title: The effect of medium structure complexity on the growth of Saccharomyces cerevisiae in gelatin-dextran systems.
abstract: As most food systems are (semi-)solid, the effect of food structure on bacterial growth has been widely acknowledged. However, studies on the growth dynamics of yeasts have neglected the effect of food structure. In this paper, the growth dynamics of the spoilage yeast Saccharomyces cerevisiae was investigated at 23.5 °C in broth, singular, homogeneous biopolymer systems and binary biopolymer systems with a heterogeneous microstructure. The biopolymers gelatin and dextran were used to introduce the different levels of structure. The metabolizing ability of gelatin and dextran by S. cerevisiae was examined. To study microbial behavior in the binary systems at the micro level, mixtures were imaged with confocal laser scanning microscopy (CLSM). Growth dynamics and microscopic images of S. cerevisiae were compared with those obtained for Escherichia coli in the same model system (Boons et al., 2014). Different phase-separated, heterogeneous microstructures were obtained by changing the amount of added gelatin and dextran. Regardless of the microstructure, S. cerevisiae was preferentially located in the dextran phase. Metabolizing ability-tests indicated that gelatin could be consumed by S. cerevisiae but in the presence of glucose, no change in gelatin concentration was observed. No indication of dextran metabolizing ability was observed. When supplementing broth with gelatin or dextran alone, an enhanced growth rate and maximum cell density were observed. This enhancement was further increased by adding a second biopolymer, introducing a heterogeneous microstructure and hence increasing the medium structure complexity. The results obtained indicate that food structure complexity plays a significant role in the growth dynamics of S. cerevisiae, an important food spoiler.
authors.affiliation: CPMF(2)-Flemish Cluster Predictive Microbiology in Foods, Belgium(1); BioTeC-Chemical and Biochemical Process Technology and Control, Department of Chemical Engineering, KU Leuven, Leuven, Belgium. Electronic address: kathleen.boons@cit.kuleuven.be.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Boons
authors.affiliation: CPMF(2)-Flemish Cluster Predictive Microbiology in Foods, Belgium(1); BioTeC-Chemical and Biochemical Process Technology and Control, Department of Chemical Engineering, KU Leuven, Leuven, Belgium. Electronic address: estefania.noriegafernandez@cit.kuleuven.be.
authors.forename: Estefanía
authors.initials: E
authors.lastname: Noriega
authors.affiliation: BioTeC-Chemical and Biochemical Process Technology and Control, Department of Chemical Engineering, KU Leuven, Leuven, Belgium. Electronic address: niels.verherstraeten@student.kuleuven.be.
authors.forename: Niels
authors.initials: N
authors.lastname: Verherstraeten
authors.affiliation: Molecular Visualization and Photonics, KU Leuven, Leuven, Belgium. Electronic address: charlotte.david@chem.kuleuven.be.
authors.forename: Charlotte C
authors.initials: CC
authors.lastname: David
authors.affiliation: Molecular Visualization and Photonics, KU Leuven, Leuven, Belgium. Electronic address: johan.hofkens@chem.kuleuven.be.
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.affiliation: CPMF(2)-Flemish Cluster Predictive Microbiology in Foods, Belgium(1); BioTeC-Chemical and Biochemical Process Technology and Control, Department of Chemical Engineering, KU Leuven, Leuven, Belgium. Electronic address: jan.vanimpe@cit.kuleuven.be.
authors.forename: Jan F
authors.initials: JF
authors.lastname: Van Impe
mesh_terms: D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism* / Q000592:standards; D003911:Dextrans / Q000737:chemistry / Q000378:metabolism; D005780:Gelatin / Q000737:chemistry / Q000378:metabolism; D018613:Microscopy, Confocal; D008954:Models, Biological; D012441:Saccharomyces cerevisiae / Q000254:growth & development* / Q000378:metabolism
chemical_list: D001704:Biopolymers; D003470:Culture Media; D003911:Dextrans; D005780:Gelatin
keywords: Confocal laser scanning microscopy; Food biopolymers; Growth kinetics; Heterogeneous microstructure; Metabolizing ability; Yeast