Methods to improve rice protein dispersal at moderate pH
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Methods to improve rice protein dispersal at moderate pH Saehun Mun1
•
Jeonghee Surh2 • Malshick Shin3
Received: 2 October 2019 / Revised: 4 May 2020 / Accepted: 13 July 2020 Ó The Korean Society of Food Science and Technology 2020
Abstract Dispersion of rice protein (RP) at a neutral pH is highly important for its application in the food industry. We analyzed the solubility of RP at different pH conditions and found higher solubility at pH \ 3 and pH [ 8 than at a neutral pH. Furthermore, at pH 2, the RP solubility improved from 30 to 63% with sonication; however, the samples precipitated when the pH was increased from 2 to 7. To circumvent this, anionic pectin and sodium alginate were added to the RP solution at pH 2. Pectin formed a complex with RP at pH 2, showing a shift in the zetapotential from 17.3 mV (RP only) to - 1.0 mV (RP plus 1% pectin). Interestingly, the formation of this RP-pectin complex allowed RP to remain dispersed when the pH was increased to 7. Moreover, a stable emulsion could be prepared using the RP-pectin complex as an emulsifier. Keywords Rice protein Water solubility Emulsion Pectin
& Saehun Mun [email protected] Jeonghee Surh [email protected] Malshick Shin [email protected] 1
Center for Food and Bioconvergence, Seoul National University, Seoul 08826, Republic of Korea
2
Department of Food and Nutrition, Kangwon National University, Samcheok 25949, Republic of Korea
3
Department of Food and Nutrition, Chonnam National University, Gwangju 61186, Republic of Korea
Introduction Recently there have been efforts to replace milk proteins with plant proteins due to allergenicity, economic, sustainability and dietary issues (Ozturk and McClements, 2016; Xu et al., 2016). In particular, rice protein (RP) has garnered increasing interest in the food industry because it is hypoallergenic, rich in essential amino acids, and reportedly has higher digestibility and nutritive value than other major cereals, such as wheat, corn, and barley (Amagliani et al., 2017a; Han et al., 2015). RP is also considered one of the vegetable protein sources that can replace milk and soy in infant formulas and add variety to gluten-free diets. However, the applications of RP in the food industry are limited because of its relatively low water-solubility. RP consists of four fractions with different solvent solubilities: albumin (watersoluble, 1–5%), globulin (salt-soluble, 4–15%), glutelin (alkali/acid-soluble, 80%), and prolamin (alcohol-soluble, 2–8%). The predominant RP, glutelin, is hydrophobic and highly aggregated by disulfide bonds; thus, the extracted RPs are highly insoluble (Amagliani et al., 2017a). Many attempts have been made to improve the solubility of RP and increase its functional properties, including physical modification, enzymatic hydrolysis, and chemical modification. Several studies indicated that limited proteolysis was able to increase RP solubility, expose buried hydrophobic groups, increase surface hydrophobicity, reduce molecular weight, and increase the emulsionforming
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