Volatilome, Microbial, and Sensory Profiles of Coffee Leaf and Coffee Leaf-Toasted Maté Kombuchas

Abstract

Kombucha is a fermented beverage traditionally made from the leaves of Camelia sinensis. The market has drastically expanded recently, and the beverage has become more elaborated with new, healthy food materials and flavors. Pruning and harvesting during coffee production may generate tons of coffee leaves that are discarded although they contain substantial amounts of bioactive compounds, including those found in maté tea and coffee seeds. This study characterized the changes in volatilome, microbial, and sensory profiles of pure and blended arabica coffee leaf tea kombuchas between 3-9 days of fermentation. Acceptance was also evaluated by consumers from Rio de Janeiro (n = 103). Kombuchas (K) were prepared using black tea kombucha starter (BTKS) (10%), sucrose (10%), a symbiotic culture of Bacteria and Yeasts (SCOBY) (2.5%), and a pure coffee leaf infusion (CL) or a 50:50 blend with toasted maté infusion (CL-TM) at 2.5%. The RATA test was chosen for sensory profile characterization. One hundred volatile organic compounds were identified when all infusions and kombucha samples were considered. The potential impact compounds identified in CL K and CL-TM K were: methyl salicylate, benzaldehyde, hexanal, nonanal, pentadecanal, phenylethyl-alcohol, cedrol, 3,5-octadien-2-one, β-damascenone, α-ionone, β-ionone, acetic acid, caproic acid, octanoic acid, nonanoic acid, decanoic acid, isovaleric acid, linalool, (S)-dihydroactinidiolide, isoamyl alcohol, ethyl hexanoate, and geranyl acetone. Aroma and flavor descriptors with higher intensities in CL K included fruity, peach, sweet, and herbal, while CL-TM K included additional toasted mate notes. The highest mean acceptance score was given to CL-TM K and CL K on day 3 (6.6 and 6.4, respectively, on a nine-point scale). Arabica coffee leaf can be a co-product with similar fingerprinting to maté and black tea, which can be explored for the elaboration of potentially healthy fermented beverages in food industries.

Keywords: Rate-All-That-Apply; coffee by-product; coffee leaf; coffee production waste; fermented beverages; novel foods; toasted maté tea; volatile compounds; yerba mate.

Figure 1

Characterization of the bacterial composition of the black tea kombucha starter (BT K) and that of coffee leaf (CL K) and coffee-leaf-toasted maté (CL-TM K) kombucha consortia after 9 days of fermentation.

Figure 2

Yeast composition of the black tea kombucha starter (BT K) and the coffee leaf (CL K) and coffee-leaf-toasted maté (CL-TM K) kombucha consortia after 9 days of fermentation.

Figure 3

Relative peak areas (%) of volatile organic compounds in black tea kombucha starter (BT K), coffee leaf (CL K), and coffee leaf-toasted maté (CL-TM K) kombucha beverages grouped into chemical classes. Note.; Inf: infusion; d0, d3, d6, and d9: days of fermentation; HAOC: heterocyclic aromatic organic compounds.

Figure 4

Mean acceptance scores (A) and mean purchase intent scores (B) of coffee leaf (CL K) and coffee leaf-toasted maté (CL-TM K) kombuchas by Rio de Janeiro consumers (n = 103). Different letters over the bars indicate significant difference (at p < 0.05) by ANOVA followed by the Tukey test. Note: d0, d3, d6, and d9: 0, 3, 6, and 9 days of fermentation.

Figure 5

Intensity means for odor (A), taste (B), flavor (C), and mouthfeel and appearance (D) for coffee leaf kombuchas (CL K) with 3, 6, and 9 days of fermentation (3d, 6d, and 9d). Note: O: odor; T: taste; F: flavor; M: mouthfeel; A: appearance. d0, d3, d6, and d9: 0, 3, 6, and 9 days of fermentation.

Figure 6

Intensity means for odor (A), taste (B), flavor (C), and mouthfeel and appearance (D) for CL-TM kombuchas with 3, 6 and 9 days of fermentation. Note: O: odor; T: taste; F: flavor; M: mouthfeel; A: appearance; CL-TM: coffee leaves with toasted maté. d0, d3, d6, and d9: 0, 3, 6, and 9 days of fermentation.

Figure 7

Correspondence analysis (CA): bi-dimensional plot of the samples of coffee leaf (CL K) and coffee-toasted maté leaf (CL-TM K) kombuchas after 3, 6, and 9 days of fermentation (d3, d6, and d9) (A) and sensory descriptors attributed by consumer assessors (n = 103) through the RATA test, distributing volatile compounds and descriptors that make up the best acceptance of samples among consumers (B). Overall liking and the volatile compounds were considered to be supplementary variables. Note: O: odor; T: taste; F: flavor; M: mouthfeel; A: appearance.

Figure 8

Biplot of the principal component analysis (PCA) of the volatile compounds relevant for RATA attributes, as summarized in Table 4. Coffee leaf (CL K) and coffee-toasted maté leaf (CL-TM K) kombuchas after 3, 6, and 9 days of fermentation (d3, d6, and d9).