Crude Sunflower oil is a non–volatile oil expressed from sunflower (Helianthus annuus) seeds. Sunflower oil is commonly used in food as a frying oil, and in cosmetic formulations as an emollient. There are several types of sunflower oils produced, such as (i) High Linoleic (Linoleic acid is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3). (ii) High Oleic (Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated omega–9 fatty acid, abbreviated with a lipid number of 18:1 cis-9. It has the formula CH3(CH2)7CH=CH(CH2)7COOH.) and (iii) Mid Oleic.
Sunflower oil is a food ingredient which is actively used in culinary. Thanks to oil, the product does not stick during frying and salads acquire nice taste. Moreover, some fats contain sunflower oil in their composition, for example margarine. It is also used for industrial purposes: this ingredient can be used in paints and lacquers production as well as in soap making. Among the varieties of Oleic product, crude oil made of sunflower seeds is considered to be the most healthy.
This oil contains such necessary elements for human body as:
It has a pleasant flavor and taste. However, it is not recommended to store it for a long time, as this can lead to the buildup of bitter taste and turbidity. The oil also contains unsaturated fatty acids. It is subjected to one pressing method, filtering, which allows saving all the healthy and necessary substances. Depending on the pressing method, the product may contain essential trace nutrients that are necessary for health: Vitamin “A”, “B”, “D”, “E” and Vitamin “F” which is an important element of the healthy state of fat metabolism. In the cosmetic industry, the sunflower oil is almost never used, but it can be found in popular traditional remedies and beauty recipes.
Crude pressed sunflower oil obtained from a local oil mill was refined using chemical method by degumming, neutralization, bleaching and de–waxing. The quality and composition of crude and refined oil were analyzed compared. Reduction in phosphorous content from 6.15ppm to 0, Free Fatty Acid (FFA) content from 1.1% to 0.24 % (oleic acid), peroxide value from 22.5 to 7.9 meq/kg, wax content from 1,420ppm to 200ppm and colour absorbance value from 0.149 to 0.079 (in spectrophotometer at 460nm) were observed from crude to refined oil. It was observed that refining did not have significant effect on fatty acid compositions as found in the percentage peak area in the GC–MS chromatogram. The percentage of unsaturated fatty acid in both the oils were recorded to be about 95% containing 9 – Octadecenoic acid (Oleic acid) and 11,14 – Eicosadienoic acid (elongated form of linoleic acid). The research results will be useful to small entrepreneurs and farmers for refining of sunflower oil for better marketability.
Crude sunflower oil is obtained from partially dehulled seeds by mechanical pressing followed by hexane extraction and water degumming. Quality and stability are the major factors in the production, acceptance and marketing of vegetables oil products. These properties depend mainly on seed quality, seed treatment prior to extraction, extraction method and processing conditions. They are influenced by the presence of some minor components, such as free fatty acids, Tocopherols, Phospholipids, Trace Metals and Waxes which have pro or anti oxidant properties. The stability and quality of vegetable oils are influenced by the presence of minor constituents such as Phosphatides and waxes. Processing of oils causes alterations in their chemical composition, affecting their quality and oxidative stability.
Vegetable oils are refined in order to remove the non–glyceride impurities that are present in the crude oil. Some of these impurities are naturally present in the seeds or formed during harvesting and storage of seeds or during extraction of crude oil and subsequently during its refining. Oil refining processes for vegetable oils are designed to remove these impurities from the oil or reduce them to a level where their deleterious effects on oil stability are minimum and made suitable for human consumption. Vegetable oil undergoes degradation almost immediately after the seed is crushed. The oil starts to show the sign of primary oxidation as measured by its peroxide value. Under certain circumstances the oil may develop a darker colour or higher free fatty acids and eventually an unpleasant flavour. Gums, phosphatides and mucilaginous substances act as emulsifier increasing loss of oil and decompose at high temperature, increasing colour of the refined oil. Free fatty acids increase foaming, reduce smoke point and diminish keeping properties of oil.
Presence of compounds such as Phosphatides, free fatty acids, odiferous volatiles, colourant, waxes and metal compounds in oil negatively affect taste, smell, appearance and storage stability of the refined oil and hence must be removed to yield a stable product with a bland or pleasant taste. In modern society, consumers cannot use crude oil directly without proper processing due to the unacceptable colour and odor. This has led to efficient refining process which involves removing these unpleasant impurities with the least possible effect on the desired components (Tocopherols, phenols, sterols) with the minimum losses of oil.
Chemical refining includes (1) Degumming (2) Neutralizing (3) Bleaching (4) Winterizing and (5) Deodorizing stages. When used for salad oil, the refined oil was winterized for wax removal and then deodorized. Though chemical refining decreased yield, higher investment cost, high chemicals used and higher waste, but has less effect on oil desirable components and oil stability. The objective of refining is to remove the objectionable impurities with the least possible damage to the neutral oil and minimum loss of oil during processing.
Development of oil refining unit:
An experimental oil refining unit has been developed for minimal refining of sunflower oil. The unit consists of:
(i) One open mild steel tank with conical bottom for degumming/neutralization;
(ii) One closed oval tank for vacuum drying/bleaching and;
(iii) One filter for filtration of oil. The oil de–waxing section consists of a (1) Well insulated oil tank, (2) Cooling coil, (3) Water cooler and (4) Filtration unit. The helical pipe is immersed in the oil in the tank and the cold water from the cooler is re–circulated for cooling the oil to crystallize the wax. The centrifugal pump is connected to the tank outlet to force the oil through the pressure leaf filtration unit to filter the wax.
Testing of the refining unit:
Mechanically pressed crude sunflower oil was obtained from a local oil mill. The crude oil was kept in tin container away from the light, high temperature and oxygen to avoid auto oxidation.
The crude oil in the open conical tank was heated to 45 °C (113 ºF) and degummed by adding 0.2% phosphoric acid (50% w/w strength) with slow agitation for 30 min. Then the oil was settled for 30 min and the water with dissolved gum was drained out.
The temperature of oil was further increased to 71 °C (159.8 ºF) and mixed with desired quantity of sodium hydroxide solution (12%) as per FFA content of the oil with slow agitation for 15 min followed by settling for 30 min. The soap stock with residual gum was removed by draining. The neutralized oil was washed with 20% hot soft water at 75 °C (167 ºF) and residual soap was removed by settling.
Vacuum drying and bleaching:
The washed oil was heated at 77 °C (170.6 ºF) under 75 mmHg vacuums for 30 min to remove the moisture traces. The oil was next mixed with 1.5% bleaching earth (w/w) with vigorous stirring for 30 min under vacuum for bleaching. Then oil was cooled to 60 °C (140 ºF) and filtered to obtain the bleached oil.
The bleached oil was cooled gradually at 15 °C (59 ºF) for 4 h for crystallization of wax and filtered to remove the wax.
Quality analysis of Sunflower Oil:
The crude oil, refined oil obtained from the experimental refining unit and commercially available refined sunflower oil sample were analyzed for moisture content, specific gravity, kinematic viscosity, total phosphorous content (indication of phospholipids), Free Fatty Acid (FFA) content, peroxide value, colour value and wax content using standard procedure.
The specific gravity of oil samples were measured by pycnometer method and viscosity by Kinematic Viscometer at 40 °C (104 ºF). Moisture content was determined by oven drying at 105 °C (221 ºF) for 24 h.
The free fatty acid content was measured using the titration method with 0.1 normal sodium hydroxide solution and phenopthaline indicator and expressed as % Oleic Acid. The absorbance of oil was measured at wavelength of 460 nm in a spectrophotometer using Carbon tetrachloride as blank which was taken as an indicator for colour comparison. Peroxide value was determined by Sodium Thiosulphate titration method.
Phosphorus content (An indicator of phospholipid content) of oil was determined by wet digestion using di–acid mixture (Nitric Acid and Perchloric Acid @ 3;2). Phosphorus content in the digest was estimated spetrophotometrically at 470nm wavelength after developing yellow colour with vanado–molybdate reagent. The standard curve was prepared using 0ppm to 20ppm phosphorus prepared with analytical grade KH2PO4.
The wax content was determined gravimetrically by dissolving oil in acetone, cooling at 0 ºC (32 ºF) for 24 h and filtering through Gooch crucible.
Standard Specification of Crude Sunflower Oil: