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Article

The Effect of Cooking and Simulated Digestion on the Antioxidants and Minerals in Rice Grains: A Predictor for Nutritional Efficiency

by
Shaker H. Alotaibi
,
Elfadil E. Babiker
,
Ghedeir M. Alshammari
* and
Mohammed Abdo Yahya
Department of Food Science and Nutrition, College of Food and Agricultural Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia
*
Author to whom correspondence should be addressed.
Agriculture 2024, 14(8), 1270; https://doi.org/10.3390/agriculture14081270 (registering DOI)
Submission received: 29 June 2024 / Revised: 22 July 2024 / Accepted: 31 July 2024 / Published: 2 August 2024
(This article belongs to the Section Agricultural Product Quality and Safety)
Browse Figures
Versions Notes

Abstract

:
Antinutrients in rice tend to impair nutrient bioavailability; hence, this study aimed to investigate the effects of cooking and simulated digestion on the antioxidant activity and phenolic content of white and brown rice, as well as the bioavailability of some minerals. The rice grains were cooked in a pressure cooker, using a 1:2 (w/v) rice-to-water ratio. The digestion of the cooked rice grains was then simulated using pepsin and pancreatin systems. The phenolic (total, free, and bound) and flavonoid content; antioxidant activity (DPPH, ABTS, and FRAP); phytic acid and tannin levels; and mineral HCl-extractability were all determined in the raw, cooked, and digested grains. The cooking process significantly lowered (p ≤ 0.05) the phenolic content of the white rice; however, the phenolic content increased significantly (p ≤ 0.05) when these cooked grains were digested. The phenolic content of brown rice decreased at a higher rate during cooking than that of white rice, and it recovered at a lower rate after digestion. The flavonoid content in both cooked and digested white and brown rice followed a similar trend with the phenolic content. This reduction in the phenolic and flavonoid content in both types of rice after cooking was associated with a large decrease in antioxidant activity, whereas, after digestion, it was associated with a considerable increase. After cooking, the levels of phytate and tannin in both types of rice decreased significantly (p ≤ 0.05), and this drop was even more pronounced in the digested grains. Although the mineral content in the cooked samples of white and brown rice decreased, it recovered after digestion; however, the mineral content remained lower than that of the raw samples. Despite this, there was also a rise in the bioavailability of the minerals in the cooked rice after digestion (p ≤ 0.05), which was considerably higher than the rise in the mineral content itself. The findings indicate that, while cooking rice decreases its phenolic content and antioxidant activity, it also lowers its antinutrient content. Additional benefits were also noted following the simulated digestion.

1. Introduction

In addition to providing the body with essential vitamins, minerals, and amino acids, rice (Oryza sativa L.) is a significant source of energy. About 20% of the world’s dietary energy supply comes from rice, 19% from wheat, and 5% from maize [1]. Moreover, for about one-third of the world’s population, rice is a staple food, and it is the third most important cereal after maize and wheat [2]. More than 60% of the global population eats rice, which has many nutritional benefits [3]; energy, protein, vitamins, fiber, minerals, and phenolic chemicals are all abundant in rice [4]. Together with its nutritional value, rice contains a variety of phytochemicals, which are bioactive compounds with high biological activities, such as antioxidant, anticancer, antidiabetic, and anti-inflammatory properties. Rice is high in calories and includes many vital vitamins, minerals, and other nutritional elements. Its nutrients surpass those found in maize, wheat, and potatoes. It is also known for being high in vitamins E and B5, as well as carbohydrates, thiamine, calcium, folate, and iron [5].
Mohidem et al. [5] and Verma et al. [3] reported that aside from sterols, flavonoids, terpenoids, anthocyanins, tocopherols, tocotrienols, and oryzanol, the other phenolic chemicals present in rice include phenols and phytic acid. These substances have been demonstrated to have beneficial antioxidant qualities and to help prevent diabetes and cardiovascular disease. The bran of rice is a phenolic-compound-rich component of whole-grain rice flour, and red- and purple-colored bran contain significantly more phenolic compounds than white- or light-brown-colored bran [6].
Studies have shown that processing methods have an effect on foods’ nutritional contents, which makes many consumers concerned about how the quality of their food is affected [7]. According to Bagchi et al. [8], cooking rice increases its fat, protein, vitamin B1, and ash contents, while decreasing the levels of water-soluble phenolic compounds, which promotes health. According to one study, rice that had been heat-treated showed lower levels of phenolic compounds and anthocyanins, though the heat treatment may have helped to release bound phenolic acids [9]. In another study, heat processing significantly reduced rice’s total phenolic and anthocyanin levels, as well as its antioxidant activity [10]. It also influenced the free and bound phenolic contents and antioxidant capacities in brown, purple, and red rice bran [11]. It has also been reported that cooking rice using all methods reduces its total mineral content (calcium, phosphorus, magnesium, iron, and zinc), while also significantly increasing the HCl extractability of minerals in the cooked rice, compared to raw rice [12].
Dietary phenolic compounds are an important class of natural antioxidants and chemopreventive agents. Phenolics are not completely released when used as a food component, and those that are released are not well absorbed [13]. Additionally, the phenolic compounds that are absorbed are unable to reach the site of action to exert biological effects. Important factors to take into account in this regard are their physicochemical traits, which include their degree of polymerization or glycosylation, molecular characteristics, polarity, and nutrient interaction status. Additionally, certain physiological parameters, such as transport protein expression and tissue state, must be considered [13]. One study discovered that the functional properties of phenolics, flavonoids, and anthocyanins influence the overall quantity and activity of antioxidants in vegetables, fruits, and their extracts after simulated gastrointestinal digestion [14]. Moreover, mineral deficits may result from meals with a low mineral content and also from the low bioavailability of minerals: only a specific amount of a food’s total mineral content is bioavailable after intake [15].
Some chemicals produced by plants, known as “antinutritional factors”, can interfere with metabolic processes, thereby altering the availability of nutrients [16]. It was further reported that phytate and oxalates can chelate with di- and trivalent metallic ions—including Cd, Mg, Zn, and Fe—to create poorly soluble compounds, which are difficult for the digestive system to absorb, thus lowering their bioavailability [16]. Samtiya et al. [17] discovered that, while legumes and cereals such as rice contain significant levels of macronutrients and micronutrients, antinutritional factors limit their utilization in a regular diet. Saponins, tannins, phytic acid, gossypol, lectins, protease inhibitors, and amylase inhibitors are some of the most common antinutritional substances found in food crops. They also observed that antinutritional factors combine with nutrients to induce lower nutrient bioavailability, which is an important issue. Other variables, such as trypsin inhibitors and phytates, found primarily in legumes and cereals, affect protein digestibility and mineral bioavailability, including iron, calcium, and zinc [17]. It is possible to reduce these antinutritional components using a variety of processing methods, including soaking, germination, boiling, and roasting. The goal of the current study was to determine how heating and simulated digestion affect rice’s antioxidant and antinutrient levels and the bioavailability of specific minerals.

2. Materials and Methods

2.1. Materials

Four types of imported rice (Oryza sativa) that are consumed in Saudi Arabia were collected from the local market in Riyadh: two types of white rice (White-1 and White-2) and two types of brown whole-seed rice (Brown-1 and Brown-2). After cleaning, cooking, and freeze-drying, all grains were put in polyethylene bags before analysis. The materials employed in this study were of analytical grade and obtained from Sigma-Aldrich (St. Louis, MO, USA).

2.2. Cooking the Rice

Preliminary trials for this treatment were conducted to optimize the cooking settings, resulting in rice that was soft enough to be palatable and tasty. Brown and white rice samples were pressure-cooked for 20 min (rice/water ratio: 1:2, w/v). The cooked rice was thoroughly freeze-dried and stored at 4 °C until it was analyzed. The cooking process was repeated three times.

2.3. Cooked Rice Simulated Digestion

The sample digestion was carried out using the technique described by Faller et al. [18]. In brief, 55 mL of saline solution containing 140 mM NaCl, 5 mM KCl, and 150 µM butylated hydroxy-toluene (BHT) was mixed with 20 g of cooked rice. Using an XHF-D homogenizer (Ningbo Xin-Zhi-Bio Technology Co., Ningbo, China), the mixture was homogenized for five minutes at room temperature. It was then acidified to pH 2.0, using 0.1 M HCl. After that, the sample was combined with 2 mL of pepsin (1:10,000) solution (0.2 g of pepsin dissolved in 5 mL of 0.1 mol/L HCl) and incubated at 37 °C for 1 h. Using 1 M NaHCO3, the pH of the digested medium was brought to 7.0 for intestinal digestion. The mixture was then incubated with 20 mL of pancreatin bile solution (0.9 g of bile extract and 0.15 g of pancreatin in 75 mL of 0.1 M NaHCO3) for two hours at 37 °C, in a thermostatic water bath. The digested solution was freeze-dried. Three replicates of the digestion process were completed.

2.4. Total Phenolic Content (TPC) Determination

The TPC was extracted using methanol. The TPC in rice extract was determined using the Folin–Ciocalteu reagent and the Singleton and Rossi [19] method. In summary, 4.0 mL of distilled water, 400 µL of Folin–Ciocalteu reagent, and 200 µL of extract were mixed. After thoroughly mixing and incubating at the same temperature for two hours, a Na2CO3 solution (20 g/100 mL, w/v) was added and the mixture was incubated for another ten minutes at 25 °C. The absorbance was measured at 765 nm with a PD-303UV spectrophotometer (Apel, Saitama, Japan), and the TPC was expressed as mg gallic acid equivalent per 100 g (GAE/100 g) extract.

2.5. Extraction of Free Phenolics

The method used by Sun et al. [20] was applied. Approximately 50 mL of a solution comprising 85:15, v/v, 95% methanol to 1 mol/L HCl was combined with a 2 g sample of raw, cooked, or digested rice after it had been chilled to 5 °C. After homogenizing the extract for five minutes at 10,000 rpm in an ice bath, using the XHF-D homogenizer (Ningbo Xin-Zhi-Bio Technology Co., Ningbo, Zhejiang, China), it was centrifuged at 2500× g for ten more minutes. The supernatants from the two centrifugations were mixed, and the extraction process was repeated before being evaporated at 45 °C. To create the free phenolic extract solution, the residue was dissolved in 10 mL of methanol and kept at 4 °C until its analysis. Every test was run three times.

2.6. Determination of Bound Phenolics

The method proposed by Sun et al. [20] states that the bound phenolic content is equal to the total phenolic content minus the free phenolic content.

2.7. Determination of Total Flavonoid Content (TFC)

The TFC of the samples was estimated using the method described by Bao et al. [21]. In total, 4 mL of distilled water, 0.3 mL of sodium nitrite (5% solution), and 0.3 mL of aluminum chloride (10% solution) were mixed with 1 mL of methanolic extract. The mixture was then held at 25 °C for around five minutes. The absorbance after the addition of 10 mL of distilled water and 2 mL of 1 M NaOH was measured at 510 nm using a PD-303UV spectrophotometer (Apel, Saitama, Japan). The results were given in mg/100 g catechin equivalents (mg CE 100 g−1), with catechin as the standard.

2.8. Antioxidant Activity Determination

2.8.1. 2,2-Diphenyl-1-picrylhydrazyl (DPPH)

The DPPH of rice methanolic extracts was calculated using the method proposed by Lee et al. [22]. After diluting the methanol, the DPPH reagent (2 mL) and 1 mL of each extract were thoroughly combined with a vortex mixer. The control substance was methanol. The mixes’ absorbance at 518 nm was determined using a spectrophotometer (PD-303UV spectrophotometer, Apel, Saitama, Japan). The DPPH was estimated with the following formula:
DPPH (%) = (1 − Asample/Acontrol) × 100
where A is the absorbance that was observed.

2.8.2. 2,2′-Azino-bis (3-Ethylbenzothiazoline-6-sulfonic Acid (ABTS))

The ABTS was estimated using the techniques proposed by Re et al. [23]. Aqueous solutions of 7 mM ABTS and 2.4 mM potassium persulfate were reacted for 12–16 h at room temperature and in the dark to generate ABTS. Before the experiment, this solution was diluted in ethanol (1:89 v/v) and allowed to equilibrate at 30 °C, which resulted in an absorbance of 0.700 ± 0.02 at 734 nm, as measured spectrophotometrically (Mod. 4050, Biochrom, Cambridge, UK). Thirty minutes later, at thirty degrees Celsius, the absorbance was measured after 10 µL of the test sample in ethanol was mixed with 1 mL of diluted ABTS solution. The inhibition percentage for the blank absorbance at 734 nm was computed. The Trolox equivalents per gram of sample, or micromoles of TE/g, were used to quantify the radical scavenging activity.

2.8.3. Ferric Reducing Antioxidant Power (FRAP)

FRAP was computed using the technique proposed by Yen and Duh [24]. The methanol extract (0.5 mL, diluted 10 times) and 2 mL of the FRAP solution were combined in a 10 mL test tube. The mixture was then diluted to 10 mL using distilled water. The combination was left in the dark for 20 min. The absorbance of the leftover FRAP solution was measured at 593 nm against a blank, using a spectrophotometer (PD-303UV spectrophotometer, Apel, Saitama, Japan). The Trolox equivalents—in micromoles per gram of material (μmol TE/g)—were used to express the results.

2.9. Phytate Determination

The procedure outlined by Wheeler and Ferrel [25] was used to ascertain the phytate content of the samples. A sample of approximately 5 g was extracted over three hours in 50 mL of 0.5 mol/L HCl. The sample was then centrifuged for thirty minutes at 3000× g rpm. Approximately 0.5 mL of the extract was put in a 15 mL centrifuge tube. Next, 1 mL of ammonium iron (III) sulfate solution was added. After 30 min of incubation in a bath of boiling water, the tubes were cooled to room temperature by placing them in cold water. Once the tubes had reached room temperature, 1.5 mL of 2, 20-bipyridine solution (1% v/v) was added. The absorbance was measured immediately at 519 nm. A reference curve was created to represent the outcomes in terms of the Fe (NO3)3 equivalent. The results were given in mg/100 g.

2.10. Tannin Determination

The tannins were measured quantitatively using the modified vanillin-HCl technique [26]. A 200 mg sample was extracted by placing 10 mL of 1% (v/v) concentrated HCl in methanol in covered rotating test tubes for 20 min. The extract (1 mL) was then combined with 0.5% vanillin reagent (5 mL), and after 20 min at 30 °C, the absorbance of the resulting color was measured at 500 nm. A standard curve was created to illustrate the results in terms of catechin equivalents. After accounting for the blank, the amount of catechin (mg/mL) required to provide color intensity was determined to be comparable to that provided by tannins. Tannin content was given as mg/100 g.

2.11. Determination of Mineral Concentration

For the mineral calculation, all samples were digested using dry-ashing, as described by Pearson [27]. For ashing, the sample was put in a muffle furnace and heated to 450 °C for 72 h. In cases where completely white ash could not be obtained, approximately 5 drops of an oxidizing agent were added to complete the ashing process. Double-distilled water (5 mL) and 2 mL of sub-boiled 65% HNO3 were added to the ash. The mixture was then boiled for two minutes. The subsequent steps involved filtering the solution into a graduated 30 mL test tube with a stopper and adding distilled water to fill the remaining space. The Perkin Elmer Optima 4300DV ICP-OES, an optical emission spectrometer (PD-303UV spectrophotometer, Apel, Saitama, Japan), was used to determine the minerals’ concentration in the digested sample solutions. The samples were examined for the presence of calcium, iron, magnesium, and zinc. Every sample was analyzed in triplicate. The results were expressed as mg/kg.

2.12. HCl Extractability of Minerals (Bioavailability)

The minerals in the samples were extracted using Chauhan and Mahjan’s [28] technique. Before being filtered, one gram of the material was agitated with ten milliliters of 0.03 M HCl at 37 °C, for three hours. Before the dry acid digestion, the clear extract was oven-dried at 100 degrees Celsius. The amount of minerals that could be extracted was calculated using the aforementioned approach.

2.13. Multivariate and Statistical Analysis

According to Vicente-Villardón’s method [29], MULTBIPLOT software (version 1.5) was used for the multivariate analysis (principal component and hierarchical cluster analyses), as instructed in the user handbook. Every determination was made using three different samples, each of which was examined three times. The results were then averaged. An analysis of variance (ANOVA) was used to evaluate the data. The means were separated using Duncan’s multiple-range tests. At p ≤ 0.05, significance was deemed to exist.

3. Results

3.1. Changes in Rice’s Phenolic and Flavonoid Content

Figure 1 depicts the impact of cooking and simulated digestion on the phenolic content (total, free, and bound) of two white (White-1 and White-2) and two brown (Brown-1 and Brown-2) types of rice. The raw sample of White-1 had total, free, and bound phenolic contents of 19.67, 11.87, and 7.80 mg GAE/100 g dry weight (DW), respectively. Cooking this rice significantly reduced (p ≤ 0.05) its phenolic contents to 15.18, 9.14, and 6.04 mg GAE/100 g DW, resulting in losses of 22.83%, 23.00%, and 22.56%. However, after the digestion of the cooked rice, the phenolic contents significantly (p ≤ 0.05) increased, rising to higher levels than those in the raw rice: 54.87, 31.49, and 23.38 mg GAE/100 g DW, with increments of 178.95%, 165.29%, and 199.74%, respectively (Figure 1A). The raw White-2 rice sample had values of 20.85, 11.77, and 9.08 mg GAE/100 g DW for its total, free, and bound phenolic contents, respectively (Figure 1A). Cooking significantly reduced (p ≤ 0.05) the contents to 13.96, 8.14, and 5.82 mg GAE/100 g DW, resulting in losses of 33.04%, 30.84%, and 35.91%, respectively. However, the phenolic content was significantly (p ≤ 0.05) higher in the digested samples than in the raw ones, increasing to 52.88, 29.85, and 23.03 mg GAE/100 g DW for the total, free, and bound phenolic contents, resulting in increases of 153.63%, 153.61%, and 153.63%, respectively.
The total, free, and bound phenolic concentrations of raw Brown-1 were 66.64, 43.38, and 23.26 mg GAE/100 g DW, respectively. Cooking the raw Brown-1 was found to significantly reduce (p ≤ 0.05) the total phenolic content from 66.64 to 25.54, the free phenolic content from 43.38 to 16.14, and the bound phenolic content from 23.26 to 9.40 mg GAE/100 g DW. This gave cooking loss percentages of 61.67, 62.79, and 59.59% for total, free, and bound phenolics, respectively (Figure 1B). However, the digestion of the total phenolic content of the Brown-1 rice increased significantly (p ≤ 0.05), from 66.64 to 85.17; the free phenolic content increased from 43.38 to 57.81; and the bound phenolic content increased from 23.26 to 27.36 mg GAE/100 g DW. The percentage increment in the total, free, and bound phenolic content was found to be 27.81, 33.26, and 17.63%, respectively (Figure 1B). In the raw Brown-2, the total, free, and bound phenolic content was 62.84, 42.17, and 20.67 mg GAE/100 g DW, respectively (Figure 1B). Cooking the raw Brown-2 was found to reduce the total phenolic content from 62.84 to 25.54; the free phenolic content from 42.17 to 15.44; and the bound phenolic content from 20.67 to 10.10 mg GAE/100 g DW. The cooking loss percentage was estimated to be 59.36, 63.39, and 51.14% for the total, free, and bound phenolics, respectively (Figure 1B). The digestion of Brown-2 significantly (p ≤ 0.05) increased the total phenolic content from 62.84 to 81.42; the free phenolic content from 42.17 to 56.89; and the bound phenolic content from 20.67 to 24.53 mg GAE/100 g DW. The percentage increments in the total, free, and bound phenolics were found to be 29.57, 34.91, and 18.67%, respectively (Figure 1B).
Figure 2 illustrates how heating and simulated digestion affected the total flavonoid content of the white and brown rice. There were minor variations among the flavonoid concentrations of cooked, raw, and digested white and brown rice. In White-1, the total flavonoid concentrations were as follows: 1.97, 0.59, and 2.31 mg CE/100 g DW for the raw, cooked, and digested samples, respectively. In White-2, the total flavonoid values were 1.69, 0.68, and 2.08 mg CE/100 g DW for the raw, cooked, and digested samples, respectively. In Brown-1, the total flavonoid concentrations in the raw, cooked, and digested samples were 4.69, 2.19, and 3.89 mg CE/100 g DW, respectively. In the Brown-2, they were 3.11, 2.61, and 3.55 mg CE/100 g DW for the raw, cooked, and digested samples, respectively.

3.2. Changes in Antioxidant Activity of Rice

Table 1 displays the impact of cooking and simulated digestion on the antioxidant activity levels of white and brown rice. Three distinct techniques were used to assess the antioxidant activity of raw, cooked, and digested rice including DPPH, ABTS, and FRAP. The mean DPPH values in the raw, cooked, and digested white and brown rice showed significant (p ≤ 0.05) differences. There were also significant differences between the DPPH values of the white and brown rice. The DPPH percentages in the raw, cooked, and digested White-1 samples were 26.48, 18.71, and 63.27%, whereas, in the White-2 samples these were 25.26, 18.01, and 60.13%, respectively. The DPPH percentages in the raw, cooked, and digested Brown-1 samples were 71.74, 30.52, and 81.82%, whereas in the Brown-2 samples, they were 69.14, 31.17, and 79.29%, respectively. Moreover, the mean ABTS values of the raw, cooked, and digested white and brown rice also showed significant (p ≤ 0.05) differences (Table 1). There were also significant differences between the ABTS values of the white and brown rice. The ABTS mean values of the raw, cooked, and digested White-1 samples were 1.97, 1.20, and 3.92 μmol TE/g, whereas in the White-2 sample, they were 1.41, 1.36, and 3.18 μmol TE/g, respectively. The mean ABTS values of the raw, cooked, and digested Brown-1 samples were 6.21, 3.21, and 7.81 μmol TE/g, whereas in the Brown-2 samples, they were 5.21, 2.96, and 6.91 μmol TE/g, respectively.
The FRAP mean values in white rice were found to be 1.90, 1.31, and 2.89 μmol TE/g for the raw, cooked, and digested White-1 samples, whereas, for the White-2 samples, they were 1.69, 1.23, and 2.19 μmol TE/g, respectively (Table 1). In the brown rice, the FRAP mean values were observed to be 2.49, 1.91, and 4.27 μmol TE/g for the raw, cooked, and digested Brown-1 samples, while for the Brown-2 samples, they were 2.11, 1.87, and 3.78 μmol TE/g, respectively. The data obtained indicated that the antioxidant activity of both types of rice increased significantly (p ≤ 0.05) upon digestion, while the antioxidant activity of both types of rice decreased significantly (p ≤ 0.05) upon cooking. Furthermore, the antioxidant activity of raw, cooked, and digested brown rice was significantly (p ≤ 0.05) higher than that of white rice, regardless of the type of antioxidant activity applied.

3.3. Effect of Cooking and Digestion on Phytate and Tannin Levels in Rice

The contents of phytate and tannin in the raw, cooked, and digested white and brown rice are displayed in Figure 3. The phytic acid and tannin levels in the white rice (Figure 3A) samples varied: the phytic acid levels for White-1 and White-2 were 14.52 and 17.21 mg/100 g DW, and the tannin levels were 13.21 and 15.43 mg/100 g DW, respectively. A significant (p ≤ 0.05) reduction in phytic acid (8.89 and 9.78 mg/100 g DW) and tannin (9.35 and 10.09 mg/100 g DW) for both White-1 and White-2 was observed after cooking. Moreover, further reductions in phytic acid and tannin were observed when the rice was digested: phytic acid decreased to 5.87 and 6.38, while tannin decreased to 7.13 and 5.89 mg/100 g DW for White-1 and White-2, respectively.
Brown-1 and Brown-2 were found to have phytate levels of 81.46 and 83.11 and tannin levels of 39.12 and 41.32 mg/100 g DW, respectively (Figure 3B). Both the phytic acid and tannin levels were significantly (p ≤ 0.05) reduced by cooking in both types of rice: the phytic acid content decreased to 54.99 and 57.24 and the tannin content decreased to 27.97 and 31.22 mg/100 g DW in Brown-1 and Brown-2, respectively. The phytic acid and tannin levels in both types of brown rice were observed to be further and significantly (p ≤ 0.05) reduced during the simulated digestion: the tannin levels decreased to 19.77 and 21.47 mg/100 g DW, while the phytic acid levels decreased to 41.68 and 47.58 mg/100 g DW in Brown-1 and Brown-2, respectively.

3.4. Effect of Cooking and Digestion on Total and Available Minerals in Rice

The mineral content varied significantly (p ≤ 0.05) between the white and brown rice and even within the same type. In this regard, brown rice was found to be superior to white rice (Table 2). Both types of brown rice were found to be richer in calcium than either type of white rice. The calcium content of the raw white rice was 67.18 and 71.68 mg/kg for White-1 and White-2, respectively; the calcium content for both White-1 and White-2 decreased significantly (p ≤ 0.05) after cooking, decreasing to 51.62 and 54.58 mg/kg, respectively (Table 2). Although the digestion of the cooked white rice increased the level of calcium, it was still lower than that of the raw samples. For both brown rice types, the cooking process also reduced the calcium content: for Brown-1 it decreased from 86.24 to 68.67 mg/kg, and for Brown-2 it decreased from 82.62 to 65.28 mg/kg. As with the white rice, the digestion of the cooked brown rice increased the level of calcium; however, it was still lower than that of the raw samples. After cooking, the Fe in the white rice had decreased significantly (p ≤ 0.05), from 9.74 to 4.43 for White-1 and from 7.34 to 4.48 mg/kg for White-2 (Table 2). However, the Fe level had slightly increased after the digestion of the cooked samples. Moreover, the Fe level in the brown rice also decreased significantly (p ≤ 0.05) after cooking: for Brown-1 it decreased from 11.65 to 6.12 mg/kg and for Brown-2 it decreased from 9.44 to 5.89 mg/kg. The digestion of the cooked brown rice also slightly increased the Fe level, compared to the cooked samples.
Moreover, the level of Mg in the white rice decreased significantly (p ≤ 0.05) after cooking: that in White-1 decreased from 23.98 to 19.9 and that in White-2 decreased from 22.5 to 16.82 mg/kg, with a loss of 16.97% and 25.24%, respectively. Furthermore, the level of Mg in brown rice also decreased significantly (p ≤ 0.05) after cooking: that in Brown-1 decreased from 43.58 ± 0.89 to 34.89 ± 0.98 and that in Brown-2 decreased from 56.85 to 41.19 mg/kg. In both the white and brown rice, the simulated digestion raised the Mg content to levels higher than those in the uncooked samples. The Zn concentration in both the white and brown rice followed a similar pattern to that of Fe and Mg. Table 2 shows the variations in the minerals’ bioavailability (extractability) among the raw, cooked, and digested white and brown rice. The HCl-extractability of calcium was significantly increased after the cooking and digestion of the white and brown rice. In the raw samples, the Ca extractability for White-1 was 55.49%, and for White-2, it was 59.68. When White-1 was cooked and digested, this increased significantly to 68.56% and 74.47%, respectively. The Ca extractability for White-2 also increased significantly when the rice was cooked and digested, to 63.44% and 68.12%, respectively. Moreover, the extractable calcium of Brown-1 and Brown-2 when raw was 53.57 and 57.35, respectively. A significant increase in calcium availability was noted after the cooking and digestion: for Brown-1, it was increased to 65.15 and 68.16% for cooked and digested rice, respectively, and, for Brown-2, it was increased to 71.34 and 74.86%, respectively. In both types of rice, the bioavailability of Fe, Mg, and Zn showed a pattern similar to that of calcium (Table 2).

3.5. Principal Component (PCA) and Hierarchical Clustering (HCA) Analysis of Variables

Figure 4 depicts the results of PCA and HCA analyses of the bioactive characteristics, mineral content, and mineral extractability of the rice, as impacted by the variety (white and brown) and treatment (raw, cooked, and digested). The treatments impacted the bioactive characteristics, mineral content, and mineral extractability of white and brown rice cultivars in various ways (Figure 4A). The raw and cooked white rice (both White-1 and White-2) had the lowest values in all of the examined qualities. Although the cooked brown rice variations were identical to the white rice, their influences on the evaluated qualities were greater than those of raw and cooked white rice.
Because they share some bioactive properties and some values for mineral content and extractability, the raw white rice and the cooked white and brown rice types are grouped (blue circle cluster). Digestion increased the bioactive characteristics and the mineral extractability of both white and brown rice cultivars (red diamond cluster) in distinct ways. The digested white rice had the highest Ca, Fe, Mg, and Zn extractability, whereas the digested brown rice had the highest bioactive characteristics: TPC, FPC, BPC, RP, ABTS, and DPPH. The raw brown rice (green triangle cluster) included more antinutritional elements (tannin and phytic acid) and minerals than the digested and cooked brown rice and the raw and treated white rice.
The HCA heatmap (Figure 4B) revealed that both varieties of brown rice had high values (red color) for the majority of the examined characteristics, while both varieties of white rice mostly had low values (green color), with a few exceptions. Digestion increased the bioactive qualities, mineral content, and extractability of the brown rice, with both varieties showing the highest values for all of these attributes, and with Brown-2 outperforming Brown-1. Cooking lowered the bioactive qualities, mineral content, and extractability of all the types of rice studied, with white rice being the most impacted. Overall, brown rice was found to have a high concentration of bioactive qualities and minerals (content and extractability), which are considerably enhanced by digestion.
The results of this study are consistent with the existing literature, confirming that brown rice contains higher nutritional components than white rice; however, it also contains high antinutritional factors, which negatively affect the biological benefits of these components. Although the processes of cooking affect the nutritional components, digestion reduces such negative effects.

4. Discussion

The antinutrients contained in rice tend to impair the bioavailability of nutrients; hence, this study aimed to investigate the effects of cooking and simulating digestion on the antioxidant activity and phenolic content of white and brown rice, as well as the bioavailability of certain minerals. This study found that digesting white and brown rice significantly increases its phenolic content (p ≤ 0.05), but cooking significantly decreases the total phenolic content. According to a previous study, different plant species, cultivars, plant parts, cultivation circumstances, and cooking methods can all have an impact on the concentrations of free and bound phenolics during thermal processing [30]. Cooked rice has far lower levels of total phenolic and flavonoids than raw rice [8]. Chmiel et al. [31] discovered that the amounts of polyphenols in both polished and unpolished rice decreased after cooking. In all rice samples evaluated, the cooking procedure had a negative effect on the polyphenol content, with thermal processing in the rice cooker resulting in the greatest loss and decline in total antioxidant activity. Furthermore, Colasanto et al. [32] demonstrated that cooked samples have a considerably lower total polyphenol concentration than raw black rice. The thermal treatment used during cooking influenced the degradation of the majority of phenolic compounds, which decreased by around 83% on average. The boiling process resulted in the largest loss. According to Nishinari and Fang [33], high temperatures during cooking trigger the oxidative destruction of polyphenols. Furthermore, due to phenolic component leaching, soaking grains for hours before cooking can diminish polyphenol concentration [34]. One possible explanation for this decline could be the degree of heat treatment applied during the cooking process, which could promote the polymerization or decarboxylation of free phenolic acids. Such degradation during cooking could be a significant source of loss [35]. The changes in the bound phenolic content noted in one study suggest that heat treatment led to better extractability or the disruption of cellular components by destabilizing the cell wall structure [36]. It has previously been noted that cooking significantly changes the amounts of bound and free phenolic compounds in polished and brown rice [35]. These researchers also discovered that cooking rice raised the proportion of free phenolics while decreasing the proportion of bound phenolics.
The data obtained in this study demonstrated that the phenolic content (free, bound, and total) and the total flavonoid content in cooked white and brown rice increased significantly after simulated digestion. It has been suggested that the bound phenolics associated with cereal grain cell walls may withstand digestion in the upper gastrointestinal tract and, eventually, reach the colon, where intestinal bacteria may release them during the process of digestion [37]. This is mostly because digestion induces the breakdown of antioxidants, releasing the beneficial molecules [38]. Furthermore, Ti et al. [35] suggested the possibility that digestive enzymes break chemical bonds in the phenolics and proteins, promoting the release of phenolics, especially phenolic acids, which are significant components of the cell wall. This could account for the increase in the total, free, and bound phenolic content of the rice following digestion. The brown rice had a higher total phenolic content than the white rice after the simulated digestion because it had a higher concentration of phenolics in its germ structure and aleurone layer, and because its cell walls released additional phenolics when digested with digestive enzymes [35]. As a result, brown rice’s antioxidant components are more easily released and extracted due to the possible disruption of its cell walls, which is caused by heating and simulated digestion treatments.
In this study, the flavonoid content of the raw, cooked, and digested brown rice was higher than that of the white rice. In both samples, cooking impacted the flavonoid content. The cooking conditions, the dietary matrix, and the composition all influence changes in flavonoid levels [39]. Wu et al. [40] reported that broccoli lost a substantial amount of its flavonoids when it was boiled, but less when it was steamed or microwaved. The combined impact of heat degradation and flavonoid components leaking into the cooking water may be the cause of the significant flavonoid loss during boiling [40]. Because of the increased release of flavonoids following digestion, the overall number of flavonoids generated after digestion was marginally higher than that of the undigested solid residue. Contrary to the more recent findings, several earlier studies showed that the total content of flavonoids decreases after gastrointestinal digestion. For example, Pellegrini et al. [41] found that five quinoa seeds had a lower total flavonoid content during the intestinal phase, while Ydjedd et al. [42] found that the total flavonoids of both encapsulated and non-encapsulated carob pulp extracts decreased under simulated intestinal conditions.
According to Ma and Chen [43], the majority of dietary polyphenols are not absorbed in the small intestine but can accumulate in the large intestine and be extensively digested by gut flora. As a result, the gut microbiota plays an important role in the biotransformation and conversion of polyphenolic structures into low-molecular-weight metabolites that are readily absorbed and contribute to host health benefits. This allows polyphenols to indirectly activate antioxidant responses and produce non-toxic amounts of intermediates, particularly the electrophilic forms of hydroquinone and quinone [44], as well as to serve as anti-inflammatory and antibacterial agents [45].
According to the findings of this study, brown rice had a higher antioxidant activity than white rice. Ti et al. [35] noted that the phenolic antioxidant activity in whole white and brown rice was consistent. According to Gong et al. [37], cooking reduces the overall antioxidant activity in rice as a result of the reduction in antioxidants. These results are in line with the current study, which found a significant drop in antioxidant levels in rice after cooking, mirroring the total phenolic content after cooking. This is possibly due to the degradation of antioxidant molecules, which causes antioxidant losses. Jiang et al. [46] stated that, while cooking can degrade and denaturize physiologically active substances, it is feasible to preserve and protect bioactive substances and their antioxidant activity by using the right cooking techniques. Therefore, the formation or breakdown of water-soluble compounds, their diffusion, and the synergistic combinations or interactions of many chemical events (Maillard reaction) may all be related to antioxidant losses. In this study, however, the overall antioxidant activity of both white and brown rice was markedly elevated upon cooking and subsequent digestion. According to Wang et al. [47], rice’s antioxidant activity can be enhanced by both boiling and simulated digestion treatments, which can greatly boost the release of bioactive compounds.
The brown rice samples had notably elevated levels of phytic acid and tannin, in contrast to the white rice. This is potentially linked to the brown rice’s pigmentation. Phytic acid has long been classified as an antinutrient due to its capacity to chelate food nutrients (proteins, minerals, etc.) and digestive enzymes, making them inaccessible for absorption and diminishing their bioavailability [48]. This study found that brown rice has higher quantities of phytic acid than Kumar et al. [49], but lower levels than Fukushima et al. [50]. Phytic acid is present in a variety of native Indian rice cultivars from different regions, with amounts varying from 1.72 to 5.59 g/kg, according to Dhaliwal et al. [51]. Even though the brown rice had high tannin levels in this study, the results did not meet the expectations of Dhaliwal et al. [51], who reported that the tannin levels in certain Indian red rice ranged from 703.4 mg/kg to 763.7 mg/kg and stayed quite stable. The tannin findings, however, were in line with those published by Muttagi and Ravindra [52], who observed a variation in the tannin levels among different types of rice, with short-grain rice varieties displaying a range from 286.5 to 422.9 mg/kg and medium-grain rice varieties exhibiting a range from 299.8 to 568.8 mg/kg. The antinutrient levels in both types of rice were significantly reduced during the cooking process for raw rice, and this reduction continued once the cooked rice was digested. Despite their harmful effects, the three main antinutrients found in cereal grains—phytic acid, tannins, and saponins—may be beneficial to health [17]. Yu et al. [53] claim that the traditional home cooking of rice may result in a considerable loss of important nutrients; however, cooking can also be advantageous because it can decrease the amount of phytic acid, an antinutrient. Kaur et al. [54] used a range of pre-treatments, such as soaking, germination, oven roasting, sand roasting, boiling, and pressure cooking at different periods and temperatures, to reduce the antinutritional content of rice beans. They discovered that the antinutrient content of rice beans may be considerably reduced by each pre-treatment. It was also observed that the phytic acid concentration of unsoaked seeds was reduced by normal cooking; however, this loss appeared to be smaller than that of the cooked seeds that had been pre-soaked. After boiling, the tannin and phytate levels may have decreased because heating denatured and broke down these antinutrients, whereas, after digestion, the enzymatic hydrolysis of tannin and phytate rendered them inactive [55].
The present data indicate that cooking significantly decreased the mineral content of the white and brown rice samples. Though it was still lower than in raw samples, the mineral content of the cooked rice increased slightly after digestion, compared to the cooked samples. Rice is often prepared in three ways: conventional cooking, high-pressure cooking, and microwave cooking, according to Liu et al. [56]. On the other hand, cooking and precooking may cause a direct loss of vitamins and minerals. Additionally, they found that the water released after washing and boiling rice included a sizable amount of minerals and that soaking rice in warm water can hasten the loss of minerals [57]. Furthermore, the water discarded after washing and boiling rice has been found to contain a considerable amount of minerals [58]. Generally, white rice has more readily available minerals than brown rice; this could be due to the two varieties’ differing antinutrient contents. The bioavailability of nutrients, as well as their quantity in a diet, affects how well they are absorbed by the body [59]. The study indisputably demonstrated that providing extra nutrients, heating, and grain digestion increased the mineral bioavailability of white and brown rice. The elimination of tannins and phytic acid—the two main antinutrients in cereal grains, which may have positive health impacts despite their unfavorable effects—may be the cause of the improvement in mineral bioavailability [46]. Washing and soaking increased the bio-accessibilities of Zn and Ca; however, heating increased the bio-accessibilities of Mg, Fe, and Ca, while decreasing those of Zn and Mn [56]. According to reports, phytic acid firmly limits the availability of minerals such as calcium, magnesium, iron, copper, and zinc. Precipitation could result from this, preventing the minerals from entering the digestive tract and being digested [60]. According to Abera et al. [61], soaking and cooking red, white, and black kidney beans dramatically reduces antinutritional components (phytate and tannin) and increases minerals’ bioavailability. Phytic acid has negative effects—such as decreased mineral bioavailability—which worsen when a person consumes a predominantly cereal-based diet; therefore, lowering phytic acid levels in these grains is essential in increasing the bioavailability of minerals in feeding both humans and animals [62].

5. Conclusions

In summary, the process of cooking and simulated digestion significantly affected the overall levels of phenolics and flavonoids, both free and bound, as well as the antioxidant activity of both white and brown rice. These results suggest that, while the heating process reduces rice’s antioxidant capacity, simulated digestion increases the amount of bioactive components and antioxidant activity in both white and brown rice. Both types of rice showed a decrease in antinutritional factors when cooked, and this reduction continued once the cooked rice was digested. Both varieties of rice had lower mineral levels, but a higher mineral bioavailability after cooking. Cooking and simulated digestion can be utilized to gather more physiologically relevant data about the health impacts of rice’s bioactive components. These findings have significant implications for increasing rice intake, particularly whole brown rice, and improving human health. More research is needed to investigate the changes in functional qualities generated by food processing, which will help to discover possible areas for their optimum application in fortifying food.

Author Contributions

Conceptualization, S.H.A., E.E.B. and G.M.A.; methodology, S.H.A. and E.E.B.; software, S.H.A.; formal analysis, E.E.B.; investigation, M.A.Y.; resources, G.M.A.; data curation, S.H.A.; writing—original draft preparation, S.H.A.; writing—review and editing, E.E.B. and G.M.A.; visualization, M.A.Y.; supervision, G.M.A. and E.E.B.; project administration, M.A.Y.; funding acquisition, G.M.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Researchers Supporting Project, King Saud University, Riyadh, Saudi Arabia (grant RSP2024R84).

Data Availability Statement

The datasets used and analyzed during the current study are available from the corresponding authors upon reasonable request.

Acknowledgments

The authors extend thanks to the Researchers Supporting Project number RSP2024R84, King Saud University, Riyadh, Saudi Arabia, for supporting this work.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agriculture 14 01270 g001
Figure 1. Total, free, and bound phenolic content of raw, cooked, and digested white (A) and brown (B) rice. Different letters (a, b, or c) are given against each parameter for each type indicating significant differences (p ≤ 0.05).
Figure 1. Total, free, and bound phenolic content of raw, cooked, and digested white (A) and brown (B) rice. Different letters (a, b, or c) are given against each parameter for each type indicating significant differences (p ≤ 0.05).
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Figure 2. Flavonoid content of raw, cooked, and digested white and brown rice. Different letters (a, c) are set against each parameter for each type’s significant difference (p ≤ 0.05).
Figure 2. Flavonoid content of raw, cooked, and digested white and brown rice. Different letters (a, c) are set against each parameter for each type’s significant difference (p ≤ 0.05).
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Figure 3. Antinutrient content (phytic acid and tannin) of raw, cooked, and digested white (A) and brown rice (B). Different letters (a, b, or c) are given against each parameter for each type’s indicated significant difference (p ≤ 0.05).
Figure 3. Antinutrient content (phytic acid and tannin) of raw, cooked, and digested white (A) and brown rice (B). Different letters (a, b, or c) are given against each parameter for each type’s indicated significant difference (p ≤ 0.05).
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Figure 4. (A): Principal component analysis (PCA) of bioactive properties, antinutritional factors, and mineral content of different rice varieties, as affected by different treatments (cooking and digestion): BRWALR—raw Brown-1; BRWALC—cooked Brown-1; BRWALD—digested Brown-1; BRMUHR—raw Brown-2; BRMUHC—cooked Brown-2; BRMUHD—digested Brown-2. WRWALR—raw White-2; WRWALC—cooked White-2; WRWALD—digested White-2; WRABUR—raw White-1; WRABUC—cooked White-1; WRABUD—digested White-1; TPC—total phenolic content; FPC—free phenolic content; BPC—bound phenolic content; and RP—reducing power. (B): Hierarchical clustering analysis (HCA) of bioactive properties, antinutritional factors, and mineral content of different rice varieties, as affected by different treatments (cooking and digestion). BRWALR—raw Brown-1; BRWALC—cooked Brown-1; BRWALD—digested Brown-1; BRMUHR—raw Brown-2;, BRMUHC—cooked Brown-2; BRMUHD—digested Brown-2; WRWALR—raw White-2; WRWALC—cooked White-2; WRWALD—digested White-2; WRABUR—raw White-1; WRABUC—cooked White-1; WRABUD—digested White-1; TPC—total phenolic content; FPC—free phenolic content; BPC—bound phenolic content; and RP—reducing power.
Figure 4. (A): Principal component analysis (PCA) of bioactive properties, antinutritional factors, and mineral content of different rice varieties, as affected by different treatments (cooking and digestion): BRWALR—raw Brown-1; BRWALC—cooked Brown-1; BRWALD—digested Brown-1; BRMUHR—raw Brown-2; BRMUHC—cooked Brown-2; BRMUHD—digested Brown-2. WRWALR—raw White-2; WRWALC—cooked White-2; WRWALD—digested White-2; WRABUR—raw White-1; WRABUC—cooked White-1; WRABUD—digested White-1; TPC—total phenolic content; FPC—free phenolic content; BPC—bound phenolic content; and RP—reducing power. (B): Hierarchical clustering analysis (HCA) of bioactive properties, antinutritional factors, and mineral content of different rice varieties, as affected by different treatments (cooking and digestion). BRWALR—raw Brown-1; BRWALC—cooked Brown-1; BRWALD—digested Brown-1; BRMUHR—raw Brown-2;, BRMUHC—cooked Brown-2; BRMUHD—digested Brown-2; WRWALR—raw White-2; WRWALC—cooked White-2; WRWALD—digested White-2; WRABUR—raw White-1; WRABUC—cooked White-1; WRABUD—digested White-1; TPC—total phenolic content; FPC—free phenolic content; BPC—bound phenolic content; and RP—reducing power.
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Table 1. Antioxidant activity (DPPH, ABTS, and reducing power) of raw, cooked, and digested white and brown rice.
Table 1. Antioxidant activity (DPPH, ABTS, and reducing power) of raw, cooked, and digested white and brown rice.
White RiceBrown Rice
White-1White-2Brown-1 Brown-2
RawCookedDigestedRawCookedDigestedRawCookedDigestedRawCookedDigested
DPPH (%)
26.48 ± 1.12 b18.71 ± 1.05 c63.27 ± 1.22 a25.26 ± 0.95 b18.01 ± 0.45 c60.13 ± 1.67 a71.74 ± 1.23 b30.52 ± 0.88 c81.82 ± 1.44 a69.14 ± 1.12 b31.17 ± 0.79 c79.29 ± 1.32 a
ABTS (μmol TE/g)
1.97 ± 0.34 b1.2 ± 0.21 b3.92 ± 0.47 a1.41 ± 0.41 b1.36 ± 0.31 b3.18 ± 0.26 a6.21 ± 0.52 b3.21 ± 0.65 c7.81 ± 0.57 a5.21 ± 0.41 b2.96 ± 0.42 c6.91 ± 0.67 a
Reducing power (μmol TE/g)
1.9 ± 0.15 b1.31 ± 0.21 b2.89 ± 0.33 a1.69 ± 0.42 b1.23 ± 0.38 b2.19 ± 0.19 a2.49 ± 0.51 b1.91 ± 0.44 c4.27 ± 0.56 a2.11 ± 0.37 b1.87 ± 0.31 b3.78 ± 0.3 6 a
Different letters (a, b, or c) given against each parameter, for each type, indicate significant differences (p ≤ 0.05).
Table 2. Content (mg/kg) and HCl-extractability (availability%) of minerals of raw, cooked, and digested white and brown rice.
Table 2. Content (mg/kg) and HCl-extractability (availability%) of minerals of raw, cooked, and digested white and brown rice.
White Rice
MineralsWhite-1 White-2
RawCookedDigestedRawCookedDigested
TotalAvailable TotalAvailable TotalAvailable TotalAvailable TotalAvailable TotalAvailable
Ca67.18 ± 1.45 b55.49 ± 0.62 e51.62 ± 0.96 f68.56 ± 0.77 b58.62 ± 0.46 d74.47 ± 1.23 a71.68 ± 1.68 a59.68 ± 0.62 d54.58 ± 0.99 e63.44 ± 0.82 c59.74 ± 0.78 c68.12 ± 0.47 b
Fe9.74 ± 0.21 a30.33 ± 0.36 e4.43 ± 0.43 c40.66 ± 0.55 c4.73 ± 0.47 c45.55 ± 0.99 a7.34 ± 0.34 b24.17 ± 0.66 f4.48 ± 0.25 c38.23 ± 0.47 d5.03 ± 0.51 c43.24 ± 0.79 b
Mg23.98 ± 0.81 a27.41 ± 0.45 e19.91 ± 0.98 c36.45 ± 0.39 c20.14 ± 0.79 c41.65 ± 0.59 a22.5 ± 0.67 b29.37 ± 0.48 d16.82 ± 0.69 d38.42 ± 0.57 b17.01 ± 0.88 d41.75 ± 0.98 a
Zn2.32 ± 0.12 a50.16 ± 0.81 d1.88 ± 0.13 b40.37 ± 0.58 f2.16 ± 0.48 a45.67 ± 0.78 e2.26 ± 0.07 a52.43 ± 0.44 c2.04 ± 0.17 a53.44 ± 0.78 b2.08 ± 0.42 a54.97 ± 0.98 a
Brown Rice
MineralsBrown-1Brown-2
RawCookedDigestedRawCookedDigested
TotalAvailableTotalAvailableTotalAvailableTotalAvailableTotalAvailableTotalAvailable
Ca86.24 ± 1.25 a53.57 ± 1.38 f68.67 ± 0.95 c65.15 ± 1.54 d69.71 ± 0.87 c68.16 ± 1.33 c82.62 ± 0.88 b57.35 ± 1.12 e65.28 ± 0.91 d71.34 ± 2.23 b68.71 ± 1.96 c74.86 ± 0.84 a
Fe11.65 ± 0.79 a28.46 ± 0.47 e6.12 ± 0.76 d39.11 ± 0.56 d7.03 ± 0.79 c41.88 ± 0.69 c9.44 ± 0.79 b24.17 ± 0.58 f5.89 ± 0.49 d44.31 ± 0.83 b7.08 ± 0.99 c47.16 ± 0.69 a
Mg43.58 ± 0.89 b20.38 ± 0.99 f34.89 ± 0.98 e28.25 ± 0.29 e36.87 ± 1.22 d32.05 ± 0.57 d56.85 ± 0.96 a36.25 ± 0.73 c41.19 ± 0.89 c56.46 ± 0.57 b42.95 ± 1.55 b58.75 ± 0.69 a
Zn3.83 ± 0.41 a47.13 ± 0.76 c2.89 ± 0.17 a41.34 ± 0.96 f2.97 ± 0.66 a43.97 ± 0.88 e4.18 ± 0.12 a45.55 ± 0.71 d3.09 ± 0.66 a61.48 ± 1.17 b3.88 ± 0.73 a63.67 ± 1.08 a
Values are means of three different samples ± standard deviation. According to Duncan’s multiple range tests, means without a common superscript(s) (a, b, c, d, e or f) in a row are substantially different, at p ≤ 0.05.
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MDPI and ACS Style

Alotaibi, S.H.; Babiker, E.E.; Alshammari, G.M.; Yahya, M.A. The Effect of Cooking and Simulated Digestion on the Antioxidants and Minerals in Rice Grains: A Predictor for Nutritional Efficiency. Agriculture 2024, 14, 1270. https://doi.org/10.3390/agriculture14081270

AMA Style

Alotaibi SH, Babiker EE, Alshammari GM, Yahya MA. The Effect of Cooking and Simulated Digestion on the Antioxidants and Minerals in Rice Grains: A Predictor for Nutritional Efficiency. Agriculture. 2024; 14(8):1270. https://doi.org/10.3390/agriculture14081270

Chicago/Turabian Style

Alotaibi, Shaker H., Elfadil E. Babiker, Ghedeir M. Alshammari, and Mohammed Abdo Yahya. 2024. "The Effect of Cooking and Simulated Digestion on the Antioxidants and Minerals in Rice Grains: A Predictor for Nutritional Efficiency" Agriculture 14, no. 8: 1270. https://doi.org/10.3390/agriculture14081270

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