Določanje oksidacijskih lastnosti jedilnih olj in maščob z metodami termične analize

Kurent, Maja (author), Čelan Korošin, Nataša (mentor)

V svoji diplomski nalogi sem raziskovala termično in oksidativno stabilnost različnih jedilnih olj (oljčno, repično, bučno) ter svinjske masti. Olja so estri glicerola in višjih maščobnih kislin in spadajo v podskupino lipidov, kar pomeni, da so slabo oz. popolnoma netopni v vodi, od njihove sestave pa so odvisne vse njihove lastnosti. Pri termični analizi se lastnosti materialov preučujejo v odvisnosti od temperature. Kako se material, kot je na primer olje ali maščoba, obnaša pri določeni temperaturi pa je dobro vedeti, saj lahko določena olja začnejo pri visokih temperaturah, ki jih dosegamo tudi pri pripravi hrane, termično razpadati na zdravju škodljive produkte. Termično stabilnost sem proučevala med segrevanjem v pretoku zraka, meritve sem izvajala na simultanem TGA/DSC instrumentu. Čas inducirane oksidacije (OIT) pri različnih temperaturah je bil določen z DSC meritvijo. Iz meritev sem na koncu izračunala aktivacijsko energijo termičnega razpada ter aktivacijsko energijo oksidacije. Glede na aktivacijsko energijo termičnega razpada s TGA analizo, sem z vsemi metodami dokazala, da sta izmed vseh štirih vzorcev najbolj stabilna oljčno olje in svinjska mast in tako najbolj primerna za daljšo uporabo pri visokih temperaturah. Z OIT rezultati sem določila aktivacijsko energijo oksidacije. Oljčno in bučno olje sta med seboj najbolj primerljiva in po kvaliteti presegata vrednosti literaturnih podatkov. Analizirano območje znotraj kriterijev za OIT meritev je vse do 180 °C, kar je za 30 °C višje kot je analizirana svinjska mast. Repično olje je po vseh kriterijih najmanj stabilno.

• Language: Slovenian
• Keywords: diferenčna dinamična kalorimetrija, jedilna olja, termogravimetrija, toplotna oksidacija
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2023
• PID: 20.500.12556/RUL-149227
• COBISS.SI-ID: 167319811
• Publication date in RUL: 05.09.2023

Secondary language

• Language: English
• Title: Determination of the oxidative properties of edible oils and fats by thermal analysis methods

Abstract

In my thesis, I researched the thermal and oxidative stability of various edible oils (olive, rapeseed, pumpkin seed) and lard. Oils are esters of glycerol in higher fatty acids and belong to the subgroup of lipids which means that they are partially or completely insoluble in water, and all their properties depend on their composition. In thermal analysis, the properties of materials are studied as a function of temperature. It is good to know how a material, such as oil or fat, behaves at a certain temperature, because certain oils can begin to thermally decompose into harmful products at high temperatures, which are also reached during food preparation. Thermal stability was studied while heating the oil sample in air atmosphere using a simultaneous TGA/DSC instrument. The oxidation induction time (OIT) at different temperatures was determined by DSC measurements. With the measurements, I was finally able to calculate the activation energy of thermal decomposition and oxidation. With regard to the activation energy of thermal decomposition by TGA analysis, I have shown by all methods that olive oil and lard are the most stable of the four samples and thus the most suitable for use in prolonged use at high temperatures. I determined the activation energy of oxidation using the OIT results. Olive oil and pumpkin seed oil are the most comparable to each other and exceed the literature data in quality. The analysed range within the OIT measurement criteria is up to 180 °C, which is 30 °C higher than the analysed lard. Rapeseed oil is the least stable according to all criteria.

• Keywords: differential scanning calorimetry, edible oils, thermal oxidation, thermogravimetry