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Postharvest Fruit Detachment in Oil Palm Bunches with Ethephon and
Ethylene Gas Application Postharvest Fruit Detachment in Oil Palm Bunches
with Ethephon and Ethylene Gas Applicat...
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DOI: 10.3390/agriculture11111030
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2. agriculture
Article
Postharvest Fruit Detachment in Oil Palm Bunches with
Ethephon and Ethylene Gas Application
Arutchelvam Balakrishnan, Mohd Ibnur Syawal Zakaria, Bee Aik Tan * , Jaime Yoke Sum Low, Shwu Fun Kua,
Chin Ming Lim and David Ross Appleton
Citation: Balakrishnan, A.; Zakaria,
M.I.S.; Tan, B.A.; Low, J.Y.S.; Kua, S.F.;
Lim, C.M.; Appleton, D.R.
Postharvest Fruit Detachment in Oil
Palm Bunches with Ethephon and
Ethylene Gas Application. Agriculture
2021, 11, 1030. https://doi.org/
10.3390/agriculture11111030
Academic Editor: Giacomo Cocetta
Received: 8 September 2021
Accepted: 8 October 2021
Published: 21 October 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
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iations.
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Sime Darby Plantation Technology Centre Sdn Bhd, Serdang 43400, Malaysia;
arutchelvam.b@simedarbyplantation.com (A.B.); ibnur.syawal.zakaria@simedarbyplantation.com (M.I.S.Z.);
jaime.low.yokesum@simedarbyplantation.com (J.Y.S.L.); kua.shwu.fun@simedarbyplantation.com (S.F.K.);
lim.chin.ming@simedarbyplantation.com (C.M.L.); david.ross.appleton@simedarbyplantation.com (D.R.A.)
* Correspondence: tan.bee.aik@simedarbyplantation.com; Tel.: +60-3-8942-2641
Abstract: The processing of oil palm fresh fruit bunches (FFB), together with loose fruits, in the
current mill operation contributes to oil loss and high free fatty acids (FFA), affecting crude palm oil
quality. Fruit detachment induced by ethephon and ethylene may mitigate the current processing
issues. This study shows that a 0.50% (v/v) ethephon application by the evaporation method
induced the highest fruit detachment of 30.8 ± 1.1% after 24 h at room temperature, with the FFA
content in the extracted crude palm oil at 0.34 ± 0.09%. Ethephon application was effective on
bunches between 14 and 28 kg, and fruit detachment was higher in ripe and underripe bunches
at 24.1 ± 0.9% and 23.2 ± 0.1%, respectively. A significant fruit detachment of 47.2 ± 2.4% was
achieved when the bunches were also stripped mechanically, but the FFA content increased almost
4-fold, from 1.0 ± 0.2% to 3.8 ± 1.2%. The application of ethylene gas at 750 ppm yielded 29.4 ± 1.9%
fruit detachment. The findings present the possibility of using ethylene as an indirect method for
minimizing oil loss without increasing the FFA content in future crude palm oil production systems.
Keywords: oil palm; fresh fruit bunches; postharvest treatment; ethephon; ethylene; fruit detachment;
crude palm oil; free fatty acids; oil quality
1. Introduction
Conventionally, oil palm (Elaeis guineensis) milling involves the processing of fresh
fruit bunches (FFB) that arrive from the estates and are transported to the mill. FFB and
loose fruits (LF) on the ground are collected and transported to mills for crude palm oil
(CPO) production. The harvesting, transporting, and dumping of FFB from ramp to mill
conveyors often damages the fruits and triggers the release of endogenous lipases, the
enzymes responsible for the hydrolysis of triglycerides to free fatty acid (FFA) [1,2]. The
bruises caused by the bunch-to-bunch impact and the bunch-to-conveyor friction further
elevate the formation of FFA, depending on the conveyor length and mill design. In
practice, achieving a balance between maximizing the oil yield and maintaining oil quality
within the commercial limits of 5% FFA [3] are critical to plantation and mill operations.
FFB mixed with LF ends up in the sterilizer cage, where sterilization deactivates the
lipolytic enzymes and restricts the FFA content from increasing further in the fruits. How-
ever, sterilizing FFB and LF together in batches under the same conditions is unfavorable,
as it leads to the overcooking of the LF. Oil seepage is higher in overcooked fruits, and the
oil is either absorbed by the empty fruit bunches (EFB), or lost in the sterilizer condensate,
resulting in a lower oil extraction rate (OER) [4]. The OER is one of the key factors in
determining the performance of a mill. Therefore, efforts to reduce oil loss due to empty
fruit bunch (EFB) absorption, while maintaining good CPO quality during the sterilization
step, are needed. Furthermore, the CPO extracted from the LF collected from the field have
significantly higher FFA due to the delays in LF collection and processing.
Agriculture 2021, 11, 1030. https://doi.org/10.3390/agriculture11111030 https://www.mdpi.com/journal/agriculture

3. Agriculture 2021, 11, 1030 2 of 10
In the future, for oil palm mill design, the most ideal process would be to sterilize
the fruits, which are detached from the FFB without EFB [5]. On top of that, separate
LF collected from the estates, and overripe FFB, should also be processed separately to
avoid spoilage of the good CPO quality, since the LF and overripe bunches are commonly
the largest contributor to high FFA content and low CPO quality. Currently, there are
no suitable mechanical methods for removing oil palm fruits from the bunches before
sterilization, as it tends to be too harsh and can cause significant damage to the resulting
detached fruits. Alternatively, fruit detachment can be induced by treating the bunches
with ethylene, a natural plant hormone that promotes ripening in climacteric fruits [6–10]
and initiates fruits abscission [11,12]. It was demonstrated that the postharvest treatment of
oil palm FFB with exogenous ethylene was able to enhance fruit detachment and increase
oil yields with lower FFA content [13].
Commercially, ethylene is available either as pure gas or from a synthetic releasing
compound, such as ethephon (2-chloroethanephosphonic acid) [14]. The hydrolysis of
ethephon at greater than pH 5 yields ethylene, chloride, and phosphate [15]. The use of
ethephon for inducing fruit abscission has been demonstrated in peaches [15], mangoes [16],
and grapes [17]. Although some studies have shown that ethephon was able to loosen oil
palm fruits, and significantly reduce the force needed for fruit detachment, the details of
the underlying mechanisms were not known [18,19].
In this study, we further investigate the factors affecting ethephon efficacy on posthar-
vest oil palm FFB processing, and the optimum application dosage on the detachment rate.
A study was also conducted to compare the effectiveness of using ethephon and ethylene
gas for oil palm fruit detachment.
2. Materials and Methods
2.1. Fruit Materials
‘Tenera’ variety oil palm fresh fruit bunches were harvested from commercial fields
in Banting and Carey Island, Malaysia. Only bunches that had undergone color change
(from deep violet to yellowish orange), and weighing between 14 and 28 kg, were selected
for this study. Bunch ripeness was determined according to the number of empty sockets
resulting from the freshly detached fruits. The bunches were transported to the research
facility within two hours of harvesting.
2.2. Ethephon Treatment
The first phase of the study was designed to determine the optimal conditions for
ethephon treatment, including the application method, dosage, and incubation period.
Ethephon treatment was performed on individual ripe bunches, and each treatment con-
sisted of five replicates (n = 5). The bunches were individually placed inside a covered
incubation box (V = 150 L), slightly elevated from the bottom using a metal rack.
Ethephon was prepared as an aqueous solution (200 mL, pH 9) and the initial dosage
was fixed at 0.50% (v/v). Two application methods were tested, namely, spraying and
evaporation. In spraying, ethephon was applied directly onto the bunches using a hand
sprayer, while for evaporation, ethephon was poured into the box and allowed to evaporate.
No ethephon was applied to the control bunches (untreated). The bunches were incubated
at room temperature for 24 h. Once a suitable application method was established, the
ethephon dosage was varied at 0.25% (v/v), 0.50% (v/v), and 1.00% (v/v). The decomposi-
tion of ethephon into ethylene was measured using a portable gas detector (PG610, Henan
Inte Electrical Equipment Co., Ltd., Zhengzhou, China). The dosage with the highest fruit
detachment was used for the remainder of the study. Subsequent treatments were carried
out with 6 h, 12 h, and 24 h incubation periods.
2.3. Bunch Ripeness and Bunch Size
The second phase of the study was conducted to evaluate the effects of bunch ripeness
and bunch size on ethephon-induced fruit detachment. An internal ripeness standard

4. Agriculture 2021, 11, 1030 3 of 10
was used that consisted of four categories, namely, unripe: 0 empty sockets, under-ripe:
1–9 empty sockets, ripe: 10–49 empty sockets, and overripe: 50 empty sockets. Ethephon
treatment was carried out under optimal conditions (as determined in 2.2), and each
ripeness category was comprised of five bunches with three replicates (n = 15). In the
following treatment, the size of ripe bunches was determined according to the bunch
weight as either: small: 14–18 kg; medium: 19–23 kg; or large: 24–28 kg. Ethephon
treatment was performed on individual bunches under optimal conditions and each size
category consisted of five replicates (n = 5).
2.4. Fruit Detachment (%) and FFA Content (%)
After the incubation period, the detached fruits were stripped manually from bunches
by hand and weighed. Fruit detachment (%) was determined for each treatment according
to the formula (total weight of detached fruits/total weight of bunches × 100%). Approxi-
mately 1 kg of detached fruits were collected and sterilized at 120 ◦C (HVE-50, Hirayama,
Kasukabe, Japan) for 90 min. Crude palm oil was then pressed from the mesocarp sepa-
rated from the nut, centrifuged, and the acidity value was determined using a rapid FFA
analyzer (PalmOil Tester, CDR Florence, Italy).
2.5. Mechanical Bunch Stripping
In the third phase of the study, oil palm bunches treated with ethephon, and control
bunches under the optimal conditions from 2.2, were subjected to mechanical bunch
stripping using a rotating thresher (L 183 cm × W 112 cm × H 172 cm) with a speed of
1000 rpm. Fruit detachment (%) and the FFA content without threshing (manual), and with
threshing (mechanical), were determined, as described earlier.
2.6. Ethylene Gas Treatment
The fourth phase of the study was designed to explore the feasibility and reproducibil-
ity of ethylene as an ethephon alternative for fruit detachment. The same setup used
for ethephon treatment was replicated by using ethylene gas, incubated for 24 h. Each
treatment consisted of five replicates (n = 5). Ethylene gas (Gaslink, Puchong Selangor,
Malaysia) was transferred into the box by a fixed pressure at a 0.3 bar and a flow of
0.1 L/min. Ethylene concentration was varied at 500 ppm, 750 ppm, and 1250 ppm, which
was calculated based on the ethylene concentration detected during the previous ethephon
treatment at 0.25% (v/v), 0.5% (v/v), and 1.00% (v/v).
2.7. Statistical Analysis
All results were presented as means of the replicates and data accuracy was deter-
mined using standard deviation. The statistical analysis of a one-way analysis of variance
(ANOVA) with a post-hoc Tukey test (p = 0.05) between the control and treatment groups
were determined using Minitab software version 20.4.0.0.
3. Results and Discussion
3.1. Effect of Ethephon Treatment on Fresh Fruit Bunches
Ethephon was used in the first phase of the study to evaluate the application method,
dosage, and incubation period. As shown in Figure 1A (column), fruit detachment
was significantly higher (p 0.001) for the ethephon-treated bunches, for both spray-
ing (28.5 ± 2.1%) and evaporation (28.5 ± 0.4%), in comparison to the control (9.7 ± 3.6%).
Visibly, most of the detached fruits came from the outer layer, while the loosened fruits in
the middle and inner layers were trapped between the spikelets on the bunch. The total
fruits from a fresh fruit bunch typically consist of 50% from the total bunch weight. The
middle and inner layers will be made up of 22–25% of the total fruits (internal data). The
results in Figure 1B show that the FFA content was lower (p = 0.001) in the detached fruits
from the ethephon-treated bunches, whether by spraying (0.6 ± 0.1%), or the evaporation
method (0.7 ± 0.3%), as opposed to the control (1.9 ± 0.8%). A higher proportion of fruits

5. Agriculture 2021, 11, 1030 4 of 10
with minimal bruising were observed in both treatment groups, which most likely con-
tributed to the low FFA content in the extracted crude palm oil. However, ethephon did not
have any effect on the FFA content if the fruits were bruised prior to treatment (unpublished
data). Similar results were reported previously [19], where the spraying of a bunch with
ethephon had loosened fruits mainly from the outer layer while the FFA content was not
influenced. However, a separate study found that treated fruits from bunches fumigated
with gaseous ethylene had a lower FFA content than control fruits [13]. Ethylene induced
ripening, and abscission activated the senescence pathway and cell-wall deterioration by
multiple enzymes, such as expansin, polygalacturonase mannosidase, beta-galactosidase,
and xyloglucan endotransglucosylase/hydrolase [20,21]. The senescence process in oil
palm fruits will start 160 days after anthesis and once abscission occurs [22]. This alludes
that ethephon-treated bunches will not likely have an increase in the FFA content in the
fruits once abscised, provided no damages occur that will release lipases and hydrolyze
the triglycerides.
Agriculture 2021, 11, x FOR PEER REVIEW 5 of 10
Figure 1. Detachment % and FFA level (%) in detached fruits after ethephon treatment by different
application method, variable concentration and incubation period in oil palm bunches. Ethephon
decomposition to ethylene gas (in ppm) was measured during the 24 h incubation period. (A) Fruit
detachment (%); (B) FFA content, (%) after 0.50% (v/v) ethephon treatment for 24 h by spraying and
evaporation methods; (C) Fruit detachment, (%) after 0.25% (v/v), 0.50% (v/v), and 1.00% (v/v)
ethephon treatment for 24 h by evaporation method; (D) Decomposition of ethephon into ethylene
measured at 2 h intervals for a period of 24 h; (E) Fruit detachment (%); (F) FFA content, (%) after
Figure 1. Detachment % and FFA level (%) in detached fruits after ethephon treatment by different applica-
tion method, variable concentration and incubation period in oil palm bunches. Ethephon decomposition

6. Agriculture 2021, 11, 1030 5 of 10
to ethylene gas (in ppm) was measured during the 24 h incubation period. (A) Fruit detachment
(%); (B) FFA content, (%) after 0.50% (v/v) ethephon treatment for 24 h by spraying and evaporation
methods; (C) Fruit detachment, (%) after 0.25% (v/v), 0.50% (v/v), and 1.00% (v/v) ethephon
treatment for 24 h by evaporation method; (D) Decomposition of ethephon into ethylene measured
at 2 h intervals for a period of 24 h; (E) Fruit detachment (%); (F) FFA content, (%) after 0.50% (v/v)
ethephon treatment applied by evaporation method for 6 h, 12 h, and 24 h incubation periods. The
data were presented as means of the replicates (n = 5) and vertical bars indicate standard deviation.
Means that do not share a letter were significantly different at p 0.05 according to Tukey’s range test.
Although both application methods produced comparable fruit detachment (p 0.999),
with relatively low FFA content (p = 0.770), the evaporation method was preferred as it
avoids direct contact of the ethephon solution with the oil palm bunches. This eliminates
the risk of having any residual ethephon, chloride, and phosphate in the extracted crude
palm oil.
Significantly higher (p 0.001) fruit detachment was achieved for all three ethephon
dosages in relation to the control, as shown in Figure 1C. The highest fruit detachment
was achieved for 0.50% (v/v) and 1.00% (v/v) ethephon, with 30.8 ± 1.1% and 32.0 ± 3.4%
detachment, respectively. The loosened fruits trapped in the middle and inner layers
between the spikelets in the bunch could not be removed during manual bunch stripping.
Thus, increasing the ethephon dosage from 0.50% (v/v) to 1.00% (v/v) did not significantly
improve (p = 0.860) fruit detachment. Therefore, 0.50% (v/v) ethephon was established as
the optimum dosage to be used in subsequent studies.
Ethephon decomposed into ethylene at pH 6–9, but at a faster rate at pH 9 [23]. Hence,
pH 9 was maintained throughout this study. The decomposition of ethephon into ethylene
was evident based on the initial accumulation of ethylene inside the incubation box, as
shown in Figure 1D. The ethylene levels increased steadily with time, and maximized at
900 ppm, 1500 ppm, and 2330 ppm for 0.25% (v/v), 0.50% (v/v), and 1.00% (v/v) dosages.
From the data, it was observed that with ethylene concentration at the 1500 mL/L for
0.5% (v/v), the detachment of fruits was optimum at 30.8 ± 1.1%. The subsequent decline
in the ethylene levels could be an indicator of ethephon exhaustion while exogenous
ethylene was being absorbed by the bunches to bind to the ethylene receptors to induce
abscission. Up to 70 mL/L of ethylene was detected for the control after 24 h, most likely
attributed to the endogenous ethylene released during postharvest ripening. This explains
the fruit detachment of 5.2 ± 2.5% observed in the untreated bunches after 24 h (Figure 1E).
Similarly, the release of endogenous ethylene after postharvest fruit abscission has been
reported in bananas, [24], apples [25], and peaches [26], mainly during the ripening process.
However, it was unlikely that the small amount of endogenous ethylene had any significant
impact in this study, as enhanced fruit detachment was only achieved in the ethephon-
treated bunches.
The effects of different incubation periods on fruit detachment and FFA content are
shown in Figure 1E,F. The results reveal that the minimum incubation period needed to
achieve the minimum fruit detachment at 27.6 ± 4.4%, was 12 h with 0.5% (v/v) ethephon.
Although fruit detachment increased slightly to 30.8 ± 1.1% when the incubation period
was prolonged to 24 h, the difference was not significant (p = 0.233). There was no pre-
sentable FFA data at 6 h, as the number of detached fruits collected was insufficient for
oil extraction. The FFA content difference in the ethephon-treated bunches (0.23 ± 0.12%)
was insignificant (p = 0.758) to the control (0.30 ± 0.08%) after 12 h. When the incubation
period was extended to 24 h, the FFA level increased slightly (p = 0.420) to 0.34 ± 0.09%
for the ethephon-treated bunches, while the control increased significantly (p 0.001) to
0.71 ± 0.05%. On the basis of these results, the incubation periods of 12 h and 24 h were
proven to be equally effective in terms of fruit detachment and FFA content. However,
when considering convenience and commercial feasibility, 24 h would be ideal, as the
bunches can be treated with ethephon immediately after harvesting and the incubation

7. Agriculture 2021, 11, 1030 6 of 10
can be carried out overnight. The detached fruits will then be ready for processing the
following morning, within the usual mill operating hours.
3.2. Effects of Bunch Ripeness and Bunch Size on Ethephon-Induced Fruit Detachment
A further study was performed to investigate if oil palm bunch ripeness and size
would affect ethephon-induced fruit detachment. As shown in Figure 2A, fruit detachment
was significantly higher (p 0.001) in the ethephon-treated bunches compared to the
control for every ripeness category. Unripe oil palm bunches were responsive to ethylene,
similar to other climacteric fruits, such as tomatoes, bananas, and pears, which are usually
harvested at the mature green stage and subjected to postharvest ripening [27,28]. Between
the treatments, the highest fruit detachment was observed in underripe and ripe bunches,
at 24.1 ± 0.9% and 23.2 ± 0.1%, respectively. Fruit detachment was lower in overripe
bunches, as most of the outer layer fruits had detached prior to ethephon treatment. The
control untreated bunches showed a high percentage of detachment due to the natural
senescence activity that causes abscission [29]. The results suggest that ethephon-induced
fruit detachment can be advantageous in commercial application, as oil palm bunches with
mixed ripeness (predominantly ripe) cannot be avoided during harvesting.
extraction. The FFA content difference in the ethephon-treated bunches (0.23 ± 0.12%) was
insignificant (p = 0.758) to the control (0.30 ± 0.08%) after 12 h. When the incubation period
was extended to 24 h, the FFA level increased slightly (p = 0.420) to 0.34 ± 0.09% for the
ethephon-treated bunches, while the control increased significantly (p 0.001) to 0.71 ±
0.05%. On the basis of these results, the incubation periods of 12 h and 24 h were proven
to be equally effective in terms of fruit detachment and FFA content. However, when con-
sidering convenience and commercial feasibility, 24 h would be ideal, as the bunches can
be treated with ethephon immediately after harvesting and the incubation can be carried
out overnight. The detached fruits will then be ready for processing the following morn-
ing, within the usual mill operating hours.
3.2. Effects of Bunch Ripeness and Bunch Size on Ethephon-Induced Fruit Detachment
A further study was performed to investigate if oil palm bunch ripeness and size
would affect ethephon-induced fruit detachment. As shown in Figure 2A, fruit detach-
ment was significantly higher (p 0.001) in the ethephon-treated bunches compared to the
control for every ripeness category. Unripe oil palm bunches were responsive to ethylene,
similar to other climacteric fruits, such as tomatoes, bananas, and pears, which are usually
harvested at the mature green stage and subjected to postharvest ripening [27,28]. Be-
tween the treatments, the highest fruit detachment was observed in underripe and ripe
bunches, at 24.1 ± 0.9% and 23.2 ± 0.1%, respectively. Fruit detachment was lower in over-
ripe bunches, as most of the outer layer fruits had detached prior to ethephon treatment.
The control untreated bunches showed a high percentage of detachment due to the natu-
ral senescence activity that causes abscission [29]. The results suggest that ethephon-in-
duced fruit detachment can be advantageous in commercial application, as oil palm
bunches with mixed ripeness (predominantly ripe) cannot be avoided during harvesting.
Figure 2. Fruit detachment (%) in different categories of oil palm fruit bunches ripeness and bunch
size. The impact of (A) bunch ripeness and (B) bunch size on fruit detachment after treatment with
0.50% ethephon for 24 h applied by evaporation method. The data were presented as means of the
replicates (n = 5) and vertical bars indicate the standard deviation. Means that do not share a letter
were significantly different at p 0.05 according to Tukey’s range test.
The results in Figure 2B show that fruit detachment decreased slightly with increas-
ing bunch size, from small (30.4 ± 6.3%), and medium (27.6 ± 4.3%), to large (26.8 ± 4.2%).
However, the difference was not significant (p = 0.496). The decreasing ratio of ethylene
to bunch (ethylene/kg) with increasing bunch size could explain the small differences in
the fruit detachment observed. Since the bunches selected for this study were limited to a
range between 14 and 28 kg, the impact of bunch size may be more apparent outside this
range. Another reason could be due to the lower ratio of outer fruits to inner fruits, where
Figure 2. Fruit detachment (%) in different categories of oil palm fruit bunches ripeness and bunch
size. The impact of (A) bunch ripeness and (B) bunch size on fruit detachment after treatment with
0.50% ethephon for 24 h applied by evaporation method. The data were presented as means of the
replicates (n = 5) and vertical bars indicate the standard deviation. Means that do not share a letter
were significantly different at p 0.05 according to Tukey’s range test.
The results in Figure 2B show that fruit detachment decreased slightly with increasing
bunch size, from small (30.4 ± 6.3%), and medium (27.6 ± 4.3%), to large (26.8 ± 4.2%).
However, the difference was not significant (p = 0.496). The decreasing ratio of ethylene
to bunch (ethylene/kg) with increasing bunch size could explain the small differences in
the fruit detachment observed. Since the bunches selected for this study were limited to
a range between 14 and 28 kg, the impact of bunch size may be more apparent outside
this range. Another reason could be due to the lower ratio of outer fruits to inner fruits,
where larger oil palm bunches often have multiple layers of fruits attached to the spikelets
forming a compact structure [30], causing the penetration and effectiveness of ethylene to
be reduced.
3.3. Mechanical Bunch Stripping on Ethephon-Treated Bunches
Manual stripping by human labor is considered ineffective commercially because
of the large scale of oil palm bunches involved. A mechanical thresher was used to
release the detached fruits from the spikelets at a fast-rotating speed. Figure 3A shows
that fruit detachment in the ethephon-treated bunches increased significantly (p 0.001),
from 28.5 ± 0.4% before threshing (manual) to 47.2 ± 2.4% after threshing (mechanical).
The comparatively higher force used during threshing resulted in additional fruits being

8. Agriculture 2021, 11, 1030 7 of 10
detached from the outer layer, while some portions of the fruits trapped in the middle and
inner layers were also dislodged. Although the FFA content increased (p = 0.026) almost
4-fold, from 1.0 ± 0.2% to 3.8 ± 1.2% (Figure 3B), due to the increased bruising in the
detached fruits, this was still within the commercial oil quality limit, which is commonly
set at a 5% maximum [3]. These results prove that the ethephon-treated bunches can be
mechanically stripped to further increase fruit detachment without compromising overall
oil quality. It must be emphasized, however, that the entirety of this study was carried
out in a controlled environment and the bunches were not subjected to the harsh handling
otherwise encountered in actual plantation and mill conditions. Achieving similar fruit
detachment and FFA content in a commercial setting will only be feasible if optimum
facilities and machineries are put in place to overcome such handling issues.
3.3. Mechanical Bunch Stripping on Ethephon-Treated Bunches
Manual stripping by human labor is considered ineffective commercially because of
the large scale of oil palm bunches involved. A mechanical thresher was used to release
the detached fruits from the spikelets at a fast-rotating speed. Figure 3A shows that fruit
detachment in the ethephon-treated bunches increased significantly (p 0.001), from 28.5
± 0.4% before threshing (manual) to 47.2 ± 2.4% after threshing (mechanical). The compar-
atively higher force used during threshing resulted in additional fruits being detached
from the outer layer, while some portions of the fruits trapped in the middle and inner
layers were also dislodged. Although the FFA content increased (p = 0.026) almost 4-fold,
from 1.0 ± 0.2% to 3.8 ± 1.2% (Figure 3B), due to the increased bruising in the detached
fruits, this was still within the commercial oil quality limit, which is commonly set at a 5%
maximum [3]. These results prove that the ethephon-treated bunches can be mechanically
stripped to further increase fruit detachment without compromising overall oil quality. It
must be emphasized, however, that the entirety of this study was carried out in a con-
trolled environment and the bunches were not subjected to the harsh handling otherwise
encountered in actual plantation and mill conditions. Achieving similar fruit detachment
and FFA content in a commercial setting will only be feasible if optimum facilities and
machineries are put in place to overcome such handling issues.
Figure 3. Mechanical stripping of ethephon-treated oil palm bunches by rotating threshing. (A) Fruit
detachment (%) and (B) FFA content of oil palm bunches treated with 0.50% (v/v) ethephon for 24 h
applied by evaporation method before threshing (manual) and after threshing (mechanical). The
data are presented as means of the replicates (n = 5) and vertical bars indicate standard deviation.
Means that do not share a letter are significantly different at p 0.05 according to Tukey’s range test.
3.4. Comparison between Ethephon and Ethylene Treatment
Ethephon can be costly and acidic-buffered conditions are recommended for stabil-
ity. The usage of ethephon will generate waste and needs to be disposed of. Hence, the
usage of ethylene gas was explored. Table 1 depicted the concentration of ethylene in ppm
after conversion from the average ethylene amount released from three different ethephon
concentrations. Figure 4 illustrates that both ethephon and ethylene application produced
comparable results (p 0.05), where 750 ppm and 1250 ppm ethylene yielded 29.4 ± 1.9%
and 30.1 ± 2.2% fruit detachment, respectively. In addition, increasing the ethylene from
750 ppm to 1250 ppm did not significantly improve fruit detachment (p = 1.00). Ethylene
concentration at 750 ppm should be considered in the future, as approximately 66% of the
chemical costs could be saved. If ethephon is substituted with ethylene gas, approximately
Figure 3. Mechanical stripping of ethephon-treated oil palm bunches by rotating threshing. (A) Fruit
detachment (%) and (B) FFA content of oil palm bunches treated with 0.50% (v/v) ethephon for 24 h
applied by evaporation method before threshing (manual) and after threshing (mechanical). The
data are presented as means of the replicates (n = 5) and vertical bars indicate standard deviation.
Means that do not share a letter are significantly different at p 0.05 according to Tukey’s range test.
3.4. Comparison between Ethephon and Ethylene Treatment
Ethephon can be costly and acidic-buffered conditions are recommended for stability.
The usage of ethephon will generate waste and needs to be disposed of. Hence, the usage
of ethylene gas was explored. Table 1 depicted the concentration of ethylene in ppm
after conversion from the average ethylene amount released from three different ethephon
concentrations. Figure 4 illustrates that both ethephon and ethylene application produced
comparable results (p 0.05), where 750 ppm and 1250 ppm ethylene yielded 29.4 ± 1.9%
and 30.1 ± 2.2% fruit detachment, respectively. In addition, increasing the ethylene from
750 ppm to 1250 ppm did not significantly improve fruit detachment (p = 1.00). Ethylene
concentration at 750 ppm should be considered in the future, as approximately 66% of the
chemical costs could be saved. If ethephon is substituted with ethylene gas, approximately
266% of the total chemical costs could be further reduced (internal study). Further potential
cost savings could be achieved, as there will be no wastewater generated by using ethylene
gas in the process. All these factors imply that ethylene has the potential to be used as an
alternative fruit detachment agent in future up-scaling studies.
Table 1. Average ethephon concentration decomposed into ethylene in 24 h.
Ethephon Concentration (%) 0.25 0.50 1.00
Average ethylene detected, ppm 500 750 1250

9. Agriculture 2021, 11, 1030 8 of 10
ethylene gas in the process. All these factors imply that ethylene has the potential to be
used as an alternative fruit detachment agent in future up-scaling studies.
Table 1. Average ethephon concentration decomposed into ethylene in 24 h.
Ethephon Concentration (%) 0.25 0.50 1.00
Average ethylene detected, ppm 500 750 1250
Figure 4. Ethephon and ethylene treatment at different concentrations induced fruit detachment in
oil palm bunches. The data were presented as means of the replicates (n = 5) and vertical bars indi-
cate standard deviation. Means that do not share a letter are significantly different at p 0.05 ac-
cording to Tukey’s range test.
4. Conclusions
The postharvest treatment of oil palm fresh fruit bunches with ethephon produced
high-quality detached fruits that reduced the free fatty acid content in the extracted crude
palm oil. Application of ethephon by the evaporation method effectively induced fruit
detachment in underripe, ripe, and overripe bunches, irrespective of the bunch size. Fruit
detachment was enhanced further when the ethephon-treated bunches were stripped me-
chanically. Ethylene gas, as an ethephon alternative, also effectively induced fruit detach-
ment by providing a competitive advantage over ethephon in terms of cost reduction and
wastewater elimination. These findings can potentially pave the way for new milling tech-
nologies to improve the efficiency of the separate processing of high-quality loose fruits.
A combination of mechanization stripping coupled with a sterilization process must be
integrated in automating the separation of detached fruits from the empty fruit bunch in
order to maintain the low level of free fatty acids in the extracted crude palm oil.
Author Contributions: A.B.: investigation, formal analysis, writing—original draft, writing—re-
view and editing; M.I.S.Z.: methodology, writing—original draft, writing—review editing; B.A.T.:
visualization, investigation, writing—original draft, writing—review and editing; J.Y.S.L.: method-
ology, visualization, investigation; S.F.K.: methodology, visualization, investigation, writing—re-
view and editing; C.M.L.: project administration, resources, supervision, writing—review and edit-
ing; D.R.A.: writing-review and editing. All authors have read and agreed to the published version
of the manuscript.
Funding: This research was fully funded by Sime Darby Plantation Berhad.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Figure 4. Ethephon and ethylene treatment at different concentrations induced fruit detachment
in oil palm bunches. The data were presented as means of the replicates (n = 5) and vertical bars
indicate standard deviation. Means that do not share a letter are significantly different at p 0.05
according to Tukey’s range test.
4. Conclusions
The postharvest treatment of oil palm fresh fruit bunches with ethephon produced
high-quality detached fruits that reduced the free fatty acid content in the extracted crude
palm oil. Application of ethephon by the evaporation method effectively induced fruit
detachment in underripe, ripe, and overripe bunches, irrespective of the bunch size. Fruit
detachment was enhanced further when the ethephon-treated bunches were stripped
mechanically. Ethylene gas, as an ethephon alternative, also effectively induced fruit
detachment by providing a competitive advantage over ethephon in terms of cost reduction
and wastewater elimination. These findings can potentially pave the way for new milling
technologies to improve the efficiency of the separate processing of high-quality loose
fruits. A combination of mechanization stripping coupled with a sterilization process must
be integrated in automating the separation of detached fruits from the empty fruit bunch
in order to maintain the low level of free fatty acids in the extracted crude palm oil.
Author Contributions: A.B.: investigation, formal analysis, writing—original draft, writing—review
and editing; M.I.S.Z.: methodology, writing—original draft, writing—review editing; B.A.T.:
visualization, investigation, writing—original draft, writing—review and editing; J.Y.S.L.: methodol-
ogy, visualization, investigation; S.F.K.: methodology, visualization, investigation, writing—review
and editing; C.M.L.: project administration, resources, supervision, writing—review and editing;
D.R.A.: writing-review and editing. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was fully funded by Sime Darby Plantation Berhad.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data within this paper are available from the corresponding author
upon reasonable request.
Acknowledgments: We are grateful to Sime Darby Plantation estates in providing the samples. This
study was conducted in the Sime Darby Plantation RD Centre, which is fully supported by the
Sime Darby Plantation, Malaysia.
Conflicts of Interest: The authors declare no conflict of interest.

10. Agriculture 2021, 11, 1030 9 of 10
Abbreviation
ANOVA Analysis of variance
CPO Crude palm oil
EFB Empty fruit bunches
FFA Free fatty acid
FFB Fresh fruit bunches
LF Loose fruits
OER Oil extraction rate
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