Probiotic bacteria: safety, functional and technological properties

Abstract

During the past two decades probiotic (health promoting) micro-organisms have been increasingly included in various types of food products, especially in fermented milks. Several aspects, including safety, functional and technological characteristics, have to be taken into consideration in the selection process of probiotic micro-organisms. Safety aspects include specifications such as origin (healthy human GI-tract), non-pathogenicity and antibiotic resistance characteristics. Functional aspects include viability and persistence in the GI-tract, immunomodulation, antagonistic and antimutagenic properties. Before probiotic strains, chosen on the basis of their good safety and functional characteristics, can benefit the consumer, they must first be able to be manufactured under industrial conditions. Furthermore, they have to survive and retain their functionality during storage, and also in the foods into which they are incorporated without producing off-flavours. Factors related to the technological and sensory aspects of probiotic food production are of utmost importance since only by satisfying the demands of the consumer can the food industry succeed in promoting the consumption of functional probiotic products in the future.

Introduction

Probiotics are live microbial food supplements which benefit the health of consumers by maintaining or improving their intestinal microbial balance (Fuller, 1989). Due to their perceived health benefits probiotic bacteria have been increasingly included in yoghurts and fermented milks during the past two decades. Most commonly they have been lactobacilli such as Lactobacillus acidophilus, and bifidobacteria often referred to as ‘bifidus’ (Daly and Davis, 1998). A major development in functional foods pertain to foods containing probiotics and prebiotics which enhance health promoting microbial flora in the intestine. There is growing scientific evidence to support the concept that the maintenance of healthy gut microflora may provide protection against gastrointestinal disorders including gastrointestinal infections, inflammatory bowel diseases, and even cancer (Haenel and Bendig, 1975, Mitsuoka, 1982, Salminen et al., 1998a). The use of probiotic bacterial cultures stimulates the growth of preferred micro-organisms, crowds out potentially harmful bacteria, and reinforces the body's natural defence mechanisms. Today, plenty of evidence exists on the positive effects of probiotics on human health. However, this has usually been demonstrated in diseased human populations only (Salminen et al., 1998a). Thus there is an urgent need for evidence for probiotic health benefits in average (generally healthy) populations.

Before a probiotic can benefit human health it must fulfil several criteria: It must have good technological properties so that it can be manufactured and incorporated into food products without loosing viability and functionality or creating unpleasant flavours or textures; it must survive passage through the upper gastrointestinal (GI) tract and arrive alive at its site of action; and it must be able to function in the gut environment. To study the probiotic strain in the GI-tract, molecular techniques must be established for distinguishing the ingested probiotic strain from the potentially thousands of other bacterial strains that make up the gastrointestinal ecosystem. Additionally, techniques are required to establish the effect of the probiotic strain on other members of the intestinal microbiota and importantly on the host. This includes not only positive health benefits, but also demonstration that probiotic strains do not have any deleterious effects. Armed with this knowledge, the probiotics can then enter human pilot studies that attempt to assess their health benefits to consumers (Mattila-Sandholm and Salminen, 1998, Mattila-Sandholm et al., 1999).