Citation
Thang, Yin Mee
(2021)
Monitoring chemical changes of binding carbohydrates and simulation of temperature profiles during sterilization of oil palm fruit bunches.
Doctoral thesis, Universiti Putra Malaysia.
Abstract
In a typical palm oil milling process, 30 tons to 60 tons of fresh fruit bunches are
processed together and this may cause difficulties for heat to penetrate especially to those
fruitlets located at the centre of a large and compact bunch. A complete detachment of
the fruitlets is possible only if the moist heat can reach the abscission zone of the fruits
to the stalk. A greater understanding of the fundamentals of fruit detachment is necessary
as it is shown that the strippability of the sterilized fruitlets would ultimately affect the
oil extraction rate.
The study began with the characterization of the binding carbohydrates at the abscission
zone of fruitlets before and after sterilization. Response surface methodology (RSM)
was applied to model the sugar compositions in sterilized fruits by varying the
parameters of pressures, sterilization time, and ripeness of FFBs. Finally, a heat transfer
modelling using sophisticated gPROMS software was conducted to provide insights into
the heat transfer mechanism inside the sterilizer and FFBs.
The FFBs were collected according to the number of empty fruit sockets: (i) nil; (ii) 1-9;
(iii) ≥10 as unripe, under-ripe, and ripe bunches, respectively. The PCA plots revealed
that the oligomers are the chemical markers that are responsible for differentiating the
ripe samples from the others. Both non-structural and structural sugars are the factors
that differentiate under-ripe samples from the rest.
All experiments showed some level of the detachment of sterilized fruits after the
sterilization. Low sterilization pressure or short holding time resulted in insufficient cell wall rupture, thus a high percentage of unstripped bunches. HPLC analysis showed that
large percentages of oligomers were observed in sterilized fruits, ranging from 2.05-
11.44 w/v%. Only about 0.15-1.19 w/v% of simple sugars were detected in sterilized
fruits. RSM optimization confirmed that oligomers could be used as a biomarker to relate
to fruits strippability after sterilization.
In addition, gPROMS has successfully predicted the temperature profiles in the
sterilization experiments. The simulation proposed that the sterilized fruits could only
be 100% stripped if the temperature of FFBs is kept above 48oC for at least 53.5 mins.
In addition, the oligomers content of sterilized fruits must be more than 3.8 w/v%. Under
this optimum condition, the rate of oil loss will be lower and the OER will ultimately be improved.
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