S/O/W-based milk mineral-fortified emulsion: a delivery platform offering stability, enhanced bioavailability, and bone health support.

Milk minerals (MMS) are a superior natural calcium source limited by poor dispersibility and stability. Although solid-in-oil-in-water (S/O/W) emulsions improve their stability and in vitro bioaccessibility, their in vivo efficacy remains unconfirmed. This study evaluated the efficacy of S/O/W-based MMS-fortified emulsions (MFEs) in enhancing calcium absorption and bone health using an ovariectomized (OVX) and low-calcium rat model. Over an 8-week period, rats were divided into a sham-operated group and several OVX groups. The OVX rats were randomized into seven subgroups receiving ultrapure water, alendronate (ALN, 1 mg/kg bw), CaCO₃ (Ca2+: 133.3 mg/kg bw), or low and high doses (Ca2+: 66.65 and 133.3 mg/kg bw, respectively) of MMS or MFEs. Compared to the low-dose MMS group (MMS-L), the low-dose MFEs group (MFEs-L) significantly increased calcium absorption by 17.06% and the retention rate by 18.35% (p < 0.05). Furthermore, MFEs-L improved bone mineral density (BMD) by 20.21%, preserved trabecular microarchitecture, enhanced bone biomechanics, and reduced osteoclast numbers. Additionally, MFEs upregulated tight junction proteins (ZO-1 and Occludin) and improved intestinal transit, alleviating the constipation typically caused by traditional calcium supplements. Concurrently, MFEs modulated the gut microbiota composition by enriching beneficial taxa, such as the Bacillota, Bifidobacterium and Lactobacillus, and promoted short-chain fatty acid (SCFA) production. These results indicate that S/O/W-based MFEs represent a promising dietary delivery strategy for MMS, effectively enhancing calcium bioavailability, supporting bone health, and alleviating constipation.