Applying a heat transfer mathematical model for the cryopreservation of rainbow trout (Oncorhynchus mykiss) sperm: How straw location over liquid nitrogen level affects freezing rate and fertilization yield.

Cryopreservation of rainbow trout semen under field conditions was analyzed. Straw location over liquid nitrogen level is a crucial variable that affects freezing rate and fertilization yield due to changes in nitrogen vapor external temperature. The objectives were: to analyze cryopreservation protocols by experimentally measuring the cooling rates and fertilization yield of 0.5 ml plastic straws located in nitrogen vapor at different heights corresponding to different external temperatures; to numerically simulate the freezing process, by solving the heat transfer partial differential equations with the corresponding thermo-physical properties of the biological system and the plastic straw; to evaluate and analyze the surface heat transfer coefficient (h) during the freezing process of the straws; to introduce a new variable, the characteristic freezing time (tc), that enables comparison between protocols; this variable was defined as the elapsed period between the initial freezing temperature and a final reference temperature of -40 °C (temperature in which more than 80 % of the water is in a frozen state). The mathematical model predicted the temperature distribution inside the straw, showing a low effect of straw plastic materials (polyethylene-terephthalate glycol, polyvinyl-chloride, and polypropylene) on freezing rates. The average h value obtained from numerical simulations was 25.5 W/m2 K, close to that obtained from the analytical Nusselt correlation for natural convection. An improvement on fertilization trials was observed when the average external nitrogen temperature was -129.6 °C (temperature range: -94 to -171 °C) with an average tc of 56.8 s (ranging between 47 and 72 s). These results corresponded to a height above the level of liquid nitrogen of 2 cm. Comparison with literature reported data showed satisfactory results. Applying mathematical models in the cryobiology field achieved results that are relevant for cryopreservation activities.

New insights into halophilic prokaryotes isolated from salting-ripening anchovies (Engraulis anchoita) process focused on histamine-degrading strains.

Salted and ripened fish foods are susceptible to cause histamine poisoning. The present study focuses on microbial histamine degradation from high salted fermented fishery products to deepen our understanding about this new and growing field of research. As a result of this first study related to salted-ripened anchovies (Engraulis anchoita), fifty seven moderate and extreme halophilic microbial isolates from salt and salted-ripened anchovy processes were characterized in terms of their phenotype and histamine-degrading capacity. Only 7%-4 isolates-were able to degrade histamine. None of the histamine-degrading isolates presented proteolytic and/or lipolytic activity. One of them designated A18 was chemotactic toward histamine, an interesting property not previously reported for that chemoattractant. However, the S18 and A18 isolates, genotypically identified as Halobacterium sp. and Halomonas sp. respectively, produced indole and/or H2S, both undesirable characteristics associated to off-flavors occurrence. On the other hand, A28 and S20, identified as Halovibrio sp. and Halobacterium sp. respectively, presented desirable properties, such as cytochrome oxidase and catalase activity, and non-production of H2S and indole. These strains also showed characteristics previously reported as dominant in the ripened stage. The results are promising, and A28 and S20 may have the desirable features to improve the anchovy salting-ripening process.

Effect of the desiccation tolerance and cryopreservation methods on the viability of Citrus limon L. Burm cv. Eureka seeds.

Cryopreservation of the germplasm for long-term periods is of great importance to maintain the genetic resource. Argentina is one of the world's highest lemon producing country. The performance of different cooling/warming rates in the cryopreservation method of Citrus limon L. Burm cv. Eureka seeds and their influence on the interval of optimal moisture content in the desiccation stage were analyzed. Water sorption isotherm was determined and modeled using D'Arcy & Watt equation; it provided important information concerning the amounts of water associated to strong, weak and multimolecular binding sites along the sorption isotherm. Seeds tolerated a wide range of desiccation conditions (0.180%), however desiccation to 0.0526 g H2O g-1 d.b. (aw = 0.0901) produced a significant loss of viability. Differential Scanning Calorimetry was used to identify the thermal transitions of lipids and water in the seed; enthalpies were used to calculate the unfrozen water fraction (0.19 g H2O g-1 d.b. corresponding to aw = 0.64). Two cooling/warming rates were tested on desiccated seeds (0.110.64 corresponding to the unfrozen water fraction. The use of higher cooling/warming rates enables a wider range of desiccation conditions (0.33

In-vitro development of vitrified-warmed bovine oocytes after activation may be predicted based on mathematical modelling of cooling and warming rates during vitrification, storage and sample removal.

Heat transfer during cooling and warming is difficult to measure in cryo-devices; mathematical modelling is an alternative method that can describe these processes. In this study, we tested the validity of one such model by assessing in-vitro development of vitrified and warmed bovine oocytes after parthenogenetic activation and culture. The viability of oocytes vitrified in four different cryo-devices was assessed. Consistent with modelling predictions, oocytes vitrified using cryo-devices with the highest modelled cooling rates had significantly (P < 0.05) better cleavage and blastocyst formation rates. We then evaluated a two-step sample removal process, in which oocytes were held in nitrogen vapour for 15 s to simulate sample identification during clinical application, before being removed completely and warmed. Oocytes exposed to this procedure showed reduced developmental potential, according to the model, owing to thermodynamic instability and devitrification at relatively low temperatures. These findings suggest that cryo-device selection and handling, including method of removal from nitrogen storage, are critical to survival of vitrified oocytes. Limitations of the study include use of parthenogenetically activated rather than fertilized ova and lack of physical measurement of recrystallization. We suggest mathematical modelling could be used to predict the effect of critical steps in cryopreservation.

Assessment of the performance of a symbiotic microalgal-bacterial granular sludge reactor for the removal of nitrogen and organic carbon from dairy wastewater.

Cheese whey (CW) is a nutrient deficient dairy effluent, which requires external nutrient supplementation for aerobic treatment. CW, supplemented with ammonia, can be treated using aerobic granular sludge (AGS) in a sequencing batch reactor (SBR). AGS are aggregates of microbial origin that do not coagulate under reduced hydrodynamic shear and settle significantly faster than activated sludge flocs. However, granular instability, slow granulation start-up, high energy consumption and CO2 emission have been reported as the main limitations in bacterial AGS-SBR. Algal-bacterial granular systems have shown be an innovative alternative to improve these limitations. Unfortunately, algal-bacterial granular systems for the treatment of wastewaters with higher organic loads such as CW have been poorly studied. In this study, an algal-bacterial granular system implemented in a SBR (SBRAB) for the aerobic treatment of ammonia-supplemented CW wastewaters was investigated and compared with a bacterial granular reactor (SBRB). Mass balances were used to estimate carbon and nitrogen (N) assimilation, nitrification and denitrification in both set-ups. SBRB exhibited COD and ammonia removal of 100% and 94% respectively, high nitrification (89%) and simultaneous nitrification-denitrification (SND) of 23% leading to an inorganic N removal of 30%. The efficient algal-bacterial symbiosis in granular systems completely removed COD and ammonia (100%) present in the dairy wastewater. SBRAB microalgae growth could reduce about 20% of the CO2 emissions produced by bacterial oxidation of organic compounds according to estimates based on synthesis reactions of bacterial and algal biomass, in which the amount of assimilated N determined by mass balance was taken into account. A lower nitrification (75%) and minor loss of N by denitrifying activity (<5% Ng, SND 2%) was also encountered in SBRAB as a result of its higher biomass production, which could be used for the generation of value-added products such as biofertilizers and biostimulants.

Partial dehydration and cryopreservation of Citrus seeds.

BACKGROUND: Three categories of seed storage behavior are generally recognized among plant species: orthodox, intermediate and recalcitrant. Intermediate seeds cannot be stored in liquid nitrogen (LN) without a previous partial dehydration process. The water content (WC) of the seeds at the moment of immersion in LN must be regarded as the most critical factor in cryopreservation. The purpose of this study was to investigate the basis of the optimal hydration status for cryopreservation of Citrus seeds: C. sinensis (sweet orange), C. paradisi (grapefruit), C. reticulata (mandarin) in LN. RESULTS: To study the tolerance to dehydration and LN exposure, seeds were desiccated by equilibration at relative humidities between 11 and 95%. Sorption isotherms were determined and modeled; lipid content of the seeds was measured. Seed desiccation sensitivity was quantified by the quantal response model. Differential scanning calorimetry (DSC) thermograms were determined on cotyledon tissue at different moisture contents to measure ice melting enthalpies and unfrozen WC. Samples of total seed lipid extract were also analyzed by DSC to identify lipid transitions in the thermograms. CONCLUSIONS: The limit of hydration for LN Citrus seeds treatment corresponded to the unfrozen WC in the tissue, confirming that seed survival strictly depended on avoidance of intracellular ice formation.

Performance of oxalic acid-chitosan/alumina ceramic biocomposite for the adsorption of a reactive anionic azo dye.

A biocomposite system was developed and tested for the removal of the azo dye Reactive Red (RR195) from wastewater. The biocomposite was synthesized using ceramic particles containing 75% alumina which were coated using chitosan cross-linked with oxalic acid. The biocomposite showed high performance at low pH (maximum adsorption capacity = 345.3mg.g-1 at pH=2.0). The physicochemical and structure characteristics of the matrix were evaluated by Z-potential, FTIR-ATR, SEM-EDS, XRD, and porosity. Langmuir sorption isotherm and pseudosecond-order model gave the best fit. The electrostatic interaction between RR195 (due to the sulfonate groups) and the free amino groups of chitosan, enabled successive desorption/regeneration cycles. The maximum removal percentage (>80%) occurred at pH=2.0 due to the cross-linking effect. Experiments at different temperatures allowed the calculation of thermodynamic parameters (ΔG, ΔS, ΔH); adsorption was spontaneous, exothermic, and enthalpy controlled. The presence of inorganic ions ([Formula: see text] ) was analyzed during the adsorption process. This novel biocomposite can be applied as a cost-effective and environmentally friendly adsorbent for anionic azo dye removal from wastewater. The application of chitosan cross-linked with oxalic acid as a coating of the ceramic support enhanced the adsorption capacity and enabled its use under acidic conditions without solubilization.

Nanoferulic: From a by-product of the beer industry toward the regeneration of the skin.

BACKGROUND: Brewers' spent grain (BSG) is one of the most abundant by-products of the beer industry and causes serious environmental problems. Ferulic acid (FA) is an antioxidant with potential cosmeceutical applications. FA was extracted from BSG, developing a method of high extraction performance in order to be encapsulated in ultradeformable liposomes (Nanoferulic, NF). AIMS: To obtain a product with high added value such as FA, from a residue currently underused, using simple and economical chemical methods. To load FA into a nanosystem designed for the topical route, its encapsulation has the purpose to take profit from its photoprotective, anti-inflammatory, and antioxidant properties in the deep layers of the skin. METHODS: Ferulic acid was obtained from dried BSG using acid and basic treatments in series. NF was prepared by lipid film resuspension of a solution containing FA obtained from BSG. Size and Z-potential were determined. Cytotoxicity was assessed in vitro. Skin penetration was assessed by NF determination at different skin depths and by confocal microscopy. RESULTS: The yield of the extraction process was 0.43% on a dry basis. Encapsulation rendered liposomes of around 140 nm with 92% of encapsulation efficiency. No toxicity was observed in all the tested concentrations. Successful results were obtained from the regeneration studies. CONCLUSIONS: It was possible to develop a nanosystem containing FA, generating a high-value commercial input for the pharmaceutical and cosmeceutical industry. The use of BSG generated in industrial scale would help to reduce the volume of highly polluting waste.

Functional iron chitosan microspheres synthesized by ionotropic gelation for the removal of arsenic (V) from water.

Arsenic (As) is considered one of the most serious inorganic contaminants in groundwater. The maximum limit of As in drinking water is 0.010mgAs L-1 according to the World Health Organization. Functional Iron Chitosan Microspheres (F-ICM) were synthesized by ionotropic gelation of chitosan and ferric nitrate for removal of As (V) from water. The effects of iron concentration (0.7, 5.5 and 11.2gFe+3/100g chitosan), pH range (4-9), sorbent dosage, possibility of reuse and presence of interfering anions were analyzed. F-ICM were effective for As (V) adsorption in a wide range of pH with removals higher than 88.9%, reaching concentrations < 0.010mgAs L-1. A higher proportion of iron in the matrix favored the removal of As(V) in a pH range 6 to 9. Kinetic data of As(V) adsorption onto 0.7 F-ICM under all tested initial concentrations fitted well with the pseudo second-order kinetic model. Sorption isotherm experimental data were satisfactorily fitted with the Langmuir equation; the maximum sorption capacity for As(V) was 120.77mgAs(V) (gF-ICM1) and the Langmuir constant was 0.331 L mg1. A good performance of the adsorption capacity was obtained in four successive adsorption cycles of reuse and in the presence of interfering anions, indicating the high adsorption capacity of the synthesized microspheres.

Film forming capacity of chemically modified corn starches.

Native starch can be chemically modified to improve its functionality and to expand its uses. Modified starches were characterized and the rheological behavior of filmogenic suspensions was analyzed. The film forming capacity of different chemical modified corn starches was evaluated. Acetylated starch was selected by the characteristics of the resulted films; its optimum concentration was 5% w/w since their films exhibited the lowest water vapor permeability (WVP, 1.26×10(-10)g/msPa). The effect of glycerol as plasticizer on film properties depend on its concentration, being 1.5% w/w those that allows to obtain the lowest WVP value (1.64×10(-11)g/msPa), low film solubility in water and a more compact structure than those of unplasticized films. Mechanical behavior of plasticized acetylated starch films depends on glycerol concentration, being rigid and brittle the unplasticized ones, ductile those containing 1.5% w/w of glycerol and very flexible those with a higher plasticizer content.

Reduction of hexavalent chromium by Sphaerotilus natans a filamentous micro-organism present in activated sludges.

Wastewaters produced by various industries may contain undesirable amounts of hexavalent chromium (Cr(VI)), as chromate and dichromate, a hazardous metal affecting flora and animals of aquatic ecosystems as well as human health. One removal strategy comprises the microbial reduction of Cr(VI) to Cr(III), a less soluble chemical species that is less toxic than Cr(VI). In this work, the ability to reduce Cr(VI) of Sphaerotilus natans, a filamentous bacterium usually found in activated sludge systems, was evaluated. In aerobic conditions, S. natans was able to efficiently reduce Cr(VI) to Cr(III) from dichromate solutions ranging between 4.5 and 80 mg Cr(VI)l(-1) in the presence of a carbonaceous source. A simultaneous evaluation of the microbial respiratory activity inhibition was also carried out to analyze the toxic effect of Cr(VI). Cr(VI) reduction by S. natans was mathematically modeled; chromium(VI) reduction rate depended on both Cr(VI) concentration and active biomass concentration. Although it is known that S. natans removes heavy metal cations such as Cr(III) by biosorption, the ability of this micro-organism to reduce Cr(VI), which behaves as an oxyanion in aqueous solutions, is a novel finding. The distinctive capacity to reduce Cr(VI) to Cr(III) than remain soluble or precipitated becomes S. natans a potential micro-organism to decontaminate wastewaters.

Modelling phenol biodegradation by activated sludges evaluated through respirometric techniques.

In this paper respirometric techniques were used to study the effect of pH, phenol and dissolved oxygen (DO) concentrations on the phenol biodegradation kinetics by activated sludges. In addition, a mathematical model was developed to interpret the obtained respirometric curves. Closed respirometer experiments showed that phenol inhibited the respiration rate of unacclimated sludges. On the contrary, oxygen uptake rate (OUR) of phenol acclimated sludges exhibiting the typical Haldane's substrate inhibition curve. The Monod equation adequately represented the relation between OUR of acclimated biomass and DO concentration. Within the tested pH range (4-12) the oxygen saturation coefficient was independent of pH. On the contrary, the maximum OUR was strongly affected by the pH, being its maximum between 9.5 and 10.5. Open respirometer experiments shows that as pH decreased from 10.2 to 5.8, the maximum OUR also decreased, in accordance with the trend observed in the closed respirometer experiments. Although the respiration rate of phenol degrading bacteria was strongly affected by pH, a constant phenol oxidation coefficient was observed within the studied pH interval. A mathematical model was proposed to interpret the open respirometry curves. The coefficients of the model were estimated using both pseudo steady state and dynamic conditions for different biomass concentrations. The model adequately predicted the whole OUR and DO profiles as a function of time during the biodegradation of phenol under different DO conditions. The mathematical model proposed in the present work is useful for predicting transient responses such as substrate concentration and DO concentrations as a function of time in bioreactors treating phenolic wastewaters under an overload of phenolic compounds.

Modelling Cr(VI) removal by a combined carbon-activated sludge system.

The combined carbon-activated sludge process has been proposed as an alternative to protect the biomass against toxic substances in wastewaters; however, the information about the effect of powdered-activated carbon (PAC) addition in activated sludge reactors for the treatment of wastewaters containing Cr(VI) is limited. The objectives of the present study were: (a) to evaluate the removal of hexavalent chromium by (i) activated sludge microorganisms in aerobic batch reactors, (ii) powdered-activated carbon, and (iii) the combined action of powdered-activated carbon and biomass; (b) to propose mathematical models that interpret the experimental results. Different Cr(VI) removal systems were tested: (S1) biomass (activated sludge), (S2) PAC, and (S3) the combined activated carbon-biomass system. A Monod-based mathematical model was used to describe the kinetics of Cr(VI) removal in the system S1. A first-order kinetics with respect to Cr(VI) and PAC respectively, was proposed to model the removal of Cr(VI) in the system S2. Cr(VI) removal in the combined carbon-biomass system (S3) was faster than both Cr(VI) removal using PAC or activated sludge individually. Results showed that the removal of Cr(VI) using the activated carbon-biomass system (S3) was adequately described by combining the kinetic equations proposed for the systems S1 and S2.

Stress relaxation characteristics of low-fat chicken sausages made in Argentina.

Low-fat sausages were prepared with fresh chicken breast meat and formulated with different levels of added fat, whey protein concentrate, and hydrocolloids (xanthan and guar gums) to study the effect of composition on the stress relaxation behavior of the products. Stress relaxation experiments were conducted on precooked sausages at 25°C. Generalized Maxwell and empirical Peleg models were used to predict the stress relaxation behavior of the material. A model with seven maxwellian elements in parallel with a pure elastic element showed a very good agreement with experimental data. Results show that the proposed model satisfactorily fits the experimental data better than Peleg's model or Maxwell models with less elements. The relaxation time distribution functions were obtained. The characteristic relaxation time was shorter (2500s) for the formulations with no added fat which produced a less elastic product while the sausages with added fat showed longer characteristic relaxation time (5000s). The stress relaxation experiment differentiated the viscoelastic nature of different formulations due to reduction of fat content.

Microstructural Behaviors of Matrices Based on Polylactic Acid and Polyhydroxyalkanoates.

Individual films of polyhydroxyalkanoates (PHA) and polylactic acid (PLA) and their blends were developed by solvent casting. PHA was obtained from activated sludges from a wastewater-treatment system at a laboratory scale. This work focused on analyzing the microstructural properties and thermal behaviors of individual films of PHA and PLA as well as those of their blends. The behaviors of the biodegradation processes of the individual films and blends were examined from a microstructural point of view. ATR-FTIR spectra indicated the existence of weak molecular interactions between the polymers. The formulation of blend films improved the crystallinity of PLA; additionally, it induced the polymer-recrystallization phenomenon, because crystallized PHA acted as a PLA-nucleating agent. This phenomenon explains the improvements in the films' water-vapor-barrier properties. The blends exposed to a biodegradation process showed an intermediate behavior between PLA and PHA, leading to a consistent basis for designing systems tailored to a particular purpose.

Monitoring and modeling 4-chlorophenol biodegradation kinetics by phenol-acclimated activated sludge by using open respirometry.

The aim of this study was to analyze the mechanisms, stoichiometry, and stability of 4-chlorophenol (4CP) biodegradation kinetics by phenol-acclimated activated sludge using open respirometry. While the removal of 4CP was higher than 98%, the removal of chemical oxygen demand (COD) ranged between 69 and 79% due to the accumulation of an intermediate metabolite. The value obtained from respirometric profiles for the stoichiometric ratio of O2 to 4CP (YO2/4CP) was 1.95 ± 0.04 mol of oxygen consumed per mol of 4CP removed. This YO2/4CP value reflected the action of the oxygenases responsible for the first steps of the aerobic oxidation of 4CP. The 4CP degradation activity decreased noticeably when successive pulses of 4CP were added to the respirometer. A mathematical model was developed to represent the aerobic biodegradation of 4CP. The fitted model adequately predicted the oxygen consumption rate, total phenols, and soluble COD concentrations as a function of time. The results presented could help to predict the dynamic of biodegradation of chlorophenols in a biological wastewater treatment system.

Monitoring the characteristics of cultivable halophilic microbial community during salted-ripened anchovy (Engraulis anchoita) production.

The halophilic microbial community of the salted-ripened anchovy process was studied. Samples from raw materials (salt and fresh anchovies) and from the stages of brining and ripening were collected and analyzed for their bacterial counts at 15 and 20% NaCl. No halophilic colonies were found in fresh anchovy and counts of about 103 CFU/g were determined in salt samples. A fluctuation of bacterial counts during the process was found. At the end of brining, ~104 CFU/g were determined in anchovy samples and this value was reduced to not detectable counts at the beginning of the ripening stage. After one month, counts increased to ~104 CFU/g and remained stable until the end of the process. From each sample, colonies having different morphotypes were isolated and submitted to a macro and microscopic characterization, a study of salt requirement for growth, and biochemical and phenotypic tests. The results were submitted to Univariate, Bivariate and Multiple Correspondence Factorial Analysis (MCFA). A total of 79 colonies were isolated during the salting-ripening anchovy process. Among the isolates, about 40-50% was positive for indole production and lipolytic activity and a 25% showed ability to produce H2S and proteolytic capacity. Proteolytic and lipolytic activities were well balanced along the process and resulted independent from the isolation stage, which is a desirable condition due to the contribution of microbial proteolysis and lipolysis to the development of texture and final aroma, respectively. H2S and indole producers practically were not detected during ripening. This fact is important because indole and H2S are associated with the development of off-flavors and spoilage in salted fish products. MFCA and Cluster Analyses complemented the Bivariate Analyses. The factor map showed proximity between the isolates from salt samples and from ripening. Isolates were statistically clustered in two groups. Cluster 1 grouped non-desirable activities (H2S and indole production) with cultures proceeding from brining whereas Cluster 2 related isolates mainly from salt samples and during ripening with some desirable microbial capacities (Cytochrome oxidase activity and non-H2S and non-indole production). These results would indicate that during the ripening process of salted anchovies, a natural selection of beneficial microorganisms for the development of the typical product sensory attributes occurred.

Kinetic Parameters for the Thermal Inactivation of Peroxidase and Lipoxygenase in Precooked Frozen Brassica Species.

Thermal inactivation of peroxidase (POD) and lipoxygenase (LOX), both enzymes present in broccoli and Brussels sprouts, is required before freezing, to obtain high-quality precooked frozen vegetables. Rate constants of a 1st-order biphasic model for the heat-labile and heat-resistant POD and LOX isoenzymes were determined at different temperatures (75, 80, and 90 °C) and the corresponding activation energies were estimated using nonlinear regressions. In the case of Brussels sprouts, the activation energies for the resistant and labile fractions were 56.3 and 62.5 kJ/mol for POD and 63.7 and 65.8 kJ/mol for LOX, respectively. For Brussels sprouts, different precooking times were tested to analyze the effect of residual enzyme activity on quality parameters and sensory attributes, after a frozen storage of 4 mo at -20 °C. A significant reactivation of enzyme activity after frozen storage was observed (especially in the case of POD) for short precooking times (<6 min) leading to low-quality parameters at the interior zone of the vegetable. A precooking time of 6 min at 90 °C allowed an adequate inactivation of LOX and POD obtaining a high-quality final frozen vegetable. A sensory analysis confirmed the global acceptability of the product. The obtained results are relevant to define the precooking stage conditions in the production of frozen cruciferous vegetables.

Influence of hydrogenated oil as cocoa butter replacers in the development of sugar-free compound chocolates: Use of inulin as stabilizing agent.

The effect of the addition of inulin as a surfactant or stability agent on white compound chocolate sweetened with sucralose and Stevia was studied. Samples were stored at 7, 15 and 30°C during 100days and the influence of inulin on rheological properties, sensorial attributes, shelf-life, physical properties such as melting, crystallization and blooming were analyzed. The shelf-life of the compound chocolate with the incorporation of inulin was higher than the control sample without replacement. Compound chocolate with inulin at 10%w/w showed a dense matrix structure, reducing the size and number of fat crystals formed during storage; furthermore they presented higher values of brightness and WI. This chocolate also showed less fracturability and improved thermal properties. DSC studies revealed increased values of onset and peak temperatures and enthalpy of melting of the polymorphic form V, at higher storage temperatures, achieving greater stability against degradation processes.

Effect of sweetener combination and storage temperature on physicochemical properties of sucrose free white chocolate.

The influence of a combination of sweeteners (Stevia (St) and sucralose (Su)) and storage temperature on thermal properties, microstructure, water content, texture and Bloom of sucrose free white chocolate was investigated. A strong relationship between the microstructure and the highest percentage of Bloom was observed. The samples with 100%Su and 50%S+50%Su presented microstructures with channels through which solids and fat could more easily spread to the surface, increasing the fat and sugar Bloom formation. However, 50%St+50%Su and 75%St+25%Su samples showed a minimum Bloom formation, probably due to its dense microstructure with no void spaces. The differential scanning calorimetry studies demonstrated that the samples containing 100%St and 75%St+25%Su showed the smallest decrease of melting enthalpy with increasing temperature. Besides, non-isothermal crystallization kinetics was studied by applying Avrami model. The sample 75%St+25%Su presented the highest values of activation energy showing the greatest stability in the temperature range studied (7°C-30°C).