Elsevier

Anaerobe

Volume 14, Issue 3, June 2008, Pages 184-189
Anaerobe

Food microbiology
Metabolism of prebiotic products containing β(2-1) fructan mixtures by two Lactobacillus strains

https://doi.org/10.1016/j.anaerobe.2008.02.002Get rights and content

Abstract

The capacity of two probiotic strains, isolated from human breast milk, to use several β(2-1) fructan mixtures as carbon and energy source in in vitro cultures has been tested. Results showed that both strains, Lactobacillus gasseri CECT5714 and Lactobacillus fermentum CECT5716, reached higher growth levels on culture media containing fructooligosaccharide mixtures produced by enzymatic synthesis, compared to those obtained by inulin hydrolysis. Furthermore, the shortest β(2-1) fructan, kestose, was the only prebiotic compound in the mixtures significantly metabolized in all growth media tested. Analysis of short-chain fatty acid production showed no correlation between the fatty acid profile produced and the carbon source used in each experiment. These data could serve to select appropriate β(2-1) fructans to be used as prebiotics for L. gasseri CECT5714 and L. fermentum CECT5716 and to design suitable symbiotic food products containing the mentioned lactobacilli.

Introduction

Human breast milk can be considered as a source of safe and potentially probiotic bacteria. It contributes to the initiation and development of neonatal gut microflora, since this substrate represents a continuous source of microorganisms to the infant gut during several weeks after birth [1]. In addition, the lactic acid bacteria isolated from human breast milk fulfil some of the principal criteria recommended for probiotics designed for human consumption, such as: being of human origin, a history of safe use and adaptability to lactic substrates [1]. The capacity to metabolize prebiotics is not an essential property for a probiotic strain, although it is desirable, as it may contribute to improve another series of recommendable characteristics that probiotics should possess [2], [3], [4]. Among these characteristics are being resistant to technological procedures [5] and the capacity to colonize and to persist in the human intestinal tract [6].

Prebiotics are defined as non-digestible food ingredients that have a beneficial effect on the health of the host, selectively stimulating growth and/or the activity of a limited number of bacteria in the colon [7]. Among the available products on the market, the β(2-1) fructans are the most documented prebiotic compounds [8], [9], [10]. There are several mixtures of β(2-1) fructans commercially available with differences in the polymerization degree (DP) and also in their origin. In this sense, inulin is a heterofructan (DP 10–60) constituted by D-fructoses linked by β(2-1)-glycosidic bonds and a terminal α(1-2) D-glucose at the reducing end, obtained from chicory roots. The oligofructose is synthesized through partial hydrolysis of inulin, showing a polymerization degree from 2 to 9, and is mainly constituted by oligosaccharides of D-fructose (Fn), and in smaller proportions, by oligosaccharides of D-fructose joined to a terminal D-glucose (GFn). The fructooligosaccharides, with a lower degree of polymerization (2–4), are synthesized through sucrose transglycosilation in reactions catalysed by β-fructofuranosidases from bacteria or fungi, leading to mixtures of oligosaccharides with GFn structure [11].

The prebiotic effect of the β(2-1) fructans has been studied in both in vivo and in vitro experiments. In humans, several studies have demonstrated that the presence of β(2-1) fructans in the diet induces an increase in the population of bifidobacteria in the colon [12], [13], [14]. On the other hand, the ability of β(2-1) fructans to stimulate in vitro the growth of various species of bifidobacteria [15], [16], [17], [18] and lactobacilli has been proved [3], [19]. However, this capacity to use β(2-1) fructans as a source of carbon and energy does not appear to be an universal characteristic in these two bacterial families. Some Bifidobacterium and Lactobacillus strains have been identified as unable to grow in media with β(2-1) fructans as the only carbon source [3], [18], [20]. Furthermore, fructans with different degrees of polymerization exhibit differences in the capacity to stimulate bacterial growth [15], [21], [22]. Although the prebiotic effect is assigned to the three types of fructans which have been described previously, some studies indicate that short-chain oligosaccharides (DP 2–5), present in fructooligosaccharides and oligofructose, are more efficiently metabolized in most of bifidobacteria [17], [18], [20], [23]. In the case of the lactobacilli, with fewer studies reported concerning fructan consumption, the preference for short-chain fructooligosaccharides appears to be stricter, only using compounds of DP from 2 to 3 [3], [21], [22], [24].

It appears necessary, therefore, to test the prebiotic capacity of different fructans among different probiotic species. The results of these studies, apart from establishing the real prebiotic potential, can also be applicable in the design of products that combine optimized mixtures of pre and probiotics—those called symbiotics [9], [18], [25].

In the present study we have evaluated the capacity of the bacterial strains Lactobacillus gasseri CECT5714 and Lactobacillus fermentum CECT5716, isolated from human breast milk and with demonstrated probiotic characteristics [26], [27], [28] to metabolize various mixtures of β(2-1) fructans. This study establishes the first step in the characterization of the prebiotic effect of certain mixtures in the mentioned bacterial strains.

Section snippets

Microorganisms and media

L. gasseri CECT5714 and L. fermentum CECT5716 were isolated as previously described [29]. Strains were maintained in MRS broth (Oxoid, Basingstore, UK) and routinely incubated anaerobically at 37 °C. The MRS(-C) medium was used in the fermentation experiments and it has the same composition than MRS but without glucose. Glucose, fructooligosaccharides (Actilight® 950P, FOS-AES), oligofructose (Raftilose® P95) and inulin (Raftiline® HP) were used as energy and carbon sources at 20 g/L. Actilight®

Growth of lactobacillus strains in the presence of different β(2-1) fructans as carbon sources

The two strains under study showed growth levels and extra cellular pH values very similar comparing them with results obtained with broth media containing glucose and FOS-AES (Fig. 1). This result was not surprising due to the high glucose content of FOS-AES that can be used as primary carbon source during the first stages of fermentation. Both probiotics reached the stationary phase after 12 h of incubation, although in the case of the L. gasseri CECT5714 strain, a slow growth was observed

Discussion

The prebiotic capacity of different compounds is being intensely investigated during last years. Among these compounds, the non-digestible oligosaccharides and especially the β(2-1) fructans deserve special attention as they constitute the most extensively studied and reported prebiotic group [9], [10]. However, results found in the scientific bibliography sometimes are inconclusive or even contradictory. This is the case of the prebiotic effect observed in vivo with mixtures of β(2-1) fructans

Conclusions

Our results indicate that L. gasseri CECT5714 and L. fermentum CECT5716 prefer to use GF2 as a carbon and energy source among all β(2-1) fructans under study in our in vitro experiments. FOS-AES and Actilight®, as the β(2-1) fructans mixtures with higher GF2 content, can be considered effective prebiotics for these strains, especially Actilight® due to its low content in other non-fructan carbohydrates. On the contrary, the β(2-1) fructans derived from inulin, independen of their DP, do not

Acknowledgements

The authors thank Antonio Carceles and María C. Membrilla for the excellent technical assistance. Layla Fernández, José M. Corral and Magdalena Valdivieso-Ugarte received a research fellowship from Fundación Universidad-Empresa (University of Granada) and Puleva Biotech, S.A.

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    1

    Present address: Max-Planck-Institut f. KohlenforschungKaiser-Wilhelm-Platz, Muelheim an der Ruhr, Germany.

    2

    Present address: IPK-Institute of Plant Genetics and Crop Plant Research, Department of Cytogenetics and Genome Analysis, Apomixis, Gatersleben, Germany.

    3

    Present address: Neuron BPh, Parque Tecnológico de la Salud, Granada, Spain.

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