Effect of Variety on Rehydration Characteristics of Dried Apples

Dehydration-rehydration vegetables: Evaluation and future challenges

In this review, the rehydration kinetics model, the quality factors affecting of vegetables during rehydration process, the future challenges and development direction of rehydration process were comprehensively analyzed. Based on the fitting equation for the change in moisture content during rehydration, a suitable rehydration model can be selected to describe the rehydration process of vegetables. Optimal pre-treatment, drying and rehydration methods were selected by considering quality, energy consumption and environmental aspects, and new technologies were developed to improve the quality characteristics of rehydrated vegetables. It is necessary to classify vegetables according to their shape and type to establish the criteria of rehydration processing through mathematical modeling. Industrial production from pre-treatment to product packaging will be precisely adjusted through process parameters. Furthermore, improvements the quality of rehydrated vegetables can be considered in terms of the structural and compositional aspects of the cell wall and cell membrane.

Impact of Pretreatment and Drying Factors on Chemical and Biochemical Attributes of Moroccan Thompson Seedless Grapes

Drying is a common technique in the agrifood industry, but insufficient control in the drying process can result in changes to the fruit's appearance due to physiological damage during processing. The aim of this study was to investigate the impact of pretreatment and drying process parameters on Moroccan raisins' quality and safety. The experimental levels of pretreatment factors (blanching, browning agents) and drying temperature were defined at the beginning. Subsequently, a 24-factorial design was employed to provide a simple and reliable model capable of relating directly the response factor (drying time, color intensity change (E∗), chromaticity (C∗), and browning rate) to the variables (NaOH concentration, antibrowning agent concentration, temperature, and relative humidity). All four parameters had a statistically considerable effect on studied responses. Blanching for 5 minutes at 1% of NaOH solution, using an appropriate concentration of antibrowning agent (5% Na2S2O5), and drying at 70°C with 30% of relative moisture can lead to better preservation of grapes' appearance and quality (chromaticity (C∗) and color change (E∗)). Also, in these conditions, a lower browning rate (14.48%), a lower 5-hydroxymethylfurfural content (12.40 mg/100 g DW), and a higher level of polyphenols (135.79 ± 13.17 mg GAE/100 g DW) and flavonoid content (57.81 ± 3.08 mg Qeq/100 g DW) have been recorded while meeting international standards for SO2 content and microbial quality.

Drying and rehydration kinetics of peeled and unpeeled green apple slices (Granny Smith cv)

In this work, the kinetics of drying and rehydration of green apple slices peeled and unpeeled (Granny Smith cv) were studied. The apple slices were dried at 50, 60, and 70 °C, and after that, rehydrated at ambient (T_a) and boiling temperature (T_b). The drying kinetics were adjusted with the Dincer and Dost model, giving a good fit. Effective diffusivity (D_eff) and the convective mass transfer coefficient (h_m) were also determined, both coefficients increase with drying temperature, being 1.25 × 10^-9 m² s^-1 and 9.53 × 10^-7 m² s^-1 the highest values obtained for the peeled apple slices respectively. Peleg and Weibull models were adjusted to the rehydration experimental data obtaining a good fit (R² > 0.99). D_eff values increase significantly with rehydration temperature but take similar values between peeled and unpeeled samples. Acidity, pH, moisture content, solid soluble content, and equivalent diameter were determined to compare the fresh apple slices with those after dehydration and the post-rehydration process. The apple slices rehydrated at boiling temperature better preserved the characteristics of fresh samples due to the short immersion times in water, no significant differences were observed between peeled and unpeeled apples. According to the results, it is convenient to dry the apple slices unpeeled at 70 °C and rehydrate them at T_b.

Effects of cutting and drying method (vacuum freezing, catalytic infrared, and hot air drying) on rehydration kinetics and physicochemical characteristics of ginger (Zingiber officinale Roscoe)

The purpose of this study was to discuss the effects of cutting methods (transverse cutting [TC] and longitudinal cutting [LC]) and drying methods (vacuum freeze-drying [FD], hot air drying [HD], catalytic infrared drying [CID]) on rehydration kinetics and physical and chemical characteristics of rehydrated ginger. The research results showed that the rehydration rate and equilibrium moisture content increased with an increase in temperature. LC samples had a higher rehydration rate, while TC samples showed higher equilibrium moisture. Peleg model can fit the rehydration curve of the sample well. The highest coefficient of determination (R2 ) was 0.99, while the sum of squares error and lowest chi-square (χ2 ) was close to zero. Compared with fresh samples, the rehydrated ginger slices had lower gingerol content, total phenol content (TPC), total flavonoid content (TFC), and higher antioxidant activity. The different cutting methods had no significant effect on the physical and chemical properties of rehydrated ginger. In conclusion, TC-CID rehydrated products have better retention of gingerol, TPC, TFC, and antioxidant properties, which was similar to the principal component analysis. PRACTICAL APPLICATION: The results of this study show that transverse cutting combined with catalytic infrared drying is a unique processing technology. Due to the short xylem of transverse cutting ginger, the xylem diameter can be restored during rehydration, the balanced water content was high, and the quality of dried ginger can be restored to the greatest extent. This makes food processors competitive in the operation process and provides better services to consumers.