Flavour formation in ghee

Field: Agricultural and Biological Sciences (Life Sciences)

Consumers place a high level of importance on flavour when assessing the acceptability of food. The flavour of dairy products can be affected by heating both during processing and by consumers during food preparation. Of particular importance to the flavour of heated dairy products is the highly complex network of Maillard reactions. Previously, emphasis has been placed on undesirable flavours generated through the Maillard reaction in dairy products and efforts have been made to minimise the formation of these flavours. However, beneficial flavours are also formed by the Maillard reaction. Dairy products such as ghee are formed by heating and are characterised by their unique flavours; these flavours are generated by the Maillard reaction. The objective of this thesis was to unravel the factors that influence the Maillard and caramelisation reactions that occur during the cooking of ghee. Particular focus was placed on the impact that the structure of the cream had on the reaction, and how manipulation of these parameters could provide an avenue for the control of the Maillard reaction. The development and validation of model reaction systems for the Maillard and caramelisation reactions involved the variation of parameters including cooking time, temperature, pH, phosphate buffers and salt. A group of eleven compounds including acetic acid, furfural, 2-acetylfuran, butyrolactone, 2(5H)-furanone, furfuryl alcohol, maltol, 2- acetylpyrrole, hydroxymaltol, hydroxymethylfurfural (HMF) and dihydro-4-hydroxy-2(3H)- furanone (DHHF) were monitored to determine the impact of these parameter changes. These results provided a starting point to assess the impact of food structure on these reactions. To assess the impact of food structure a series of matrix structures were designed starting from an aqueous matrix. The first component that was added to the aqueous matrix was fat to generate a two phase structure. Emulsion structures were then formed from the two phase structure using emulsifiers and high pressure homogenisation. Analysis of the volatile compounds formed as the matrix structures were altered was carried out using headspace solid phase microextraction/ gas chromatography mass spectrometry (SPME/GCMS). Results indicated that fat is a key structural component in flavour generation via the Maillard reaction. This could have implications for low fat foods where the flavour developed during cooking is important. The addition of fat indicated a significant impact on the Maillard reaction with a less significant impact seen on the caramelisation reaction. The formation of two emulsions with inverted structures provided a means to alter the ratio of volatile compounds in the cooked samples. The oil in water emulsion generated a volatile compound profile similar to that of the fat containing matrix, whereas the water in oil emulsion produced a different ratio of these same compounds. The results reported in this thesis shed some light on the relationship between food structure and flavour formation during the cooking of milk fat emulsions. These structures will create future opportunities to manipulate the structure of food to control flavour formation.