Modifying the Parboiling of Rice to Remove Inorganic Arsenic, While Fortifying with Calcium

Abstract

Using village-based rice processing plants in rural Bangladesh, this study considered how parboiling rice could be altered to reduce the content of the carcinogen inorganic arsenic. Parboiling is normally conducted with rough rice (i.e., where the husk is intact) that is soaked overnight at ambient temperatures, and then either steamed or boiled for ∼10 min, followed by drying. Across 13 geographically dispersed facilities it was found that a simple alteration parboiling wholegrain, instead of rough rice, decreased the inorganic arsenic content by 25% (P = 0.002) in the final polished grain. Also, parboiling wholegrain had little impact on milling quality of the final polished rice. The wholegrain parboiling approach caused statistically significant median enrichment of calcium, by 213%; and a reduction in potassium, by 40%; with all other nutrient elements tested being unaffected. Milled parboiled rough rice had an enriched inorganic arsenic compared to nonparboiled milled rice, but parboiling of wholegrain rice did not enrich inorganic arsenic in the final milled product. Polished rice produced from the parboiling of both rough and wholegrain rice significantly reduced cadmium compared to nonparboiled polished rice, by 25%. This study also identified that trimethylarsine oxide and tretramethylarsonium are widely elevated in the husk and bran of rice and, therefore, gives new insights into the biogeochemical cycling of arsenic in paddy ecosystems.

Reducing the cadmium, inorganic arsenic and dimethylarsinic acid content of rice through food-safe chemical cooking pre-treatment

“…Post-harvest processing of rice can be used to lower grain inorganic arsenic, primarily parboiling (Rahman et al, 2019) or cooking (Carey et al, 2015;Raab et al, 2009), but such simple cooking technologies are ineffective for cadmium and DMA. A high water:rice volume removes up to 45% (Raab et al, 2009), while percolating rice with boil water removes up to 70-80% (Carey et al, 2015), of grain inorganic arsenic.…”

Carryover effects of silicon‐rich amendments in rice paddies

“…Trimethylarsine oxide has been reported at low porewater concentrations (similar to DMA) in a pot study and was enhanced by the application of manure (Afroz et al., 2019). Trimethylarsine oxide is also occasionally observed in rice grain at low concentrations (Rahman et al., 2019). How Si interacts with TMAO is unknown.…”

Global geographical variation elemental and arsenic species concentration in paddy rice grain identifies a close association of essential elements copper, selenium and molybdenum with cadmium.

“…Hidden hunger is one of the greatest issues facing society globally, de ned as where food delivers adequate calories but is de cient in essential nutrients (Gashu et al, 2021). This is nowhere so prominent than in subsistence diets that rely on polished grains, where milling grains unfortunately removes a substantial portion of nutrients present in wholegrain (Rahman et al, 2019). Grain mineral nutrition varies due to soil conditions and cultivation and fertilization practice (Nyachoti et al, 2021;Gashu et al, 2021;Welsh and Graham, 2004; White and Broadlley, 2005) and to crop genetics (Cobb et al, 2021;Huang et al, 2015;Norton et al, 2014).…”

“…Grain mineral nutrition varies due to soil conditions and cultivation and fertilization practice (Nyachoti et al, 2021;Gashu et al, 2021;Welsh and Graham, 2004; White and Broadlley, 2005) and to crop genetics (Cobb et al, 2021;Huang et al, 2015;Norton et al, 2014). Maximizing grain nutrient density to deliver as great a quantity of each essential element as feasible, given that bioavailability in the gut is also an issue for elements such as iron (Hoekenga et al, 2011), is a major goal for those wishing to improve human health (Gashu et al, 2021;Rahman et al, 2019).…”

“…Food security, supplying a population su cient quantities of nutritionally balanced foods, has to be combined with food safety, minimizing exposure to toxic compounds. White rice is particularly problematic in both regards as it is not overly nutrient dense, while at the same time being widely elevated, ~ 10-fold compared to other grains, in cadmium and arsenic (Rahman et al, 2019). There is evidence that for certain elements such as arsenic (Williams et al, 2007), cadmium (Nan et al, 2002) and selenium (Zhu et al, 2009) that rice grain concentration is linked to the concentration in the soils in which they are grown.…”