Differential metabolic signatures in naturally and lactic acid bacteria (LAB) fermented ting (a Southern African food) with different tannin content, as revealed by gas chromatography mass spectrometry (GC–MS)-based metabolomics

Author(s): Oluwafemi Ayodeji Adebo1, Eugenie Kayitesi1, Fidele Tugizimana2,3, Patrick Berka Njobeh1

1. Department of Biotechnology and Food Technology, University of Johannesburg

2. Research Centre for Plant Metabolomics, Department of Biochemistry, University of Johannesburg

3. International R&D, Omnia Group, Ltd

Published By: Food Research International

Issue: Vol. 121, July 2019

Year of Publication: 2019

Link: https://www.sciencedirect.com/science/article/pii/S0963996919302017

Abstract: Fermented whole grain (WG) sorghum food products including WG-ting can be obtained from different sample sources and fermentation conditions, leading subsequently to variations in the molecular composition of the products. There is however, a lack of detailed understanding and description of differential molecular profiles of these food products. Thus, the current study is a nontargeted gas chromatography-mass spectrometry (GC–MS)-based metabolomics approach to descriptively elucidate metabolic profiles of two WG-sorghum types [high tannin (HT) and low tannin (LT)] and their derived WG-ting products obtained via fermentation. Metabolites were extracted with 80% aqueous methanol and analyzed on a gas chromatography high resolution time of flight mass spectrometry (GC-HRTOF-MS) system. Chemometric methods such as principal component analysis (PCA) and orthogonal partial least square-discriminant analysis (OPLS-DA) were applied to mine the generated data. Our results showed that tannin contents influenced the composition of the raw sorghum and derived WG-ting samples. Metabolite signatures that differentiated raw HT- and LT-sorghum included cyclic compounds, pesticides, 2,4-di-tert-butylphenol, fatty acid esters, and sugar derivatives. Furthermore, fermentation of the HT- and LT-sorghum into WG-ting led to an increase in the levels of fatty acids, fatty acid esters and some other compounds which are vital from a dietary and health context. Equally observed were reduction of some phenols, cyclic compounds, a pesticide and ketone. Thus, the results demonstrated that the inherent metabolic composition of raw sorghum would lead to differential metabolic changes in the fermented products such as WG-ting, with subsequent dietary and health implications. Fermenting ting with Lactobacillus fermentum FUA 3321 was most desirable as relevant metabolites were observed in both HT- and LT-ting samples. Furthermore, the study highlights the applicability of GC–MS metabolomics in understanding WG-ting fermentation.

Note(s): The study was done using the Rxi-5ms column.