Thin layer mathematical modeling of convective, vacuum and microwave drying of intact and brined onion slices

Effect of microwave vacuum drying time on the quality profiles, microstructures and in vitro digestibility of pork chip snacks

In present study, the quality profiles, microstructures and in vitro digestibility of pork chip snacks (PCS) prepared by microwave vacuum drying (MVD) under different drying times (20, 21, 22, 23, and 24 min) were investigated. The results revealed significant decreases in the moisture content and L*-value of PCS, while the protein/ash contents, a*-value, and b*-value of PCS markedly increased with prolonged MVD time (P < 0.05). Additionally, as MVD time extended from 20 to 24 min, the textural characteristics of PCS, particularly brittleness and crunchiness, initially increased and then gradually decreased (P < 0.05). Scanning electron microscopy (SEM) images showed that a moderate MVD time (22 min) resulted in the formation of larger pores in PCS, enhancing brittleness and crunchiness. However, excessive MVD time (24 min) led to the melting of these pores, subsequently reducing the brittleness and crunchiness of PCS. Furthermore, in vitro protein digestibility of PCS gradually decreased with increasing MVD time, primarily attributed to increased protein aggregation, as indicated by changes in sulfhydryl contents. In summary, our findings highlight that PCS subjected to 22 min of MVD exhibited the highest overall acceptability. This study provides a novel strategy for the application of MVD in the processing of meat snacks.

Thin-layer modelling of sweet potato slices drying under naturally-ventilated warm air by solar-venturi dryer

The drying of agricultural produce is an important food preservation measure. However, high energy requirements for drying, limited access to energy sources, small-medium scale farmers experience high post-harvest losses of their produce. Therefore, there is a need to develop and optimize low-cost food preservation technologies. In this study, eleven mathematical models were used to estimate the drying coefficients following non-linear regression method, in hot-air oven and naturally-ventilated solar-venturi drying to find the best fit of the moisture ration models. Sweet potato tubers were sliced at 3, 5 and 7 mm thickness sizes with and without pre-drying treatments. The prepared sweet potato slices were dried in a hot-air oven dryer at a constant temperature of 70 °C in comparison to the naturally-ventilated solar-venturi dryer with a heated ambient air that varied according to the outside environmental conditions. The drying rate of the samples in a hot-air oven dryer was higher than for those in the naturally-ventilated solar-venturi dryer. The results showed that the drying time was significantly (P < 0.05) affected by the thickness size of sweet potato slices (SPS) and that the drying took place at the falling rate period and a constant drying time. The Midilli et al. model was the best fit for predicting the moisture ratio of SPS dried in hot-air oven dryer and naturally-ventilated solar-venturi dryer based on statistical analysis (R² = 0.982-0.999, χ² = 4.60 × 10^-6-5.56 × 10^-5 and RMSE = 0.011-0.067). The D_eff was 3.32 × 10^-9- 6.31 × 10^-9 m s^-1 for the naturally-ventilated solar-venturi dryer and 1.02 × 10^-8 - 2.19 × 10^-8 m s^-1 for the hot-air oven dryer. According to the results obtained, naturally-ventilated, solar-venturi dryer and lemon juice pre-drying treatment are the suitable application for small-medium scale drying of SPS under Pietermaritzburg conditions.

Effect of ultrasonication and vacuum impregnation pretreatments on the quality of beef marinated in onion juice a natural meat tenderizer

This study aimed to determine the effect of ultrasonication (US) and vacuum impregnation (VI) pretreatment techniques applied for the improvement of tenderness on the quality of beef (Longissimus dorsi) traditionally marinated (TM) in onion juice by immersion. TM conditions were 1:5 meat to marinade ratio, final NaCl concentration of 9% (w/v), 4.3 °C and 24 h. US and VI pretreatments significantly (P < 0.05) improved the marinade uptake, but did not alter the lightness (L*) values of beef samples compared to TM. US for 60 min and VI for 40 min pretreatments reduced the hardness of beef by 28.25 and 21.62%, respectively, compared to TM. US and VI pretreatments significantly (P < 0.05) reduced tyramine levels of uncooked and marinated beef samples. Marination in onion juice was found to reduce the lipid oxidation level of beef and increase the general liking score in the sensorial evaluation. Onion juice can be used as a natural marinade for the traditional marination of beef with the help of ultrasonication and vacuum impregnation pretreatments.

Estimation of moisture ratio for apple drying by convective and microwave methods using artificial neural network modeling

Two different drying methods were applied for dehydration of apple, i.e., convective drying (CD) and microwave drying (MD). The process of convective drying through divergent temperatures; 50, 60 and 70 °C at 1.0 m/s air velocity and three different levels of microwave power (90, 180, and 360 W) were studied. In the analysis of the performance of our approach on moisture ratio (MR) of apple slices, artificial neural networks (ANNs) was used to provide with a background for further discussion and evaluation. In order to evaluate the models mentioned in the literature, the Midilli et al. model was proper for dehydrating of apple slices in both MD and CD. The MD drying technology enhanced the drying rate when compared with CD drying significantly. Effective diffusivity (D_eff) of moisture in CD drying (1.95 × 10^-7-4.09 × 10^-7 m²/s) was found to be lower than that observed in MD (2.94 × 10^-7-8.21 × 10^-7 m²/s). The activation energy (Ea) values of CD drying and MD drying were 122.28-125 kJ/mol and 14.01-15.03 W/g respectively. The MD had the lowest specific energy consumption (SEC) as compared to CD drying methods. According to ANN results, the best R² values for prediction of MR in CD and MD were 0.9993 and 0.9991, respectively.

An improved protocol for natural convective drying of pumpkin

The most effective way to preserve agricultural product is drying. However, vegetable drying is an energy-consuming procedure. Convective drying is the mode considered in this work. The study intends to explore a new way of pumpkin drying, which reduces drying time and minimizes heat consumption. The study considers pumpkin thin slices and pumpkin samples with cubic shape. The samples were subjected to free convection airflow at different temperatures (40 °C, 46 °C, 52 °C, and 60 °C) for each run. A varying airflow temperature was also considered. Airflow velocity was generated by buoyancy forces for each temperature. Drying curves were plotted and fitted to the widely used thin-layer drying models. The modified Page model came out as the best-fitted model. The effective diffusivity coefficient was determined for each case using the slope moisture curve. It appeared that diffusivity was high and drying time was short, for high temperature. Drying processes for slice configuration and cube configuration showed that the latter was more efficient. When applying the regime of increasing temperatures to the cubic samples, data analysis showed that effective diffusivity was higher during the third step in comparison to all the other drying temperatures and the total drying time was similar to that obtained at drying regime on high temperature. With this procedure, the final consumed energy was much less and the time was shorter.

Kinetic modelling of vitamin C losses in fresh citrus juices under different storage conditions

The degradation kinetics of vitamin C in different citrus juice types (tangerine, grapefruit, orange and lime) were investigated during four hours storage at temperatures of 4 and 25°C under different storage conditions in terms of light and oxygen presence. The loss of vitamin C at each sample followed the first-order kinetic model. During storage, predicted half-life of vitamin C ranged from 137.586 to 467.486 min for tangerine; 105.444 to 203.100 min for grapefruit; 365.702 to 1044.668 min for orange and 540.076 to 722.016 min for lime juices. These results indicated that the highest and lowest retentions of vitamin C were observed in orange and grapefruit juices respectively during storage. Additionally, storage time, light penetration and oxygen presence were the most effective factors on vitamin C degradation while the storage temperature revealed no significant effect on the vitamin C content.