MASS TRANSFER KINETICS DURING CONVECTIVE DRYING OF RED PEPPER VAR. HUNGARIAN (CAPSICUM ANNUUM L.): MATHEMATICAL MODELING AND EVALUATION OF KINETIC PARAMETERS

Assessment of the Effects of Roasting, Contact Grilling, Microwave Processing, and Steaming on the Functional Characteristics of Bell Pepper (Capsicum annuum L.)

Bell peppers (Capsicum annuum L.) in various stages of maturity are widely used in the diets of individuals and in the food industry; they are consumed both fresh and after thermal processing. However, every type of processing impacts the overall textural and bioactive characteristics of this plant-based food. In order to quantify the changes in the bioactive substances and color-structural characteristics that occur during selected heat treatments (contact grilling, roasting, roasting combined with microwaving, and steam cooking) of bell peppers at three maturity stages (green, yellow, and red), analyses of antioxidant activity, reducing sugar content, polyphenolic compound content, textural properties, and color coordinates in the L*a*b* system were carried out. Some of the processes used, such as contact grilling (15.43 mg GAE/g d.b.) and roasting combined with microwaving (15.24 mg GAE/g d.b.), proved to be beneficial as the total polyphenol content of green peppers (2.75 mg GAE/g d.b.) increased. The roasting (3.49 mg TE/g d.b.) and steaming (6.45 mg TE/g d.b.) methods decreased the antioxidant activity of yellow bell peppers (14.29 mg TE/g d.b.). Meanwhile, the roasting (0.88 mg Glc/g d.b.), contact-grilling (2.19 mg Glc/g d.b.), simultaneous microwaving and roasting (0.66 mg Glc/g d.b.), and steaming (1.30 mg Glc/g d.b.) methods significantly reduced the content of reducing sugars and reducing substances in red bell peppers (4.41 mg Glc/g d.b.). The studies proved that in order to preserve the antioxidant and bioactive properties of bell peppers, it is necessary to consider the use of appropriately selected heat treatments, depending on the different stages of maturity. The proper selection of adequate thermal treatment can not only increase digestibility, but also improve the bioavailability of bioactive substances from this raw material.

Kinetic Studies and Moisture Diffusivity During Cocoa Bean Roasting

Cocoa bean roasting allows for reactions to occur between the characteristic aroma and taste precursors that are involved in the sensory perception of chocolate and cocoa by-products. This work evaluates the moisture kinetics of cocoa beans during the roasting process by applying empirical and semi-empirical exponential models. Four roasting temperatures (100, 140, 180, and 220 °C) were used in a cylindrically designed toaster. Three reaction kinetics were tested (pseudo zero order, pseudo first order, and second order), along with 10 exponential models (Newton, Page, Henderson and Pabis, Logarithmic, Two-Term, Midilli, Verma, Diffusion Approximation, Silva, and Peleg). The Fick equation was applied to estimate the diffusion coefficients. The dependence on the activation energy for the moisture diffusion process was described by the Arrhenius equation. The kinetic parameters and exponential models were estimated by non-linear regression. The models with better reproducibility were the pseudo first order, the Page, and the Verma models (R2 ≥ 0.98). The diffusion coefficients that were calculated were in the order of 1.26 to 5.70 × 109 m s−2 and the energy activation for moisture diffusion obtained was 19.52 kJ mol−1.

Drying kinetics of probiotic-impregnated murta (Ugni molinae T.) berries

The aim of this study was to evaluate dehydrated murta berries enriched with probiotic (Lactobacillus casei var. rhamnosus) bacteria. L. casei was incorporated to fresh murta by vacuum impregnation at alternative conditions (pressure 50, 150 and 300 mbar; time 5, 10 and 15 min; temperature 20 ± 0.2 °C) and impregnated murta samples were dehydrated by two drying methods at 40 °C, vacuum and convective drying. Both drying processes were modeled by three mathematical models (Weibull, Page and modified Page). According to the statistical tests applied, the Weilbull model obtained the best-fit quality on experimental data. Effective moisture diffusivity varied between 1.23-1.75 × 10^-10 m²/s and 1.16-1.44 × 10^-10 m²/s for vacuum and convective drying, respectively. After impregnation, murta berries contained approximately 10⁷ CFU/g L. casei although maximum counts were found at 150 mbar for 15 min. Drying decreased L. casei viability in 1.5-1.9 log and 0.5-1.2 log for vacuum and convective drying, respectively. Thus, impregnation at 150 mbar for 15 min followed by convective drying at 40 °C appears as the method of choice to produce probiotic enriched murta berries that can be commercialized as probiotic dried snacks.

Quality Assessment and Mathematical Modeling of Hot-Air Convective Drying of Persimmon (Diospyros kaki L.) Fruit

The influence of drying on the color, porosity, shrinkage and moisture of persimmon fruit during convective drying was determined by computer vision. The experiments were performed with persimmon fruit that were cut into slab 20 × 20 mm, which were arranged into a bigger slab, 60 × 60 mm. Drying process was carried out at 60 °C. Noticeable changes in quality parameters (color, porosity and shrinkage) could be observed during the drying process, where the central region of the sample evidenced less changes. Persimmon’s physical properties were experimentally obtained as the temperature function and heat and mass convective coefficients were adjusted as a time function. A numerical simulation using the Finite Volume Method allowed to describe the evolution of temperature and moisture content distributions during drying. The numerical and experimental results of temperature and moisture during persimmon drying were found to be in a good agreement.

Mathematical modeling of drying kinetics of untreated and pretreated cocoyam slices

The effect of pretreatment and drying temperature on the drying kinetics and quality of cocoyam was investigated in this study. The best model to predict the drying kinetics was also determined. Cocoyam slices were pretreated by water blanching (WB) and soaking in sodium metabisulphite (SM) and dried in a hot air oven at temperatures of 50, 60 and 70 °C while untreated samples were sun dried. Seventhin layer drying models (Exponential, Generalized Exponential, Page, Logarithmic, Parabolic, Wang and Singh and Two-term) were fitted to the experimental data and selection was done basedon model with highest correlationcoefficient (R(2)), and lowest reduced chi-square (χ (2)), sum square error (SSE) and root mean square error (RMSE) respectively. The Logarithmic and Parabolic model was found to best describe the oven and sun drying of cocoyam respectively. The vitamin C and beta-carotene value of the dried cocoyam slices, which varied from 0.0038 to 0.0075 and 4.1 to 5.888 mg/100 g respectivelygenerally decreased with an increase in drying temperature.