Abstract:

The relationship between structural changes and bromelain activity was investigated. After bromelain was treated
at various pressure levels, its secondary structure changes were observed by Fourier transform infrared spectroscopy (FTIR),
its tertiary structure changes were examined by fluorescence spectroscopy, and its activity was tested using Folin phenol
method. The results showed that compared with the control group (0.1 MPa), the bromelain activity significantly changed
after treatment at 37 ℃ for 20 min at 100-500 MPa (P ＜ 0.05). The maximum level (3 524 U/g) of bromelain activity was
observed after treatment of the enzyme at 200 MPa, representing a 8.29% increase over the control group. Moreover, the
treated enzyme displayed a 2.76-fold increase in β-sheet content as analyzed by Fourier transform infrared spectroscopy. The
maximum endogenous fluorescence spectral intensity of 4 934 was found at excitation wavelength of 280 nm. Therefore,
bromelain activity is related to the β-sheet content and the exposure degree of Tyr residues.

Key words: ultra high static pressure, bromelain, enzyme activity, conformation, infrared spectroscopy, fluorescence spectroscopy