**1. Introduction**

Potato starch (PoS) has attracted extensive attention in regard to its physicochemical characteristics, such as digestibility, fine textural properties, high swelling power, and transparency. In addition to producing sacchariferous products, potato starch not only plays a unique role in processing flour products, snacks, and chemical starch, but it also serves as a food additive, including gelling agents and film-forming agents used in dairy products, baked foods, beverages, and other foods [1,2]. However, the application of native potato starch has sometimes been limited due to its thermal instability, easy retrogradation, and high content of rapidly digesting starch. Mixing potato starch with polyphenols has been a research hotspot, because polyphenols could play an important role in enhancing starch performance in different applications [3–6].

Polymeric proanthocyanidins (PPC) are a kind of polyphenol widely distributed in the plant realm [7]. These compounds are complicated polymers of flavan-3-ol monomer units, with a degree of polymerization (DP) that is generally more than five [8]. Evidence suggests that they are more efficient in the regulation of starch digestion compared to monomeric polyphenols. Li et al. [9] and Mkandawire et al. [10] indicated a positive relationship between the DP value (DP ≥ 5) of proanthocyanidin and the inhibition of α-amylase and α-glucosidase, accordingly modifying starch intestinal glucose release. Barros et al. [11] found that proanthocyanidin-rich sorghum extracts elevated the content of resistant starch in corn starch to nearly three times that of monomer polyphenols. Extensive research

**Citation:** Xu, J.; Dai, T.; Chen, J.; He, X.; Shuai, X.; Liu, C.; Li, T. Effects of Three Types of Polymeric Proanthocyanidins on Physicochemical and In Vitro Digestive Properties of Potato Starch. *Foods* **2021**, *10*, 1394. https:// doi.org/10.3390/foods10061394

Academic Editor: Mario M. Martinez

Received: 20 May 2021 Accepted: 7 June 2021 Published: 16 June 2021

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has shown that physicochemical properties and biological activities of proanthocyanidins depend on the DP. The physical conformation of high DP proanthocyanidins provides more hydrophobic sites, while lower DP counterparts exhibit a stronger water-soluble capacity due to their considerable external hydroxyl groups [12]. Besides this, Arimboor and Arumughan [13] and Dai et al. [14] discovered that smaller-molecular proanthocyanidins had stronger antioxidant effects. Khadri et al. [15] illustrated that the anti-inflammatory activity of lemon grass proanthocyanidin relied on the DP. Pierini et al. [16] and Kawahara et al. [17] found that proanthocyanidin with a higher DP achieved a stronger growth inhibition influence on some specific cancer cells (e.g., hepatoma carcinoma, esophageal adenocarcinoma, and colon cancer cells).

To date, several papers have focused on the influence of proanthocyanidin on pasting, thermal, rheological, and digestion characteristics of potato starch. Zhang et al. [18] found that grape seed proanthocyanidins increased thermostability, reduced rapid digestion, and decreased the final viscosity and hardness of PoS gel significantly. Gao et al. [19] reported that oligomeric procyanidins (DP ≈ 2.88) improved the viscoelasticity and restrained the retrogradation of PoS paste. However, these studies concentrated on the influence of proanthocyanidins of a certain DP on the potato starch properties, while there have been few studies that have investigated the association between the DP value and the effect, especially for polymeric proanthocyanidin with different DPs. Proanthocyanidins with different degrees of polymerization might exert varied effects on the characteristics of potato starch. Thus, this research provides a new perspective for the influences of DPsensitive polymeric proanthocyanidin with different DPs on the physical and chemical characteristics and in vitro starch digestibility of potato starch. It is likely to supply a theoretical basis for quality improvement of PoS-based foodstuffs.

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

#### *2.1. Materials*

Polymeric proanthocyanidins (PPC, purity ≥ 95%) derived from grape seed were purchased from Solarbio Technology Co., Ltd. (Beijing, China). Potato starch (PoS) was obtained from Rogate Starch Co., Ltd. (Jiangsu, China), and the contents of lipid, water, ash, and amylose were 0.32%, 9.86%, 0.25%, and 26.61% (*w/w*), respectively. All other chemicals were of reagent grade and supplied by Aladdin Co., Ltd. (Shanghai, China).
