Potential of calcium-chelating bamboo shoot peptides as a novel calcium supplement: preparation, structural characterization, physical properties, and bioactivities

Calcium, a micronutrient essential for maintaining structural integrity and metabolic regulation, constitutes 1.5 %–2.2 % of total body weight and is primarily acquired through dietary sources (Daengprok et al., 2003). However, national nutritional surveys conducted in China indicate a significant deficiency in calcium intake, as the average daily calcium consumption (400–500 mg/day) falls nearly 50 % below the threshold of 800 mg/day. Chronic suboptimal calcium intake poses significant public health risks, as calcium deficiency is implicated in skeletal pathologies such as rickets, osteopenia, osteoporosis, and osteomalacia (Bass & Chan, 2006). Moreover, emerging evidence links inadequate calcium levels to systemic conditions, including hypertension (Verstappen, 2022; Wilson & Metzler-Wilson, 2015) and, notably, in women, heightened risks of breast cancer, ovarian cancer, and premenstrual syndrome (Chen et al., 2021; Chew & Clarke, 2018).

Maintaining adequate calcium supplementation is crucial not only for skeletal health but also for the proper functioning of numerous physiological processes. Various calcium supplements have been developed to address calcium deficiencies. Inorganic calcium salts, such as calcium carbonate and calcium chloride, are cost-effective and contain a high calcium content. However, poor solubility and gastrointestinal (GI) irritability often lead to adverse effects including abdominal discomfort, arteriosclerosis, and nephrolithiasis (Ackley et al., 1983; Heaney, 2000). Organic calcium salts, such as calcium citrate, exhibit improved solubility and absorption rates; however, lower calcium levels and excessive consumption may still induce GI disturbances (Martin et al., 2002). Scientists have developed amino acid–chelated calcium, which partially resolves solubility and bioavailability challenges but faces high cost, instability, and potential long-term risks of negative nitrogen balance (Chen et al., 2014; Kitts & Weiler, 2003; Straub, 2007). By contrast, peptide-chelated calcium, which is formed by the binding of calcium to bioactive peptides (derived from protein hydrolysis), offers superior stability and potential bioavailability. The neutral charge of peptide–calcium chelates often facilitates efficient intestinal absorption (Alpers, 1986; Jung & Kim, 2007) and is more effective than inorganic calcium salts at restoring bone quality in calcium-deficient animal models (Huang et al., 2011). Furthermore, this form provides dual nutritional benefits by delivering both bioavailable calcium and functional peptides, highlighting its clinical potential (Tian et al., 2025).

Numerous studies have explored the use of food-derived peptides to synthesize calcium-chelating peptides or peptide–calcium chelates, highlighting their potential as next-generation supplements (Qu et al., 2022; Zhang et al., 2023). Cai et al. found that the addition of short peptides can effectively protect calcium ions from forming precipitates with dietary inhibitors such as tannic acid, oxalate, phytates, and metal ions (Cai et al., 2017). In rat experiments, skipjack tuna protein peptide-chelated calcium not only promoted weight gain in rats and inhibited ALP activity but also increased the calcium absorption rate, enhanced bone mineral density, improved trabecular microstructure, and promoted bone growth and development (Yang et al., 2024). In addition, some of these peptides may exhibit multiple biological activities, including antioxidant, antimicrobial, immunomodulatory, and lipid-lowering effects, highlighting their great potential as ingredients for nutraceuticals and functional food applications.

With the growing interest in plant-based protein sources, forest-based proteins are increasingly being explored to produce high-quality protein and peptide ingredients, including those for calcium delivery (Hu et al., 2024; Liu et al., 2013). Bamboo shoots, which are abundant in China and India, are a promising sustainable nutritional resource for feeding the future human population and ensuring food security, owing to their fast growth and maturation, short production cycle, and high nutritional value. The protein content of bamboo shoots ranges from 14.9 to 40.4 g/kg (fresh weight) to 190.1–351.0 g/kg (dry weight) (Wang et al., 2020), which is significantly higher than that of other vegetables or cereals (Zhang et al., 2024). The essential amino acids (EAA) in bamboo shoot are even comparable to those in fish protein (Wang, Wang, Liu, Li & He, 2011). Moreover, bamboo shoots are particularly rich in aspartic acid, glutamic acid, and serine, which exhibit strong affinities for calcium, making them ideal raw materials for the production of peptide-chelated calcium (Zhang et al., 2024). In our previous study, bamboo shoot protein extraction was optimized using commercial protein extraction methods combined with ethanol-enhanced solvent extraction. These advancements support the development of calcium-chelating peptides using bamboo shoot proteins (Xiao et al., 2024).

Therefore, in this study, a peptide–calcium chelate (BSH–Ca2+) was prepared using bamboo shoot hydrolysates, and the conditions for efficient calcium delivery were optimized. The structural characteristics, chelation mechanism, and functional properties of BSH and BSH–Ca2+ were investigated to confirm the successful preparation and optimization using a multi-technique analytical approach (Fig. S1). The findings highlight the dual functionality of BSH–Ca2+ for efficient calcium delivery and potent antioxidant activity, which is promising for future functional foods.