General starches that exist in nature have characteristics not suitable for consumption, so they are modified and manufactured by the food industry (Ashogbon & Akintayo, 2014). Many commercial starches are chemically modified via substitution, cross-linking, and acid hydrolysis (Kim, Kim, & Baik, 2012). However, recent changes in consumer perception of chemical materials have led to increased research into physically modified starches that could be categorized as clean label rather than chemically modified. Hydro-thermal treatment is the most widely used method for manufacturing physically modified starch. Hydro-thermal treatment is a common heat treatment method. There are two main methods, heat moisture treatment (HMT) and annealing (ANN). HMT is manufactured by lowering the moisture content of starch and heating it at a temperature higher than the general gelatinization temperature. Contrary to HMT, ANN is manufactured by increasing the moisture content and heating it below the gelatinization temperature (Kim & Baik, 2022). Both methods are heated above the glass transition temperature (Tg) and below the melting temperature (Tm). In general, HMT is heat-treated after adjusting the starch to a moisture content of 20%–35%. On the other hand, 30%–35% moisture content of starch destroys the crystal structure and dissociate the double helix in the amorphous region of starch, resulting in partial gelatinization of starch during HMT treatment (Liu, Zhang, Chen, Li, & Zheng, 2019).
Another method for preparing physically modified starch is hydro-pressure treatment. High hydrostatic pressure (HHP) uses pressure instead of heat under the same water content conditions. HHP is a food preservation technology that inactivates disease-associated microorganisms with minimal impact on the organoleptic and nutritional aspects of food (Park & Kim, 2021; Song et al., 2017). Since HHP is an eco-friend and can modify non-covalent bonds with minimal change in covalent bonds, it can be used to transform properties of native starches that are not suitable for food processing (Sehrawat, Kaur, Nema, Tewari, & Kumar, 2021). As with heat, if starch is made into a suspension with excess water and then high pressure is applied, the water present around the starch forcibly hydrates as it penetrates the starch, and as a result, gelatinization occurs in a form different from that of heat treatment (Katopo, Song, Jane, & l., 2002; Song et al., 2017).
A commonality of hydro-thermal treatment and hydro-pressure treatment is that they transform starch by a physical treatment method without modifying covalent bonds. Additionally, by changing only the molecular arrangement and structure in the starch granule, only the functional properties of starch such as pasting, gel, thermal, and digestibility are affected (BeMiller & Huber, 2015). The principle of denatured starch is to increase the mobility of water molecules using heat and pressure energy to induce changes from inside the starch. Currently known hydro-pressure treatments are mostly associated with starch gelatinization, and there is debate whether it is possible to change the molecular structure of starch by pressure treatment instead of heat treatment because both thermal energy and pressure mobilize water molecules from inside the starch. Therefore, we devised a new pressure treatment method as an alternative to heat treatment that uses low-moisture content conditions: pressure moisture treatment (PMT) (Kim, Ye, & Baik, 2023). In this study, PMT, a newly developed physical modification method was applied to various crystal-type starches and compared with HMT by analyzing and comparing their physicochemical properties.
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