Factors Affecting Quality and Content Properties of Olive Oil
There are multiple variables that have an impact on the quality of the oil at every stage of the process, from the geographical location and climatic conditions in which the olive tree grows, to the type of olive, from the cultivation and harvesting to the technology used to separate the oil, to the storage and preservation of the oil obtained in the final stage. All of these variables play a role in the quality criteria of the oil and the amount of micronutrients it contains.
Pre-Harvest Variables
The main variables are the geography and climate where the tree grows, the type of olive, the harvest time, the characteristics of the soil in which it is rooted, the cultivation technique, the agricultural struggle methods applied, fertilization and irrigation.
Climate
Climate can degrade oil quality by impairing the maturation process. Olive can withstand high temperatures up to a maximum of 40 °C, provided that it is well watered, the lowest temperature it can withstand is -7 °C, and below this temperature, frost damage increases. The duration of sunshine, the temperature to which it is exposed, the amount of seasonal precipitation (the annual precipitation requirement of olive is 700-800 mm) are the factors affecting it. Relative humidity (the percentage of moisture the air can hold at a given temperature), moist air from the sea and large water surfaces are beneficial for olives. Light winds in May-early June help fertilization. It has been revealed by research that these climate-based variables are effective in the formation of the chemical composition of the oil. In cold regions, the fruit ripens slowly, the ripening period is prolonged, and it causes bad woody flavored oil to be obtained with the danger of frost. In the southern regions, a more viscous oil is obtained. The lack of water in the spring generally affects the flower formation negatively, while the lack of water in the summer causes wrinkling and shedding of the fruits. Abundant precipitation causes a more fluid oil to be obtained, and a pleasant-light-smelling oil is obtained that is resistant to rancidity due to high chlorophyll.
The composition of the major and minor components in olive oil varies depending on the latitude where it is grown and the climatic conditions at this latitude, as well as the olive variety. For example; Olive oil, which is located in the warm climate zone, shows an increase in palmitic acid and linoleic acid levels.
Soil
The olive tree likes rough, sloping terrain, prefers permeable soils and sufficiently airy and moist soils. The ideal soil for olives is deep, calcareous, sandy, clayey soil. The oil of olives grown in clay soils is dark in color. Oil with different properties can be obtained from the fruit of the same type of olive in different geographical and soil characteristics.
Agricultural Control Methods
Olive cotton louse, olive moth (flower generation), olive flower stalk stinger, etc. Spraying against pests such as flowers can turn into fruit without being damaged, and increase yield and quality. If possible, it should be preferred that this struggle be done in natural ways based on good agricultural practices.
During this period, nutritional supplementation in olives is also very important, and flowering and fruiting should be supported by foliar fertilization and eliminating the deficiency of nutrients.
Olive fly (Bactrocera olea Gml.), which is known to damage olives before harvest, should be adequately controlled. Quality defects can be observed in oils obtained from olives exposed to olive fly pests due to various biochemical activities. Depending on the intensity of olive fly damage, the saturated fatty acids (usually palmitoleic, stearic and linolenic) compositions of oils increase, and the amounts of oleic acid decrease. In addition, it reduces the amount of polyphenol, which is one of the unsaponifiable components and also a natural antioxidant, and has some negative effects on the sterol composition.
It is essential to provide the tree with sufficient moisture to ensure high yields. The oleic/linoleic acid ratios of the oils obtained from the irrigated olive groves are variable, the amount of linoleic acid is less, and it has a slightly pleasant smell.
Harvest Related Factors
Olives that are harvested early produce oil with low acidity, low yield, green color and fruity taste. Oleic acid/Palmitic acid ratio is high. When harvest is delayed, a yellow oil with slightly higher acidity is obtained. Linoleic / Palmitic acid ratio is high. Very ripe olives have a pleasant ripe fruit flavor.
Olive harvest should be done with care; The acid and peroxide values of the oils to be obtained from crushed, aged, poorly cleaned, late harvested, soil-contacted olives will be high. Hand-picked olives from the tree, olives picked from the ground and damaged olives should be transported to the facility separately and processed separately. Olives that have fallen to the ground spontaneously during harvest and have matured and become soil-contaminated should be processed separately from intact olives. Beneficial components related to human health have been oxidized in the oil separated from the olive, which is defined as the "bottom olive" collected from the ground, and the oil from these olives cannot be eaten without refining in terms of smell and taste.
Harvested olives should be transported to the production area in the shortest possible way and as soon as possible, within 6 hours if possible, in latticed and perforated plastic crates that do not exceed 25 cm, allow air to breathe and do not damage the grain, and prevent escalation that causes deterioration. must enter the oil separation process without waiting. In particular, pans, jute or nylon sacks batter and crush the olive grain and accelerate the activity of micro-organisms, causing the start of fermentation (rot).
If the olives had to be kept waiting before the oil is processed, they can be kept in piles not exceeding 25 to 30 cm in height and in a well-ventilated, cool and dark place, if possible, on wooden or plastic slats for a maximum of 2-3 days. To prevent this situation, the harvest program should be done well.
Olive Type and Genetic Factors
Oil can be obtained from any type of olive. There is no scientific basis for the approach that only defines "oil of one kind is edible" or "olives for oil or table olives". Oil is obtained from all varieties. There is no olive variety that gives bad oil genetically. However, the oil obtained will differ according to the olive variety, especially in terms of the sensory qualities of the oil.
The size of the fruit, the ripening stage, the resistance to spillage affect the quality of the oil. Depending on the olive variety, its color may vary. Oil will be obtained from two different species in the same olive grove with different colors and characteristics. The phenolic compounds in the obtained oil also vary depending on the cultivation practices and processing conditions.
Pruning increases fruit size and meat ratio and provides more oil yield.
Oil Separation Method/Technology
Regular cleaning and maintenance of the machine unit where olives are processed is essential. The temperature of the olive paste formed by the machine should not exceed 25 °C. In this step, the application of high heat by giving hot water causes the micronutrients in the oil to be deteriorated. In the meantime, there is a loss of volatile substances with antimicrobial activity, one of the minor compounds in olives. High temperature changes the friction coefficient of the oil, which affects the fluidity, and allows the oil to separate from water and olive pomace more easily and quickly, and to obtain more oil from the same amount of olives. This approach will result in the loss of polyphenols and many healthful micronutrients in the oil, degrading the quality of the oil, sacrificing quality for the sake of cost.
The uninterrupted method used for production and the minimization of the system's contact with air throughout the production line have a positive effect on the quality of the oil. The use of a closed system in the kneading step of the olive paste and the introduction of nitrogen gas into the cavity in the boiler are methods used to improve the quality.
The working principles of modern uninterrupted system oil production machines require attention and knowledge. Users need to act consciously in the processing of olives of different quality. It should be cleaned frequently with automatic or manual cleaning and necessary adjustments should be made.
Oil Storage/Storage
The two most important factors that deteriorate the quality of olive oil are oxygen and heat. Oxygen degrades olive oil by oxidizing it with substances that give its smell, taste and color, but dissolve in oil and water, and antioxidant substances that have proven beneficial for human health, and heat accelerates this deterioration process, which is called oxidation. In addition, the quality characteristics of olive oil exposed to strong and continuous light (especially sunlight) will be adversely affected.
The obtained natural olive oil should be stored under suitable conditions to prevent deterioration in quality before it reaches the final consumer. An effective and healthy storage is related to the biological chemical properties of olive oil and the properties of storage materials. Tanks must be made of liquid impermeable materials and be physically and chemically stable against oil. It should not contain oil-degrading odors and flavors, it should not contain metals that will cause oxidation, it should protect oils from air and light, and keep the oil at a constant temperature. The most suitable material used to preserve the quality of olive oil by preserving it in the best way is stainless steel tanks. The temperature should preferably be around 15 °C.
It is not appropriate to store the oil in a plastic environment in terms of protecting the components it contains in terms of human health, the oil catches some substances in the plastic and this process causes the oil to oxidize and deteriorate. Natural olive oils preserved under suitable conditions do not lose their properties for 24 months, and riviera and refined olive oils for 18 months.
Quality Measurement Methods
The simplest method is to ignite the oil. The oils taken from various oil samples in a small scale are placed on a plate. A wick is made from cotton and all samples are lit simultaneously, like an oil lamp. The oil that burns the longest without soot is the oil with the lowest acidity. In contrast to this thin oil with low acidity, oil lamp with high acidity burns more quickly naturally.
In another simple method; oil is poured into a tea glass and the glass shakes slightly around its axis. Olive oil ripples. If the oil slowly descends from the rim of the glass, it is heavy, pure oil. Oil that has undergone the refining process, mixed with hazelnut or flower oil, goes down the rim of the glass quickly.
Quality control parameters; It is divided into two parts as analyzes that indicate quality and purity.
At the beginning of the parameters indicating the quality; free fatty acidity, peroxide, UV absorption values (specific absorbance-K232, K270, AK), ether-insoluble impurities, moisture and volatile matter, heavy metals and sensory properties (includes natural olive oils).
The parameters that indicate its purity are; refractive index, fatty acid composition, sterol composition, total sterol amount, ß-position palmitic and stearic acid amount, wax amount, triglyceride composition and stigmastadiene amount.
One of the natural olive oil quality indicators, sensory properties, is trying to measure flavor and smell by tasting and smelling. Although it is not an objective and measurable method, it is still very important. If an olive oil has a bad smell, there is no need to look at its color or taste. Such an oil, at the first step of all exams, failed the class. This process, performed by tasting experts, is called degustation. Degustation, which is carried out depending on the experience of tasting experts, is an important olive oil quality criterion. It is thought that more than 70 molecules create the taste and smell of olive oil. When a piece of fresh village bread is dipped in a good olive oil, a light fruit flavor is felt in the nose. When a sip of olive oil is circulated in the mouth; If it tastes fruity, this is a sign that the oil is of good quality, it is normal to have a bit of a burning sensation in the throat after swallowing the oil.
Compiled by: Uğur Saraçoğlu (ugisaracoglu@yahoo.com.tr)
Resources:
1. Olive Oil Quality, Ümmühan Tibet, Aegean Analysis Food Laboratory, İzmir, Power Point Presentation, 2010.
2. Innovations in Olive Oil Production Technology, Prof. Dr. Aytaç Sargın Gümüşkesen, Ege University Engineering Faculty, Food Engineering Department, Power Point Presentation, 2010.
3. Effects of Storage and Packaging of Olive Oil on Oil Quality, Türkan Keçeli, Çukurova University Faculty of Agriculture Department of Food Engineering Balcalı, Adana, Turkey 10th Food Congress; 21-23 May 2008, Erzurum.
4. World Olive Encyclopedia; International Olive Council; Fausso Luchetti, 1997.
5. Olive oil; Fahrettin Göğüş, Mücahit Taha Özkaya, Semih Ötleş, Eflatun Publishing House, 2009.
6th Izmir Olive Symposium; In Search of the Immortal Tree/Don't Touch My Olive, 2-3 September 2015.