The Impact of Non-Concentrated Storage on the Centrifugation Yield of Microchloropsis gaditana: A Pilot-Scale Study.

Non-concentrated algae storage can bridge the period between algae harvesting and processing while avoiding the stress conditions associated with the concentration step required for concentrate storage. This study aimed to examine organic matter losses during the non-concentrated storage of Microchloropsis gaditana at pilot-scale. Algae cultures (400-500 L) were stored for up to 12 days either at an 8 °C target temperature or at 19 °C as the average temperature. The centrifugation yield of stored algal cultures decreased from day 5 or day 8 onwards for all storage conditions. After 12 days, the centrifugation yields were between 57% and 93% of the initial yields. Large differences in centrifugation yields were noted between the algae batches. The batch-to-batch difference outweighed the effect of storage temperature, and the highest yield loss was observed for the 8 °C cooled algae batch. The analysis of stored algae before and after centrifugation suggested that the decreasing yields were not related to respiration losses, but rather, the decreasing efficiency with which organic matter is collected during the centrifugation step.

Applications of Microalgae in Foods, Pharma and Feeds and Their Use as Fertilizers and Biostimulants: Legislation and Regulatory Aspects for Consideration.

Microalgae are a rich resource of lipids, proteins, carbohydrates and pigments with nutritional and health benefits. They increasingly find use as ingredients in functional foods and feeds as well as in cosmetics and agricultural products including biostimulants. One of their distinct advantages is their ability to grow on wastewaters and other waste streams, and they are considered an environmentally friendly and cheap method to recover nutrients and remove pollutants from the environment. However, there are limits concerning their applications if grown on certain waste streams. Within, we collate an overview of existing algal applications and current market scenarios for microalgal products as foods and feeds along with relevant legislative requirements concerning their use in Europe and the United States. Microalgal compounds of interest and their extraction and processing methodologies are summarized, and the benefits and caveats of microalgae cultivated in various waste streams and their applications are discussed.

The Impact of Nutrient Limitation and Harvest Method on the Wet Preservation of Chlorella vulgaris Biomass.

The temporary storage of wet algae concentrates enables the decoupling in time of algae harvests and their biorefinery. However, the impact of cultivation and of the harvest conditions on algae quality during preservation is largely unknown. This study aimed to determine the impact of nutrient limitation and of harvest methods on the preservation of Chlorella vulgaris biomass. Algae were either well-fed until harvest or received no nutrients for one week, and were harvested by either batch or continuous centrifugation. The organic acid formation, lipid levels, and lipolysis were monitored. Nutrient limitation had a large impact and resulted in lower pH values (4.9 ± 0.4), high levels of lactic acid and acetic acid, and a slightly higher degree of lipid hydrolysis. Concentrates of well-fed algae had a higher pH (7.4 ± 0.2) and another pattern of fermentation products with mainly acetic acid, succinic acid, and, to a smaller extent, lactic acid and propionic acid. The effect of the harvest method was smaller, with, most often, higher lactic acid and acetic acid levels for algae harvested by continuous centrifugation than for those obtained by batch centrifugation. In conclusion, nutrient limitation, a well-known method to enhance algae lipid levels, can impact several quality attributes of algae during their wet storage.

Nutritional Profiling and Preliminary Bioactivity Screening of Five Micro-Algae Strains Cultivated in Northwest Europe.

This study aimed to map the nutritional profile and bioactivities of five microalgae that can be grown in Northwest Europe or areas with similar cultivation conditions. Next to the biochemical composition, the in vitro digestibility of carbohydrates, proteins, and lipids was studied for Chlamydomonas nivalis, Porphyridium purpureum, Chlorella vulgaris, Nannochloropsis gaditana, and Scenedesmus species biomass. These microalgae were also assessed for their ability to inhibit the angiotensin-1-converting enzyme (ACE-1, EC 3.4.15.1), which is known to play a role in the control of blood pressure in mammals. Large differences in organic matter solubility after digestion suggested that a cell disruption step is needed to unlock the majority of the nutrients from N. gaditana and Scenedesmus species biomass. Significant amounts of free glucose (16.4-25.5 g glucose/100 g dry algae) were detected after the digestion of C. nivalis, P. purpureum, and disrupted Scenedesmus. The fatty acid profiles showed major variations, with particularly high Ω-3 fatty acid levels found in N. gaditana (5.5 ± 0.5 g/100 g dry algae), while lipid digestibility ranged from 33.3 ± 6.5% (disrupted N. gaditana) to 67.1 ± 11.2% (P. purpureum). C. vulgaris and disrupted N. gaditana had the highest protein content (45-46% of dry matter), a nitrogen solubility after digestion of 65-71%, and the degree of protein hydrolysis was determined as 31% and 26%, respectively. Microalgae inhibited ACE-1 by 73.4-87.1% at physiologically relevant concentrations compared to a commercial control. These data can assist algae growers and processors in selecting the most suitable algae species for food or feed applications.

Modifying wheat bran to improve its health benefits.

Consumption of wheat bran (WB) has been associated with improved gastrointestinal health and a reduced risk for colorectal cancer, cardiovascular diseases and metabolic disorders. These benefits are likely mediated by a combination of mechanisms, including colonic fermentation of the WB fiber, fecal bulking and the prevention of oxidative damage due to its antioxidant capacities. The relative importance of those mechanisms is not known and may differ for each health effect. WB has been modified by reducing particle size, heat treatment or modifying tissue composition to improve its technological properties and facilitate bread making processes. However, the impact of those modifications on human health has not been fully elucidated. Some modifications reinforce whereas others attenuate the health effects of coarse WB. This review summarizes available WB modifications, the mechanisms by which WB induces health benefits, the impact of WB modifications thereon and the available evidence for these effects from in vitro and in vivo studies.

Microbial succession during wheat bran fermentation and colonisation by human faecal microbiota as a result of niche diversification.

The human gut can be viewed as a flow-through system with a short residence time, a high turnover rate and a spatial gradient of physiological conditions. As a consequence, the gut microbiota is exposed to highly fluctuating environmental determinants presented by the host and diet. Here, we assessed the fermentation and colonisation of insoluble wheat bran by faecal microbiota of three individuals at an unprecedented sampling intensity. Time-resolved 16S rRNA gene amplicon sequencing, revealed a dynamic microbial community, characterised by abrupt shifts in composition, delimiting states with a more constant community, giving rise to a succession of bacterial taxa alternately dominating the community over a 72 h timespan. Early stages were dominated by Enterobacteriaceae and Fusobacterium species, growing on the carbohydrate-low, protein rich medium to which wheat bran was supplemented. The onset of wheat bran fermentation, marked by a spike in short chain fatty acid production with an increasing butyrate proportion and an increased endo-1,4-ß-xylanase activity, corresponded to donor-dependent proportional increases of Bacteroides ovatus/stercoris, Prevotella copri and Firmicutes species, which were strongly enriched in the bran-attached community. Literature and database searches provided novel insights into the metabolic and growth characteristics underlying the observed succession and colonisation, illustrating the potency of a time-resolved analysis to increase our understanding of gut microbiota dynamics upon dietary modulations.

Isolation of wheat bran-colonizing and metabolizing species from the human fecal microbiota.

Undigestible, insoluble food particles, such as wheat bran, are important dietary constituents that serve as a fermentation substrate for the human gut microbiota. The first step in wheat bran fermentation involves the poorly studied solubilization of fibers from the complex insoluble wheat bran structure. Attachment of bacteria has been suggested to promote the efficient hydrolysis of insoluble substrates, but the mechanisms and drivers of this microbial attachment and colonization, as well as subsequent fermentation remain to be elucidated. We have previously shown that an individually dependent subset of gut bacteria is able to colonize the wheat bran residue. Here, we isolated these bran-attached microorganisms, which can then be used to gain mechanistic insights in future pure culture experiments. Four healthy fecal donors were screened to account for inter-individual differences in gut microbiota composition. A combination of a direct plating and enrichment method resulted in the isolation of a phylogenetically diverse set of species, belonging to the Bacteroidetes, Firmicutes, Proteobacteria and Actinobacteria phyla. A comparison with 16S rRNA gene sequences that were found enriched on wheat bran particles in previous studies, however, showed that the isolates do not yet cover the entire diversity of wheat-bran colonizing species, comprising among others a broad range of Prevotella, Bacteroides and Clostridium cluster XIVa species. We, therefore, suggest several modifications to the experiment set-up to further expand the array of isolated species.

Modification of wheat bran particle size and tissue composition affects colonisation and metabolism by human faecal microbiota.

Dietary modulation can alter the gut microbiota composition and activity, in turn affecting health. Particularly, dietary fibre rich foods, such as wheat bran, are an important nutrient source for the gut microbiota. Several processing methods have been developed to modify the functional, textural and breadmaking properties of wheat bran, which can affect the gut microbiota. We therefore studied the effect of enzyme treatment, particle size reduction and wheat kernel pearling on the faecal microbiota of ten healthy individuals. The most commonly studied health marker, associated to the gut microbiota activity is Short Chain Fatty Acid (SCFA) production. This study shows that modifying wheat bran physicochemical properties allows control over the extent and the rate of SCFA production by the faecal microbiota. Wheat bran pericarp fractions, depleted in starch and enriched in cellulose and highly branched arabinoxylans, were poorly fermentable compared to unmodified wheat bran, thus resulting in a reduced SCFA production with up to 20 mM. The nature of the SCFA, however, largely depends on the donor and can be linked to the individual's gut microbiota composition. The latter changed in an individually dependent manner in response to wheat bran modification. Some product dependent significant differences could still be identified across the ten donors. This product effect is more pronounced in the microbial community attached to the wheat bran residue as compared to the luminal microbial community. Generally, we find lower levels of Firmicutes, Bacteroidetes and Bifidobacterium and a higher abundance of Proteobacteria in the pericarp enriched wheat bran fractions, compared to unmodified wheat bran.

Kluyveromyces marxianus yeast enables the production of low FODMAP whole wheat breads.

There is evidence that a diet low in Fermentable Oligo-, Di-, Monosaccharides And Polyols (FODMAPs) alleviates symptoms in approx. 70% of the patients suffering from irritable bowel syndrome. Through fructans, wheat containing products are a major source of FODMAPs in the western diet. Although fructans are partially degraded during dough fermentation by Saccharomyces cerevisiae invertase, wheat bread contains notable fructan levels. In this study, it was shown that Kluyveromyces marxianus strain CBS6014 can degrade more than 90% of the fructans initially present in wheat whole meal during bread making, which can be attributed to its high inulinase activity. As K. marxianus CBS6014 was not able to consume maltose during fermentation, alternative sugars (sucrose) or glucose releasing enzymes (amyloglucosidase) had to be included in the bread making recipe to ensure sufficient production of CO2 and high bread quality. Five volatile flavor compounds were produced in significantly different levels when K. marxianus CBS6014 was used as starter culture compared with the conventional S. cerevisiae bakery strain. These differences were, however, not detected when sensory analysis of the crumb was performed. This study demonstrates the potential of inulinase-producing K. marxianus strains for the production of (whole meal) breads low in FODMAPs.

Introducing insoluble wheat bran as a gut microbiota niche in an in vitro dynamic gut model stimulates propionate and butyrate production and induces colon region specific shifts in the luminal and mucosal microbial community.

The spatial organization of gut microorganisms is important with respect to their functional role in the gut ecosystem. Regional differences in the longitudinal and lateral direction are, however, not frequently studied, given the difficulty to sample these human gut regions in vivo. Particularly the insoluble food particle-associated microbiota is poorly studied. Therefore, the long-term effects of insoluble wheat bran supplementation on the composition and functionality of the gut microbial community derived from six individuals were explored in the Dietary Particle-Mucosal-Simulator of the Human Intestinal Microbial Ecosystem in vitro model. Wheat bran stimulated propionate and butyrate production and induced shifts in the luminal and mucosal microbial community composition. The insoluble wheat bran residue and the mucus layer were identified as crucial platforms in sustaining diversity by selectively enriching species, which are not thriving in the luminal environment, including Lactobacillus, Bifidobacterium and Dialister species, Roseburia faecis, Prevotella copri and Bacteroides ovatus. Despite the evident habitat preference, some parallels could be drawn between the enrichment of taxa on bran platforms and their stimulation in the luminal and mucosal communities. Removing wheat bran during the wash-out period reversed the functional effects and gave rise to a blooming of some taxa that are considered opportunistic pathogens.

Reduced-Particle-Size Wheat Bran Is Efficiently Colonized by a Lactic Acid-Producing Community and Reduces Levels of Enterobacteriaceae in the Cecal Microbiota of Broilers.

In the present study, we investigated whether reducing the particle size of wheat bran affects the colonizing microbial community using batch fermentations with cecal inocula from seven different chickens. We also investigated the effect of in-feed administration of regular wheat bran (WB; 1,690 µm) and wheat bran with reduced particle size (WB280; 280 µm) on the cecal microbial community composition of broilers. During batch fermentation, WB280 was colonized by a lactic acid-producing community (Bifidobacteriaceae and Lactobacillaceae) and by Lachnospiraceae that contain lactic acid-consuming butyric acid-producing species. The relative abundances of the Enterobacteriaceae decreased in the particle-associated communities for both WB and WB280 compared to that of the control. In addition, the community attached to wheat bran was enriched in xylan-degrading bacteria. When administered as a feed additive to broilers, WB280 significantly increased the richness of the cecal microbiota and the abundance of bacteria containing the butyryl-coenzyme A (CoA):acetate CoA-transferase gene, a key gene involved in bacterial butyrate production, while decreasing the abundances of Enterobacteriaceae family members in the ceca. Particle size reduction of wheat bran thus resulted in the colonization of the bran particles by a very specific lactic acid- and butyric acid-producing community and can be used to steer toward beneficial microbial shifts. This can potentially increase the resilience against pathogens and increase animal performance when the reduced-particle-size wheat bran is administered as a feed additive to broilers.IMPORTANCE Prebiotic dietary fibers are known to improve the gastrointestinal health of both humans and animals in many different ways. They can increase the bulking capacity, improve transit times, and, depending on the fiber, even stimulate the growth and activity of resident beneficial bacteria. Wheat bran is a readily available by-product of flour processing and is a highly concentrated source of (in)soluble dietary fiber. The intake of fiber-rich diets has been associated with increased Firmicutes and decreased Proteobacteria numbers. Here, we show that applying only 1% of a relatively simple substrate which was technically modified using relatively simple techniques reduces the concentration of Enterobacteriaceae This could imply that in future intervention studies, one should take the particle size of dietary fibers into account.

Simultaneous glucose production from cellulose and fouling reduction using a magnetic responsive membrane reactor with superparamagnetic nanoparticles carrying cellulolytic enzymes.

This work aimed at investigating simultaneous hydrolysis of cellulose and in-situ foulant degradation in a cellulose fed superparamagnetic biocatalytic membrane reactor (BMRSP). In this reactor, a dynamic layer of superparamagnetic bionanocomposites with immobilized cellulolytic enzymes were reversibly immobilized on superparamagnetic polymeric membrane using an external magnetic field. The formation of a dynamic layer of bionanocomposites on the membrane helped to prevent direct membrane-foulant interaction. Due to in-situ biocatalysis, there was limited filtration resistance. Simultaneous separation of the product helped to avoid enzyme product inhibition, achieve constant reaction rate over time and 50% higher enzyme efficiency than batch reactor. Stable enzyme immobilization and the ability to keep enzyme in the system for long period helped to achieve continuous productivity at very low enzyme but high solid loading, while also reducing the extent of membrane fouling. Hence, the BMRSP paves a path for sustainable production of bioethanol from the cheaply available lignocellulose.

Saccharomyces cerevisiae and Kluyveromyces marxianus Cocultures Allow Reduction of Fermentable Oligo-, Di-, and Monosaccharides and Polyols Levels in Whole Wheat Bread.

Fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs) are small molecules that are poorly absorbed in the small intestine and rapidly fermented in the large intestine. There is evidence that a diet low in FODMAPs reduces abdominal symptoms in approximately 70% of the patients suffering from irritable bowel syndrome. Wheat contains relatively high fructan levels and is therefore a major source of FODMAPs in our diet. In this study, a yeast-based strategy was developed to reduce FODMAP levels in (whole wheat) bread. Fermentation of dough with an inulinase-secreting Kluyveromyces marxianus strain allowed to reduce fructan levels in the final product by more than 90%, while only 56%  reduction was achieved when a control Saccharomyces cerevisiae strain was used. To ensure sufficient CO2 production, cocultures of S. cerevisiae and K. marxianus were prepared. Bread prepared with a coculture of K. marxianus and S. cerevisiae had fructan levels ≤0.2% dm, and a loaf volume comparable with that of control bread. Therefore, this approach is suitable to effectively reduce FODMAP levels in bread.

Building a fructan LC-MS2 library and its application to reveal the fine structure of cereal grain fructans.

A liquid chromatography-mass spectrometry (LC-MS) library is presented containing the relative retention times of 28 fructan oligomers and MS2 spectra of 18 of them. It includes the main representatives of all fructan classes occurring in nature and with a degree of polymerization between three and five. This library enables a rapid and unambiguous detection of these 18 fructan structures in any type of sample without the need for fructan purification or the synthesis of fructan standards. Its wide applicability is demonstrated by the analysis of fructans in a set of cereal flour samples. Marked differences were observed in the types of fructans present in oat, barley, rye, spelt and wheat flour. A putative link between the accumulation of certain fructan types and cereal phylogeny is described.

Fat binding capacity and modulation of the gut microbiota both determine the effect of wheat bran fractions on adiposity.

The aim of this study was to determine the impact of different wheat bran fractions on the gut microbiota and fat binding capacity to explain their differential effects on metabolic and inflammatory disorders induced by a western diet (WD) in mice. Wheat bran derived arabinoxylan oligosaccharides (AXOS), a crude fraction of wheat bran (WB), or the same wheat bran with reduced particle size (WBs) were added to the WD of mice for 8 weeks. AXOS shifted the gut microbiota composition, blunted Clostridium and Turicibacter genera and strongly promoted Bifidobacterium and Butyricicoccus genera, independently of changes in gut antimicrobial peptide expression. AXOS was the most efficient to reduce adiposity. Only WB fraction promoted fat excretion and differed from the other fractions by the capacity to increase the Akkermansia genus and to counteract gut interleukin 1 beta (IL1ß) overexpression. Strikingly, WBs promoted steatosis and adipose tissue inflammation, despite its ability -like WB- to increase bacterial diversity. In conclusion, wheat bran fractions differently affect metabolic and inflammatory disorders associated with WD feeding, depending on their particle size, their fat binding capacity and their influence on the gut microbiota. Those results might be useful to take into account in nutritional advices to control obesity.

Inter-individual differences determine the outcome of wheat bran colonization by the human gut microbiome.

Gut microbiota research reveals a vital role for the luminal and mucosal gut microbiota in human health. Fewer studies, however, have characterized the microbiome associated with undigested, insoluble dietary particles in the gut. These particles can act as a food source for bacteria and offer a physical platform to which they can attach. In this study, the microbiome colonizing wheat bran particles was analyzed. In a batch experiment, wheat bran particles were separately incubated with the faecal microbiota derived from 10 donors and washed after 48 h to remove loosely attached bacteria. The response of the luminal community to wheat bran and inulin, acting as a well-characterized control, was largely donor-dependent, both functionally, and with respect to the microbiome composition. Depending on the donor, wheat bran and inulin fermentation yielded proportionally higher propionate or butyrate production. Clostridium cluster XIVa and, depending on the donor, Prevotella, Roseburia, Megamonas, Bifidobacterium and Bacteroides species were enriched on the wheat bran particles. These genera include species with the documented ability to serve as primary degraders of wheat bran components and other species depending on cross-feeding to obtain their energy. Both functional groups were present in all donors, despite the large inter-individual differences.

Substrate-Limited Saccharomyces cerevisiae Yeast Strains Allow Control of Fermentation during Bread Making.

Identification and use of yeast strains that are unable to consume one or more otherwise fermentable substrate types could allow a more controlled fermentation process with more flexibility regarding fermentation times. In this study, Saccharomyces cerevisiae strains with different capacities to consume substrates present in wheat were selected to investigate the impact of substrate limitation on dough fermentation and final bread volume. Results show that fermentation of dough with maltose-negative strains relies on the presence of fructan and sucrose as fermentable substrates and can be used for regular bread making. Levels of fructan and sucrose, endogenously present or added, hence determine the extent of fermentation and timing at the proofing stage. Whole meal is inherently more suitable for substrate-limited fermentation than white flour due to the presence of higher native levels of these substrates. Bread making protocols with long fermentation times are accommodated by addition of substrates such as sucrose.

Wheat Bran Does Not Affect Postprandial Plasma Short-Chain Fatty Acids from 13C-inulin Fermentation in Healthy Subjects.

Wheat bran (WB) is a constituent of whole grain products with beneficial effects for human health. Within the human colon, such insoluble particles may be colonized by specific microbial teams which can stimulate cross-feeding, leading to a more efficient carbohydrate fermentation and an increased butyrate production. We investigated the extent to which WB fractions with different properties affect the fermentation of other carbohydrates in the colon. Ten healthy subjects performed four test days, during which they consumed a standard breakfast supplemented with 10 g 13C-inulin. A total of 20 g of a WB fraction (unmodified WB, wheat bran with a reduced particle size (WB RPS), or de-starched pericarp-enriched wheat bran (PE WB)) was also added to the breakfast, except for one test day, which served as a control. Blood samples were collected at regular time points for 14 h, in order to measure 13C-labeled short-chain fatty acid (SCFA; acetate, propionate and butyrate) concentrations. Fermentation of 13C-inulin resulted in increased plasma SCFA for about 8 h, suggesting that a sustained increase in plasma SCFA can be achieved by administering a moderate dose of carbohydrates, three times per day. However, the addition of a single dose of a WB fraction did not further increase the 13C-SCFA concentrations in plasma, nor did it stimulate cross-feeding (Wilcoxon signed ranks test).

Bread Dough and Baker's Yeast: An Uplifting Synergy.

Yeast-mediated dough fermentation is an important phase in the bread making process. The fermentative performance of yeast cells during fermentation is of critical importance for final bread quality, since yeast cells produce CO2 and other metabolites that have an influence on dough rheology and bread texture, volume, and taste. Different factors affect the fermentative performance of yeast cells during dough fermentation, including dough ingredients, fermentation conditions, the type of yeast strain used and yeast pregrowth conditions. Bread dough is a complex matrix that contains several ingredients that can affect the fermentation rate of yeast cells. Although the individual effects of sugar availability and salt level on the leavening ability of yeast have been studied extensively, a comprehensive overview of the relationship between bread dough constituents, fermentation conditions and yeast functionality is still lacking. Moreover, the dough environment is highly variable as several types of dough like lean, sweet or frozen doughs are currently produced by commercial bread producers. For optimal fermentation rates in different types of dough, the use of appropriate yeast strains with specific phenotypic traits is required. Therefore, many researchers have focused on the improvement of yeast strains for optimal fermentation in different types of dough like lean, sweet or frozen dough. Against this background, this review summarizes the current knowledge on the interaction between bread dough and baker's yeast and how to improve this interaction, thereby providing a useful background for further research concerning the functionality of yeast in bread dough.

Establishing the relative importance of damaged starch and fructan as sources of fermentable sugars in wheat flour and whole meal bread dough fermentations.

It is generally believed that maltose drives yeast-mediated bread dough fermentation. The relative importance of fructose and glucose, released from wheat fructan and sucrose by invertase, compared to maltose is, however, not documented. This is surprising given the preference of yeast for glucose and fructose over maltose. This study revealed that, after 2h fermentation of wheat flour dough, about 44% of the sugars consumed were generated by invertase-mediated degradation of fructan, raffinose and sucrose. The other 56% were generated by amylases. In whole meal dough, 70% of the sugars consumed were released by invertase activity. Invertase-mediated sugar release seems to be crucial during the first hour of fermentation, while amylase-mediated sugar release was predominant in the later stages of fermentation, which explains why higher amylolytic activity prolonged the productive fermentation time only. These results illustrate the importance of wheat fructan and sucrose content and their degradation for dough fermentations.