Evolution of cranberry juice compounds during in vitro digestion and identification of the organic acid responsible for the disruption of in vitro intestinal cell barrier integrity

Abstract

Cranberry juice is increasingly consumed for its richness in polyphenols having a positive impact on human health. Unfortunately, when regularly consumed, its high concentration in organic acids may cause some intestinal discomforts. In the present study, its organic acid content was reduced of 41% by electrodialysis with bipolar membrane (EDBM), and the resulted deacidified juice was divided in five different juices readjusted or not with different concentrations of citric and/or malic acid(s) corresponding to the concentration of this/these acid(s) recovered during EDBM or at the titratable acidity (TA) of the non-deacidified cranberry juice. The evolution of the cranberry juice main interesting compounds (organic acids and polyphenols), according to the concentration and nature of the organic acids present, was studied for the first time at each specific stages of the digestion. After digestion, Caco-2 cells were exposed to all digested juices to identify the organic acid(s) responsible for the loss of integrity of the epithelial barrier. It appeared that organic acid contents did not change during the different steps of the digestion while polyphenolic compounds decreased starting from the gastric phase. Whatever the organic acid concentration or nature, the concentration of PACs significantly decreased between the salivary and the gastric steps but was different according to their structure when the concentration of most of anthocyanins significantly decreased at the gastric step. Also, to the best of our knowledge, it was the first time that citric acid was demonstrated as the organic acid responsible for the loss of integrity of Caco-2 cell monolayers.

Keywords: Caco-2 cells; Cranberry juice; Electrodialysis with bipolar membrane; Epithelial barrier; In vitro digestion; Integrity; Organic acid removal; Organic acids; Polyphenols.

Fig. 1

Measurement of a citric and b malic acid contents in non-deacidified cranberry juice and deacidified juices with or without extra content of organic acids during the three digestion steps and in comparison with the initial juice. Columns with different capital letters are significantly different at a probability level of 0.05 (MANOVA, Tukey test). Columns with different lowercase letters are significantly different at a probability level of 0.05 (ANOVA) (n = 3)

Fig. 2

Flavylium ion conversion at increasing pH. Adapted from Zhao and Temelli (2017)

Fig. 3

Effect of different deacidified cranberry juices with or without extra content of organic acids in comparison with a non-deacidified cranberry juice on the variation in TransEpithelial Electrical Resistance (ΔTEER) (Ω cm²) of Caco-2 monolayers (*p < 0.05). HBSS is Hank’s Balanced Salt Solution, non-deacidified juice is the digested non-deacidified cranberry juice, deacidified juice is the digested non-deacidified cranberry juice after organic acid removal by electrodialysis treatment, deacidified + malic acid, deacidified + citric acid and deacidified + malic and citric acid correspond to the deacidified/digested cranberry juice where the concentration lost during organic acid removal treatment of these organic acids is added and deacidified + TA malic acid is the deacidified/digested cranberry juice where the concentration of malic acid at the titratable acidity of the non-deacidified cranberry juice is added. S.E.M corresponds to Standard Error of the Mean (n = 3)

Fig. 4

Proposed mechanism of citric acid present in cranberry juice on the opening of tight junctions and resulting chronic inflammatory response. Step 1: intestinal cell barrier with a normal integrity, step 2: disruption of tight junction complexes, via depletion of intracellular calcium following the transport of citric acid and step 3: paracellular absorption in the epithelium through opened tight junctions and resulting chronic inflammatory response