Effects of pulsed vacuum drying temperature on drying kinetics, physicochemical properties and microstructure of bee pollen

Study on the quality characteristics of jujube slices under different pretreatment and drying methods

This study investigates the effects of different pretreatment methods, cold plasma (CP) and ultrasound (US), as well as different drying techniques, including vacuum freeze-drying (FD), hot air drying (HAD), and microwave coupled with pulsed vacuum drying (MPVD), on the quality characteristics of winter jujube slices. The physical, chemical, and functional properties were analyzed, encompassing farinograph attributes, particle size, cation exchange capacity, total phenolic and flavonoid content, and flavor compounds were analyzed. In terms of physical properties, jujube slices subjected to MPVD demonstrate superior water-holding capacity at 2.93 g/g and enhanced fluidity, with a sliding angle of 34.98° and an angle of repose of 43.47°, compared to FD jujube slices. Additionally, it exhibits a rehydration capacity of 2.98 g/g and a bulk density of 0.49 g/mL. Regarding chemical composition, the cation exchange capacity of US-FD jujube slices is measured at 0.64 mmol/g, while the total phenolic content reaches 11.97 mg/g, and the flavonoid content in CP-MPVD jujube slices is 5.21 mg/g. Notably, the cation exchange capacity of MPVD jujube slices pretreated by CP and US is 0.46 and 0.55 mmol/g, respectively. Concerning volatile compounds and flavor, FD slices retain higher concentrations of aldehydes (11.39 %) and alkenes (16.88 %), whereas MPVD slices contain 21.20 % alkanes. HAD slices contain the highest aromatic hydrocarbon content at 34.97 %. In summary, the optimized combination of CP and MPVD can enhance the drying efficiency of jujube slices, increase the flavonoid content in jujube slices, and improve their quality characteristics.

Quantifying the Impact of High-Pressure Processing on the Phenolic Profile, Antioxidant Activity, and Pollen Morphology in Honey

Honey can benefit from non-thermal processing techniques such as high-pressure processing (HPP) to improve its quality and bioactivity. This study investigated the impact of HPP (600 MPa for 5, 10, and 15 min) on honey's quality, including the levels of hydroxymethylfurfural (HMF), antioxidant activity, total phenolic content (TPC), and phenolic profile. HPP treatment did not significantly affect HMF or TPC levels but led to selective changes in the phenolic profile. Despite a reduction in certain phenolic compound content, HPP for 5 and 15 min caused a significant increase in the antioxidant activity (2,2-diphenyl-1-picrylhydrazyl [DPPH]) of honey from the mean value of 41.8% to values of 45.4% and 49.6%, respectively. On the other hand, HPP for 10 min did not change the antioxidant activity of tested honey. A 27.5% reduction in the equatorial diameter of pollen grains was observed after HPP combined with temperature at 75°C, suggesting an improved release of bioactive compounds. The content of specific phenolic compounds, including caffeic acid, p-coumaric acid, sinapic acid, naringin, kaempferol, and the TPC, significantly affected the DPPH activity. The increment in the antioxidant activity of HPP honey may be attributed to selective changes in the content of certain phenolic compounds and improved their extraction from pollen grains.

Enhancing the Nutritional and Bioactive Properties of Bee Pollen: A Comprehensive Review of Processing Techniques

Bee pollen is recognized as a superfood due to its high content of nutrients and bioactive compounds. However, its bioavailability is restricted by a degradation-resistant outer layer known as exine. Physical and biotechnological techniques have recently been developed to degrade this layer and improve pollen's nutritional and functional profile. This review examines how processing methods such as fermentation, enzymatic hydrolysis, ultrasound, and drying affect pollen's chemical profile, nutrient content, and bioactive compounds. The review also considers changes in exine structure and possible synergistic effects between these methods. In addition, the challenges associated with the commercialization of processed bee pollen are examined, including issues such as product standardization, stability during storage, and market acceptance. The objective was to provide an understanding of the efficacy of these techniques, their physicochemical conditions, and their effect on the nutritional value of the pollen. The work also analyzes whether pollen transformation is necessary to maximize its benefits and offers conclusions based on the analysis of available methods, helping to determine whether pollen transformation is a valid strategy for inclusion in functional foods and its impact on consumer health. Although the literature reports that pollen transformation influences its final quality, further studies are needed to demonstrate the need for pollen exine modification, which could lead to greater market availability of pollen-based products with functional properties.

Pulsed vacuum drying of fruits, vegetables, and herbs: Principles, applications and future trends

Pulsed vacuum drying (PVD) is a novel vacuum drying method that has demonstrated significant potential in improving energy efficiency and product quality in the drying of foods and agricultural products. The current work provides a comprehensive analysis of the latest advancements in PVD technology, including its historical development, fundamental principles, and mechanistic aspects. The impact of periodic pulsed pressure changes between vacuum and atmospheric pressure on heat and moisture transfer, as well as structural changes in foods at micro- and macro-scales, is thoroughly discussed. The article also highlights the influential drying parameters, the integration of novel auxiliary heaters, and the applications of PVD across various fruits, vegetables, and herbs. Furthermore, the review examines the current status and needs for mathematical modeling of PVD processes, identifying key challenges, research opportunities, and future trends for industrial application. The findings suggest that PVD not only enhances drying efficiency and reduces energy consumption but also preserves the nutritional value, color, and texture of dried products better than traditional methods. Future research should focus on optimizing process parameters and integrating advanced control systems to further improve the scalability and applicability of PVD technology in the food industry.

Flavor Chemical Research on Different Bee Pollen Varieties Using Fast E-Nose and E-Tongue Technology

Bee pollen, derived from various plant sources, is renowned for its nutritional and bioactive properties, aroma, and taste. This study examined the bee pollen with the highest yield in China obtained from four plant species, namely Brassica campestris (Bc), Nelumbo nucifera (Nn), Camellia japonica (Cj), and Fagopyrum esculentum (Fe), using fast e-nose and e-tongue technology to analyze their flavor chemistry. Results showed substantial differences in scent profiles among the varieties, with distinct odor compounds identified for each, including n-butanol, decanal, and ethanol, in Bc, Nn, and Cj, respectively. The primary odorants in Fe consist of E-2-hexen-1-ol and (Z)-3-hexen-1-ol. Additionally, e-tongue analysis revealed seven distinct tastes in bee pollen samples: AHS, PKS, CTS, NMS, CPS, ANS, and SCS, with variations in intensity across each taste. The study also found correlations between taste components and specific odor compounds, providing insights for enhancing product quality control in bee pollen processing.

Uncovering proteome variations and concomitant quality changes of differently drying-treated rape (Brassica napus) bee pollen by label-free quantitative proteomics

High moisture content of fresh bee pollen makes it difficult to preserve and thus makes drying a necessary process during the bee pollen production. Drying treatment will affect its quality and the effects of sun drying, hot-air drying and freeze drying on the proteome of rape (Brassica napus) bee pollen have been evaluated using label-free quantitative proteomics by liquid chromatography-tandem mass spectrometer (LC-MS/MS). A total of 8377 proteins are identified, among which the most abundant differential proteins were found in freeze drying-treated samples. Also freeze-drying treatment maximizes the content of antioxidant, antibacterial and anemic bioactive pollen protein. Besides, rape bee pollen is found to adjust its metabolism to protect itself during the drying process. These results can be favorable to evaluate the effects of drying treatment on the nutrition and function of processed rape bee pollen and insight into how rape bee pollen proteins respond to dehydration.

Quality and Process Optimization of Infrared Combined Hot Air Drying of Yam Slices Based on BP Neural Network and Gray Wolf Algorithm

In this paper, the effects on drying time (Y1), the color difference (Y2), unit energy consumption (Y3), polysaccharide content (Y4), rehydration ratio (Y5), and allantoin content (Y6) of yam slices were investigated under different drying temperatures (50-70 °C), slice thicknesses (2-10 mm), and radiation distances (80-160 mm). The optimal drying conditions were determined by applying the BP neural network wolf algorithm (GWO) model based on response surface methodology (RMS). All the above indices were significantly affected by drying conditions (p < 0.05). The drying rate and effective water diffusion coefficient of yam slices accelerated with increasing temperature and decreasing slice thickness and radiation distance. The selection of lower temperature and slice thickness helped reduce the energy consumption and color difference. The polysaccharide content increased and then decreased with drying temperature, slice thickness, and radiation distance, and it was highest at 60 °C, 6 mm, and 120 mm. At 60 °C, lower slice thickness and radiation distance favored the retention of allantoin content. Under the given constraints (minimization of drying time, unit energy consumption, color difference, and maximization of rehydration ratio, polysaccharide content, and allantoin content), BP-GWO was found to have higher coefficients of determination (R2 = 0.9919 to 0.9983) and lower RMSEs (reduced by 61.34% to 80.03%) than RMS. Multi-objective optimization of BP-GWO was carried out to obtain the optimal drying conditions, as follows: temperature 63.57 °C, slice thickness 4.27 mm, radiation distance 91.39 mm, corresponding to the optimal indices, as follows: Y1 = 133.71 min, Y2 = 7.26, Y3 = 8.54 kJ·h·kg-1, Y4 = 20.73 mg/g, Y5 = 2.84 kg/kg, and Y6 = 3.69 μg/g. In the experimental verification of the prediction results, the relative error between the actual and predicted values was less than 5%, proving the model's reliability for other materials in the drying technology process research to provide a reference.

Optimization of the pulsed vacuum drying process of green walnut husk through temperature adaptive regulation

This study aimed to optimize the temperature adaptive conditions of pulsed vacuum drying (PVD) for green walnut husk (GWH) to tackle the issues of severe environmental pollution and limited utilization of GWH. The results of the single-factor experiment revealed that the optimal drying temperature for PVD of GWH was 65°C, with a pulsed ratio of 9 min: 3 min. The drying time decreased from 10.87 to 6.32 h with increasing drying temperature and from 8.83 to 6.23 kW·h/kg with increasing pulsed ratio. Energy consumption also decreased with shorter drying time and shorter vacuum time. Under this optimal variable temperature drying condition, GWH exhibited the highest total active substance content, with respective values of 9.43 mg/g for total triterpenes, 35.68 mg/g for flavonoids, 9.51 mg/g for polyphenols, and 9.55 mg/g for quinones. The experimental drying data of GWH were best fitted by a logarithmic model, with R2 values ranging from 0.9927 to 0.9943. Furthermore, the observed microstructure of GWH corresponded to the variations in total active substance content. This study provided valuable theoretical guidance for addressing environmental pollution associated with GWH and facilitating the industrialization and refinement of GWH drying processes. PRACTICAL APPLICATION: There is a growing interest in harnessing the potential value of agricultural waste to transform low-cost raw materials into high-value products while mitigating environmental pollution. In this study, for the first time, the effects of variable temperature pulsed vacuum drying on the content of active substances, drying time, and energy consumption of green walnut husk (GWH) were investigated. The findings serve as a theoretical foundation for addressing environmental pollution issues associated with GWH and enabling the industrialization and precision drying of GWH.

Effect of Combined Infrared Hot Air Drying on Yam Slices: Drying Kinetics, Energy Consumption, Microstructure, and Nutrient Composition

Using hot air drying (HAD) and combined infrared hot air drying (IR-HAD) test devices, the drying kinetics, unit energy consumption, color difference values, rehydration rate, microstructure, and changes in polysaccharide and allantoin contents of yam slices were examined at various temperatures (50 °C, 55 °C, 60 °C, 65 °C, and 70 °C). The findings demonstrated that each of the aforementioned parameters was significantly impacted by the drying temperature. IR-HAD dries quicker and takes less time to dry than HAD. The Deff of IR-HAD is higher than that of HAD at the same temperature and increases with the increase in temperature. The activation energy required for IR-HAD (26.35 kJ/mol) is lower than that required for HAD (32.53 kJ/mol). HAD uses more energy per unit than IR-HAD by a factor of greater than 1.3. Yam slices treated with IR-HAD had higher microscopic porosity, better rehydration, lower color difference values, and higher polysaccharide and allantoin levels than HAD-treated yam slices. The IR-HAD at 60 °C had the greatest comprehensive rating after a thorough analysis of the dried yam slices using the coefficient of variation method. Three statistical indicators were used to evaluate six thin-layer drying models, and the Weibull model was most applicable to describe the variation of drying characteristics of yam slices.

The Effect of Different Drying Methods on Bioactive and Nutrition Contents of Bee Bread and Mathematical Modeling of Drying Characteristics

In this study, the aim was to determine the effect of different drying methods (with microwave and hot air) on the color, nutrient and bioactive contents of fresh bee bread. Drying characteristics were also investigated. Microwave and hot air drying were applied at different microwave powers and temperatures, respectively. Lower moisture ratios and highest effective diffusion coefficients were obtained with microwave drying in a shorter time. The Midilli model was found to be the most suitable thin-layer drying model for both methods. Regardless of the drying conditions, moisture, ash, protein, carbohydrate, and lipid proportions were observed to vary in the ranges of 4.9-8.2 %, 1.61-2.67 %, 17.47-32.54 %, 39.92-60.84 %, and 7.10-8.89 %, respectively. The lowest color difference was obtained for the sample dried at 210 W. As a result, it was determined that microwave drying is more suitable for preserving the nutritional and bioactive content of bee bread during drying.