Potential of lactic acid bacteria to modulate coffee volatiles and effect of glucose supplementation: fermentation of green coffee beans and impact of coffee roasting.

BACKGROUND: Coffee flavor can be significantly influenced by microbial activities in spontaneous fermentation of coffee cherries. The potential of lactic acid bacteria for flavor modulation through controlled fermentation of green coffee beans has not been explored. RESULTS: Fermentation by Lactobacillus rhamnosus HN001 with and without 1% w/w glucose supplementation led to modification of flavor-related constituents in green coffee beans, which translated into modulation of coffee volatiles upon roasting. The lactic acid bacteria consumed almost all glucose and fructose, leaving sucrose behind. Amino acids and malic, citric, and succinic acids were partially catabolized. Glucose supplementation enhanced lactic acid production but repressed acetic acid formation. After roasting at 235 °C for 9 min, 12 min, and 15 min, the levels of furfurals in glucose-supplemented-fermented coffee were 10.5-, 2.7-, and 1.1-fold higher than those in the controls (nonsupplemented-unfermented coffee); furthermore, the levels of pyrazines in the controls were 11.9-, 10.1-, and 6.5-fold higher than those in the treated coffee. Glucose-supplemented fermentation yielded roasted coffee with stronger caramelic and burnt characteristics but weaker nutty notes. In roasted non-supplemented-fermented coffee, volatile production was generally reduced, resulting in a milder overall aroma. CONCLUSION: Lactic acid fermentation of green coffee beans is a new strategy for coffee flavor modulation, creating novel aroma characteristics. © 2018 Society of Chemical Industry.

Celluclast 1.5L pretreatment enhanced aroma of palm kernels and oil after kernel roasting.

BACKGROUND: The aroma of palm kernel oil (PKO) affects its applications. Little information is available on how enzymatic modification of palm kernels (PK) affects PK and PKO aroma after kernel roasting. RESULTS: Celluclast (cellulase) pretreatment of PK resulted in a 2.4-fold increment in the concentration of soluble sugars, with glucose being increased by 6.0-fold. Higher levels of 1.7-, 1.8- and 1.9-fold of O-heterocyclic volatile compounds were found in the treated PK after roasting at 180 °C for 8, 14 and 20 min respectively relative to the corresponding control, with furfural, 5-methyl-2-furancarboxaldehyde, 2-furanmethanol and maltol in particularly higher amounts. Volatile differences between PKOs from control and treated PK were also found, though less obvious owing to the aqueous extraction process. Principal component analysis based on aroma-active compounds revealed that upon the proceeding of roasting, the differentiation between control and treated PK was enlarged while that of corresponding PKOs was less clear-cut. Celluclast pretreatment enabled the medium roasted PK to impart more nutty, roasty and caramelic odor and the corresponding PKO to impart more caramelic but less roasty and burnt notes. CONCLUSION: Celluclast pretreatment of PK followed by roasting may be a promising new way of improving PKO aroma. © 2017 Society of Chemical Industry.

Solid-state fermentation of palm kernels by Yarrowia lipolytica modulates the aroma of palm kernel oil.

Solid-state fermentation with Yarrowia lipolytica was applied to palm kernels (PK) with the aim to modulate the aroma of palm kernel oil (PKO) obtained after kernel roasting. The results showed that, the metabolic activities of Y. lipolityca brought about significant changes to the volatile profile of obtained PKO either by providing thermal reaction reactants or by directly contributing aroma compounds. After fermentation, a decreased content in glucose (60%) while an elevated amount (7-fold) in free amino acids was found in PK, which further impacted the formation of volatile compounds by influencing the Maillard reaction and Strecker degradation during roasting. More Strecker aldehydes and N-heterocyclic compounds were formed in PKO derived from fermented PK especially after intensified roasting. In addition, the catabolism of Y. lipolytica imparted some distinct volatile compounds such as 2-phenylethanol to the obtained PKO. However, the lipase excreted by Y. lipolytica hydrolysed PK lipids and released 5-fold more free fatty acids in fermented PKO, relative to the blank and control PKO, which likely contributed to the off-flavor. On the basis of all volatile categories, principal component analysis (PCA) clearly separated the fermented PKO from the blank and control PKO, with light roasted, fermented PKO being correlated with acids, alcohols and aliphatic aldehydes; medium and dark roasted, fermented PKO tending to be dominated by pyrroles, pyrazines and furanones, which is in correspondence with sensory changes of PKO. This study demonstrated that combining fermentation with roasting could provide a novel way to modulate the volatile composition and aroma of PKO.

Viscozyme L pretreatment on palm kernels improved the aroma of palm kernel oil after kernel roasting.

With an interest to enhance the aroma of palm kernel oil (PKO), Viscozyme L, an enzyme complex containing a wide range of carbohydrases, was applied to alter the carbohydrates in palm kernels (PK) to modulate the formation of volatiles upon kernel roasting. After Viscozyme treatment, the content of simple sugars and free amino acids in PK increased by 4.4-fold and 4.5-fold, respectively. After kernel roasting and oil extraction, significantly more 2,5-dimethylfuran, 2-[(methylthio)methyl]-furan, 1-(2-furanyl)-ethanone, 1-(2-furyl)-2-propanone, 5-methyl-2-furancarboxaldehyde and 2-acetyl-5-methylfuran but less 2-furanmethanol and 2-furanmethanol acetate were found in treated PKO; the correlation between their formation and simple sugar profile was estimated by using partial least square regression (PLS1). Obvious differences in pyrroles and Strecker aldehydes were also found between the control and treated PKOs. Principal component analysis (PCA) clearly discriminated the treated PKOs from that of control PKOs on the basis of all volatile compounds. Such changes in volatiles translated into distinct sensory attributes, whereby treated PKO was more caramelic and burnt after aqueous extraction and more nutty, roasty, caramelic and smoky after solvent extraction.