The potential of bamboo seeds for natural biofortification of dietary zinc and iron

Iron (Fe) and zinc (Zn) are essential micronutrients for human health; deficiencies lead to anemia, impaired immunity, and developmental issues, particularly affecting preschool children and pregnant women in low-income regions. Strategies to address Fe/Zn malnutrition include supplementation, food biofortification, reducing anti-nutrients (e.g., phytate, tannins), and dietary diversification. Bamboo seeds are occasionally consumed in parts of Asia and may offer high nutritional value. Prior work showed high Fe and Zn in Moso bamboo seeds, but their bioaccessibility/bioavailability and cellular localization were unclear. This study aimed to: (i) confirm Fe and Zn concentrations in Moso bamboo seeds collected from different sites, (ii) evaluate Fe and Zn bioaccessibility and bioavailability versus rice, including the effect of boiling, and (iii) determine Fe and Zn cellular localization in the seeds.

Seed materials: Wild-type Moso bamboo (Phyllostachys edulis) seeds were collected from three sites in Guangxi, China: Haiyang County (25°18′N, 110°33′E; 1601 mm precipitation; 17.5 °C), Fusui County (22°57′N, 107°03′E; 1300 mm; 21.7 °C), Lingchuan County (25°48′N, 110°07′E; 1941 mm; 18.7 °C). Soils (krasnozem, pH 4.4–5.6) had available Fe 15.9–81.3 mg kg−1 and Zn 0.8–1.9 mg kg−1. Rice (Oryza sativa cv. Nipponbare) was used as control. Elemental determination: Seeds were dried at 70 °C for 3 days, microwave-digested (3 mL HNO3 + 3 mL H2O2 up to 180 °C), diluted, and Fe/Zn quantified by ICP-MS (Thermo Scientific X Series 2). In vitro gastrointestinal digestion for bioaccessibility/bioavailability: Ground raw or boiled seeds (boiled 1.5 h in deionized water) were subjected to a simulated digestion protocol (after Coelho et al., 2021, with slight modifications). Oral phase: 200 µL of 1% α-amylase in pH 6.8 NaHCO3 buffer. Gastric phase: 3 mL of 0.5% pepsin at pH 1.2 (HCl-adjusted), 37 °C, 70 rpm, 2 h. Intestinal phase: 3 mL of 3% pancreatin + 2.5% bile salts in pH 7.4 NaHCO3 buffer; a 14 kDa MWCO dialysis membrane containing pH 7.4 NaHCO3 was inserted; 37 °C, 70 rpm, 2 h. After chilling on ice, the inner dialysate (bioavailable fraction) and outer supernatant after centrifugation at 4000 rpm for 10 min (bioaccessible fraction) were collected. Blanks were included. Fe/Zn in both fractions measured by ICP-MS. Anti-nutrient assays: Phytic acid (PA) quantified via Wade reagent method after HCl extraction and spectrophotometry at 500 nm; PA:Fe and PA:Zn molar ratios calculated. Tannins extracted with 60% ethanol and quantified colorimetrically using Folin phenol/Na2CO3 with absorbance at 700 nm. Histochemical localization: Seeds were soaked 2 days at 4 °C and sectioned at root primordium, shoot primordium, and endosperm. Fe localization by Prussian blue staining; Zn by dithizone staining. Sections imaged under stereo microscope. Elemental mapping: LA-ICP-MS (Agilent 8900; NWR213 laser) on 40 µm longitudinal and transverse cryosections (−15 °C sectioning; dried at −20 °C). Elemental images generated using iQuant2; carbon used as control for tissue distribution. Statistics: Data presented as mean ± SD with n reported per assay; one-way ANOVA with Tukey’s test; significance at P < 0.05.

- Fe and Zn concentrations: Moso bamboo seeds contained higher Fe (45.6–56.2 mg kg−1; mean ~50.9 mg kg−1) and Zn (71.6–84.9 mg kg−1; mean ~79.0 mg kg−1) than rice (Fe ~20.8 mg kg−1; Zn ~42.8 mg kg−1). - Bioaccessibility and bioavailability: In vitro Fe bioaccessibility in bamboo seeds was ~25.1–25.6 mg kg−1 and significantly higher than rice; Fe bioavailability was also significantly higher than rice. Zn bioaccessibility in bamboo was ~18.6–22.8 mg kg−1 and Zn bioavailability was significantly higher than rice. Abstract-level fold increases versus rice: Fe bioaccessibility and bioavailability 1.6× and 1.7×; Zn bioaccessibility and bioavailability 1.9× and 2.6×, respectively. - Effect of boiling: Boiling reduced both bioaccessibility and bioavailability of Fe and Zn in bamboo seeds and rice; despite reductions, bamboo remained higher than rice. - Anti-nutrients: Bamboo seeds had significantly lower phytic acid than rice (6.7–7.8 mg g−1 vs 16.7 mg g−1). PA:Fe molar ratios in bamboo were 11–12:1 vs 68:1 in rice; PA:Zn 8–9:1 vs 38:1 in rice, indicating PA likely not the main inhibitor in bamboo. Tannins were higher in bamboo (0.77–1.31 mg g−1) than rice (0.46 mg g−1); after boiling, ~80% PA degraded while ~23% tannins degraded, implicating tannins as a key inhibitor of Fe/Zn bioaccessibility in bamboo. - Localization: Histochemical staining and LA-ICP-MS mapping showed Fe and Zn predominantly localized in the embryo and aleurone layer; Zn also accumulated in the groove region (transfer cells/crease vascular bundle). Starchy endosperm contained much less Fe/Zn. - Site comparisons: Seeds from three geographic sites consistently showed higher Fe and Zn than rice, suggesting external environmental variability was not the primary driver of high accumulation.

The study demonstrates that Moso bamboo seeds naturally contain substantially higher Fe and Zn than major cereals such as rice, maize, and wheat, and that these minerals are comparatively more bioaccessible and bioavailable in vitro. Although cooking (boiling) reduces measurable bioaccessible and bioavailable fractions, bamboo seeds still outperform rice. Lower phytic acid and favorable PA:Fe and PA:Zn ratios suggest PA is not the major inhibitor in bamboo; higher tannins levels, with limited degradation upon boiling, likely contribute to reduced bioaccessibility/bioavailability relative to total content. Elemental localization in the embryo and aleurone layer indicates that processing that preserves these tissues (analogous to brown vs white rice) would maximize micronutrient retention and potential human uptake. Consistent high Fe/Zn across three sites implies that intrinsic plant factors (e.g., transporter expression, internal allocation) may underlie the high accumulation, though mechanisms in bamboo remain to be elucidated. Collectively, findings support bamboo seeds as a promising dietary resource for natural Fe/Zn biofortification, particularly in contexts where dietary diversity is limited.

Moso bamboo seeds are rich in iron and zinc and exhibit higher in vitro bioaccessibility and bioavailability of these minerals than rice. Although boiling reduces these metrics, bamboo seeds still retain advantages over rice. Lower phytic acid and higher tannins content indicate tannins as a likely key inhibitor, while mineral localization to embryo and aleurone layer suggests processing strategies should preserve these tissues to optimize micronutrient intake. Bamboo seeds may serve as a valuable food resource for natural Fe and Zn biofortification. Future research should investigate the physiological and molecular mechanisms (e.g., transporter systems) underpinning high Fe/Zn accumulation in bamboo and evaluate in vivo bioavailability and the impacts of diverse processing methods.

- Bioavailability assessed via in vitro digestion; no in vivo human or animal absorption studies were conducted. - Only one processing method (boiling) was evaluated; other culinary processes were not tested. - Samples were collected from three sites with similar climates; broader environmental variability and soil/microbiome influences were not fully characterized, and microbial community data were not available. - Mechanistic underpinnings (e.g., specific Fe/Zn transporters in bamboo) were not examined. - The study focused on Fe and Zn; potential interactions with other nutrients and anti-nutrients were not comprehensively assessed.