Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Rapid Communication Parboiling reduced the crystallinity and in vitro digestibility of non-waxy short grain rice Jinhu Tian a,b , Yidi Cai a , Wei Qin a , Yoshitaka Matsushita c , Xingqian Ye b , Yukiharu Ogawa a, ⁎ a Graduate School of Horticulture, Chiba University, 648, Matsudo, Matsudo 271-8510, Japan b Zhejiang University, Department of Food Science and Nutrition, Hangzhou 310058, China c National Institute for Materials Science (NIMS), Research Network and Facility Services Division, Ibaraki 305-0047, Japan ARTICLE INFO Keywords: Parboil Crystallinity Microstructure In vitro digestion Starch hydrolysis ABSTRACT The impact of parboiling on starch digestibility of cooked rice was examined through an in vitro digestion model. Results indicated that the equilibrium starch hydrolysis of polished rice was the highest (86.55%), followed by that of parboiled-polished (83.94%), brown (80.59%) and parboiled rice (76.95%). X-ray diffraction analysis indicated that A-type crystals were predominant in brown rice and polished rice, while A-, B- and V-type crystalline structures coexisted in parboiled rice and parboiled-polished rice. Thin and compact layers were observed on the surfaces of parboiled rice and were considered to be physical barriers that reduce the starch digestibility. The study demonstrates that parboiling could change the crystallinity and reduce the starch di- gestion of rice significantly. 1. Introduction As an important and stable starch food for nearly one half of the global population, rice (Oryza sativa L.) has been widely planted around the world and contributes about 21% energy for humans (Oli, Ward, Adhikari & Torley, 2014). Normally, rice is consumed after polishing. However, polished rice is considered a high glycaemic index (GI) food, as it is digested rapidly. Studies have confirmed that long-term over- consumption of polished rice is closely associated with hyperglycaemia or type II diabetes (Van Hung, Chau & Phi, 2016). Thus, ways to slow the digestion rate of rice have attracted intense attention. Examples include various cooking methods (Reed, Ai, Leutcher & Jane, 2013), improving the amylose content by transgenic engineering or retaining the physical barriers against enzymes via alternative pre-processing techniques (Alsaffar, 2011; Ordonio & Matsuoka, 2016). In particular, the pre-processing strategies have gained considerable interest, pro- viding an option to reduce the starch digestion while simultaneously retaining the nutrients in rice. Parboiling, which is the main step in the pre-processing of rice grain, has been widely used in Asian countries, such as India, Pakistan and Bangladesh and is also gaining popularity in Europe (Leethanapanich, Mauromoustakos & Wang, 2016). According to lit- erature reviews, about 20% of the world’s rice is parboiled (Bhattacharya, 2013; Buggenhout, Brijs, Celus & Delcour, 2013). Par- boiling was considered an effective pre-processing technique to increase the storage stability of rice, with minimal changes in nutri- tional quality (Paiva et al., 2016). During parboiling, the starch is ge- latinised by the thermal treatment, and the subsequent dehydration causes starch retrogradation, irreversibly modifying the microstructure of the biopolymer (Hapsari, Kim & Eun, 2016). Thus, the digestibility of parboiled rice might differ from the polished rice grains. However, to the best of our knowledge, few studies have focused on the relation- ships between the digestibility of parboiled rice and its microstructure, despite numerous studies comparing the differences in nutrition, mi- crostructure and starch properties between the parboiled and polished rice. To expand our understanding of the impact of parboiling on rice microstructure, crystallinity and digestibility, the present study focuses on the microstructure changes and in vitro digestibility of brown, par- boiled, polished and parboiled-polished rice. Additionally, a first-order reaction equation was also introduced, to calculate the kinetics of starch hydrolysis. The work provides some new insight into the mi- crostructure and crystalline structure of parboiled rice, as well as its digestibility. The results will help other researchers and industries better understand the impacts of parboiling on rice. https://doi.org/10.1016/j.foodchem.2018.03.005 Received 21 November 2017; Received in revised form 28 February 2018; Accepted 1 March 2018 ⁎ Corresponding author. E-mail address: ogwy@faculty.chiba-u.jp (Y. Ogawa). Food Chemistry 257 (2018) 23–28 Available online 02 March 2018 0308-8146/ © 2018 Elsevier Ltd. All rights reserved. T