Pectin content and composition from different food waste streams

Challenges of pectic polysaccharides as a prebiotic from the perspective of fermentation characteristics and anti-colitis activity

Several studies are described that contribute to the systematic exploration of new aspects of digestion, fermentation, and biological activities of pectic polysaccharides (PPS) leading to a better understanding of prebiotics. Inflammatory bowel disease (IBD) is thought to be associated with the dysbacteriosis induced by different environmental agents in genetically susceptible persons. PPS are considered as an indispensable gut-microbiota-accessible carbohydrate that play a dominant role in maintaining gut microbiota balance and show a better effect in ameliorating IBD than some traditional prebiotics. The aim of this review is to summarize the fermentation characteristics of PPS, highlight its role in improving IBD, and propose a view that PPS may be a new and effective prebiotic.

Substrate-activated expression of a biosynthetic pathway in Escherichia coli

Microbes can facilitate production of valuable chemicals more sustainably than traditional chemical processes in many cases: they utilize renewable feedstocks, require less energy intensive process conditions, and perform a variety of chemical reactions using endogenous or heterologous enzymes. In response to the metabolic burden imposed by production pathways, chemical inducers are frequently used to initiate gene expression after the cells have reached sufficient density. While chemically inducible promoters are a common research tool used for pathway expression, they introduce a compound extrinsic to the process along with the associated costs. We developed an expression control system for a biosynthetic pathway for the production of d-glyceric acid that utilizes galacturonate as both the inducer and the substrate, thereby eliminating the need for an extrinsic chemical inducer. Activation of expression in response to the feed is actuated by a galacturonate-responsive transcription factor biosensor. We constructed variants of the galacturonate biosensor with a heterologous transcription factor and cognate hybrid promoter, and selected for the best performer through fluorescence characterization. We showed that native E. coli regulatory systems do not interact with our biosensor and favorable biosensor response exists in the presence and absence of galacturonate consumption. We then employed the control circuit to regulate the expression of the heterologous genes of a biosynthetic pathway for the production d-glyceric acid that was previously developed in our lab. Productivity via substrate-induction with our control circuit was comparable to IPTG-controlled induction and significantly outperformed a constitutive expression control, producing 2.13 ± 0.03 g L^-1  d-glyceric acid within 6 h of galacturonate substrate addition. This work demonstrated feed-activated pathway expression to be an attractive control strategy for more readily scalable microbial biosynthesis.

Physicochemical characterization and emulsifying properties evaluation of RG-I enriched pectic polysaccharides from Cerasus humilis

Rhamnogalacturonan I (RG-I) enriched pectic polysaccharides were extracted from Cerasus humilis fruits (RPCF, RG-I: 74.46 %). Structural characterization including FTIR, XRD, NMR, HPAEC and SEM demonstrated that RPCF was a high-methoxy acetylated pectin macromolecule with abundant arabinose and galactose side chains (DM: 53.41 %, MW: 1098 kDa, (Ara + Gal)/Rha: 5.37 %). RPCF afforded additional lipid oxidation stability for emulsions, and exhibited significantly better emulsification performance than citrus pectin. In addition, RPCF formed a weak gel network that stabilized the emulsions (G' > G″). Interestingly, RPCF had behaviors that are divergent from those of commercial high-methoxy pectin because it demonstrated potential in forming sugar-free gels systems. Overall, Cerasus humilis is a new source of pectin rich in RG-I. RPCF can be used as a novel emulsifier with gelling and antioxidant effects, providing its alternative application as a natural emulsifier and rheological modifier in a wide range of products, including those with oil-in-water and low sugar.

Effects of different extraction methods on structural and physicochemical properties of pectins from finger citron pomace

The functionality and property of pectin are correlated with its structure which is affected by the extraction method used. In this study, three different methods of extracting pectin, the microwave-assisted extraction (MAE), the ultrasonic-assisted extraction (UAE) and the conventional heating extraction (CHE), were used at three different temperatures with both an acid and alkali extraction solution. It was found that temperature mainly influenced pectin yield, while pectin structures and physicochemical properties were affected by the pH condition and extraction technology. The alkali-extraction with MAE and UAE at short time promoted the yield of low-ester pectin. Monosaccharide composition analysis showed a high galacturonic acid (GalA) content in the pectin derived from MAE and UAE. The high viscosity and desirable viscoelastic properties of the acid-MAE pectin were due to its large molecular weight and particle size. The results contribute to our understanding of the association among pectin extraction, structure and properties.

The Potential of Grape Pomace Varieties as a Dietary Source of Pectic Substances

Grape pomace is one of the most abundant solid by-products generated during winemaking. A lot of products, such as ethanol, tartrates, citric acid, grape seed oil, hydrocolloids, bioactive compounds and dietary fiber are recovered from grape pomace. Grape pomace represents a major interest in the field of fiber extraction, especially pectin, as an alternative source to conventional ones, such as apple pomace and citrus peels, from which pectin is obtained by acid extraction and precipitation using alcohols. Understanding the structural and functional components of grape pomace will significantly aid in developing efficient extraction of pectin from unconventional sources. In recent years, natural biodegradable polymers, like pectin has invoked a big interest due to versatile properties and diverse applications in food industry and other fields. Thus, pectin extraction from grape pomace could afford a new reason for the decrease of environmental pollution and waste generation. This paper briefly describes the structure and composition of grape pomace of different varieties for the utilization of grape pomace as a source of pectin in food industry.

Sustainable processing of food waste for production of bio-based products for circular bioeconomy

Sustainable development of circular bioeconomy concept is only possible upon adopting potential advanced technologies for food waste valorization. This approach can simultaneously answer resources and environmental challenges incurred due to capital loss and greenhouse gases accumulation. Food waste valorization opens new horizons of economical growth, bringing waste as an opportunity feedstock for bio processes to synthesize biobased products from biological source in a circular loop. Advanced technologies like Ultrasound assisted extraction, Microwave assisted extraction, bioreactors, enzyme immobilization assisted extraction and their combination mitigates the global concern caused due to mismanagement of food waste. Food waste decomposition to sub-zero level using advanced techniques fabricates food waste into bio-based products like bioactive compounds (antioxidants, pigments, polysaccharides, polyphenols, etc.); biofuels (biodiesel, biomethane, biohydrogen); and bioplastics. This review abridges merits and demerits of various advanced techniques extended for food waste valorization and contribution of food waste in revenue generation as value added products.

Modelling the Extraction of Pectin towards the Valorisation of Watermelon Rind Waste

Watermelon is the second largest fruit crop worldwide, with great potential to valorise its rind waste. An experimental design was used to model how extraction parameters (temperature, pH, and time) impact on the efficiency of the process, purity, esterification degree, monosaccharide composition and molar mass of watermelon rind pectin (WRP), with an insight on changes in their structural properties (linearity, branching degree and extraction severity). The models for all responses were accurately fitted (R2 > 90%, lack of fit p ≥ 0.05) and experimentally validated. At optimum yield conditions, WRP yield (13.4%), purity (540 µg/g galacturonic acid) and molar mass (106.1 kDa) were comparable to traditional pectin sources but showed a higher branching degree with longer galactan side chains and a higher protein interaction. Harsher conditions (pH 1) generated purer homogalacturonan fractions with average molar masses (80 kDa) at the expense of yield, while mild extraction conditions (pH ≥ 2) produced highly branched entangled pectin structures. This study underlines novel compositional features in WRP and the possibility of producing novel customized pectin ingredients with a wider potential application scope depending on the targeted structure.

High pressure processing accelarated the release of RG-I pectic polysaccharides from citrus peel

High pressure processing (HPP) has become a promising strategy for extracting bioactive constituents. In this study, the impact of HPP treatment at various pH values (2.0, 8.0, and 12.0) on the macromolecular, structural, antioxidant capacity, rheological characteristics and gel properties of citrus pectic polysaccharide was investigated. The results showed that pressure and pH significantly affected the yield and Rhamnogalacturonan I (RG-I) characterizations. The yields of high pressure extraction at pH 12 (28.13 %-33.95 %) were significantly higher than the yields at pH 2 (14.85 %-16.11 %) and pH 8 (8.75 %-9.65 %). The yield of HPP (500 MPa/10 min) assisted alkali extraction is more than 2 times of that of HPP assisted acid extraction. The RG-I structure ratio of HPP-alkali extraction pectic polysaccharide (74.51 %) was significantly higher than that of traditional pectin (41.83 %). The results showed that HPP assisted alkali is a potential pectic polysaccharide extraction technology.

Ensiling sorghum with unsalable pumpkin improves feed digestibility with minimal influence on the rumen microbial population using the rumen simulation technique

This study aimed to determine the influence of sorghum ensiled with unsalable pumpkin at 20 or 40% dry matter (DM) basis on rumen fermentation characteristics and rumen microbial communities using the rumen simulation technique (RUSITEC). The experiment used a completely randomised design including silages comprising (1) 100% sorghum; (2) 80% sorghum + 20% DM pumpkin; or (3) 60% sorghum + 40% DM pumpkin. Each RUSITEC run (n = 2) was 15 d long, including 6 d of adaptation and 9 d of sampling. Dry matter digestibility (DMD) was measured on d 8 and 10-13. Gas production was measured daily, whereas methane and volatile fatty acids (VFA) production were measured from d 7-15. Solid-associated microbes (SAM) were collected on d 5, 10 and 15, whereas liquid-associated microbes (LAM) were collected after 15-d incubation. The V4 region of the 16S rRNA gene and the ITS1 region were sequenced to identify archaeal, bacterial and fungal communities. Ensiling 40% DM pumpkin with sorghum increased DMD and decreased the ratio of acetate to propionate (P ≤ 0.01). Both bacterial SAM and LAM communities were dominated by Megasphaera, and had the highest relative abundance (P = 0.03) with 40% DM pumpkin after 5 d incubation in the SAM community, while species of the Aspergillus genus dominated fungal SAM and LAM communities with 20 or 40% DM unsalable pumpkin. Therefore, ensiling up to 40% DM unsalable pumpkin with sorghum produces a high-quality ruminant feed with minimal influence on the rumen microbial population. KEY POINTS: • Including 40% DM unsalable pumpkin decreased acetate:propionate • Ensiling unsalable pumpkin with sorghum increases digestibility in a RUSITEC • Rumen microbial communities were slightly influenced by unsalable pumpkin inclusion.

Assessing Green Methods for Pectin Extraction from Waste Orange Peels

In this work, we assess three different methods for the extraction of pectin from waste orange peels, using water as extracting solvent. “Hot-water”, Rapid Solid Liquid Dynamic (RSLD) and microwave-assisted extractions have been compared and evaluated in terms of amount and quality of extracted pectin, as well as embodied energy. This analysis provides useful guidelines for pectin production from food waste according to green procedures, enabling the identification of acidic “hot-water” as the most sustainable extraction route.

Complete Utilization of the Major Carbon Sources Present in Sugar Beet Pulp Hydrolysates by the Oleaginous Red Yeasts Rhodotorula toruloides and R. mucilaginosa

Agro-industrial residues are low-cost carbon sources (C-sources) for microbial growth and production of value-added bioproducts. Among the agro-industrial residues available, those rich in pectin are generated in high amounts worldwide from the sugar industry or the industrial processing of fruits and vegetables. Sugar beet pulp (SBP) hydrolysates contain predominantly the neutral sugars d-glucose, l-arabinose and d-galactose, and the acidic sugar d-galacturonic acid. Acetic acid is also present at significant concentrations since the d-galacturonic acid residues are acetylated. In this study, we have examined and optimized the performance of a Rhodotorula mucilaginosa strain, isolated from SBP and identified at the molecular level during this work. This study was extended to another oleaginous red yeast species, R. toruloides, envisaging the full utilization of the C-sources from SBP hydrolysate (at pH 5.0). The dual role of acetic acid as a carbon and energy source and as a growth and metabolism inhibitor was examined. Acetic acid prevented the catabolism of d-galacturonic acid and l-arabinose after the complete use of the other C-sources. However, d-glucose and acetic acid were simultaneously and efficiently metabolized, followed by d-galactose. SBP hydrolysate supplementation with amino acids was crucial to allow d-galacturonic acid and l-arabinose catabolism. SBP valorization through the production of lipids and carotenoids by Rhodotorula strains, supported by complete catabolism of the major C-sources present, looks promising for industrial implementation.

The Identification of Genetic Determinants of Methanol Tolerance in Yeast Suggests Differences in Methanol and Ethanol Toxicity Mechanisms and Candidates for Improved Methanol Tolerance Engineering

Methanol is a promising feedstock for metabolically competent yeast strains-based biorefineries. However, methanol toxicity can limit the productivity of these bioprocesses. Therefore, the identification of genes whose expression is required for maximum methanol tolerance is important for mechanistic insights and rational genomic manipulation to obtain more robust methylotrophic yeast strains. The present chemogenomic analysis was performed with this objective based on the screening of the Euroscarf Saccharomyces cerevisiae haploid deletion mutant collection to search for susceptibility phenotypes in YPD medium supplemented with 8% (v/v) methanol, at 35 °C, compared with an equivalent ethanol concentration (5.5% (v/v)). Around 400 methanol tolerance determinants were identified, 81 showing a marked phenotype. The clustering of the identified tolerance genes indicates an enrichment of functional categories in the methanol dataset not enriched in the ethanol dataset, such as chromatin remodeling, DNA repair and fatty acid biosynthesis. Several genes involved in DNA repair (eight RAD genes), identified as specific for methanol toxicity, were previously reported as tolerance determinants for formaldehyde, a methanol detoxification pathway intermediate. This study provides new valuable information on genes and potential regulatory networks involved in overcoming methanol toxicity. This knowledge is an important starting point for the improvement of methanol tolerance in yeasts capable of catabolizing and copying with methanol concentrations present in promising bioeconomy feedstocks, including industrial residues.

Structural and emulsion stabilizing properties of pectin rich extracts obtained from different botanical sources

The presented research studied the emulsifying and emulsion stabilizing capacity of pectin samples isolated from different plant origin: apple, carrot, onion and tomato. The acid extracted pectin samples showed distinct structural properties. Specifically, apple pectin showed a high degree of methylesterification (78.41 ± 0.83%), carrot pectin had the lowest concentration of other co-eluted cell wall polymers, onion pectin displayed a bimodal molar mass distribution suggesting two polymer fractions with different molar mass and tomato pectin was characterized by a high protein content (16.48 ± 0.05%). The evaluation of the emulsifying and emulsion stabilizing potential of the pectin samples included investigating their ability to lower the interfacial tension next to a storage stability study of pectin stabilized o/w emulsions. Creaming behavior as well as the evolution of the oil droplet size were thoroughly examined during storage using multiple analytical techniques. Overall, smaller oil droplet sizes were obtained at pH 2.5 compared to pH 6.0 indicating better emulsifying capacity at lower pH. The lowest emulsion stability was observed in emulsions formulated with tomato pectin in which weak flocculation and relatively fast creaming affected emulsion stability. Onion pectin clearly showed the most promising emulsifying and emulsion stabilizing potential. At both pH conditions, emulsions stabilized by the onion pectin sample displayed highly stable oil droplet sizes during the whole storage period. The presence of the two polymer fractions in this sample can play an important role in the observed stability. In future work, it could be evaluated if both fractions contribute to emulsion stability in a synergistic way. In conclusion, this work showed that pectin samples extracted from different plant origin display diverse structural properties resulting in varying emulsifying and emulsion stabilizing potential. Polymer molar mass potentially plays a major role in the structure-function relation.

Grape pectic polysaccharides stabilization of anthocyanins red colour: Mechanistic insights

Grape pectic polysaccharides-malvidin-3-O- β -d-glucoside binding was studied, aiming to unveil the impact of structural diversity of polysaccharides on anthocyanins-polysaccharides interactions. Polysaccharides were extracted with solutions of imidazole (ISP) and carbonate at 4 °C (CSP-4 °C) and room temperature (CSP-RT) and also recovered from the dialysis supernatant of the remaining cellulosic residue after the aqueous NAOH extraction of hemicellulosic polysaccharides (Sn-CR). Polysaccharides richer in homogalacturonan domains, like those present in the CSP-4 °C fraction had approximately 50-fold higher binding affinity to malvidin-3-O- β-d-glucoside, than polysaccharides with side chains (as ISP and CSP-RT extractable polysaccharides). CSP-4 °C polysaccharides showed a positive effect on malvidin-3-O- β-d-glucoside colour fading. Hydration equilibrium constant of malvidin-3-O- β-d-glucoside in the presence of CSP-4 °C polysaccharides was higher, showing the preferential stabilization of the flavylium cation. The results showed that anthocyanins colour stabilization can be promoted by pectic polysaccharide structures such as those extracted by cold carbonate.

Production of D-Glyceric acid from D-Galacturonate in Escherichia coli

A microbial production platform has been developed in Escherichia coli to synthesize D-glyceric acid from D-galacturonate. The expression of uronate dehydrogenase (udh) from Pseudomonas syringae and galactarolactone isomerase (gli) from Agrobacterium fabrum, along with the inactivation of garK, encoding for glycerate kinase, enables D-glyceric acid accumulation by utilizing the endogenous expression of galactarate dehydratase (garD), 5-keto-4-deoxy-D-glucarate aldolase (garL), and 2-hydroxy-3-oxopropionate reductase (garR). Optimization of carbon flux through the elimination of competing metabolic pathways led to the development of a ΔgarKΔhyiΔglxKΔuxaC mutant strain that produced 4.8 g/l of D-glyceric acid from D-galacturonate, with an 83% molar yield. Cultivation in a minimal medium produced similar yields and demonstrated that galactose or glycerol serve as possible carbon co-feeds for industrial production. This novel platform represents an alternative for the production of D-glyceric acid, an industrially relevant chemical, that addresses current challenges in using acetic acid bacteria for its synthesis: increasing yield, enantio-purity and biological stability.

Structural, physicochemical and emulsifying properties of sweet potato pectin treated by high hydrostatic pressure and/or pectinase: a comparative study

BACKGROUND

Sweet potato (Ipomoea batatas L.) is the sixth most important food crop in the world, and China is the largest producer. Large amounts of sweet potato residues are generated during starch extraction, leading to environmental pollution and resource waste. However, these residues can be used as a viable source for pectin extraction. As a natural biopolymer with high molecular weight and complex structure, the usefulness of pectin has been limited, and it needs to be modified in order to improve its physicochemical properties, thus expanding its applications in the food industry. Therefore, the reported study was conducted to modify sweet potato pectin (SPP) using high hydrostatic pressure (HHP) and/or pectinase treatment, and to determine the effects of such treatment on structural, physicochemical and emulsifying properties.

RESULTS

The results demonstrated that the molecular weight of SPP decreased following HHP and pectinase treatment, which was evidenced using scanning electron microscopy and atomic force microscopy. The degree of esterification was also decreased, confirmed by decreased intensity of the peak at 1739 cm^-1 in the Fourier transform infrared spectrum and decreased peaks at 3.6 and 3.8 ppm in the ¹ H NMR spectrum. Moreover, the content of monosaccharides and uronic acids increased and emulsifying properties improved after HHP and pectinase treatment.

CONCLUSIONS

HHP-assisted pectinase treatment could be used as novel technique for the modification of pectin to give better emulsifying properties with great potential for application in the food industry. © 2020 Society of Chemical Industry.

Assessing protopectin transformation potential of plant tissue using a zoned criterion space

Introduction. The existing diversity of plant raw materials and products predetermine the prospects of studying their potential as sources of pectin substances. However all current classifications are either fragmented or inconsistent. Study objects and methods. Our theoretical ivestigation aimed to develop an adequate classification for all taxa of plant origin, as well as their tissues and derivatives as pectin-containing materials. We developed criteria for assessing transformation potential of the protopectin complex based on the mass fractions of biologically active non-uronide components, native water-soluble pectin, the protopectin complex, and pectin substances. Individual boundary conditions were based on individual pectin potential, protopectin fragmentation potential, and pectin isolation potential. Results and discussion. Based on the boundary conditions, we defined an universal criterion space that included a set of points M in the coordinates expressed by three main criteria. According to individual boundary conditions, the criterion space was divided, or zoned, into four domains corresponding to protopectin fragmentation potential. They were characterized by: 1) lack of pectin potential, 2) ineffective protopectin fragmentation, 3) ineffective isolation of fragmentation products, and 4) effective isolation. Finally, we developed a generalized algorithm to determine the location of points M[μ1, μ2 , μ3 ] in the zoned criterion space, characterizing the plant tissue. Conclusion. Our approach can be used to assess any plant tissue for its protopectin transformation potential, which determines the technological influence on its pectin potential. This approach is universal, i.e., applicable to both plant tissue and its derivatives.

Low methyl-esterified pectin protects pancreatic β-cells against diabetes-induced oxidative and inflammatory stress via galectin-3

Insufficient intake of dietary fibers in Western societies is considered a major contributing factor in the high incidence rates of diabetes. The dietary fiber pectin has been suggested to be beneficial for management of both Diabetes Type 1 and Type 2, but mechanisms and effects of pectin on insulin producing pancreatic β-cells are unknown. Our study aimed to determine the effects of lemon pectins with different degree of methyl-esterification (DM) on β-cells under oxidative (streptozotocin) and inflammatory (cytokine) stress and to elucidate the underlying rescuing mechanisms, including effects on galectin-3. We found that specific pectins had rescuing effects on toxin and cytokine induced stress on β-cells but effects depended on the pectin concentration and DM-value. Protection was more pronounced with low DM5 pectin and was enhanced with higher pectin-concentrations. Our findings show that specific pectins might prevent diabetes by making insulin producing β-cells less susceptible for stress.

Sequential combination of laccase pretreatment and acid extraction for high-yield pectin production from pomelo peels

A sequential combination of laccase pretreatment and acid extraction of pectin from pomelo peels was performed in this study. By using a laccase dose of 10 U/g, the yield and galacturonic acid content of the extracted pectin were 21.67% and 75.74%, respectively, which reflected an improvement by nearly 30% and 44% relative to the extraction process without laccase. Moreover, the degree of esterification of the extracted pectin was significantly improved as the laccase concentration was increased from 0 to 10 U/g but did not affect the molecular weight. Besides, the enzyme-treated sample displayed more than 29% loss of total lignin, in which the acid soluble lignin and the acid insoluble lignin were removed by over 15% and 33%, respectively. Scanning electron microscopy indicated that the penetration and partial destruction of the pomelo peel cell wall due to laccase might be one of the main reasons why laccase pretreatment could release pectin from cell wall complexes and increase the pectin yield in subsequent acid extraction processes.

Valorisation of pectin-rich agro-industrial residues by yeasts: potential and challenges

Pectin-rich agro-industrial residues are feedstocks with potential for sustainable biorefineries. They are generated in high amounts worldwide from the industrial processing of fruits and vegetables. The challenges posed to the industrial implementation of efficient bioprocesses are however manyfold and thoroughly discussed in this review paper, mainly at the biological level. The most important yeast cell factory platform for advanced biorefineries is currently Saccharomyces cerevisiae, but this yeast species cannot naturally catabolise the main sugars present in pectin-rich agro-industrial residues hydrolysates, in particular D-galacturonic acid and L-arabinose. However, there are non-Saccharomyces species (non-conventional yeasts) considered advantageous alternatives whenever they can express highly interesting metabolic pathways, natively assimilate a wider range of carbon sources or exhibit higher tolerance to relevant bioprocess-related stresses. For this reason, the interest in non-conventional yeasts for biomass-based biorefineries is gaining momentum. This review paper focuses on the valorisation of pectin-rich residues by exploring the potential of yeasts that exhibit vast metabolic versatility for the efficient use of the carbon substrates present in their hydrolysates and high robustness to cope with the multiple stresses encountered. The major challenges and the progresses made related with the isolation, selection, sugar catabolism, metabolic engineering and use of non-conventional yeasts and S. cerevisiae-derived strains for the bioconversion of pectin-rich residue hydrolysates are discussed. The reported examples of value-added products synthesised by different yeasts using pectin-rich residues are reviewed. Key Points • Review of the challenges and progresses made on the bioconversion of pectin-rich residues by yeasts. • Catabolic pathways for the main carbon sources present in pectin-rich residues hydrolysates. • Multiple stresses with potential to affect bioconversion productivity. • Yeast metabolic engineering to improve pectin-rich residues bioconversion. Graphical abstract.

Engineering marine fungi for conversion of D-galacturonic acid to mucic acid

BACKGROUND

Two marine fungi, a Trichoderma sp. and a Coniochaeta sp., which can grow on D-galacturonic acid and pectin, were selected as hosts to engineer for mucic acid production, assessing the suitability of marine fungi for production of platform chemicals. The pathway for biotechnologcial production of mucic (galactaric) acid from D-galacturonic acid is simple and requires minimal modification of the genome, optimally one deletion and one insertion. D-Galacturonic acid, the main component of pectin, is a potential substrate for bioconversion, since pectin-rich waste is abundant.

RESULTS

Trichoderma sp. LF328 and Coniochaeta sp. MF729 were engineered using CRISPR-Cas9 to oxidize D-galacturonic acid to mucic acid, disrupting the endogenous pathway for D-galacturonic acid catabolism when inserting a gene encoding bacterial uronate dehydrogenase. The uronate dehydrogenase was expressed under control of a synthetic expression system, which fucntioned in both marine strains. The marine Trichoderma transformants produced 25 g L-1 mucic acid from D-galacturonic acid in equimolar amounts: the yield was 1.0 to 1.1 g mucic acid [g D-galacturonic acid utilized]-1. D-Xylose and lactose were the preferred co-substrates. The engineered marine Trichoderma sp. was more productive than the best Trichoderma reesei strain (D-161646) described in the literature to date, that had been engineered to produce mucic acid. With marine Coniochaeta transformants, D-glucose was the preferred co-substrate, but the highest yield was 0.82 g g-1: a portion of D-galacturonic acid was still metabolized. Coniochaeta sp. transformants produced adequate pectinases to produce mucic acid from pectin, but Trichoderma sp. transformants did not.

CONCLUSIONS

Both marine species were successfully engineered using CRISPR-Cas9 and the synthetic expression system was functional in both species. Although Coniochaeta sp. transformants produced mucic acid directly from pectin, the metabolism of D-galacturonic acid was not completely disrupted and mucic acid amounts were low. The D-galacturonic pathway was completely disrupted in the transformants of the marine Trichoderma sp., which produced more mucic acid than a previously constructed T. reesei mucic acid producing strain, when grown under similar conditions. This demonstrated that marine fungi may be useful as production organisms, not only for native enzymes or bioactive compounds, but also for other compounds.

Comparative Characterization of Aspergillus Pectin Lyases by Discriminative Substrate Degradation Profiling

Fungal genomes often contain several copies of genes that encode carbohydrate active enzymes having similar activity. The copies usually have slight sequence variability, and it has been suggested that the multigenecity represents distinct reaction optima versions of the enzyme. Whether the copies represent differences in substrate attack proficiencies of the enzyme have rarely been considered. The genomes of Aspergillus species encode several pectin lyases (EC 4.2.2.10), which all belong to polysaccharide lyase subfamily PL1_4 in the CAZy database. The enzymes differ in terms of sequence identity and phylogeny, and exhibit structural differences near the active site in their homology models. These enzymes catalyze pectin degradation via eliminative cleavage of the α-(1,4) glycosidic linkages in homogalacturonan with a preference for linkages between methyl-esterified galacturonate residues. This study examines four different pectin lyases (PelB, PelC, PelD, and PelF) encoded by the same Aspergillus sp. (namely A. luchuensis), and further compares two PelA pectin lyases from two related Aspergillus spp. (A. aculeatus and A. tubingensis). We report the phylogeny, enzyme kinetics, and enzymatic degradation profiles of the enzymes' action on apple pectin, citrus pectin, and sugar beet pectin. All the pectin lyases exerted highest reaction rate on apple pectin [degree of methoxylation (DM) 69%, degree of acetylation (DAc) 2%] and lowest reaction rate on sugar beet pectin (DM 56%, DAc 19%). Activity comparison at pH 5-5.5 produced the following ranking: PelB > PelA > PelD > PelF > PelC. The evolution of homogalacturonan-oligomer product profiles during reaction was analyzed by liquid chromatography with mass spectrometry (LC-MS) detection. This analyses revealed subtle differences in the product profiles indicating distinct substrate degradation preferences amongst the enzymes, notably with regard to acetyl substitutions. The LC-MS product profiling analysis thus disclosed that the multigenecity appears to provide the fungus with additional substrate degradation versatility. This product profiling furthermore represents a novel approach to functionally compare pectin-degrading enzymes, which can help explain structure-function relations and reaction properties of disparate copies of carbohydrate active enzymes. A better understanding of the product profiles generated by pectin modifying enzymes has significant implications for targeted pectin modification in food and biorefinery processes.

Comparison of enzymatic and microwave-assisted alkaline extraction approaches for the generation of oligosaccharides from American Cranberry (Vaccinium macrocarpon) Pomace

Cranberry pomace obtained from industrial juice production was characterized by proximate composition analysis and monosaccharide profile of the dietary fiber. Extraction of carbohydrates from pomace was investigated using microwave-assisted alkaline method and five commercial biocatalysts (pure endo-galactanase and four multienzyme biocatalysts). The extracts obtained from microwave-assisted approach had average total sugars yield of 21.3% and contained mostly oligosaccharides in the degree of polymerization range of 7 to 10. All multienzyme biocatalysts led to yields similar or higher than microwave-assisted approach (23.4% to 42.0%), but mainly generated shorter oligosaccharides with a degree of polymerization of 2 to 5. Compared to cranberry pomace dietary fiber, microwave-assisted extracts were enriched in pectic oligosaccharides, whereas the enzymatic extracts were enriched in glucans and had less rhamnose and galactose. Pomace ground for 5 min or more by ball mill assumed a powdery consistence. Longer milling did not affect particle size but increased their roughness. Such physical changes had no effect on the efficiency of multienzymatic treatment. PRACTICAL APPLICATION: The increased production of cranberries and cranberry products will continuously generate more pomace, a potentially valuable material for the generation of added-value products. Up to 60% to 70% of cranberry pomace is composed of plant cell wall material. The properties of naturally occurring plant cell wall polysaccharides and their corresponding oligosaccharides have been of a great interest, and many of them find application as functional food ingredients. Despite the fact that the cranberry pomace is rich in plant cell polysaccharides, it has been mainly explored as a source of phenolic antioxidants. This study reveals the efficiency of cranberry pomace as a source of nondigestible oligosaccharides. The use of microwave-assisted extraction and different biocatalysts for the enzymatic extraction led to oligosaccharides with well-defined monosaccharide composition and molecular weight distribution. The study of the effects of these extraction techniques on the yield and the characteristics of generated oligosaccharides would allow the modulation of their properties. As an overall, the findings of this study would contribute to lay the scientific ground for the development of innovative process for the isolation of nondigestible oligosaccharides as functional ingredients from cranberry pomace by products.

Manosonication extraction of RG-I pectic polysaccharides from citrus waste: Optimization and kinetics analysis

To better understanding the potential of manosonication to accelerate the extraction of RG-I pectic polysaccharides from citrus wastes, alkaline-mediated manosonication extraction (MSE) was optimized using a Box-Behnken design, and the extraction kinetics model was analyzed. The single-factor method revealed that NaOH significantly impacted on the yield and RG-I characterizations (Rha mol% and (Gal+Ara)/Rha ratio), whereas other factors were focused on influences of yields. In the developed quadratic polynomial model, the maximum extraction yield of 25.51 ± 0.81 % was obtained with sonication at 42 ℃, 40 % amplitude, and 250 kPa for 20 min. The kinetics study demonstrated that MSE facilitated the extractability, dissolution and degradation of pectin, resulting in the highest extractability of 27.83 % compared with ultrasonic extraction (22.86 %) and alkaline extraction at high (24.71 %) and low temperature (20.21 %). Rheology and thermal analyses verified the change in polymerization by MSE and the potential functional applications of the RG-I pectic polysaccharides.

Ability of a Wild Weissella Strain to Modify Viscosity of Fermented Milk

Despite the fact that strains belonging to Weissella species have not yet been approved for use as starter culture, recent toxicological studies open new perspectives on their potential employment. The aim of this study was to evaluate the ability of a wild Weissella minor (W4451) strain to modify milk viscosity compared to Lactobacillus delbrueckii subsp. bulgaricus, which is commonly used for this purpose in dairy products. To reach this goal, milk viscosity has been evaluated by means of two very different instruments: one rotational viscometer and the Ford cup. Moreover, water holding capacity was evaluated. W4451, previously isolated from sourdough, was able to acidify milk, to produce polysaccharides in situ and thus improve milk viscosity. The ability of W4451 to produce at the same time lactic acid and high amounts of polysaccharides makes it a good candidate to improve the composition of starters for dairy products. Ford cup turned out to be a simple method to measure fermented milk viscosity by small- or medium-sized dairies.

Synchronous role of coupled adsorption and photocatalytic oxidation on the hybrid nanomaterials of pectin and nickel ferrite leads to the excellent removal of toxic dye effluents

Ecofriendly and robust hybrid nanomaterials of pectin and nickel ferrite were succesfully employed for the adsorptive degradation of toxic dye molecules in waste water treatment.

Effects of acoustic power and pH on pectin-enriched extracts obtained from citrus by-products. Modelling of the extraction process

BACKGROUND

The ultrasound-assisted extraction of pectic polysaccharides from orange by-products was investigated. Kinetics of mechanical agitation (0.2 × g) and acoustic (US1: 542 W L^-1 and US2: 794 W L^-1 ) extractions, were obtained and modelled at different pH values (1.5 and 2.0). All extractions were carried out at 25 °C, using citric acid as the extraction solvent.

RESULTS

Higher pectic polysaccharides extraction yields were obtained with ultrasonic assistance, in comparison with the results obtained using mechanical agitation. Moreover, yield increases were significantly higher using the more acidic pH. Thus, at pH 1.5, pectin yield increased from ∼19%, obtained with agitation, to ∼47%, applying ultrasound; whereas, at pH 2.0, this increase was from ∼10%, with agitation, to ∼18%, applying ultrasound. A considerable decrease of the galacturonic acid proportion was observed on the extracts when ultrasound were applied for 60 min under pH 2.0. High methoxyl pectins were extracted at pH 1.5 whereas at pH 2.0, pectins exhibited a low methylation degree. Curves of acoustic and mechanical agitation extractions were properly represented by a second-order rate model (average mean relative error ≤ 7.4%). The extraction rate constant, initial extraction rate and maximum yield were determined for all experimental conditions.

CONCLUSION

Overall, the results clearly indicated that the effect of ultrasound was highly dependent on the pH. Therefore, adequate acidic conditions must be applied in order to improve the efficiency of ultrasound on the pectin extraction process. © 2019 Society of Chemical Industry.

Recovery of High Value-Added Nutrients from Fruit and Vegetable Industrial Wastewater

The industrial processing water of fruit and vegetables has raised serious environmental concerns due to the presence of many important bioactive compounds being disposed in the wastewater. Bioactive compounds have great potential for the food industry to optimize their process and to recover these compounds in order to develop value-added products and to reduce environmental impacts. However, to achieve this goal, some challenges need to be addressed such as safety assurance, technology request, product regulations, cost effectiveness, and customer factors. Therefore, this review aims to summarize the recent advances of bioactive compounds recovery and the current challenges in wastewater from fruit and vegetable processing industry, including fruit and beverage, soybean by-products, starch and edible oil industry. Moreover, future direction for novel and green technology of bioactive compounds recovery are discussed, and a prospect of bioactive compounds reuse and sustainable development is proposed.

Production pectin oligosaccharides using Humicola insolens Y1-derived unusual pectate lyase

The economical production of pectin oligosaccharides with a specific degree of polymerization and structure from agro-food waste is an industrially important process. This study identified a novel pectate lyase gene (plhy1) from the thermophilic cellulolytic fungus H. insolens Y1 and tested its ability to produce pectin oligosaccharides. The recombinant PLHY1 produced in Pichia pastoris was superior to other similar enzymes due to its high thermal and pH stability. PLHY1 demonstrated optimal enzymatic activity at 55°C and pH 10.0 in the presence of 0.4 mM Ca²⁺, and preferred methyl esterified substrates for digestion. High performance anion exchange chromatography-pulsed amperometric detector and ultra high performance liquid chromatography in combination with electrospray ionization tandem mass spectrometry analysis showed that galacturonic acid-oligosaccharides with a small degree of polymerization (4-6) were the major hydrolysates produced by the degradation of apple peel pectin by PLHY1. The properties of PLHY1 make it valuable for application in the agro-food industry for the production of pectin oligosaccharides.

Ultrasound-Assisted Extraction of Pectin from Malus domestica ‘Fălticeni’ Apple Pomace

The use of an ultrasonic treatment for the extraction of pectin from Malus domestica ‘Fălticeni’ apple pomace, its effects on extraction yield and galacturonic acid content, and degree of esterification of the extracted pectin were investigated. The optimization of the extraction process showed that the highest yield of 9.183% pectin, with a 98.127 g/100 g galacturonic acid content and 83.202% degree of esterification, was obtained at 100% amplitude, pH of 1.8, SLR of 1:10 g/mL, and 30 min. The pectin obtained in optimal extraction conditions was compared to commercial citrus and apple pectin in terms of chemical composition (determined by FT-IR), thermal behaviour (analyzed by differential scanning calorimetry), rheological properties, and morphological structure (analyzed by scanning electron microscopy). By comparison to commercial citrus and apple pectin samples, the FT-IR analysis of pectin extracted by ultrasound treatment confirmed the high degree of esterification and showed similarity to that of apple pectin (88.526%). It was found that the thermal behaviour of the pectin obtained by ultrasound-assisted extraction was influenced by the narrower distribution of molecular weights and the orderly molecular arrangement, while the rheological properties (high viscosity, G0, and G1) of this sample were influenced by the morphological structure and the galacturonic acid content. The correlation coefficient showed a strong positive relationship between viscosity and galacturonic acid content (r = 0.992**).