Before we recycle used cooking oil, we use it to prepare food. And does the frying process affect its quality?

Does the frying process affect the quality of the cooking oil?

Food oils of vegetable origin are made up of glycerides, esters derived from glycerin and fatty acids, which can assume 3 constitutions:

  • Monoglycerides;
  • Diglycerides;
  • Triglycerides.

These 3 elements are distinguished by the number of fatty acid molecules attached to the glycerol molecule (Thomas, 2002).

The options available on the market regarding oils for food use present significant differences in their chemical composition, influencing chemical-physical parameters such as, for example, hydrophobicity.

Saturated oils exhibit a higher degree of viscosity, as well as superior resistance to oxidation, as opposed to oils with a high content of linoleic acid, which are quickly degradable (Fox, NJ et. al., 2007).

When in contact with a heat source, heating the oil above 180ºC causes the formation of polyunsaturated compounds, as well as soot and suspended ash (which darkens the natural tone of the oil) whenever it is exposed to a temperature above 250ºC.

During the frying process, food releases part of the water it contains, which leads to the hydrolysis of triglycerides and subsequent decomposition into free fatty acids and diglycerides, which results in an increase in the degree of acidity (see figure below).

Likewise, oil oxidation phenomena can occur whenever there is contact between oxygen, dissolved in the oil, reacts with unsaturated fatty acids, leading to the formation of hydroperoxides, which in turn are oxidized to alcohols, aldehydes, ketones, esters and others. Hydrocarbons.

In this way, it was possible to verify that the oxidation of oils causes changes in their physicochemical and organoleptic characteristics.

Do changes during frying prevent the recovery of used cooking oils?

However, after having ascertained the specific differences inherent to virgin and used oils, it was observed that the properties of Used Cooking Oils (UCO) do not impede the valorization of these resources as raw materials, as long as they are not intended for use in products. of human consumption and which have been filtered and decanted to separate components of heterogeneous mixtures.

Currently, the recovery of this type of waste has very little recognition on the part of the market, and as a rule, they are always found clusters with corrosive and dermatologically dangerous saponifying agents.

Research has shown that vegetable oils and animal fats are the main saponifiable materials ( Caster, JM et. al. , 2000).

In the saponification reaction, the triglyceride is treated with a strong base to accelerate the cleavage of the ester bond and release the fatty acid salt and glycerol. However, another technique used consists of the precipitation of glycerol through the addition of sodium chloride to the saponifiable raw material, obtaining formulations with high concentrations of alkaline agents such as sodium metasilicate, sodium hydroxide or potassium hydroxide.

This practice limits the use of saponified compounds in domestic consumption and in some industries due to the fact that they are highly corrosive elements.

EcoXperience studied alternative saponification techniques that did not pose health risks, verifying that triglycerides subjected to a hydrolysis process give rise to carboxylic acid and glycerol, and then the fatty acid is neutralized with a base agent. , thus creating soap.

In this process, the soap is purified, resulting in cleaning products with increased quality and without negative impact on dermatological and environmental levels.