Changes in volatile profile of soybean residue (okara) upon solid-state fermentation by yeasts

Area of Science:

• Food Science
• Microbiology
• Biotechnology

Background:

• Okara, a soybean by-product, is abundant but often discarded due to its poor flavor.
• Okara's rich protein and fat content offer potential for biotransformation and value addition.
• Improving okara's flavor through fermentation presents an opportunity for its alternative utilization in the food industry.

Purpose of the Study:

• To evaluate the efficacy of 10 different yeast strains in the solid-state fermentation of okara.
• To analyze the volatile profiles of fermented okara to identify flavor improvements.
• To determine the potential of okara as a substrate for bioflavor production.

Main Methods:

• Solid-state fermentation of okara using ten yeast strains (four dairy yeasts, six wine yeasts).
• Analysis of volatile compounds using Headspace-Solid Phase Microextraction Gas Chromatography-Mass Spectrometry/Flame Ionization Detection (HS-SPME GC-MS/FID).
• Quantification and identification of key aroma compounds, including off-odors, methyl ketones, and esters.

Main Results:

• Fermentation significantly reduced key okara off-odors (hexanal and trans-2-hexenal) through bioconversion.
• Dairy yeasts promoted the formation of methyl ketones, while wine yeasts favored ethyl and acetyl esters.
• Williopsis saturnus fermentation resulted in a substantial increase in esters (380-fold), imparting a distinct fruity aroma.

Conclusions:

• Okara can be effectively utilized as an inexpensive substrate for yeast fermentation.
• Yeast fermentation can transform okara into a more palatable food ingredient with enhanced flavor profiles.
• This biotransformation process opens avenues for bioflavor extraction and novel food product development using okara.