Bromelain Precipitation Temperature Control: Development and Experimental Testing
In this work, bromelain was recovered from triturated pineapple stem and rind (usually kitchen waste) through the precipitation process with alcohol at a low temperature. Bromelain is the name of a group of powerful protein-digesting, or proteolytic, enzymes that are particularly useful for reducing muscle and tissue inflammation and as a digestive aid. Temperature control is crucial to avoid the irreversible protein denaturation (upper bound for bulk temperature is 10ºC) and consequently to improve the precipitation yield. The process was carried out in a fed-batch stirred tank (500mL), so that its dynamic nature would present a challenging control system design. Samples containing 100mL of pineapple "juice" were fed into the tank. A micropump was employed to continuously feed the alcohol (ethanol 99.5%) into the tank, at room temperature, until the volume reached 500mL. Inside the jacketed tank, the protein was exposed to a range of unsteady operating conditions during the addition of the precipitating agent. The precipitated material will form at different rates. In order to avoid protein denaturation, the coolant flow rate was manipulated through a variable speed pump. Conventional and adaptive PID controllers were properly designed and on-line implemented through a fieldbus digital control system. Data obtained from these experiments were used to train an artificial neural network (ANN) and results show that the neural model was able to "learn" the action of feedback controllers.