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Bulletin UASVM Agriculture, 67(2)/2010
Print ISSN 1843-5246; Electronic ISSN 1843-5386
Researches Regarding the Processing of the
Hemp Seed by Cold Pressing
Maria-Virginia MORAR, Katalin DRAGAN, Costantin BELE, Cristian MATEA, Iustin
TARTA, Ramona SUHAROVSCHI, Cristina SEMENIUC
USAMV, Cluj-Napoca,Calea Manastur Nr. 3-5, 400372 Cluj-Napoca, Email: mvmorar@yahoo.de
Abstract The hemp (Cannabis sativa L.) seeds present an important raw material resource for
the industry due to processing possibilities of plants components. The hemp oil and the pressing cake
resulted by the cold pressing of the hemp presents excellent alimentary and therapeutic properties.
The purpose of the research was to study the technology of obtaining of the hemp oil by cold
pressing of the seeds, the influence of the process parameters and raw materials quality upon the
products quality.
The pressing was made with screw press of small using press nozzle in diameters of 5, 6, 7, 8
and 10 mm. For the hemp seed there were determined the organoleptic characteristics (total volatile
matter and the raw fat content by Soxhlet extraction). For the hemp oil there were determined the acid
value and the peroxide value. There werde determined the working parameters of the press (the rate
efficiency and the productivity of the press).
The results emphasized important data for the practice. The fat content of the seed was
between 30,89 and 33,25 % and the volatile matter was between 90,42 and 93,68 %. The rate efficieny
of the cold pressing of the hemp seed was between 23,89 and 27,69 % obtained oil, being influenced
by the characteristics of the seeds. The pressing process was also influenced by the quality of the seed,
presenting optimal values in the case of using pressing nozzle 8 and 10 mm in diameter. The acid
values of the hemp oil was between 0,65 and 4,45 mg KOH/g oil and the peroxide values was between
0,62 and 26,91 mEg O2/g. Further studies are recommended be made and there are the initiations of ab
informational programme, in order to inform the farmers and consumer about the benefic and
therapeutic effects of the hemp oil upon the health.
Key words: hemp seed, cold pressing, hemp oil.
INTRODUCTION
The hemp (Cannabis sativa L.) seeds present an important raw material resource for
the industry due to its value provided by the several processing possibilities and products
obtained from all the components of the plants. From the hemp grown for non-drug purposes
there are obtained several products as food, fuels, textiles, paper or even biodegradable
plastics.
The processing of the hemp seed by cold pressing results in oil and pressing cakes,
with alimentary use, having also excellent therapeutic properties. Their use were attested to be
known since ancient time by Chinese, 12000 years ago, or by the traces founded in the tombs
of the ancient Egyptians.
The composition and the principal characteristics of the hemp seed compared to those
of the most important oleaginous seeds are presented in Tab. 1. There is to be observed that in
the hemp seed the fat content is considerable.
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Tab. 1
Composition and characteristics of the hemp seed compared to other oleagionous seeds
(Banu, 2009)
Specification oil
seed
Hectolitric
weight
kg⋅hL
-1
Hulls
content
Chemical composition (%)
Moisture Fat Proteine NfE
1
Celulosis Ash
Hemp 48-58 20-25 5-12 28-34 15-27 15-25 12-16 3-5
Sun flower 38-42 14-28 9-11 44-48 18-20 10-15 14-18 2-3
Soya 70-75 7-12 11-13 17-19 33-36 20-23 4-5 3-5
Linen 65-69 4-6 9-11 35-38 25-27 20-23 4-5 3-4
Rape (Canola) 65-70 4-6 6-8 35-42 25-28 17-20 4-6 3-5
1
Nf.E. – Azot free extract
The hemp seeds contain all the essential amino acids and considerable essential fatty
acids in the composition of its fat content. These are also a source of calcium, iron,
phosphorus, magnesium, zinc, copper and manganese. The psychoactive Cannabinoide
∆-9-THC is not synthesized in the seeds and therefore there exists special requirements
concerning the purity of the industrial hemp seed (proper removing of impurities as other
parts of the plant) in order to avoid eventual THC traces in the processed products. The
composition of the hemp oil is presented in the table 2, together with the composition of other
vegetable oil.
Tab. 2
Fatty acid composition of oils (%) (Sanders, on: http://www.goodwebsite.co.uk/kingsreport.pdf).
SFA- Saturated Fatty Acids, MUFA-Mono-Unsaturated Fatty Acids, PUFA-Poli-Unsaturated Fatty Acids
Fatty
acids
Edible
oil
% SFA MUF
A PUFA Linoleic
18:2
ω-6
GLA
18:3
ω-6
ALA
18:3
ω-3
Steara-
donic
18:4
ω-3
ω
-6
ω
-3
ω
-6/
ω-3
Hemp seed
oil 99,9 7,31 10,57 75,96 53,82 3,31 17,19 1,63 57,13 18,82 3,1
Walnut oil 99,9 9,10 16,40 69,90 58,40 0,00
11,50 0,00 58,40 11,50 5,1
Rapeseed
oil 99,9 6,60 59,20 29,30 19,70 0,00 9,60 0,00 19,70 9,60 2,1
Soya oil
99,9 15,60 21,20 58,80 51,50 0,00 7,30 0,00 51,50 7,30 7,1
Sunflower
oil 99,9 12,00 20,50 63,30 63,20 0,00 0,10 0,00 63,20 0,10 632,0
Linseed/
flaxseed 99,9 9,4 20,2 66,00 12,7 0,00 53,3 0,00 12,7 53,3 0,2
The data emphasizes the ideal rate of the essential fatty oil ω-6 to ω-3 of 3 to 1, which
are considered by the specialist to be the most optimal rate for the intake of these essential
fatty acids by the human body. The considerable content of γ-linolenic acid (GLA) and the
stearadonic acid content provide to the oil a distinct value. The hemp oil contains antioxidants
and possesses a remarkable radical scavenging activity and oxygen radical absorption
capacity, as recorded in the literature (Ramadan, 2006, Boskou, 2006). The alimentary and
therapeutic properties are also provided by active principles with very important biological
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function, as the for example the phenolic compounds (0.44 mg GE/g, gallic acid equivalent
(GE) per gramme) of the cold-pressed hemp seed oil (L.L.Yu,2005), tocopherols and
terpenes.
MATHERIALS AND METHODS
The purpose of the research was to study the technology of cold pressing of the hemp
seed and the influence of its quality upon the obtained products.
There were tested 3 types of hemp seeds, of different provenience, and certified by an
authorized laboratory for being free of ∆-9-THC (with a concentration below 1 ppm). The
hemp seeds were conditioned (i.e. selected, purified and dried) for a proper storage.
There were analysed for the hemp seeds: the organoleptic characteristics, the moisture
contents (total volatile matter) and the raw fat content (by Soxhlet extraction).
The pressing of the seeds was made with a screw press of small capacity (up to 5 kg
oleaginous seed per hour and fixed rotations speed: 60 rpm) in the vegetal oil technology
laboratory of the USAMV, Cluj-Napoca. The technological characteristics of the press was
varied by using different press nozzles, in diameters of 4, 5, 6, 7, 8 (hemp seeds I, II and III)
and also of 10 mm (hemp seed I and II).
In order to study cold pressing technology of the hemp seed there were evaluated the
working parameters of the press (the rated efficiency of the extracted oil η
O/S
) and the
productivity of the press. The productivity of the press was related to hemp seed processed
per hour -
P
Hemp seed
(kg/h)
and to hemp oil obtained per hour -
P
Hemp oil
(kg/h)
. Therefore there were
recorded for each variant of pressing process the data of the input (hemp seed) and output (oil
and pressing cake), as well as the pressing time (s).
For the raw cold pressed hemp oil there were determined the acid value and the
peroxide value.
RESULTS AND DISSCUSIONS
The organoleptic analysis of the hemp seed did not revealed modified smell and taste.
The data of the determination of the dry matter and fat content are presented in the
table 3. The analysed hemp seed had a fat content with values between 30,89 and 33,25%.
The total volatile matter of the tested hemp seed was of 6,32 % (hemp seed I), of 8,18 %
(hemp seed II) and 9,58 % (hemp seed III).
Tab. 3
The dry matter content and fat content of the studied hemp seed
Crt.
No. Specification of the sample Dry matter
(%) Fat content
(%)
1. Hemp seed I 93,68 33,25
2. Hemp seed II 91,82 31,34
3. Hemp seed III 90,42 30,89
The obtained cold pressed hemp oil emphasized a pleasant nutty, also with a lightly
grassier flavor. The color of cold pressed raw oil was dark green to a bit lighter green,
depending on the different pressing conditions, i.e. the diameter of the press nozzle, and
therefore different temperatures developed in the screw press.
The pressing rate efficiency related to the hemp seed (kg hemp oil processed from 100
kg seed η
O/S
(%)
and the press productivity
P
Hemp seed
(related to the quantity of hemp seed
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processed per hour: kg hemp Seed/h) and P
HempOil
(related to the quantity of hemp oil
processed per hour: kg hemp oil/h) are presented in the Tab. 4.
Tab. 4
The working the parameters of the screw press at the processing of the hemp seed by cold pressing: the rate
efficiency (η
O/S
obtained oil from processed seed , %) and press productivity (P
Hemp seed
- kg hemp seed/h and
P
Hemp oil
- kg hemp seed oil/h)
Crt.
Nr. Specification
pressing variant
φ
(mm) Pressing rate efficiency Press productivity
η
O/S
(%) P
Hemp seed
(kg/h) P
Hemp oil
(kg/h)
Hemp seed I 4 30,00 0,41 0,12
Hemp seed I 5 27,48 3,11 0,85
Hemp seed I 6 27,92 2,23 0,62
Hemp seed I 7 27,69 3,62 1,00
Hemp seed I 8 26,64 4,50 1,20
Hemp seed I 10 27,10 3,90 1,06
Hemp seed II 5 27,60 3,31 0,91
Hemp seed II 6 26,80 2,72 0,73
Hemp seed II 7 25,60 3,47 0,89
Hemp seed II 8 25,60 3,67 0,94
Hemp seed II 10 24,80 4,92 1,22
Hemp seed III 5 26,67 4,00 1,07
Hemp seed III 6 27,22 3,90 1,06
Hemp seed III 7 23,89 4,32 1,03
Hemp seed III 8 23,89 4,24 1,01
The pressing rate efficiency varies between 23,89 and 27,69 kg processed oil from 100
kg hemp seeds and depended on the diameter of the press nozzle as well as on the hemp seed
characteristics. The oil quantity processed from 100 kg hemp seed is higher in the case of
using a press nozzle smaller in diameter. It depends also on the humidity content of the hemps
seed and showed different optimal values by pressing with nozzle in diameter of 5 mm (hemp
seed II) and 6 mm for the hemp seed I and III. The using of the press nozzle of 4 mm was
possible only in the case of the hemp seed I, with lower total volatile contents of 6,32 %.
Fig. 1. Pressing rate of the process (oil obtained by pressing of 100 kg hemp seed); I, II, III – the three hemp
seeds sorts used for the processing of oil.
288
As to be seen in the Fig. 1, the rate efficiency was higher for the hemp seed with lower
total volatile matter (sort I- 6,32 %) and lower for the sorts II and III (8,18 % and 9,58 %)
with higher values in total volatile matter.
The highest quantity of oil obtained per hour by pressing of the hemp seed was also
related to the characteristics of the press and input characteristics. The best values for the
hemp oil obtained per hour were for hemp seed sorts with lower total volatile matter and by
using press nozzles with diameters of 8 mm (1,20 kg hemp oil/h for the seeds I) and 10 mm
(1,22 kg hemp oil/h for the seeds II).
Compared to the processing of other oleaginous seeds by cold pressing, the
productivity of the press for hemp seeds processing is lower as for sunflower seed (Morar,
2004) or rape seed processing (Morar, 2004).
From the Fig. 2 there can be observed that the values for the press productivity varies
more for the hemp seed with lower value of the total volatile matter (I) than for the sorts with
higher total volatile content (hemp seeds II and II).
Fig. 2. Press productivity (quantity of hemp oil in kg processed in one hour)
The acidity values, expressed in mg KOH/g oil and oleic acid (%), as well as the
peroxide values of some of the cold pressed hemp oils are presented in the Tab. 4.
Tab. 5
The acidity values and the peroxide values of the hemp oil obtained by cold pressing with the screw
press with different press nozzle of diameter of
φ
: 4, 5, 6, 7, 8 and 10 mm
Crt.
No. Sample specification
φ
(mm) Free acidity of the oils Peroxide value
mEq O
2
/g
mg KOH/g oil Oleic acid (%)
1. Hemp oil I
2
5 0,65 0,33 n.d.
2. Hemp oil I
2
6 1,95 1,00 0,62
3. Hemp oil I
2
7 2,83 1,46 1,50
4. Hemp oil II 5 0,65 0,34 n.d.
5. Hemp oil II 6 0,77 0,39 7,49
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6. Hemp oil II 7 0,74 0,38 26,91
7. Hemp oil III 4 7,42 3,82 n.d.
8. Hemp oil III 5 4,34 2,23 n.d.
9. Hemp oil III 6 4,45 2,29 17,28
10. Hemp oil III 7 4,21 2,16 19,41
2
- values of the acidity after 6 month of the pressing, respectively storage of the oil; n.d.- not determined
The acid values of the hemp oil was between 0,65 and 4,45 mg KOH/g, excepting one
value of 7,42 mg KOH/g oil. The acidity values are comparable with those reported for the
hemp oil by the literature (Carvalho, 2006). The peroxide value varied between 0,62 and
26,91 mEg O
2
/g, the lowest one being determined for the oil processed from hemp seed I with
a lower total volatile matter content with values under 1,50 mEqO
2
/g (the acid values under 3
mg KOH/g oil). Correlating the acidity value with the peroxide value, there was ascertained
that only the oil processed from the seeds with lower total volatile content (6,32%) are
according to the quality criteria.
CONCLUSIONS
The approach of the technology of oil production from the studied sorts of hemp seed
by cold pressing has revealed important principles regarding the practice. There was
processed from 100 kg hemp seeds (with 30,89 to 33,25 % fats content and total volatile
matter of 6,3 % to 9,58 %) between 23,89 and 27,69 kg oil, depending on the diameter of the
press nozzle attached to the screw press. The efficiency of process was provided by the press
productivity with optimal values of 1,20 and 1,22 kg hemp oil processed per hour. The results
are providing also information regarding the possibility of varying of the pressing process, in
order to achieve by products with foreseen composition. The hemp seed pressing cake can be
classified into the category of functional products, due to their, also, valuable nutritional
properties. The study of hemp oil composition pointed out its alimentary and therapeutic
qualities, provided by the high polyunsaturated fatty acids and the ideal rate of the essential
fatty acids ω-6:ω-3 of 3:1. Further studies are necessary in order to analyse the composition
of the hemp oil processed from hemp seed cultivated in Romania.
With regard to the realized researches, we recommend also the initiation of an
information programme addressed to the consumer and to the farmers concerning new
acknowledgements of the importance of the hemp culture, as well as the importance of the
processed products
REFERENCES
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2. Boskou D. (2006). Sources of natural Phenolic antioxidants. Trends in Food Science &
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suitable for human nutrition, Industrial Crops and Products, 24, 75–78.
2. Liangli Lucy Yu, Kequan Kevin Zhou and John Parry. (2005). Antioxidant properties of cold-
pressed black caraway, carrot, cranberry and hemp seed oils, Food Chemistry 91723–729.
3. Morar, Maria V., Zoe Dancea, C. Bele, D. Salagean and F.
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