The shelf life of food products is often limited by oxidative reactions or by microbial growth. Food products that are rich in oils or fats are particularly prone to oxidation even under ambient atmosphere – they turn rancid. These changes lead to sensorial distortions (taste, odor, color) and ultimately, food products become inedible.

The food industry verifies on a daily basis the sensorial quality of ingredients. Because they are particularly sensitive, fats and oils are routinely tested for peroxide content and volatile compounds that arise during storage (commonly measured by the rancimat method). These methods allow an objective assessment of the products’ current condition without relying on subjective sensorial impressions of the testing person. However, these methods are unsuited for the prediction of oxidative reactions. For this task, the chemiluminescence technology of ACL Instruments provides a valuable alternative.

Oxidation of cocoa butter in air. Measurement condition: non-isothermal (dynamic) temperature profile from 20 to 100°C, heating rate = 0.02 Kmin-1, gasflow = 30 mlmin-1.
cocoa butter
Oxidation of ground almond in air (green curve) and in pure oxygen (blue curve): because of the higher partial pressure of the pure oxygen atmosphere, the oxidation starts earlier and is more intensive than in air. Measurement conditions: non-isothermal (dynamic) temperature profile from 25 to 200°C, heating rate = 0.061 Kmin-1, gasflow = 30 mlmin-1.
ground almond
Comparison of the oxidation of food oils in air: while linseed oil (blue curve) oxidises early (~13h; ~102°C), the oxidation of rapeseed oil (green curve; ~16.5h; 121°C) and olive oil (orange curve; ~18h; ~128°C) is delayed due to higher intrinsic stability. Measurement conditions: non-isothermal (dynamic) temperature profile from 25 to 160°C, heating rate = 0.031 Kmin-1, gasflow = 30 mlmin-1.
food oils
Oxidation of beta-carotene (E150) in pure oxygen. Measurement conditions: non-isothermal (dynamic) temperature profile from 25 to 100°C, heating rate = 0.052 Kmin-1, gasflow = 50 mlmin-1.
E150
Oxidation of instant coffee in air. Measurement conditions: non-isothermal (dynamic) temperature profile from 25 to 160°C, heating rate = 0.074 Kmin-1, gasflow = 30 mlmin-1.
instant coffee

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