Using near infrared spectroscopy (NIRS) for rapid determination of oil content in dried oil palm mesocarp

The bunch analysis technique is widely used for studying bunch and fruit traits of oil palm frees by oil palm breeders. The bunch analysis method as first proposed by Blaak et. al. (1963) has been reviewed many times over the years but remained basically the same with minor modifications, especially in the sub-sampling procedures. The whole procedure is laborious and time-consuming. One of the important stages of bunch analysis is the oil content determination which is traditionally conducted using Soxhlet extraction method. Due to the toxicity and harmfulness of N-Hexane as employed in the Soxhlet oil extraction procedure, an alternative method more environment-friendly and rapid will be most welcomed by oil palm breeders. In this paper, we share our experience in the development and employment of near infrared reflectance spectroscopy (NIRS) for rapid, high accuracy, precision and minimal chemical risk method for the determination of oil content of dried oil palm mesocarp. A total of 2,891samples were collected during four years (2013 to 2016). The oil content of each sample was determined by the conventional Soxhlet extraction method and, correspondingly, its corresponding NIRS reflectance obtained by scanning using NIRS instrument (XDS -FOSS). Samples of varying oil contents ranging from 1.3 and 88.0% on dry matter basis were used. These data were further analysed and processed chemometrically to develop and test various calibration models. By using modified partial least square (MPLS) regression, data sets of each year (2013, 2014 and 2015) and its combination were used to generate four calibration models i.e. K-13, K-14, K-15 and K-13-14-15. For model assessment, external validation was conducted using samples of 2016. Oil contents of validation samples determined by Soxhlet extraction and those generated by NIRS calibration models were compared and studied statistically. The results showed that the model generated from the combination data sets (K-13-14-15) provided the best fit with r² = 0.977, SEP= 1.42, and RPDp = 6.27. The correlation between reference and predicted values of validation samples were in agreement with high linearity, accuracy and robustness. The results demonstrated that NIR spectroscopy can be used as an alternative. rapid and reliable technique to estimate the oil content in the mesocarp. NIRS is being routinely used in our bunch analysis laboratory as an alternative to the Soxhlet oil extraction method which is currently being employed in most bunch analysis laboratories.