Selection of a Bi®dobacterium strain to complement resistant starch in a synbiotic yoghurt R.G. Crittenden 1 , L.F. Morris 1 , M.L. Harvey 2 , L.T. Tran 2 , H.L. Mitchell 1 and M.J. Playne 1 1 Food Science Australia, Highett, Victoria, and 2 DSM Food Specialties Australia Pty Ltd, Moorebank, NSW, Australia 381/5/00: received 25 May 2000, revised 13 October 2000 and accepted 25 October 2000 R.G. CRITTENDEN, L.F. MORRIS, M.L. HARVEY, L.T. TRAN, H.L. MITCHELL AND M.J. PLAYNE. 2001. Aims: To employ an in vitro screening regime to select a probiotic Bi®dobacterium strain to complement resistant starch (Hi-maizeä) in a synbiotic yoghurt. Methods and Results: Of 40 Bi®dobacterium isolates examined, only B. lactis Laftiä B94 possessed all of the required characteristics. This isolate hydrolysed Hi-maizeä, survived well in conditions simulating passage through the gastrointestinal tract and possessed technological properties suitable for yoghurt manufacture. It grew well at temperatures up to 45°C, and grew to a high cell yield in an industrial growth medium. In addition to resistant starch, the organism was able to utilize a range of prebiotics including inulin, and fructo-, galacto-, soybean- and xylo-oligosaccharides. Pulse ®eld gel electrophoresis of restriction enzyme cut chromosomal DNA revealed that B. lactis Laftiä B94 was very closely related to the B. lactis Type Strain (DSM 10140), and to the commercial strains B. lactis Bb-12 and B. lactis DS 920. However, B. lactis Laftiä B94 was the only one of these isolates that could hydrolyse Hi-maizeä. This phenotypic difference did not appear to be due to the presence of plasmid encoded amylase. Bi®dobacterium lactis Laftiä B94 survived without substantial loss of viability in synbiotic yoghurt containing Hi-maizeä during storage at 4°C for six weeks. Conclusions: Bi®dobacterium lactis Laftiä B94 is a promising new yoghurt culture that warrants further investigation to assess its probiotic potential. Signi®cance and Impact of the Study: In vitro screening procedures can be used to integrate complementary probiotic and prebiotic ingredients for new synbiotic functional food products. INTRODUCTION In addition to traditional starter cultures, probiotic bacteria are now often included in yoghurts with the aim of contributing to the health and well-being of consumers through the maintenance of an advantageous balance of intestinal bacterial populations. The bacteria used as pro- biotics are predominantly selected from the genera Lactobacillus and Bi®dobacterium, both of which form part of the normal human intestinal microbiota (Mitsuoka 1978,1982; Tannock 1995). A second approach to increasing the number of probiotic bacteria in the intestinal microbiota is through the use of prebiotics. Prebiotics are non-digestible dietary components that selectively stimulate the growth and/or activity of indigenous probiotic bacteria in the intestinal tract (Gibson and Roberfroid 1995). The prebiotics identi®ed thus far have been carbohydrates such as lactulose, inulin, and various oligosaccharides (Crittenden 1999). Consumption of these non-digestible ingredients has been demonstrated to alter intestinal bacterial populations, in particular promoting the proliferation of bi®dobacteria (Fuller and Gibson 1997; Roberfroid et al. 1998; Van Loo et al. 1999 1 ). Recent studies performed in vitro (Wang et al. 1999), in rodents (Kleessen et al. 1997 2 ; Brown et al. 1998) including rats Correspondence to: Dr R.G. Crittenden, VTT Biotechnology, PO Box 1500, FIN-02044 VTT, Finland (e-mail: ross.crittenden@vtt.®). ã 2001 The Society for Applied Microbiology Journal of Applied Microbiology 2001, 90, 268±278