Comparative analysis of exopolysaccharide-producing Lactiplantibacillus plantarum with ropy and non-ropy phenotypes on the gel properties and protein conformation of fermented milk.

In this study, we evaluated the impact of Lactiplantibacillus plantarum (L. plantarum) with ropy and non-ropy phenotypes on gel structure and protein conformation of fermented milk. Ropy L. plantarum (T1 & CL80) secreted EPS with high molecular weight (1.41 × 106, 1.19 × 106 Da) and intrinsic viscosity (486.46, 316.32 mL/g), effectively enhances fermented milk viscosity and water holding capacity (WHC) (65.4%, 84.6%) by forming a dense gel structure. Non-ropy L. plantarum (CSK & S-1A) fermented milk gel's high surface hydrophobicity and free sulfhydryl content caused high hardness and low WHC. Raman spectroscopy combined with circular dichroism analysis showed that high levels of α-helix (29.32-30.31%) and random roil (23.06-25.36%) protein structures are the intrinsic factors that contribute to the difference among fermented milk gels of ropy and non-ropy strains. This study provides a basis for understanding the structural variability of fermented milk gels using ropy or non-ropy lactic acid bacteria.

Structural characteristics and gel properties of pectin from citrus physiological premature fruit drop.

This study is the first to extract and characterize pectin from citrus physiological premature fruit drop. The extraction yield of pectin reached 4.4 % by acid hydrolysis method. The degree of methoxy-esterification (DM) of citrus physiological premature fruit drop pectin (CPDP) was 15.27 %, indicating it was low-methoxylated pectin (LMP). The monosaccharide composition and molar mass test results showed CPDP was a highly branched macromolecular polysaccharide (ß: 0.02, Mw: 2.006 × 105 g/mol) with rich rhamnogalacturonan I domain (50.40 %) and long arabinose and galactose side chain (32.02 %). Based on the fact that CPDP is LMP, Ca2+ was used to induce CPDP to form gels. Textural and rheological tests showed that the gel strength and storage modulus of CPDP were higher than commercial citrus pectin (CP) used in this paper due to the lower DM and rich neutral sugar side chains of CPDP. Scanning electron microscope (SEM) results showed CPDP had stable gel network structure.

Exploration of proper heating protocol for injectable horizontal platelet-rich fibrin gel.

PURPOSE: Platelet-rich fibrin (PRF) has been proposed as promising biomaterials with the advantages of host accumulation of platelets and leukocytes with entrapment of growth factors and fibrin scaffold. However, limitations including fast resorption rate (~ 2 weeks) restricts its clinical application. Recent studies have demonstrated heating treatment can prolong PRF degradation. Current published articles used the method of 75 °C for 10 min to obtain longer degradation, while few studies investigated the most suitable temperature for heating horizontal PRF. Our present study was to discover and confirm the optimum temperature for heat treatment before obtaining H-PRF gels by investigating their structure, mechanical properties, and bioactivity of the H-PRF gels after heating treatment. METHODS: In the present study, 2-mL upper layer of horizontal PRF was collected and heated at 45 °C, 60 °C, 75 °C, and 90 °C to heat 2-mL upper layer of horizontal PRF for 10 min before mixing with the 2-mL lower layer horizontal PRF. The weight, solidification time and the degradation properties were subsequently recorded. Scanning electron microscopy (SEM) and rheologic tests were carried out to investigate the microstructure and rheologic properties of each H-PRF gel. The biological activity of each H-PRF gel was also evaluated using live/dead staining. RESULTS: H-PRF gel prepared at 75 °C for 10 min had the fast solidification period (over a tenfold increase than control) as well as the best resistance to degradation. The number of living cells in H-PRF gel is greater than 90%. SEM showed that H-PRF gel becomes denser as the heating temperature increases, and rheologic tests also revealed that the heat treatment improved the mechanical properties of H-PRF gels when compared to non-heated control group. Future clinical studies are needed to further support the clinical application of H-PRF gels in tissue regeneration procedures. CONCLUSIONS: Our results demonstrated that the H-PRF gel obtained at 75 °C for 10 min could produce a uniform, moldable gel with a short time for solidification time, great rheologic behavior and, high percent of live cells in PRF gel. A promising use of the commonly utilized PRF gel was achieved facilitating tissue regeneration and preventing degradation.

A mathematical model for cell-induced gel contraction incorporating osmotic effects.

Biological tissues are composed of cells surrounded by the extracellular matrix (ECM). The ECM can be thought of as a fibrous polymer network, acting as a natural scaffolding to provide mechanical support to the cells. Reciprocal mechanical and chemical interactions between the cells and the ECM are crucial in regulating the development of tissues and maintaining their functionality. Hence, to maintain in vivo-like behaviour when cells are cultured in vitro, they are often seeded in a gel, which aims to mimic the ECM. In this paper, we present a mathematical model that incorporates cell-gel interactions together with osmotic pressure to study the mechanical behaviour of biological gels. In particular, we consider an experiment where cells are seeded within a gel, which gradually compacts due to forces exerted on it by the cells. Adopting a one-dimensional Cartesian geometry for simplicity, we use a combination of analytical techniques and numerical simulations to investigate how cell traction forces interact with osmotic effects (which can lead to either gel swelling or contraction depending on the gel's composition). Our results show that a number of qualitatively different behaviours are possible, depending on the composition of the gel (i.e. its chemical potentials) and the strength of the cell traction forces. A novel prediction of our model is that there are cases where the gel oscillates between swelling and contraction; to our knowledge, this behaviour has not been reported in experiments. We also consider how physical parameters like drag and viscosity affect the manner in which the gel evolves.

Health Risk Assessment of Heavy Metals (Pb, Cd, Hg) in Hydroalcoholic Gels of Abidjan, Côte d'Ivoire.

Despite the high consumption of hydroalcoholic gels worldwide and particularly in Côte d'Ivoire since the outbreak of the COVID-19 pandemic, very few studies have measured the heavy metal content and human exposure in this product. Thus, 30 samples from supermarkets in Abidjan, Côte d'Ivoire, were collected for the study of risk assessment of exposure to heavy metals contained in hydroalcoholic gels. This study consists of the characterization of the danger by calculating the carcinogenic and non-carcinogenic risk by skin contact. Almost all samples analysed contain trace of lead, cadmium and mercury but at concentrations below the Canadian limit in cosmetic products applied to the skin and below the US FDA limit as an impurity in colour additives used in cosmetic products. The mean values of chronic daily intake via dermal absorption (CDIdermal) for adults were found in the order of mercury > lead > cadmium. The health risk estimation indicated that the mean total hazard quotient for dermal adsorption (HIdermal) obtained is 7.10 × 10-5 ± 5.52 × 10-5. This value was below 1, the acceptable limit, representing a non-carcinogenic risk for Abidjan residents through dermal adsorption. Moreover, the incremental lifetime cancer risk (ILCR) evaluation for lead and cadmium was insignificant, and the cancer risk can be neglected, but in case of their overusing, they can cause long-term health problems for consumers.

NMR spectral fingerprint patterns as diagnostics for the unambiguous configurational analysis of the classic organo-gelator 1,3:2,4-dibenzylidene-d-sorbitol (DBS) and its derivatives.

On the basis of experimental data and density functional theory (DFT) chemical shift and scalar coupling predictions, simple spectral nuclear magnetic resonance (NMR) fingerprint patterns have been established for the determination of the configuration in 1,3:2,4-dibenzylidene-d-sorbitol (DBS), a classic low molecular weight gelator, and its derivatives. The results rigorously prove the orientation of the phenyl rings in DBS that had been previously assumed in the literature on the basis of thermodynamic arguments.

Using inulin-based emulsion gels as fat substitute in salt reduced Bologna sausage.

BACKGROUND: A high-fiber emulsion gel (EG) containing inulin, soy protein isolate, and soybean oil was applied as animal fat replacer in reduced salt and fat Bologna sausage containing mechanically deboned chicken meat, pork meat, and pork back fat. Technological and microbiological properties were evaluated for 60 days at 4 °C. RESULTS: A reduction of 11 to 34% and 35 to 45% of fat and sodium were obtained in reformulated products, respectively. An increase in fiber content and polyunsaturated fatty acid was noticed in the formulations with EG. The addition of EG in Bologna increased L* (lightness) values and reduced a* (redness/greenness) values comparing to control treatment. Microstructural properties of sausages exhibited a denser network with the presence of EG. Softer, more elastic, cohesive and resilient samples with a higher intensity of lipid oxidation (P < 0.05) were observed in EG added sausages. The nuclear magnetic resonance (NMR) data shows that the presence of EG recovers the matrix that has been weakened due to reduction of fat and salt. Sensory evaluation showed that the incorporation of the EGs resulted in acceptable scores. CONCLUSION: These results suggest that inulin-based EG is a potential fat substitute for developing healthier meat products, with better fatty acids composition and stable to chilled storage. © 2020 Society of Chemical Industry.

Effect of laver powder on textual, rheological properties and water distribution of squid (Dosidicus gigas) surimi gel.

In order to ameliorate the gel quality of Dosidicus gigas surimi, the effects of laver powder on gel properties, rheological properties, and water-holding capacity (WHC) were investigated. Results indicated that the addition of laver powder could significantly increase the hardness, chewiness, and breaking force of surimi gels. However, the texture indexes and gel strength began to decline when additional amount exceeded 0.6%. Rheological results demonstrated that the addition of laver powder increased the storage modulus (G') and viscosity of surimi, prolonged protein denaturation temperature in surimi gels. Moreover, the WHC of surimi gel was improved with the increase of laver powder. Further analyses in low-field nuclear magnetic resonance revealed that laver powder could shorten the transverse relaxation time, enhanced the combination with water, and altered the distribution of different water categories. The proportion of bound water and immobilized water reached its maximum and minimum at 0.6% of laver powder, respectively. Correlation analyses showed that WHC of surimi gel was negatively correlated well with the proportion of loose-bound water, but positively correlated with the strong-bound water and free water. In conclusion, the results supported that 0.6% was the optimal additional amount of laver powder for the squid-based surimi production based on the current ingredients of surimi products.

Characteristic and shelf life of fish sausage: fortification with fish oil through emulsion and gelled emulsion incorporated with green tea extract.

BACKGROUND: Silver carp (Hypophthalmichthys moltrix) fish sausages incorporated with three forms of refined cod liver oil (as a source of polyunsaturated fatty acids: fish oil, oil-in-water emulsion (E), gelled oil-in-water emulsion (G)) and lyophilized aqueous extract of green tea (Camellia sinensis; 700 and 900 mg kg-1 ) were developed. The composition, technological properties (cooking loss, pH, texture, and color), sensory analysis, and microbial and oxidative stability of fish sausages during storage (4 °C) were evaluated. RESULTS: Lower value of cooking loss and thiobarbituric acid value were observed by addition of fish oil in emulsions forms. The incorporation of green tea showed no significant differences in preventing oxidation in related samples. Gelled-emulsified fish oil had better textural properties, including hardness and decreased springiness of the sausages. The G and E sausages showed higher values of lightness (L* ) than the control did. Emulsification had no significant effect on total viable count. Panelists could not distinguish between samples incorporated with fish oil whether in emulsified, gelled-emulsified, or control. Gelled-emulsified treatments were awarded higher scores by panelists for all of the sensory attributes (P < 0.05). Eicosapentaenoic acid and docosahexaenoic acid quantities significantly increased from control (0.48 mg g-1 and 0.46 mg g-1 sample respectively) to the enriched batches (>1.50 mg g-1 sample). The lowest ratio of ω6 to ω3 in batches was observed for gelled-emulsified samples. CONCLUSION: Overall, the addition of free fish oil affected the properties of the sausages. The gelled-emulsified treatment was a suitable fish oil delivery system in fish sausages, which maintained sensory properties during refrigerated storage.

Changes in the physicochemical properties and starch structures of rice grains upon pre-harvest sprouting.

In rice production, pre-harvest sprouting (PHS) of late ripening seeds is one of the most serious quality defects in rice grain quality. In the present study, PHS impact was investigated by examining the physicochemical properties, eating and cooking quality (ECQ) of rice grain. Four rice cultivars suffering from PHS had impaired ECQ, reduced apparent amylose content, and decreased total starch content, with an increase in total protein content. The viscosity of flours and starches prepared from the PHS grains was significantly reduced. Starch molecular structure analysis also showed remarkable decreases in the short chains of amylopectin, long amylose chains and reduced starch crystallinity of the PHS grains. Moreover, the PHS native starch tended to have low starch digestibility. This provides useful information for understanding the effects of PHS on white rice grain quality as well as on starch fine structure and its physicochemical properties.

Development of healthy gummy jellies containing honey and propolis.

BACKGROUND: The objective of this work was to develop gummy jellies containing honey and propolis, keeping the natural antioxidant principles of the beehive ingredients and satisfying consumer requirements. RESULTS: A gummy jelly containing honey and propolis (HPGJ) was developed. A sensory study with consumers (n = 74) performed an intensity level evaluation test analyzing color, hardness, adhesiveness, gumminess, sweet taste and honey taste. A penalty analysis indicated that HPGJ was too hard. However, in the global acceptance study, more than 90% of consumers gave liking categories. Regarding the potential functional properties, the antioxidant capacity (AC) of HPGJ was 8.17 ± 0.55 mmol Trolox equivalent kg-1 , and up to 40% AC was retained after in vitro digestion. Additionally, AC of HPGJ was up to ten times higher than that of similar commercial products. A storage study at 25 °C showed that color and AC increased significantly over 90 days owing to the development of Maillard reaction. Storage under darkness allowed keeping low values of global color change for up to 45 days. Another positive facet was that the addition of propolis delayed fungal growth during storage. CONCLUSION: An organoleptically palatable gummy jelly was obtained. Among the positive features, it showed higher AC than similar commercial candies. Additionally, HPGJ offered a high bioaccesible AC input detected upon in vitro digestion. Overall, HPGJ could be considered an interesting, appetizing and healthier alternative to regular gummy jellies available in the market. Adequate packaging should be considered in order to extend HPGJ shelf life, reducing browning reactions. © 2019 Society of Chemical Industry.

Effects of transdermal administration of testosterone gel on the urinary steroid profile in hypogonadal men: Implications in antidoping analysis.

Testosterone is one of the most abused pseudo-endogenous anabolic steroids in sport doping. The current method adopted to detect the abuse of testosterone and other pseudo-endogenous steroids (endogenous steroids when administered exogenously) is first based on the longitudinal monitoring of several urinary biomarkers, which constitute the so called "steroidal module" of the Athlete Biological Passport (ABP): atypical samples undergo a confirmation analysis based on the measurement of the 13C/12C isotopic ratio of selected target compounds, to distinguish their endogenous or exogenous origin. At the same time, testosterone administration can be allowed in athletes diagnosed with hypogonadism, provided they are granted a therapeutic use exemption by the relevant medical authority. In this pilot study we have investigated whether the approach based on the preliminary determination of the urinary steroid profile, in the format considered in the steroidal module of the ABP, also integrated with the inclusion of the sulfo-conjugates and of additional target steroids, can retain its validity also in the case of hypogonadal athletes. We have studied the effects of a single low dose (40 mg) of testosterone gel (T-gel) on the urinary concentration of the markers of steroidal module of the ABP, as well as on some additional steroid markers. The study was based on the analysis of urinary samples from 19 non-hospitalized hypogonadal men, 10 of them with late-onset hypogonadism (LOH), collected before, after 4 h and after 24 h the transdermal self-administration of 40 mg of T-gel. None of the patient had any co-morbidities possibly affecting the urinary excretion of the steroidal markers. The steroidal markers were quantified by gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) after the enzymatic hydrolysis of the respective glucuro-conjugates and the chemical hydrolysis of the respective sulfo-conjugates. Targeted GC-MS/MS analysis was carried out operating in electron impact (EI) ionization mode, with acquisition in multiple reaction monitoring (MRM) mode. Our preliminary results show that, as expected, the treatment with T-gel leads, in all hypogonadal men, to an increase of the urinary concentration of the glucuro-conjugate metabolites of testosterone and its main metabolites, with special relevance to those with 5α-reduction. Furthermore, samples collected from non-LOH hypogonadal men showed an increase also in the levels of epitestosterone glucuronide, testosterone sulfate and epitestosterone sulfate. Apart from their biochemical and pharmacological relevance, these outcomes could be leveraged to refine the analytical strategy currently followed in the antidoping field for the analysis of the urinary steroidal markers, with potential implications also in other forensic and/or clinical investigations.

In vitro assessment of stiffness-dependent histotripsy bubble cloud activity in gel phantoms and blood clots.

As a bubble-based ablative therapy, the efficacy of histotripsy has been demonstrated in healthy or acutely diseased models. Chronic conditions associated with stiff tissues may require additional bubble activity prior to histotripsy liquefaction. In this study, histotripsy pulses were generated in agarose phantoms of Young's moduli ranging from 12.3 to 142 kPa, and in vitro clot models with mild and strong platelet-activated retraction. Bubble cloud emissions were tracked with passive cavitation imaging, and the threshold acoustic power associated with phantom liquefaction was extracted with receiver operator characteristic analysis. The power of histotripsy-generated emissions and the degree of liquefaction were tabulated for both clot models. For the agarose phantoms, the acoustic power associated with liquefaction increased with Young's modulus. When grouped based on agarose concentration, only two arms displayed a significant difference in the liquefaction threshold acoustic power (22.1 kPa versus 142 kPa Young's modulus). The bubble cloud dynamics tracked with passive cavitation imaging indicated no strong changes in the bubble dynamics based on the phantom stiffness. For identical histotripsy exposure, the power of acoustic emissions and degree of clot lysis did not vary based on the clot model. Overall, these results indicate that a fixed threshold acoustic power mapped with passive cavitation imaging can be utilized for predicting histotripsy liquefaction over a wide range of tissue stiffness.

Heat-induced gelation of mixtures of micellar caseins and plant proteins in aqueous solution.

The aim of this work was to investigate how the heat-induced gelation of micellar casein (MC)-plant protein mixtures in aqueous solution is affected by protein composition (MC/plant proteins = 100/0 to 0/100) and total protein content (4%, 6% and 8% w/w) at pH 5.8 and 6.0. Two types of plant proteins were used: soy proteins (SP) and pea proteins (PP). Storage moduli (G') were measured during heating ramps from 20 to 90 °C and heat-induced gelation was characterised by a sharp increase in G' at a critical temperature (Tc). The gel stiffness (Gel) was determined after 1 h at 90 °C and the microstructure before and after heating was investigated by confocal laser scanning microscopy (CLSM). Tc was found to increase with increasing the fraction of MC replaced by SP or PP, due to binding of calcium to the plant proteins. The effect was stronger for SP, which bound calcium more efficiently than PP. Tc decreased with decreasing pH, possibly caused by decreased electrostatic repulsion and increased calcium release from MC. Gel increased with increasing total protein content and did not depend significantly on the pH. Interestingly, Gel showed a minimum as a function of the plant protein fraction (40% for SP and 70% for PP) in the mixtures. It is concluded that MC and plant proteins did not co-aggregate in the mixtures during heating, and that each type of protein formed networks independently.

Development of hydrophilic gels containing coenzyme Q10-loaded liposomes: characterization, stability and rheology measurements.

OBJECTIVE: The aim of this study was to develop, characterize and evaluate stability of a gel containing coenzyme Q10 (Q10)-loaded liposomes, and enhance the stability of Q10 in the nanocarrier-containing gel compared to the conventional gel. METHODS: Q10-loaded liposome dispersions prepared from unsaturated or saturated lecithin, were characterized for particle size, polydispersity index (PDI), zeta-potential, pH value, oxidation index, Q10-content and morphology, and incorporated into carbomer gel. Liposome gels and liposome-free gel were analyzed for flow properties, pH values, Q10-content, and liposomes size and PDI (liposome gels), 48 h after preparation and in predetermined time intervals during 6 months storage at different temperatures in order to predict their long term stability. RESULTS: Liposomes were of small particle size, homogeneous, negatively charged, and their incorporation into gel did not significantly change (p > .05) their particle size and PDI. All gels revealed non-Newtonian, shear-thinning plastic flow behavior during storage with no marked changes in rheological parameters. Storage of gels did not significantly influence the pH value (p > .05), while it significantly decreased Q10-content (p < .05). Q10 was significantly more (p < .05) stable in liposome gel containing unsaturated lecithin liposomes (G1) than in gel containing saturated lecithin liposomes (G2) and liposome-free gel (G3). CONCLUSIONS: Q10-loaded liposome gel G1 was the optimal formulation, since during storage at different temperatures, it did not show significant increase in liposome size and PDI, it provided significantly higher stability for Q10 than other gels and its pH value was suitable for skin application. Due to limited Q10-stability it should be stored at 4 °C.

Physiochemical properties and tastes of gels from Japanese Spanish mackerel (Scomberomorus niphonius) surimi by different washing processes.

The study investigated the properties of gels from Japanese Spanish mackerel (Scomberomorus niphonius) (JSM) surimi received conventional washing (CW) or alkaline-saline washing (AW) and un-washing (UW). AW gel exhibited the highest breaking force and deformation as well as water-holding capacity, but CW gel only had higher breaking force than UW gel. Low-field NMR analysis showed that peak P22 in AW gel was shifted to higher relaxation time and the areas of peak P21 and P22 in AW gel were higher than those in UW and CW gels. Compared with UW gel, network structure of AW gel was more continuous with many tiny voids, but CW gel microstructure showed partially uneven area with large voids. SDS-PAGE showed that band intensity of myosin heavy chain attenuated more in AW gel than in UW and CW gels in nonreducing electrophoresis and it recovered more pronounced in reducing electrophoresis. Solubility attributed to hydrophobic interaction, hydrogen and disulfide bonds increased in CW and AW gels. AW gel gave stronger bitterness and aftertaste A while CW gel showed heavier sourness, astringency, and aftertaste B than UW gel. Results suggest that AW improved physiochemical properties of gel and preserved a closer taste pattern to UW gel. It is recommended for JSM surimi producing. PRACTICAL APPLICATIONS: Surimi food has great potential due to its convenience, elasticity, and nutritional value. Japanese Spanish mackerel (JSM), a popular fish species in China, is widely used for producing surimi food, such as fish ball, dumpling, and sausage. Washing is a practical way to improve its gel properties. This study investigated the gel strength, water status, protein pattern, molecular interactions, microstructure, color, and taste of gels from JSM surimi received conventional washing or alkaline-saline washing and un-washing. Some practical information of effects of washing on gel properties was obtained. These results provide supports to the gel properties improvement by appropriate washing for JSM.

Effects of cornstarch on the gel properties of black bean protein isolate.

The effects of common starch (CS) and high amylopectin starch (HAS) from corn on the properties of heat induced black bean protein isolate (BBPI) gels prepared by heating at 95°C for 30 min were investigated by using dynamic oscillatory rheometer, texture analyzer, and scanning electron microscopy (SEM). Compared with BBPI alone, the presence of cornstarch (1-4%, wt/vol) could improve storage modulus (G') and textural properties of BBPI (10%, wt/vol) gels. The mixed system of BBPI and 4% (wt/vol) HAS exhibited the highest G' and formed the gel faster and more easily, which resulted in firmer and more elastic gel than BBPI-CS at all starch concentrations. It was possible that HAS had lower pasting temperature and higher viscosity than CS, which was beneficial to the formation of BBPI gel network and strengthened the stability of network structure. Moreover, it might also be related to the synergistic effect between protein and starch. The CS and HAS existed in the BBPI gel network could bind water, leading to the increase in the water-holding capacity (WHC) of mixed gels, especially 4% (wt/vol) HAS, which was related to homogeneous and compact microstructure with small pores.

Gelling properties of duck albumen powder as affected by desugarization and drying conditions.

The effects of desugarization using glucose oxidase/catalase and spray-drying conditions on gelling properties of duck albumen powder were studied. Gelling temperatures increased as spray-drying inlet temperatures (140-180C) were increased (p < .05). ΔE*, a*-, and b*- values of gel increased but L* and whiteness decreased when higher spray-drying temperatures were used (p < .05). However, whiteness and lightness of albumen gel were drastically increased after desugarization (p < .05). Texture profile analysis showed that hardness, springiness, gumminess, and chewiness of gel decreased with increasing spray-drying temperatures. Moreover, gel of freeze-dried desugarized albumen powder had higher hardness, springiness, gumminess, and chewiness than that of spray-dried nondesugarized counterpart (p < .05). Albumen gel prepared from desugarized albumen powder showed the compact network with more connectivity and smaller voids than that from nondesugarized one as visualized by scanning electron microscopy, regardless of drying conditions. Prior desugarization could lower browning and increased gelling properties of duck albumen powder. Higher spray drying inlet temperature generally exhibited the adverse effect on properties of resulting albumen powder. Both desugarization and drying conditions had the profound influence on characteristics and textural property of duck egg albumen.

Destabilization of UHT milk by protease AprX from Pseudomonas fluorescens and plasmin.

Destabilization of UHT milk during its shelf life is mainly promoted by the residual proteolytic activity attributed to the psychrotrophic bacterial proteases and native milk proteases. In this study, we built skim UHT milk-based model systems to which either the major bacterial protease (AprX from Pseudomonas fluorescens), or the major native milk protease (plasmin) was added, to allow a direct comparison between the destabilization of skim UHT milk by both categories of enzymes. The physical and chemical properties were studied during 6 weeks. Our results showed AprX induced compact gels when almost all the κ-casein was hydrolyzed and the degree of hydrolysis (DH) exceeded 1.3%. Plasmin induced soft gels when around 60% of both ß- and αs1-casein were hydrolyzed and the DH reached 2.1%. The knowledge gained from this study may be used for developing diagnostic tests for determining the protease responsible for UHT milk destabilisation.

Thermal Scanning Conductometry (TSC) as a General Method for Studying and Controlling the Phase Behavior of Conductive Physical Gels.

The thermal scanning conductometry protocol is a new approach in studying ionic gels based on low molecular weight gelators. The method is designed to follow the dynamically changing state of the ionogels, and to deliver more information and details about the subtle change of conductive properties with an increase or decrease in the temperature. Moreover, the method allows the performance of long term (i.e. days, weeks) measurements at a constant temperature to investigate the stability and durability of the system and the aging effects. The main advantage of the TSC method over classical conductometry is the ability to perform measurements during the gelation process, which was impossible with the classical method due to temperature stabilization, which usually takes a long time before the individual measurement. It is a well-known fact that to obtain the physical gel phase, the cooling stage must be fast; moreover, depending on the cooling rate, different microstructures can be achieved. The TSC method can be performed with any cooling/heating rate that can be assured by the external temperature system. In our case, we can achieve linear temperature change rates between 0.1 and approximately 10 °C/min. The thermal scanning conductometry is designed to work in cycles, continuously changing between heating and cooling stages. Such an approach allows study of the reproducibility of the thermally reversible gel-sol phase transition. Moreover, it allows the performance of different experimental protocols on the same sample, which can be refreshed to initial state (if necessary) without removal from the measuring cell. Therefore, the measurements can be performed faster, in a more efficient way, and with much higher reproducibility and accuracy. Additionally, the TSC method can be also used as a tool to manufacture the ionogels with targeted properties, like microstructure, with an instant characterization of conductive properties.