Pulsed Vacuum Drying of Persimmon Slices: Drying Kinetics, Physicochemical Properties, Microstructure and Antioxidant Capacity

In order to explore an alternative drying method to enhance the drying process and quality of persimmon slices, pulsed vacuum drying (PVD) was employed and the effects of different drying temperatures (60, 65, 70, and 75 °C) on drying kinetics, color, rehydration ratio (RR), microstructure, bioactive compounds, and the antioxidant capacity of sliced persimmons were investigated in the current work. Results showed that the rehydration ratio (RR) of the samples under PVD was significantly higher than that of the traditional hot air-dried ones. Compared to the fresh samples, the dried persimmon slices indicated a decrease in the bioactive compounds and antioxidant capacity. The total phenolic content (TPC) of PVD samples at 70 °C was 87.96% higher than that of the hot air-dried persimmon slices at 65 °C. Interestingly, at 70 °C, the soluble tannin content and TPC of the PVD samples reached the maximum values of 6.09 and 6.97 mg GAE/g, respectively. The findings in the current work indicate that PVD is a promising drying method for persimmon slices as it not only enhances the drying process but also the quality attributes.

Influence of Drying Methods on Jackfruit Drying Behavior and Dried Products Physical Characteristics

Drying processes including solar, oven, and refractance window were studied to determine their influence on the drying behavior of jackfruit slices and properties of resultant jackfruit powders. The loss of sample mass, converted to the ratio between the water content at time t and the initial water content (moisture ratio), was used as the experimental parameter for modelling drying processes. Fifteen thin layer drying models were fitted to the experimental data using nonlinear regression analysis. Based on the highest R² and lowest SEE values, the models that best fit the observed data were Modified Henderson and Pabis, Verma et al., and Hii et al. for RWD, oven, and solar drying, respectively. The effective moisture diffusivity coefficients were 5.11 × 10⁻⁹, 3.28 × 10⁻¹⁰, and 2.55 × 10⁻¹⁰ for RWD, oven and, solar drying, respectively. The solubility of freeze-dried jackfruit powder (75.7%) was not significantly different from the refractance window dried powder (73.2%) and was higher than oven-dried jackfruit powder (66.1%). Oven-dried jackfruit powder had a lower rehydration ratio and porosity. Differences in rehydration ratio and porosity under different drying methods could be explained by the microstructure. Fractal dimension (FD) and lacunarity were applied to study the structure and irregularities of jackfruit dried with the different methods. FD was significantly (P < 0.05) affected by the drying method. FD ranged from 1.809 to 1.837, while lacunarity ranged between 0.258 and 0.404.

Aloe vera Gel Drying by Refractance Window®: Drying Kinetics and High-Quality Retention

In most cases, conventional drying produces inferior quality products and requires higher drying times. A continuous pilot Refractance Window^® equipment was used to dry Aloe vera gel slabs of 5 and 10 mm thick at 60, 70, 80, and 90 °C, seeking a dry product with high-quality retention. Based on five empirical models, drying kinetics, diffusion coefficient, and activation energy were analyzed. Midilli–Kuck was the best predicting model. Short drying times (55–270 min) were needed to reach 0.10 g water/g solid. In addition, the technique yielded samples with high rehydration capacity (24–29 g water/g solid); high retention of color (∆E, 3.74–4.39); relatively low losses of vitamin C (37–59%) and vitamin E (28–37%). Regardless of the condition of temperature and sample thickness, a high-quality dried Aloe vera gel could be obtained. Compared with other methods, Refractance Window^® drying of Aloe vera achieved shorter drying times with higher quality retention in terms of color, vitamins C and E, and rehydration. Finally, the dried Aloe vera gel could be reconstituted to a gel close to its fresh state by rehydration.

Natural Drying of Astringent and Non-Astringent Persimmon "Rojo Brillante". Drying Kinetics and Physico-Chemical Properties

Persimmon (Diospyros kaki L.f.) crop has markedly increased in Spain, and “Rojo Brillante” persimmon is the main cultivated variety. This astringent cultivar requires de-astringency treatment before commercialization, which may involve an extra cost. Its short commercial season implies handling large volumes of fruits with consequent postharvest losses. Therefore, the development of derived added-value products is of much interest. In this study, astringent and non-astringent “Rojo Brillante” persimmons were dehydrated by following a natural drying method used in Asia. The drying kinetics and physico-chemical properties were analyzed for 81 days. The results indicated subsequent reductions in weight, water content, and water activity throughout the drying process, and the equatorial diameter decreased. All the employed thin-layer mathematical models were suitable for representing the drying characteristics of both products with similar behavior. The effective water diffusivity values were 5.07 × 10⁻¹¹ m² s⁻¹ and 6.07 × 10⁻¹¹ m² s⁻¹ for astringent and non-astringent persimmon samples, respectively. The drying treatment significantly decreased the soluble tannins content, and the astringent samples obtained similar values to those obtained for the non-astringent samples in 20 days. The external and internal flesh of the astringent fruit remained orange through the drying period, while brown coloration in the non-astringent fruit was observed after 57 drying days. Therefore, prior de-astringency treatment would not be necessary.

Effects of hot air, microwave and vacuum drying on drying characteristics and in vitro bioaccessibility of medlar fruit leather (pestil)

The effects of microwave (90 W and 180 W), hot air (60 and 70 °C) and vacuum (60 and 70 °C with 200 and 300 mbar) drying methods on drying characteristics, total phenolic content, antioxidant capacity, color and in vitro gastrointestinal digestion of medlar pestil were investigated. Medlar showed a good potential for pestil production while being the most applicable in microwave treatments. For drying kinetics, five thin-layer drying models were applied and the Page and Modified Page were the best fitted models. L*, b*, chroma and hue angle decreased while a* generally increased in dried pestils. Dried samples showed a general decrement in phenolics and antioxidant capacity. According to in vitro gastrointestinal digestion, intestinal phase of all the samples resulted with an increment in phenolics, FRAP and DPPH compared to undigested extracts. In conclusion, different drying methods may affect the release of phenolics and antioxidant capacity, while leading to increased bioaccessibility during intestinal digestion.

Drying kinetic of tucum fruits (Astrocaryum aculeatum Meyer): physicochemical and functional properties characterization

The aim of the present study was to assess the drying kinetic of tucum fruits (epicarp and mesocarp) Astrocaryum aculeatum Meyer at three different temperatures (50, 60, and 70 °C). The physicochemical characterization, water activity, moisture content, including β-carotene and vitamin C content in-natura and dried fruits were analyzed. The fruit fractions presented high β-carotene, protein and lipid levels. Fatty acid profile showed oleic acid as the major fatty acid. Different mathematical models were computed to assess the drying process. The Page model was observed to be the best to describe the drying kinetic with the highest correlation coefficient (R²) 0.99 and the least Chi squared (χ²) close to 10⁵ at the studied temperatures. The drying process reduced water activity to desirable levels in all trials and β-carotene retentions after drying remained at satisfactory levels, fact that resulted in minimum value of 63% and approximately 94% in some cases. Vitamin C retention was comparatively more around 20-40% compared to control.