In vitro evaluation of prebiotic activity, pathogen inhibition and enzymatic metabolism of intestinal bacteria in the presence of fructans extracted from agave: A comparison based on polymerization degree

Highlights

• Effect of fructans fractions from different agave species as prebiotics.

• Changes in the enzymatic metabolism of probiotics in the presence of agave fructans.

• Growth inhibition of pathogens when probiotics metabolize agave fructans.

Abstract

The prebiotic effect of fructans is well known, including their beneficial influence on health. This study shows agave fructans impact as potential prebiotics, depending on their structure and polymerization degree (PD). The growth of seven probiotics and three pathogens was estimated by turbidimetric analysis and the latter (Salmonella typhimurium, Staphylococcus aureus and Listeria monocytogenes) were submitted to growth inhibition tests in the presence of metabolites produced by probiotics. Lactobacillus casei and L. paracasei growth was optimal when supplemented with agave fructans. L. casei was grown in the presence of the extracted fractions obtained from Agave salmiana spp. crassipina (optical density (O.D.) 1.09 ± 0.02, 0.98 ± 0.03, 0.98 ± 0.07, low, medium and high PD, respectively), A. salmiana var. liso (0.85 ± 0.13), A. atrovirens (0.79 ± 0.03) and A. tequilana spp. (0.89 ± 0.03). The growth of L. paracasei was optimal when supplemented with those fractions obtained from the A. salmiana (O.D. 1.12 ± 0.02, 1.18 ± 0.02, 1.13 ± 0.007, low, medium and high PD, respectively) and A. tequilana var. cenizo (1.18 ± 0.01 and 1.15 ± 0.02, medium and high PD, respectively) species. Both bacteria were tested in order to assess enzyme activity using API ZYM galleries after they were grown on agave fructans. The results show an increase of five enzymes (cysteine-arylamidase, α-chymotrypsin, β-galactosidase, N-acetyl-β-glucosaminidase and α-fucosidase).

Introduction

The prebiotic effect of fructans has been documented by some authors because they possess the ability to significantly modify intestinal microbiota (Krumbeck, Maldonado-Gomez, Ramer-Tait, & Hutkins, 2016). Fructans are molecules bonded by fructosyl linkages and generally they have a terminal glucose moiety. They may be present in approximately 15% of all flowering plants. Regarding their structure, five different types may be distinguished: inulin (β 2 → 1 linkage), levan (β 2 → 6 linkage) graminan (β 2 → 1 and β 2 → 6 linkages), inulin neoseries and levan neoseries (fructans possessing an internal glucose residue) (Peshev and Van den Ende, 2014, Ritsema and Smeekens, 2003). In Mexico, Agave is used as an important source of fructans. However, it has been reported that these plants contain more than one fructan structure. Agave contains branched graminan fructans, also known as “agavins”. These contain a complex mixture of fructans possessing different polymerization degrees (PD) (Mellado-Mojica and López, 2012, Praznik et al., 2013, Velázquez-Martínez et al., 2014). Because of their β linkages, fructans are not hydrolyzed by the human digestive enzymes and they are fermented only by some bacterial species found as intestinal colonic microbiota. This fermentation is beneficial to health as it may be translated into improved results from clinical blood tests, i.e. it regulates glucose and triglyceride levels, it enhances resistance against both intestinal and extra-intestinal pathogens, it modulates the immune response and it attenuates allergies. It has also been reported that fructans prevent body weight increases as it impacts on food intake and it regulates the satiety-related hormones (Delgado et al., 2010, Márquez-Aguirre et al., 2013, Santiago-García and López, 2014). Nevertheless, it was demonstrated that fructans possessing several PD display a different prebiotic activity (González-Avila et al., 2014, Mueller et al., 2016). Bacteria from the Lactobacillus and Bifidobacterium genera metabolize fructans exhibiting low PD, whereas bacteria residing at both proximal and distal colon metabolize those with high PD (Mueller et al., 2016, Van De Wiele et al., 2007). A recent study demonstrated that low PD fructans obtained from Agave tequilana prevent weight gain, hyperglycemia and fatty liver disease. Moreover, fructans showing several PD are involved in short-chain fatty acids biosynthesis, playing an important role on gastrointestinal health (Kleessen et al., 2001, Koenen et al., 2016). Among the approximately 300 described Agave species, nearly 75% are found on Mexican territory. However, less than 5% of these species are used during the production of alcoholic beverages and many others are not used for industrial purposes. The aim of this study was to evaluate in vitro the prebiotic activity displayed by those fructans obtained from seven agave species, which are characterized by different PD.