Modelling the Water Sorption Isotherms of Quinoa Seeds (<Emphasis Type="Italic">Chenopodium quinoa</Emphasis> Willd.) and Determination of Sorption Heats

Adsorption and desorption isotherms of quinoa seeds (Chenopodium quinoa Willd.) were measured using the static gravimetric method at three temperatures (20, 40 and 60 °C). Water activity ranged from 0.118 to 0.937. The moisture sorption behaviour of quinoa was temperature dependent, as indicated by a decrease in equilibrium moisture content, at all levels of a _w, with increasing temperature. Eight mathematical equations available in the literature were used to model the experimental data, namely, GAB, BET, Caurie, Henderson, Oswin, Halsey, Smith and Iglesias–Chirife. All the equations showed generally a good fit; however, the Iglesias–Chirife and Oswin equations were considered the best to predict the experimental data for both isotherms. Effect of temperature on model parameters was analysed and studied through an Arrhenius-type equation. The net isosteric heats of desorption and adsorption were determined by applying the Clausius–Clapeyron equation resulting in 69.24 kJ mol⁻¹ for desorption and 61.26 kJ mol⁻¹ for adsorption. The experimental heat data were satisfactorily modelled by Tsami’s equation.     

Kinetics of Mass Transfer in Microwave Precooked and Deep-Fat Fried Ostrich Meat Plates

The aim of this study was to evaluate the effect of microwave precooking on mass transfer during deep-fat frying of ostrich meat plates. The influence of microwave power level, frying temperature, and time on mass transfer was determined. Among all treatments, the plates being precooked at 5.23 W/g of microwave power and then deep-fat fried at 135 °C had the minimum fat content. The effective moisture diffusivity ranged between 1.47 × 10⁻⁸ and 4.17 × 10⁻⁸ m²/s. Fat transfer rate constant was in the range of 0.024 and 19.708 s⁻¹. The activation energy obtained from Arrhenius plot for the effective moisture diffusivity ranged between 38.84 and 51.07 kJ/mol.     

Characteristics of Convective Drying of Pepino Fruit (Solanum muricatum Ait.): Application of Weibull Distribution

The aim of this research was to study the behaviour of the drying kinetics of pepino fruit (Solanum muricatum Ait.) at five temperatures (50, 60, 70, 80 and 90 °C). In addition, desorption isotherms were determined at 20, 40 and 60 °C over a water activity range from 0.10 to 0.90. The Guggenheim, Anderson and de Boer model was suitable to depict the desorption data. A monolayer moisture content from 0.10 to 0.14 g water g⁻¹ d.m. was reported. The equations of Newton, Henderson–Pabis, Modified Page, Wang–Singh, Modified Henderson–Pabis, Logarithmic as well as standardised Weibull were tested for modelling drying kinetics. Besides, Fick’s second law model was used to calculate the water diffusion coefficient which increased with temperature from 2.55 to 7.29 × 10⁻¹⁰ m² s⁻¹, with estimated activation energy of 27.11 kJ mol⁻¹. The goodness of fit of the models was evaluated using sum squared error and chi-square statistical tests. The comparison of the experimental moisture values with respect to the calculated values showed that the standardised Weibull model presented the best goodness of fit, showing that this equation is very accurate for simulating drying kinetics for further optimisation of drying times.     

Relationship between lysyl oxidase activity,pyridinoline content and muscle texture during ice storage of jumbo squid (Dosidicus gigas)

Collagen fibres, stabilised by lysyl oxidase (LOX), play an important role in jumbo squid because they are responsible for the union between various cells; therefore, a close interdependence between their functions and muscle firmness during ice storage has been suggested. In this study, the relationship between LOX activity, pyridinoline (Pyr) content and muscle texture (SF) during ice storage of jumbo squid mantle was evaluated. LOX activity was confirmed within the range of 4.1–7.1 × 10^?3 U g^?1 of protein, leading to an increase in Pyr content, detected in the range of 0.85–1.32 mmol mol^?1 of collagen after 5–20 days. The SF of the muscle became harder during the ice storage time, increasing from 21.08 to 37.95 N. It was therefore possible to establish the relationship between LOX activity, collagen cross‐links (Pyr content) and texture patterns during ice storage of jumbo squid muscle, which increased after 20 days.     

Kinetics Modeling of Mass Transfer Using Peleg’s Equation During Osmotic Dehydration of Seedless Guava (<Emphasis Type="Italic">Psidium guajava</Emphasis> L.): Effect of Process Parameters

Peleg’s equation was used to study the effect of process parameters on kinetics of mass transfer in terms of solids gain and water loss during osmotic dehydration using 30–50% (w/w) sucrose solution at 30, 40 and 50 °C. The experimental data were successfully fitted employing Peleg’s equation with the coefficient of determination (R ²) higher than 0.88, the root mean square error, and the mean relative percentage deviation modulus (E) of less than 0.003% and 6.40% for all treatments, respectively. In all cases, initial mass transfer rate parameter (K ₁) decreased significantly (p < 0.05) as the solution concentration and solution temperature increased suggesting a corresponding increase in the initial mass transfer rate. Initial mass transfer rate followed an Arrhenius relationship which showed that solids gain had the highest temperature sensitivity (E _a = 21.93–33.84 kJ mol⁻¹) during osmotic dehydration. Equilibrium mass transfer parameter (K ₂) decreased significantly (p < 0.05) as solution concentration increased demonstrating that the equilibrium solid and water contents increased with increase in solution concentration. The equilibrium solid and water contents were also estimated adequately using Peleg’s equation (R ² > 0.78). The results of this work allow estimating the kinetics of mass transfer during osmotic dehydration in order to obtain products with determined solid and water contents.     

Kinetics of Crude Peroxidase Inactivation and Color Changes of Thermally Treated Seedless Guava (Psidium guajava L.)

Thermal treatment of seedless guava (Psidium guajava L.) cubes was carried out in the temperature range of 80–95 °C. The kinetics of peroxidase inactivation and color changes due to thermal treatments were determined. Peroxidase inactivation followed a first-order kinetic model, where the activation energy was 96.39 ± 4 kJ mol⁻¹. Color was quantified in terms of L, a, and b values in the Hunter system. The color changes during processing were described by a first-order kinetic model, except total color difference which followed a zero-order kinetic model. The temperature dependence of the degradation followed the Arrhenius relation. The activation energies (E _a) for L, a, b, and total color difference (ΔE) were 122.68 ± 3, 88.47 ± 5, 104.86 ± 5, and 112.65 ± 5 kJ mol⁻¹, respectively. The results of this work are a good tool to further optimize seedless guava thermal treatment conditions.     

In vitro studies on calf thymus DNA interaction and 2-tert-butyl-4-methylphenol food additive

The interaction of native calf thymus DNA (CT-DNA) with 2-tert-butyl-4-methylphenol (TBMP) at physiological pH has been investigated by spectrofluorometric and viscosimetric techniques. TBMP molecules were found to intercalate between base pairs of DNA, demonstrated by an increase in the specific viscosity of DNA and decrease in the fluorescence of TBMP solutions in the presence of increasing amounts of DNA and the calculated binding constants (K _f) at different temperatures. Furthermore, the enthalpy and entropy of the reaction between TBMP and CT-DNA showed that the reaction is exothermic and enthalpy favored (ΔH = −19.18 kJ mol⁻¹; ΔS = −26.98 J mol⁻¹ K⁻¹) which are other evidences to indicate that TBMP is able to be intercalated in the DNA base pairs.     

Effect of air temperature,slice thickness and pretreatment on drying and rehydration of tomato

The effect of air temperature, pretreatment with alkaline emulsion of ethyl oleate (AEEO) and slice thickness on drying and rehydration characteristics of tomato slices was studied. Drying time decreased with pretreatment, but it increased considerably with the increase in air temperature and slice thickness of tomato. Besides, pretreatment was found to improve the rehydration ratio of tomato slices. The experimental drying curves obtained show only falling rate period. To estimate and select the suitable form of drying curves, five different mathematical models were applied to the experimental data. Among the mathematical models investigated, the Midilli et al. and logarithmic models satisfactorily described the drying characteristics of tomato slices with highest R² and lowest χ² and root mean square error. The effective moisture diffusivity varied from 3.123 to 10.03 × 10^?11 m² s^?1 over the temperature range studied, and the activation energy values varied from 59.6 to 70.2 kJ mol^?1.     

Water Diffusion and Concentration Profiles During Osmodehydration and Storage of Apple Tissue

The objective of this work was to study the mobility of water and sucrose during osmotic dehydration and storage of apple tissue and to conduct an analysis of the behavior of the effective diffusion coefficients determined from concentration profiles. Osmotic dehydration (OD) of apple was carried out at 40°C for 1 h, and the solution: sample ratio was 20:1 (w/w). Samples of 20-mm diameter were extracted from the dehydrated apple immediately after the OD process and after 4 and 24 h of storage at 25 °C. Moisture of these samples and soluble solids content were analyzed. Our results showed, after 1 h of OD, the outer layer of the apple sample lost 0.37 kg water/kg apple and gained 0.30 kg sucrose/kg apple. These values decreased toward the internal layers of the apple. A fine layer of greatly dehydrated cells was formed on the surface around the sample, which determined the mass transfer rate in the whole tissue. Smaller mass transport rates were observed in the development of concentration profiles during storage. Diffusion coefficients obtained for the outer layer after 1 h of OD were 1.53 × 10⁻¹⁰ and 1.05 × 10⁻¹⁰ m²/s for water and sucrose, respectively. The analysis of compositional profiles developed during osmodehydration was a useful tool to get a better understanding of the changes in the water activity of the outer layer of the apple tissue.     

Flavour binding mechanism between a typical meat flavour compound (nonanal) and porcine myofibrillar proteins with consideration of conformational changes

Flavour binding or release behaviour from the meat matrix is very important for its sensory properties. The interaction between flavour substance (nonanal) and myofibrillar proteins (MPs) was investigated using protein fluorescence quenching at different temperatures. The results suggested that nonanal caused the fluorescence quenching mechanism of MPs combining dynamic and static quenching mode, and dynamic quenching played a dominant role. Nonanal mainly combined with tryptophan residues rather than tyrosine residues. The results of synchronous fluorescence spectra and circular dichroism (CD) revealed that the interaction between nonanal and MPs induced no significant conformational changes in MPs. The binding constant (K) and number of binding sites (n) (1.45–2.03) increased with temperature. The negative value of ?G (?383.16 kJ mol^?1 to ?397.30 kJ mol^?1) showed that the interaction of nonanal and MPs was spontaneous. The positive ?H (180.18 kJ mol^?1, 181.48 kJ mol^?1) and ?S (696.17 J mol^?1 K^?1, 688.32 J mol^?1 K^?1) indicated that the binding of nonanal to MPs driven by hydrophobic force.     

Effect of Air Temperature on Drying Kinetics,Vitamin C,Antioxidant Activity,Total Phenolic Content,Non-enzymatic Browning and Firmness of Blueberries Variety O´Neil

Effect of air temperature on drying kinetics, vitamin C, antioxidant capacity, total phenolic content (TPC), colour due to non-enzymatic browning (NEB) and firmness during drying of blueberries was studied. Drying curves were satisfactorily simulated with the Weibull model at 50, 60, 70, 80 and 90°C. The scale parameter (β) decreased as air temperature increased and an activation energy value of 57.85 kJ mol⁻¹ was found. Important losses of vitamin C were reported during drying for all the working temperatures (p < 0.05). Although TPC decreased as air-drying temperature increased (p < 0.05) in comparison to its initial value, the dehydration at high temperatures (e.g., 90°C) presented high values for these antioxidant components. Discoloration due to NEB reaction was observed at all the working temperatures showing a maximum value at 90°C (p < 0.05). The radical scavenging activity showed higher antioxidant activity at high temperatures (80 and 90°C) than at low temperatures (50, 60 and 70°C) (p < 0.05). A tissue firmness reduction was observed with increasing temperature (p < 0.05).     

Mass Transfer Kinetic and Quality Changes During High-Pressure Impregnation (HPI) of Jumbo Squid (<Emphasis Type="Italic">Dosidicus gigas</Emphasis>) Slices

Jumbo squid is an important marine resource commercialized in Chile as well as American countries such as Perú, México, and USA. In order to find the best conditions for prevention of squid meat degradation, this study presented the simultaneous application of high hydrostatic pressure and osmotic dehydration (high-pressure impregnation (HPI)) on jumbo squid (Dosidicus gigas) slices. Diffusion coefficients for both components water and solids are improved by the high-pressure processing. The pressures used were 100, 250, and 400 MPa for a 15 g/100 mL salt concentration for time intervals of 30 s. The mathematical expressions used for mass transfer simulations of both water and salt were those corresponding to Newton, Henderson and Pabis, Page, and Weibull models, where the Weibull model presented the best fitted to the experimental data for both components. As to quality parameters studied for texture profile analysis, the treatment at 250 MPa yielded on the samples a minimum hardness, whereas springiness, cohesiveness, and chewiness at 100-, 250-, and 400-MPa treatments presented statistical differences regarding unpressurized samples. The color parameters L^* (lightness) increased; however, b^* (yellowish) and a^* (reddish) parameters decreased when increasing pressure level. This way, samples presented a brighter aspect and a mildly cooked appearance. The results presented in this study could support the potential of high hydrostatic pressure application as a technique novel for other compound impregnation under high pressure.     

Desorption isotherms,net isosteric heat and the effect of temperature and water activity on the antioxidant activity of two varieties of onion (Allium cepa L)

The standard static gravimetric method was used to determine moisture desorption isotherms (MDIs) of two onion varieties (Goudami and Galmi Violet) at 30 °C, 45 °C and 60 °C in the water activity ranging from 0.055 to 0.83. The combined effects of temperature and water activity on the antioxidant activities of the onion varieties were also studied. GAB, Oswin, Smith and BET equations were tested to fit the experimental data. The net isosteric heat of sorption was calculated. Equilibrium moisture content (EMC), total phenolic content (TPC) and antiradical activity were also measured. The isotherm and the EMC vary significantly with the onion variety and drying temperature, irrespective of water activity (a_w). Desorption isotherms were best described by the GAB model. The maximum net isosteric heats for Galmi Violet (32.58 kJ mol^?1) were greater than those of Goudami (23.50 kJ mol^?1) at each EMC. The TPC and antiradical activity of the Galmi Violet were significantly (P ≤ 0.05) higher than that of the Goudami at all investigated temperatures and water activities.     

Drying kinetics and thermal degradation of phenolic compounds and anthocyanins in pomegranate arils dried under vacuum conditions

The effects of temperature and pretreatment on drying kinetics and thermal degradation of phytonutrients present in pomegranate arils were investigated. The arils were divided into two groups, and half of the samples were pretreated by dipping into 80 °C hot water for 2 min. The drying process was conducted in the vacuum drier at the temperatures of 55, 65 and 75 °C. The fastest drying was completed at 75 °C after pretreatment of the samples. The highest anthocyanin–phenolic compound contents and antioxidant capacity were detected in the arils dried at 55 °C. Seven thin‐layer drying models were used to predict drying curves, and Arrhenius and Eyring–Polanyi models were employed to predict phytonutrient degradation kinetics. Activation energy for drying was 24.26 kJ mol^?1 for pretreated samples and 31.54 kJ mol^?1 for untreated samples. Effective moisture diffusivities were ranged from 1.43 × 10^?9 to 6.03 × 10^?9 m² s^?1.     

Aqueous solubility of calcium citrate and interconversion between the tetrahydrate and the hexahydrate as a balance between endothermic dissolution and exothermic complex formation

Aqueous solubility of calcium citrate tetrahydrate was found to decrease with increasing temperature, while solubility of hexahydrate increased with a transition temperature at 51.6 °C. Excess citrate increased calcium citrate solubility but decreased the calcium ion activity of the saturated solution with an initial solubility overshooting to form supersaturated solutions indicating binding of calcium to citrate with an association constant of 3.6 ± 0.1 × 10⁴, ΔHº = −5.07 ± 0.04 kJ mol⁻¹, ΔSº = 70.3 ± 0.3 J mol⁻¹ K⁻¹ at 25 °C. Dissolution of the tetrahydrate and hexahydrate was found to have ΔHº = 27 ± 9 kJ mol⁻¹, ΔSº = −218 ± 30 J mol⁻¹ K⁻¹ and ΔHº = 57 ± 7 kJ mol⁻¹, ΔSº = −126 ± 24 J mol⁻¹ K⁻¹, respectively, as determined from the temperature dependence of solubility corrected for complex formation. The exothermic complex formation results in inverse solubility only for the tetrahydrate with its moderate endothermic dissolution, which also precipitates at ambient temperature rather than the less soluble hexahydrate.     

Sorption Isotherms of Barnyard Millet Grain and Kernel

The moisture sorption isotherms of grain and kernel of barnyard millet (Echinochloa frumentacea) were determined at 20, 30, 40, and 50 °C. A gravimetric static method was used under 0.112–0.964 water activity (a _w) range for the determination of sorption isotherms. The models were compared using the coefficient of determination (r ²), reduced chi-square (χ ²) values, and on the basis of residual plots. In grain, modified Chung–Pfost (r ² > 0.99; χ ² < 0.7) and modified Oswin (r ² > 0.99; χ ² < 0.55) models were found suitable for predicting the M _e –a _w relationship for adsorption and desorption, respectively. Modified Henderson model was found to give the best fit (r ² > 0.99 and χ ² < 0.55) for describing the adsorption and desorption of the kernel. The isosteric heat, calculated using Clausius–Clapeyron equation, was varied between 46.76 and 61.71 kJ g⁻¹ mol⁻¹ at moisture levels 7–21% (d.b.) for grain and 47.11–63.52 kJ g⁻¹ mol⁻¹ at moisture level between 4% and 20% (d.b.) for kernel. The monolayer moisture content values ranged from 4.3% to 6% d.b. in the case of adsorption of barnyard millet grain and 5.2–6.6% d.b. in the case of desorption at the temperature ranges of 50–20 °C. The monolayer moisture values of barnyard millet kernel ranged from 4.4% to 6.67% d.b. in adsorption and 4.6% to 7.3% d.b. in desorption in the temperature ranges of 50–20 °C.     

The Influence of Oxygen Volumetric Mass Transfer Rates on Cyclodextrin Glycosyltransferase Production by Alkaliphilic Bacillus circulans in Batch and Fed-Batch Cultivations

In this work, the influence of oxygen mass transfer rates on the production of cyclodextrin glycosyltransferase (CGTase) by the alkaliphilic bacterium Bacillus circulans ATCC 21783 was investigated. Experimental design and response surface methodology were applied to optimize agitation speed and air flow rate in batch cultivations, in order to identify their significant effects and interactions with the synthesis of CGTase. Results were expressed as the volumetric mass transfer rates of oxygen (k_la, [per hour]). The maximal CGTase productivity of 155 U mL⁻¹ h⁻¹ was achieved with k_la of 48 h⁻¹. CGTase production was also studied in fed-batch cultures using the optimized parameters obtained in the batch experiments. The maximal CGTase productivity on fed-batch cultivations was 137 U mL⁻¹ h⁻¹ with feeding rates of starch at 0.17 g L⁻¹ h⁻¹.     

Hot Air Puffing Kinetics for Soy-fortified Wheat-based Ready-to-Eat (RTE) Snacks

The soy-fortified wheat-based flat cold extrudate, after requisite steaming, was puffed in hot air using the high-temperature short-time (HTST) whirling-bed puffing system. The hot-air puffing was conducted at five different hot air temperatures, 200 to 240 °C at constant fluidizing air velocity of 3.95 m s⁻¹ for 50 s of puffing time. The initial moisture of sample was 0.4617 kg kg⁻¹ dm. The already existing 15 different thin layer-drying models were applied to determine the hot air puffing kinetics, based on puffing temperatures. It was found that the Page model could represent hot air puffing kinetics of the steamed flat cold extrudate within 99.3% accuracy. The effective diffusivity was found to be between 1.15623 × 10⁻⁹ and 2.58631 × 10⁻⁹ m² s⁻¹ for steamed flat cold extrudate in the temperature range of 200 to 240 °C. The activation energy for diffusion was found to be 2,341.824 kJ kg⁻¹. The optimum puffing conditions with respect to expansion ratio (ER) and sensory color score were found at puffing temperature of 220 °C and puffing time of 30 s. The variation in ER for the product was found to follow a linear relationship with moisture content of steamed flat cold extrudate during puffing. The Dincer Number for steamed flat cold extrudate puffed in fluidizing air at temperature 220 °C and 3.95 m s⁻¹ velocity was determined to be 276,223.8. This Dincer Number was used to predict the puffing time required to achieve predetermined moisture content of product. The prediction was found to be effective within 10% deviation from the values of experimental puffing time except during the initiation of puffing.     

Quenching of excited states of red-pigment zinc protoporphyrin IX by hemin and natural reductors in dry-cured hams

Zinc protoporphyrin IX (ZnPP), the major red pigment in hams dry-cured without nitrates/nitrites, is an efficient photosensitizer, which upon absorption of visible light forms short-lived excited singlet state (¹ZnPP*) and by intersystem crossing yields the very reactive triplet-excited state (³ZnPP*). Using nano-second laser flash photolysis and transient absorption spectroscopy NADH, ascorbic acid, hemin and dehydroascorbic acid were each found to be efficient quenchers of ³ZnPP*. The deactivation followed, in homogeneous dimethyl sulfoxide (DMSO) or DMSO:water (1:1) solutions, second-order kinetics. The rate constant for ascorbic acid and NADH for reductive quenching of ³ZnPP* was at 25 °C found to be 7.5 ± 0.1 × 10⁴ L mol⁻¹ s⁻¹ and 6.3 ± 0.1 × 10⁵ L mol⁻¹ s⁻¹, respectively. The polyphenols catechin and quercetin had no effect on ³ZnPP*. The quenching rate constant for oxidative deactivation of ³ZnPP* by dehydroascorbic acid and hemin was at 25 °C: 1.6 ± 0.1 × 10⁵ L mol⁻¹ s⁻¹ and 1.47 ± 0.1 × 10⁹ L mol⁻¹ s⁻¹, respectively. Oxidized glutathione did not act as an oxidative quencher for ³ZnPP*. After photoexcitation of ZnPP to ¹ZnPP*, fluorescence was only found to be quenched by the presence of hemin in a diffusion-controlled reaction. The efficient deactivation of ³ZnPP* and ¹ZnPP* by the metalloporphyrin (hemin) naturally present in meat may accordingly inherently protect meat proteins and lipids against ZnPP photosensitized oxidation.     

Effect of Air-Drying Conditions on Physico-chemical Properties of Osmotically Pre-treated Pomegranate Seeds

The drying of pomegranate seeds was investigated at 40 °C, 50 °C and 60 °C with air velocity of 2 m/s. Prior to drying, seeds were osmodehydrated in 55 °Brix sucrose solution for 20 min at 50 °C. The drying kinetics and the effects of osmotic dehydration (OD) and air-drying temperature on antioxidant capacity, total phenolics, colour and texture were determined. Analysis of variance revealed that OD and air-drying temperature have a significant influence on the quality of seeds. Both anthocyanin and total phenolic contents decreased when air-drying temperature increased. The radical diphenylpicril-hydrazyl activity showed the lowest antioxidant activity at 60 °C. Both chromatic parameters (L*, C* and h°) and browning index were affected by drying temperatures, which contributed to the discolouring of seeds. The final product has 22%, 20% and 16% of moisture; 0.630, 0.478 and 0.414 of a _w; 151, 141 and 134 mg gallic acid equivalent/100 g fresh matter (FM) of total phenolics; 40, 24, 20 mg/100 g FM of anthocyanins and 46%, 39% and 31% of antioxidant activity, for drying temperatures of 40 °C, 50 °C and 60 °C, respectively. In view of these results, the temperature of 40 °C is recommended as it has the lowest impact on the quality parameters of the seeds. Differential scanning calorimetry data provided complementary information on the mobility changes of water during drying. Glass transition temperature (Tg′) depends on moisture content and as consequence, on drying conditions. In fact, Tg′ of seeds dried at 60 °C (Tg′ = −21 °C) was higher than those dried at 50 °C (Tg′ = −28 °C) or 40 °C (Tg′ = −31 °C) and osmodehydrated seeds (Tg′ = −34 °C). During OD and drying process, the texture of seeds changed. The thickness of seeds shrank by 55% at 60 °C.