ARTICLE
Auteur(s) : Gerrit van Duijn, Gerrit
den Dekker
Unilever Supply Chain Technology Unit, P.O. Box 114, 3130AC
Vlaardingen, The Netherlands
<Gerrit-van.Duijn@unilever.com>
The oil refining process was introduced in 1900, to improve the
quality of oils and fats for application in margarine production,
and as cooking oil. The process was optimized to reduce the natural
taste and colour, and to remove most of the free fatty acids
present in the crude oil. It was discovered years later that under
these optimized conditions, the process also reduces the levels of
many of the contaminants like metals, poly-aromatic hydrocarbons,
and minor components like pesticide residues.
Toward the end of the twentieth century, most of the food
companies started a Food Safety Assurance System intended for the
ingredients used in their products. Unilever developed a specific
system for the supply chains of oils and fats. This system included
an assessment for the presence of contaminants and pesticide
residues in crude oils and the validation of the refining process
for the removal (reduction to below safe limit) of these
components:
- – the crude oil risk assessment combined visits of all
steps of the crude oil supply chains with analyses of contaminants
and pesticide residues in crude oils. These analyses were done on
all crude oils bought by Unilever for own or toll refining in North
West Europe for a period of four years (01/2001–12/2004). The crude
oil risk assessment resulted in a crude oil risk matrix;
- – oil containing a high level of a specific contaminant
or pesticide residue was refined under standard process conditions,
and the removal was checked by analyzing the level of this
contaminant or pesticide residue in the refined oil.
Crude oil risk assessment
Supply chain visits
In the period from January 2003 until July 2007, the supply chains
of five major oils used by Unilever were inspected for chemicals
use, drying procedures, and housekeeping practices. The following
supply chains were assessed:
- – soybean oil from central Brazil and mid-west USA;
- – sunflower oil from South Africa and France;
- – rapeseed oil from Germany;
- – palm oil from Malaysia (Sabah and peninsular Malaysia)
and Indonesia (Sumatra);
- – coconut oil from the Philippines.
Farmers, plantation companies, seed storage companies, oil
mills, oil transportation, and oil storage companies were visited,
and their procedures were examined using questionnaires. Special
attention was paid to the following contaminants and chemicals:
- – pesticides used during growth and crop protection
after harvesting;
- – poly-Aromatic Hydrocarbon adsorption from exhaust
gases during drying;
- – mineral oil from leaking equipments or transport
vehicles;
- – residues from previous cargoes during transport and
storage of crop or crude oil.
The following qualitative observations were done:
Pesticides in oil seeds (for more details
on pesticides see van Duijn (2008)
Pesticides are not applied in the last two weeks before harvesting
to limit the residue levels in the seeds. Insecticides are
sometimes used as post harvest treatment to protect seeds during
transport and storage. Carry over of insecticides from previously
treated grains may occur in storage silos.
Pesticides in palm oil
Herbicides are used to control weeds in the circle under the oil
palm tree. Contamination of loose fruits by herbicides is minimized
by direct application after harvesting. Insects are increasingly
controlled by biological pest control; in this case, chemicals are
only used to control pest outbreaks. Palm fruits are not stored for
long, and therefore postharvest treatment is not applied.
Pesticides in palm kernel and coconut
Application of pesticides for these crops has not been observed.
Drying practices
When moisture is too high, oil seeds are dried to a specified water
level. This drying can be in direct contact with exhaust gases.
This has been observed for soybeans in wood-fired packed bed dryers
and sunflower seeds in diesel-fired counter current dryers. Direct
dryers are not allowed to be used in Europe and the United States
of America.
Drying is an essential operation in the coconut oil supply
chain, it avoids Aflatoxin formation and it releases the copra
(coconut meat) from the shell. In the method, which is predominant,
halved coconuts are dried upside down on a grid of a bamboo over an
open fire, burning the coconut shells.
Palm kernels are washed and dried after cracking in the palm oil
mill. Most, but not all mills, dry in indirect dryers.
Mineral oil leakages
Small, but visible mineral oil leakages have been observed in palm
oil mills and at oil seed reception areas. More and more oil mills
use food-grade lubricants and hydraulic oils when there is an
unavoidable contamination risk.
Residues from previous cargoes:
Measures were in place in all the visited locations to avoid
contamination with previous cargoes. Crop transport from farm or
plantation to oil mill was carried out in clean and inspected
conveyances. Crude oils were transported from the mill to the port
or customer in dedicated and sealed trucks (sealing of empty return
trips would further improve security), tank parks were all
foodstuff dedicated and overseas transport was according to the
previous cargo regulations of the European Union (EU) or Federation
of Oils, Seeds and Fats Associations (FOSFA).
Crude oil analyses
The crude oils bought by Unilever for own or toll refining in North
West Europe in the period from January 2001 until December 2004
were analyzed for pesticides, poly-aromatic hydrocarbons
(Benz(a)Pyrene) and hydrocarbons (C10–C24). In total, 1595 samples
were analyzed, which included crude rapeseed oil (566 samples),
crude sunflower oil (154 samples), water-degummed soybean oil (157
samples), crude palm oil (318 samples) crude palm kernel oil (236
samples), and crude coconut oil (164 samples). The samples were
taken by an independent superintendent from different levels in the
ship tanks and were analyzed in an independent laboratory
(Laboratory Dr. A Verweij, Coolhaven 32, 3024 AC Rotterdam,
The Netherlands). The results were as follows:
Pesticides
All samples were analyzed for 24 organochlorine pesticides,
28 organophosphorus pesticides, 9 nitrogen-based
pesticides and 4 pyrethroids. The palm oil samples were also
analyzed for 14 pesticides frequently used by palm plantations
as reported during the supply chain visits.
Only a limited selection of mainly organophosphorus insecticides
was detectable in crude seed oils (soybean, sunflower and rapeseed
oil). Figure 1
gives an overview of the maximum pesticide levels found in
rapeseed, sunflower and soybean oil.
No pesticide residues were detected in crude palm oil, palm
kernel oil, and coconut oil.
Poly-Aromatic Hydrocarbons
All crude oil samples were analyzed for Benz(a)Pyrene (BaP) levels.
The BaP is generally used as a marker for the presence of
Poly-Aromatic Hydrocarbons in crude and refined oils. The EC
regulation 1881/2006 (EC, 2006) limits the BaP level in oils and
fats intended for direct human consumption or as ingredient in
foods at max. 2 ppb.
For the analyses, a sample with a BaP level above 1 ppb was
considered to be contaminated. The fraction of contaminated samples
was very high for crude coconut oil (79%), high for crude sunflower
oil (12%) and below 10% for crude rapeseed oil (9%), water
de-gummed soybean oil (7%), and crude palm kernel oil (6%). None of
the palm oil samples had a BaP level above 1 ppb. Figure 2 gives an
overview of the average and maximum BaP levels found in the crude
oil samples with a BaP level higher than 1 ppb. This shows
that all oils except palm oil may occasionally have a BaP level
before refining, which is higher than the EU limit of
2 ppb.
Hydrocarbons
Hydrocarbons in Mineral oil can be roughly divided in four
fractions, depending on the carbon numbers:
- – gasoline (C5–C10), purified hexane (C6) is used as a
solvent in oil extraction and the residue level in crude oils is
restricted in the contracts by the flashpoint (<
121 °C);
- – kerosene and diesel (C10–C24);
- – fuel and lubricant oil (> C16);
- – asphalt (> C35).
All tested crude oils were analyzed for kerosene and diesel
contamination (C10–C24), since these components were observed to be
at a high level in crude palm oil in 1999. Detectable levels of
these hydrocarbons were only found in crude palm oil. Figure 3 shows the average
and maximum observed levels of hydrocarbons in the range C10–C24
for the years 2001 until 2004. Palm oil also contains natural
hydrocarbons in the range of C10–C25; it is not clear so far as to
the level of natural hydrocarbons. In 2007, the tri-partnership
project of the Malaysian, Indonesian, and Dutch government agreed a
maximum level of 25 ppm for C10–C24 hydrocarbons in crude palm
oil.
Other contaminants
The levels of other contaminants like dioxins, PCB's and heavy
metals (lead) were monitored in some crude oil and refined oil
samples. The levels in none of these samples were above
the limits set in EC regulation 1881/2006.
Crude oil risk matrix
The risk assessment for the presence of a specific contaminant or
pesticide residue in crude oil is a combination of the observations
made during the supply chain visits and the results of the crude
oil analyses. The identified risks are used to establish a crude
oil risk matrix. This matrix shows the risk classification (high,
medium, low) for presence of a contaminant or pesticide residue in
a crude oil, in case the origin of the crude oil is unknown (table 1). The justification of this
classification is:
Pesticides
In total, eight different organophosphorus insecticides were found
at detectable levels in seed oils. Crude sunflower oil had the
highest maximum observed levels (6 insecticides above 100 ppb
of which 1 was higher than 1000 ppb), crude rapeseed
followed (3 insecticides above 100 ppb), while for soybean
oil, only the maximum observed level for Endosulfan was above
100 ppb. Pesticides were not found in the tropical oils (palm,
palm kernel, and coconut oil).
Table 1 The crude oil risk matrix. This matrix shows
the risk that a specific contaminant or pesticide residue
is present in a crude oil of unknown origin.
|
Pesticides
|
PAH
|
Mineral oil in edible oil imported in EU
|
Dioxins and PCB's
|
Heavy metals (lead)
|
|
LIMIT
|
MRL
|
BaP < 2 ppb
|
Fediol CoP
|
EC/1881/2006
|
EC/1881/2006
|
|
Soybean oil
|
Medium
|
Medium
|
Low
|
Low
|
Low
|
|
Sunflower oil
|
High
|
High
|
High
|
Low
|
Low
|
|
Rapeseed oil
|
Medium
|
Medium
|
Low
|
Low
|
Low
|
|
Palm oil
|
Low
|
Low
|
High
|
Low
|
Low
|
|
Palm kernel oil
|
Low
|
Medium
|
Medium
|
Low
|
Low
|
|
Coconut oil
|
Low
|
Very high
|
Medium
|
Low
|
Low
|
Benz(a)Pyrene
The occurrence and maximum level of BaP in coconut oil were very
high: occurrence 79%, maximum level 73 ppb. Sunflower oil had
a lower maximum level (43 ppb) and occurrence (12%). The
maximum levels for rapeseed, palm kernel, and soybean oil were
between 2 (EC-regulated level) and 10 ppb while the occurrence
was below 10%. No detectable level of BaP in palm oil has been
observed.
Hydrocarbons of mineral oil origin
Incidents with high levels of hydrocarbons in edible oils have
occurred for palm oil (diesel contamination) and sunflower oil
(grease oil contamination in 2008). In both the cases, the origins
of contamination were never published. The customer cannot be sure
if the causes for contamination have been eliminated, therefore the
risk of classification remains high. Palm kernel and coconut oil
may originate from the same regions as the contaminated palm oil,
and are therefore considered as medium risk products.
Other contaminants
Risks here are classified as low, since; so far, all detected
levels are below the EC-regulated limits.
Risk matrix based analyses
The risk matrix can be used to determine the frequency of the
contaminant or pesticide residue analyses in crude oils from an
unknown origin. The proposed frequency is:
- – very high and high risk → check every delivery;
- – medium risk → quarterly monitoring;
- – low risk → annual monitoring
Process validation contaminant or pesticide residue
removal
The following procedure was applied to all crude oils delivered to
Unilever, for own or toll refining, with a contaminant or pesticide
residue level above detection limit (for hydrocarbons and
pesticides) or EC-regulated limit (for BaP):
- – the refinery was informed of the contamination of the
oil, and the contaminated lot was blocked;
- – the refining process was validated for removal of the
contaminant or residue level to below detection limit (for
hydrocarbons or pesticides) or EC-regulated limit (for BaP). This
process validation was done by processing a minimum batch with the
standard Unilever recipe for neutralization, bleaching (with active
coal for Poly-Aromatic Hydrocarbon removal), and deodorization and
analyzing the contaminant or pesticide level in the processed
oil;
- – the crude oil was de-blocked and the whole lot was
processed when the level of tested deodorized oil was below the
limit;
- – this process was repeated for every delivery of crude
oil with a contaminant or pesticide level higher than the levels of
the oils used in previous process validations.
Pesticides
All pesticides found in the analytical survey were extensively
removed to below detection limit under the standard Unilever
process conditions (neutralization, bleaching and deodorization at
T > 230 °C). Some of the pesticides were already removed
during neutralization (e.g., Dichlorvos), others during bleaching
(e.g., Pirimiphos-methyl), but all were removed during
deodorization because of their volatility.
The process conditions of the European refining industry are not
so different from the conditions applied by Unilever. Therefore,
most of the industrial refineries will reduce organophosphorus
pesticides to a level well below the level in the crude oil.
However, for each refinery, a process validation is required for
pesticide removal.
Poly-Aromatic Hydrocarbons
Heavy Poly-Aromatic Hydrocarbons (5 rings or more) are removed by
active carbon adsorption, while light Poly-Aromatic Hydrocarbons
are also removed by stripping at high temperature deodorization
(200-240 °C). The BaP is a heavy Poly-Aromatic Hydrocarbon and
needs active carbon treatment for removal.
The Unilever process validation experience shows the following
active carbon levels needed to reduce BaP to below 1 ppb:
Coconut oil: 0.19% carbon for every 10 ppb BaP in crude
oil.
Sunflower and rapeseed oil: 0.17% carbon for every 10 ppb
BaP in crude oil.
A higher active carbon dosage is needed at lower deodorization
temperatures. These levels are relatively conservative and result
in a reduction to a level well-below EC-regulated limit.
Hydrocarbons of mineral origin
Process validations were carried out with oils containing less than
25 ppm hydrocarbons in the range C10–C24. High
temperature deodorization (T > 230 ˚C) reduced these
hydrocarbons to below detection limit. The reduction of
hydrocarbons in the range C20–C35 was less successful; the
volatility of this range is apparently insufficient.
Conclusions
- – The findings of the risk assessment visits correlated
very well with the results of the crude oil analyses.
- – The pesticides found in crude seed oils
are mainly organophosphorus insecticides used to protect oil
seeds during storage and transport after harvesting. No
pesticides were found in crude palm oil, crude
palm kernel oil, and crude coconut oil. Organophosphorus
insecticides were extensively removed during refining.
- – Poly-Aromatic Hydrocarbons in crude oils originate by
absorption from exhaust gases when these are used for direct drying
of the oil crop. High levels were found in crude coconut oil since
direct drying is a common practice in the coconut oil supply chain.
High levels may also occur in crude sunflower oil, while in most
other crude oils occasional contaminations may occur. Palm fruits
are never dried and Poly-Aromatic Hydrocarbon contamination has not
been observed in crude palm oil. Heavy Poly-Aromatic
Hydrocarbons are removed by active carbon treatment, while light
components will also be reduced by high temperature
deodorization.
- – Hydrocarbons in the diesel oil range (C10–C24) in
crude palm oil reduced over the testing period from max.
45 ppm and average 10 ppm to max. 21 ppm and average
8 ppm. Parts of these hydrocarbons are of natural origin. High
temperature deodorization (T > 230 ˚C) reduced these
hydrocarbons to below detection limit.
- – The effectiveness of the Food Safety Assurance System
for vegetable oils and fats was confirmed by monitoring of
deliveries of industrially refined oils to the Unilever product
manufacturing sites.
References
[Van Duijn, 2008] Van Duijn G. Industrial experiences with
pesticide removal during edible oil refining. Eur J Lipid Sci
Technol 2008; 110: 982-9.
[EC commission regulation] EC commission regulation N°1881.
Setting Maximum levels for certain contaminants in foodstuffs.
Official Journal of the European Union: L364/5-24, 2006.
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