Zhihua Geng

Sea buckthorn is highly popular due to its rich nutritional content. However, sea buckthorn berries are characterized by thin skins, abundant juice, a concentrated maturation period, and an extremely short shelf life. Therefore, drying has become an important method for the processing of sea buckthorn fruits. The three main drying methods currently used for sea buckthorn—hot-air drying, infrared drying, and vacuum freeze drying—are introduced in detail in this paper. The advantages and disadvantages of each of these processing methods are analyzed. In addition, the existing problems in the research on sea buckthorn drying processes are summarized, and the material properties of sea buckthorn are analyzed. The research progress on the application of new drying technologies in berry materials is also reviewed. Finally, we consider the development direction of sea buckthorn in the field of drying processing, with the hope of providing new insights and references for researchers.

Single or combined heat pump technologies are generally used to dry fruits and vegetables, with combined heat pump technologies offering superior performance. This review summarizes the applications of single and combined heat pump drying technologies for fruits and vegetables in China and globally, discusses their current advantages and disadvantages, and outlines future development directions for heat pump-based drying methods. Future research should focus on improving combined heat pump technologies and enhancing the performance of single heat pump drying systems to enhance the effectiveness and feasibility of these technologies for drying fruits and vegetables. Improved technologies would also help meet the increasing demand for high-quality food and social development. Moreover, changes in the mechanisms of key indicators, such as mechanical and thermodynamic properties, should be continuously monitored while drying various fruits and vegetables. Future research into combined heat pump technologies should focus on determining the conversion methods between pairs of drying technologies and identifying the most effective drying technology combinations. Future research into single heat pump technologies should focus on improving the performance levels of core components, such as compressors and drying media.

Sea buckthorn has garnered significant attention owing to its nutritional richness; however, it has a limited shelf life. In this study, the drying process of sea buckthorn was categorized into the first-, second-, and third-drying stages. Regression models were employed to examine the effects of the drying temperature, relative humidity of the medium, and prolonged high humidity retention on various parameters during the first- and second-drying stages. Comparative analysis revealed that the optimal drying conditions for the first-drying stage of sea buckthorn were a drying temperature of 80 °C, relative humidity of 28%, and high humidity retention time of 84 min. In the second-drying phase, the optimal conditions were a drying temperature of 78 °C, a relative humidity of 17%, and a high humidity retention time of 84 min. One-way optimization revealed that the optimal drying temperature for the third-drying stage was 70 °C. The implementation of temperature- and humidity-controlled infrared hot-air drying (TH-IRHAD) techniques considerably improved the outcomes. Specifically, the drying time, energy consumption, and degree of browning decreased by 34.43%, 36.29%, and 21.43%, respectively, whereas the brightness, rehydration ratio, total flavonoid content, and total phenol content increased by 8.94%, 16.99%, 20.57%, and 28.32%, respectively. Staged TH-IRHAD substantially reduced the drying duration, increased the efficiency, and enhanced the drying quality.

Sea buckthorn is a kind of berry rich in nutritional and industrial value. Due to its thin skin, juicy pulp, and short shelf life, it is usually preserved via freezing methods or directly processed into sea buckthorn puree after harvest. It can also be dried and processed into products such as dried sea buckthorn fruit, freeze-dried sea buckthorn powder, and sea buckthorn oil. This review, therefore, provides an overview of the existing state of drying and high-quality processing of sea buckthorn. The effects of different pretreatment and drying techniques on the drying characteristics and quality of sea buckthorn and the existing problems of superior-quality processing of sea buckthorn products are summarised. The development trend of sea buckthorn drying methods and the ways to achieve high-quality processing of sea buckthorn products are indicated. These ways are mainly related to the following: (1) The application of combined pretreatment and drying techniques to find a balance between economy, ecology, and efficiency; (2) Introducing new online measurement and control technology into drying equipment; (3) Optimising the existing process to form a complete sea buckthorn industrial chain and develop the sea buckthorn deep-processing industry.

A drying device based on infrared radiation heating technology combined with temperature and humidity process control technology was created to increase the drying effectiveness and quality of sea buckthorn. Based on the conventional k-turbulence model, the velocity field in the air distribution chamber was simulated using COMSOL 6.0 software. The airflow of the drying medium in the air distribution chamber was investigated, and the accuracy of the model was verified. Given that the inlet of each drying layer in the original model had a different velocity, the velocity flow field was improved by including a semi-cylindrical spoiler. The results showed that installation of the spoiler improved the homogeneity of the flow field for various air intakes, as the highest velocity deviation ratio dropped from 26.68% to 0.88%. We found that sea buckthorn dried more rapidly after being humidified, reducing the drying time by 7.18% and increasing the effective diffusion coefficient from 1.12 × 10⁻⁸ to 1.23 × 10⁻⁸ m²/s. The L*, rehydration ratio, and vitamin C retention rate were greater after drying with humidification. By presenting this hot-air drying model as a potential high-efficiency and high-quality preservation technology for sea buckthorn, we hope to advance the development of research in the sea buckthorn drying sector.

To realize the classification of sea buckthorn fruits with different water content ranges, a convolution neural network (CNN) detection model of sea buckthorn fruit water content ranges was constructed. In total, 900 images of seabuckthorn fruits with different water contents were collected from 720 seabuckthorn fruits. Eight classic network models based on deep learning were used as feature extraction for transfer learning. A total of 180 images were randomly selected from the images of various water content ranges for testing. Finally, the identification accuracy of the network model for the water content range of seabuckthorn fruit was 98.69%, and the accuracy on the test set was 99.4%. The program in this study can quickly identify the moisture content range of seabuckthorn fruit by collecting images of the appearance and morphology changes during the drying process of seabuckthorn fruit. The model has a good detection effect for seabuckthorn fruits with different moisture content ranges with slight changes in characteristics. The migration deep learning can also be used to detect the moisture content range of other agricultural products, providing technical support for the rapid nondestructive testing of moisture contents of agricultural products.

Seabuckthorn berries are difficult to dry because the outermost surface is covered with a dense wax layer, which prevents moisture transfer during the drying process. In this study, uses of ultrasonic-assisted alkali (UA), pricking holes in the skin (PH) and their combination (UA + PH) as pretreatment methods prior to hot air drying and their effects on drying characteristics and quality attributes of seabuckthorn berries were investigated. Selected properties include color, microstructure, rehydration capacity, as well as total flavonoids, phenolics and ascorbic acid contents. Finally, the coefficient of variation method was used for comprehensive evaluation. The results showed that all pretreatment methods increased the drying rate; the combination of ultrasonic-assisted alkali (time, 15 min) and pricking holes (number, 6) (UA15 + PH6) had the highest drying rate that compared with the control group, the drying time was shortened by 33.05%; scanning electron microscopy images revealed that the pretreatment of UA could dissolve the wax layer of seabuckthorn berries, helped to form micropores, which promoted the process of water migration. All the pretreatments reduced the color difference and increased the lightness. The PH3 samples had the highest value of vitamin C content (54.71 mg/100 g), the UA5 and PH1 samples had the highest value of total flavonoid content (11.41 mg/g) and total phenolic content (14.20 mg/g), respectively. Compared to other pretreatment groups, UA15 + PH6 achieved the highest quality comprehensive score (1.013). Results indicate that UA15 + PH6 treatment is the most appropriate pretreatment method for improving the drying characteristics and quality attributes of seabuckthorn berries.

The effects of temperature, air velocity, and infrared radiation distances on the drying characteristics and quality of apple slices were investigated using infrared-assisted-hot air drying (IRAHAD). Drying temperature and air velocity had remarkable effects on the drying kinetics, color, total phenol content, total flavonoid content, and vitamin C content (VCC) of apple slices. Infrared radiation distance demonstrated similar results, other than for VCC and color. The shortest drying time was obtained at 70 °C, air velocity of 3 m/s and infrared radiation distance of 10 cm. A deep neural network (DNN) was developed, based on 4526 groups of apple slice drying data, and was applied to predict changes in moisture ratio (MR) and dry basis moisture content (DBMC) of apple slices during drying. DNN predicted that the coefficient of determination (R²) was 0.9975 and 1.0000, and the mean absolute error (MAE) was 0.001100 and 0.000127, for MR and DBMC, respectively. Furthermore, DNN obtained the highest R² and lowest MAE values when compared with multilayer perceptron (MLP) and support vector regression (SVR). Therefore, DNN can provide new ideas for the rapid detection of apple moisture and guide apple processing in order to improve quality and intelligent control in the drying process.

Glycyrrhiza uralensis is used to treat alcoholic liver injury in China; however, its pharmacological mechanism remains to be clarified. Here, the potential of G. uralensis for the treatment of alcoholic liver injury was explored using a network pharmacology and molecular docking approach. The effective components and targets of G. uralensis were searched in a traditional Chinese medicine systems pharmacology database and analysis platform. Disease targets were obtained using the GeneCards and OMIM databases. The target genes of G. uralensis and alcoholic liver injury were compared to obtain common target genes. Symbol conversion was carried out using the Uniport database, and the composition–target network of G. uralensis and alcoholic liver injury was prepared. A protein–protein interaction network was constructed. Gene Ontology functional enrichment and the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed. AutoDock was used for the molecular docking of core compounds and key targets. One hundred and ninety-three common target genes of G. uralensis and alcoholic liver injury were screened. We identified targets of five active components of G. uralensis, namely, formononetin, 3′-methoxyglabridin, glypallichalcone, 1-methoxyphaseollidin, and glabridin. The main targets identified via the protein–protein interaction network analysis were JUN, MAPK3, STAT3, AKT1, and MAPK1. The biological processes associated with xenobiotic stimulus and lipopolysaccharide metabolism were involved. These biological processes were common between Glycyrrhiza treatment and liver injury. They mainly involved lipid and atherosclerosis, chemical carcinogenic gene-receptor activation, and Kaposi sarcoma-associated herpesvirus. Shinpterocarpin and 7-methoxy-2-methyl-isoflavone had good docking effects with MAPK3, and their binding energies were less than −5 kcal/mol. Based on the network pharmacology and molecular docking analyses, the chemical compositions, potential targets, and pathways involved in G. uralensis treatment of alcoholic liver injury were successfully predicted. This study lays a foundation for the selection of drugs to treat alcoholic liver injury.