Impact of Silicon Addition on the Development of Gelled Pork Lard Emulsions with Controlled Lipid Digestibility for Application as Fat Replacers

Pork lard gelled emulsions stabilized with two proteins [soy protein concentrate (SPC) or a pork rind protein extract (PRP)], both with and without added silicon (Si) from diatomaceous earth powder, were gelled by microbial transglutaminase and к-carrageenan. These gelled emulsions (GEs), intended as fat replacers, were evaluated in different aspects, including microstructure and technological properties during chilling storage. In addition, in vitro gastrointestinal digestion (GID) with an analysis of lipolysis and lipid digestibility was also evaluated. All GEs showed adequate technological properties after 28 days of chilling storage, although the SPC-stabilized GEs showed better gravitational and thermal stability (~4% and ~6%, respectively) during chilling storage than the PRP-stabilized ones (~8 and ~12%, respectively). PRP developed larger flocculates restricting pancreatic lipase-mediated lipolysis during intestinal digestion. The addition of Si to both GE structures protected them against disruption during in vitro digestion. Accordingly, Si appears to slow down fat digestion, as reflected by higher triacylglycerides content after GID (15 and 22% vs. 10 and 18% in GEs without Si) and could become a potential candidate for use in the development of healthier meat products.

Recent Advances in the Study of Wheat Protein and Other Food Components Affecting the Gluten Network and the Properties of Noodles

Upon hydrating and mixing wheat flour, wheat protein forms a network that strongly affects the structure and physicochemical properties of dough, thus affecting the properties of noodles. Different approaches have been taken to alter the gluten network structure in order to control the dough properties. In the current review, we summarize the structure and function of wheat protein, including glutenin and gliadin, and describe food components that may affect noodle quality by interacting with wheat protein. In fact, the ratio of glutenin to gliadin is closely related to the viscosity of dough, and disulfide bonds also contribute to the gluten network formation. Meanwhile, wheat protein coexists with starch and sugar in wheat dough, and thus the nature of starch may highly influence gluten formation as well. Salts, alkali, enzymes and powdered plant food can be added during dough processing to regulate the extensional properties of wheat noodles, obtaining noodles of high quality, with improved sensory and storage properties. This review describes specific methods to reinforce the wheat protein network and provides a reference for improving noodle quality.

Effects of microbial transglutaminase on textural, water distribution, and microstructure of frozen-stored longtail southern cod (Patagonotothen ramsayi) fish mince gel

Frozen-stored fish mince tend to have poor gelling ability due to significant myosin denaturation caused by freezing. In this study, microbial transglutaminase (MTGase) was used to improve the quality of fish mince gel products made from frozen-stored longtail southern cod (LSC). The gel strength of the gel product increased with the addition of MTGase and reached a plateau value of ~19 N mm beyond 300 U/kg of MTGase, at the same condition, T₂₂ was reduced from 57.22 to 49.77 ms, T₂₃ was reduced from 1,273.88 to 1,072.27 ms. As the MTGase addition increased from 0 to 400 U/kg, the hardness of the fish surimi gel increased from 14.52 to 21.36 N, and the microstructure changed from loose to dense, respectively. This study showed that MTGase could promote gelation to improve the quality of frozen-stored LSC fish mince gel, especially at 300 U/kg, which potentially can be utilized to produce good surimi gel products out of frozen-stored fish.

In vitro trypsin digestion and identification of possible cross-linking sites induced by transglutaminase (TGase) of silver carp (Hypophthalmichthys molitrix) surimi gels with different degrees of cross-linking

Surimi gels with different cross-linking degrees (18.52%, 34.67%, 62.87% and 79.11%) were prepared to identify the numbers and locations of lysine residues involved in TGase-induced cross-linking, and to reveal the quantity and location relationships among cross-linking degrees, cross-linking sites and digestion sites by using trypsin digestion, SDS-PAGE and LC-MS/MS methods. The results showed that with the increase in cross-linking degree from 18.52% to 79.11%, 1) the quantity of cross-linking sites gradually increased from 25 sites to 47 sites, 2) the main possible cross-linking domain moved from myosin head to rod, 3) the numbers of digestion sites first decreased from 1262 sites to 1194 sites, and then increased to 1302 sites, 4) the changes in the values of digestion sites were mainly concentrated in myosin rod and it was also the main region of digestion. This study can help exploring the relationship between enzymatic cross-linking and nutritional properties of food.

Preparation of Pickering emulsion gels based on κ-carrageenan and covalent crosslinking with EDC: Gelation mechanism and bioaccessibility of curcumin

Pickering emulsions stabilized by zein/carboxymethyl dextrin nanoparticles were added to the κ-carrageenan-based gel matrix to prepare emulsion gels via EDC - induced covalent crosslinking. Texture, WHC and freeze-thaw stability of the emulsion gels increased after crosslinking. The Confocal laser scanning microscope and SEM suggested that droplet clusters could be observed in gel with higher concentration of emulsion. The rheological measurements indicated that the viscosity and gel-like structure were relied on crosslinking agent and emulsion concentration. The photothermal stability of curcumin was significantly enhanced after crosslinking. In addition, in vitro digestion study suggested that the bioaccessibility of curcumin in emulsion gel crosslinked was lower compared to emulsion gel without crosslinking agent. These studies might facilitate the preparation of emulsion gels with excellent stability for bioactive compounds delivery in food and pharmaceutical applications.

Transglutaminase crosslinking promotes physical and oxidative stability of filled hydrogel particles based on biopolymer phase separation

In the present study, the effect of transglutaminase (TGase) concentration on the physical and oxidative stabilities of filled hydrogel particles created by biopolymer phase separation was investigated. The results showed that filled hydrogels had relatively smaller particle sizes, higher absolute zeta-potentials, higher interfacial layer thicknesses and lightness values with the increasing of TGase concentration (P < 0.05), as evidenced by the apparent viscosity and viscoelasticity behavior. However, the relatively higher TGase concentration promoted the protein aggregation, which weakens the protection of the surface protein layer, having the negatively impacted the physical stability of filled hydrogels. Microstructural images which obtained via cryo-scanning electron microscopy also verified the above results. In particular, it is noted that filled hydrogels displayed the lowest degrees of lipid and protein oxidation during 10 days of storage (P < 0.05) at TGase concentration of 10 U/g. Prevention against oxidation was attributed mainly to TGase crosslinking of protein molecules on the surface of droplets, which likely provided a denser interface around lipid droplets. Our results indicated that TGase was a favourable agent to crosslink protein on the surface of lipid and improve the physical and oxidative stability of filled hydrogel particles.

In Vitro Pepsin Digestion Characteristics of Silver Carp (Hypophthalmichthys molitrix) Surimi Gels with Different Degrees of Cross-Linking Induced by Setting Time and Microbial Transglutaminase

Surimi gels are favored for their abundant proteins and unique taste. In this study, the pepsin digestion behaviors of surimi gels with different degrees of cross-linking induced by microbial transglutaminase (MTGase) and different setting times were investigated. For gels without (CK group) and with (TG group) MTGase, the slowest digestion rate (t_M/2 = 20.13 and 79.19 min for CK and TG group, respectively), the least amino acid concentration (5.32 and 3.73 μmol/mL for CK and TG group, respectively), and the peptide amounts (1355 and 1788 for CK and TG group, respectively) were obtained at a moderate setting time (1-4 h) with the finest microstructure. However, the excessive setting time (8-12 h) formed an inhomogenous network, which accelerated the hydrolysis of gel proteins (t_M/2 = 9.40 and 52.33 min for CK and TG group, respectively) and produced more amino acids (6.63 and 5.15 μmol/mL for CK and TG group, respectively) and peptide amounts (1644 and 2143 for CK and TG group, respectively). The above results also demonstrated that the presence of MTGase strengthened the compactness of gels as well as slowed down the digestion process with the release of less amino acids but more peptides. A large proportion of unique peptides were from the tail domain of myosin heavy chain. The discrepancy in bioactive peptides between different gels might be reduced in the subsequent intestinal digestion according to the in silico methods, demonstrating the diminished difference in the gastrointestinal digestion process in the aspect of releasing functional peptides. This study provides the theoretical basis and guideline in the field of gelation food digestion and surimi food industry to produce healthier surimi-based food.

Current insight and futuristic vistas of microbial transglutaminase in nutraceutical industry

Microbial transglutaminase (MTGase) has become a driving force in the food industry cross-linking the food proteins. MTGase-the nature's molecular glue is recognized to reorient food protein's functional properties without affecting its nutritive value. The scope and approach of this review is to have insight on the action mechanism of MTGase and impact of molecular linkage on functional proteins in various protein moieties in development of innovative features in food production for better consumer's choice and satisfaction. The study covers a wide range of published work across food industries involving innovative use of MTGase, an environment friendly production approach for commercial utilization to get better outcome in terms of culinary delight. The intrinsic biochemical properties and structural information by sequence analysis and clustering validates the mode of reaction mechanism of the biological glue enzyme. The review singles out how the MTGase emerged as a prime choice in ever evolving food industry.

Characterization of a cold-active transglutaminase from a crayfish, Pacifastacus leniusculus

Transglutaminase (TGase) from signal crayfish (Pacifastacus leniusculus) and its activity at low temperatures was studied. TGase is an abundant protein in the hematopoietic (HPT) cells and this tissue was used for TGase enzyme preparation. The optimal temperature and pH for the activity of crayfish TGase were determined. We found that TGase activity at 4 °C showed nearly the same activity as at a temperature of 22 °C. TGase activity from crayfish was compared with guinea pig liver TGase activity at 4 °C and the crayfish TGase displayed a higher activity while guinea pig liver TGase had a very low activity at this low temperature. By comparing kinetic parameters to guinea pig liver TGase, the results showed that a high activity of crayfish TGase was due to a decreasing K_m value for pentylamine as a substrate, while it did not affect the k_cat value (at 22 °C). The amino acid sequences of a krill and a crayfish TGase, which both are cold adapted, do not give any clue to why these two enzymes are cold-adapted. These results demonstrate that crayfish TGase is adapted to have significant activity at low temperatures and since crayfish are living in quite cold waters this is an interesting adaptation of this enzyme.

Stability and digestibility of one- or bi-layered medium-chain triglyceride emulsions with gum Arabic and whey protein isolates by pancreatic lipase in vitro

Interfacial engineering approaches have been used to design functional foods so as to control lipase-induced digestion of emulsified lipids and release of bioactive lipophilic components in the gastrointestinal tract. In this study, emulsion droplets with the interface stabilized with gum Arabic (GA) and whey protein isolate (WPI) were prepared by mixing or sequential adsorption. WPI/GA intramolecular soluble complexes (ISCs) have superior emulsifying properties in stabilizing oil-in-water emulsions. The impact of the interfaces for WPI/GA ISC-layered (one-layered) and double-layered emulsions formed by sequential deposition of WPI or GA on the lipolysis of emulsions was investigated using an in vitro simulated gastrointestinal model. Transglutaminase and dithiothreitol were introduced to crosslink the interfacial proteins and improve the interfacial stability. The ISC-layered emulsion was less stable to aggregation than the double-layered ones in simulated gastric fluid due to dissociation of ISCs caused by the electrostatic screening of ions and proteolysis of interfacial proteins driven by pepsin. The ISC-layered emulsion conferred a significant slower rate and extent of lipid digestion compared to the double-layered emulsions post gastric proteolysis (P < 0.05). It is presumed for the ISC-layered emulsion that the destabilization to aggregation and coalescence within the simulated gastrointestinal fluids and the steric hindrance of the robust and thick interfacial layer might contribute to delaying free fatty acids release. It suggests that both the initial interfacial properties and the stability of the emulsified lipid droplets within the simulated gastrointestinal fluids play an important role in determining the rate and extent of lipid digestion. It is predicted that direct destabilization of emulsified lipids using interfacial engineering approaches has the potential of modifying lipid digestibility or bioactive release at specific sites within the gastrointestinal tract.

Yield and Textural Characteristics of Panela Cheeses Produced with Dairy-Vegetable Protein (Soybean or Peanut) Blends Supplemented with Transglutaminase

The study evaluated panela cheeses made from dairy-plant protein blends, using soybean or peanut protein isolates, supplemented with transglutaminase (TG). Plant proteins were isolated using an alkaline extraction method followed by acid precipitation, and added to the dairy system in order to increase 50% or 100% the protein concentration. The total protein extraction for peanut and soybean isolates was 30.3% and 54.6%, respectively (based on initial protein content of sources), and no impairment of their essential amino acid profile was detected. Cheeses supplemented with TG and soybean showed the highest moisture and crude yield (>67.8% and 20.7%, respectively), whereas protein content was higher in the peanut isolate--added samples without TG (>67.4%). Cheese solids yield (ratio between final and initial solids) was higher for treatments with TG and 100% of plant protein addition (>50.7%). Regarding texture, 4 parameters were measured: hardness, cohesiveness, chewiness, and springiness. All cheeses containing soybean isolates and TG presented the highest chewiness and cohesiveness values, similar to those of the control treatment. Springiness was similar for all treatments, but hardness was higher in cheeses prepared with the peanut protein isolate added with TG. From these results it can be concluded that panela cheeses can be elaborated following a traditional procedure, but with the addition of soybean or peanut protein to the dairy ingredients. Cheeses containing these protein isolates showed higher protein than the milk control cheese and similar textural characteristics.

Preparation and Properties of Gelatin-Immobilized β-Glucosidase fromPyrococcus furiosus

Hyperthermostable beta-glucosidase from Pyrococcus furiosus was enclosed in gelatin gel by cross-linking with transglutaminase. Gelatin-immobilized beta-glucosidase was considerably more thermostable than the native enzyme. Lyophilized immobilisate was stored at 90 degrees C for 1 month without loss of activity. The immobilized beta-glucosidase catalyzed transglucosylation of 5-phenylpentanol with 10.0 equivalent of cellobiose at pH 5.0 and 70 degrees C for 12 h to afford 5-phenylpentyl beta-D-glucopyranoside in 41% yield. The immobilized enzyme was more effective than the native one in transglucosylation. The gelatin-immobilized Pfu-beta-glucosidase recovered from the first run of the reaction was reusable on successive runs.

Saliva from obese individuals suppresses the release of aroma compounds from wine

Background

Recent evidence suggests that a lower extent of the retronasal aroma release correspond to a higher amount of ad libitum food intake. This has been regarded as one of the bases of behavioral choices towards food consumption in obese people. In this pilot study we investigated the hypothesis that saliva from obese individuals could be responsible for an alteration of the retro-nasal aroma release. We tested this hypothesis in vitro, by comparing the release of volatiles from a liquid food matrix (wine) after its interaction with saliva from 28 obese (O) and 28 normal-weight (N) individuals.

Methods and Findings

Amplicon sequencing of the 16S rRNA V4 region indicated that Firmicutes and Actinobacteria were more abundant in O, while Proteobacteria and Fusobacteria dominated in N. Streptococcaceae were significantly more abundant in the O subjects and constituted 34% and 19% on average of the saliva microbiota of O and N subjects, respectively. The Total Antioxidant Capacity was higher in O vs N saliva samples. A model mouth system was used to test whether the in-mouth wine aroma release differs after the interaction with O or N saliva. In O samples, a 18% to 60% significant decrease in the mean concentration of wine volatiles was detected as a result of interaction with saliva, compared with N. This suppression was linked to biochemical differences in O and N saliva composition, which include protein content.

Conclusion

Microbiological and biochemical differences were found in O vs N saliva samples. An impaired retronasal aroma release from white wine was detected in vitro and linked to compositional differences between saliva from obese and normal-weight subjects. Additional in vivo investigations on diverse food matrices could contribute to understanding whether a lower olfactory stimulation due to saliva composition can be a co-factor in the development/maintenance of obesity.

Enzyme-catalyzed protein crosslinking

The process of protein crosslinking comprises the chemical, enzymatic, or chemoenzymatic formation of new covalent bonds between polypeptides. This allows (1) the site-directed coupling of proteins with distinct properties and (2) the de novo assembly of polymeric protein networks. Transferases, hydrolases, and oxidoreductases can be employed as catalysts for the synthesis of crosslinked proteins, thereby complementing chemical crosslinking strategies. Here, we review enzymatic approaches that are used for protein crosslinking at the industrial level or have shown promising potential in investigations on the lab-scale. We illustrate the underlying mechanisms of crosslink formation and point out the roles of the enzymes in their natural environments. Additionally, we discuss advantages and drawbacks of the enzyme-based crosslinking strategies and their potential for different applications.

Nutritional Effects of Mechanically Deboned Chicken Meat and Soybean Proteins Cross-linking by Microbial Transglutaminase

This work studied the nutritional effects of protein cross-linking as mediated by microbial transglutaminase (TGase) using rats as biological models. Rats were divided into six groups that received diets containing casein (standard protein diet), cross-linked meat protein (CMP), meat protein (MP), cross-linked soy protein, or soy protein (SP) as the protein sources of their diets, which were compared against an aproteic diet (basal diet). The cross-linking process showed a significant (p < 0.05) impact on the true digestibility (TD) of meat and SPs, decreasing it for the first and increasing it for the second. As a consequence, the TD of modified SP became similar to that observed for CMP, although, the biological value, net protein utilization, net protein ratio, and protein retention efficiency values of meat and SPs were not affected in the process. These results suggest that the use of TGase for the reticulation of isolated SP can improve its nutritional quality.

Identification and quantification of epsilon-(gamma-glutamyl)lysine in digests of enzymatically cross-linked leguminous proteins by high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS)

A rapid and convenient method for the precise quantification of epsilon-(gamma-glutamyl)lysine isopeptide in lyophilized proteolytic digests of cross-linked plant protein samples was developed. The isopeptide was baseline-separated from three other isomers containing lysyl and glutamyl residues by reverse-phase high-performance liquid chromatography after exhaustive proteolytic digestion of the samples cross-linked by a microbial transglutaminase (MTG). Highly selective detection was performed by electrospray mass spectrometry in MS/MS mode. Demonstrating the applicability of the suggested analytical procedure, enzymatic cross-linking of protein isolates from soy [Glycine max (L.) Merr.], pea [Pisum sativum L.], and the sweet lupin species Lupinus albus L. and Lupinus angustifolius L. was investigated after incubation with 0.01 g of MTG/100 g of protein for 0-240 min at 40 degrees C. The liquid chromatography-mass spectrometry (LC-MS) method was successfully applied to monitor the kinetics of epsilon-(gamma-glutamyl)lysine isopeptide formation. Since the calculated initial levels of epsilon-(gamma-glutamyl)lysine in the genuine leguminous protein isolates were between 40 and 77 micromol/100 g, an isopeptide detection limit of 0.5 microg/mL, corresponding to approximately 50 micromol/100 g of protein, was shown to suffice for quantifying the cross-linking rate enzymatically induced by MTG. Concentrations of epsilon-(gamma-glutamyl)lysine in the texturized proteins ranged from 100 to 500 micromol/100 g of protein.

Effect of technological processing on the allergenicity of mangoes (Mangifera indica L.)

In parallel with the rising popularity of exotic fruits in Europe, allergy against mango is of increasing importance. Because mangoes are also consumed as processed products such as chutneys or beverages, the influences of different process conditions on their allergenicity were investigated. Mango purees and nectars were manufactured at small pilot-plant scale, and the allergenic potencies of the resulting intermediate and final products were determined by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting and inhibitive enzyme allergosorbent tests (EAST-inhibition), using a pool serum of 9 individuals with manifest mango allergy. The mango allergens were shown to be very stable during technological processing. Irrespective of enzymatic matrix decomposition, mechanical tissue disintegration and heating during peeling, mash treatment, and pasteurization, significant loss of allergenicity could not be observed in the extracts of mango purees and nectars derived thereof. These results were confirmed by analogous investigation of commercial mango drinks and nectars. Hence, conventional mango processing into pulp-containing products typical for this species obviously does not allow complete elimination of the allergenic potency.