Gastrointestinal Digestion Impact on Phenolics and Bioactivity of Tannat Grape Pomace Biscuits

Abstract

The search for natural sources of bioactive compounds with health-promoting properties has intensified in recent years. Among these, Tannat grape pomace (TGP), a primary byproduct of winemaking, stands out for its high phenolic content, although its bioactivity may be affected during gastrointestinal digestion. This study aimed to evaluate the impact of in vitro digestion on the antioxidant (ABTS, ORAC-FL, intracellular ROS inhibition), anti-diabetic (α-glucosidase inhibition), anti-obesity (lipase inhibition), and anti-inflammatory (NO inhibition) properties of five sugar-free biscuits formulated with varying percentages of TGP and sucralose. No significant differences were observed in the bioaccessible fractions (BFs, representing the compounds potentially released in the small intestine) between control biscuits and those enriched with TGP, suggesting limited release of phenolics at this stage. Conversely, the colonic fractions (CFs, simulating the material reaching the colon) from biscuits with higher TGP content exhibited greater bioactivities. HPLC-DAD-MS analysis of the CF from the biscuit containing 20% TGP and 4% sucralose revealed a high content of procyanidin trimers, indicating the persistence of these specific phenolic compounds after in vitro digestion. These findings suggest that TGP-enriched biscuits may deliver health benefits at the colonic level and support their potential application in the formulation of functional foods. Further microbiota and in vivo studies should be assessed to confirm the latter.

Keywords: bioaccessibility; bioactivity; biscuits; in vitro digestion; phenolic compounds; tannat grape pomace.

Figure 1

Total phenol content (TPC) of the bioaccessible and colonic fractions (BFs and CFs, respectively) of the different Tannat grape pomace (TGP) biscuits (TGP% sucralose%: 20% 4%, 20% 2%, 15% 3%, 10% 4%, and 10% 2%) and their control biscuits (sucralose%: 4%, 3%, and 2%). For BFs bars denote the mean values minus the digestion control (digestion without any sample), and for CFs bars denote the mean values. Error bars denote the standard deviation. Different lowercase letters represent significant differences between the CFs of the different biscuit formulations (Tukey test, p < 0.05). Different capital letters represent significant differences between the BFs of the different biscuit formulations (Tukey test, p < 0.05). Asterisks (*) indicate significant differences between BF and CF within the same biscuit formulation (t-test, p < 0.05).

Figure 2

Antioxidant capacity measured by (a) ABTS and (b) ORAC-FL of the bioaccessible and colonic fractions (BFs and CFs, respectively) of the different TGP biscuits (TGP% sucralose%: 20% 4%, 20% 2%, 15% 3%, 10% 4%, and 10% 2%) and their control biscuits (sucralose%: 4%, 3%, and 2%). For BFs bars denote the mean values minus the digestion control (digestion without any sample), and for CFs bars denote the mean values. Error bars denote the standard deviation. Different lowercase letters represent significant differences between the CFs of the different biscuit formulations according to the Tukey test (p < 0.05). Different capital letters represent significant differences between the BFs of the different biscuit formulations according to the Tukey test (p < 0.05). Asterisks (*) indicate significant differences between BF and CF within the same biscuit formulation (t-test, p < 0.05).

Figure 3

AAPH (1 mM)-induced ROS formation in normal human colon cells (CCD 841 CoN) treated with different concentrations of the bioaccessible and colonic fractions (BFs and CFs, respectively) of 20% 4% biscuit (TGP% sucralose%) and its control biscuit (4% sucralose) without TGP. DMEM was used as the negative control and AAPH as the positive control. A digestion without any sample was also assessed as a control. Bars represent the mean values, and error bars represent the standard error. Different letters denote significant differences between concentrations (mg/mL) of the same sample (Tukey, p < 0.05). Asterisks (*) indicate significant differences between the same concentrations (mg/mL) of both BF and CF samples (t-test, p < 0.05). + Indicates significant differences between the sample and the positive control (AAPH) (t-test, p < 0.05).

Figure 4

(a) α-glucosidase inhibition of the bioaccessible and colonic fractions (BFs and CFs, respectively) of the different TGP biscuits (TGP% sucralose%: 20% 4%, 20% 2%, 15% 3%, 10% 4%, and 10% 2%) and their control biscuits (sucralose%: 4%, 3%, and 2%). (b) Pancreatic lipase inhibition of the colonic fractions (CFs) of the different formulations of TGP biscuits. The BFs of TGP biscuits, as well as both BFs and CFs of control biscuits, are not shown due to the absence of measurable inhibitory activity under the assay conditions. Bars denote the mean values, and error bars the standard deviation. Different lowercase letters represent significant differences between the CFs of the different biscuit formulations according to the Tukey test (p < 0.05). Different capital letters represent significant differences between the BFs of the different biscuit formulations according to the Tukey test (p < 0.05). Asterisks (*) indicate significant differences between the CF and BF of the same biscuit formulation (t-test, p < 0.05).

Figure 5

LPS (1 µg/mL)-induced NO production in RAW 264.7 cells treated with the bioaccessible and colonic fractions (BF and CF, respectively) of a biscuit with 20% TGP and 4% sucralose (20% 4%) and its control biscuit (4%) without TGP. DMEM was used as the negative control and AAPH as the positive control. A digestion without any sample was also assessed as a control. Bars represent the mean values, and error bars represent the standard error. Different letters denote significant differences between concentrations (mg/mL) of the same sample (Tukey, p < 0.05). + Indicates significant differences between the sample and the positive control (LPS) (T-test, p < 0.05).