RESUMO
Macroalgae stand out for their high content of dietary fiber (30-75%) that include soluble, sulfated (fucoidan, agaran, carrageenan, and ulvan) and non-sulfated (laminaran and alginate) polysaccharides. Many studies indicate that these compounds exert varied biological activities and health-promoting effects and for this reason, there is a growing interest for using them in food products. The aim of this review was to critically evaluate prebiotic properties of algal polysaccharides, i.e., their ability to exert biological activities by modulating the composition and/or diversity of gut microbiota (GM). Pre-clinical studies show that the non-sulfated alginate and laminaran are well-fermented by GM, promoting the formation of short chain fatty acids (SCFAs) including butyrate, and preventing that of harmful putrefactive compounds (NH3, phenol, p-cresol, indole and H2S). Alginate increases Bacteroides, Bifidobacterium, and Lactobacillus species while laminaran mostly stimulates Bacteroides sp. Results with sulfated polysaccharides are more questionable. Agarans are poorly fermentable but agarose-oligosaccharides exhibit an interesting prebiotic potential, increasing butyrate-producing bacteria and SCFAs. Though carrageenan-oligosaccharides are also fermented, their use is currently limited due to safety concerns. Regarding fucoidan, only one study reports SCFAs production, suggesting that it is poorly fermented. Its effect on GM does not indicate a clear pattern, making difficult to conclude whether it is beneficial or not. Notably, fucoidan impact on H2S production has not been evaluated, though some studies report it increases sulfate-reducing bacteria. Ulvan is badly fermented by GM and some studies show that part of its sulfate is dissimilated to H2S, which could affect colonic mitochondrial function. Accordingly, these results support the use of laminaran, alginate and agaro-oligosaccharides as prebiotics while more studies are necessary regarding that of fucoidan, carrageenan and ulvan. However, the realization of clinical trials is necessary to confirm such prebiotic properties in humans.
RESUMO
RESUMEN La microbiota intestinal (MI) es considerada como un nuevo blanco para la prevención y manejo nutricional de las alteraciones inflamatorias y metabólicas asociadas a las enfermedades crónicas no-transmisibles. Los prebióticos son principalmente fibras solubles cuyo consumo favorece el crecimiento de poblaciones bacterianas beneficiosas de la MI e impacta favorablemente la salud del consumidor. Esta revisión presenta a los fitoquímicos dietarios, que incluyen a más de 8.000 compuestos, como una nueva clase de prebióticos debido a su capacidad de estimular poblaciones de Lactobacillus, Bifidobacterium, Akkermansia y de bacterias productoras de butirato en el colon, a expensa de bacterias potencialmente dañinas como C. histolyticum. Además, los fitoquímicos son transformados por la MI en múltiples metabolitos que ejercen actividades biológicas a veces más potentes que la molécula inicial de la cual provienen. Individuos con distintos metabotipos han sido descritos de acuerdo a su capacidad de responder al consumo de isoflavonas, lignanos o elagitaninos, dependiendo de la presencia en su MI de bacterias capaces de transformar dichos polifenoles en equol, enterolactona/enterodiol y urolitinas, respectivamente, los cuales exhiben actividades biológicas. Valerolactonas y ácidos aromáticos también son producidos por la MI a través del metabolismo de las proantocianidinas. El efecto prebiótico de los fitoquímicos contribuiría a explicar los efectos saludables del consumo de frutas y verduras ricos en fitoquímicos.
ABSTRACT Intestinal microbiota (IM) is considered as a new target for the prevention and nutritional management of inflammatory and metabolic alterations associated with non-transmissible chronic diseases. Prebiotics are mainly soluble fibers whose consumption favors the growth of beneficial bacterial populations of the IM and positively impacts health. This review discusses dietary phytochemicals, which include more than 8,000 compounds, as a new class of prebiotics due to its ability to stimulate populations of Lactobacillus, Bifidobacterium, Akkermansia and butyrate producing bacteria in the colon at the expense of potentially harmful bacteria, such as C. histolyticum. In addition, phytochemicals are transformed by IM into a great array of metabolites exerting biological activities and are sometimes more potent than the initial molecule from which they are derived. Individuals with different metabotypes have been described according to their ability to respond to the consumption of isoflavones, lignans or ellagitannins, depending on the presence in their IM of bacteria capable of transforming these polyphenols into equol, enterolactone/enterodiol and urolithins, respectively, which exhibit biological activities. Valerolactones and aromatic acids are also produced by the IM through proanthocyanidin metabolism. The prebiotic effect of phytochemicals would help to explain the healthy effects associated with the consumption of fruits and vegetables rich in phytochemicals.