Application of Dynamic Temperature-Humidity Chamber for Measuring Moisture Sorption Isotherms of Biomaterials as Compared to the Conventional Isopiestic Method

Measurement of water activity and moisture sorption isotherms of foods and biomaterials are important to determine the state of water. In this work, a dynamic temperature-humidity (DTH) controlled chamber was used to measure water sorption isotherm and compared with the conventional isopiestic method. Temperature and relative humidity of DTH chamber can be controlled in the range of -15 to 100°C and 0 to 98%, respectively; thus, measurement of water activity at any point can be measured within the above ranges. The DTH chamber method showed high reproducibility as compared with the conventional isopiestic method when measured isotherms of cellulose, lignin, and hemicellulase were compared at 30°C. Finally, isotherm data of cellulose, lignin, and hemicellulase were generated in the temperature range of 10-90°C using DTH chamber, and these were modelled by BET and GAB equations. The model parameters were correlated with the temperature.

Improvement of Barrier Properties of Biodegradable Polybutylene Succinate/Graphene Nanoplatelets Nanocomposites Prepared by Melt Process

Polybutylene Succinate (PBS)/Graphene nanoplatelets (GnP) nanocomposites over a range of GnP from 0 to 1.35 wt.%. were prepared by a melt process. A mixture of individual graphene nanosheets and aggregates was obtained by the addition of GnP in the PBS matrix. The presence of these fillers did not significantly modify the morphology, crystalline microstructure of the matrix or its thermal stability. However, a slight reinforcement effect of PBS was reported in the presence of GnP. The water sorption isotherm modelling with Guggenheim, Andersen and De Boer (GAB) equation and Zimm-Lundberg theory allowed a phenomenological analysis at the molecular scale. The presence of GnP did not modify the water sorption capacity of the PBS matrix. From a kinetic point of view, a decrease of the diffusion coefficient with the increasing GnP content was obtained and was attributed to a tortuosity effect. The influence of water activity was discussed over a range of 0.5 to 1 and 0 to 0.9 for water and dioxygen permeability. Improvement of the barrier properties by 38% and 35% for water and dioxygen permeability respectively were obtained.

Evaluation of water sorption isotherm, glass transistion temperature, vitamin C and color stability of mango peel powder during storage

The purpose of this work was to study the physical and chemical stability of the mango peel powder produced by hot-air drying. Sorption isotherms at 25 °C and glass transition temperatures (Tg) of the samples in equilibrium at different aw were determined. The degradation of vitamin C and color parameter b* was evaluated along storage under controlled conditions (relative humidity = 60%, temperature = 10, 25 and 35 °C) during 180 days. GAB model well-described water adsorption of the product, showing a monolayer moisture content (Xm) of 0.1260 g water/g dry solids and a critical aw of 0.56. The Gordon-Taylor model predicted the plasticizing effect of water on glass transition temperature, since Tg of the powders kept at different relative humidity conditions decreased as water activity increased. No visual signs of agglomeration and darkening were observed for samples stored at aw ≤ 0.529. The powders are a source of calcium and rich in potassium, copper, magnesium and manganese. The concentration of inorganic contaminants and pesticide residues were below the maximum allowed limits. The degradation of vitamin C and color parameter b* followed the first and zero-order kinetic models, respectively. The study indicated good stability for the powders along the storage at 10 and 25 °C, which can be incorporated into different food products, showing high retention of vitamin C, phenolic compounds, antioxidant activity and maintenance of color characteristics.

Pendugaan Umur Simpan Tiwul Instan yang Dikemas dalam Aluminium Foil dan Polietilen dengan Metode Akselerasi Berdasarkan Pendekatan Kadar Air Kritis

Penelitian bertujuan untuk menentukan umur simpan tiwul instan tinggi protein yang dibuat dari tepung ubi kayu dengan perlakuan modifikasi mikrobiawi dan kimiawi yang dikemas dalam kemasan aluminium foil dan plastik polietilen yang dihitung menggunakan metode akselerasi berdasarkan pendekatan kadar air kritis. Penelitian ini menggunakan metode eksperimental. Modifikasi mikrobiawi dilakukan dengan memfermentasi ubi kayu dengan ragi tape 4% dan diinkubasi selama 6 jam, sedangkan perlakuan kimiawi adalah dengan cara merendam ubi kayu dalam larutan soda kue selama 15 menit. Tiwul instan selanjutnya dibungkus dalam kemasan aluminium foil dan kemasan plastik polietilen. Kadar air tiwul dan tekstur dianalisis selama penyimpanan. Pembuatan pola kurva isotherm sorpsi air dan penghitungan masa simpan produk juga dilakukan pada penelitian ini. Hasilnya, tiwul instan perlakuan modifikasi kimiawi pada ubi kayu mempunyai masa simpan sekitar dua kali lipat dari perlakuan modifikasi mikrobiawi, yaitu masing-masing selama 4,88 tahun dan 2,13 tahun (yang disimpan dalam polietilen) serta 8,55 dan 3,89 tahun (yang disimpan dalam aluminium foil). Kesimpulannya, pendekatan titik air kritis dapat dilakukan untuk mendeteksi masa simpan tiwul instan, baik yang dikemas dalam aluminium foil maupun kemasan polietilen yang dapat menghasilkan masa simpan tiwul instan.“High Protein Instant Tiwul” Shelf Life Packed with Aluminum Foil and Polyethylene Using Critical Moisture Content ApproachAbstractThe research aims to determine the shelf life of high protein instant tiwul made from cassava flour with chemical and microbial modification packed in aluminum foil and polyethylene plastic packaging using the acceleration method with the critical moisture content approach. Fermented cassava (at 4% concentration for 6 hours incubation) was used as microbial modification treatment while cassava immersed in baking soda solution for 15 minutes was also applied as chemical modification. Instant tiwul was then packaged using aluminum foil and polyethylene. Moisture content of instant tiwul was determined during storage while water sorption isotherm curve patterns was also generated. Instant tiwul of cassava with chemical modified treatment had twice in shelf life, longer than those of microbial modification treatment, resulting 4.88 and 2.13 years (using polyethylene package) while 8.55 and 3.89 years (using aluminum foil), respectively. As conclusion, critical moisture approach could be used in the detection of shelf life in instant tiwul with polyethylene and aluminum foil packaging.

Modelling the Proton-Conductive Membrane in Practical Polymer Electrolyte Membrane Fuel Cell (PEMFC) Simulation: A Review

Theoretical models used to describe the proton-conductive membrane in polymer electrolyte membrane fuel cells (PEMFCs) are reviewed, within the specific context of practical, physicochemical simulations of PEMFC device-scale performance and macroscopically observable behaviour. Reported models and their parameterisation (especially for Nafion 1100 materials) are compiled into a single source with consistent notation. Detailed attention is given to the Springer–Zawodzinski–Gottesfeld, Weber–Newman, and “binary friction model” methods of coupling proton transport with water uptake and diffusive water transport; alongside, data are compiled for the corresponding parameterisation of proton conductivity, water sorption isotherm, water diffusion coefficient, and electroosmotic drag coefficient. Subsequent sections address the formulation and parameterisation of models incorporating interfacial transport resistances, hydraulic transport of water, swelling and mechanical properties, transient and non-isothermal phenomena, and transport of dilute gases and other contaminants. Lastly, a section is dedicated to the formulation of models predicting the rate of membrane degradation and its influence on PEMFC behaviour.

Effect of Sonication on the Properties of Flaxseed Gum Films Incorporated with Carvacrol

Carvacrol is a natural compound known to be a highly effective antibacterial; however, it is a hydrophobic molecule, which is a limitation to its use within food packaging. Flaxseed gum (FG) films containing different contents of carvacrol (C) were produced by a film-casting method with sonication. The effects of sonication power and time on the properties of the FG-C films were investigated by measuring the film thickness, mechanical properties, contact angle, opacity, water vapor permeability (WVP), water sorption isotherm, Fourier transform infrared spectroscopy(FTIR), differential scanning calorimetry (DSC), antibacterial and antioxidant activities, and microstructure. The results showed that sonication power and time had significant effects on mechanical and barrier properties, film opacity, and degradability (p < 0.05). The tensile strength (TS) and elongation at break (EB) values exhibited an obvious improvement after sonication, and FG-0.5C-6030 had the lowest TS (33.40 MPa) and EB (4.46%) values. FG-C films formed a denser structure and the contact angle was improved as a result of sonication, which improved the integration of carvacrol into the FG matrix. In terms of microstructure, sonication resulted in a homogeneous and continuous crosssection of FG-C films, and regular surface and cross-sectional images were obtained through the highest acoustic intensity and longest time treatment. The FG films incorporated with carvacrol displayed antibacterial properties against Staphylococcus aureus, Vibrio parahaemolyticus, Shewanella putrefaciens, and Pseudomonas fluorescens, as well as increased antioxidant properties, and sonication was proven to enhance both of them.

Moisture sorption isotherm of cross-linked wheat gluten and epoxydized oil using GAB and BET

The moisture sorption isotherm of wheat gluten/epoxydized sesame or sunflower oil resin was determined at 25, 40, and 55°C. The resin was prepared by cross-linking epoxydized oil and wheat gluten using 1, 2, and 3% zinc chloride as the catalyst. The experiment was carried out over 0.1–0.9 water activity ( a w) range using gravimetric sorption analyzer (Q 2000, TA Instruments, New Castle, PA, USA). The resin isotherms were found to be type III shape where the equilibrium moisture content (EMC) was higher at lower temperatures. The EMC of gluten epoxy resin was dependent on the degree of cross-linking because more cross-linking decreased EMC. The Guggenheim Anderson-de Boer (GAB) parameters support the theory of the free volume as it relates to monolayer absorption. This could be attributed to the decrease in the number of water binding sites due to the development of dense areas during cross-linking and increase in the free volume. The GAB and Brunauer–Emmett–Teller were found to be suitable for predicting the water sorption isotherm for gluten protein resin because it provided low root mean square error. The heat of sorption based on the Clausius–Clapeyron equation (qst) increased with decrease in moisture content.

Revisiting the water sorption isotherm of MOF using electrical measurements

Adsorption/desorption isotherms of Cr-soc-MOF-1.

Determination of Moisture Sorption Isotherm of Crosslinked Millet Flour and Oxirane Using GAB and BET

Epoxy resin was prepared by crosslinking epoxidized oil and millet flour. The reaction was carried out at three different temperatures (25, 40, and 55°C) and zinc chloride levels (1, 2, and 3%). Moisture sorption isotherms were determined at 0.1 to 0.9 water activity (aw) using a gravimetric sorption analyzer (Q 2000). The sigmoidal shape (type II) of the resin isotherms exhibited lower equilibrium moisture content (EMC) at higher temperature. The experimental data were modeled using GAB (Guggenheim–Anderson–de Boer) and BET (Brunauer–Emmett–Teller). The EMC of the resin was significantly lower than that of the flour, which could be attributed to the decrease in the number of water-binding sites due to the creation of dense areas during crosslinking. The low root-mean-square error (RMSE) indicates that GAB and BET were suitable for predicting the water sorption isotherm for millet flour resin. The heat of sorption of the resin was large at low moisture content and increased at higher relative humidity. It is recommended that millet flour resin be used at relative humidity below 60%.