Financial support: The research work was supported primarily by a project grant from the Government of India, Department of Biotechnology, Ministry of Science and Technology, New Delhi.

Keywords: cysteine proteinase, pineapple fruit extract, proteinase activity, tasar silk industry.

Abbreviations:
TCA: trichloroacetic acid;
NBFL: non-breakable filament length

Proteinases have the potential to effect partial solubilization of the proteinaceous gum sericin involved in binding the silk strands together in cocoon, an essential step in the silk cocoon cooking and reeling. Therefore, pineapple extract rich in cysteine proteinases was enzymologically characterized for its potential application in oak tasar (Antheraea proylei J.) silk cocoon cooking and reeling. Optimum sodium carbonate concentration (9.8 mM) and optimum temperature (60ºC) for the proteinase activity were determined. Though relatively thermostable, an enhanced activity loss was observed when the extract was incubated in the temperature range 70-90ºC with sodium carbonate. Bulk of the activity (80-83%) remained after 1 hr of time-dependent inactivation at 60ºC. The tasar cocoon extract neither caused inhibition of the activity nor enhanced its time-dependent loss by incubation at 60ºC. However, it caused an enhanced time-dependent loss of the activity by incubation at 60ºC with sodium carbonate. Considering these enzymological characteristics, experimental cocoon-cooking media were constituted by taking the pineapple extract with or without sodium carbonate at room temperature or 60ºC. The results of the cocoon cooking and subsequent single silk filament reeling indicated for an applicability of pineapple extract as an effective agent for the oak tasar cocoon cooking and reeling.