**1. Introduction**

Polysaccharides are inextricably associated with human health and exist in our foods, which are polymeric carbohydrate macromolecules consisting of multiple monosaccharide units linked by glycosides [1,2]. Recently, developing more bio-based or green chemical food ingredients has become a global trend to meet the increasingly diversified and healthy diet [3]. Exploring new polysaccharide material sources with useable characteristics has attracted the interest of researchers, as polysaccharides with different functions have been isolated from various plants and animals, bacteria, and fungi [4,5]. Despite the lack of large-scale industrial applications, it still makes great sense to understand the available natural resources worldwide [6]. Nondigestible polysaccharides cannot be absorbed immediately by the gastrointestinal digestive system [7]. Trillions of microorganisms coexist in the human intestine and are collectively referred to as the gut microbiota and play a vital role in human diets and host health [8]. However, indigestible polysaccharides can pass through the gastrointestinal tract to the distal gut and then be fermented by the gut microbiota [9] and produce some beneficial metabolites, such as short-chain fatty acids (SCFAs) [10]. SCFAs greatly influence the host physiology and energy homeostasis, especially in maintaining epithelial barrier function and preventing colorectal cancer [11].

**Citation:** Wang, W.; Yuan, Y.; Cao, J.; Shen, X.; Li, C. Beneficial Effects of *Holothuria leucospilota* Polysaccharides on Fermentability In Vivo and In Vitro. *Foods* **2021**, *10*, 1884. https:// doi.org/10.3390/foods10081884

#### Academic Editors:

Fani Mantzouridou, Jianhua Xie, Yanjun Zhang and Hansong Yu

Received: 4 July 2021 Accepted: 12 August 2021 Published: 15 August 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/).

As an edible marine resource and traditional medicine, sea cucumber has been used in many Asian countries to treat diverse diseases based on its antioxidant, antithrombotic, and antitumor activities. *Holothuria leucospilota* (Echinodermata: Holothuroidea, *H. leucospilota*) is a tropical sea cucumber species present in the Indo-Pacific region [12]. Among the varieties of active substances in its body wall, polysaccharides are the most noticeable ingredient, accounting for up to 31% of the total organic matter of dried sea cucumbers [13]. The HLP has been shown to be made of typical acidic polysaccharides with a backbone of intercalated 1,4-GlcA and 1,3-GalNAc, branched with fucose with different sulfate patterns and is composed of galactosamine, fucose, and glucuronic acids with ratios of 39.08%, 35.72%, and 10.72%, respectively [14,15]. Our previous works reported that HLP alleviated the symptoms of type 2 diabetes mellitus in rats by improving the gut microbiome [16]. In addition, Yuan et al. showed its excellent antioxidant activity after gastric and intestinal digestion in vitro [17]. However, the information regarding how HLP affects host health is still insufficient. The in-vitro and in-vivo fermentation characteristics and antioxidant activities of HLP have not been comparably explored.

Accordingly, the present study was designed to investigate the in-vitro and in-vivo fermentation behaviors of HLP by characterizing the pH, total sugar, reducing sugar, free monosaccharide, and SCFAs. In addition, the liver malondialdehyde (MDA), glutathione peroxidase (GSH-Px), and superoxidase dismutase (SOD) activities in mice were determined after 28 days of oral administration. This study is expected to promote the application of functional HLP in the food and pharmacological industries.
