Investigation on Crude and High-Temperature Heated Coffee Oil by ATR-FTIR Spectroscopy along with Antioxidant and Antimicrobial Properties

The coffee oil has a promising potential to be used in food industry, but an efficient use, especially in products that required high-temperature heating, depends on its chemical composition and the changes induced by processing. Since there is little information on this topic, the aim of our study was to investigate the crude green and roasted coffee oil (GCO, RCO) and heated (HGCO, HRCO) for 1 h at 200°C, by Fourier Transform Infrared (FTIR) spectroscopy and in terms of antioxidant and antimicrobial properties. The results of FTIR spectroscopy revealed that no statistically significant differences (one-way ANOVA, p>0.05) in the oxidative status of GCO and RCO were found. The coffee oils heating induced significant spectral changes in the regions 3100–3600 cm(–1), 2800–3050 cm(–1) and 1680–1780 cm(–1) proved by the differences in the absorbance ratios A 3009 cm(−1)/A 2922 cm(−1), A 3009 cm(−1)/A 2853 cm(−1), A 3009 cm(−1)/A 1744 cm(−1), A 1744 cm(−1)/A 2922 cm(−1). These alterations were related to the reduction of the unsaturation degree due to primary and secondary oxidation processes of the lipid fraction. The radical scavenging ability of oils investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay revealed that the IC50 value of GCO was significantly lower than of RCO (p<0.05). The IC50 values of crude coffee oils were lower than those of heated samples. The antioxidant activity of oils was attributed to both antioxidant compounds with free-radical scavenging capacity and to lipids oxidation products generated by heating. In the first 6 h of incubation, the inhibitory activity of crude oils against E. coli and E. faecalis was not significantly different to the control (p>0.05). Also, HGCO and HRCO showed significantly different inhibitory potential related to the control (p<0.05). The heating induced statistically significant decreases in the effectiveness of coffee oils against the tested bacteria. GCO proved to be the most effective among investigated coffee oils against the tested bacteria.