Influence of postharvest UV-B treatment and fermentation on secondary plant compounds in white cabbage leaves
In conclusion, the present study shows the possibility to use
UV-B treatment in existing postharvest processes, e.g. cabbage fermentation
or sauerkraut production, and offers the possibility to
influence the nutritional values and quality of these processed
plants. Post-harvest processes, such as UV-B irradiation, and the
following fermentation had a high impact on polyphenols and on
two elected glucobrassicin derivatives, glucobrassicin and 4-
methoxyglucobrassicin, respectively. In particular, the postharvest
use of UV-B treatment enables an increase or even new formation
of flavonoids and hydroxycinnamic acids in white cabbage leaves.
The highly bioactive flavonoid quercetintriglycoside and the
hydroxycinnamic acid derivatives p-coumaroylglycoside, feruloylglycoside,
and caffeoylglycoside were partly not present in the
original plant material but were identified with strong increased
values in UV-B treated plant material. Further, the chemical
changes in their compound structures by postharvest treatments
might lead to a changed reactivity or compound modification
and might induce the formation of new compounds, such as cinnamic
acid aglycone from p-coumaric acid by fermentation or
dihydroascorbigens from glucosinolates, by UV-B treatment, as
presented in this study. Therefore, it is mandatory to have a focus
on different compound classes during plant compound analyses
and the further estimation of changes in nutritional quality. A simple
extraction method of plant material enables the detection of
targeted analytes as well as the discovery of newly generated compounds
(possibly bioactive) during the postharvest process, which
is important for the field of plant metabolomics.
However, for future studies, further influences on plant
material, such as harvesting conditions, variety, influences during
processing steps as well as sensory quality and consumers
acceptance has to be considered. It is of future interest to evaluate
processing steps, such as storage conditions, fermentation conditions
(with or without starter culture e.g.) or the combination of
UV-B intensity and their influence on viability of microorganisms
more in detail.