A ccording to their chemical composition, fats and oils are esters of glycerol and higher fatty acids, so they are classified into triglycerides, and also into a wider group of compounds called lipids. They do not dissolve in water, but dissolve in organic solvents.
Fats are compounds with saturated fatty acids (palmitic, stearic), and are therefore at room temperature in a solid or semi-solid state, and oils are compounds with unsaturated fatty acids (MUFA, PUFA) and are therefore at room temperature in a liquid state. Due to their chemical composition, oils and fats are prone to spoilage.
HYDROLYTIC SPOILAGE
The first form of spoilage that can take place is hydrolytic spoilage that occurs in the presence of water and lipolytic enzymes, still in the fruit or seed.
The degree of hydrolytic deterioration betrays the health of the fruit / seed with which the oil was produced. It can occur in oil if water is not separated, but this rarely happens in modern oil mills. The degree of hydrolytic spoilage (often known as hydrolytic rancidity) is determined by determining the free fatty acids (% FFA). The content of free fatty acids is also determined as the acidity of the oil, the acid number or the acid degree. The acidity of the oil is the result of the hydrolysis of triacylglycerol.
For measuring acidity in olive oil we recommend you Olive Oil Acidity Test Kit – HI3897.
The HI3897 Olive Oil Acidity Test Kit is a user-friendly way to determine the percent acidity of your olive oil. The percent acidity of olive oil is a direct indicator of its quality, classification, and freshness. Normally, testing acidity is a complicated process requiring the use of various chemicals in a laboratory environment. The HI3897 kit utilizes a titration method where the endpoint is visually determined when the color changes from yellow-green to pink. With the Olive Oil Acidity Test Kit, it is possible to test the quality of olive oil at various stages of processing and storage to monitor and maintain the highest quality.
Olive Oil Acidity Test Kit – HI3897
PROOXIDANTS
Prooxidants are substances that accelerate oxidation reactions. Some of them are:
- Oxygen: in the space above the oil, mixed into the oil itself packaging under vacuum or in a stream of inert gas
- Temperature: acceleration of oxidation
- Metals: copper and iron, autooxidation catalysts
- Light: intensification of autooxidation processes
- Enzymes: peroxidases, stimulate oxidation in fruit or olive oil
- Free fatty acids
OXIDATIVE SPOILAGE
Another form of spoilage is an oxidative spoilage in which oxygen from the air, with the action of prooxidants, acts on the unsaturated bond of unsaturated fatty acids. We distinguish between autooxidation, photooxidation and thermal oxidation.
Autooxidation
The primary products of autooxidation are peroxides, hydroperoxides, and free radicals. They act as catalysts for the whole reaction and accelerate it. Secondary products are aldehydes, ketones, alcohols, fatty acids, oxy fatty acids, epoxides that cause rancidity of the product.
Peroxides easily lose one oxygen atom and turn into ordinary oxides and are therefore strong oxidizing agents.
The peroxide value tells us a lot about the quality of the oil. Peroxide number indicates the amount of hydroperoxide and peroxides present in the oil. Oils with a peroxide value ranging from 1 to 3 mmol O2 / kg are considered fresh and of good quality. Oils whose peroxide value values do not exceed 10 mmol O2 / kg are considered suitable for human consumption.The peroxide number is considered an indicator of the initial phase of oil oxidation because the resulting hydroperoxides are extremely unstable and decompose very quickly in the so-called secondary oxidation products.
Portable Photometer for Determination of Peroxide Value in Oils – HI83730-02
For measure peroxide values in oil we recommend Portable Photometer for Determination of Peroxide Value in Oils – HI83730
The HI83730 Portable Photometer for the Determination of Peroxide Value in Oils combines accuracy and ease of use in an ergonomic, portable design. A user can accurately determine the peroxide value of olive oil within a 0.0 to 25.0 meq O2/kg range using the HI83730-20 ready made reagents.
Photooxidation
Photooxidation induction occurs by excitation of the O2 molecule with a photosensitizer that absorbs and transmits light energy to other substances. The excited O2 binds directly to the unsaturated fatty acid bonds and form hydroperoxides. Therefore, it is necessary to protect the oil from light.
Thermal oxidation
Thermal oxidation occurs when oils are exposed to high temperatures. Thermal oxidation products are cyclic fatty acids, dimers and polymers of fatty acids and triglycerides, oxipolymers and other compounds. The best cooking oils (those that can withstand higher temperatures) are: canola, corn, olive, peanut, soybean, sunflower.
Every oil has its own smoke point, also referred to as the burning point. That is the temperature at which an oil or fat begins to produce a continuous bluish smoke that becomes clearly visible, dependent upon specific and defined conditions.
Smoke point for best cooking oils are:
| Food oil | Smoke point/°C |
|---|---|
Canola | 220-230°C |
Corn | 230-238°C |
Olive (refined) | 199-243°C |
Olive (Extra Virgin) | 160°C |
Peanut | 227-229°C |
Soybean | 234°C |
Sunflower | 230-238°C |
For measuring temperature of your oil we recommend Checktemp® 4 Folding Thermometer – HI151.
The HI151 Checktemp® 4 is a folding thermistor thermometer that can measure temperature up to 300 °C (572 °F). These thermometers offer many advanced features including CAL-Check for an internal verification of the electronics and a motion sensor which eliminates the need of closing and reopening the probe when the meter enters a power saving mode. The Checktemp 4 is available in six different colors which can be assigned to different products to avoid cross contamination in the restaurant, kitchen or production facility.
Checktemp® 4 Folding Thermometer – HI151
Author: Tajana Frančić, mag.nutr.
