FE475 FOOD QUALITY CONTROL LABORATORY

ANALYSIS OF OILS AND FATS

GROUP = B – 2

M. HAKAN MAVİŞ

Purpose:

The purpose of this experiment was to analyze different oils and fats labels and to compare properties of these oils and fats with each other, and to inquire about oils and fats standards.

Theory:

Olive oil: production, trade quality, and composition

The olive tree belongs to the botanical family of Oleaceae, the most important species being Olea europea sativa. It is characterized by its extended life span. The olive tree has adapted to heat and dryness and is therefore well suited to the environment in which it grows. The ideal conditions for its growth are at a mean temperature of 15 to 20 °C, i.e. especially in Mediterranean countries. During maturation, the oil content of the olive increases and reaches 15 to 30% weight of the total fruit. Harvesting takes place from November to February, using the traditional method of hand picking. Beating the olives off the tree with poles considerably increases the quantity of olives collected per day. The olives are collected in large light synthetic fibre nets positioned under the trees. After harvesting, the fruit has to be sorted, especially when it has been collected from the ground.

o   Native olive oils

Native olive oil is oil obtained from the olive by mechanical or other physical means. It is the oily juice of the fruit and not (in contrast to other vegetable oils) a seed oil. Native olive oil is virtually the only oil that can be consumed as it is actually obtained from the fruit, and when properly processed, maintains the taste and odour of the fruit unchanged.

Firstly, the olives are washed to eliminate any remaining impurities (e.g. dust or soil). Then they are crushed whole, without prior stoning, in roller mills or by modern hammer crushers. For separating the solids and liquids, the olive paste is spread onto a pulp mat, which is then stacked onto other mats to form a cylindrical load held fast by a central guide. The pressure exerted on the stack causes the liquids to run while the solids (pomace) are retained on the pulp mats. The vegetable water and oil gradually seep out, running down into a set of decanters. The mixture of water and oil produced by this traditional pressing method can be separated by gravity in decanting vats. A more rapid separation can be achieved in centrifuges.

By using modern technology the process is simplified. The pomace, oil and vegetable water are separated by continuously centrifugating the paste. After being suitably thinned with lukewarm water, the paste is injected into centrifuges. Because of the different densities of the three substances, an immediate separation can be achieved.

o   Refined olive oil

Native olive oils that have defects in the form of a low sensory rating (see appendix) and/or a high free acidity have to be made fit for consumption by refining. The process of refining includes neutralisation, decolouration and deodorising. Neutralisation is for eliminating the excess of free fatty acids in the oil. Alkaline bleaches (e.g. sodium hydroxide) are normally used for this process. Minor quality oils often have an intense or abnormal colour which has to be corrected by decolouration. This is a physical process carried out by “surface absorption” with natural colourings being absorbed onto substances such as bleaching clay and active carbon. The purpose of deodorising (treating the oil with steam in a vacuum at high temperature) is to eliminate defective odours and flavours in the oil.

Olive oils that have been refined are pale in colour and not very viscous. They have little or no taste or odour and a very low acidity.

o   Trade quality

Olive oil is traded on the international market at a higher price than other vegetable oils. Consequently, adulteration of olive oil with cheaper oils is a temptation. To guarantee a fair trade and to protect consumers, the European Commission (EC) (1) has introduced definitions and fixed criteria for olive oil and olive-pomace oil. These criteria are set in place to distinguish the different types of olive oils and to protect their quality and purity. They include limits for the fatty acid composition, free fatty acids, aliphatic alcohols, the content and composition of sterols, erythrodiol and uvaol, the peroxide level and the presence of saturated fatty acids at the 2-position within the triglycerides and trilinolein. The criteria also define the sensory characteristics for virgin olive oils.

Used generically, the term olive oil means the oil obtained solely from the fruit of the olive tree. It also excludes mixtures with oils of other kinds. Olive-pomace oil may not use this term either. Olive oil may be called by one of the following designations provided it complies with the relevant criteria fixed in the standard.

Virgin (or native) olive oils are oils obtained from the fruit of the olive tree by mechanical or other physical means under conditions, particularly thermal conditions, that do not lead to the deterioration of the oil. Virgin oils have not undergone any treatment other than washing, crushing, pressing, centrifugation, and filtration. When virgin olive oil is intended for consumption in its natural state, it is called by one of the following names:

• Extra virgin olive oil – a virgin olive oil that has a sensory rating of 6.5 or more (see appendix) and a content of free fatty acids, expressed as oleic acid, of not more than 1 gram per 100 grams.

• Virgin olive oil – a virgin olive oil with content of free fatty acids of not more than 2 g per 100 g. (Sensory rating of at least 5.5.)

• Ordinary virgin olive oil is a virgin olive oil that has a content of free fatty acids of not more than 3.3 g per 100 grams. (Sensory rating not more than 3.5.)

Olive oil is the oil consisting of a blend of refined olive oil and virgin olive oil that is deemed independently fit for consumption.

Olive-pomace oil is the oil obtained by treating olive pomace with solvents. It can be classified as follows:

• Refined olive-pomace oil is obtained from crude olive-pomace oil by refining.

• Olive-pomace oil is a blend of refined olive-pomace oil and virgin olive oil that is deemed independently fit for consumption. In no case whatsoever may it be called “olive oil”.

The different grades of olive oil and olive-pomace oil are identified by the purity and quality criteria laid down in the trade standards of the EC. For each grade, minimum or maximum limits for the content of the different parameters are prescribed.

• Composition of olive oil

Olive oil is a mixture of glycerides, which are esters of glycerol with fatty acids. In addition, olive oil contains small amounts of free fatty acids, glycerol, phosphatides, flavour compounds, sterols and other minor components.

The major fatty acid of olive oil is the monounsaturated oleic acid (C18:1). The mean fatty acid composition of olive oil is as follows:

Palmitic acid (C16:0) 7.5-20%

Palmitoleic acid (C16:1) 0.3-3.5%

Stearic acid (C18:0) 0.5-5.0%

Oleic acid (C18:1) 55.0-83.0%

Linoleic acid (C18:2) 3.5-21.0%

Others 1.5-3.2%

The fatty acid composition of olive oil is influenced by different factors, such as the variety of the olive tree, agricultural and climate factors.

The nonglyceride fraction of olive oil comprises several groups of compounds: nonglyceride fatty acid esters; hydrocarbons; sterols; triterpene alcohols; tocopherols; phenols; phospholipids; chlorophylls; and flavour compounds (see below).

Although the largest proportion of fatty acids is esterified with glycerol, small quantities of fatty acids form esters with a variety of other alcoholic compounds, including methanol, ethanol and triterpene alcohols. The main triterpene of olive oil is squalene, a biochemical precursor of sterols. Olive oil is richer in squalene than most vegetable oils. Furthermore, there are different polycyclic aromatic hydrocarbons present in olive oil, as well as small quantities of b -carotene. The main sterol present in olive oil is b -sitosterol which accounts for about 95% of the total sterols. Campesterol represents 3%, the remaining 2% are a mixture of other sterolic constituents.

Most of the tocopherol in olive oil is a -tocopherol which has the highest vitamin E activity. Its content is on average 15-25 mg/100g. In general, native olive oils have a higher vitamin E content than refined olive oils.

The olive mesocarp contains phenolic compounds which are mainly water soluble. Some quantities of phenolics, however, are carried into the olive oil. The main polyphenols of olive oil are tyrosol and hydroxytyrosol, derived from the hydrolysis of oleuropein, the bitter component of the olives. Benzoic acid and cinnamic acid, probably originating from the degradation of flavonoids, are also present in olive oil. The phenolics of olive oil decrease its oxidation rate, because they are potent antioxidants. Virgin olive oil has a characteristically pleasant flavour. The main groups of flavour substances are aliphatic and aromatic hydrocarbons, aliphatic and terpenic alcohols, aldehydes, ketones, ethers, esters, furan and thiophene derivatives. The flavour complex changes as the oil deteriorates with storage time.

Analytical quality controls for olive oil

Acidity

Lipolytic processes in the olive start to break down the triglycerides in the maturation stage. This becomes more prevalent at harvesting. These lipolytic processes are intensified by hydrolysis and autoxidation, leading to the formation of free fatty acids which decrease the sensorial quality of the oil. The lower the content of free fatty acids the higher the quality of the oil.

The content of free fatty acids is mainly influenced by the time of harvesting, the duration between harvesting and processing, and storage conditions of the olives.

Peroxidation

Lipid peroxidation leading to oxidative rancidity is the main change causing deterioration of olive oil during storage. It is due to oxidation of unsaturated fatty acids initiated by free radicals and the subsequent formation of compounds possessing unpleasant taste and odour.

The formation of peroxides depends on several factors. All influences which promote the formation of free radicals such as light, high temperature and contact with metals increase lipid peroxidation. Thus, conditions and duration of storage of both the olives and the oil are of great importance.

Purity parameters

The sterol, erythrodiol, uvaol and alkanol contents are very important for the investigation of the quality and purity of olive oil. These minor components cannot be converted or broken down but can be separated from it by suitable techniques.

The composition of sterols

It is unique for each vegetable oil. For olive oil, b -sitosterol is the main sterol, and also campesterol is present in measurable amounts. If other sterols can be detected, it is an indicator for an adulteration with other oils or fat, for example, substitution of sunflower oil for part of the olive oil is reflected by the presence of stigmasterol, which is absent from olive oil.

The total sterol content

It is much higher in native olive oils than in refined oils. Thus, the amount of sterols can indicate if a native olive oil has been adulterated with a refined olive oil. A minimum content for native olive oils is prescribed according to the EC-regulation.

The content of erythrodiol and uvaol is much higher in olive-pomace oils than in olive oils, so their presence shows if part of the olive oil has been substituted with olive-pomace oil.

Another parameter of purity is the stereospecific distribution of major fatty acids between the 1,3 and 2-position of glycerol in the oil. All vegetable oils are characterised not only by a specific fatty acid composition, but also by a specific distribution of their fatty acids within the triglycerides: saturated fatty acids are concentrated at the 1,3-positions and almost absent at the 2-position which is generally occupied by unsaturated fatty acids. If the proportion of saturated fatty acids at the 2-position is increased in olive oil then it can be assumed that there is an adulteration with a synthetic ester oil.

Sensory quality criteria of olive oil

The sensory analysis of virgin olive oil is based on a panel test, developed by the International Olive Oil Council. In this test, 8-12 selected, trained tasters analyse the flavour (which includes taste and odour) of virgin olive oil as well as the intensity of the different flavour attributes. (Examples for positive attributes are: “apple”, “fruity”, “green leaves”, “grass”, “bitter”, “harsh”, “sweet”; and for negative attributes: “winey-vinegary”, “metallic”, “earthy”, “muddy sediment”, “fusty”, “rancid”.)

The final rating is awarded on the basis of a scale of points running from 0, which indicates that the oil has extreme defects, to 9, which indicates that it has no defects at all. For extra virgin olive oils, the rating must be at least 6.5.

There are more than 50 varieties of olive trees leading to the specific odours, tastes and colours of the olive oils. For example, the olive oil from Tuscany may be fruity, but a little bit pungent, while oils from Malaga are often characterised by a light taste and a golden colour.

Furthermore, the sensory properties of oil are influenced by agricultural and climatic factors as well as by time and method of harvesting.

Results and Calculations:

Ø  Saponification value = [(B – A) / wt of sample] * 28,05

Saponification value = [(8,5 – 0,2) / 2g] * 28,05 = 116,40

Ø  % Free Fatty Acid = (V * 28,2 * N) / wt of sample g

% Free Fatty Acid = (0,7 * 28,2 * 0,1N) / 5g = 0,39 %

Ø  For iodine value  we prepared the blank = 0,1 ml 0,1N Na₂S₂O₃

Ø  Peroxide value = [(S – B) * N * 100] / wt of sample g

Peroxide value = [(5 – 0,3) * 0,1N * 100] / 5g = 9,4 %

Ø  Colour redness = 0,3 and yellowness = 2,0 with Lovibond Tintometer.

Ø  Refractive index = 1,468 with refractometer.

Discussion:

In this experiment we studied oils and fats analysis and depending on these analyses the composition of oils and fats were examined we analyzed some different labels of oils and fats according to saponification value, free fatty acid content, iodine value, peroxide value, colour and refractive index.

These tests display us some different characteristics of oils and fats that is used for quality degree.

Saponification value is an important parameter for oil and fats. Saponification value shows the weight of potassium hydroxide in mg required saponifying 1g of the oils and fats.

Free fatty acid content is crucial parameter for oils and fats. Free fatty acid content is usually calculated as oleic acid. If free fatty acid content is high oil and fat is to spoilage and free fatty acid is high and FFA content is harmful for human health. In addition; free fatty acid content shows an index of degree of hydroylsis of triglycerides (hydrolytic rancidity).

Iodine value is important for oil and fats because iodine value display the unsaturated bonds. Unsaturated bonds show the saturated ratio of oil and fat. Unsaturated bond containing oils is usually preferred.

Another important parameter is a peroxide value. Peroxide value shows that during storage of oils and fats, oxygen is absorbed of the unsaturated bond which reacts like those in peroxide. At peroxide value we examined the spoilage ratio arising from peroxide. That is; amount of oxidative deterioration (oxidative rancidity).

Another important parameter is a refractive index. Refractive index shows oil and fat whether unsaturated or saturated. If refractive index is high melting point is low and we understand that oils and fats are unsaturated.

Finally; we examined the colour of oil with Lovibond Tintometer and we measured approximately yellowness 2 and redness 0, 3.

After experiment saponification value was measured as 116, 4 ml this value is appropriate to TSE value, then free fatty acid content was measured as 0, 39 %. TSE value is maximum 0, 3 therefore our result was appropriate to TSE value. Next; iodine value was examined but we prepared the blank solution value of blank solution was measured as 0, 1. After that; peroxide value was measured as 9, 4 and TSE value is max. 20 therefore; our value is proper to TSE value. Then refractive index was examined and by refractometer was measured as 1, 468. this value also is suitable to TSE value. Finally; we said that examining oil had been produced according to TSE value and was standard oil.