fitzgerald (1999) and Callewaert et al. (2000), the use of starter cultures would be an appropriate approach for the control and optimisation of the fermentation process in order to alleviate the problems of variations in organo- leptic quality and microbiological stability observed in indigenous fermented foods. Although the concept of using bacteria as biothera- peutic agents is not new, probiotic LAB have attracted enormous attention only in recent years. Generally, probiotics are presumed to be live to exert a positive effect on the health and the well-being of the host (Ouwehand & Salminen, 1998). High tolerance to low pH and bile salts considered as important selection criteria (Schillinger et al., 2005; Maragkoudakis et al., 2006). Another criterion of the probiotic culture includes the ability to inhibit pathogenic bacteria (Ouwehand et al., 1999; Maragkoudakis et al., 2006). Dairy products such as fermented milk and yoghurt are often used as carrier for probiotic cultures. Recently, attention has been directed to use other fermented foods such as sausages, juice, fermented gruel or beverages as food carrier since these products are not heated and harbour high numbers of LAB (Mugula et al., 2003; Pennacchia et al., 2004; Fleet, 2007; Sheehan et al., 2007). Kung-Som is a traditional fermented shrimp widely distributed in the south of Thailand. It is made from shrimp, sugar, salt and water and is fermented with the natural microbial flora. The main microorganisms found in Kung-Som are LAB (Tanasupawat et al., 1998; Ko- bayashi et al., 2003). In order to use probiotics as starter cultures for fermented shrimp such as Kung-Som, probi- otic culture should be well-adapted to the fermentation conditions and becomes dominant in the final product. The objectives of this work were to characterise probiotic LAB isolated from Kung-Som, naturally fermented shrimp at different stages of the fermentation and to select the most suitable strains, according to their *Correspondent: Fax: +66 74212889; e-mail: suppasil.m@psu.ac.th International Journal of Food Science and Technology 2010, 45, 594–601 594 doi:10.1111/j.1365-2621.2010.02172.x Ó 2010 The Authors. Journal compilation Ó 2010 Institute of Food Science and Technology