Sunflower plant having the botanical name Helianthus annuus, is the source of one of the most popular vegetable oils, i.e., sunflower oil. Sunflower crop is cultivated in many countries around the world including India. Different types of sunflower seeds are available which contain oils having different unsaturation. Some varieties of sunflower seeds are eaten as a delicious and nutritious snack directly and are known as confectionary (or non-oil) sunflower seeds. Some sunflower seeds have either high oleic acid or high linoleic acid content. Other varieties are used to extract sunflower oil and their crops are called oilseed sunflower crops. Each sunflower seed variety has unique contents of saturated, monounsaturated and polyunsaturated fatty acids. Sunflower oil is used as cooking oil, while the protein-rich deoiled cake or meal is used as a component of animal feed formulations. Several perennial species of sunflower are also grown in gardens.
Sunflower plants, even while growing, tilt to face the sun during the day and gain more sunlight for photosynthesis. This tracking of the sun by the plant is known as ‘heliotropism’. This continues for a short time when the sunflower plant blooms. The young sunflower heads track the sun during the day. Hence their name ‘sunflower’!
The present series of articles discuss the crop cultivation, properties of sunflower oil, their manufacturing and refining methods, applications and commercial aspects.
CULTIVATION AND YIELD
Sunflower can be cultivated in any season, i.e., Kharif or Rabi or spring, throughout India. It takes about 80 to 90 days in Kharif, 105 to 130 days in Rabi, and 100 to 110 days in the spring season. Sunflower, unlike most other crops, is not affected by the season and day length.
In Europe, sunflower is grown annually in relatively warm areas such as France, Hungary, Romania, Bulgaria, Spain, Italy, Ukraine and Russia. Sunflower is an important crop choice for producers in the USA, especially in the northern plains of the Dakotas to the panhandle of Texas.
The oil type sunflower seeds, which are used for extraction of oil, contain about 38 to 50% oil and about 20% protein. In other terms, 1.398 kg of sunflower seeds can produce one litre (1 lit) of oil. The actual oil yield depends on the geographical factors (soil, weather), quality of seeds, extraction methods and parameters, etc. The actual yield of sunflower oil can be about 42 gm from 100 gm seeds.
Sunflower is one of the most important oilseed crop grown in temperate countries. Sunflower oil is considered as premium edible oil due to its high unsaturated fatty acids content, which is considered as healthy. Sunflower oil is the vegetable oil of preference among consumers around the world. In India, sunflower oil is the largest selling vegetable oil in the branded oils segment.
Sunflower seeds contain up to 50% of triglyceride oil and up to 20% protein. Small quantities of waxes are also present in the oil. Considerable amounts of vitamins, minerals and tocopherols (vitamin E) are also present. Magnesium, copper, iron, calcium, zinc, sodium, potassium, phosphorus, selenium, and manganese are found in sunflower seeds. Sunflower oil is also rich in omega-6 fatty acids. Sunflower oil does not contain dietary cholesterol.
Regular sunflower oil typically contains about 69% linoleic (C18:2) acid, about 20% oleic (C18:1) acid, and about 11% saturated fatty acids – stearic (C18:0) acid 6% and palmitic (C16:0) acid 5%. However, a number of strategies have been adopted to present advance range of sunflower oils with elevated levels of oleic acid, stearic (C18:0) acid, linoleic acid and palmitic (C16:0) acid and low saturated fatty acids. Research on new varieties of sunflower seeds is ongoing to try to develop seeds and modify their fatty acid profile to improve functionalities of the oil.
There are four main varieties of sunflower oil which are produced commercially from the respective sunflower seed varieties. These types are – high-linoleic acid, high-oleic acid, mid-oleic acid and high-stearic combined with high-oleic acid. The major fatty acids contents of these varieties are listed in the following table.
TABLE 1: FATTY ACIDS CONTENTS OF VARIOUS TYPES OF SUNFLOWER OIL
|SUNFLOWER OIL TYPE||MAJOR FATTY ACIDS CONTENTS, %|
|High-Linoleic Type||Linoleic (C18:2) acid 69%|
|High-Oleic Type||Oleic (C18:1) acid 82%|
|Mid-Oleic Type||Oleic (C18:1) acid 65%|
|High-Stearic with High-Oleic Type||Stearic (C18:0) acid 18% and Oleic (C18:1) acid 72%|
Sunflower is liquid at room temperature. Raw oil may get cloudy at lower temperatures in the winter due to precipitation of waxes. The refined sunflower oil is a clear, slightly amber coloured liquid with a slightly fatty odour. Typical physical properties of sunflower oil are listed in the following table.
TABLE 2: TYPICAL PHYSICAL PROPERTIES OF SUNFLOWER OIL
|Saponification value||188 – 194|
|Iodine value||120 – 145|
|Unsaponifiable matter||1.5 – 2.0 %|
|Viscosity at 25 deg. C (Unrefined Oil)||0.04914 kg/m*s|
|Smoke Point (Unrefined Oil)||107 deg. C|
|Smoke Point (Refined Oil)||232 deg. C|
Typical nutritional composition of 100 gm of sunflower oil is presented in the following table.
TABLE 3: TYPICAL NUTRITIONAL COMPOSITION OF SUNFLOWER OIL (100 gm)
|DESCRIPTION||AMOUNT IN 100 gm|
|Energy||3700 kJ / 900 kcal|
|Saturated fatty acids||11 – 12 gm|
|Mono-unsaturated fatty acids||24 – 27 gm|
|Polyunsaturated fatty acids||62 – 64 gm|
||62 – 64 gm|
|Vitamin E||45 – 90 mg|
[Source – FEDIOL]
The vitamin E content of sunflower oil is 375 to 750% of the Recommended Daily Allowance (RDA) of the vitamin. Sunflower oil is one of the best natural dietary sources of vitamin E.
Sunflower seeds obtained from oilseed sunflower crops cultivation are used to producer sunflower oil. The confectionary sunflower seeds are either processed along with their hull (shell) or after removing the hull, the resulting kernels are processed to obtain the desired snacks.
Due to high oil content, sunflower seeds can be processed to produce oil using expellers and also by using the solvent extraction methods.
To produce oil from sunflower seeds, they must be cleaned first to remove any foreign matter and dust. The cleaned seeds are usually dehulled, i.e., shell is removed to separate the kernels, using centrifugal or pneumatic sheller or dehuller. About 20% to 30% of hulls are removed during dehulling. Removal of hulls improves the quality of oil as well as meal.
The dehulled sunflower seeds are ground to produce coarse meal. This is then crushed into uniform fine particles using hammer mills or grooved rollers.
This fine meal is then heated and then pressed in expellers to obtain oil. The deoiled meal contains some residual oil which is extracted using solvent extraction.
During expeller process, sunflower kernels are crushed under pressure to expel the oil within. This method may or may not use higher temperatures. Cold pressed oil has lower free fatty acids content and lesser oxidation products as compared to the oil expelled using higher temperatures. This oil is filtered to remove any solids. The expeller sunflower oil may be used directly for consumption in various applications.
The second and most commonly used manufacturing process to produce sunflower oil is the solvent extraction process using food grade hexane as the solvent. Hexane is passed through the expeller oil cake or meal to obtain a mixture of oil and solvent called miscella. Solvent is removed from the oil and the remaining meal in separate equipments to obtain desolventized sunflower oil and meal. Large capacity solvent extraction plants are used to produce solvent-extracted sunflower oil on commercial scale. This oil is processed further to remove the free fatty acids, gums, colour, waxes and odour through alkali refining, degumming, bleaching, winterization and deodorization.
Generally, extracting the oil first by using expellers followed by removing the residual oil in the cake or meal using solvent extraction, offers several advantages in terms of yield and quality.
The oils obtained by both these processes undergo refining to produce refined sunflower oil.
A schematic diagram of sunflower seeds processing and oil extraction methods are presented in the following figure.
FIG. 1: SUNFLOWER SEEDS PROCESSING AND OIL EXTRACTION METHODS
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