Lipid Oxidation and Prevention in Food
Caramelization
Caramelization is the degradation of sugars without the presence of amino acids or proteins, heated above its melting point (pyrolysis). This process forms a series of volatile and non-volatile substances, with a characteristic taste and dark brown color.
Alteration of Lipids
Alteration of food lipids leads to changes in organoleptic and nutritional characteristics. It subsequently decreases shelf life and generates toxic products, leading to consumer rejection and potential health risks.
Oxidation of Lipids
Lipid oxidation is an autoxidation reaction with molecular oxygen, either enzyme-mediated or not. The main substrates are unsaturated fatty acids. Saturated fatty acids require temperatures above 60°C to oxidize, while polyunsaturated fatty acids oxidize at room temperature and even when frozen.
The main effect is rancidity, causing an unpleasant odor and taste in food due to the formation of aldehydes, ketones, acids, etc. It also affects carotenoids and fat-soluble vitamins A, D, E, and K. There is a loss of essential fatty acids, and potentially toxic compounds are generated.
The reaction is catalyzed by oxygen, heat, UV light, and some metals (pro-oxidants). Some reactions require high activation energy (heat).
Free Radicals
A free radical is an organic or inorganic molecule, generally extremely unstable and highly reactive. It is initiated by the addition of an electron (e-) to molecular oxygen, producing a superoxide radical. Superoxide radicals are also produced by the catalytic oxidation of oxyhemoglobin, in which about 3% is oxidized to methemoglobin daily.
Free radicals include the oxygen molecule, the hydrogen atom, and transition metals (in their ionic state). The enormous reactivity of oxygen radicals leads them to interact avidly with other molecules.
Prevention of Lipid Oxidation
An antioxidant is a substance that absorbs the activation energy in the oxidative process, preventing it from being transmitted to the lipid molecules of glycerides.
Antioxidants by Type
- Stop the chain reactions of fat oxidation.
- Absorb or dissolve oxygen trapped in the product or packaging head space (O2 absorber in active packaging).
- Remove trace metals that facilitate oxidation (chelating agents).
Antioxidants Type I
These antioxidants interrupt radical chain production, decreasing the availability of free radicals and lengthening the induction period. They have a protective effect in the presence of metals. There is a synergistic effect between low O2 pressure in the atmosphere and the antioxidant effect.
Derivatives of Phenols
Slightly soluble in water, not very heat-sensitive lipids: propyl gallate (E-310), octyl gallate (E-311), dodecyl gallate (E-312).
Lipid-Soluble, Heat-Resistant
Butylated hydroxyanisole (BHA): (E-320), Butylated hydroxytoluene (BHT): (E-321).
Wood Smoke
Phenolic compounds.
Antioxidant Type II
These compounds prevent or decrease the formation of free radicals. Chelating agents are used to bind metals. Their action depends on pH and temperature. Some also have other effects, such as acidification or preservation.
Chelating Agents
Ethylenediaminetetraacetate (EDTA), as sodium salt: (H-3247), as disodium salt and calcium: (H-3246).
Acids
Lactic acid and its salts (E-270), (E-325), (E-326), (E-327), citric acid and its salts (E-330), (E-333), (E-380), tartaric acid and its salts (E-334), (E-335), (E-336), (E-337), (E-353), (E-354).
Antioxidant Type III
Includes procedures to protect from oxidation:
- Vacuum packaging
- Packaging impervious to O2 (and other gases)
- Active packaging
- Controlled atmospheres (gas-tight) or O2 absorbers
- Decreased water activity (aw)
- Avoiding heating the product
- Protection from light (UV filters)
Reversal of Taste
Some industrially deodorized refined fats tend to develop undesirable flavors (like paint, herbaceous, or fishy) due to mild oxidation (without causing rancidity). The most susceptible are marine oils, linseed, soybean, and rapeseed oils. The flavor is enhanced by frying.
Polymerization
Elevated temperatures (frying) produce polymerization of esters of highly unsaturated fatty acids. This increases the viscosity (gel formation) of the oil, affecting its thermal conductivity. It occurs when oil is used repeatedly.