D. Mikkelsen | The University of Queensland, Australia (original) (raw)

Papers by D. Mikkelsen

Research paper thumbnail of Bacterial cellulose (BC): a model system to study in vitro fermentability of plant cell wall analogues

Research paper thumbnail of Independent fermentation and metabolism of dietary polyphenols associated with a plant cell wall model

Food & Function, 2020

The metabolic pathways of polyphenol degradation are not influenced by the presence of plant cell... more The metabolic pathways of polyphenol degradation are not influenced by the presence of plant cell walls during in vitro fermentation, but co-fermentation of cell walls may lead to faster microbial metabolism of polyphenols.

Research paper thumbnail of Biodeuteration as a tool to study cellulose and hemicellulose interactions in plant cell walls with contrast variation SANS

Research paper thumbnail of Spontaneous mutation results in lower cellulose production by a Gluconacetobacter xylinus strain from Kombucha

Carbohydrate Polymers, 2010

This study aimed to investigate the characteristics of a spontaneous mutation that results in low... more This study aimed to investigate the characteristics of a spontaneous mutation that results in lower cellulose production by a Gluconacetobacter xylinus strain isolated from Kombucha. The growth of this mutant was initially observed in Hestrin Schramm (HS) static and agitated cultures ...

Research paper thumbnail of Purified plant cell walls with adsorbed polyphenols alter porcine faecal bacterial communities during in vitro fermentation

Food & Function, 2020

A simplified in vitro model to indicate microbiota changes to polyphenols associated with dietary... more A simplified in vitro model to indicate microbiota changes to polyphenols associated with dietary fibre in whole fruits, noting differences in bacterial populations between polyphenolic groups during fermentation.

Research paper thumbnail of Large intestinal bacterial community and the effect of mango, purified pectin, and low fibre diets

Journal of Nutrition & Intermediary Metabolism

Research paper thumbnail of Biodeuteration and small angle neutron scattering as tools to understand the roles of cellulose and hemicelluloses as load bearing polymers in plant cell walls

Research paper thumbnail of Soluble arabinoxylan alters digesta flow and protein digestion of red meat-containing diets in pigs

Nutrition, 2015

The aim of this study was to investigate how a moderate increase in dietary meat content combined... more The aim of this study was to investigate how a moderate increase in dietary meat content combined (or not) with soluble fibre would influence protein digestion as well as digesta characteristics and flow. Four groups of pigs were fed Western-style diets (high-protein/high-fat) containing two types of barbecued red meat, one with and one without a wheat arabinoxylan-rich fraction. After 4 wk, digesta samples were collected from small and large intestinal sites and analyzed for protein, amino acids, dry matter, and acid-insoluble ash. Tissue samples were also collected from each site. Arabinoxylan consumption led to somewhat lower apparent protein digestibility within the small and large intestines as well as shorter mean retention times. This suggests that the lowered protein digestibility is due, at least partly, to shorter access time to digestive proteases and absorptive surfaces. Additionally, digesta mass was higher in pigs fed arabinoxylan while dry matter (%) was lower, indicating an increased digesta water-holding capacity due to the presence of a soluble dietary fiber. Data showed that solubilized wheat arabinoxylan provides potential health benefits through decreased protein digestibility, increased digesta mass, and reduced mean retention time, even for diets with a moderately higher protein content. These factors are associated with efficiency of digestion and satiety, both of which have implications for prevention of obesity and other health disorders.

Research paper thumbnail of Novel Porphyromonas species isolated from oral cavity of marsupials

Research paper thumbnail of Purified 1′acetoxychavicol acetate (1′ACA) from galangal spice affects membrane fatty acid composition and triggers a cell envelope stress response in Staphylococcus aureus

International Journal of Antimicrobial Agents, 2012

Research paper thumbnail of Binding of polyphenols to plant cell wall analogues – Part 1: Anthocyanins

Food Chemistry, 2012

Anthocyanins are located within the vacuole of plant cells, and are released following cell ruptu... more Anthocyanins are located within the vacuole of plant cells, and are released following cell rupture during eating or processing at which time they first come into contact with the plant cell wall. The extent of anthocyanin-cell wall interaction was investigated by monitoring the rate of anthocyanin depletion in the presence of pure cellulose or cellulose-pectin composites as cell wall models. It was found that anthocyanins interact with both cellulose and pectin over a two-stage process with initially (mins-hours) 13-18% of anthocyanins binding to cellulose or cellulose/pectincomposites. With prolonged exposure (days-weeks), a gradual increase in anthocyanin binding occurs, possibly due to anthocyanins stacking on top of a base layer. Binding of acylated and non-acylated anthocyanins followed a similar pattern with slightly more (5-10%) binding of the acylated forms. Composites with the highest pectin content had the greatest anthocyanin binding suggesting the existence of both ionic interactions (with pectin) and hydrophobic interactions (with cellulose) of anthocyanin with plant cell walls.

Research paper thumbnail of Lack of release of bound anthocyanins and phenolic acids from carrot plant cell walls and model composites during simulated gastric and small intestinal digestion

Food & Function, 2013

Separately, polyphenols and plant cell walls (PCW) are important contributors to the health benef... more Separately, polyphenols and plant cell walls (PCW) are important contributors to the health benefits associated with fruits and vegetables. However, interactions with PCW which occur either during food preparation or mastication may affect bioaccessibility and hence bioavailability of polyphenols. Binding interactions between anthocyanins, phenolic acids (PAs) and PCW components, were evaluated using both a bacterial cellulose-pectin model system and a black carrot puree system. The majority of available polyphenols bound to PCW material with 60-70% of available anthocyanins and PAs respectively binding to black carrot puree PCW matter. Once bound, release of polyphenols using acidified methanol is low with only ∼20% of total anthocyanins to ∼30% of PAs being released. Less than 2% of bound polyphenol was released after in vitro gastric and small intestinal (S.I.) digestion for both the model system and the black carrot puree PCW matter. Confocal laser scanning microscopy shows localised binding of anthocyanins to PCW. Very similar patterns of binding for anthocyanins and PAs suggest that PAs form complexes with anthocyanins and polysaccharides. Time dependent changes in extractability with acidified methanol but not the total bound fraction suggests that initial non-specific deposition on cellulose surfaces is followed by rearrangement of the bound molecules. Minimal release of anthocyanins and PAs after simulated gastric and S.I. digestion indicates that polyphenols in fruits and vegetables which bind to the PCW will be transported to the colon where they would be expected to be released by the action of cell wall degrading bacteria.

Research paper thumbnail of Biodeuteration as a tool to study cellulose and hemicellulose interactions in plant cell walls with contrast variation SANS

Research paper thumbnail of Influence of different carbon sources on bacterial cellulose production by Gluconacetobacter xylinus strain ATCC 53524

Journal of Applied Microbiology, 2009

To determine the effect of carbon sources on cellulose produced by Gluconacetobacter xylinus stra... more To determine the effect of carbon sources on cellulose produced by Gluconacetobacter xylinus strain ATCC 53524, and to characterize the purity and structural features of the cellulose produced. Methods and Results: Modified Hestrin Schramm medium containing the carbon sources mannitol, glucose, glycerol, fructose, sucrose or galactose were inoculated with Ga. xylinus strain ATCC 53524. Plate counts indicated that all carbon sources supported growth of the strain. Sucrose and glycerol gave the highest cellulose yields of 3AE83 and 3AE75 g l )1 respectively after 96 h fermentation, primarily due to a surge in cellulose production in the last 12 h. Mannitol, fructose or glucose resulted in consistent rates of cellulose production and yields of >2AE5 g l )1 . Solid state 13 C CP ⁄ MAS NMR revealed that irrespective of the carbon source, the cellulose produced by ATCC 53524 was pure and highly crystalline. Scanning electron micrographs illustrated the densely packed network of cellulose fibres within the pellicles and that the different carbon sources did not markedly alter the micro-architecture of the resulting cellulose pellicles. Conclusions: The production rate of bacterial cellulose by Ga. xylinus (ATCC 53524) was influenced by different carbon sources, but the product formed was indistinguishable in molecular and microscopic features. Significance and Impact of the Study: Our studies for the first time examined the influence of different carbon sources on the rate of cellulose production by Ga. xylinus ATCC 53524, and the molecular and microscopic features of the cellulose produced.

Research paper thumbnail of Archaeal diversity in two thermophilic chalcopyrite bioleaching reactors

Environmental Microbiology, 2006

This study used a culture-independent molecular approach to investigate the archaeal community co... more This study used a culture-independent molecular approach to investigate the archaeal community composition of thermophilic bioleaching reactors. Two culture samples, MTC-A and MTC-B, grown with different concentrations of chalcopyrite (CuFeS2), a copper sulfidic ore, at a temperature of 78 degrees C and pH 1.6 were studied. Phylogenetic analysis of the 16S rRNA genes revealed that both cultures consisted of Archaea belonging to the Sulfolobales. The 16S rRNA gene clone library of MTC-A grown with 4% (w/v) chalcopyrite was dominated by a unique phylotype related to Sulfolobus shibatae (69% of total clones). The remaining clones were affiliated with Stygiolobus azoricus (11%), Metallosphaera sp. J1 (8%), Acidianus infernus (2%), and a novel phylotype related to Sulfurisphaera ohwakuensis (10%). In contrast, the clones from MTC-B grown with 12% (w/v) chalcopyrite did not appear to contain Sulfolobus shibatae-like organisms. Instead the bioleaching consortium was dominated by clones related to Sulfurisphaera ohwakuensis (73.9% of total clones). The remaining microorganisms detected were similar to those found in MTC-A.

Research paper thumbnail of Bacterial cellulose (BC): a model system to study in vitro fermentability of plant cell wall analogues

Research paper thumbnail of Independent fermentation and metabolism of dietary polyphenols associated with a plant cell wall model

Food & Function, 2020

The metabolic pathways of polyphenol degradation are not influenced by the presence of plant cell... more The metabolic pathways of polyphenol degradation are not influenced by the presence of plant cell walls during in vitro fermentation, but co-fermentation of cell walls may lead to faster microbial metabolism of polyphenols.

Research paper thumbnail of Biodeuteration as a tool to study cellulose and hemicellulose interactions in plant cell walls with contrast variation SANS

Research paper thumbnail of Spontaneous mutation results in lower cellulose production by a Gluconacetobacter xylinus strain from Kombucha

Carbohydrate Polymers, 2010

This study aimed to investigate the characteristics of a spontaneous mutation that results in low... more This study aimed to investigate the characteristics of a spontaneous mutation that results in lower cellulose production by a Gluconacetobacter xylinus strain isolated from Kombucha. The growth of this mutant was initially observed in Hestrin Schramm (HS) static and agitated cultures ...

Research paper thumbnail of Purified plant cell walls with adsorbed polyphenols alter porcine faecal bacterial communities during in vitro fermentation

Food & Function, 2020

A simplified in vitro model to indicate microbiota changes to polyphenols associated with dietary... more A simplified in vitro model to indicate microbiota changes to polyphenols associated with dietary fibre in whole fruits, noting differences in bacterial populations between polyphenolic groups during fermentation.

Research paper thumbnail of Large intestinal bacterial community and the effect of mango, purified pectin, and low fibre diets

Journal of Nutrition & Intermediary Metabolism

Research paper thumbnail of Biodeuteration and small angle neutron scattering as tools to understand the roles of cellulose and hemicelluloses as load bearing polymers in plant cell walls

Research paper thumbnail of Soluble arabinoxylan alters digesta flow and protein digestion of red meat-containing diets in pigs

Nutrition, 2015

The aim of this study was to investigate how a moderate increase in dietary meat content combined... more The aim of this study was to investigate how a moderate increase in dietary meat content combined (or not) with soluble fibre would influence protein digestion as well as digesta characteristics and flow. Four groups of pigs were fed Western-style diets (high-protein/high-fat) containing two types of barbecued red meat, one with and one without a wheat arabinoxylan-rich fraction. After 4 wk, digesta samples were collected from small and large intestinal sites and analyzed for protein, amino acids, dry matter, and acid-insoluble ash. Tissue samples were also collected from each site. Arabinoxylan consumption led to somewhat lower apparent protein digestibility within the small and large intestines as well as shorter mean retention times. This suggests that the lowered protein digestibility is due, at least partly, to shorter access time to digestive proteases and absorptive surfaces. Additionally, digesta mass was higher in pigs fed arabinoxylan while dry matter (%) was lower, indicating an increased digesta water-holding capacity due to the presence of a soluble dietary fiber. Data showed that solubilized wheat arabinoxylan provides potential health benefits through decreased protein digestibility, increased digesta mass, and reduced mean retention time, even for diets with a moderately higher protein content. These factors are associated with efficiency of digestion and satiety, both of which have implications for prevention of obesity and other health disorders.

Research paper thumbnail of Novel Porphyromonas species isolated from oral cavity of marsupials

Research paper thumbnail of Purified 1′acetoxychavicol acetate (1′ACA) from galangal spice affects membrane fatty acid composition and triggers a cell envelope stress response in Staphylococcus aureus

International Journal of Antimicrobial Agents, 2012

Research paper thumbnail of Binding of polyphenols to plant cell wall analogues – Part 1: Anthocyanins

Food Chemistry, 2012

Anthocyanins are located within the vacuole of plant cells, and are released following cell ruptu... more Anthocyanins are located within the vacuole of plant cells, and are released following cell rupture during eating or processing at which time they first come into contact with the plant cell wall. The extent of anthocyanin-cell wall interaction was investigated by monitoring the rate of anthocyanin depletion in the presence of pure cellulose or cellulose-pectin composites as cell wall models. It was found that anthocyanins interact with both cellulose and pectin over a two-stage process with initially (mins-hours) 13-18% of anthocyanins binding to cellulose or cellulose/pectincomposites. With prolonged exposure (days-weeks), a gradual increase in anthocyanin binding occurs, possibly due to anthocyanins stacking on top of a base layer. Binding of acylated and non-acylated anthocyanins followed a similar pattern with slightly more (5-10%) binding of the acylated forms. Composites with the highest pectin content had the greatest anthocyanin binding suggesting the existence of both ionic interactions (with pectin) and hydrophobic interactions (with cellulose) of anthocyanin with plant cell walls.

Research paper thumbnail of Lack of release of bound anthocyanins and phenolic acids from carrot plant cell walls and model composites during simulated gastric and small intestinal digestion

Food & Function, 2013

Separately, polyphenols and plant cell walls (PCW) are important contributors to the health benef... more Separately, polyphenols and plant cell walls (PCW) are important contributors to the health benefits associated with fruits and vegetables. However, interactions with PCW which occur either during food preparation or mastication may affect bioaccessibility and hence bioavailability of polyphenols. Binding interactions between anthocyanins, phenolic acids (PAs) and PCW components, were evaluated using both a bacterial cellulose-pectin model system and a black carrot puree system. The majority of available polyphenols bound to PCW material with 60-70% of available anthocyanins and PAs respectively binding to black carrot puree PCW matter. Once bound, release of polyphenols using acidified methanol is low with only ∼20% of total anthocyanins to ∼30% of PAs being released. Less than 2% of bound polyphenol was released after in vitro gastric and small intestinal (S.I.) digestion for both the model system and the black carrot puree PCW matter. Confocal laser scanning microscopy shows localised binding of anthocyanins to PCW. Very similar patterns of binding for anthocyanins and PAs suggest that PAs form complexes with anthocyanins and polysaccharides. Time dependent changes in extractability with acidified methanol but not the total bound fraction suggests that initial non-specific deposition on cellulose surfaces is followed by rearrangement of the bound molecules. Minimal release of anthocyanins and PAs after simulated gastric and S.I. digestion indicates that polyphenols in fruits and vegetables which bind to the PCW will be transported to the colon where they would be expected to be released by the action of cell wall degrading bacteria.

Research paper thumbnail of Biodeuteration as a tool to study cellulose and hemicellulose interactions in plant cell walls with contrast variation SANS

Research paper thumbnail of Influence of different carbon sources on bacterial cellulose production by Gluconacetobacter xylinus strain ATCC 53524

Journal of Applied Microbiology, 2009

To determine the effect of carbon sources on cellulose produced by Gluconacetobacter xylinus stra... more To determine the effect of carbon sources on cellulose produced by Gluconacetobacter xylinus strain ATCC 53524, and to characterize the purity and structural features of the cellulose produced. Methods and Results: Modified Hestrin Schramm medium containing the carbon sources mannitol, glucose, glycerol, fructose, sucrose or galactose were inoculated with Ga. xylinus strain ATCC 53524. Plate counts indicated that all carbon sources supported growth of the strain. Sucrose and glycerol gave the highest cellulose yields of 3AE83 and 3AE75 g l )1 respectively after 96 h fermentation, primarily due to a surge in cellulose production in the last 12 h. Mannitol, fructose or glucose resulted in consistent rates of cellulose production and yields of >2AE5 g l )1 . Solid state 13 C CP ⁄ MAS NMR revealed that irrespective of the carbon source, the cellulose produced by ATCC 53524 was pure and highly crystalline. Scanning electron micrographs illustrated the densely packed network of cellulose fibres within the pellicles and that the different carbon sources did not markedly alter the micro-architecture of the resulting cellulose pellicles. Conclusions: The production rate of bacterial cellulose by Ga. xylinus (ATCC 53524) was influenced by different carbon sources, but the product formed was indistinguishable in molecular and microscopic features. Significance and Impact of the Study: Our studies for the first time examined the influence of different carbon sources on the rate of cellulose production by Ga. xylinus ATCC 53524, and the molecular and microscopic features of the cellulose produced.

Research paper thumbnail of Archaeal diversity in two thermophilic chalcopyrite bioleaching reactors

Environmental Microbiology, 2006

This study used a culture-independent molecular approach to investigate the archaeal community co... more This study used a culture-independent molecular approach to investigate the archaeal community composition of thermophilic bioleaching reactors. Two culture samples, MTC-A and MTC-B, grown with different concentrations of chalcopyrite (CuFeS2), a copper sulfidic ore, at a temperature of 78 degrees C and pH 1.6 were studied. Phylogenetic analysis of the 16S rRNA genes revealed that both cultures consisted of Archaea belonging to the Sulfolobales. The 16S rRNA gene clone library of MTC-A grown with 4% (w/v) chalcopyrite was dominated by a unique phylotype related to Sulfolobus shibatae (69% of total clones). The remaining clones were affiliated with Stygiolobus azoricus (11%), Metallosphaera sp. J1 (8%), Acidianus infernus (2%), and a novel phylotype related to Sulfurisphaera ohwakuensis (10%). In contrast, the clones from MTC-B grown with 12% (w/v) chalcopyrite did not appear to contain Sulfolobus shibatae-like organisms. Instead the bioleaching consortium was dominated by clones related to Sulfurisphaera ohwakuensis (73.9% of total clones). The remaining microorganisms detected were similar to those found in MTC-A.