Exopolysaccharides produced by lactic acid bacteria in fava bean matrix

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Title: Exopolysaccharides produced by lactic acid bacteria in fava bean matrix
Author: Xu, Yan
Contributor: University of Helsinki, Faculty of Agriculture and Forestry, Department of Food and Nutrition
Doctoral Programme in Food Chain and Health
Thesis level: Doctoral dissertation (article-based)
Belongs to series: EKT - URN:ISSN:0355-1180
Abstract: Fava bean is a good source of plant protein that is increasingly gaining attention due to its health benefits and sustainability. However, the addition of fava bean flour or protein concentrate at high concentrations to food products may result in an unsatisfying texture. Therefore, texture modification of the fava bean matrix is essential to improve its usability in various food systems. Microbial exopolysaccharides (EPS) are effective texture modifiers, with lactic acid bacteria (LAB) being widely used in the food industry to produce them. In this thesis, EPS were produced in situ from sucrose by LAB during the fermentation of fava bean flour or fava bean protein concentrate (FPC), and their texture modification effects on fava bean matrix were evaluated. Leuconostoc pseudomesenteroides DSM 20193 and Weissella confusa VTT E-143403 were found to be good dextran producers in fava bean matrix. With the same starter, sucrose addition strongly increased paste viscosity after fermentation. By separately hydrolyzing the fermented paste with dextranase and levanase, this increase was demonstrated to be primarily driven by dextran. The gel-strengthening ability of EPS was revealed by dynamic oscillatory rheology analysis, with obvious elasticity increases in sucrose-enriched pastes after fermentation. Dextrans produced by Ln. pseudomesenteroides DSM 20193 and W. cibaria Sj 1b showed considerable gel-strengthening ability. Two mechanisms of degradation for raffinose family oligosaccharides (RFO) were established in this thesis, involving plant-derived α-galactosidase and microbial levansucrase (LSR). In fava bean flour, RFO were preferentially degraded by endogenous α-galactosidase, producing galactose and sucrose that could be further used for EPS synthesis. In the absence of endogenous α-galactosidase, LSR could act on RFO, forming melibiose, manninotriose, and manninotetraose. A joint function of endogenous α-galactosidase and microbial LSR in RFO degradation was also observed. Texture evaluation of fermented FPC pastes revealed higher firmness, consistency, cohesiveness, and index of viscosity in sucrose-enriched pastes. Proteolysis of fava bean protein was very weak after fermentation, thus contributing less to texture modification of FPC pastes than did EPS. Confocal laser scanning microscopy of fermented fava bean protein showed more concentrated protein aggregates in dextran-enriched pastes. The study of fava bean protein-dextran interactions indicates the importance of intermolecular interactions between these two polymers in determining the rheological properties of the system. During acidification, dextran stabilized the network of fava bean protein through intermolecular interactions. Conjugation of dextran to fava bean protein through the Maillard reaction decreased both viscosity and gel elasticity during protein gelation. The molar mass and conformation of dextrans affected their behavior in the protein system, especially during protein gelation. This thesis shows for the first time the feasibility of connecting EPS production by LAB to the fermentation of fava bean matrix, and identifies two promising dextran producers for use in this matrix. Analysis of the microstructure of fava bean protein with dextran and fava bean protein–dextran interactions clearly showed the role of dextran in the protein network. Furthermore, the results indicate that different EPS producers may allow texture tailoring of the fava bean matrix, which may contribute to the development of novel plant protein-based food or meat substitutes.
URI: URN:ISBN:978-951-51-4601-4
Date: 2018-10-26
Rights: This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

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