Optimisation of sterilisation process for oil palm fresh fruit bunch at different ripeness

The optimisation of fresh fruit bunch (FFB) sterilisation process was studied using different degree of FFB ripeness (i.e. under-ripe, ripe, overripe) and loose fruits. This study was carried out with the application of Response Surface Methodology (RSM), based on the interrelation between process temperature (X1; 100 to 120oC) and time (X2; 20 to 80 min) used for FFB sterilisation process on Free Fatty Acid, FFA (Y1,underripe FFB; Y2,ripe FFB; Y3,Overripe FFB; and Y4,loose fruits). Thirteen experimental runs were conducted per degree of ripeness using laboratory scale steriliser with varying sterilisation temperature and time, as generated by Central Composite Rotatable Design (CCRD). Raw experimental data trend showed substantial FFA increment with the increment of FFB maturity. Four polynomial models were found appropriate to predict the responses within experimental regions. Analysis regarding factor influences on each response was performed using Analysis of Variance (ANOVA) and graphical analysis. For under-ripe and ripe FFB, the temperature exerted higher and significant (p<0.05) influence on FFA values as compared to time. However, as the fruit ripen, both temperature and time were found similarly strong in affecting the FFA due to highly significant p-value of interaction model term, X1X2 for both overripe FFB and loose fruits. Optimum sterilisation operating conditions corresponding to FFA content were also successfully determined using numerical optimisation method. Results revealed the optimum conditions for underripe FFB and ripe FFB at the combination of 100oC for 20min and 100oC for 80min, respectively. Both overripe FFB and loose fruits recorded similar optimum condition, i.e. 120oC and 20 min. The computed optimum conditions have resulted relatively low FFA values at 0.619%, 1.052%, 1.751% and 3.160% for each Y1, Y2, Y3, and Y4. The verification experiments were performed and the results were found satisfactory. Small standard deviation values were calculated indicated the actual values was in close agreement with the model prediction. This study has showed promising potential of extracting good quality CPO from other degrees of FFB ripeness as long as the right combination of FFB sterilisation operating condition were used during the extraction process.