Development of solid-state fermentation process of spent coffee grounds for the differentiated obtaining of chlorogenic, quinic, and caffeic acids

BACKGROUND: Spent coffee grounds (SCGs) are a good source of chlorogenic acid (CGA), which can be hydrolyzed to quinic acid (QA) and caffeic acid (CA). These molecules have antioxidant and neuroprotective capacities, benefiting human health. The hydrolysis of CGA can be done by biotechnological processes, such as solid-state fermentation (SSF). This work evaluated the use of SSF with Aspergillus sp. for the joint release of the three molecules from SCGs. RESULTS: Hydroalcoholic extraction of the total phenolic compounds (TPCs) from SCGs was optimized, obtaining 28.9 ± 1.97 g gallic acid equivalent (GAE) kg⁻¹ SCGs using 0.67 L ethanol per 1 L, a 1:9 solid/liquid ratio, and a 63 min extraction time. Subsequently, SSF was performed for 30 days, achieving the maximum yields for CGA, QA, and TPCs on the 16th day: 7.12 ± 0.01 g kg⁻¹, 4.68 ± 0.11 g kg⁻¹, and 54.96 ± 0.49 g GAE kg⁻¹ respectively. CA reached its maximum value on the 23rd day, at 4.94 ± 0.04 g kg⁻¹. The maximum antioxidant capacity was 635.7 mmol Trolox equivalents kg⁻¹ on the 14th day. Compared with unfermented SCGs extracts, TPCs and CGA increase their maximum values 2.3-fold, 18.6-fold for CA, 14.2 for QA, and 6.4-fold for antioxidant capacity. Additionally, different extracts’ profiles were obtained throughout the SSF process, allowing us to adjust the type of enriched extract to be produced based on the SSF time. CONCLUSION: SSF represents an alternative to produce extracts with different compositions and, consequently, different antioxidant capacities, which is a potentially attractive fermentation process for different applications.