The skin of almonds may exert a prebiotic effect and enhance the growth of beneficial bacteria in the gut, says new research.
Using the Model Gut Platform at the Institute of Food Research (IFR) in Norwich, England, researchers led by IFR’s Giuseppina Mandalari report that both natural and blanched almond skins produced significant increases in the population of various gut microbes, including bifidobacteria, according to findings published in the journal of the Federation of European Microbiological Societies (FEMS), Microbiology Letters.
Increases in the populations of Clostridium coccoides and Eubacterium rectale strains were also reported, and the almond skins were attributed a prebiotic index of about 3.2, which the researchers said “compared well” with a prebiotic index of 4.2 observed for commercial fructooligosaccharides.
“Almond skins contain a high amount of dietary fibre, which is made of plant cell wall polysaccharides able to provide the body with energy through fermentation and absorption of short chain fatty acids (SCFAs),” wrote Mandalari and her co-workers.
“Pectic substances encasing the cellulose microfibrils are the major component of almond skin cell walls, with small amounts of hemicelluloses such as xyloglucan and alpha-glucans.
“We believe that the beneficial effects on colonic microbiota observed in this work were produced by fermentation of the nonglycaemic carbohydrates, mainly pectin, present in almond skins,” they added.
Commenting independently on the research, Professor Glenn Gibson, a prebiotic expert from the University of Reading, told NutraIngredients that the new studies tap into the growing trend for developing new fibres with potential prebiotic activity. "There is a need for more prebiotics as there are only a few in existence," said Prof Gibson. "Almonds have a health image and this seems to contribute further to that," he added.
Despite the reported prebiotic activity in vitro, Prof Gibson said that, in order to confirm the prebiotic activity, "well controlled and designed human studies would be necessary”.
Mandalari and her co-workers investigated the effects of the almond skins in the model gut – a model of the gastrointestinal tract that includes in vitro gastric and duodenal digestion, followed by colonic fermentation with mixed bacterial cultures obtained from faeces. Blanched skins are a by-product of the almond-processing industry.
Results showed that both almond skins significantly increased levels of bifidobacteria and Clostridium coccoides/ Eubacterium rectale group, said the researchers.
“No significant differences in the proportion of gut bacteria groups and in short-chain fatty acid production were detected between natural and blanched skins, showing that polyphenols present in almond skins did not affect bacterial fermentation,” wrote the researchers.
Efficacy and safety
A separate study, performed by Chinese Center for Disease Control and Prevention and published in Food and Chemical Toxicology, found that the almond skins were also safe, with no toxic effects observed up to a dietary concentration of 10 per cent.
The research was welcomed by Nut-trition Inc., The Hughson, California-based producer of the almond skin powder used in both studies. The ingredient, a by-product from commercial blanching of almonds, is sold directly by Nut-trition as Almond Bran.
Robert Miltner, VP business development for Nut-trition said the new studies “confirm our own research that Almond Bran functions in vitro as a prebiotic”.
“We have found, for example, that Almond Bran promotes growth and extends shelf life of probiotic organisms in cultured products like yogurt,” said Miltner. “And Almond Bran is more label-friendly than other prebiotic ingredients for food and nutraceuticals. It is made directly from almonds, which have increasingly high consumer appeal due to studies linking almond consumption to improved cardiovascular health.”
Food and Chemical Toxicology
Published online ahead of print, doi: 10.1016/j.fct.2009.10.025
“A Subchronic Oral Toxicity Study of Almond Skins in Rats”
Authors: Y. Song, W. Wang, W. Cui, X. Zhang, W. Zhang, Q. Xiang, Z. Liu, N. Li, X. Jia
Microbiology Letters (Federation of European Microbiological Societies)
Published online ahead of print, doi:10.1111/j.1574-6968.2010.01898.x
“In vitro evaluation of the prebiotic properties ofalmond skins (Amygdalus communis L.)”
Authors: G. Mandalari, R.M. Faulks, C. Bisignano, K.W. Waldron, A. Narbad, M.S.J. Wickham