Levels of fecal procyanidins and changes in microbiota and metabolism in mice fed high-fat diet supplemented with apple peel

Authors: ELKAHOUI, SALEM - Centre De Biotechnologie; Levin, Carol; Bartley, Glenn; Yokoyama, Wallace - Wally; Friedman, Mendel

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2019
Publication Date: 9/10/2019
Citation: Elkahoui, S., Levin, C.E., Bartley, G.E., Yokoyama, W.H., Friedman, M. 2019. Levels of fecal procyanidins and changes in microbiota and metabolism in mice fed high-fat diet supplemented with apple peel. Journal of Agricultural and Food Chemistry. 67(37):10352-10360. https://doi.org/10.1021/acs.jafc.9b04870.
DOI: https://doi.org/10.1021/acs.jafc.9b04870

Interpretive Summary: Interest in peels from fruits and vegetables generated during food processing arises from the fact that many of them are reported to contain nutrients and biologically active compounds that have the potential to improve animal and human nutrition and health. Utilizing such peel products can therefore lead to the development of health-promoting food supplements as well as alleviating waste from the food industry. Apple peels are rich in fiber and polyphenols, which are poorly digested animals but become available to gut bacteria as they pass to the lower digestive track. There they might provide nourishment to beneficial bacteria or be metabolized into more available compounds useable by host animal or other gut bacteria. In a previous publication we showed that high-fat diets with added 10% and 20% potato peel powders induced large reductions in weight gain relative to diets without added peel powders. The objective of the present study was to use a similar diet design to test the effects of supplementing high-fat diets with apple peel powders. The results showed that dietary apple polyphenols were poorly digested and thus available to and changing the makeup of the gut bacteria, which seems to have led to a small dose-dependent decrease in weight gain and changes in liver enzymes associated with cholesterol metabolism.

Technical Abstract: Apple peels contain most of the procyanidins, other dietary polyphenols and fiber of the fruit and their potential to mitigate the deleterious effects of a high-fat diet in mice was investigated here. Peels from three distinct varieties of apples, Red Delicious, Golden Delicious and Arkansas Black, were freeze-dried and ground into powders. Mice were fed high-fat diets supplemented with 10% or 20% apple peel powder, or 1% or 2% of a commercial apple polyphenol extract for three weeks. A positive control group was fed 10% grape-seed flour that also contains polyphenols. Total extractable polyphenols in the apple products and in the feces of select mice were determined by the Folin-Ciocalteu assay. The extractable polyphenols were r analyzed further using HPLC to determine their relative extent of polymerization. Non-extractable polyphenols in the apple products were determined using the 4-dimethylaminocinnamaldehyde assay. Although there was a dose response to dietary apple peels and polyphenols in which a higher level of apple peel in the diet resulted in reduced weight gain and adipose tissue mass, none of the treatments were statistically different than the control. The expression of genes encoding for the liver enzyme stearoyl-CoA desaturase (Scd-1) was correlated with adipose weight. The expression of the genes encoding for the liver enzyme cytochrome P51 (Cyp51) was downregulated by the high-polyphenolic diets. The microbiota of feces from select mice fed Red Delicious peels, Red Delicious whole apple powder, and grape and apple phenolic extracts were analyzed using next-generation sequencing (NGS), the results of which showed differences associated with these dietary interventions.