Microwave technologies are more and more present in food applications due to their
performance in shortening the time of treatments such as drying, pasteurization, defrosting,
or postharvesting. While solvent-free microwave extraction has been extensively used as a
green procedure for essential oil and volatile compounds from aromatic herbs [1], its
applications have been extended to enhance extraction of phytocompounds simultaneously
with drying.
In this work, microwave hydrodiffusion and gravity was performed in a laboratory microwave
oven (NEOS-GR, Milestone, Italy), in order to evaluate its efficiency in the extraction of
nonvolatile compounds such as: free sugars, f1bers, colour, and phenolic compounds. Five
different matrices were tested: broccoli by-products (90% moisture), apple pomace (80%
moisture), spent coffee grounds (65% moisture), Pterospartum tridentatum inflorescences,
and brown algae, the latter two in dried state. The flow behaviour was very dependent on
matrix (Figure 1): for broccoli, the time to obtain 50 ml aliquots increased along time while
for apple pomace it was always the same after the initial and final heating periods, and for
the spent coffee grounds it was always decreasing. Good recoveries were observed when
using high water content matrices, such as apple pomace and broccoli. However, when
using hydrated matrices, such as brown algae and Pterospartum tridentatum inflorescences,
it was observed that the amount of material extracted is very low. In the case of spent coffee
qrounds (a material where water is added to the ground coffee when preparing espresso
coffee), the initial low recoveries can be overcome by the eo-addition of ethanol, allowing to
obtain fractions rich in phenolic compounds, as well as brown compounds (with antioxidant
activity) and caffeine.
NEOS-GR, using microwave hydrodiffusion and gravity is a green extraction technology
obtain hydrophilic compounds from wet matrices using its own water, allowing the
extraction of valuable non-volatile compounds.info:eu-repo/semantics/publishedVersio
