**1. Introduction**

Potato starch is widely used in the food industry owing to its low cost, abundant availability, and more importantly, its unique physicochemical properties compared to other commercially available starches [1,2]. Potato starch can hydrate quickly and forms a paste with higher viscosity when heated, and a clearer gel when cooled, which differ from those of other starches such as corn, wheat, and rice [1,3,4]. The natural properties of potato starch are exploited by the food industry to provide products the required texture, appearance, density, and storage stability. However, native potato starch has some drawbacks, such as poor solubility and poor stability against heat and shear during pasting. These drawbacks have limited its application in industry. Consequently, various physical (heat-moisture treatment, annealing, pre-gelatinization, and high pressure treatment), chemical (crosslinking, substitution, acid hydrolysis, and oxidation), and genetic modification techniques have been used to modify potato starch and enhance its physicochemical properties to meet the demands of consumers [5–7]. Pre-gelatinization is a method widely used to

**Citation:** Xu, F.; Zhang, L.; Liu, W.; Liu, Q.; Wang, F.; Zhang, H.; Hu, H.; Blecker, C. Physicochemical and Structural Characterization of Potato Starch with Different Degrees of Gelatinization. *Foods* **2021**, *10*, 1104. https://doi.org/10.3390/foods10051104

Academic Editors: Jianhua Xie, Yanjun Zhang, Hansong Yu and Joana S. Amaral

Received: 22 March 2021 Accepted: 12 May 2021 Published: 17 May 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/).

modify potato starch, and pre-gelatinized starch has been extensively applied in the food industry [8,9].

Potato starch can be gelatinized in hot water by breaking the intermolecular hydrogen bond and destroying the arrangement of micelle structure in starch granules. After being fully gelatinized, the starch granules are porous with broken hydrogen bonds, birefringence disappears, and the crystalline order is lost through rapid drying at high temperature [10]. The degree of starch gelatinization (DSG) plays a very important role in imparting desirable product textures. Many starch-based food formulations do not require fully gelatinized starch for the best product characteristics. So far, most studies have been conducted using either native or fully gelatinized potato starch, and there has been a lack of attention on incomplete gelatinized potato starch.

Nevertheless, there have been studies on partial starch gelatinization induced by preheating for different times/temperatures or ball milling for different times. Studies reported that the pre-gelatinization treatment significantly changed the granule size distribution and rheological properties of starch dispersions [11–14]. Recent studies also showed that partially gelatinized starch with a lower DSG resulted in increased pasting viscosities and gel textural parameters, while the opposite was noted at higher DSG and native starch [15]. The partially gelatinized potato starch with different DSGs can be used as a thickener or stabilizer in many food products that receive a minimal heating process, for example, instant soups, desserts, powders in beverages, frozen noodles, and baking products [14]. The thermal, rheological, and structural characteristics of partially gelatinized starch can provide essential information for the selection of optimum processing conditions of starch and starchy foods [16]. However, systematical studies involving the physicochemical and structural properties of partially gelatinized potato starch with different DSGs and their correlations are still limited.

The objective of this study is to understand the relationship between the DSG and its physicochemical and structural properties. Thus, we prepared 14 partially gelatinized potato starch samples with relatively evenly distributed DSG data points by hydrothermal treatment. The water-binding capacity and thermal, rheological, and structural properties were analyzed, and the correlations between these physicochemical properties of starch and its DSG were established.

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

#### *2.1. Raw Materials*

Potato starch (PS) containing 89.32% starch, 0.27% protein, and 0.42% ash, based on the dry matters of samples, was purchased from Aladdin Bio-Chem Technology Co., Ltd. (Shanghai, China). Moisture content was determined by drying samples to a constant weight in a 105 ◦C oven (AOAC 925.09). Crude protein was determined by the Kjeldahl method, with the total nitrogen content being converted to protein content by a conversion factor of 6.25 (AOAC 979.09). Ash content was determined by dry mineralization of samples in a muffle oven at 550 ◦C for 8 h (AOAC 923.03), and starch content was determined by a total starch assay kit (K-TSTA; Megazyme, Ireland).
