IONIȚĂ Ana Corina1, MITITELU Magdalena1*, NICOLESCU Teodor Octavian2, NICOLESCU Florica3, UDEANU Denisa Ioana1, NEACȘU Sorinel Marius1, BUŞURICU Florica5, GRIGORE Nicoleta Diana1, MOROȘAN Elena1
1 Clinical Laboratory and Food Hygiene Department, Faculty of Pharmacy, ”Carol Davila” University of Medicine and Pharmacy, 6, Traian Vuia Street, 020956, Bucharest (ROMANIA)
2 Organic Chemistry Department, Faculty of Pharmacy, ”Carol Davila” University of Medicine and Pharmacy, 6, Traian Vuia Street, 020956, Bucharest (ROMANIA)
3Toxicology Department, Faculty of Pharmacy, ”Carol Davila” University of Medicine and Pharmacy, 6, Traian Vuia Street, 020956, Bucharest (ROMANIA)
4Pharmacognosy, Phytochemistry, Phytotherapy Department, Faculty of Pharmacy, ”Carol Davila” University of Medicine and Pharmacy, 6, Traian Vuia Street, 020956, Bucharest (ROMANIA)
5Faculty of Pharmacy, Ovidius University, Mamaia Blvd. 124, 900527, Constanta (ROMANIA)
*corresponding author: magdamititelu@yahoo.com
Abstract
We find sources of lipids in both the plant and the animal kingdom. The main source in the diet of fat-soluble vitamins is represented by dietary fats. The nutritional value of vegetable oils consists in their content in polyunsaturated fatty acids, especially in essential fatty acids and fat-soluble vitamins. In the experimental part we analyzed the quality of some vegetable oils often used in food. We chose virgin soybean oil, virgin coconut oil, virgin avocado oil, extra virgin and virgin olive oil, virgin pumpkin oil, refined sunflower oil and refined rapeseed oil.
Keywords: polyunsaturated fatty acids, vegetable oils, nutritive quality, fat-soluble vitamins
Introduction
Fats are important foods in terms of energy, because by ingesting a relatively small amount, the body benefits from a large number of calories compared to other foods. In addition to the food use of fats, many industries use different fats as raw and auxiliary materials such as: leather industry, cosmetics industry, paints [1,2,3].
Vegetable oils are an important part of the human diet. Vegetable lipids have an appreciable biological value because they contain essential fatty acids (linoleic acid, linolenic acid, arachidonic acid) [4-7]. Linolenic acid and arachidonic acid are indirectly or directly precursors of leukotrienes, prostaglandins and thromboxanes with important roles in the body. Essential fatty acids have a beneficial effect on cardiovascular diseases: they reduce triglyceride levels, decrease inflammation and platelet aggregation, prevent arrhythmias and help reduce the risk of coronary events. Experts say a 1% increase in their diet reduces the risk of heart attack by 40%. These acids help reduce the risk of developing malignancies, neurological disorders or complications related to diabetes and metabolic syndrome. Their association with the favorable evolution of pregnancy, the integrity of the skeletal system in the elderly, good visual acuity and adequate cognitive development in childhood were found [8-13].
Virgin vegetable oils are an important part of organic food. These have economic advantages for oilseed producers, as virgin oils have higher costs. They have the highest nutritional value. The production of virgin oils is usually done in small operations, with simple processing that involves only pressing and purification by filtration to remove solids. The preference for cold-pressed oils is mainly due to the numerous changes in nutritional trends and consumers’ perception of natural foods as more nutritious and of superior quality compared to those obtained by chemical processes [14-16]. It is known that plant and animal products for food can be contaminated with environmental pollutants, so there is a great emphasis on the quality of the environment in which they develop when seeking to obtain products with high nutritional value [17-21].
Refined oils are obtained with high yields, the price is lower, but also the nutritional value is low because the active principles (polyunsaturated fatty acids and fat-soluble vitamins) are greatly diminished during processing [1-3].
Material and Methods
In the experimental part of the paper were analysed a series of vegetable oils sold on the market and used in food to assess quality: virgin soybean oil, virgin coconut oil, virgin avocado oil, extra virgin and virgin olive oil, pumpkin oil virgin, refined sunflower oil and refined rapeseed oil. The following characteristics were analysed: organoleptic characteristics, the dissolved soap content was determined, the acidity index, the iodine index and the peroxide index were analysed [22,23,24].
The free acidity of the studied oils was determined according to STAS 145-67. Free acidity is the percentage of free fatty acids in the oil to be analysed and is conventionally expressed in the most representative fatty acid. For ordinary soybean oils, sunflower, peanuts, pumpkin are expressed in oleic acid, for coconut oil in lauric acid, for palm oil in palmitic acid, for castor oil in ricinoleic acid, for rapeseed oil in erucic acid. The procedure consists in dissolving an amount of oil in an alcohol-ether mixture, after which it is titrated with sodium or potassium hydroxide solution, in the presence of the phenolphthalein indicator. The appearance of pink indicates that all free fatty acids have been neutralized. In the presence of atmospheric oxygen, the fatty acids in the fat composition may be partially oxidized to form peroxides or hydroperoxides. The determination of the peroxide index is based on the property of the fat peroxide to react in the acid medium with potassium iodide, releasing the iodine, which is then titrated with thiosulphate. The determination of the humidity and the content of volatiles was carried out by the oven drying process at a temperature of 1030C, up to a constant mass, after which the samples were cooled and weighed into the vial with an accuracy of 0.001 g. Oils can contain natural alkaline constituents (calcium soaps) or accidental ones (sodium soaps from imperfectly refined oils). The principle of the method for determining the soap content in the analysed samples consisted in dissolving it in a hot acetone-water mixture and titrating with hydrochloric acid. Alkalinity may be expressed as a percentage of sodium hydroxide or in mg of sodium oleate per kg of sample.
Determination of acidity index: Principle of the method: extract the fatty acids with an alcohol-ether mixture, then titrate with KOH until neutralization, in the presence of phenolphthalein.
R-COOH + KOH → R-COOK + H2O
Determination of iodine index: Principle of the method: iodine index means the number of grams of iodine that can be added to 100g of fat or oil. Iodine is the lightest of the halogens and gives no substitute products.
Hanus method: It is based on the fact that the fats dissolved in chloroform add iodine monobromide to the double bond, and the excess of iodine monobromide releases iodine from potassium iodide, iodine which is titrated with sodium thiosulphate.
2CH3-(CH2)7-CH=CH-(CH2)7-COOH + 2BrI → CH3-(CH2)7-CHI-CHBr-(CH2)7-COOH +
CH3-(CH2)7-CHBr-(CH2)7-COOH
BrI +KI → KBr + I2
I2 + Na2S2O3 → Na2S4O6 + 2NaI
Determination of the peroxide index: Principle of the method: the peroxide index is used to determine the degree of rancidity of fats.
The peroxide index is the number of ml of 0,1 N sodium thiodulphate solution used for the titration of iodine released by peroxides from 1 g of fat or by the amount of iodine in grams per 100 g of fat.
CH3– (CH2)7– CH – CH – (CH2)7 – COOH +2HI → I2 + H2O +
CH3– (CH2)7– CH – CH – (CH2)7 – COOH
I2 + 2 Na2S2O3 → 2NaI + Na2S4O6
Results and discussions
Organoleptic properties are important for assessing the quality of oils. They allow the evaluation of the correct application of the obtaining technology, the identification of the rancidity processes (table 1).
The clear appearance and the lack of sediments give indications regarding the correctness of the manufacturing technologies or of the applied refining processes. The smell and taste provide little indication of the origin, of the raw materials, in the case of refined oils. Oils should not transmit the smell and taste of food or food. The colour is given by the pigments and is completed by the refining process. Carotenes and xanthophylls give a clear, golden colour. Chlorophyll gives the green colour. The colour may change depending on storage conditions. Under the action of light and air it fades.
Table 1. Organoleptic characteristics of the analyzed edible oils
| Oil sample | Colour | Smell | Appearance |
| Soybean oil, Herbavit | Fulvous | Specifically, no foreign odor | Clear, without suspensions, without sediment, viscous, does not contain impurities |
| Coconut oil, Solaris | White | Specifically, no foreign odor | Soft consistency at room temperature, liquid above 40 ° C, free of impurities, no suspensions, no sediment |
| Avocado oil, Herbavit | Chartreuse | Specifically, no foreign odor | Clear, viscous, without suspensions, without sediment, does not contain impurities |
| Pumpkin oil | Light green | Specifically, no foreign odor | Clear, viscous, without suspensions, without sediment, does not contain impurities |
| Extra virgin olive oil | Brown – green | Specifically, the accentuated smell of olives, without a foreign smell | Clear, viscous, without suspensions, without sediment, does not contain impurities |
| Corn oil | Yellow – Reddish | Specifically, no foreign odor | Clear, viscous, without suspensions, without sediment, does not contain impurities |
| Sunflower oil, Spornic | Light yellow | Specifically, no foreign odor | Clear, the viscosity is lower compared to extra virgin and virgin oils, without suspensions, without sediment, does not contain impurities |
| Rapeseed oil | Greenish yellow | Specifically, no foreign odor | Clear, viscous, without suspensions, without sediment, does not contain impurities |
| Sunflower oil, Carrefour | Yellow straw | Specifically, no foreign odor | Transparent, cea mai redusă vâscozitate, fără suspensii, fără sediment, nu conține impurități |
The values of the analysed indices are presented in table 2. The acidity index of fats and oils is greatly influenced by the technique used to obtain them and by the way they are stored. Fresh oils and fats contain small amounts of free fatty acids, approximately 0.15%. Cold pressed vegetable oils have a lower content of free fatty acids than those obtained by hot pressing. Fats stored in bad conditions and rancid ones often contain a higher amount of acids.
Refined oils have a much lower acidity due to the acid neutralization process performed in the refining step. The lower the acidity index, the lower the free acid content.
The iodine index gives us an indication of the degree of unsaturation of the respective fats and varies between quite high limits. In vegetable oils, according to the size of the iodine index, there are three categories of oils: drying oils (flax, hemp, poppy, walnut, etc.) which have the highest iodine index, usually higher than 120, semi-drying oils (de rapeseed, cotton), which have an iodine index between 100 and 120, non-drying oils (almond, olive) with an index between 30 and 60, below 90. In general, a great influence on this index is kept in poor condition and age, because larger or smaller amounts of oxygen can be fixed at double bonds in the rancidity process, which causes a decrease in the value of the iodine index. According to experimental data, soybean oil and sunflower oil have the highest degree of unsaturation. These oils have the lowest stability to oxidative processes. The lowest iodine content is coconut oil, which is also the most stable at high temperatures (table 2).
The peroxide index indicates the degree of rancidity of a fat. The lowest peroxide indices are found in oils that also have a lower iodine index, these oils having a lower tendency to rancid (table 2).
Table 2. The values of the analysed index of edible vegetable oils
| Oil sample | Acidity index
mg KOH/g |
Alkalinity
mg sodium oleate / kg |
Iodine index g I2 / 100 g oil | Peroxide index
mEq O2 / kg |
| Soybean oil, Herbavit | 3.46 | 1 | 130.5 | 10.7 |
| Coconut oil, Solaris | 1.11 | – | 10.3 | 9.1 |
| Avocado oil, Herbavit | 3.26 | 1 | 101.3 | 9.3 |
| Pumpkin oil | 0.6 | – | 120.1 | 9.5 |
| Extra virgin olive oil | 1.12 | – | 90.2 | 9.4 |
| Corn oil | 1.06 | – | 80.7 | 9.7 |
| Sunflower oil, Spornic | 0.6 | – | 135.2 | 11.1 |
| Rapeseed oil | 0.5 | – | 110.4 | 10.4 |
| Sunflower oil, Carrefour | 0.6 | – | 130.5 | 11.9 |
By determining the alkalinity of the oils (tab. 2), the lack of soap was found in oils other than soybean and avocado oil.
Table 3 presents the experimental data obtained from the analysis of moisture and dissolved soap from the analysed oil samples.
Table 3. Determination of moisture and the free acidity in the analysed oil samples
| Oil sample | Humidity % | Acidity%
oleic acid |
| Soybean oil, Herbavit | 0.01 | 0.15 |
| Coconut oil, Solaris | 0.01 | 0.20 |
| Avocado oil, Herbavit | 0.01 | 0.18 |
| Pumpkin oil | 0.02 | 0.05 |
| Extra virgin olive oil | 0.02 | 0.14 |
| Corn oil | 0.01 | 0.11 |
| Sunflower oil, Spornic | 0.04 | 0.04 |
| Rapeseed oil | 0.03 | 0.03 |
| Sunflower oil, Carrefour | 0.04 | 0.04 |
The humidity in the analysed oils corresponds to the existing standards, being between 0.01-0.04%. The studied oils have a free acidity corresponding to the standards in force, the values being between 0.05-0.21% oleic acid [23-24].
Conclusions
Fat intake must be rational in relation to the body’s energy needs. Fat abuse leads to disease (obesity), and a low content leads to malnutrition.
In the composition of the menu, vegetable fats must represent 50% of the total fat for adults, and in children and teens products of animal origin (butter, dairy products) can reach up to 85% of total food. Thus, a diet rich in solid fats (cattle, sheep), which have a high content of saturated acids, causes an increase in serum cholesterol, and diets in which unsaturated fatty acids predominate (sunflower oil, corn, soybean oil), have the effect of reducing serum lipids. All the naturally occurring nutrients in the plants from which the oils are extracted are influenced by the technological processes of obtaining the finished product. For this reason, the more intense the processing of the product, the lower the percentage of nutritional principles.
From the experimental data we observe that the free acidity of the analysed oils corresponds to the standards in force, the oils obtained by pressing still registering a higher value which indicates a higher content in free acids. Refined oils have a much lower acidity due to the acid neutralization process performed in the refining step. Soybean oil and sunflower oil have the highest degree of unsaturation. These oils have even the lowest stability to oxidative processes. The lowest iodine content is coconut oil, which is also the most stable at high temperatures. The lowest peroxide indices are found in oils that also have a lower iodine index, these oils having a lower tendency to rancidity as well as a higher stability.
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