Characterization and Potential Application of Bromelain from Pineapple (Ananas comosus) Waste (Peel) in Recovery of Silver from X-Ray Films

Bromelain is a proteolytic enzyme, which is predominately found in all parts of a pineapple plant (Ananas comosus). It has immense application in the pharmaceutical industry as well as in food, cosmetic, and leather industries. However, bromelain from pineapple fruit peels is a less explored source for making valuable products. Therefore, the objective of this study was to characterize and investigate the potential application of bromelain enzyme extracted from pineapple juice processing waste peels in gelatin hydrolysis and removal of silver from X-ray films. Extraction of bromelain was performed with a 1 : 2 ratio (w/v) of the extraction mix, pineapple fruit peel, in phosphate buffer (pH = 7.0). The activity of a crude enzyme was 7.2 U/ml, and it was active in a broad range of pH (2.5–12) and temperature (25–85°C) without losing its activity. This implies that the enzyme is heat tolerant. The optimum temperature and pH of the enzyme were recorded at 70°C and pH 7.0, respectively. At optimum conditions (70°C and pH 7.0), complete hydrolysis of the gelatin layer from X-ray film was observed at 30 and 34 seconds, respectively. The enzyme was repeatedly used more than 50 times without significant loss of its activity. Using a minimum concentration of bromelain (3 ml = 21.6 U) along with phosphate buffer (37 ml), it is possible completely to remove gelatin within 210 seconds. The properties of the enzyme showed that it has promising potential industrial applications for repeated utilization of the enzyme in both silver recovery and recycling of the X-ray film base.