“Mo gase ntšhe tota tota” - towards a fermented sweet reed beverage.
Abstract
Ntšhe, a Setswana name for sweet reeds, a sweet sorghum variety (
Sorghum bicolor (L)) is a commercial crop consumed as a delicacy
in enormous quantities in Botswana and in southern Africa at large. Pre
and post-harvest losses due to infestation by larval stages of stem
borer moths, Chilo partellus often lead to severe financial
losses as consumers condemn the worm-infested sweet reeds as
unpalatable, “ Mo gase ntšhe tota tota” (this is not a sweet
reed). Valorisation of condemned sweet reeds is one attractive route to
reduce economic losses. Here, we took advantage of our understanding of
yeast-insect interactions to isolate yeasts associated with larval
stages of the stem borer moths and investigated their potential for
production of an alcoholic sweet reed beverage. We isolated 33 yeast
strains representing from the galleries and frass as well as from the
guts of the larval moths. Assessment of their ability to ferment the
simplest sugar, glucose, resulted in identification of 14 strains
belonging to Hanseniaspora and Candida genera. These strains were
further assessed for their capacity to ferment by calculating the rate
of accumulation of carbon dioxide and ethanol when grown in the
principal sugars found in sweet sorghum juice as sole carbon sources as
well in sweet sorghum juice. In addition, as an industrially relevant
trait, we tested the potential of the strains to tolerate
brewing/fermentation-associated stresses. Furthermore, we assessed the
aromatic complexity of the produced beverage. Our results suggest that
non-conventional yeasts associated with the larval moths have potential
for valorization of condemned sweet sorghum stalks to produce a sweet
sorghum beverage.