Process optimization for efficient extraction of soluble calcium from fishbone assisted by induced electric field

Abstract: Abundant wasted animal bone is left after processing of meat products, which is a major challenge for engineers to develop an economic and efficient technique to recycle these byproducts. Valuable compounds such as carbohydrates, minerals and amino acids can be extracted from waste biomasses using the electric-field-assisted processing technique. However, there is no report on the electric-field-assisted processing of agricultural byproducts based on the inductive methodology. Therefore, this study was aimed to develop and implement the induced electric field to process these materials. A purpose-made reactor based on the single-phase transformer structure was designed, built and used to assist with the efficient extraction of soluble calcium. The system is composed of power source, thermostatic circulating water bath, silicone steel chip, glass spring (the support tube of the secondary coil), primary coil, solvent inlet, glass chamber, sample inlet, jacket shell and 100-mesh sand core. Acid solvents acted as the secondary coil conductor with the turn number of 16, which was connected to the glass chamber to form a closed loop. Each time, dried fish bone powder was placed through the inlet into the glass chamber. Distilled water (pH value of 1.5, 2.5 and 3.5) was then added from the inlet into the chamber to immerse the samples, ensuring the glass spring was filled with the solution without forming any air bubble. The pH value of the solvent was adjusted with hydrochloric acid. When a sample was added to the solution, the solid-liquid ratio was 1:2, 1:3, 1:4, 1:5 or 1:6 g/mL. The operation of the system involved an excitation voltage (0-200 V) at varying frequency applied on the primary coil (turn number was 120) winding along the core. Then an alternating magnetic flux was generated in the silicone steel chip. Ultimately, an alternating induced electric field was formed in the glass chamber to assist the sample processing. The glass chamber had an external jacket shell with an outlet and inlet, so the temperature of the reaction system could be maintained using the thermostatic circulating water bath (25-80 ?C). The electric field frequency ranged from 400 to 700 Hz. The samples were taken out at regular time during the extraction and the soluble calcium content was examined. Meanwhile, a control was set, in which soluble calcium was extracted under the same conditions but without the addition of excitation voltage. Results showed the calcium yield was improved with the increase of excitation voltage, and increased by 224.25% at 160 V and 450 Hz compared with the control (without voltage) under the condition of the pH value of 2.5, the solid-liquid ratio of 1:5 g/mL and the temperature of 50 ?C for 25 min. Lower pH value was more conducive to the dissolution of calcium ion when the excitation voltage was constant. Electric field frequency had a negative effect on the yield of soluble calcium. Optimum parameters of the electric-field-assisted extraction of soluble calcium were 160 V, 450 Hz, pH value of 1.5 and solid-liquid ratio of 1:5 g/mL. The influence order of the processing parameters was as follows: excitation voltage > pH value > solid-liquid ratio > electric field frequency. This research provides a potential method based on inductive methodology for rapid extraction of valuable compounds from agricultural byproducts.