Effects of heating on virgin olive oils and their blends: focus on modifications of phenolic fraction

Studying heating effects on desi ghee obtained from buffalo milk using fluorescence spectroscopy

Characterisation and thermal deterioration of desi ghee obtained from buffalo milk is presented for the first time using the potential of Fluorescence spectroscopy. The emission bands in non-heated desi ghee centred at 375 nm is labelled for vitamin D, 390 nm for vitamin K, 440–460 nm for isomers of conjugated linoleic acid (CLA), 490 nm for vitamin A and the region 620–700 nm is assigned to chlorophyll contents. Fluorescence emission spectra from all the heated and non-heated ghee samples were recorded using excitation wavelengths at 280, and 410 nm which were found best for getting maximum spectral signatures. Heating of desi ghee affects its molecular composition, however, the temperature range from 140 to 170°C may be defined safe for cooking /frying where it does not lose much of its molecular composition. Further, the rise in temperature induces prominent spectral variations which confirm the deterioration of valuable vitamins, isomers of CLA and chlorophyll contents. Fluorescence emission peak at 552 nm shows oxidation product and an increase in its intensity with the rise in temperature is observed. In order to classify heated samples at different temperatures, principal component analysis (PCA) has been applied on heated and non-heated ghee samples that further elucidated the temperature effects.