Optimized extraction of calcium malate from eggshell treated by PEF and an absorption assessment in vitro

Under optimized pulsed electric field (PEF) treatment for production of eggshell calcium malate (ESCM) by one-factor-at-a-time test and ternary quadratic regression orthogonal combination design (TQROCD), an absorption assessment of ESCM treated by the best conditions of PEF were performed in male mice with apparent calcium absorption rate (ACAR), serum alkalinity phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP), serum calcium and serum phosphorus, length of femurs and skeletal calcium content were studied. The highest dissoluble calcium malate content (7.075 mg/mL) was obtained with the 6.0% malic acid, the electric field intensity of 20 kV/cm, and pulse duration of 24 μs. In vitro, ESCM prepared by the best conditions of PEF at doses of 133.0 mg kg(-1) d(-1) for 70 d not only significantly improve the ALP activity, the femur length and calcium content of bone of the mice (P<0.05) but also decreased the levels of TRAP (P<0.05). The ratio of calcium and phosphorus was in the normal range. PEF could be taken as a highly effective, environmentally friendly and energy-saving method for preparation of ESCM, which treated by PEF could promote the absorption of calcium in vitro, extraordinary can promote bone development and a healthy bone.