Comparison of the Antioxidant Activities and Volatile Compounds of Coffee Beans Obtained Using Digestive Bio-Processing (Elephant Dung Coffee) and Commonly Known Processing Methods

Abstract

There are different types of coffee processing methods. The wet (WP) and dry processing (DP) methods are widely practiced in different parts of coffee-growing countries. There is also a digestive bioprocessing method in which the most expensive coffee is produced. The elephant dung coffee is produced using the digestive bioprocessing method. In the present experiment, the antioxidant activity and volatile compounds of coffee that have been processed using different methods were compared. The antioxidant activity, total phenolic content (TPC), total flavonoid content (TFC), and total tannin content (TTC) of green coffee beans from all treatments were higher as compared to roasted coffee beans. Regarding the green coffee beans, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of elephant dung coffee beans was higher as compared to that of the DP and WP coffee beans. The green coffee beans had higher DPPH activity and ferric reducing antioxidant power (FRAP) value compared to the roasted coffee beans. The green beans of elephant dung coffee had a high TPC than the beans obtained by WP and DP methods. TFC in elephant dung coffee in both green and roasted condition was improved in contrast to the beans processed using dry and wet methods. The elephant dung coffee had an increased TTC in comparison to the DP and WP coffee (green beans). About 37 volatile compounds of acids, alcohols, aldehydes, amide, esters, ethers, furans, furanones, ketones, phenols, pyrazines, pyridines, Heterocyclic N, and pyrroles functional classes have been found. Some of the most abundant volatile compounds detected in all treatments of coffee were 2-furanmethanol, acetic acid, 2-methylpyrazine, 2,6-dimethylpyrazine, pyridine, and 5-methylfurfural. Few volatile compounds have been detected only in elephant dung coffee. The principal component analysis (PCAs) was performed using the percentage of relative peak areas of the volatile compound classes and individual volatile compounds. This study will provide a better understanding of the impacts of processing methods on the antioxidants and volatile compounds of coffee.

Keywords: antioxidants; elephant dung coffee; processing methods; volatile compounds.

Figure 1

The elephant dung coffee right after the coffee cherry passed through the elephant digestive tract and collected from the elephant feces.

Figure 2

2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition (%) of green and roasted coffee beans obtained using different processing methods. ((A): Green beans; (B): Light roasted, (C): Medium roasted; (D): Dark roasted). EP1: elephant dung coffee (pulp was completely digested); EP2: elephant dung coffee (pulp was not digested); WP: wet-processed beans; DP: dry-processed beans. Different letters above the bars indicate statistically significant difference at p < 0.05.

Figure 3

Ferric-reducing antioxidant power (FRAP) of green and roasted coffee beans that were processed with different methods. ((A): Green beans; (B): Light roasted, (C): Medium roasted; (D): Dark roasted). EP1: elephant dung coffee (pulp was completely digested); EP2: elephant dung coffee (pulp was not digested); WP: wet-processed beans; DP: dry-processed beans. Different letters above the bars indicate statistically significant difference at p < 0.05.

Figure 4

Total phenolic content of green and roasted coffee beans that obtained using different processing methods. ((A): Green beans; (B): Light roasted, (C): Medium roasted; (D): Dark roasted). EP1: elephant dung coffee (pulp was completely digested); EP2: elephant dung coffee (pulp was not digested); WP: wet-processed beans; DP: dry-processed beans. Different letters above the bars indicate statistically significant difference at p < 0.05.

Figure 5

Total flavonoid content of green and roasted coffee beans that processed with different methods. ((A): Green beans; (B): Light roasted, (C): Medium roasted; (D): Dark roasted). EP1: elephant dung coffee (pulp was completely digested); EP2: elephant dung coffee (pulp was not digested); WP: wet-processed beans; DP: dry-processed beans. Different letters above the bars indicate statistically significant difference at p < 0.05.

Figure 6

Total tannin content of green and roasted coffee beans that obtained using different processing methods. ((A): Green beans; (B): Light roasted, (C): Medium roasted; (D): Dark roasted). EP1: elephant dung coffee (pulp was completely digested); EP2: elephant dung coffee (pulp was not digested); WP: wet-processed beans; DP: dry-processed beans. Different letters above the bars indicate statistically significant difference at p < 0.05.

Figure 7

Total ion chromatograms (TICs) of volatile compounds of coffee (brewed samples). (EP1: elephant dung coffee (pulp was completely digested); EP2: elephant dung coffee (pulp was not digested); WP: wet-processed coffee beans; DP: dry-processed coffee beans). RT: Retention time (minutes).

Figure 8

The total concentration of volatile compounds as functional classes. EP1: elephant dung coffee (pulp was completely digested); EP2: elephant dung coffee (pulp was not digested); WP: wet-processed coffee beans; DP: dry-processed coffee beans.

Figure 9

Biplot of the principal component analysis of the volatile classes (A) and individual compounds (B) of coffee obtained using different processing methods. EP1: elephant dung coffee (pulp was completely digested); EP2: elephant dung coffee (pulp was not digested); WP: wet-processed coffee beans; DP: dry-processed coffee beans.