Continuous and intermittent microwave‐vacuum drying of apple: Drying kinetics, protein, mineral content, and color

Asparagus (Asparagus racemosus L.) roots: nutritional profile, medicinal profile, preservation, and value addition

Asparagus (Asparagus racemosus L.) is one of the most significant traditional medicinal plants, containing phytochemicals that are non-nutritive but beneficial to health. It contains bioactive metabolites such as fructo-oligosaccharides, polysaccharides, asparosides, shatavarins, sapogenins, racemosols, isoflavones, glycosides, mucilage, and fatty acids, while saponin is one of the main active constituents of asparagus roots. Asparagus helps in fertility promotion, stress management, and hormone modulation. It also treats stomach ulcers, kidney disorders, and Alzheimer's disease. Substitution of asparagus powder or extract for value addition of food products (such as beverages, bakery, and milk) enhances the nutritional and functional properties. Currently, the plant is considered endangered in its natural habitat because of its destructive harvesting, habitat destruction, and deforestation. As it is a highly perishable commodity, it needs proper handling, preservation, and storage. This review will outline the medicinal properties, uses, value addition, and preservation techniques of asparagus roots. The study found that, till now, the only preservation techniques used to increase the shelf life of asparagus roots are drying and irradiation. © 2022 Society of Chemical Industry.

Effects of ultrasound pretreatment assisted drying methods on drying characteristics, physical and bioactive properties of windfall apples

BACKGROUND

Drying is one of the most important post-harvest processes in order to ensure that the products harvested in certain periods are consumed throughout the year. In this study, Golden Delicious, Oregon Spur and Granny Smith apple cultivars (fallen apples) were dried in open-sun, a controlled glasshouse, microwave oven (200 W), hybrid system (100 W + 60 °C), convective greenhouse (70 °C) and freeze-dryer (-55 °C) with and without ultrasound pretreatments.

RESULTS

Present findings revealed that the longest drying duration was observed in freeze-drying and the shortest in microwave drying. The greatest color change (ΔE) was observed in ultrasound pretreated Oregon Spur apples dried in a controlled glasshouse. The greatest total phenolics (40.08 mg GAE g^-1 ), DPPH (2,2-diphenyl-1-picrylhydrazyl) inhibition activity (46.96%), FRAP (ferric reducing ability of plasma) antioxidant activity (68.01 μg Trolox g^-1 ) and ascorbic acid content (1.52 mg AAE g^-1 ) were observed in open sun-dried Granny Smith apples without ultrasound pretreatment.

CONCLUSIONS

Generally, microwave and hybrid drying yielded better outcomes for bioactive, HMF (5-hydroxymethyl-2-furfural) and drying characteristics of windfall apples. © 2022 Society of Chemical Industry.

Influence of ultrasonic pretreatments on microwave hot-air flow rolling drying mechanism, thermal characteristics and rehydration dynamics of Pleurotus eryngii

BACKGROUND

In order to improve the drying efficiency and reduce the drying energy consumption of Pleurotus eryngii, microwave hot-air flow rolling drying (MHARD) coupled with ultrasonic pretreating time (0, 20, 40, and 60 min) was used to investigate the drying profile, thermal characteristics, water migration, microstructure and rehydration dynamics of P. eryngii using differential scanning calorimetry (DSC), low-field nuclear magnetic resonance (LF-NMR) analysis and scanning electron microscopy (SEM).

RESULTS

Results showed that the drying time of P. eryngii was 80, 70, 60 and 50 min, accordingly. Energy consumption was significantly reduced by ultrasonic pretreatment, and moisture effective diffusivity (D_eff ) was increased with the increase of ultrasonic pretreating time. DSC curves showed that the drying process was accelerated by ultrasonic pretreatment significantly by enhancing the heat transfer. Meanwhile, SEM images showed that the cell was broken and numbers of irregular holes appeared in the ultrasound-pretreated samples. In terms of rehydration dynamics, Page model could well model the rehydration kinetics of dried P. eryngii with R²  > 0.99.

CONCLUSION

The findings indicate that ultrasonic pretreatment is a promising method for MHARD of P. eryngii as it can enhance the drying process, and show potential for industrial application. © 2021 Society of Chemical Industry.

Experimental Study and Mathematical Modeling of Convective Thin-Layer Drying of Apple Slices

This work represents an experimental study and mathematical modeling of convective apple slice drying. The influence of multiple process parameters such as temperature, air humidity, air velocity and slice thickness on process kinetics, product water activity and parameters of empirical models has been investigated. Drying characteristics of apple slices were monitored at temperatures of 40, 45 and 50 °C, air velocities of 0.6, 0.85 and 1.1 m/s., slice thicknesses of 4, 6, 8, 10 and 12 mm, and in relative air humidity ranges of 25–28, 35–38 and 40–45%. During the process, samples were dried from an initial moisture content of 86.7% to that of 20% (w.b), corresponding to product water activity of 0.45 ± 0.05. By increasing the temperature from 40 to 50 °C, the time for reaching the required product water activity decreased by about 300 min. Sample thickness is the most significant parameter; by increasing the slice thickness from 4 to 12 mm, the time required to achieve the required water activity increased by more than 500 min. For all experimental runs, parameters of five different thin-layer empirical models were estimated. A thin-layer model sensible to process conditions such as temperature, air velocity, layer thickness and air relative humidity was developed and statistically analyzed.