Three Varieties of Grape Pomace, with Distinctive Extractable:Non-Extractable Polyphenol Ratios, Differentially Reduce Obesity and Its Complications in Rats Fed a High-Fat High-Fructose Diet

Abstract

Grape pomace is a commonly discarded by-product characterized by high extractable (EPP) and non-extractable (NEPP) polyphenol contents which exhibits anti-obesogenic effects. However, the relevance of each fraction needs to be elucidated. In this work, we examined the effects of three pomaces with different concentrations of EPPs and NEPPs on metabolic alterations associated with obesity. The NEPP:EPP ratio of the grape pomaces was 1.48 for Malbec, 1.10 for Garnacha, and 5.76 for Syrah grape varieties. Rats fed a high-fat high-fructose diet supplemented with Malbec grape pomace (HFFD + MAL) Syrah grape pomace (HFFD + SYR) or Garnacha grape pomace (HFFD + GAR) showed significantly less weight gain: 20%, 15%, and 12% less, respectively, compared to HFFD controls. The adiposity index was also significantly decreased by 20% in the HFFD + MAL and HFFD + SYR groups, and by 13% in the HFFD + GAR group. Serum triglycerides were significantly decreased by 46% in the HFFD + MAL group and by 31% in the HFFD + GAR group, compared to the HFFD group, but not in the HFFD + SYR group. All pomace supplementations regulated postprandial glucose in an oral glucose tolerance test. Therefore, grape pomaces containing both EPPs and NEPPs exert beneficial effects on body weight and glucose homeostasis, while EPPs seem to control triglyceride levels more effectively.

Keywords: extractable polyphenols; grape pomace; non-extractable polyphenols; obesity.

Figure 1

Hierarchical analysis of extractable polyphenol profiles of different varieties of grape pomace. Each colored cell on the map corresponds to a concentration value. * Identification confirmed with commercial standards.

Figure 2

Mesenteric adipose tissue histology analysis and adipocyte area of rats fed a high-fat high-fructose diet supplemented with different varieties of grape pomace. (A) Representative histological images of adipose tissue. (B) Adipocyte area (µm²). Values are reported as mean ± SD (n = 8). Different letters indicate significant (p < 0.05) differences according to Tukey’s test. STD; standard diet, HFFD; high-fat high-fructose diet, MAL; Malbec, Gar; Garnacha, SYR; Syrah.

Figure 3

Effect of different varieties of grape pomace on glucose tolerance in rats fed a high-fat high-fructose diet. (A) Postprandial blood glucose levels and (B) area under the curve (AUC) measured between 0 and 120 min after glucose load. Data are reported as means ± SE for eight animals per group. Statistically significant differences were determined by ANOVA, followed by Tukey’s test (p < 0.05). STD; standard diet, HFFD; high-fat high-fructose diet, MAL; Malbec, GAR; Garnacha, SYR; Syrah.

Figure 4

Principal component analysis (PCA) of physiological effects on rats fed a high-fat high-fructose diet supplemented with different varieties of grape pomace (A,B). Principal component analysis (C) and biplot (D) of the physiological effects on rats of supplementation of the high-fat high-fructose diet with different varieties of grape pomace. Principal component analysis (E) and biplot (F) of extractable and non-extractable polyphenol contents in different grape pomace varieties. AUC, area under the curve; EPA, extractable proanthocyanidins; GAR, Garnacha; HFFD, high-fat high-fructose diet; HPP, hydrolyzable polyphenols; MA, extractable monomeric anthocyanins; MAL, Malbec; NEPAs, non-extractable proanthocyanidins; STD, standard diet; SYR, Syrah; TAG, triacylglycerols; TF, total flavonoids; TPC, total phenolics content.

Figure 5

Partial least squares discriminant analysis PLS-DA of the phenolic profile of grape pomace varieties and (A) triglycerides in serum, (B) weight increase, (C) AUC from OGTT, and (D) mesenteric adipose tissue.