Abstract
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.
Highlights
The oil extracted from green and roasted coffee beans is a naturally rich source of valuable bioactive phytochemicals, most of them showing promising significance in nutrition, in the pharmaceutical industry and in cosmetics [1,2,3,4]
Considering all the information mentioned above, our purpose in this paper is to address two important practical questions: (1) What are the differences among green coffee oil (GCO) and roasted coffee oil (RCO) evaluated by Attenuated Total Reflectance–Fourier Transform Infrared (ATR-FTIR) spectroscopy as well as the differences in their DPPH radical scavenging activity and antimicrobial properties? (2) How does the hightemperature heating influence the crude coffee in terms of oxidative stability, antioxidant and antimicrobial properties? To this end, GCO and RCO were extracted from green and roasted Arabica coffee beans in a Soxhlet extractor apparatus, and both crude coffee oils were continuously heated to 200°C over 1 h
The antioxidant activity of GCO and RCO is related to their content of natural antioxidants like sterols, phosphatides, tocopherols and diterpenes [5,8]. These results clearly show that the presence of antioxidant compounds in crude coffee oils decreased the absorbance of DPPH and increased the percentage of inhibition proportionally to the oil concentration
Summary
The oil extracted from green and roasted coffee beans is a naturally rich source of valuable bioactive phytochemicals, most of them showing promising significance in nutrition (because of its antioxidant activity), in the pharmaceutical industry (dry and cracked skin, eczema, psoriasis and other skin-related diseases) and in cosmetics (due to its balanced composition in fatty acids) [1,2,3,4]. There is little information about the differences among green and roasted coffee oil as well as how the exposure to high temperature influences the oxidative stability, the antioxidant and the antimicrobial activity of coffee oil, respectively This was the main reason that drove us towards the systematic study of chemical and functional properties of crude and heat-treated green and roasted coffee oil. The roasting of green coffee beans induces many chemical changes such as the formation of volatile compounds [10] and Maillard reaction products These products are responsible for the intense aroma of roasted coffee [2,11], but the coffee roasting has no effect on the oxidation level of the lipid fraction [12,13]
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