In this article we will discuss about:- 1. Extraction of Mustard Oil 2. Yield of Mustard Oil 3. Properties and Utilization 4. Medicinal Uses.
Extraction of Mustard Oil:
The major portion of rapeseed and mustard produced in India (c 95%) is utilized for extraction of oil. The type of machinery commonly employed for crushing are the primitive bullock-driven ghani (crusher), the power-driven rotary mill, and the expellers; solvent extraction method is used only to a small extent. Hydraulic presses have not found favour for this purpose.
The ghani consists essentially of a wooden mortar fixed to the ground and a wooden pestle connected to a shaft, which is operated by bullocks. The ghanis are employed in villages for pressing out the oil. The size and capacity of ghanis vary considerably in different regions, from 5 kg in Madhya Pradesh to 15 kg in Tamil Nadu, Orissa and West Bengal. During crushing, 500 to 750 ml of water is added for a seed charge of 10-12 kg depending upon the dryness of the seed.
The first extraction is warmed and added back to the mortar for speeding up the subsequent extractions. The oil is pressed out in 1.5-2 hr at a temperature of 38-40°. The addition of water helps in the hydrolysis of thioglucosides (glucosinolates) present in the seeds, thus releasing the pungency producing essential oil of mustard. Although ghani is not a very effective means of producing the oil, it has the advantage of initial low investment, providing work to the villagers and dispensing with considerable cost of transport of seed, oil and cake.
Besides, the pungent smelling oil obtained from ghanis is preferred in many areas by consumers for edible purposes. The All India Khadi and Village Industries Commission, Wardha, has developed an improved bullock-drawn crusher which has a higher capacity, takes less time and yields more oil. The proportion of rapeseed and mustard seed crushed by ghanis is estimated at about 37 per cent; the power-operated units account for the remaining proportion.
Rotary mills are commonly employed for crushing rapeseed and mustard. The power-driven rotary mill is an adaptation of the ghani. The mortar is made of either wood or iron, and the pestle of iron. The seeds are mixed with c 5-10 per cent water and pressing is done at 40-45° for 40-60 min. These conditions are favourable for hydrolysis of thioglucosides and development of pungency in the oil. Since the yield is somewhat lower than that from expellers, many mills crush the seeds in two stages, viz. first in rotary mill for pungency and later in expeller, for higher yield.
Expellers are used for the extraction of oil in the larger units and in regions where pungent oil is not much in demand. The cleaned seed is rolled into a meal in 3-high or 5-high rollers, and fed into a steam-jacketed or tempering apparatus where it is heated to a temperature of 75-95°, and then passed through a chamber having a series of rotating ‘worms’. The pressure developed expels the oil which is drained and filtered through a filter press.
Solvent extraction is the most modern method, in which the seed or cake is exposed to the action of a solvent like food grade n-hexane. The rapeseed oil so obtained retains the smell of the solvent used, and needs to be deodorized later. This method is very efficient leaving only about 0.5-1.0 per cent oil in the residue. Even the expeller, ghani or rotary mill cakes can be subjected to solvent extraction to recover an additional 6 per cent of the oil suitable for industrial purposes.
Yield of Mustard Oil:
The yield of oil from the seeds of different forms and cultivars is variable. The bold, sound and clean seeds yield a higher percentage of oil than the damaged ones or those containing higher content of refraction. The oil content of various types of rapeseed and mustard is as follows – yellow sarson, 35.0-48.0% brown Sarson, 35.0-48.0% toria, 33.0-46.0%, lahi, 30-0-38.0% and rai, 30.0-42.0%. The yield also depends upon the machinery used for extraction.
The expellers yield 34-38% oil, rotary mills 33-35% and ghanis 30-32%. The average yield of oil in rapeseed and mustard is 33.3 per cent. The oil left in the cake obtained from the ghanis is 11-16% from the rotary mills 9-11% and from the expellers 7-8%. Oil content of 20 different improved cultivars of Indian brassicas showed a range of 40 to 48 per cent, which compares favourably with the oil content of European brassicas.
Properties and Utilization of Mustard Oil:
The crude mustard oil is dark brown in colour and has a characteristic sharp taste and pungent odour. It is generally refined by treating with sulphuric acid which precipitates impurities and colouring matter. After settling, the oil is repeatedly washed with hot water and when thus refined, it is yellow in colour. Refining with caustic soda removes free acids and the soap-stock obtained is used in the manufacture of soft soap.
The refined oil has a pungent, mustard-like odour which can be removed by deodorization. But the deodorized oil is inclined to revert in flavour and acquire an unpleasant taste different from that of the un-deodorized oil. Refined rapeseed and mustard oils are being increasingly used in the manufacture of vanaspati which is finding increasing demand among people due to rise in the standard of living and development of sophisticated tastes.
Mustard oil is slightly more viscous and has a lower saponification value and a higher refractive index compared to other vegetable oils. It does not readily thicken when heated or exposed to air, and is placed between non-drying and semi-drying oils.
Mustard oil is characterized by high content of erucic acid (40-55% of total fatty acids) which is responsible for the low saponification value of this oil compared to other vegetable oils. Oleic, linoleic, linolenic and eicosenoic acids together constitute over 40 per cent of the total fatty acids. The presence of lignoceric acid (0.80-1.0% of total fatty acids) has been reported in indigenous oils.
The components glycerides of the oil according to a study consist of mono-oleo-di-erucins, 54; di-oleo-mono-erucins, 28%; and mono-saturated mono-oleo-mono-erucins, 18%.
The high content of erucic acid in mustard oil has been reported to affect the metabolism of experimental animals in various ways. The poor digestibility of the oil by rats has been attributed to slow rate of absorption of erucic acid from the intestine. However, later work has shown that the oil is highly digestible.
Erucic acid is considered to be the cause for the increase in adrenal cholesterol in rats, with growth depressive effect. Monkeys fed on diets containing 18 per cent protein and 20 per cent fat as mustard oil showed marked localization of erucic acid in the heart muscles thereby resulting in the myocardial lesions.
At 5 per cent and 10 per cent oil intake, there was no myocardial change in monkeys. Feeding of the oil at 5, 10 and 15 per cent by female rats showed marginal increase of total lipids in kidneys, adipose tissues, adrenal glands and ovaries but no change in liver and spleen. However, the accumulation of erucic acid gradually declines on prolonged feeding. The organs probably develop the ability to oxidise the erucic acid to varying degrees.
The fatty acid profile of myocardial lipids in humans whose habitual diets contained mustard oil showed that the level of erucic acid is low and the risk of developing myocardial fibrosis is less at the level of intake of mustard oil prevalent in India. Cultivars of rapeseed lacking in erucic acid and having high contents of oleic and linoleic acids have been developed in Canada and some European countries.
In Canada a “double low” rapeseed containing less than 5 per cent erucic acid (the Canadian Government’s ‘zero effect’ level) and not more than 3 mg/g of glucosinolate of dry meal has been released for commercial production in 1974. The name ‘Canola’ (implying Canadian low acid seed or Canadian oil) was officially recognized in 1980. Similar breeding work is also in progress at the Indian Agricultural Research Institute, New Delhi.
The un-saponifiable matter in mustard and rapeseed oil varies from 0.6 to 1.2 per cent, about half of which is sterols with β – Sitosterol, campesterol, and brassicasterol as major constituents. Cholesterol and 24-dehydrocampesterol are also present in small amounts. Among the vegetable oils, rapeseed oil is one of the richest in sterols except stigmasterol which finds important applications in the synthesis of steroid drugs. Processes have been developed for the extraction of sterols from soap-stock obtained from rapeseed oil refining.
Medicinal Uses of Mustard Oil:
Mustard oil possesses mild rubefacient properties. It is employed as a liniment for rheumatic pains and as a substitute for camphorated oil. The volatile oil of mustard is given internally in colic; in overdoses it is highly poisonous, producing gastro-enteric inflammations and probably interfering with vital processes by pervading the whole system. In mild bronchitic affections in children, it is used as a mild counter-irritant on the chest.