Determination Of Water Activity Research Articles

Fermentação de farelo de cacau por Aspergillus niger para obtenção de lipase

The aim of this study was to use cocoameal as substrate for obtaining fungal lipase producedby solid state fermentation by Aspergillus niger .The spore concentration used was 107 spores/gsubstrate. Fermentations were conducted in a bacteriologicalincubator at 35°C with an initial moisturecontent of 60% and the fermentation time was 96hours. The determination of enzyme activity, pH,water activity and moisture were taken every 24hours. The higher enzyme activity was quantifi ed11.67 U/g aft er 48 hours of fermentation. Aft er thistime there was reduction in enzyme production.The moisture content and water activity decreasedduring the fermentation process and the pH remainedconstant. Key words: water activity, fermentation time, solidstatefermentation.

A calorimetric method to determine water activity

A calorimetric method to determine water activity covering the full range of the water activity scale is presented. A dry stream of nitrogen gas is passed either over the solution whose activity should be determined or left dry before it is saturated by bubbling through water in an isothermal calorimeter. The unknown activity is in principle determined by comparing the thermal power of vaporization related to the gas stream with unknown activity to that with zero activity. Except for three minor corrections (for pressure drop, non-perfect humidification, and evaporative cooling) the unknown water activity is calculated solely based on the water activity end-points zero and unity. Thus, there is no need for calibration with references with known water activities. The method has been evaluated at 30 °C by measuring the water activity of seven aqueous sodium chloride solutions ranging from 0.1 mol kg(-1) to 3 mol kg(-1) and seven saturated aqueous salt solutions (LiCl, MgCl(2), NaBr, NaCl, KCl, KNO(3), and K(2)SO(4)) with known water activities. The performance of the method was adequate over the complete water activity scale. At high water activities the performance was excellent, which is encouraging as many other methods used for water activity determination have limited performance at high water activities.

Application of hazard analysis critical control points system for the control of aflatoxins in the Brazilian groundnut-based food industry

Summary This study was conducted to identify and assess the critical control points (CCPs) in groundnut-based food production in southern Brazil in order to reduce or eliminate aflatoxin contamination. This methodology has been suggested by the Food and Agriculture Organization (FAO) of the United Nations. Reception of prime matter, groundnut storage, roasting and thermal treatment were the main CCPs identified. Critical factors were the determination of aflatoxin, moisture content and water activity (Aw) during groundnut reception and storage, control of temperature, roasting time and thermal treatment in the groundnut-based food manufacturing. The critical limit for moisture was 8.2% and 0.6 was established for Aw. In Brazil, the limit for aflatoxins B1, B2, G1 and G2 has been established at 20 ppb. Temperatures of 180 °C/1 h and 80 °C/40 min were established for roasting and thermal treatment stages of groundnut-based food, respectively.

Determination of Tritiated Water Activity Using EPR Spectrometry

In this paper, the possibility for determination of the tritiated water activity using Electron Paramagnetic Resonance (EPR) spectrometry was analyzed. The method relies on estimation of hydroxyl radicals resulted from self-radiolytical processes using EPR spectrometers. The mechanisms of inducing of free radical by self radiolysis of tritiated water, the accumulation time of hydroxyl radicals and the corroboration of signals amplitude with the tritiated water concentration have been studied.

Rapid FTIR determination of water, phenolics and antioxidant activity of olive oil

AbstractA rapid Fourier transformed infrared (FTIR) attenuated total reflectance (ATR) spectroscopic method was applied to the determination of water content (WC), total phenol amount (TP) and antioxidant activity (ABTS.+) of virgin olive oils (VOO) and olive oils. Calibration models were constructed using partial least squares regression. Oil samples with WC ranging from 289 to 1402 mg water/kg oil, with TP from 46 to 877 mg gallic acid/kg oil and with ABTS.+ from 0 to 5.7 mmol Trolox/kg oil were considered for chemometric analysis. Better results were obtained when selecting suitable spectral ranges; in particular, from 2260 to 1008 cm−1 for WC, from 3610 to 816 cm−1 for TP and from 3707 to 1105 cm−1 for ABTS.+. Satisfactory LOD values by the FTIR‐chemometric methods were achieved: 9.4 (mg/kg oil) for WC; 12.5 (mg gallic acid/kg oil) for TP, and 0.76 (mmol Trolox/kg oil) for ABTS.+. The evaluation of the applicability of these analytical approaches was tested by use of validation sample sets (n = 16 for WC, n = 11 for TP and n = 14 for ABTS) with nearly quantitative recovery rates (99–114%). The FTIR–ATR method provided results that were comparable to conventional procedures.Practical applications: The presented method is based on ATR–FTIR in combination with multivariate calibration methodologies and permits a simultaneous evaluation of important quality parameters of VOO (WC, TP and ABTS.+). This approach represents an easy and convenient means for monitoring olive oil quality with the advantage of ease of operation, speed, no sample pretreatment and no consumption of solvents. The data obtained with this method are comparable to those obtained using the official reference method. Therefore, the technique is highly plausible as an alternative to the standard procedure for routine analysis or control at‐line of production processes.

Evaluation of sample preparation methods for water activity determination in jerky and kippered beef: A research note

Commercially available packaged whole muscle beef jerky, chopped and formed beef jerky, and kippered beef steak were obtained from retail stores to determine the effect of two sample preparation methods on water activity (a(w)). Intact samples were prepared by cutting product into a hexagonal shape with a 3.2 cm diameter. Diced samples were prepared by cutting the product into 0.4 x 0.4 cm squares. Whole muscle jerky a(w) was higher (0.016 units; P<0.001) using the intact method compared to the diced method. There was no difference (P>0.05) in a(w) levels between the two preparation methods for chopped and formed jerky or kippered beef steak. An intact sample preparation method is recommended for a(w) determination of whole muscle jerky to obtain a more conservative value, especially if a(w) is near the margin of safety.

Application of FT NIR Spectroscopy in the Determination of Basic Physical and Chemical Properties of Sausages

The objectives of this study were to develop calibration models for determination of water activity and the content of fat, dry matter, salt, non collagen muscle protein and pH in dry cooked sausages. Samples (n = 42) were scanned in FT-NIR Analyzer and simultaneously analyzed by standard methods. The spectra were measured in the reflectance mode with a compressive cell between 10 000 and 4 000 cm-1, averaging 100 scans. Calibration models were developed using the partial least squares (PLS) method. These calibration models were checked later by crossvalidation. The following statistical values were obtained: R (correlation coefficient) = 0.997 and SEC (standard error of calibration) = 0.002 for water activity, R = 0.966 and SEC = 0.023 for pH, R = 0.995 and SEC = 0.970 for dry matter content, R = 0.995 and SEC = 0.045 for salt content, R = 0.965 and SEC = 0.652 for non collagen muscle protein, R = 0.996 and SEC = 0.559 for fat content. The results of the study showed that FT-NIR is a suitable method for rapid analysis of physical and chemical properties of sausages.

JESS, a Joint Expert Speciation System—V: Approaching thermodynamic property prediction for multicomponent concentrated aqueous electrolyte solutions☆

Considerable difficulties persist in modelling the thermodynamics of multicomponent aqueous electrolyte solutions, especially at high concentrations. The widely adopted Pitzer formalism suffers from severe disadvantages, particularly with the combinatorial increase in mixing parameters required in multicomponent systems. As an alternative, the simple mixing rules of Young, of Harned and of Zdanovskii have been employed to predict the properties of mixtures using only the properties of the binary constituents with few or no additional parameters. Among these, Zdanovskii's rule is particularly promising because it constitutes a fundamental criterion for ideal mixing, i.e. when solutions having the same solvent activity are mixed in any proportion, the solvent activity remains unchanged. Many mixtures of strong electrolyte solutions are known from experiment to obey Zdanovskii's rule. This is important because application to aqueous electrolyte systems of practical interest has been hindered due to the process-intensive determination of water activities using the Gibbs-Duhem relation. This paper describes an alternative method which efficiently calculates the water activity of a multicomponent solution obeying Zdanovskii's rule. Some specific examples of the method are presented and various applications considered. In some systems, where deviations from Zdanovskii's rule occur, a single empirical parameter can be obtained and can be easily incorporated into the calculations.

Proposed technical specifications for a survey on Listeria monocytogenes in selected categories of ready‐to‐eat food at retail in the EU

Proposed technical specifications for a survey on Listeria monocytogenes in selected categories of ready‐to‐eat food at retail in the EU

Determination of moisture content and water activity in algae and fish by thermoanalytical techniques

The water content in seafoods is very important since it affects their sensorial quality, microbiological stability, physical characteristics and shelf life. In this study, thermoanalytical techniques were employed to develop a simple and accurate method to determine water content (moisture) by thermogravimetry (TG) and water activity from moisture content values and freezing point depression using differential scanning calorimetry (DSC). The precision of the results suggests that TG is a suitable technique to determine moisture content in biological samples. The average water content values for fish samples of Lutjanus synagris and Ocyurus chrysurus species were 76.4 ± 5.7% and 63.3 ± 3.9%, respectively, while that of Ulva lactuca marine algae species was 76.0 ± 4.4%. The method presented here was also successfully applied to determine water activity in two species of fish and six species of marine algae collected in the Atlantic coastal waters of Bahia, in Brazil. Water activity determined in fish samples ranged from 0.946 - 0.960 and was consistent with values reported in the literature, i.e., 0.9 - 1.0. The water activity values determined in marine algae samples lay within the interval of 0.974 - 0.979.

Comparison of Various Methods for Water Activity Determination

The water activities at the transition point of ten inorganic hydrates were determined by different techniques. The techniques used were compared and evaluated aiming to identify which one is the most efficient. It could be shown that measuring the relative humidity is an easy, accurate, direct, and low-priced method and as such more efficient than other methods tested (measuring the density, hardness, and heat of fusion).

The quality of Minas Frescal cheese produced by different technological processes

The present work evaluated the influence of three different cheesemaking processes on the physicochemical characteristics and the microbiological quality of the Brazilian Minas Frescal cheese. A survey was conducted with 93 samples of Minas Frescal cheese collected from supermarkets located in the city of Campinas-Sao Paulo, 31 samples being processed by the addition of a lactic culture (LC), 31 by direct acidification (DA) with lactic acid and 31 by ultrafiltration (UF). The analyses of the physicochemical characteristics involved the determination of water activity, pH, titratable acidity and moisture content. All the samples were analysed for the presence of fecal coliforms, coagulase positive staphylococci, Salmonella spp. and Listeria monocytogenes. The results showed that the UF processed cheese presented the best microbiological quality among the technological processes considered in this survey, despite of the more favourable conditions for the growth of pathogenic microorganisms provided by its physicochemical characteristics, when compared to the LC and DA ones.

Isotermas de sorção de sementes de Eucaliptus grandis e Pinus taeda

As sementes florestais devem ser armazenadas adequadamente, a fim de reduzir ao mínimo o processo de deterioração. É possível estabelecer uma relação entre o teor de água livre na semente e sua conservação, expresso pela atividade de água, através da relação entre a pressão de vapor de água em equilíbrio sobre a semente e a pressão de vapor de água pura, à mesma temperatura. Uma isoterma é uma curva que descreve, em uma umidade específica, a relação de equilíbrio de uma quantidade de água sorvida por componentes da semente e a pressão de vapor ou umidade relativa, a uma temperatura específica. O objetivo deste trabalho foi estudar as isotermas de sorção para sementes de Eucalyptus grandis e Pinus taeda, que são espécies florestais de interesse econômico. Os graus de umidade das sementes foram ajustados, antes do armazenamento, usando-se dessecadores com sílica gel ou através de reidratação sobre água. Para o controle da quantidade de água removida ou absorvida, as subamostras foram pesadas periodicamente, sendo o processo encerrado ao ser atingido o peso correspondente ao grau de umidade final desejado para cada tratamento. Foram realizadas determinações de umidade e de atividade de água e utilizados diferentes modelos de equações empíricas que correlacionam dados experimentais das isotermas de sorção em materiais biológicos. O melhor ajuste das isotermas de sorção foi alcançado pelos modelos de três parâmetros de Langmuir e de quatro parâmetros de Peleg para sementes de E. grandis e de P. taeda, respectivamente.

Experimental Determination of Water Activity for Binary Aqueous Cerium(III) Ionic Solutions: Application to an Assessment of the Predictive Capability of the Binding Mean Spherical Approximation Model

This work is aimed at a description of the thermodynamic properties of actinide salt solutions at high concentration. The predictive capability of the binding mean spherical approximation (BIMSA) theory to describe the thermodynamic properties of electrolytes is assessed in the case of aqueous solutions of lanthanide(III) nitrate and chloride salts. Osmotic coefficients of cerium(III) nitrate and chloride were calculated from other lanthanide(III) salts properties. In parallel, concentrated binary solutions of cerium nitrate were prepared in order to measure experimentally its water activity and density as a function of concentration, at 25 degrees C. Water activities of several binary solutions of cerium chloride were also measured to check existing data on this salt. Then, the properties of cerium chloride and cerium nitrate solutions were compared within the BIMSA model. Osmotic coefficient values for promethium nitrate and promethium chloride given by this theory are proposed. Finally, water activity measurements were made to examine the fact that the ternary system Ce(NO3)3/HNO3/H2O and the quaternary system Ce(NO3)3/HNO3/N2H5NO3/H2O may be regarded as "simple solutions" (in the sense of Zdanovskii and Mikulin).

Cryoscopic studies of α-amino acids in water

Freezing temperature lowering of aqueous solution of α-amino acids namely glycine, l-serine, l-proline, dl-valine, dl-alanine, l-threonine, hydroxy- l-proline, l-isoleucine and dl-methionine were determined. These values were used in the determination of osmotic coefficient, water activity, activity coefficients and number of ions formed by an electrolyte molecule. Regression analysis was further done for the above-mentioned α-amino acids in order to test the validity of Δ T f (theo.) and Δ T f (obs.).

On-Line Determination of Water Activity at the Lean Surface of Meat Products During Drying and Its Relationship with the Crusting Development

One of the main problems in drying of meat products is the surface hardening or crusting. The crusted surface layer is harder and less permeable than the inner part of the product. A dramatic increase of hardness during drying in dry-cured meat products has been found when the water content reaches a critical value. The water content can be related with the water activity by sorption isotherms. Therefore, an on-line measurement of the water activity at the surface (aws) could be used by the control system in order to avoid the crusting problem. The aim of this study was to evaluate a methodology for the on-line water activity determination at the lean surface of raw or salted meat during drying and relate this determination with the crusting development. Water activity at the surface was estimated from the heat balance (aws h) in salted meat slices and in unsalted and in salted loin samples. The proposed methodology was able to monitor the aws in both products. The estimated aws h was related with the crusting development in loin samples, showing its potential application in control systems for avoiding the crusting development during the drying of meat products.

Hygrometric determination of water activities, and osmotic and activity coefficients of NH 4Cl–CaCl 2–H 2O at T = 298.15 K

The water activities of aqueous electrolyte mixture NH 4Cl–CaCl 2–H 2O were experimentally determined at T = 298.15 K by the hygrometric method at total ionic-strength from (0.6 to 9) mol · kg −1 for different ionic-strength fractions y of NH 4Cl with y = 1/3, 1/2, and 2/3. The data allow the deduction of new osmotic coefficients. The results obtained were correlated by Pitzer’s model and our proposed mixing rule ECA (extended composed additivity) for calculations of water activity in mixed aqueous electrolytes. From these measurements, the Pitzer mixing ionic parameters are estimated and used to predict the solute activity coefficients in the mixture.

Determination of water activities, osmotic and activity coefficients of the system NH 4NO 3–LiNO 3–H 2O at the temperature 298.15 K

The water activities of the mixed aqueous electrolyte {( y) NH 4NO 3+(1− y) LiNO 3)}(aq) are measured at total molalities from 0.2 mol kg −1 to about saturation for different ionic-strength fractions y of NH 4NO 3 with y = 0.20 , 0.50 , 0.80 . The results allow the deduction of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii–Stokes–Robinson (ZSR), Robinson and Stokes (RS), Lietzke and Stoughton (LS II), Reilly–Wood–Robinson (RWR) mixing rules and the Pitzer model. From these measurements, the Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The excess Gibbs energy is also determined.

Determination of Water Activities, Osmotic and Activity Coefficients of the System {yNH4Cl + (1 - y)CsCl}(aq) at 298.15 K

Determination of Water Activities, Osmotic and Activity Coefficients of the System {yNH4Cl + (1 - y)CsCl}(aq) at 298.15 K

A new formula for accurate calculation of water activity in sorption calorimetric experiments

A sorption calorimetric method proposed by Wadsö and Markova allows determination of water activity. Calculation of water activity is based on Fick’s first law. The correct form of the Fick’s law takes into account not only vapour diffusion itself but also bulk flow of vapour. A new formula, which uses the correct form of the diffusion law for direct calculation of water activity, is proposed.