  Complex organic molecules (COMs) detected in the gas phase are thought to be
mostly formed on icy grains, but no unambiguous detection of icy COMs larger
than CH3OH has been reported so far. Exploring this matter in more detail has
become possible with the JWST the critical 5-10 $\mu$m range. In the JOYS+
program, more than 30 protostars are being observed with the MIRI/MRS. This
study explores the COMs ice signatures in the low and high-mass protostar, IRAS
2A and IRAS 23385, respectively. We fit continuum and silicate subtracted
observational data with IR laboratory ice spectra. We use the ENIIGMA fitting
tool to find the best fit between the lab data and the observations and to
performs statistical analysis of the solutions. We report the best fits for the
spectral ranges between 6.8 and 8.6 $\mu$m in IRAS 2A and IRAS 23385,
originating from simple molecules, COMs, and negative ions. The strongest
feature in this range (7.7 $\mu$m) is dominated by CH4 and has contributions of
SO2 and OCN-. Our results indicate that the 7.2 and 7.4 $\mu$m bands are mostly
dominated by HCOO-. We find statistically robust detections of COMs based on
multiple bands, most notably CH3CHO, CH3CH2OH, and CH3OCHO. The likely
detection of CH3COOH is also reported. The ice column density ratios between
CH3CH2OH and CH3CHO of IRAS 2A and IRAS 23385, suggests that these COMs are
formed on icy grains. Finally, the derived ice abundances for IRAS 2A correlate
well with those in comet 67P/GC within a factor of 5. Based on the MIRI/MRS
data, we conclude that COMs are present in interstellar ices, thus providing
additional proof for a solid-state origin of these species in star-forming
regions. The good correlation between the ice abundances in comet 67P and IRAS
2A is in line with the idea that cometary COMs can be inherited from the early
protostellar phases.
