Metabolism of phenolic acids in whole wheat and rye malt sourdoughs

Use of Bacillus spp. as beneficial fermentation microbes in baking

The development of minimally processed baked goods is dependent on new "clean label" functional ingredients that allow substitution of additives without compromising quality. We investigated the use of fermentation with Bacillus spp. as a novel approach to improve bread quality. Bacillus velezensis FUA2155 and Bacillus amyloliquefaciens Fad WE ferments were prepared using white wheat flour, wheat bran or buckwheat, and were added at a level of 2.5-20 % to bread dough. Ropy spoilage of bread was controlled by sourdough addition at a level of 10 or 20 %. The volume of white wheat bread and wheat bran bread increased by 47.4 and 62.5 % respectively with 2.5 % Bacillus ferments. Bread shelf-life was prolonged by the Bacillus ferment only at higher dosages that also reduced bread volume. The use of unfermented or sourdough fermented buckwheat improved bread volume and delayed mould spoilage. The characterization of water-soluble polysaccharides from sourdoughs and Bacillus ferments revealed that solubilization of arabinoxylans contributed to the increase in volume after fermentation of wheat but not after fermentation of buckwheat. In conclusion, Bacillus fermentation can be used to improve bread quality, adding to the diversity of microbes that are suitable for baking applications.

Evaluation of structure, quality, physicochemical properties, and phenolics content of pea proteins: A novel strategy through the incorporation of fermentation

The utilization of pea proteins (PPs) is limited due to their relatively low protein digestibility (∼81%) compared to animal-based proteins, such as whey. The present investigation involved the fermentation of PPs at a concentration of 1% (w/v) using 5% (w/v) water kefir for 60 h at 25°C to improve the functional properties of PPs. The results showed a significant (p < 0.05) increase in lactic acid and acetic acid production during fermentation. These findings suggest that PPs can be effectively fermented using water kefir as a starter culture for the increased protein digestibility of PPs. The PP conformation underwent modifications, including secondary and tertiary protein structure alterations. The total phenolic compounds increased throughout the fermentation, reaching around 695.32 ± 15 mg gallic acid equivalent/100 g after 24 h of fermentation. Furthermore, the fermentation process has culminated in significant (p < 0.05) changes in the surface charge and hydrophobic properties of the fermented PPs, from -38.1 to -45.73 and 362.7 to 550.2, respectively. Fermentation using water kefir is a promising technique for improving the digestibility, protein structure, and nutritional values of PPs.

The quest for the perfect loaf of sourdough bread continues: Novel developments for selection of sourdough starter cultures

Sourdough fermentation, one of the oldest unit operations in food production, is currently experiencing a revival in bread production at the household, artisanal, and the industrial level. The expanding use of sourdough fermentation in bread production and the adaptation of fermentation to large scale industrial bread production also necessitate the development of novel starter cultures. Developments in the last years also have expanded the tools that are used to assess the metabolic potential of specific strains, species or genera of the Lactobacillaceae and have identified multiple ecological and metabolic traits as clade-specific. This review aims to provide an overview on the clade-specific metabolic potential of members of the Lactobacillaceae for use in sourdough baking, and the impact of these clade-specific traits on bread quality. Emphasis is placed on carbohydrate metabolism, including the conversion of sucrose and starch to soluble polysaccharides, conversion of amino acids, and the metabolism of organic acids. The current state of knowledge to compose multi-strain starter cultures (synthetic microbial communities) that are suitable for back-slopping will also be discussed. Taken together, the communication outlines the current tools for selection of microbes for use in sourdough baking.

Gut microbial metabolites of dietary polyphenols and their potential role in human health and diseases

Polyphenols contribute as one of the largest groups of compounds among all the phytochemicals. Common sources of dietary polyphenols are vegetables, fruits, berries, cereals, whole grains, etc. Owing to their original form, they are difficult to get absorbed. Dietary polyphenols after undergoing gut microbial metabolism form bioaccessible and effective metabolites. Polyphenols and derived metabolites are all together a diversified group of compounds exhibiting pharmacological activities against cardiovascular, cancer, oxidative stress, inflammatory, and bacterial diseases. The formed metabolites are sometimes even more bioavailable and efficacious than the parent polyphenols. Studies on gut microbial metabolism of dietary polyphenols have introduced new approach for the use of polyphenol-rich food in the form of supplementary diet. This review provides insights on various aspects including classification of polyphenols, gut microbiota-mediated metabolism of polyphenols, chemistry of polyphenol metabolism, and pharmacological actions of gut microbial metabolites of polyphenols. It also suggests the use of polyphenols from marine source for the microbial metabolism studies. Till date, gut microbial metabolism of polyphenols from terrestrial sources is extensively studied as compared to marine polyphenols. Marine ecosystem is a profound but partially explored source of phytoconstituents. Among them, edible seaweeds contain high concentration of polyphenols, especially phlorotannins. Hence, microbial metabolism studies of seaweeds can unravel the pharmacological potential of marine polyphenol-derived metabolites.

Effects of Fermentation on Bioactivity and the Composition of Polyphenols Contained in Polyphenol-Rich Foods: A Review

Polyphenols, as common components with various functional activities in plants, have become a research hotspot. However, researchers have found that the bioavailability and bioactivity of plant polyphenols is generally low because they are usually in the form of tannins, anthocyanins and glycosides. Polyphenol-rich fermented foods (PFFs) are reported to have better bioavailability and bioactivity than polyphenol-rich foods, because polyphenols are used as substrates during food fermentation and are hydrolyzed into smaller phenolic compounds (such as quercetin, kaempferol, gallic acid, ellagic acid, etc.) with higher bioactivity and bioavailability by polyphenol-associated enzymes (PAEs, e.g., tannases, esterases, phenolic acid decarboxylases and glycosidases). Biotransformation pathways of different polyphenols by PAEs secreted by different microorganisms are different. Meanwhile, polyphenols could also promote the growth of beneficial bacteria during the fermentation process while inhibiting the growth of pathogenic bacteria. Therefore, during the fermentation of PFFs, there must be an interactive relationship between polyphenols and microorganisms. The present study is an integration and analysis of the interaction mechanism between PFFs and microorganisms and is systematically elaborated. The present study will provide some new insights to explore the bioavailability and bioactivity of polyphenol-rich foods and greater exploitation of the availability of functional components (such as polyphenols) in plant-derived foods.

Lychee pulp phenolics fermented by mixed lactic acid bacteria strains promote the metabolism of human gut microbiota fermentation in vitro

Lychee pulp phenolics possess excellent biological activities, however, changes in phenolic substances after microbial treatments are unknown. Herein, lychee pulp was fermented by Lactobacillus plantarum, Lactobacillus rhamnosus, and a mixed strain of the two, followed by an investigation of the products' colonic fermentation. In comparison to single-strain fermentation, mixed-strain fermentation significantly increased catechin and quercetin. In addition, lychee phenolics fermented by mixed strains were more conducive to the growth of gut microbiota. The results of HPLC-DAD showed that colonic fermentation further promoted the release of lychee phenolics. There was a notable increase in the content of gallic acid and quercetin, while multiple phenolics were degraded. Quercetin-3-O-rutinose-7-O-α-L-rhamnoside (QRR) and rutin were catabolized into quercetin by gut microbiota, and 4-hydroxybenzoic acid was produced from the metabolism of QRR and procyanidin B2. Lychee phenolics fermented by mixed lactic acid bacteria were easily metabolized and transformed by gut microbiota. These findings indicate that lychee pulp fermented by mixed lactic acid bacteria possesses probiotic potential, which is of great significance for the development of functional probiotic products.

The Genus Capsicum: A Review of Bioactive Properties of Its Polyphenolic and Capsaicinoid Composition

Chili is one of the world's most widely used horticultural products. Many dishes around the world are prepared using this fruit. The chili belongs to the genus Capsicum and is part of the Solanaceae family. This fruit has essential biomolecules such as carbohydrates, dietary fiber, proteins, and lipids. In addition, chili has other compounds that may exert some biological activity (bioactivities). Recently, many studies have demonstrated the biological activity of phenolic compounds, carotenoids, and capsaicinoids in different varieties of chili. Among all these bioactive compounds, polyphenols are one of the most studied. The main bioactivities attributed to polyphenols are antioxidant, antimicrobial, antihyperglycemic, anti-inflammatory, and antihypertensive. This review describes the data from in vivo and in vitro bioactivities attributed to polyphenols and capsaicinoids of the different chili products. Such data help formulate functional foods or food ingredients.

Conversion of hydroxycinnamic acids by Furfurilactobacillus milii in sorghum fermentations: Impact on profile of phenolic compounds in sorghum and on ecological fitness of Ff. milii

The conversion of phenolic compounds by lactobacilli in food fermentations contributes to food quality. The metabolism of phenolics by lactobacilli has been elucidated in the past years but information on the contribution of specific enzymes in food fermentations remains scarce. This study aimed to address this gap by disruption of genes coding for the hydroxycimmanic acid reductase Par1, the hydroxycinnamic acid decarboxylase Pad, the hydrocinnamic esterase EstR, and strains with disruption of all three genes in Furfurilactobacillus milii FUA3583. The conversion of phenolics by Ff. milii and its isogenic mutants in sorghum fermentations was studied by LC-UV and LC-UV-MS/MS analyses. Ff. milii FUA3583 converted hydroxycinnamic acids predominantly with Par1. Vinylphenols were detected only in mutants lacking par1. A phenotype for the estR defective mutant was not identified. The formation of pyrano-3-deoxyanthocyanidins was observed only after fermentation with strains expressing Pad. Specifically, formation of these compounds was low with Ff. milii FUA3583, substantially increased in the Par1 mutant and abolished in all mutants with disrupted pad. Competition experiments with Ff. milii FUA3583 and its isogenic mutants demonstrated that expression of one of the two metabolic pathways for hydroxycinnamic acids increases the ecological fitness of the strain. Disruption of EstR in a Δpar1Δpar2Δpad background improved ecological fitness, indirectly demonstrating a phenotype of the esterase in Ff. milii. The documentation of the functionality of genes coding for conversion of hydroxycinnamic acids may support the selection of starter cultures for improved quality of fermented cereal products.

Characterization of isogenic mutants with single or double deletions of four phenolic acid esterases in Lactiplantibacillus plantarum TMW1.460

In plants, hydroxycinnamic and hydroxybenzoic acids occur mainly as esters. This study aimed to determine the contribution of individual phenolic acid esterases in Lp. plantarum TMW1.460, which encodes for four esterases: TanA, Lp_0796, Est_1092 and a homolog of Lj0536 and Lj1228 that was termed HceP. To determine which of the phenolic acid esterases present in Lp plantarum TMW1.460 are responsible for esterase activity, mutants with deletions in lp_0796, est_1092, tanB, hceP, or hceP and est_1092 were constructed. The phenotype of wild type strain and mutants was determined with esters of hydroxycinnamic acids (chlorogenic acid and ethyl ferulate) and of hydroxybenzoic acids (methyl gallate, tannic acid and epigallocatechin-3-gallate). Lp. plantarum TMW1.460 hydrolysed chlorogenic acid, methyl ferulate and methyl gallate but not tannic acid or epigallocatechin gallate. The phenotype of mutant strains during growth in mMRS differed from the wild type as follows: Lp. plantarum TMW1.460ΔhceP did not hydrolyse esters of hydroxycinnamic acids; Lp. plantarum TMW1.460ΔtanB did not hydrolyse esters of hydroxybenzoic acids; disruption of est_1092 or Lp_0796 did not alter the phenotype. The phenotype of Lp. plantarum TMW1.460ΔΔhceP/est_1092 was identical to Lp. plantarum TMW1.460ΔhceP. The metabolism of phenolic acids during growth of the mutant strains in broccoli puree and wheat sourdough did not differ from metabolism of the wild type strain. In conclusion, esters of hydroxycinnamic and hydroxybenzoic acids each are hydrolysed by dedicated enzymes. The hydroxycinnamic acid esterase HceP is not expressed, or not active during growth of Lp. plantarum TMW1.460 in all food substrates.

Conversion of Phenolic Acids in Canola Fermentation: Impact on Antimicrobial Activity against Salmonella enterica and Campylobacter jejuni

Canola meal (CM) is commonly used in poultry feeds. CM has a high protein content but also contains high levels of antimicrobial phenolic acids. Lactic acid bacteria can alter CM phenolic composition during fermentation and influence its antimicrobial activity against pathogens. Fermented CM was analyzed for phenolic composition using tandem mass spectrometry (LC-MS/MS) and high-performance liquid chromatography (HPLC). Sinapic acid and derivatives were the major phenolic acids in CM. Growth of lactobacilli in CM was attenuated when compared to cereal substrates. Glucosides and esters of sinapic acid were extensively hydrolyzed during fermentation with Lactiplantibacillus plantarum and Furfurilactobacillus milii. Lp. plantarum transformed hydroxycinnamic acids to dihydro, 4-vinyl, and 4-ethyl derivatives, Ff. milii reduced hydroxycinnamic acids to dihydroderivatives, but Limosilactobacillus reuteri did not convert hydroxycinnamic acids. The minimum inhibitory concentration of phenolic extracts was assessed with lactobacilli, Salmonella, and Campylobacter jejuni as indicator strains. Fermentation of CM with Lp. plantarum or Ff. milii increased the antimicrobial activity of phenolic extracts against Salmonella enterica and Campylobacter jejuni. Fermentation with Lm. reuteri TMW1.656 but not fermentation with Lm. reuteri TMW1.656ΔrtcN increased the antimicrobial activity of extracts owing to the production of reutericyclin. This study demonstrates that fermentation of CM with lactobacilli converts hydroxycinammic esters and may increase the antimicrobial activity of phenolic compounds in CM against pathogens.

Conversion of (poly)phenolic compounds in food fermentations by lactic acid bacteria: Novel insights into metabolic pathways and functional metabolites

Lactobacillaceae are among the major fermentation organisms in most food fermentations but the metabolic pathways for conversion of (poly)phenolic compounds by lactobacilli have been elucidated only in the past two decades. Hydroxycinnamic and hydroxybenzoic acids are metabolized by separate enzymes which include multiple esterases, decarboxylases and hydroxycinnamic acid reductases. Glycosides of phenolic compounds including flavonoids are metabolized by glycosidases, some of which are dedicated to glycosides of plant phytochemicals rather than oligosaccharides. Metabolism of phenolic compounds in food fermentations often differs from metabolism in vitro, likely reflecting the diversity of phenolic compounds and the unknown stimuli that induce expression of metabolic genes. Current knowledge will facilitate fermentation strategies to achieve improved food quality by targeted conversion of phenolic compounds.

Toward Sourdough Microbiome Data: A Review of Science and Patents

Technological prospecting was performed on documents related to sourdough microbiota using SCOPUS, Web of Science, Google Scholar, Espacenet and Patent Inspiration databases. Scientific articles and patents were analyzed based on three different perspectives: macro (year of publication, country, and institutions), meso (categorization as different taxonomies according to the subject evaluated), and micro (in-depth analysis of the main taxonomies, gathering the documents in subcategories). The main subject addressed in patents was the starter and product preparation, while 58.8% of the scientific publications focused on sourdough starter microbiota (identification and selection of microorganisms). Most patents were granted to companies (45.9%), followed by independent inventors (26.4%) and universities (21.8%). Sourdough products are in the spotlight when the subject is the bakery market; however, a closer integration between academia and industry is needed. Such a collaboration could generate a positive impact on the sourdough market in terms of innovation, providing a bread with a better nutritional and sensory quality for all consumers. Moreover, sourdough creates a new magnitude of flavor and texture in gastronomy, providing new functional products or increasing the quality of traditional ones.

Metabolite Pattern Derived from Lactiplantibacillus plantarum-Fermented Rye Foods and In Vitro Gut Fermentation Synergistically Inhibits Bacterial Growth

SCOPE

Fermentation improves many food characteristics using microbes, such as lactic acid bacteria (LAB). Recent studies suggest fermentation may also enhance the health properties, but mechanistic evidence is lacking. The study aims to identify a metabolite pattern reproducibly produced during sourdough and in vitro colonic fermentation of various whole-grain rye products and how it affects the growth of bacterial species of potential importance to health and disease.

METHODS AND RESULTS

The study uses Lactiplantibacillus plantarum DSMZ 13890 strain, previously shown to favor rye as its substrate. Using LC-MS metabolomics, the study finds seven microbial metabolites commonly produced during the fermentations, including dihydroferulic acid, dihydrocaffeic acid, and five amino acid metabolites, and stronger inhibition is achieved when exposing the bacteria to a mixture of the metabolites in vitro compared to individual compound exposures.

CONCLUSION

The study suggests that metabolites produced by LAB may synergistically modulate the local microbial ecology, such as in the gut. This could provide new hypotheses on how fermented foods influence human health via diet-microbiota interactions.

Effect of Tomato Pomace Addition on Chemical, Technological, Nutritional, and Sensorial Properties of Cream Crackers

The aim of this research was to determine the influence of tomato pomace (TP) addition on the chemical, nutritional, and technological characteristics of cream crackers made from wheat flour and 4%, 6%, 8%, and 10% TP. The TP-enriched cream crackers showed progressively increasing ash (from 0.69 of the control to 1.22 g/100 g dry matter of the 10% TP sample), fat (from 11.39 to 13.04 g/100 g), protein (from 13.53 to 15.60 g/100 g), total dietary fibre (from 4.08 to 7.80), carotenoids (from 0.55 to 8.56 mg/kg), tocols (from 57.59 to 71.63 mg/kg), free phenolic acids (from 100.08 to 277.37 mg/kg), free flavonoids (from 0.0 to 45.28 mg/kg), bound flavonoids (from 0.0 to 27.71 mg/kg), and fatty acids contents, antioxidant activity and dough viscosity. The colour coordinates increased via augmenting the amounts of TP. Thickness, volume, and specific volume decreased gradually with increasing TP; the enrichment reduced cracker hardness from 65.42 N (control) to 26.28 N (crackers with 10% TP), while the snapping force rose. Cream crackers with 8% TP showed the best sensory quality. Tomato pomace addition improves the nutritional quality of foods; furthermore, its recycling will help to solve the problems linked to the disposal of this industry waste.

Performance of Thermoplastic Extrusion, Germination, Fermentation, and Hydrolysis Techniques on Phenolic Compounds in Cereals and Pseudocereals

Bioactive compounds, such as phenolic compounds, are phytochemicals found in significant amounts in cereals and pseudocereals and are usually evaluated by spectrophotometric (UV-VIS), HPLC, and LC-MS techniques. However, their bioavailability in grains is quite limited. This restriction on bioavailability and bioaccessibility occurs because they are in conjugated polymeric forms. Additionally, they can be linked through chemical esterification and etherification to macro components. Techniques such as thermoplastic extrusion, germination, fermentation, and hydrolysis have been widely studied to release phenolic compounds in favor of their bioavailability and bioaccessibility, minimizing the loss of these thermosensitive components during processing. The increased availability of phenolic compounds increases the antioxidant capacity and favor their documented health promoting.

Furfurilactobacillus milii sp. nov., isolated from fermented cereal foods

Genomic characterization of Furfurilactobacillus rossiae revealed that strains which were previously identified as F. rossiae are genetically heterogeneous. The 16S rRNA gene sequences of strains FUA3430, FUA3583, C5, FUA3115 and FUA3119, were 99.6 % identical to F. rossiae but the core genome analysis revealed that these strains share less than 93 % average nucleotide identity (ANI) with the F. rossiae type strain DSM 15814T. Because the ANI value is below the threshold for delineation of bacterial species, we propose the novel species Furfurilactobacillus milii sp. nov. with the type strain FUA3430T (=DSM 113338T=LMG 32478T). Strains of F. milii have smaller genomes than F. rossiae , lack the pdu-cbi-cob-hem cluster which is responsible for 1,2-propanediol utilization in F. rossiae , and lack genes involved in ethanolamine utilization. Two strains of the novel species (FUA3430T and FUA3583) were compared to F. rossiae FUA3214. Analysis of the cellular fatty acid composition and metabolite analysis did not reveal significant differences between F. milii sp. nov. and F. rossiae FUA3124. Although the growth requirements with respect to temperature and pH were very similar, only the strain of F. rossiae utilized melibiose and d-xylose. Morphological differences were also seen in the colony and cell size of the novel compared to F. rossiae .

A comprehensive review of wheat phytochemicals: From farm to fork and beyond

The health benefits of whole wheat consumption can be partially attributed to wheat's phytochemicals, including phenolic acids, flavonoids, alkylresorcinols, carotenoids, phytosterols, tocopherols, and tocotrienols. It is of increasing interest to produce whole wheat products that are rich in bioactive phytochemicals. This review provides the fundamentals of the chemistry, extraction, and occurrence of wheat phytochemicals and includes critical discussion of several long-lasting issues: (1) the commonly used nomenclature on distribution of wheat phenolic acids, namely, soluble-free, soluble-conjugated, and insoluble-bound phenolic acids; (2) different extraction protocols for wheat phytochemicals; and (3) the chemistry and application of in vitro antioxidant assays. This review further discusses recent advances on the effects of genotypes, environments, field management, and processing techniques including ultrafine grinding, germination, fermentation, enzymatic treatments, thermal treatments, and food processing. These results need to be interpreted with care due to varied sample preparation protocols and limitations of in vitro assays. The bioaccessibility, bioavailability, metabolism, and potential health benefits of wheat phytochemicals are also reviewed. This comprehensive and critical review will benefit scientific researchers in the field of bioactive compounds of cereal grains and also those in the cereal food industry to produce high-quality functional foods.

Potential Health Benefits of Whole Grains: Modulation of Mitochondrial Biogenesis and Energy Metabolism

Mitochondria play an essential role in maintaining cellular metabolic homeostasis. However, its dysfunction will cause different pathophysiological consequences. A specific mechanism of action has been developed by cells to adapt to changes in physiological conditions or in response to different stimuli, by meditating mitochondrial number, structure, and energy metabolism. Whole grains are considered healthier than refined grains for their higher amounts of bioactive components, with proven multiple health benefits. The modulation of an appropriate mitochondrial function contributes to the bioactive-component-based health improvements. Thus, this review aims to represent current studies that identify the impact of natural bioactive components in whole grains against metabolic disorders by modulating mitochondrial biogenesis and energy metabolism. It seems most attractive to aim nutritional intervention at the prevention or treatment of metabolic abnormalities and hence to target dietary management at improvement of mitochondrial function.

Antimicrobial plant secondary metabolites, MDR transporters and antimicrobial resistance in cereal-associated lactobacilli: is there a connection?

Cereal-associated lactobacilli resist antimicrobial plant secondary metabolites. This study aimed to identify multi-drug-resistance (MDR) transporters in isolates from mahewu, a Zimbabwean fermented cereal beverage, and to determine whether these MDR-transporters relate to resistance against phenolic compounds and antibiotics. Comparative genomic analyses indicated that all seven mahewu isolates harbored multiple MATE and MFS MDR proteins. Strains of Lactiplantibacillus plantarum and Limosilactobacillus fermentum encoded for the same gene, termed mahewu phenolics resistance gene mprA, with more than 99% nucleotide identity, suggesting horizontal gene transfer. Strains of Lp. plantarum were more resistant than strains of Lm. fermentum to phenolic acids, other antimicrobials and antibiotics but the origins of strains were not related to resistance. The resistance of several strains exceeded EFSA thresholds for several antibiotics. Analysis of gene expression in one strain each of Lp. plantarum and Lm. fermentum revealed that at least one MDR gene in each strain was over-expressed during growth in wheat, sorghum and millet relative to growth in MRS5 broth. In addition, both strains over-expressed a phenolic acid reductase. The results suggest that diverse lactobacilli in mahewu share MDR transporters acquired by lateral gene transfer, and that these transporters mediate resistance to secondary plant metabolites and antibiotics.

Sourdough production: fermentation strategies, microbial ecology, and use of non-flour ingredients

Sourdough production is an ancient method to ferment flour from cereals for the manufacturing of baked goods. This review deals with the state-of-the-art of current fermentation strategies for sourdough production and the microbial ecology of mature sourdoughs, with a particular focus on the use of non-flour ingredients. Flour fermentation processes for sourdough production are typically carried out by heterogeneous communities of lactic acid bacteria and yeasts. Acetic acid bacteria may also occur, although their presence and role in sourdough production can be criticized. Based on the inoculum used, sourdough productions can be distinguished in fermentation processes using backslopping procedures, originating from a spontaneously fermented flour-water mixture (Type 1), starter culture-initiated fermentation processes (Type 2), and starter culture-initiated fermentation processes that are followed by backslopping (Type 3). In traditional recipes for the initiation and/or propagation of Type 1 sourdough productions, non-flour ingredients are often added to the flour-water mixture. These ingredients may be the source of an additional microbial inoculum and/or serve as (co-)substrates for fermentation. An example of the former is the addition of yoghurt; an example of the latter is the use of fruit juices. The survival of microorganisms transferred from the ingredients to the fermenting flour-water mixture depends on the competitiveness toward particular strains of the microbial species present under the harsh conditions of the sourdough ecosystem. Their survival and growth is also determined by the presence of the appropriate substrates, whether or not carried over by the ingredients added.

Improving Phenolic-Linked Antioxidant, Antihyperglycemic and Antibacterial Properties of Emmer and Conventional Wheat Using Beneficial Lactic Acid Bacteria

Beneficial lactic acid bacteria (LAB)-based fermentation is an effective bioprocessing approach to improve human-health-targeted functional benefits of plant-based food substrates, such as cereal grains. Previously, we observed high phenolic bioactive-linked antioxidant and anti-hyperglycemic properties in whole grain Emmer (hulled). In this study, beneficial LAB (Lactiplantibacillus plantarum) was recruited to ferment (0–72 h) aqueous extracts (0.4 g/mL concentration) of previously optimized hulled Emmer wheat and conventional red spring wheat cv. Barlow. The fermented and unfermented (control) wheat extracts were analyzed for phenolic content, phenolic profile, antioxidant activity, and antihyperglycemic properties (α-amylase and α-glucosidase enzyme inhibitory activity) using in vitro assay models. Additionally, antimicrobial activity against pathogenic bacteria Helicobacter pylori, and potential prebiotic activity supporting the growth of beneficial Bifidobacterium longum were also investigated. Improvement in antioxidant activity and antihyperglycemic functional benefits were observed, while soluble phenolic content remained high after 72 h fermentation. Antimicrobial activity against H. pylori was also observed in 48 and 72 h fermented wheat extracts. This study provides an insight into the efficacy of LAB-based fermentation as a safe bioprocessing tool to design health-targeted functional foods and ingredients from underutilized whole grains like Emmer for targeting type 2 diabetes dietary benefits.

Liberation of insoluble-bound phenolics from lentil hull matrices as affected by Rhizopus oryzae fermentation: Alteration in phenolic profiles and their inhibitory capacities against low-density lipoprotein (LDL) and DNA oxidation

Fermentation is an effective non-thermal food processing operation used for enhancing the nutritional and functional properties of food. HPLC-ESI-MS/MS analysis and inhibitory capacity of the soluble- and insoluble-bound phenolics in lentil hulls in retarding the oxidation of LDL and DNA strand scission were determined following fermentation. In HPLC-ESI-MS/MS analysis, most insoluble-bound phenolics in lentil hulls were significantly decreased, indicating their liberation from the cell wall matrix upon fermentation. However, the released insoluble-bound phenolics did not show an efficient conversion into the bioavailable soluble phenolics as reflected in the inhibitory capacity against oxidation of LDL and DNA strands. The low efficiency in bioconversion from insoluble-bound to soluble phenolics might be due to the loss of the released bound phenolics during the fermentation process. Following the alterations of individual insoluble-bound phenolics in legumes upon fermentation in this work may fill the existing gap in the related areas.

Changes in extractable phenolic profile during natural fermentation of wheat, sorghum and teff

Whole grain polyphenols are associated with structure-specific bioactive properties. However, the phenolic profile of grain ingredients can be significantly altered by processes like fermentation. This study investigated how polyphenol profiles in different cereal grains respond to microbial metabolism during sourdough fermentation. Whole grain wheat (white and red), sorghum (white and lemon-yellow), and teff (white and brown) flours were subjected to natural sourdough fermentation for 48-96 h, and phenolic profiles and their metabolites monitored using UPLC-tandem quadrupole MS. Flavonoid O-glycosides (dominant in sorghum) were rapidly metabolized (66% reduction in 48 h) to release aglycones (2.5 fold increase). O-Glycoside groups in mixed O/C-glycosides (dominant in teff) were selectively hydrolyzed, but more slowly (11-32% reduction in 48 h) than homo-O-glycosides, suggesting steric hindrance from the C-glycoside groups. Flavonoid C-glycosides (dominant in wheat) and aglycones (white sorghum) were generally stable to microbial degradation. Extractable phenolic acids and their esters (most abundant in white sorghum) were extensively degraded (80% reduction in 48 h) with few metabolites detected at the end of fermentation. Thus, extractable phenolics in sorghum were generally most extensively metabolized, whereas those in wheat were the least impacted by sourdough fermentation. New microbial metabolites, putatively identified as O-methylcatechol-vinyl-isoflavans, were detected in all fermented samples, with levels increasing with fermentation time. Based on structure, these compounds were likely derived from cell wall C-C linked diferulic acid metabolism. As expected, Folin reactive phenols and antioxidant capacity increased in fermented samples, but the extent was distinctly smaller in sorghums (1.3-1.9 fold) vs teff (2.4-3.2 fold) and wheat (2.0-6.1 fold), likely due to higher presence of easily metabolizable phenolics in sorghum. The phenolic profile of a cereal grain affects the products of microbial metabolism during fermentation, and may thus alter phenolic-dependent bioactive properties associated with a specific grain.

Sourdough improves the quality of whole-wheat flour products: Mechanisms and challenges-A review

Increasing the intake of whole-wheat flour (WWF) products is one of the methods to promote health. Sourdough fermentation is increasingly being used in improving the quality of WWF products. This review aims to analyze the effect of sourdough fermentation on WWF products. The effects of sourdough on bran particles, starch, and gluten, as well as the rheology, antinutritional factors, and flavor components in WWF dough/products are comprehensively reviewed. Meanwhile, sourdough fermentation technology has a promising future in reducing anti-nutritional factors and toxic and harmful substances in WFF products. Finally, researchers are encouraged to focus on the efficient strain screening and metabolic pathway control of sourdough for WWF products, as well as the use of bran pre-fermentation and integrated biotechnology to improve the quality of whole-wheat products. This review provides a comprehensive understanding of the effect of sourdough fermentation technology on wholemeal products to promote WWF production.

Progress in pretreatment and analysis of organic Acids: An update since 2010

Organic acids, as an important component of food, have great influence on the flavor, texture, freshness of food. By lowering the pH of food to bacteriostatic acidity, organic acids are also used as additives and preservatives. Because organic acids are crucial to predict and evaluate food maturity, production and quality control, the rapid and sensitive determination methods of organic acids are necessary. This review aims to summarize and update the progress of the determination of organic acids in food samples. Pretreatment methods include simple steps (e.g., "dilute and shoot," protein precipitation, filtration, and centrifugation) and advanced microextraction methods (e.g., hollow fiber liquid phase microextraction, stir bar sorptive extraction and dispersive micro-solid phase extraction). Advances in novel materials (nanomaterial), solvents (ionic liquids and supercritical fluids) and hybrid methods are clearly displayed in detail. Continuous progress which has been made in electrochemical method, two-dimensional chromatography, high resolution mass is thoroughly illustrated.

Fermentation transforms the phenolic profiles and bioactivities of plant-based foods

Phenolics are a group of compounds derived from plants that have displayed potent biological activities and health-promoting effects. Fermentation is one of the most conventional but still prevalent bioprocessing methods in the food industry, with the potential to increase phenolic content and enhance its nutritive value. This review details the biotransformation of different classes of phenolics (hydroxycinnamic and hydroxybenzoic acids, flavonoids, tannins, stilbenoids, lignans, alkylresorcinols) by various microorganisms (lactic acid bacteria, yeast, filamentous fungi) throughout the fermentation process in plant-based foods. Several researchers have commenced the use of metabolic engineering, as in recombinant Saccharomyces cerevisiae yeast and Escherichia coli, to enhance the production of this transformation. The impact of phenolics on the metabolism of microorganisms and fermentation process, although complex, is reviewed for the first time. Moreover, this paper highlights the general effect of fermentation on the food's phenolic content, and its bioaccessibility, bioavailability and bioactivities including antioxidant capacity, anti-cancer, anti-diabetic, anti-inflammation, anti-obesity properties. Phenolics of different classes are converted into compounds that are often more bioactive than the parent compounds, and fermentation generally leads to a higher phenolic content and antioxidant activity in most studies. However, biotransformation of several phenolic classes is less studied due to its low concentration and apparent insignificance to the food system. Therefore, there is potential for application of metabolic engineering to further enhance the content of different phenolic classes and bioactivities in food.

Ferulic acid content variation from wheat to bread

The health-promoting effects of whole-grain consumption have been attributed in a large part to the phytochemical profile of the wheat grain, and particularly to the bioactive molecules present in bran. This study shed light on the impact of human practices, especially harvesting sites (terroirs) and wheat species and varieties, as well as bread-making conditions on the variation of the antioxidant and antimicrobial ferulic acid (FA) content. FA concentration in the bran of wheat species (durum and bread wheat) and varieties (Chevalier, Renan, Redon, Saint Priest le vernois rouge, Bladette de Provence, Pireneo, Rouge de Bordeaux, LA1823, Claudio et Bidi17) harvested in five sites in France on 2015 and 2017, has been evaluated. Statistical analysis showed significant differences in FA content for wheat varieties and terroirs. During bread making, baking and type of leaven impacted the FA content of dough and bread. The differences were not due to the type of fermentation (sourdough/commercial yeast) but rather to the diversity of fermenting microbial strains and flour used for backslopping.

Sourdough yeast-bacteria interactions can change ferulic acid metabolism during fermentation

The metabolism of ferulic acid (FA) was studied during fermentation with different species and strains of lactic acid bacteria (LAB) and yeasts, in synthetic sourdough medium. Yeast strains of Kazachstania humilis, Kazachstania bulderi, and Saccharomyces cerevisiae, as well as lactic acid bacteria strains of Fructilactobacillus sanfranciscensis, Lactiplantibacillus plantarum, Lactiplantibacillus xiangfangensis, Levilactobacillus hammesii, Latilactobacillus curvatus and Latilactobacillus sakei were selected from French natural sourdoughs. Fermentation in presence or absence of FA was carried out in LAB and yeasts monocultures, as well as in LAB/yeast co-cultures. Our results indicated that FA was mainly metabolized into 4-vinylguaiacol (4-VG) by S. cerevisiae strains, and into dihydroferulic acid (DHFA) and 4-VG in the case of LAB. Interactions of LAB and yeasts led to the modification of FA metabolism, with a major formation of DHFA, even by the strains that do not produce it in monoculture. Interestingly, FA was almost completely consumed by the F. sanfranciscensis bFs17 and K. humilis yKh17 pair and converted into DHFA in 89.5 ± 19.6% yield, while neither bFs17, nor yKh17 strains assimilated FA in monoculture.

4-Vinylguaiacol, an Active Metabolite of Ferulic Acid by Enteric Microbiota and Probiotics, Possesses Significant Activities against Drug-Resistant Human Colorectal Cancer Cells

Ferulic acid, a hydroxycinnamic acid, is abundant in vegetables, grains, and medicinal plants. Emerging evidence suggests that ferulic acid may exert beneficial effects against colorectal cancer. However, the anticancer activity of ferulic acid is relatively low, and its metabolism after oral administration is largely unknown. In this study, mimicking the enteric environment, human intestinal microflora and commercial probiotics were used to metabolize ferulic acid to its metabolites, and their anticancer activities were evaluated. Ferulic acid can be biotransformed to 4-vinylguaiacol (2-methoxy-4-vinylphenol), and the contents of ferulic acid and 4-vinylguaiacol in bio-transformed extracts were determined by high-performance liquid chromatography (HPLC). Using the chemotherapy-sensitive cell line HCT-116 and the chemo-resistant cell line HT-29, the cell proliferation was determined by the modified trichrome stain assay. The cell cycle and induction of apoptosis were assayed using flow cytometry. HPLC data showed that there was a marked transformation from ferulic acid to 4-vinylguaiacol, and the conversion rates of intestinal microflora and four probiotics were from 1.3 to 36.8%. Both ferulic acid and 4-vinylguaiacol possessed dose- and time-related anticancer activities on the two cell lines, while 4-vinylguaiacol showed more potent effects than ferulic acid. Interestingly, 4-vinylguaiacol exhibited significantly higher antiproliferative effects on the HT-29 cell line than that on HCT-116. The IC50 of the metabolite 4-vinylguaiacol on HT-29 cells was 350 μM, 3.7-fold higher than its parent compound. The potential of cancer cell growth inhibition of 4-vinylguaiacol was mediated by cell cycle arrest at the G1 phase and induction of apoptosis. Data from this study indicate that the oral administration of ferulic acid offers a promising approach to increase its anticancer activity through gut microbial conversion to 4-vinylguaiacol, and the biotransformation could also be achieved by selected commercial probiotics. 4-Vinylguaiacol is a potential anticancer metabolite from ferulic acid for chemotherapy-resistant colon cancer cells.

The combined effect of fermentation of lactic acid bacteria and in vitro digestion on metabolomic and oligosaccharide profile of oat beverage

Oat (Avena sativa L.) is widely appreciated for its beneficial properties for human health, which have led to the introduction of more food products on the market, including oat beverages. The fibre components found in the oat are recognized for their beneficial effects, despite other bioactive compounds with healthy properties being present. This work aimed to evaluate the metabolites profile of a commercial oat beverage, either fermented with lactic bacteria or not, following in vitro gastro-intestinal digestion. UHPLC-QTOF untargeted metabolomics allowed investigation of the bioaccessibility of health-related metabolites from the oat beverage at the intestinal level. The results identified flavonoids, phenolic acids (avenanthramides), amino acids and steroids as the major classes of compounds. In particular, after in vitro digestion, amino acids, peptides, and phenolic acids showed the highest increases. The co-fermentation of oat milk by Lactobacillus spp. and Bifidobacterium spp. strains decreased the levels of both lignans and phytic acid, while increased the levels of some polyphenols like avenanthramides. Furthermore, fermentation by microorganisms increased the bioaccessibility of specific amino acids, vitamins, and polyphenols (flavonoids and phenolic acids). Interestingly, despite lacking a significant part of beta-glucans, the HPAEC-PAD profiling of our oat beverage evidenced that the fermentation process did not alter the oligosaccharides profile, thus preserving its prebiotic potential. The phytochemical profile of oat milk was shown to have a functional potential. Nonetheless, the fermentation by bacterial strains changed the profile of metabolites during in vitro digestion, thus offering an interesting option in the future development of cereal-based beverages.

Optimization of Plant Extract Purification Procedure for Rapid Screening Analysis of Sixteen Phenolics by Liquid Chromatography

A solid-phase extraction (SPE) procedure was developed for simultaneous monitoring of sixteen different phenolics of various polarity, quantified by high-performance liquid chromatography (HPLC). The procedure allowed screening the accumulation of intermediates in different metabolic pathways that play a crucial role in plant physiology and/or are beneficial for human health. Metabolites mostly involved in phenylpropanoid, shikimate, and polyketide pathways comprise chlorogenic acid, gentisic acid, vanillic acid, caffeic acid, protocatechuic acid, ferulic acid, rutin, quercetin, epicatechin, gallic acid, sinapic acid, p-coumaric acid, o-coumaric acid, vanillin; two rarely quantified metabolites, 2,5-dimethoxybenzoic acid and 4-methoxycinnamic acid, were included as well. The procedure offered low cost, good overall efficiency, and applicability in laboratories with standard laboratory equipment. SPE recoveries were up to 99.8% at various concentration levels. The method allowed for routine analysis of compounds with a wide range of polarity within a single run, while its applicability was demonstrated for various model plant species (tobacco, wheat, and soybean), as well as different tissue types (shoots and roots).

Buckwheat Secondary Metabolites: Potential Antifungal Agents

Research groups have put significant emphasis on the evaluation of nutritional, health-promoting, and other biological activities of secondary metabolites from buckwheat. Among these phytochemicals, phenolic and lipophilic antioxidants, particularly, phenolic acids, flavonoids, and tocopherols, have been the focus of the latest studies since antioxidant activity has recently been associated with the possibility of inhibiting fungal growth and mycotoxin biosynthesis. The mycotoxin contamination of cereal and pseudocereal grains caused primarily by Fusarium, Penicillium, and Aspergillus species poses a significant hazard to human health. Therefore, efforts to examine the involvement of plant antioxidants in the biosynthesis of mycotoxins at the transcriptional level have emerged. In addition, hydrophobic interactions of buckwheat phenolics with cell membranes could also explain their capacity to reduce fungal development. Eventually, possibilities of enhancing the biological activity of cereal and pseudocereal phytochemicals have been studied, and sourdough fermentation has been proposed as an efficient method to increase antioxidant activities. This effect could result in an increased antifungal effects of sourdough and bakery products. This review reports the main advances in research on buckwheat phenolics and other antioxidant phytochemicals, highlighting possible mechanisms of action and processes that could improve their biological activities.

Persistence and Effect of a Multistrain Starter Culture on Antioxidant and Rheological Properties of Novel Wheat Sourdoughs and Bread

Food consumers make decisions primarily on the basis of a product's nutritional, functional, and sensorial aspects. In this context, this study evaluated the persistence in sourdough of a multistrain starter culture from laboratory to bakery plant production and the effect of the starter on antioxidant and rheological properties of sourdoughs and derived bread. Lactobacillus sanfranciscensis B450, Leuconostoc citreum B435, and Candida milleri L999 were used as a multispecies starter culture to produce a sourdough subsequently used to modify two traditional sourdoughs to make novel bread with improved health and rheological properties. Both these novel bakery sourdoughs showed the persistence of L. sanfranciscensis B450 and C. milleri L999, and showed a significantly different lactic acid bacteria (LAB) concentration from the traditional sourdoughs. The novel sourdough PF7 M had a higher phenolic content (170% increase) and DPPH (8% increase) than the traditional bakery sourdough PF7 F. The novel sourdough PF9 M exhibited an improvement in textural parameters. Further research would be useful on the bioavailability of bio-active compounds to obtain bread with improved characteristics.

Commercial Saccharomyces cerevisiae as a starter culture in "Wanergao": A traditional fermented food in China

To explore the effect of commercial Saccharomyces cerevisiae on the quality of traditional "Wanergao" for reasonable consuming guidance, the dominant microbes, physicochemical property, free amino acid content, texture, and sensory properties during fermentation of "Wanergao" were illustrated in this paper. Compared with the samples in the control group, "Wanergao" samples in the two groups that were subjected to S. cerevisiae inoculation had weaker acidity (the pH values dropped from 4.39 ± 0.08 to 4.36 ± 0.07 and 4.36 ± 0.07 within 2 h during fermentation), higher fermenting rate (volume increased from 100 ± 1.31 to 305 ± 4.61 and 316 ± 4.93 mL separately within 3 h), and the dominant lactic acid bacteria and yeast being leukonid and S. cerevisiae. More amylose, ethanol, and free amino acid were detected in "Wanergao" produced with S. cerevisiae inoculation compared with "Wanergao" produced by sourdough. The two kinds of "Wanergao" presented various hardness (2318 ± 112, 2279 ± 103), springiness (0.76 ± 0.03, 0.71 ± 0.03), chewiness (1.43 ± 0.05, 1.41 ± 0.06), and cohesiveness (0.68 ± 0.03, 0.62 ± 0.03) after fermentation. The result of sensory analysis revealed that "Wanergao" in the S. cerevisiae group had higher elasticity, aroma, and restoring force. The experiment demonstrated that "Wanergao" produced by using S. cerevisiae is a kind of fermented rice product with rich fragrance, high amount of nutrients, and strong elasticity.

Prolonging the Shelf Life of Cherry Tomatoes by Pullulan Coating with Ethanol Extract of Propolis During Refrigerated Storage

Cherry tomatoes are one of the most popular tomato varieties known for their bioactive compounds and sensory properties. One way to reduce the contamination of tomato is to coat them with natural or antimicrobial substances. In this study, an ethanolic extract of propolis (EEP) was obtained, and its chemical composition was analyzed using high-performance liquid chromatography with diode array detector (HPLC-DAD), and minimum inhibitory concentration (MIC) and the minimum bactericidal/fungicidal concentration (MBC/MFC) were determined using the serial microdilution method. The antimicrobial activity of 5 and 10% EEP and pullulan films containing EEP (5 and 10%) against Listeria monocytogenes, Salmonella Typhimurium, Escherichia coli O157, Penicillium chrysogenum, Fusarium solani, and Botrytis cinerea were compared. The influence of a pullulan coating containing EEP (5 and 10%) on reducing the number of bacteria and molds, physicochemical properties (weight loss (WL), total soluble solids (TSS), titratable acidity (TA), maturity index, pH, and color), and sensory properties (color and brightness of skin, aroma, flavor, overall quality, and general preference) of cherry tomatoes during refrigerated storage was evaluated. Pullulan films with EEP inhibited the growth of microorganisms on cherry tomatoes. These coatings did not affect the TSS and pH values of tomatoes, but a slight decrease in TA and WL was observed. Cherry tomatoes coated with pullulan coatings containing EEP did not show any adverse changes in their sensory properties. It was found that the addition of EEP to the pullulan coatings enriched them with antimicrobial properties and enhanced their action while reducing the WL and maturation time of cherry tomatoes.

Monitoring Hydroxycinnamic Acid Decarboxylation by Lactic Acid Bacteria Using High-Throughput UV-Vis Spectroscopy

Hydroxycinnamic acid (HCA) decarboxylation by lactic acid bacteria (LAB) results in the production of 4-vinylplenols with great impact on the sensorial characteristics of foods. The determination of LAB decarboxylating capabilities is key for optimal strain selection for food production. The activity of LAB strains from the Ohio State University-Parker Endowed Chair (OSU-PECh) collection potentially capable of synthesizing phenolic acid decarboxylase was evaluated after incubation with HCAs for 36 h at 32 °C. A high-throughput method for monitoring HCAs decarboxylation was developed based on hypsochromic shifts at pH 1.0. Out of 22 strains evaluated, only Enterococcus mundtii, Lactobacillus plantarum and Pediococcus pentosaceus were capable of decarboxylating all p-coumaric, caffeic and ferulic acids. Other strains only decarboxylated p-coumaric and caffeic acid (6), only p-coumaric acid (2) or only caffeic acid (1), while 10 strains did not decarboxylate any HCA. p-Coumaric acid had the highest conversion efficiency, followed by caffeic acid and lastly ferulic acid. Results were confirmed by HPLC-DAD-ESI-MS analyses, showing the conversion of HCAs into their 4-vinylphenol derivatives. This work can help improve the sensory characteristics of HCA-rich foods where fermentation with LAB was used during processing.

(Poly)phenolic Content and Profile and Antioxidant Capacity of Whole-Grain Cookies are Better Estimated by Simulated Digestion than Chemical Extraction

It is widely recognized that the biological effects of phytochemicals cannot be attributed to the native compounds present in foods but rather to their metabolites endogenously released after intake. Bioavailability depends on bioaccessibility, which is the amount of the food constituent that is released from the matrix in the gastrointestinal tract. The use of chemical extraction to evaluate the content and profile of phytochemicals does not mirror the physiological situation in vivo, and their bioaccessibility should be considered while assessing their nutritional significance in human health. The current study was designed to compare the (poly)phenolic profile and content and antioxidant capacity of whole-grain (WG) cookies using chemical extraction and a more physiological approach based on simulated digestion. Three types of organic WG cookies (made with durum, Italian khorasan, or KAMUT^® khorasan wheat) were considered, either fermented by Saccharomyces Cerevisiae or sourdough. Although the flour type and the fermentation process influenced the release of phytochemicals from the cookie matrix, in almost all samples, the simulated digestion appeared the most efficient procedure. Our results indicate that the use of chemical extraction for evaluation of the phytochemicals content and antioxidant capacity of food could lead to underestimation and underline the need for more physiological extraction methods.

A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae

The genus Lactobacillus comprises 261 species (at March 2020) that are extremely diverse at phenotypic, ecological and genotypic levels. This study evaluated the taxonomy of Lactobacillaceae and Leuconostocaceae on the basis of whole genome sequences. Parameters that were evaluated included core genome phylogeny, (conserved) pairwise average amino acid identity, clade-specific signature genes, physiological criteria and the ecology of the organisms. Based on this polyphasic approach, we propose reclassification of the genus Lactobacillus into 25 genera including the emended genus Lactobacillus, which includes host-adapted organisms that have been referred to as the Lactobacillus delbrueckii group, Paralactobacillus and 23 novel genera for which the names Holzapfelia, Amylolactobacillus, Bombilactobacillus, Companilactobacillus, Lapidilactobacillus, Agrilactobacillus, Schleiferilactobacillus, Loigolactobacilus, Lacticaseibacillus, Latilactobacillus, Dellaglioa, Liquorilactobacillus, Ligilactobacillus, Lactiplantibacillus, Furfurilactobacillus, Paucilactobacillus, Limosilactobacillus, Fructilactobacillus, Acetilactobacillus, Apilactobacillus, Levilactobacillus, Secundilactobacillus and Lentilactobacillus are proposed. We also propose to emend the description of the family Lactobacillaceae to include all genera that were previously included in families Lactobacillaceae and Leuconostocaceae. The generic term 'lactobacilli' will remain useful to designate all organisms that were classified as Lactobacillaceae until 2020. This reclassification reflects the phylogenetic position of the micro-organisms, and groups lactobacilli into robust clades with shared ecological and metabolic properties, as exemplified for the emended genus Lactobacillus encompassing species adapted to vertebrates (such as Lactobacillus delbrueckii, Lactobacillus iners, Lactobacillus crispatus, Lactobacillus jensensii, Lactobacillus johnsonii and Lactobacillus acidophilus) or invertebrates (such as Lactobacillus apis and Lactobacillus bombicola).

Impact of Fermentation on the Phenolic Compounds and Antioxidant Activity of Whole Cereal Grains: A Mini Review

Urbanization, emergence, and prominence of diseases and ailments have led to conscious and deliberate consumption of health beneficial foods. Whole grain (WG) cereals are one type of food with an array of nutritionally important and healthy constituents, including carotenoids, inulin, β-glucan, lignans, vitamin E-related compounds, tocols, phytosterols, and phenolic compounds, which are beneficial for human consumption. They not only provide nutrition, but also confer health promoting effects in food, such as anti-carcinogenic, anti-microbial, and antioxidant properties. Fermentation is a viable processing technique to transform whole grains in edible foods since it is an affordable, less complicated technique, which not only transforms whole grains but also increases nutrient bioavailability and positively alters the levels of health-promoting components (particularly antioxidants) in derived whole grain products. This review addresses the impact of fermentation on phenolic compounds and antioxidant activities with most available studies indicating an increase in these health beneficial constituents. Such increases are mostly due to breakdown of the cereal cell wall and subsequent activities of enzymes that lead to the liberation of bound phenolic compounds, which increase antioxidant activities. In addition to the improvement of these valuable constituents, increasing the consumption of fermented whole grain cereals would be vital for the world's ever-growing population. Concerted efforts and adequate strategic synergy between concerned stakeholders (researchers, food industry, and government/policy makers) are still required in this regard to encourage consumption and dispel negative presumptions about whole grain foods.

Genetic Determinants of Hydroxycinnamic Acid Metabolism in Heterofermentative Lactobacilli

Phenolic acids are among the most abundant phenolic compounds in edible parts of plants. Lactic acid bacteria (LAB) metabolize phenolic acids, but the enzyme responsible for reducing hydroxycinnamic acids to phenylpropionic acids (HcrB) was only recently characterized in Lactobacillus plantarum In this study, heterofermentative LAB species were screened for their hydroxycinnamic acid metabolism. Data on strain-specific metabolism in combination with comparative genomic analyses identified homologs of HcrB as putative phenolic acid reductases. Par1 and HcrF both encode putative multidomain proteins with 25% and 63% amino acid identity to HcrB, respectively. Of these genes, par1 in L. rossiae and hcrF in L. fermentum were overexpressed in response to hydroxycinnamic acids. The deletion of par1 in L. rossiae led to the loss of phenolic acid metabolism. The strain-specific metabolism of phenolic acids was congruent with the genotype of lactobacilli; however, phenolic acid reductases were not identified in strains of Weissella cibaria that reduced hydroxycinnamic acids to phenylpropionic acids. Phylogenetic analysis of major genes involved in hydroxycinnamic acid metabolism in strains of the genus Lactobacillus revealed that Par1 was found to be the most widely distributed phenolic acid reductase, while HcrB was the least abundant, present in less than 9% of Lactobacillus spp. In conclusion, this study increased the knowledge on the genetic determinants of hydroxycinnamic acid metabolism, explaining the species- and strain-specific metabolic variations in lactobacilli and providing evidence of additional enzymes involved in hydroxycinnamic acid metabolism of lactobacilli.IMPORTANCE The metabolism of secondary plant metabolites, including phenolic compounds, by food-fermenting lactobacilli is a significant contributor to the safety, quality, and nutritional quality of fermented foods. The enzymes mediating hydrolysis, reduction, and decarboxylation of phenolic acid esters and phenolic acids in lactobacilli, however, are not fully characterized. The genomic analyses presented here provide evidence for three novel putative phenolic acid reductases. Matching comparative genomic analyses with phenotypic analysis and quantification of gene expression indicates that two of the three putative phenolic acid reductases, Par1 and HcrF, are involved in reduction of hydroxycinnamic acids to phenylpropionic acids; however, the activity of Par2 may be unrelated to phenolic acids and recognizes other secondary plant metabolites. These findings expand our knowledge on the metabolic potential of lactobacilli and facilitate future studies on activity and substrate specificity of enzymes involved in metabolism of phenolic compounds.