Plant-Based Functional Custard Enriched with Vitamin D3: Insight into Technological Properties, Nutrition and Bone Tissue Regeneration

A plant-based or vegan diet is considered one of the most important dietary patterns, often followed for religious or health reasons. It should contain vital nutrients such as protein, iron, zinc, calcium, vitamin D, and others. The objective of this study was to produce a plant-based food product with high nutritional value (vegan custard, VC) and fortify it with vitamin D3 (vegan custard + D3). Thirty-five female albino rats, with an average body weight of 160 ± 5 g, were divided equally into five groups (seven rats per group): Negative control group: Rats were fed only on a normal-calcium diet. Positive control group: Rats were fed only on a low-calcium diet. Group I: Low-calcium diet supplemented with 10% commercial custard; Group II: Rats were fed a low-calcium diet supplemented with 10% vegan custard; Group III: Rats were fed a low-calcium diet supplemented with 10%-D3-fortified vegan custard. The quality, nutritional values, and calcium bioaccessibility of the custard samples were compared with commercial custard. The effect of feeding rats all types of custard on body changes, as well as certain serum biochemical markers such as calcium, parathyroid hormone (PTH), calcitonin, tartrate-resistant acid phosphatase (TRACP), and alkaline phosphatase (ALP), was assessed. Additionally, femur calcium content and bone tissue improvement were histologically examined. Results showed that the innovative vegan custard samples (VC and VC+D3) achieved the highest scores in consumer palatability, nutritional value, and manufacturing properties. Notably, the D3-fortified vegan custard increased calcium bioaccessibility by up to 85.3% and can provide 333.3% of the daily vitamin D requirements per approximately 100 g. The product also provides 3.12–4.40% of the recommended daily calcium intake per 100 g, depending on age-specific requirements. Furthermore, histological investigations and histomorphometric evaluations revealed significant improvements in femoral bone tissue improvement. Finally, a daily serving of vegan custard prepared from 30 g of D3-fortified custard powder is recommended to meet vitamin D requirements.