**1. Introduction**

Anthocyanins, a class of phenolic compounds belonging to the flavonoid group, are mainly found in the epidermal tissues of plants, such as vegetables, fruits, and flowers [1]. Anthocyanins are responsible for organoleptic colors such as red, purple, and blue [2]. Cyanidin-3-*O*-glucoside (C3G) is one of the most widely distributed anthocyanins in fruits [3], accounting for 94% of the total anthocyanin content in blackberries [4,5]. C3G serves as key antioxidant. Anthocyanins are glycosides of polyhydroxy and polymethoxy derivatives of 2-phenylbenzopyrylium or flavylium salts [2]. These compounds have a high antioxidant capacity [6] and the ability to prevent a variety of chronic diseases associated with inflammation [7,8] and improve the colon environment [9].

Dietary phenols, such as C3G, are substrates for a variety of enzymes in the liver, small intestine, and colon [10,11], mainly enzymes produced by gut microbiota. The colon is therefore an active site for C3G metabolism. When C3G is present in the gastrointestinal tract (GIT), colonic microbiota decompose them into a variety of bioactive substances

**Citation:** Yang, Z.; Huang, T.; Li, P.; Ai, J.; Liu, J.; Bai, W.; Tian, L. Dietary Fiber Modulates the Fermentation Patterns of Cyanidin-3-*O*-Glucoside in a Fiber-Type Dependent Manner. *Foods* **2021**, *10*, 1386. https:// doi.org/10.3390/foods10061386

Academic Editors: Jianhua Xie, Yanjun Zhang and Hansong Yu

Received: 11 May 2021 Accepted: 8 June 2021 Published: 16 June 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

and phenolic acids, such as protocatechuic acid (PCA) and 2,4,6-trihydroxybenzaldehyde (TB) [12], derived from the parent compound [12–14]. C3G is likely to primarily exert its influence through C3G metabolites [15]. In addition, in our previous study [16], we found that C3G plays a role in regulating the prebiotic activity of the microbial composition in rats. Another study found that the fermentation of C3G stimulated the proliferation of *Bifidobacteria* and *Lactobacillus*; both effects can affect intestinal health [17].

In addition to polyphenols, dietary fiber could modulate gut microbiota in a structuredependent manner, releasing short-chain fatty acids (SCFAs) in the GIT. In recent years, the interactions between anthocyanins and dietary fibers have attracted extensive attention. A significant increase in plasma antioxidant capacity was found 8 h after the acute ingestion of high dietary fiber and polyphenols (antioxidant capacity determined by ABTS•<sup>+</sup> and FRAP assays) [18]. The previous study has suggested that certain pectin fractions can increase C3G stability during in vitro digestion [19] in upper GIT, and consequently change the substrates for microbiota in the colon. The interactions between anthocyanins and dietary fibers could benefit gut health. However, how this interaction affects the fermentation of dietary fiber and C3G is still unclear, especially in terms of how different dietary fibers modulate C3G fermentation patterns depending on fiber type.

In this study, we investigated the interplay of C3G with four different dietary fibers during in vitro fermentation. We used in vitro fermentation model to determine the effects of different dietary fibers (β-glucan, arabinoxylan, fructo-oligosaccharide, and pectin) on the C3G metabolites, antioxidant capacity, SCFAs, and the microbiota composition in the colonic environment.

#### **2. Materials and Methods**

#### *2.1. Materials*

Oat β-glucan (BG) and wheat arabinoxylan (AX) were purchased from Shaanxi Pioneer Biotech Co., Ltd. (Xi'an, Shaanxi, China). Pectin (PEC) with 71% degree of esterification was provided by Herbstreith & Fox (Neuenbürg, Germany). Fructo-oligosaccharide (FOS) was obtained from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). Cyanidin-3-*O*-glucoside (C3G) was extracted and purified from black soybean peels (Anhui province, China) according to the method we described before [20,21]. The purity of the C3G was 95%.
