Abstract
The production of natural flavors by means of microorganisms is of great interest for the food and flavor industry, and by-products of the agro-industry are particularly suitable as substrates. In the present study, Citrus side streams were fermented using monokaryotic strains of the fungus Pleurotus sapidus. Some of the cultures exhibited a pleasant smell, reminiscent of woodruff and anise, as well as herbaceous notes. To evaluate the composition of the overall aroma, liquid/liquid extracts of submerged cultures of a selected monokaryon were prepared, and the volatiles were isolated via solvent-assisted flavor evaporation. Aroma extract dilution analyses revealed p-anisaldehyde (sweetish, anisic- and woodruff-like) with a flavor dilution factor of 218 as a character impact compound. The coconut-like, herbaceous, and sweetish smelling acyloin identified as (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone also contributed to the overall aroma and was described as an aroma-active substance with an odor threshold in air of 0.2 ng L−1 to 2.4 ng L−1 for the first time. Supplementation of the culture medium with isotopically substituted l-tyrosine elucidated this phenolic amino acid as precursor of p-anisaldehyde as well as of (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone. Chiral analysis via HPLC revealed an enantiomeric excess of 97% for the isolated product produced by P. sapidus.
Highlights
Introduction published maps and institutional affilWith about 200 million tons in 2019, Citrus fruits belong to the most important plant species cultivated worldwide [1]
In order to investigate differences in aroma formation between di- and monokaryons of Pleurotus sapidus (PSA), the strains were grown in surface cultures on an agar medium containing Citrus side stream substrate (CSSM)
Our work focused on the two aroma-active compounds p-anisaldehyde (33) and
Summary
Introduction published maps and institutional affilWith about 200 million tons in 2019, Citrus fruits belong to the most important plant species cultivated worldwide [1]. After the production of Citrus juice and extraction of essential oils, the peels remain as a by-product. Their current utilization for pectin extraction or animal feed is economically only modestly attractive. These byproducts contain numerous bioactive compounds [2], which may be transformed through fermentation and channeled back into food production. An alluring option is the production of flavorings, whereby the biotechnological route leads to natural flavors, which offers a considerable economic advantage. In which industrial or agricultural by-products, such as Eucalyptus waste, molasses, and apple pomace were used for the production of natural flavors have been reported [3,4,5]. Fungi from the division basidiomycota have become a focus of research, as they have a highly complex enzyme system, which enables them to degrade iations
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