A STUDY OF CELITE FILTRATION AND NEAR INFRARED POLARIMETRY FOR JUICE ANALYSIS

PREVIOUS work on celite filtration of juice samples and polarisation (pol) analysis using near infrared (NIR) wavelengths was carried out prior to ICUMSA extending the valid wavelength range to 900 nm in 1998. Systems developed for cane payment analysis had been forced to account for lack of recognition of NIR wavelengths for pol analysis, as well as uncertainty in relativity to recognised wavelengths, and quartz plate calibration. In 1998, new definitions for the specific rotary dispersion of quartz, and the relative rotary dispersion of sucrose solutions at different wavelengths between 546 nm and 900 nm were expressed. This project sought to examine whether celite filtration, followed by pol analysis at an NIR wavelength was suitable as a stand alone method for juice analysis in light of developments since previous work in this area was undertaken. Celite filtration was performed using a Schmidt and Haensch AutoFilt filtration apparatus. Schmidt and Haensch W2 polarimeter, 100 mm flow through polarimeter tube and quartz plate were used in this project, all having been BSES-certified. In order to reduce the potential for errors, a nominal wavelength of 882.60 nm was adopted as the standard in the Mulgrave laboratory, and used for all polarimeter analysis for juice, mud, bagasse, and sucrose by double pol, as well as in this project. A methodology for using the AutoFilt apparatus was developed prior to evaluation of the technique and comparison to the lead clarification method. Juice trials involved preparing duplicate samples of lead clarified and celite filtered juices. Data analysis indicated the 95% repeatability of the celite filtration method was virtually identical to the lead clarification method, with both corresponding to the figure quoted in BSES Method 2. It also suggested that the procedures followed in preparing juice samples using the celite filtration method caused an increase in pol reading of 0.057oZ over the original sample. In spite of this, the lead clarification method returned results on average 0.165oZ higher than the celite filtration method. Equity issues aside, use of the AutoFilt apparatus for celite filtration, with pol analysis at NIR wavelengths was confirmed as a potential alternative to the standard lead clarification method.