Screening of Rice Germplasm and Processing Methods to Produce Low Glycemic Rice

Sali Atanga Ndindeng, Koichi Futakuchi, Marie-Noelle Ndjiondjop

Letter

Screening of Rice Germplasm and Processing Methods to Produce Low Glycemic Rice

Sali Atanga Ndindeng, Koichi Futakuchi, Marie-Noelle Ndjiondjop

()

The search for low glycemic rice to manage type 2 diabetes is of utmost importance due to the increasing trend in diabetic cases and the importance of rice as a staple worldwide. This study aimed to investigate the effect of combinations of rice varieties and processing regimes on human glycemic index (GI), and elucidate the relationship between physicochemical properties of rice and human GI. Parboiled polished rice recordedthe lowest human GI. Parboiled unpolished rice, brown parboiledunpolished and brown parboiled polished rice recorded intermediate human GI while non-parboiled polished and non-parboiled unpolished rice recorded the highest human GI. Weak but significant positive correlations were observed for amylose and protein contents of parboiled polished rice and human GI while a negative correlation was observed for human GI and yellowness of parboiled grain. The varieties (ORYLUX 6, NERICA 11 and TOG 6813) identified as low GI after parboiling and polishing can be promoted as a component of improved parboiling technology when the goal is to produce low GI rice for the market.

Rice is one of the most widely consumed grains in the world with about 493 million metric tons (MT) consumed in 2020 up from about 487 million MT in 2019 (USDA, 2021). Rice consumers mostly appreciate the appearance, cooking time, swelling capacity, texture and aroma of rice (Ndindeng et al, 2021a, b). Some consumers for health reasons (diabetes, obesity and metabolic syndrome) are more interested in its GI index and glycemic load. According to the International Diabetes Federation (IDF, 2019), approximately 463 million adults (20–79 years) were living with diabetes in 2019, and the diseased will rise to 700 million by 2045. Randomized controlled trials, conducted over the past two decades, showed that the prevention or delay of type 2 diabetes is possible in many ethnic groups through changes in lifestyle or the administration of pharmacological agents (Cefalu et al, 2016). Meta-analysis and systematic review studies showed an association between intake of non-parboiled polished (white) rice and the incident of type 2 diabetes, especially in Asianpopulations with higher incidence among women (Hu et al, 2012; Ren et al, 2021). In addition, a multinational Prospective Urban Rural Epidemiology study showed that higher intake of non-parboiled polished rice (≥450 g/d) is associated with increased risk of diabetes with the strongest association being observed in South Asia, while in other regions, a modest to non-significant association was observed (Bhavadharini et al, 2020). Promotion of low GI rice diets for high-risk populations can be an integral part of a strategy to reduce type 2 diabetes especially if this fits into the processing, cooking and eating habits of the target population. Thermally treated (roasted or fried) black rice show pronouncedactivity against starch digesting enzymes (α-amylase, α-glucosidase and glycation), whereas their cooked counterparts show reducedGI and enhanced resistant starch (Aalim et al, 2021). Rice parboiling which is the hydrothermal treatment of rice before processing has also been explored as a strategy to improve the physicochemical and nutritional quality of rice including its digestibility (Zohoun et al, 2018a, b; Kongkachuichai et al, 2020). Zohoun et al (2018b) showed that severely parboiled rice (steamed for 25, 35 or 45 min) records lower GIs compared to non-parboiled or mildly parboiled counterparts (< 25 min). At the moment, it is unclear which physicochemical properties of parboiled rice are linked to its GI. The effect of amylose content on rice digestibility is unclear. Non-parboiled high amylose varieties recorded high GI (88.2–92.4) (Gunaratne et al,2020), while a parboiled high and low amylose variety recorded low and high GIs respectively (Larsen et al, 1996). Rice polishing strongly reduces bioactive compounds such as polyphenols, ferulic acid and gamma-aminobutyric acid (Kongkachuichai et al, 2020) and digestible proteins (Ohdaira et al, 2009). In addition, parboiling has less effect on bioactive compounds and the human GI for the parboiled unpolished products was 55 in pre-diabetic subjects (Kongkachuichai et al, 2020). Studies on the effect of rice milling regimes (polished versus unpolished) on GI are absent in literature.

In this study, rice products were evaluated by human test subjects to identify low GI rice processing methods and varieties for promotion and exploitation. Furthermore, relationships between human GI and physicochemical properties of processed varieties were investigated. Detailed methods are recorded in File S1.Six rice products (non-parboiled unpolished, non-parboiledpolished, parboiled unpolished, parboiled polished, brown parboiled unpolished and brown parboiled polished) were produced using two germplasm (CB1 and ORYLUX 6), cooked and served to ten test subjects with white bread as the reference meal. The highest blood glucose was recorded 30 min after meal (172 mg/L) while the lowest was recorded 60 min after meal (55 mg/L). All subjects demonstrated pre-diabetic blood glucose level confirming the test subject selection criteria. The change in blood glucose level was higher for white bread than for the rice products after meal except at 15 min where slightly higher changes were recorded for non-parboiled unpolished, parboiled unpolished and brown parboiled polished products (Fig. 1-A). Human GI of rice depended on the processing regime and the rice germplasm (Fig. 1-B). Test subject-2, -6 and -10 recorded similar human GIs after consumption of the rice products (> 0.05), and their human GIs were lower than the other seven test subjects (< 0.05).

Fig. 1. Blood glucose curves for different rice products in comparison with white bread (A), analysis of variance between human glycemic index (GI) and test subject, rice variety as well as type of processing (B), and the least square mean human glycemic index (LS-GI) and rank for parboiled rice varieties (C).

In A, data are Mean ± SD (= 10).

Parboiling is the hydrothermal treatment of rice and thermally treated rice have been shown to inhibit starch digesting enzymes (α-amylase, α-glucosidase and glycation) with the severity of the thermal treatment linked to the degree of inhibition of those starch digesting enzymes (Aalim et al, 2021). The parboiling conditions used in this study (soaking at 70oC for 16 h and steaming for 25 min) influenced human GI (> 0.05) and can be considered as severe and alike to those used in previous studies where lower GI were recorded for soaking at 85oC for16 h and steaming for 25?45 min (Zohoun et al, 2018b). Mildly parboiled rice has been shown to record a higher GI compared to severely parboiled rice (Larsen et al, 1996; Zohoun et al, 2018b).Non-parboiled rice recorded similar human GIs which were higher than the other four products (< 0.05; Table 1). Based on the least square (LS) means ranking, parboiled polished rice variety recorded the lowest human GI (Fig. 1-C). Milling is a crucial step in post-production of rice. The basic objective of rice milling is to remove the husk and the bran layers and produce an edible kernel that is sufficiently milled and free of impurities. Decreased human GI in polished rice (LS mean = 39.4) compared to unpolished counterparts (LS mean = 49.8) suggests that the presence of bioactive compounds favors rice starch digesting in human subjects, although more studies are needed to confirm this finding. In addition, highly milled rice (80% milling) recorded the highest content of digestible proteins in the bran (Ohdaira et al, 2009), indicating that milling reduces both bioactive compounds and digestible proteins that both reduce human GI. When parboiling and variety were constant, milling influenced human GI with unpolished rice recording higher GI than polished rice (= 0.03). When parboiling and milling were constant, variety also influenced human GI with CB1 recording higher GI than ORYLUX6 (< 0.0001).

Twenty-three parboiled polished rice varieties (Table S1) including CB1 and ORYLUX 6 were further produced, cooked and served to test subjects and human GI determined. Non-parboiled unpolished CB1 is widely consumed in Cote d’Ivoire as a variety of choice for managing diabetes due to anecdotal evidence that darker rice has a weak glycemic response. In China, a black rice variety is also used in traditional folk medicine for the managing of diabetes (Aalim et al, 2021). However, a rice variety with a white endosperm (ORYLUX 6) recorded lower GI compared to CB1 (black rice), suggesting that grain color alone is a weak indicator of digestive properties.The LS means of human GI of test subjects who were served with parboiled polished rice ranged from 19.3 to 46.6 while the glycemic load ranged from 13.66 to 42.07. TOG 6813 recorded the lowest GI while IR55411-53 recorded the highest. Seven parboiled polished germplasm (NERICA 7, KANA OLELA, TOG5427, IR841, ORYLUX 6, NERICA 11 and TOG6813) recorded human GIs less than 26, which was lower than the GI reported by other authors using different rice products and GI testing systems (Zohoun et al, 2018b; Gunaratne et al, 2020; Kongkachuichai et al, 2020; Aalim et al, 2021).

Table 1. Physicochemical and human glycemic index (GI) of some parboiled polished rice varieties grown in sub-Sahara Africa.

L, Lightness, where 0 means dark and 100 means white; a is the ratio of green (negative-value) to red (positive-value); b is the ratio of blue (negative-value) to yellow (positive-value); CI, Color intensity; DMC, Dry matter content; AC, Amylose content; PV, Peak viscosity; SV, Setback viscosity; GT, Gelatinization temperature; H, Cooked grain hardness; S, Cooked grain stickiness; WU, Water uptake ratio; TSC, Total starch content; DSC, Damaged starch content; RSC, Resistant starch content; GL, Glycemic load per 100 g serving.

Parboiling turns rice light yellow to amber due to Maillard type nonenzymatic browning and the diffusion of the husk and bran pigments into the endosperm during soaking (Lamberts et al, 2006). The more severe the parboiling the yellower the grains, confirming that severely parboiled rice inhibits the action of starch digesting enzymes and as such lowers the GI of rice (Zohoun et al, 2018b; Aalim et al, 2021). Generally, parboiled rice records lower amylose content compared to non-parboiled counterparts due to amylose leaching during the parboiling process (Patindol et al, 2008). In addition, parboiled samples become harder, less sticky with lower viscosities and yellower as parboiling becomes severe. The physicochemical properties and human GIs are shown in Table 1. Pearson correlation coefficients were used to demonstrate relationships between the variables studied (Table S2). Grain lightness was negatively correlated with protein and amylose contents. The redness of the kernel was positively correlated with protein content while the yellowness of the kernel was negatively correlated with amylose,protein contents and human GI. Human GI was positively correlatedwith amylose and protein contents but these content correlations are weak (= 0.54;= 0.038 and= 0.61;= 0.016). Protein content was positively correlated with human GI. High protein samples were darker, redder, and less yellow in color. However, no relationships were observed between the human GIs of parboiled polished rice and grain lightness, redness, gelatinization temperature, water uptake ratio, paste viscosity, cooked grain texture and starch fractions (> 0.05). Gunaratne et al (2020) found no relationship between pasting properties and GI either.

This study demonstrates that human GI of rice depends on processing regime and rice germplasm. The parboiled polished protocol identified to produce low GI rice is already a component of the GEM parboiling technology being disseminated in innovation platforms in different sites across Africa (Ndindeng et al, 2020). This protocol produced rice with LS mean GI < 50 irrespective of the variety which is lower than the standard cutoff value for low glycemic foods (GI < 55) (The Glycemic Diet Guide, 2021), and can be easily integrated into any improved parboiling technology worldwide. Although the severity of rice parboiling and polishing are major factors affecting the human GI of rice, it is important to couple the low GI germplasms such as ORYLUX 6, NERICA 11 and TOG 6813 to these processing regmes if the goal is to promote low GI rice for markets. In addition, low GI rice research should not focus only on varietal development but also on the processing/ cooking methods and eating habits of the target population.

Acknowledgements

The authors thank volunteer subjects who participated in this study and the following technicians Mr. Ahmed Dembele, Mr. Kouadio Ghyslain Konan, Mr. Konan Narcisse Kouamé and Ms. Ouathara Massara Marcelle for their assistance.

Supplemental data

The following materials are available in the online version of this article at http://www.sciencedirect.com/journal/rice-science; http://www.ricescience.org.

File S1. Methods.

Table S1. Rice germplasm selected for digestibility studies and some of their agronomic and grain quality characteristics.

Table S2. Pearson correlation coefficient between physicochemicalproperties and human glycemic index of parboiled polished rice.

Aalim H, Wang D, Luo Z S. 2021. Black rice (L.) processing: Evaluation of physicochemical properties,starch digestibility, and phenolic functions linked to type 2 diabetes.,141: 109898.

Bhavadharini B, Mohan V, Dehghan M, Rangarajan S, Swaminathan S, Rosengren A, Wielgosz A, Avezum A, Lopez-Jaramillo P, Lanas F, Dans AL, Yeates K, Poirier P, Chifamba J, Alhabib KF, Mohammadifard N, Zatońska K, Khatib R, Vural Keskinler M, Wei L, Wang C S, Liu X Y, Iqbal R, Yusuf R, Wentzel-Viljoen E, Yusufali A, Diaz R, Keat N K, Lakshmi P V M, Ismail N, Gupta R, Palileo-Villanueva L M, Sheridan P, Mente A, Yusuf S. 2020. White rice intake and incident diabetes: A study of 132,373participants in 21 countries.,43(11):2643?2650.

Cefalu W T, Buse J B, Tuomilehto J, Fleming G A, Ferrannini E, Gerstein H C, Bennett P H, Ramachandran A, Raz I, Rosenstock J, Kahn S E. 2016. Update and next steps for real-world translation of interventions for type 2 diabetes prevention: Reflections from a diabetes care editors’ expert forum., 39(7): 1186?1201.

Gunaratne A, Wu K, Kong X L, Gan RY, Sui Z Q, Kumara K, Ratnayake UK, Senarathne K, Kasapis S, Corke H. 2020. Physicochemical properties, digestibility and expected glycaemic index of high amylose rice differing in length-width ratio in Sri Lanka., 55(1):74?81.

Hu E A, Pan A, Malik V, Sun Q. 2012. White rice consumption and risk of type 2 diabetes: Meta-analysis and systematic review., 344:e1454.

IDF (International Diabetes Federation). 2019. IDF DIABETES ATLAS. [2021-03-17]. https://diabetesatlas.org/en/.

Kongkachuichai R, Charoensiri R, Meekhruerod A, Kettawan A. 2020. Effect of processing conditions on bioactive compounds and glycemic index of the selected landrace rice variety in pre-diabetes., 94:102994.

Lamberts L, Brijs K, Mohamed R, Verhelst N, Delcour J A. 2006. Impact of browning reactions and bran pigments on color of parboiled rice., 54(26):9924?9929.

Larsen H N, Christensen C, Rasmussen O W, Tetens I H, Choudhury N H, Thilsted S H, Hermansen K. 1996. Influence of parboiling and physico-chemical characteristics of rice on the glycaemic index in non-insulin-dependent diabetic subjects., 50(1):22?27.

Ndindeng S A. 2020. Upgrading the rice value chain in Nigeria for competitive markets.: Green I. Africa Rice Center (AfricaRice) Annual Report 2019: Toward Rice-Based Food Systems Transformation in Africa. Abidjan, C?te d’Ivoire: 12.

Ndindeng S A, Candia A, Mapiemfu D L, Rakotomalala V, Danbaba N, Kulwa K, Houssou P, Mohammed S, Jarju O M, Coulibaly S S, Baidoo E A, Moreira J, Futakuchi K. 2021a. Valuation of rice postharvest losses in sub-Saharan Africa and its mitigation strategies., 28(3): 212?216.

Ndindeng S A, Twine E E, Mujawamariya G, Fiamohe R, Futakuchi K. 2021b. Hedonic pricing of rice attributes, market sorting, and gains from quality improvement in the Beninese market., 50(1): 170–186.

Ohdaira Y, Takeda H, Sasaki R. 2009. Distribution of seed proteins in rice grain of seed-protein mutant cultivars., 78(1): 58?65.

Patindol J, Newton J, Wang Y J. 2008. Functional properties as affected by laboratory-scale parboiling of rough rice and brown rice., 73(8): E370?E377.

Ren G Y, Qi J, Zou Y L. 2021. Association between intake of white rice and incident type 2 diabetes: An updated meta-analysis., 172: 108651.

The Glycemic Diet Guide. 2021. The GI Diet: List of low GI Foods.[2021-03-17]. http://www.the-gi-diet.org/lowgifoods.

USDA (United States Department of Agriculture). 2021. Foreign Agricultural Service, Statista.[2021-03-17]. https://www.statista. com/statistics/739168/global-top-pear-producing-countries/.

Zohoun E V, Ndindeng SA, Soumanou M M,Tang E N, Bigoga J, Manful J, Sanyang S D, Akissoe N H, Futakuchi K. 2018a. Appropriate parboiling steaming time at atmospheric pressure and variety to produce rice with weak digestive properties.,6(4): 757?764.

Zohoun E V, Tang E N, Soumanou M M, Manful J, Akissoe N H, Bigoga J, Futakuchi K, Ndindeng SA. 2018b. Physicochemical and nutritional properties of rice as affected by parboiling steaming time at atmospheric pressure and variety., 6(3): 638?652.

Sali Atanga Ndindeng (S.Ndindeng@cgiar.org)

16 April 2021;

2 August 2021

Copyright ? 2022, China National Rice Research Institute. Hosting by Elsevier B V

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Peer review under responsibility of China National Rice Research Institute

http://dx.doi.org/10.1016/j.rsci.2022.01.001