FIBRE DETERMINATION BY HYDRAULIC PRESSING—WHICH METHOD IS CORRECT?

ROUTINE ANALYSES of quality components of sugarcane for calibration development of near infra-red spectroscopic applications are enhanced if hydraulic press extraction of juice is used. This results in high-level extraction comparable to that achieved by the first mill in a commercial milling train. A bonus is that fibre also can be estimated with this process. Scepticism has been expressed within the BSES/CSIRO JV breeding team as to the correctness of the method used to determine fibre for the SpectraCaneTM calibration. This paper reports on research that establishes the relationship between two methods of determining fibre from hydraulic press data (Berding and Pollock, 1982 (FB&P), Tanimoto, 1964 (FT)) and fibre determined by a standard method (FB). Harvest samples were taken from a replicated final assessment trial containing 2 × 72 entries. Two sub-samples from a sample from each entry were processed to yield data for Brix, expressed juice weight, two fibre determinations (FB&P and FT), and polarimeter reading, all from hydraulic pressing, FB, and moisture content. Total analytical results were accurate with an average mass balance of 1000.9 g/kg. Use of two sub-samples per sample was satisfactory for all traits, with FB and expressed juice having the lowest error ratios of 6.8 and 6.2, respectively. Mean values for FB (138.1 g/kg) and FB&P (137.8 g/kg) were similar while that for FT was lower (127.2 g/kg). All fibre determinations were highly correlated, particularly FB&P and FT but their regressions against FB produced significantly different regression coefficients (t140 = 3.129**). Both regressions were skewed, with the latter being more so. The computation of FB&P adjusts the dry plug weight for residual Brix, taking into account hygroscopic water. The FT computation does not, which results in underestimation of fibre content, The FT estimates are consistently lower than FB&P and FB values, and so the FT methodology must be considered flawed.