Subcritical water mediated conversion of spent coffee grounds into physiologically active biomaterials for utilization in food industry

This study examined the effects of subcritical water (SW) extraction on the compositional and physiological changes in spent coffee grounds (SCG). SW at 250 °C effectively reduced the residual solid content in SCG. However, Maillard interactions limited protein recovery from SCG, and SCG extracted at a temperature greater than 250 °C exhibited lower angiotensin-converting enzyme (ACE) inhibitory activity compared with those extracted at a temperature below 200 °C, indicating that the bioactivities of the SCG extracts were depended on the applied SW temperature. The SCG extracted at lower than 200 °C exhibited prebiotic potential for Lactobacillus rhamnosus GG (LGG) and Enterococcus faecium, whereas those extracted at greater than 250 °C demonstrated an antimicrobial ability toward the probiotic strains owing to the production of thermal derivatives of sugars such as acids and 5-hydroxymethylfurfural (HMF). The temperature-dependent thermochemical changes in SCG afforded a complex taste profile with less bitterness. Therefore, this study revealed that SW had the potential to convert coffee byproducts into useful food ingredients.