2.8. Flavours of lipid foods
According to Pokorny (1989) more than 30% of identified aroma substances in food are derived from the fat component. The dependence of this statement on the kind of food may be illustrated by the following examples: fish contains about 83%, beef 52%, coffee 41% and tea 30% lipid derived aroma compounds (Schrödter, 1990).
Fats and oils that are essential components of shortening, mayonnaise, and cooking oils contribute unique flavours to foods. Fats and oils are chemically referred to as lipids and occur in food mainly as triglycerides. These fats and oils may have a positive or negative affect on the flavour of foods depending on the chemical reactions taking place during processing and storage.
Fats and oils are susceptible to oxidation, which produces undesirable volatile compounds and cause detrimental flavour effects to food.
The types of volatile compounds produced from the oxidation of fats and oils are influenced by the composition of the peroxides and the extent of oxidation cleavage of double bounds contained in the fatty acids. Due to the many possible reactions pathways, a variety of volatile compounds such as hydrocarbons, alcohols, furans, aldehydes, ketones, and acids are formed during oxidation. Most of the compounds responsible for the oxidation flavours, however, are the aliphatic carbonyl compounds. The flavour characteristics and threshold values of aldehydes vary as shown in next table.
| Aldehyde | Description | Threshold Value in Oil (ppm) | |
|---|---|---|---|
| Odor | Taste | ||
| 3:0 | Sharp-irritating | 3.60 | 1.00 |
| 5:0 | Sharp-bitter | 0.24 | 0.15 |
| 6:0 | Green | 0.32 | 0.08 |
| 7:0 | Oily-putty | 3.20 | 0.05 |
| 8:0 | Fatty-soapy | 0.32 | 0.04 |
| 9:0 | Tallowy-soapy | 13.5 | 0.20 |
| 10:0 | Orange peels | 6.70 | 0.70 |
| 5:1 | Sharp-paint-green | 2.30 | 1.00 |
| 6:1 | Green | 10.00 | 0.60 |
| 7:1 | Putty-fatty | 14.00 | 0.20 |
| 8:1 | Woodbugs-fatty | 7.00 | 0.15 |
| 9:1 | Tallowy-cucumber | 3.50 | 0.04 |
| 10:1 | Tallowy-orange | 33.80 | 0.15 |
| 7:2 | Frying odour | 4.00 | 0.04 |
| 9:2 | Fatty-oily | 2.50 | 0.46 |
| 10:2 | Deep-fried | 2.15 | 0.10 |
The isolation, separation, and identification of volatile compounds are difficult due to the complexity of volatile compounds oils, the variations of concentration and volatilities of flavour compounds, interactions between volatile compounds, and reactions between volatile compounds and food components such as proteins and carbohydrates during isolation. The mechanisms responsible for the production of volatile compounds during oxidation must be thoroughly studied and understood to improve the flavour quality of fat oils.
Milk fat is recognized as important for different sensory attributes of dairy products. This importance is related not only with volatile compounds arising from milk fat, but also with the physical properties of the product, who are related with the fat level, and the fact that milk fat serves as a solvent for flavour compounds.