Yeast flavour production by solid state fermentation of orange peel waste

• Bioflavour production from orange peel (OP) waste.
• Autoclave treatment of OP eliminated the toxic volatile substances and natural microflora.
• Solid state fermentation ensured high yields of volatile aroma esters.
• Biotransformation of naturally occurring aroma compounds by yeast may occur.
• The new process could be applied to a sustainable biorefinery for OP waste valorization.

Consumer demand for natural products and the requirement for eco-friendly processes promote development of innovative processes for flavour synthesis via biotechnology. In this direction, cultivation of selected industrial yeast strain under solid state fermentation of orange peel (OP) was studied. For this purpose, autoclave sterile OP for the elimination of d-limonene and natural microflora was evaluated with regard to yeast viability, nutrient consumption and cell ability to produce flavour active compounds. Non-sterile OP was also used to follow pros and cons of the sterilization process. Yeast cells showed better growth performance under sterilized process conditions, than under non-sterilized ones. In the first case, the enhanced de novo synthesis of “fruity” esters was demonstrated (48.7, 25.2, 9.3, 6.3 and 4.5 mg/kg of fermented OP for isoamyl acetate, ethyl dodecanoate, decanoate, octanoate and phenyl ethyl acetate, respectively, after 72 h). Yeast cells exhibited accelerated synthesis of ethyl hexanoate (154.2 mg/kg OP at 48 h). Biotransformation of naturally occurring aroma compounds by yeast may be considered in this process. The proposed process, resulting in high yields of industrially important volatile aroma esters (total of ∼250 mg/kg OP), could be applied to a sustainable biorefinery for the valorization of OP waste.