Development of double network gels based on soy protein isolate and sugar beet pectin induced by thermal treatment and laccase catalysis

Ferulic acid- and gallic ester-acylated pectin: Preparation and characterization

In this study, pectin was modified with ferulic acid (Fa), trans-ferulic acid (trans-Fa), methyl gallate (MG), and ethyl gallate (EG) via the enzymatic method using aqueous/organic phases to enhance its physiochemical and bio-active properties. Results revealed that lipase might catalyze the hydrolysis of the ester bond within pectin in aqueous phase and prompt the transesterification between the hydroxyl group in the para position in Fa/trans-Fa or the 2'-OH group of MG/EG and the carboxylic group of pectin in the organic phase. The graft ratio was 21.00%, 21.67%, 13.24%, and 11.93% for the Fa-, trans-Fa-, MG-, and EG-modified pectin, respectively. In addition, compared with native pectin, the modified pectin exhibited improved apparent viscosity and emulsion activity. Moreover, the clearance of 1,1-diphenyl-2-picryl hydrazine (DPPH) and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) was effectively enhanced for the modified pectin. Furthermore, the modified pectin exhibited strong antibacterial activity against Escherichia coli and Staphylococcus aureus while no cytotoxic effects based on the results of cell culture experiments. Our results provide a theoretical basis for the expansion of pectin applications in the food and pharmaceutical industries.

Fabrication of agarose/fish gelatin double-network hydrogels with high strength and toughness for the development of artificial beef tendons

Agarose/fish gelatin (AR/FGA) double-network hydrogels (DNs) were fabricated via a one-step heating-cooling method. The structure, mechanical and textural properties, water-holding capacity, swelling behavior and sensory characteristics of the DNs were analyzed and compared with the corresponding single-network hydrogels (SNs) and beef tendons. An increase in FGA concentration (10-40 wt%) significantly enhanced the mechanical strength and toughness of DNs, while a moderate increase in AR concentration (0.5-1.5 wt%) only improved their mechanical strength. The 1.5 wt% AR/40 wt% FGA DNs attained excellent fracture stress and strain compared with the single AR and single FGA gels. This can be attributed to the energy dissipation effect, intermolecular hydrogen bond interactions and higher entanglement density of molecule chains. Furthermore, AR/FGA DNs attained a higher hardness, water holding capacity and lower swelling rate compared with SNs. The principal component analysis and correlation analysis showed that the 1.5 wt% AR/30 wt% FGA DNs displayed the most comparable correlation with beef tendons, which was consistent with the results of the sensory evaluation, showing great potential as artificial beef tendons. Our findings provide guidance for the modulation of gel properties and development of artificial foods.

Candelilla wax-based oleogels versus palm oil: evaluation of physical properties of innovative and conventional lipids using optical techniques

BACKGROUND

The widespread use of palm oil in food production affects high consumption of long-chain saturated fatty acids, which increases the risk of cardiovascular disease. Solid or semi-solid wax-based oleogels obtained as a result of edible oils structuring can be an alternative.

RESULTS

Oleogels, obtained by structuring a mixture of refined rapeseed and linseed oils (1:1) with 30-80 g kg^-1 candelilla wax (CW), were investigated using optical techniques: multi-speckle diffusing wave spectroscopy, centrifugal stability analysis, reflection method, and polarized light microscopy. Refined palm oil was a comparative sample. Increasing CW concentration resulted in an increase in values of L^* parameter and opacity, a decrease in the Yellowness Index and a slight increase in the average crystal size. The microstructure of oleogels with 30 or 40 g kg^-1 CW was least like the crystal network. Solidification of oleogels took place in two stages. Increase in CW concentration shortened solidification time and increased solidification temperature (greater elasticity of oleogels). Palm oil solidified the longest (497.1 min) and at the lowest temperature (29.3 °C). It showed lower resistance to centrifugal force than oleogels at 20 and 30 °C. All oleogels were stable (no oil release occurred) at 20 °C.

CONCLUSION

Optical methods allow for an objective and detailed analysis of physical properties of palm oil and oleogels, as well as identification and tracking changes at the microstructural level over time. It has great potential in the edible lipid quality control at various stages of processing or storage. © 2021 Society of Chemical Industry.

Protein-polysaccharide interactions for the fabrication of bioactive-loaded nanocarriers: Chemical conjugates and physical complexes

As unique biopolymeric architectures, covalently and electrostatically protein-polysaccharide (PRO-POL) systems can be utilized for bioactive delivery by virtue of their featured structures and unique physicochemical attributes. PRO-POL systems (i. e, microscopic /nano-dimensional multipolymer particles, molecularly conjugated vehicles, hydrogels/nanogels/oleogels/emulgels, biofunctional films, multilayer emulsion-based delivery systems, particles for Pickering emulsions, and multilayer coated liposomal nanocarriers) possess a number of outstanding attributes, like biocompatibility, biodegradability, and bioavailability with low toxicity that qualify them as powerful agents for the delivery of different bioactive ingredients. To take benefits from these systems, an in-depth understanding of the chemical conjugates and physical complexes of the PRO-POL systems is crucial. In this review, we offer a comprehensive study concerning the unique properties of covalently/electrostatically PRO-POL systems and introduce emerging platforms to fabricate relevant nanocarriers for encapsulation of bioactive components along with a subsequent sustained/controlled release.

Comparative Study of Heat- and Enzyme-Induced Emulsion Gels Formed by Gelatin and Whey Protein Isolate: Physical Properties and Formation Mechanism

Emulsion gels have received increasing attention due to their unique physicochemical properties. In this paper, gelatin and whey protein isolate (WPI) were used to construct emulsion-filled gels by heat-induced or enzyme-induced methods, and their rheology, texture properties and microstructure were explored and compared. The effect of the preparation methods, emulsion droplet characteristics and gel matrix concentration on the elastic modulus and hardness of the gels were firstly investigated, then the key control factors were picked out by calculating the Pearson correlation index, and the design principle was constructed by combining these factors flexibly for emulsion gels with adjustable texture. The results show that the emulsion gels formed by different preparation methods have completely distinct microstructures and emulsion distributions, as well as the macroscopic properties of the gels, specifically the enzyme-induced gels exhibited greater elastic modulus and hardness, while heat-induced gels were softer and more delicate. In addition, the droplet sizes of filled emulsions and matrix concentration mainly affected the rheological properties and hardness of the gels. This study successfully established the design principles of emulsion gels with tunable texture structure, which provided a reference for targeted gels preparation according to the texture properties required by specific application scenarios.

Rheological and gelling properties of Nicandra physalodes (Linn.) Gaertn. pectin in acidic media

Nicandra physalodes (Linn.) Gaertn. polysaccharide (NPGP) was previously recognized as a pectic polysaccharide, with a high galacturonic acid content (87.8%) and a low methoxylation degree (28%). In the present study, it was found that NPGP can form self-supporting gels when cooling its heated solutions (2.0%, w/v) acidified by citric acid. It was demonstrated that the decrease in pH led to the suppression in electrostatic repulsions between the pectin chains, thereby promoting pectin chain-chain association mainly through hydrogen bonding. As the pH decreased from 3.2 to 2.4, the gel strength and gel thermal stability were continuously increased. Moreover, it was shown that sucrose addition slightly promoted the gelation and gel thermal stability of NPGP, but the effect of monovalent ions (Na⁺) and divalent ions (Ca²⁺) was not significant. Conclusively, our results indicate that NPGP is a new gelling polysaccharide that shows great potential in formulation of acidic gel foods.

Enzymatic synthesis, characterization and properties of the protein-polysaccharide conjugate: A review

Poor solubility of proteins negatively affects their functional properties and greatly limits their application. Enzymatic cross-linking with polysaccharides can improve solubility and functional properties of proteins. The enzymes used include transglutaminase, laccase and peroxidase. Therefore, this work introduces the cross-linking mechanisms of these enzymes and the characterization techniques, the improved properties and the potential applications of the enzymatically-synthesized protein-polysaccharide conjugate. Transglutaminase catalyzes the formation of a new peptide bond and thus works on amino-containing polysaccharides to conjugate with proteins. However, laccase and peroxidase catalyze oxidation of various compounds with phenol and aniline structures. Therefore, these two enzymes can catalyze the conjugate reaction between proteins and feruloylated polysaccharides which are widely distributed in cereal bran. Compared with the unmodified protein, the enzymatically-synthesized protein-polysaccharide conjugate usually has higher solubility and better functional properties. Thus, it is inferred that enzymatic conjugation with polysaccharide molecules can extend the application of proteins.

Trends in "green" and novel methods of pectin modification - A review

Modification of hydrocolloids to alter their functional properties using chemical methods is well documented in the literature. There has been a recent trend of adopting eco-friendly and "green" methods for modification. Pectin, being a very important hydrocolloid finds its use in various food applications due to its gelling, emulsifying, and stabilizing properties. The adoption of various "green" methods can alter the properties of pectin and make it more suitable for incorporation in food products. The novel approaches such as microwave and pulsed electric field can also be utilized for solvent-free modification, making it desirable from the perspective of sustainability, as it reduces the consumption of organic chemicals. Pectic oligosaccharides (POSs) produced via novel approaches are being explored for their biological properties and incorporation in various functional foods. The review can help to set the perspective of potential scale-up and adoption by the food industry for modification of pectin.

Preparation and Characterization of a Novel Soy Protein Isolate-Sugar Beet Pectin Emulsion Gel and Its Application as a Multi-Phased Nutrient Carrier

Emulsion gel, a novel oral delivery carrier, provides the possibility to co-load hydrophilic and lipophilic nutrients simultaneously. In this study, duo-induction methods of laccase and glucono-δ-lactone (L&GDL) or laccase and transglutaminase (L&MTG) were used to prepare the soy protein isolate-sugar beet pectin (SPI-SBP) emulsion gel. The textural data of the emulsion gel was normalized to analyze the effect of different induction methods on the gel property of the SPI-SBP emulsion gels. The characterization studies showed the structure of L&MTG emulsion gel was denser with a lower swelling ratio and reduced degree of digestion, compared with L&GDL emulsion gel. Moreover, the release profiles of both β-carotene and riboflavin co-loaded in the SPI-SBP emulsion gels were correlated to the digestion patterns of the gel matrix; the controlled-release of encapsulated functional factors was regulated by a gel network induced by different induction methods, mainly due to the resulting porosity of the structure and swelling ratio during digestion. In conclusion, SPI-SBP emulsion gels have the capability of encapsulating multiple functional factors with different physicochemical properties.

Fabrication and biomedical applications of Arabinoxylan, Pectin, Chitosan, Soy protein, and Silk fibroin hydrogels via laccase - ferulic acid redox chemistry

The unique physiochemical properties and the porous network architecture of hydrogel seek the attention to be explored in broad range of fields. In the last decade, numerous studies on the development of enzymatically cross-linked hydrogels have been elucidated. Implementing enzyme based cross-linking for fabrication of biomaterials over other crosslinking methods harbor various advantages, especially hydrogels designed using laccase exhibits mild reaction environment, high cross-linking efficiency and less toxicity. To our knowledge this is the first report reviewing the formulation of laccase mediated cross-linking for hydrogel preparation. Here, laccase catalyzed synthesis of hydrogel using polysaccharide viz. arabinoxylan, sugar beet pectin, galactomannan, chitosan etc. and proteins namely soy protein, gelatin, silk fibroin were discussed on highlighting their mechanical properties and its possible field of application. We have summarized the role of phenolic acids in laccase mediated crosslinking particularly ferulic acid which is a component of lignocellulose, serving cell rigidity via crosslinkage. The review also discusses on various biomedical applications such as controlled protein release, tissue engineering, and wound healing. It is anticipated that this review will give a detailed information on different laccase mediated reaction strategies that can be applied for the synthesis of various new biomaterials with tailor made properties.

Improved functional properties of meat analogs by laccase catalyzed protein and pectin crosslinks

The gap between the current supply and future demand of meat has increased the need to produce plant-based meat analogs. Methylcellulose (MC) is used in most commercial products. Consumers and manufacturers require the development of other novel binding systems, as MC is not chemical-free. We aimed to develop a novel chemical-free binding system for meat analogs. First, we found that laccase (LC) synergistically crosslinks proteins and sugar beet pectin (SBP). To investigate the ability of these SBP-protein crosslinks, textured vegetable protein (TVP) was used. The presence of LC and SBP improved the moldability and binding ability of patties, regardless of the type, shape, and size of TVPs. The hardness of LC-treated patties with SBP reached 32.2 N, which was 1.7- and 7.9-fold higher than that of patties with MC and transglutaminase-treated patties. Additionally, the cooking loss and water/oil-holding capacity of LC-treated patties with SBP improved by up to 8.9-9.4% and 5.8-11.3%, compared with patties with MC. Moreover, after gastrointestinal digestion, free amino nitrogen released from LC-treated patties with SBP was 2.3-fold higher than that released from patties with MC. This is the first study to report protein-SBP crosslinks by LC as chemical-free novel binding systems for meat analogs.

Acid-induced mixed methylcellulose and casein gels: Structures, physical properties and formation mechanism

In this study, caseins and methylcellulose (MC) were selected as building materials to prepare a class of mixed gels by adding glucono-δ-lactone (GDL) to induce the gelation of composite MC/casein systems, where the casein concentration was fixed at 8.0% (w/v) and the MC concentration varied from 0 to 1.0% (w/v). It was found that with increasing amount of MC addition (0-0.4%), the mixed gels exhibited a structural conversion from a casein-dominant gel network to a "water-in-water emulsion structure", with the caseins as the continuous gelling phase and the MC as the dispersed phase; further MC addition (0.4-1.0%, w/v) caused a more significant phase separation phenomenon. The structural conversion was in consistent with the determination result of gel hardness. Furthermore, by a combination of confocal laser scanning microscope (CLSM) and rheological studies, the structural evolution process of the mixed gels was revealed to explore the underlying formation mechanism of the mixed gels.

Fabrication of food-grade Pickering high internal phase emulsions stabilized by the mixture of β-cyclodextrin and sugar beet pectin

Food-grade Pickering high internal phase emulsions (HIPEs) stabilized by a mixture of β-cyclodextrin (β-CD) and sugar beet pectin (SBP) were fabricated for the first time. The factors affecting the microstructures, mechanical properties, and stabilities of the Pickering HIPEs were systematically investigated. The corresponding hybrid particles were also separated and characterized to reveal the formation mechanism. The results indicated that the mixture could induce the formation of HIPEs with an oil phase volume fraction (φ) of 75% using a one-step high-speed shearing process at room temperature. The composition (the mass ratio of β-CD to SBP, R_c/s) and concentration (W) of the mixture had significant effects on the formation and properties of HIPEs. When W ≥ 1.0% and R_c/s = 2:2 or 3:1, HIPEs had smaller oil droplets, higher gel strengths, better centrifugation stabilities and lutein protection effects. The spectral analysis suggested that SBP could adhere to the surface of β-CD particles to form hybrid particles during the homogenization. Compared with native β-CD particles, these hybrid particles had higher ζ-potential absolute values, and the SBP could also increase the viscosity of the aqueous phase, which contributed to the formation and properties of these HIPEs.

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.

Investigation of the Formation Mechanism and Curcumin Bioaccessibility of Emulsion Gels Based on Sugar Beet Pectin and Laccase Catalysis

In this study, modified whey protein hydrolysates (WPH) were obtained after succinic anhydride succinylation and linear dextrin glycation, and emulsion gels were prepared on the basis of unmodified/modified WPH stabilized emulsions with sugar beet pectin (SBP) addition and laccase-catalyzed cross-linking. The influences of emulsifier types and SBP contents on the texture of emulsion gels were estimated. The texture and rheological properties of emulsion gels were characterized. An ideal gel emulsion was formed when the SBP content was 3% (w/w). A uniform network was observed in emulsion gels stabilized by W-L, W-L-S, and W-S-L. In addition, the effect of the emulsifier type on the bioaccessibility of curcumin encapsulated in emulsion gels was investigated and the W-S-L stabilized emulsion gel exhibited the highest curcumin bioaccessibility (65.57%). This study provides a theoretical basis for the development of emulsion gels with different textures by SBP addition and laccase cross-linking as encapsulation delivery systems.

Double-Network Hydrogels of Corn Fiber Gum and Soy Protein Isolate: Effect of Biopolymer Constituents and pH Values on Textural Properties and Microstructures

Corn fiber gum (CFG) -soy protein isolate (SPI) double-network (DN) hydrogels were fabricated using laccase and a heat treatment process, in which CFG solution formed the first gel network via laccase oxidation, while SPI formed the second network through heating, as described in our previous research. The aim of this study was to investigate the influences of CFG/SPI constituents (CFG concentration 0-3%, w/v; SPI concentration 8-10%, w/v) and pH values (5.0-7.5) on the textural properties, microstructures and water-holding capacities (WHC) of the CFG-SPI DN hydrogels. Confocal Laser Scanning Microscopy (CLSM) results showed an apparent phase separation when the CFG concentration was above 1% (w/v). The textural characteristics and WHC of most DN hydrogels were enhanced with increasing concentrations of CFG and SPI. Scanning Electron Microscopy (SEM) observations revealed that the microstructures of DN hydrogels were converted from coarse and irregular to smooth and ordered as pH values increased from 5.0 to 7.5. Excellent textural properties and WHC were observed at pH 7.0. This study developed various CFG-SPI DN hydrogels with diverse textures and structures, governed by the concentrations of protein/polysaccharide and pH values, and also contributes to the understanding of gum-protein interactions in DN hydrogels obtained under different conditions.

Mild Enzyme-Induced Gelation Method for Nanoparticle Stabilization: Effect of Transglutaminase and Laccase Cross-Linking

Low-environment-sensitive nanoparticles were prepared by enzymatic cross-linking of electrostatic complexes of dextran-grafted whey protein isolate (WPI-Dextran) and chondroitin sulfate (ChS). The effect of transglutaminase (TG) and laccase cross-linking on nanoparticle stability was investigated. Covalent TG cross-linking and grafted dextran cooperatively contributed to the stability of nanoparticles against dissociation and aggregation under various harsh environmental conditions (sharply varying pH, high ionic strength, high temperature, and their combined effects). However, fragmentation induced by laccase treatment did not promote nanoparticle stability. Structural characterization showed that the compact structure promoted by TG-induced covalent isopeptide bonds repressed dissociation against varying environmental conditions and thermal-induced aggregation. Furthermore, the increasing α-helix and decreasing random coil contents benefited the formation of disulfide bonds, further contributing to the enhanced stability of nanoparticles cross-linked by TG, whereas weak hydrophobic interactions and hydrogen bonding as evidenced by the increase in β-sheet and microenvironmental changes were not able to maintain the stability of nanoparticles treated with laccase. Encapsulated cinnamaldehyde presented sustained release from TG-cross-linked nanoparticles, and the bioaccessibility was considerably enhanced to 50.7%. This research developed a novel mild strategy to enhance nanoparticle stability in harsh environments and digestive conditions, which could be an effective delivery vehicle for hydrophobic nutrients and drug applications in food and pharmaceutical industries.

Effect of soybean oil content on textural, rheological, and microstructural properties of WBAXs-SPI emulsion-filled gels

This study aimed to prepare wheat bran arabinoxylans-soy protein isolate (WBAXs-SPI) emulsion-filled gels with different oil contents and investigate their rheological, textural, water-holding capacity (WHC), and microstructural properties. The rheological analysis results showed that the maximum correlation interaction occurs when the soybean oil concentration was 10%, and the elastic modulus (G') reaches the highest value of 13,562 Pa. Interestingly, the WHC and texture change trend of WBAXs-SPI emulsion-filled gel were consistent with rheology. Meanwhile, confocal laser scanning microscopy (CLSM) observation indicated that the emulsion-filled gels formed an interpenetrating polysaccharide-protein complex network system. Therefore, the filling emulsion performance could be adjusted by changing the concentration of oil droplets as the active filler. This provides the possibility of developing new food materials encapsulating fat-soluble substances with a low oil rate and more stable structure.

Recent advances in the structure, synthesis, and applications of natural polymeric hydrogels

Hydrogels, polymeric network materials, are capable of swelling and holding the bulk of water in their three-dimensional structures upon swelling. In recent years, hydrogels have witnessed increased attention in food and biomedical applications. In this paper, the available literature related to the design concepts, types, functionalities, and applications of hydrogels with special emphasis on food applications was reviewed. Hydrogels from natural polymers are preferred over synthetic hydrogels. They are predominantly used in diverse food applications for example in encapsulation, drug delivery, packaging, and more recently for the fabrication of structured foods. Natural polymeric hydrogels offer immense benefits due to their extraordinary biocompatible nature. Hydrogels based on natural/edible polymers, for example, those from polysaccharides and proteins, can serve as prospective alternatives to synthetic polymer-based hydrogels. The utilization of hydrogels has so far been limited, despite their prospects to address various issues in the food industries. More research is needed to develop biomimetic hydrogels, which can imitate the biological characteristics in addition to the physicochemical properties of natural materials for different food applications.

Structural, gelation properties and microstructure of rice glutelin/sugar beet pectin composite gels: Effects of ionic strengths

In this study, the rice glutelin (RG)/sugar beet pectin (SBP) composite gels were prepared by laccase induced cross-linking and subsequent heat treatment, and the effects of different calcium ion concentrations (0-400 mM) on the gelation, structural properties and microstructure of the RG/SBP composite gels were investigated. The results showed that the addition of 200 mM calcium ion could improve the rheological, textural properties and water holding capacity of the RG/SBP composite gels. The addition of SBP and calcium ions enhanced the hydrophobic interaction between RG molecules, thereby increased the gel properties of RG. The changes in Raman spectroscopy reflected the positive effect of the addition of SBP and calcium ions on the formation of a denser and more homogeneous protein gel, as evidenced by the results of scanning electron microscopy. Overall, SBP and calcium ions could be applied to the plant protein gel systems as gel-strengthening agents.

WITHDRAWN: Reinforcing the rheological and mechanical properties of WPI nanocomposite hydrogels with birefringence morphologies

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New insights into food hydrogels with reinforced mechanical properties: A review on innovative strategies

Enhancement on the mechanical properties of hydrogels leads to a wider range of their applications in various fields. Therefore, there has been a great interest recently for developing new strategies to reinforce hydrogels. Moreover, food gels must be edible in terms of both raw materials and production. This paper reviews innovative techniques such as particle/fiber-reinforced hydrogel, double network, dual crosslinking, freeze-thaw cycles, physical conditioning and soaking methods to improve the mechanical properties of hydrogels. Additionally, their fundamental mechanisms, advantages and disadvantages have been discussed. Important biopolymers that have been employed for these strategies and also their potentials in food applications have been summarized. The general mechanism of these strategies is based on increasing the degree of crosslinking between interacting polymers in hydrogels. These links can be formed by adding fillers (oil droplets or fibers in filled gels) or cross-linkers (regarding double network and soaking method) and also by condensation or alignment of the biopolymers (freeze-thaw cycle and physical conditioning) in the gel network. The properties of particle/fiber-reinforced hydrogels extremely depend on the filler, gel matrix and the interaction between them. In freeze-thaw cycles and physical conditioning methods, it is possible to form new links in the gel network without adding any cross-linkers or fillers. It is expected that the utilization of gels will get broader and more varied in food industries by using these strategies.

The functionality of laccase- or peroxidase-treated potato flour: Role of interactions between protein and protein/starch

Potato flour is used in bakery products, extruded products and snacks. However, it displays weaker gel strengths and thus the wholesome utility is curtailed significantly. To improve viscoelastic properties and stability of potato gels, herein potato flour was treated with laccase and peroxidase to create a protein network structure leading to stable gels. The results revealed that the secondary structure of potato proteins altered upon the enzyme treatment. The gels of peroxidase-treated potato flour (PPF) and laccase-treated potato flour (LPF) displayed larger anti-shear ability, thermal stability and stronger three-dimensional network structure compared to the native potato gel. The PPF and LPF gels exhibited stronger viscoelastic properties and structural stability compared to peroxidase-treated potato protein and laccase-treated potato protein gels. The outcome serves as a theoretical basis to improve the properties of potato gels and to promote the designing and the development of novel potato flour based functional food.

Upgrading Grape Pomace through Pleurotus spp. Cultivation for the Production of Enzymes and Fruiting Bodies

Grape pomace, a by-product derived from winery industries, was used as fermentation media for the production of added-value products through the cultivation of two Pleurotus species. Solid-state (SSF), semiliquid (SLF), and submerged (SmF) fermentations were carried out using grape pomace as substrate. The effect of the different fermentations on the consumption of phenolic compounds, the production of mycelial mass and enzymes was evaluated using P. ostreatus and P. pulmonarius. The production of fungal biomass and enzymes was influenced by the fermentation mode. The maximum biomass values of ~0.5 g/g were obtained for both P. pulmonarius and P. ostreatus in SmF. Laccase production was induced in SSF and a maximum activity of 26.247 U/g was determined for P. ostreatus, whereas the highest endoglucanase activity (0.93 U/g) was obtained in the SmF of the same fungi. Analysis of phenolic compounds showed that both strains were able to degrade up to 79% of total phenolic content, regardless the culture conditions. Grape pomace was also evaluated as substrate for mushroom production. P. pulmonarius recorded the highest yield and biological efficiency of 14.4% and 31.4%, respectively. This study showed that mushroom cultivation could upgrade winery by-products towards the production of valuable food products.