Effects of Cultivar and Processing Condition on Physicochemical Properties and Starch Fractions in Parboiled Rice

Starch can be classified into rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) according to its resistance to amylolytic enzymes. This study investigated the effects of cultivar and feedstock under varying parboiling conditions on the physicochemical properties and starch fractions of parboiled rice. Rice (rough or brown) was soaked, steamed under pressure, dried immediately or stored at room temperature for 24 hr prior to drying, and then treated with or without a repeated steam cycle prior to milling. The storage treatment significantly increased the retrograded amylopectin enthalpy and amylose‐lipid complex melting temperature of parboiled rice. Parboiled rice samples prepared from brown rice feedstock had higher peak melting temperatures but lower enthalpy values of retrograded amylopectin than samples prepared from rough rice after the storage treatment. The pasting viscosity of parboiled rice was most affected by the repeated autoclaving treatment and cultivar. Starch fractions in parboiled rice were significantly affected by cultivar and storage and by the interactions of cultivar and parboiling conditions. The storage treatment significantly increased SDS and generally decreased RDS in parboiled rice. Parboiled rice with different SDS and RS contents can be produced by varying rice cultivar and parboiling conditions.     

Impact of browning reactions and bran pigments on color of parboiled rice

Rice color changes from white to amber during parboiling (soaking and steaming). Color parameters indicated that, during soaking, yellow bran pigments leached out in the water. The levels of the Maillard precursors (i.e., reducing sugars (RS) and free alpha-amino nitrogen (FAN)) depended on soaking temperature and time: leaching of RS was compensated by enzymic formation for long soaking times (>60 min), while proteolytic activity was too low to compensate for FAN leaching. Rice soaking under nitrogen, oxygen, or ambient conditions and determination of polyphenol oxidase activity allowed us to conclude that the effect of enzymic color changes on the soaked rice color was rather small. Color measurements of brown and milled mildly, intermediately, and severely parboiled rice samples showed that both brown and milled rice samples were darker and more red and yellow after parboiling and that the effect depended on the severity of parboiling conditions. Furthermore, steaming affected the rice color more and in a way opposite to that observed in soaking. The changes in RS and the loss of FAN during parboiling suggested that Maillard type reactions occur during brown rice steaming. Analyses of furosine levels confirmed Maillard browning of outer bran layers and endosperm during steaming. The level of this Maillard indicator increased with the severity of parboiling conditions in both brown and milled parboiled rice. Measurements of the levels of bran pigments indicated that bran pigments diffuse into the endosperm during parboiling and contribute to the parboiled rice color.     

Effect of Processing Conditions on Color Change of Brown and Milled Parboiled Rice

The effects of the soaking and steaming steps in rice parboiling on color changes and the levels of reducing sugars in rice were studied. Brown rice was soaked to different moisture contents (MC, 15, 20, 25, and 30%). The L*, a*, b* color parameters of the Commission Internationale de L'Eclairage (CIE 1976) indicated that during soaking, red and yellow bran pigments diffused from the bran into the endosperm. The increase in brightness brought about by soaking rice was attributed to migration of rice compounds (e.g., lipids) from the inner to the outer bran layers (rice surface). The levels of reducing sugars in brown and milled soaked rice samples increased with increasing brown rice MC after soaking. The total color difference (ΔE) between parboiled and nonparboiled rice increased with increasing MC after soaking and depended on the intensity of the steaming conditions as reflected in the degree of starch gelatinization. Parboiling affected yellowness more than redness in mildly steamed brown rice and most in intermediately steamed brown rice. Severe steaming of brown rice affected redness more than yellowness. All three parboiling conditions equally affected the yellow color more than the red color in milled rice. Linear regression analyses indicated that parboiling had a larger effect on ΔE of milled parboiled rice than of brown parboiled rice. Furthermore, the linear relationship between the level of gelatinized starch and ΔE of the milled parboiled rice samples showed that both parameters are indicators for the degree of parboiling. Reducing sugars were formed and lost during steaming, suggesting Maillard reactions during steaming.     

Effect of zinc sulfate fortification in germinated brown rice on seed zinc concentration, bioavailability, and seed germination

Rice is the staple food for more than half of the world's population and, hence, the main source of a vital micronutrient, zinc (Zn). Unfortunately, the bioavailability of Zn from rice is very low not only due to low content but also due to the presence of some antinutrients such as phytic acid. We investigated the effect of germination and Zn fortification treatment on Zn bioavailability of brown rice from three widely grown cultivars using the Caco-2 cell model to find a suitable fortification level for producing germinated brown rice. The results of this study showed that Zn content in brown rice increased significantly (p < 0.05) as the external Zn concentrations increased from 25 to 250 mg/L. In contrast, no significant influence (p > 0.05) on germination percentage of rice was observed when the Zn supply was lower than 150 mg/L. Zn fortification during the germination process has a significant impact on the Zn content and finally Zn bioavailability. These findings may result from the lower molar ratio of phytic acid to Zn and higher Zn content in Zn fortified germinated brown rice, leading to more bioavailable Zn. Likewise, a significant difference (p < 0.05) was found among cultivars with respect to the capacity for Zn accumulation and Zn bioavailability; these results might be attributed to the difference in the molar ratio of phytic acid to Zn and the concentration of Zn among the cultivars evaluated. Based on global intake of Zn among the world population, we recommend germinated brown rice fortified with 100 mg/L ZnSO(4) as a suitable concentration to use in the germination process, which contains high Zn concentration and Zn bioavailability. In the current study, the cultivar Bing91185 fortified with Zn through the germination process contained a high amount as well as bioavailable Zn, which was identified as the most promising cultivar for further evaluation to determine its efficiency as an improved source of Zn for target populations.     

土壤中Cd、P、Zn含量对水稻产量和植株中矿物浓度的影响

在温室中进行了剖析添加的Cd、P、Zn对稻谷产量、植株和稻草中的矿物含量以及糙米中Cd的浓度的研究。P增加了稻谷和植株产量,而Cd、Zn和P-Zn的交互作用使其降低。稻谷和植株产量有类似的线性回归方程式,其稻谷的线性回归方程为: Y=17.24+0.0466(P)-0.1850(Cd)-0.1115(Zn)-0.0005(P-Zn) 其R²=0.97^**,式中Y为稻谷产量(克/株);P为添加的P浓度(毫克/公斤);(Cd)为添加的Cd浓度(毫克/公斤);(Zn)为添加的Zn浓度(毫克/公斤);(P-Zn)为P和Zn的交互作用。所有处理均明显地影响着稻草中矿物元素的含量。粕米中的Cd浓度随着添加的Cd、P、Zn浓度的增加而增加;但多元回归分析表明只有Cd的影响是显著的。粕米中Cd的浓度与收获时用0.05M HCI所提取的风干土中的Cd浓度有极显著相关性(Y=0.75^**).对糙米中Cd浓度的评价进行了简要的讨论。     

大气CO2浓度升高对矿质元素在水稻中分配及其根际有效性的影响

在开放式空气CO_2浓度升高(free-air CO_2 enrichment, FACE)条件下,研究了籼稻IIY084与粳稻WYJ23根际土壤矿质元素(Fe、Mn、Cu、Zn、Ca和Mg)有效态含量及其在水稻各组织中的吸收与分配,结合前期稻米矿质元素含量下降的研究结果,探讨了其下降的机制。结果表明:大气CO_2浓度升高,显著增加水稻穗、茎、根和整株生物量,两个品种平均增加19.4%、9.3%、23.4%、16.0%;根际土壤中矿质元素的有效态含量大体呈增加趋势;除Ca吸收量增加外,水稻其他矿质元素总吸收量未发生显著变化;显著促进大部分矿质元素在穗中的吸收与分配,而降低其在茎中的分配比;在穗内有增加大部分矿质元素在壳梗中滞留的趋势,相应地减少其在糙米中的分配比。品种效应分析显示,IIY084的茎和整株生物量,以及穗中Fe、Mn、Cu,叶中Zn、Mg,茎中Cu的吸收量与分配百分数均显著高于WYJ23,而叶中Mn、茎中Fe和根中Cu、Zn则呈相反趋势。可见,大气CO_2浓度升高条件下,碳水化合物与矿质元素从植株营养器官到籽粒的不平衡转运以及在壳梗中的滞留可能是导致两水稻品种糙米中矿质元素含量降低的重要原因。     

外源锌对水稻植株镉的累积差异分析

通过水稻威优46盆栽种植试验,研究了外源Zn施用(0,40,80,160 mg/kg 4个水平)对Cd中度(0.72mg/kg)和重度(5.26mg/kg)污染土壤中Cd生物有效性及水稻Cd累积的差异。结果表明:施Zn对各检测指标存在影响,但土壤Cd总量仍是土壤Cd活性和水稻Cd累积差异变动的主控因素。在Cd中度污染土壤中,施Zn降低了土壤交换态Cd含量1.9%~17.0%,但水稻根表铁膜、根和糙米中Cd含量随Zn施用浓度的增大而增大,糙米Cd含量从0.09mg/kg上升到0.17mg/kg,相关分析显示糙米Cd含量与土壤交换态Zn含量显著正线性相关。在Cd重度污染土壤中,施Zn增大了土壤交换态Cd含量2.1%~4.8%,但降低了水稻各部位中Cd含量,当施Zn浓度超过80mg/kg时,糙米Cd含量可从对照组的0.45mg/kg降低到0.12mg/kg,符合国家食品污染物限量标准(GB 2762-2017)的要求,相关分析显示糙米Cd含量与土壤交换态Zn含量显著负线性相关。对2种Cd污染程度的土壤,施Zn均可增大Cd在水稻地下部的累积率,从而降低水稻地上部Cd的累积率。在Cd重度污染土壤中,可通过施Zn降低糙米Cd含量,施Zn量80mg/kg是试验中最佳施用量;但在Cd中度污染土壤中,施Zn有增大糙米Cd含量的风险。     

Effect of foliar application of zinc, selenium, and iron fertilizers on nutrients concentration and yield of rice grain in China

Zn, Se, and Fe levels in 65 Chinese rice samples were investigated, and the results indicated that these micronutrients contents of rice products from different location varied considerably. The mean contents of Zn, Se and Fe in these rice samples were 21.5+/-1.8, 0.020+/-0.012, and 12.4+/-4.3 mg kg(-1), respectively, which were too low to meet the micronutrient demands for the population feeding on the rice as staple. A field orthogonal experiment L9 (3(4)) was conducted on rice cultivar Wuyunjing 7, to evaluate the effect of Zn, Se, and Fe foliar fertilization on the concentration of these micronutrients, yield, and protein and ash content of rice grain. The results indicated that Zn and Se were the main variables influencing the Zn, Se, and Fe content of rice, and the optimal combination of fertilization for enhancing these micronutrients was 0.90 kg ha(-1) Zn, 0.015 kg ha(-1) Se, and 0.90 kg ha(-1) Fe. Under the optimal application condition, Zn, Se, and Fe content of rice could be significantly increased by 36.7%, 194.1%, and 37.1%, respectively, compared with the control, without affecting grain yield and protein and ash content of rice products. Moreover, in the confirmation experiment on rice cultivar Ninggeng 1, the optimal fertilization could increase the Zn, Se, and Fe content of rice up to 17.4, 0.123, and 14.2 mg kg(-1), respectively.     

Effect of wastewater irrigation on mineral com‐position of corn and sorghum plants in a pot experiment

Effect of wastewater irrigation was investigated on mineral composition of corn and sorghum plants in a pot experiment. The ranges for the concentration of different minerals in corn plants were 0.67–0.89% calcium (Ca), 0.38–0.58% magnesium (Mg), 0.09–1.29% sodium (Na), 0.81–1.87% nitrogen (N), 1.81–2.27% potassium (K), 0.12–0.16% phosphorus (P), 190–257 mg/kg iron (Fe), 3.5–5.6 mg/kg copper (Cu), 37.1–44.5 mg/kg manganese (Mn), 21.6–33.6 mg/kg zinc (Zn), 1.40–1.84 mg/kg molydbenum (Mo), 11.0–45.7 mg/kg lead (Pb), and 2.5–10.8 mg/kg nickel (Ni). Whereas for sorghum plants, the ranges were: 0.56–0.68% Ca, 0.19–0.32% Mg, 0.02–0.27% Na, 0.69–1.53% N, 1.40–1.89% K, 0.10–0.14% P, 190–320 mg/kg Fe, 3.8–6.0 mg/kg Cu, 29.2–37.6 mg/kg Mn, 21.1–29.9 mg/kg Zn, 2.2–3.7 mg/kg Mo, 12.3–59.0 mg/kg Pb, and 2.5–15.2 mg/kg Ni. Heavy metals such as cobalt (Co) and cadmium (Cd) were below detection limits at mg/kg levels. The concentrations of Ca, N, K, P, Cu, and Mn in corn plants were in the deficient range except for Mg, Fe, Zn, and Al. The concentrations of Ca, N, P, K, Cu, Mn, Mg, and Zn in sorghum plants were in the deficient range except for Fe and aluminum (Al). The analysis of regression indicated a strong interaction between Pb, Ni, Ca, and Fe in corn and sorghum plants. In conclusion, waste water irrigation did not increase mineral concentrations of either macro‐ and micro‐elements or heavy trace metals in corn and sorghum plants to hazardous limits according to the established standards and could be used safely for crop irrigation.     

Variation of major minerals and trace elements in seeds of tartary buckwheat (Fagopyrum tataricum Gaertn.)

Tartary buckwheat (Fagopyrum tataricum Gaertn.) contains protein of high nutritional value, polyphenols, vitamins and minerals. It is one of the most important minor crops in China and has a great potential as a health and functional food. However, information on the elemental mineral composition of its seeds remains limited. The concentrations of Cu, Zn, Fe, K, and Mg in seeds of 123 tartary buckwheat accessions from the same cultivation were studied by means of flame atomic absorption spectrometry. The results revealed that the average concentrations of Cu (x₁), Zn (x₂), Fe (x₃), K (x₄), and Mg (x₅) elements in the accessions are 19.49 (with a range of 5.74–36.01 mg/kg), 27.41 (8.44–66.63 mg/kg), 656.24 (21.8–3,990 mg/kg), 3,639.23 (1,737–5,831 mg/kg), and 1,523.89 mg/kg (729–3,104 mg/kg) respectively. Among them, Fe concentration has the highest coefficient of variation (114.7 %). The results also revealed five significant positive correlations among Cu, Zn, Fe, K, and Mg concentrations. Therefore, distinct genotypes with high concentration of mineral elements should be effective for the development of special buckwheat varieties and improvement of its food nutritional quality.     

Soaking Conditions During Brown Rice Parboiling Impact the Level of Breakage‐Susceptible Rice Kernels

If properly executed, parboiling, a hydrothermal treatment consisting of soaking, steaming, and drying of rice, substantially reduces its milling breakage susceptibility. Here, brown rice was soaked at 40, 55, or 65°C for different times (150 s to 240 min) and subsequently parboiled under standardized steaming and drying conditions. The moisture absorption during initial soaking induced fissures in more than 90% of the rice grains, which disappeared with further soaking. The fissuring incidence in the soaked rice samples was related to that of the parboiled rice samples. The extent of starch gelatinization during steaming increased with the moisture content of the soaked grains. In addition, as a result of starch gelatinization, the level of white bellies (i.e., parboiled grains with translucent outer layers and an opaque center) decreased from over 90% to less than 3%. Rice grains need to absorb sufficient moisture during soaking to minimize the level of breakage‐susceptible white bellies and fissured rice grains in the parboiled end product.     

Natural levels of dimethyl sulfide in rough rice and its products

Natural levels of dimethyl sulfide (DMS) in rough rice and its products (polished rice, brown rice, and broken rice) were determined by a gas chromatograph equipped with a flame photometric detector and sulfur mode, after extraction with 25% KBr solution in a sealed system. DMS was found to occur naturally in nine newly harvested and stored Australian varieties of rough rice and its products and decreased during storage after harvesting. Natural levels of DMS in rough rice and its products varied with variety, fraction, and period of storage. The order of levels of DMS was rough rice = brown rice > polished rice = broken rice. The range of values was 0.002-30 mg kg(-1) (ppm, w/w).     

硅酸盐调控抑制水稻对富硒水稻土中Cd吸收

研究目的:通过水稻盆栽试验,探讨了海泡石(SP)、硅钙复合矿物(CS)和水溶性叶面硅肥(YS)3种硅酸盐不同复配处理对富Se水稻土中Cd的迁移和转运和Se的生物有效性的调控效果,以及对糙米中矿质元素吸收的影响。结果表明,海泡石(SP)、海泡石-硅钙复合矿物(SPC)和海泡石-硅钙复合矿物-水溶硅肥(SCY)处理水稻根际土pH值增加0.15～0.31个单位,使土壤Cd由可交换态向碳酸盐结合态和有机结合态转变,而土壤Se由残渣态向生物可利用态转变。与对照(CK)相比,SP、SPC和SCY处理水稻根际土CaCl2-Cd含量降低了19.5%～34.0%,而土壤有效态Se的含量增加了17.8%～36.8%。且SPC和SCY处理糙米中的Cd含量显著降低,比食品安全国家标准(0.2mg/kg)降低了25.0%～90.0%。各处理在降低糙米中Cd的同时,对糙米中Se含量和各矿质元素(Cu、Fe、Zn、Mg和Mn)无显著影响。该研究可为进一步利用SP有效修复富Se水稻土中Cd污染和提高土壤Se的生物有效性提供了有益途径。     

Impact of Starch Gelatinization and Kernel Fissuring on the Milling Breakage Susceptibility of Parboiled Brown Rice

Parboiling, a hydrothermal treatment of paddy or brown rice, improves the texture and nutritional characteristics of cooked rice. We investigated milling breakage susceptibility of brown rice parboiled under different soaking and steaming conditions, resulting in samples with different degrees of starch gelatinization and levels of fissured grains and white bellies, that is, parboiled grains with translucent outer layers and an undesirable opaque center. The milling breakage susceptibility was 2.1% for raw rice and ranged from less than 1% up to 11.3% for parboiled rice. Parboiled samples with increased milling breakage susceptibility contained higher levels of white bellies and fissured grains. In white bellies, starch gelatinization is incomplete. Scanning electron microscopy revealed inhomogeneities in individual white bellies and fissured rice grains, indicating moisture gradients inside the grains during parboiling. Starch needs to be completely gelatinized to ensure the absence of white bellies and minimal fissured grain levels in the parboiled end product and, as a consequence, a decreased milling breakage.     

供磷水平对铁、锰、铜、锌在稻株中分布和糙米品质的影响

用室内盆栽试验,研究了不同磷肥施用量对铁、锰、铜、锌在水稻中分布和糙米品质的影响。结果表明,盆栽条件下,施用磷肥显著降低了Fe、Mn、Cu、Zn在IR68144地上部的积累量,显著增加了Fe、Mn、Cu、Zn在两个品种糙米中的分布。在不同磷肥施用水平下,Fe、Mn、Cu、Zn在IR68144地上部的积累量显著高于IR64,表明IR68144从根到地上部运输微量元素Fe、Mn、Cu、Zn的能力更强。此外,施用磷肥促进了富铁水稻糙米对蛋白质的积累,抑制其对直链淀粉的积累,且导致胶稠度变软,对IR64糙米品质的影响较小。说明合理的磷肥管理措施可在一定程度上调控子粒微量元素积累,改善稻米营养品质。     

甘肃主要农业土壤中Cu、Zn、Mn、Fe的形态及有效性研究

本文对甘肃省主要农业土壤中Ｃｕ、Ｚｎ、Ｍｎ、Ｆｅ的形态及其有效性进行了研究。结果表明，供试土壤的全Ｃｕ含量范围为２２－２４ｍｇ／ｋｇ，全Ｍｎ为５４２－７７２ｍｇ／ｋｇ，全Ｆｅ为３５６８５－３８３５５ｍｇ／ｋｇ。四种元素均以灌漠土的含量最低，褐土最高。土壤中Ｃｕ、Ｚｎ、Ｍｎ、Ｆｅ的大部分以残留矿物态和氧化铁结合态存在。生物试验和统计分析表明，Ｃｕ、Ｚｎ、Ｍｎ、Ｆｅ的交换态和松结有机态对植物最为有效，     

Factors affecting the concentration of Zn,Fe and Mn in herbage from organic farms and in relation to dietary requirements of ruminants

To obtain a general picture of the herbage zinc, iron and manganese concentrations and their relation to dietary requirements of ruminants on organic farms, we analysed soil and herbage samples from four regions in Norway. The soil median Zn, Fe and Mn concentrations were 0.18, 13 and 0.84 mg/L, respectively. The herbage median (10th–90th percentile) Zn, Fe and Mn concentrations (mg/kg) in herbage in the first cut were 19 (14–34), 50 (36–88), 34 (22–86) and in the second cut 21 (16–37), 84 (52–171) and 66 (36–205), respectively. The results of mixed model analysis of herbage Zn, Fe and Mn indicate that soil pH, soil texture, soil mineral concentration and botanical composition are the most influencing factors. We conclude that Zn, Fe and Mn did not limit plant growth, and that the herbage concentrations, except for Zn, were sufficient to meet the dietary needs of ruminants on organic dairy farms.     

Contents of vitamins, mineral elements, and some phenolic compounds in cultivated mushrooms

The aim of the study was to determine the contents of mineral elements (Ca, K, Mg, Na, P, Cu, Fe, Mn, Cd, Pb, and Se), vitamins (B(1), B(2), B(12), C, D, folates, and niacin), and certain phenolic compounds (flavonoids, lignans, and phenolic acids) in the cultivated mushrooms Agaricus bisporus/white, Agaricus bisporus/brown, Lentinus edodes, and Pleurotus ostreatus. Selenium, toxic heavy metals (Cd, Pb), and other mineral elements were analyzed by ETAAS, ICP-MS, and ICP methods, respectively; vitamins were detected by microbiological methods (folates, niacin, and vitamin B(12)) or HPLC methods (other vitamins), and phenolic compounds were analyzed by HPLC (flavonoids) or GC--MS methods (lignans and phenolic acids). Cultivated mushrooms were found to be good sources of vitamin B(2), niacin, and folates, with contents varying in the ranges 1.8--5.1, 31--65, and 0.30--0.64 mg/100 g dry weight (dw), respectively. Compared with vegetables, mushrooms proved to be a good source of many mineral elements, e.g., the contents of K, P, Zn, and Cu varied in the ranges 26.7--47.3 g/kg, 8.7--13.9 g/kg, 47--92 mg/kg, and 5.2--35 mg/kg dw, respectively. A. bisporus/brown contained large amounts of Se (3.2 mg/kg dw) and the levels of Cd were quite high in L. edodes (1.2 mg/kg dw). No flavonoids or lignans were found in the mushrooms analyzed. In addition, the phenolic acid contents were very low.     

Effects of chromium stress on the subcellular distribution and chemical form of Ca,Mg, Fe,and Zn in two rice genotypes

A hydroponic experiment was carried out to study effects of chromium (Cr) stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypes differing in Cr accumulation. The results showed that Ca, Mg, Fe, and Zn ions were mainly located in cell walls and vacuoles in roots. However, large amounts of metal ions were transferred from the vacuole to the nucleus and to other functional organelles in shoots. Chromium concentrations in the nutrient solution of 50 μM and above significantly decreased Ca concentrations in the chloroplast/trophoplast, the nucleus, and in mitochondria. It further increased Mg concentrations in the nucleus and in mitochondria, as well as Zn and Fe concentrations in the chloroplast/trophoplast. These Cr‐induced changes in ion concentrations were associated with a significant reduction in plant biomass. It is suggested that Cr stress interferes with the functions of mineral nutrients in rice plants, thus causing a serious inhibition of plant growth. The chemical forms of the four nutrients were determined by successive extraction. Except for Ca, which was mainly chelated with insoluble phosphate and oxalic acid, Mg, Zn, and Fe were extractable by 80% ethanol, d‐H₂O, and 1μM NaCl. The results indicated that these low–molecular weight compounds, such as organic acids and amino acids, may play an important role in deposition and translocation of Mg, Zn, and Fe in the xylem system of rice plants.     

Bioavailability of zinc from cooked philippine milled,undermilled, and brown rice,as assessed in rats by using growth,bone zinc,and zinc-65 retention

The nutritional bioavailability of zinc from cooked milled, undermilled, and brown Philippine rice (variety PSB Rc14) was evaluated in rats, comparing results based on weight gain, tibia zinc incorporation (slope ratio analyses), and zinc radiotracer retention. Milling reduced the phytic acid and mineral content of the rice, resulting in zinc concentrations of 16.5, 19.4, and 27.2 microg/g and phytate/zinc molar ratios of 4, 20, and 28 for milled, undermilled, and brown rice, respectively. Measured zinc bioavailability was similar whether using growth, bone zinc, or radioisotope retention as criteria, at approximately 92, 86, and 77% of zinc sulfate, for milled, undermilled, and brown rice, respectively. However, the higher percent bioavailability of the zinc after milling was insufficient to compensate for the lower zinc content. With respect to zinc, the nutritional value was inversely related to milling, providing approximately 15, 17, and 21 microg bioavailable zinc/g rice, respectively, for milled, undermilled and brown rice of this variety.