Effect of CaCl₂ pre-treatment on the succinylation of potato starch

Highlights

• The idea of chemical surface gelatinization was applied in starch succinylation.

• Pre-treatment with 1.0 M CaCl₂ increased reaction efficiency of succinylation.

• OSA-1.0 M-starch showed improved functional properties over OSA-starch.

Abstract

Potato starch was pre-treated with CaCl₂ solutions prior to modification with octenyl succinic anhydride (OSA). Starch pre-treated with 1.0 M CaCl₂ showed higher degree of substitution (DS) and reaction efficiency (RE) on OSA modification, whereas pre-treatment with CaCl₂ solutions at 0.05 M, 0.1 M and 0.5 M had no effect on DS and RE. CaCl₂ pre-treatment decreased the swelling power, paste clarity, peak viscosity (PV), breakdown (BD) and some textural parameters of potato starch, with the effects being greater at higher concentrations of CaCl₂. Pre-treatment with 1.0 M CaCl₂ caused a small disruption to starch crystallinity and granule morphology. OSA modification significantly decreased the textural parameters, PV, BD, relative crystallinity, swelling power, gelatinization temperatures and enthalpy of potato starch, but it increased the paste clarity and emulsifying activity. OSA-1.0 M-starch showed improved functional properties over OSA-starch, indicating that CaCl₂ pre-treatment provides advantages for improving the functional characters of succinylated starch.

Introduction

The functional limitations of native starch restrict its use in some industries. Hence, modification of starch using chemical, physical and enzymatic methods has been the subject of intensive research over the last 50 years (BeMiller and Huber, 2015, Wang and Copeland, 2015). Chemical modification often involves introducing functional groups into the starch molecules to provide a variety of physico-chemical benefits by enhancing the functionality of the starch to suit specific industrial applications (Masina et al., 2017). Octenyl succinic anhydride (OSA), a dicarboxylic acid anhydride, can form starch octenylsuccinate containing bi-functional groups with both hydrophilic (sugar part) and hydrophobic (octenyl part) character (Han and Lim, 2012, Sweedman et al., 2013). OSA-starch produces strong films at the oil-water interface and emulsions that are resistant to breaking up, which find uses in applications in salad dressings, creams and coatings (Liu et al., 2008).

The synthesis of OSA-starch is performed typically by mixing granular starch and OSA in mild aqueous alkaline medium. Due to the low solubility of OSA in water, the reaction can be slow and often occurs heterogeneously (Shogren, Viswanathan, Felker, & Gross, 2000). To improve the reaction efficiency, several starch pre-treatment methods have been developed, including hydrothermal (Chen et al., 2014, Jiranuntakul et al., 2014), hydrothermal-alkali and freezing-thawing (Wang, Li, Wang, & Copeland, 2017), ball milling (Zhang, Zhao, & Xiong, 2010), enzymatic (Bai and Shi, 2011, Huang et al., 2010), and ultrasound (Chen, Huang, Fu, & Luo, 2014).

The CaCl₂ and LiCl solutions are known to induce starch gelatinization at room temperature, with the extent of gelatinization depending on the types and concentrations of salts (Jane, 1993). Potato starch granules have been shown to undergo gelatinization from the granule periphery in a high concentration CaCl₂ solution (4 M), (Jane and Shen, 1993, Koch and Jane, 2000). Chemical surface gelatinization has been used as an approach to investigate the internal structure of starch granules by removing the gelatinized granule surface from the ungelatinized remaining parts (Kuakpetoon and Wang, 2007, Pan and Jane, 2000). Chemical surface gelatinization following modification of starch with OSA in the presence of acetic anhydride and hypochlorite has also been used to investigate the reaction sites of chemical reagents on starch molecules (Huang et al., 2010, Kuakpetoon and Wang, 2008, Wang et al., 2013).

In the present study, the idea of chemically gelatinizing the surface of granules to render them more susceptible to modification reactions was applied for the first time in the modification of potato starch with OSA. Low concentrations of CaCl₂ solutions (0.05–1.0 M) were used to reduce the extent of disruption of starch structure. The effects of CaCl₂ pre-treatment on the subsequent OSA modification were investigated by characterizing the structure and physico-chemical properties of the pre-treated and derivatized starches. This study provides an alternative way to improve the reaction efficiency of starch modification with OSA, which will be potentially interesting for food and other industries.