Performance of Leuconostoc citreum FDR241 during wheat flour sourdough type I propagation and transcriptional analysis of exopolysaccharides biosynthesis genes

Rossana Coda,Yan Xu,David Sàez Moreno,Dominik Mojzita,Luana Nionelli,Carlo G Rizzello,Kati Katina

doi:10.1016/j.fm.2018.05.003

Rossana Coda, Yan Xu + Show 5 more

Open Access

https://doi.org/10.1016/j.fm.2018.05.003

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Abstract

This study focused on the performance of the dextran producer Leuconostoc citreum as starter culture during 30 days of wheat flour type I sourdough propagation (back-slopping). As confirmed by RAPD-PCR analysis, the strain dominated throughout the propagation procedure, consisting of daily fermentations at 20 °C. The sourdoughs were characterized by consistent lactic acid bacteria cell density and acidification parameters, reaching pH values of 4.0 and mild titratable acidity. Carbohydrates consumption remained consistent during the propagation procedure, leading to formation of mannitol and almost equimolar amount of lactic and acetic acid. The addition of sucrose enabled the formation of dextran, inducing an increase in viscosity of the sourdough of 2–2.6 fold, as well as oligosaccharides. The transcriptional analysis based on glucosyltransferases genes (GH70) showed the existence in L. citreum FDR241 of at least five different dextransucrases. Among these, only one gene, previously identified as forming only α-(1–6) glycosidic bonds, was significantly upregulated in sourdough fermentation conditions, and the main responsible of dextran formation. A successful application of a starter culture during long sourdough back-slopping procedure will depend on the strain robustness and fermentation conditions. Transcriptional regulation of EPS-synthetizing genes might contribute to increase the efficiency of industrial processes.

Highlights

The positive influence of sourdough on bread quality has been the subject of many studies, focusing on the complex reactions occurring during microbial metabolism of lactic acid bacteria and yeasts, and their interactions with the endogenous enzymatic activity of the raw material (De Vuyst and Neysens, 2005; Gänzle, 2014)
Compared to commercial hydrocolloids which need to be declared on the product label and might not meet the consumers' request for additive-free food, EPS synthetized in the sourdough do not require labelling and constitute a clear advantage for food producers
In order to confirm the presence of the starter, 170 isolates of presumptive lactic acid bacteria isolated from T2, T5, T15 and T30 were subjected to random amplification of polymorphic DNA (RAPD)-PCR analysis using the single primers M13, P1 and P4

Summary

Introduction

The positive influence of sourdough on bread quality has been the subject of many studies, focusing on the complex reactions occurring during microbial metabolism of lactic acid bacteria and yeasts, and their interactions with the endogenous enzymatic activity of the raw material (De Vuyst and Neysens, 2005; Gänzle, 2014). The use of EPS has been explored for baked goods manufacturing with the aim of enhancing the quality of the final products Due to their hydrocolloid activity, EPS deeply affect dough textural properties, influencing several attributes of baked goods, including improved structure and volume, increased softness and delayed staling (Lynch et al, 2017). In this respect, the synthesis of EPS in situ during sourdough fermentation can substitute additives of plant origin such as xanthan for bread manufacturing. Compared to commercial hydrocolloids which need to be declared on the product label and might not meet the consumers' request for additive-free food, EPS synthetized in the sourdough do not require labelling and constitute a clear advantage for food producers

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