057: Characterization of Protein-Derived Volatile/Semi-Volatile Metabolites of Alkaline Fermented Cowpeas Using Gas Chromatography-Mass Spectrometry (GC-MS)

Introduction

Cowpea (Vigna unguiculata) is a rich source of plant protein but is often limited in culinary applications due to its strong beany flavor. Alkaline fermentation of legumes like cowpeas is characterized by extensive hydrolysis of the proteins into peptides, amino acids, and ammonia, resulting in pH increasing to about 8–10 in the final product, thus affecting its flavor and aroma profile. This study aimed to determine how alkaline fermentation affects the volatile and semi-volatile flavor metabolites in cowpea flour and the resultant protein isolates.

Methods

Cowpea flours and isolates were fermented under alkaline conditions at 30°C for 96 h. A sample of alkaline fermented cowpea flour or protein isolate was placed in sealed vials and heated in a water bath at 45°C for 15 minutes. The headspace above the sample was then analyzed with a Divinylbenzene/Carboxen/Polydimethylsiloxane, (DVB/CAR/PDMS) fiber. Head Space Sampling with Solid-phase micro extraction and gas chromatography-mass spectrometry (SPME-GC-MS) was used to extract and analyze these metabolites.

Results

The analysis identified 140 metabolites in all the cowpea flour and protein isolate samples fermented at different fermentation times. These metabolites included aldehydes (7), acids (6), ketones (7), esters (10), pyrazines (4), alcohols (7), miscellaneous compounds (5), cycloalkanes compounds (14) furans (2), alkanes (48), alkenes (1), benzene-containing compounds (18), nitrogen-containing compounds (2), and terpenes (9). The terpenes were the most abundant metabolites in concentration, followed by alkanes, aromatic compounds, and alcohols in cowpea flour and protein samples. Unfermented and fermented cowpea protein isolates showed a higher concentration of volatile and semi-volatile metabolites than the cowpea flour. Multivariate data analysis helped identify distinct volatile profiles associated with different fermentation times and sample types. Key volatile metabolites such as benzaldehyde, hexanal, and 2,3-butanedione significantly contributed to the flavor of the fermented cowpea.

Significance

The protein isolate, having a higher concentration of flavor compounds than flour, can be utilized as a concentrated flavor source in food products. The findings suggest that alkaline fermented cowpea flour and protein isolates could serve as an effective seasoning agent, offering novel and nutritious food options.

Authors: M. Muhau, S.M Moyo, K.G. Duodu and E. Kayitesi