DEVELOPMENT OF NIRS METHOD FOR ENERGETIC VALUE OF HIGH FIBER CANE CLONES

Sypecar is a project carried out by Cirad which aims at studying high fibre cane for energetic valorisation. One component of this project deals with fast and easy assessment of raw material. Partner in the project, eRcane laboratory facilities have been equipped with a semi-automatic Near Infra-Red Spectroscopy (NIRS) device (CPS instrument from Bruker based on Matrix F) dedicated to fresh cane analysis. Usual method to determine sugarcane quality at eRcane consists in shredding stalk cane sample, pressing the resulting pulp in a hydraulic press and collecting plug and juice obtained. Then plug is weighed for determination of fibre content (fibre% cane) while juice is filtered for determination of dry content (known as brix) and sugar content (known as pol). Those information were collected for high fibre cane and were completed by moisture content (MC) and Net Calorific Value (NCV).
A calibration per component given by wet chemistry was developed. They were based on around 330 samples dataset from heterogeneous samples of the project Sypecar, including different varieties, two locations and varying ages. Calibrations were done on pre-treated spectra (first derivative and SNV) using PLS regression with the help of OPUS Software (Bruker Optic). Calibrations performances were estimated using calibration and validation sets, for this a random selection of 75% of the dataset was use for calibration and the 25% remaining samples were used for validation. The predictions exhibited reliable results, since the coefficients of determination (R2) of regressions between predicted and observed values exceeded 0.9 for all traits and Ratio Performance to Deviation (RPD=Standard deviation/standard deviation of residuals) were higher than 4. Brix calibration led to a SEP of 0,40%, with R² equal to 0,978, with non-significant bias (0.014), the corresponding standard error of laboratory (SEL) was 0,14%. The sugar (POL) calibration had a SEP equal to 0,60%, with R² equal to 0,974 and a non-significant bias (0,02), the SEL for Pol was 0.15%. The fibre calibration SEP was 1.84%, with a R² equal to 0,940 and a non-significant bias (-0.023), the SEL was 1.08 %. The cane moisture content SEP was 0,77% with a R² equal to 0,986 and non-significant bias (-0,049%). The SEL for MC was 0,29%. The calibration for Net Caloric Value led to a SEP equal to 279 Kj/Kg, a R² equal to 0,933 with a non-significant bias (-3.4). The NCV SEL was 100kj/kg, NCV minimum and maximum values were respectively 188 and 5022 Kj/Kg, with a SD equal to 1209Kj/Kg.
The calibration developed enables a rapid assessment of energetic potential for whole, fresh, shredded cane material. This is a major achievement in the Sypecar project.