Effect of the ripening stage on the pulsed vacuum drying behavior of goji berry (Lycium barbarum L.): Ultrastructure, drying characteristics, and browning mechanism.

In current work, the effect of ripening stages (I, II, and III) on pulsed vacuum drying (PVD) behavior of goji berry was explored. The shortest drying time of goji berry was observed at stage I (6.99 h) which was 13.95 %, and 28.85 % shorter than those at stages II, and III, respectively. This phenomenon was closely associated with the ripening stage, as contributed by the initial physiochemical differences, ultrastructure alterations, and moisture distribution. In addition, lower maturity suffered more severe browning, primarily due to the enzymatic and non-enzymatic reactions of phenolics, followed by pigment degradation and the Maillard reaction. Additionally, the PVD process promoted the rupture and transformation of the pectin fractions, also causing browning either directly or indirectly through participation in other chemical reactions. These findings suggest that the appropriate ripening stage of goji berry should be considered as having a significant impact on drying behaviors and quality attributes.

Quality Evaluation and Browning Control in the Multi-Stage Processing of Mume Fructus (Wumei).

The dried Mume Fructus (MF), called Wumei in China, is a unique food with medicinal and edible effects. But its actual production method is outdated with low efficiency and inconsistent quality. This study systematically investigated the influence of moisture content (MC), temperature, and relative humidity (RH) on the browning reaction and quality characteristics of the MF and proposed a continuous processing strategy of the three-stage variable process for MF production based on the precise process control of the temperature and the RH. The production process of MF was divided into three stages: preliminary dehydration, browning, and drying. The results showed that the browning reaction rate and drying efficiency were optimal when the MC of the raw materials was reduced to 50%. In the browning stage, the degree of browning was better, and the antioxidant capacity reached the maximum of 64.38 mg/g DM under a processing temperature of 80 °C and an RH of more than 60%. As the RH increased, the drying rate decreased, and the ash content exhibited an increase. Therefore, the optimal processing parameters for the browning stage were determined to be a temperature of 80 °C and an RH of 60%. In the final drying stage, a temperature of 60 °C coupled with a dehumidification mode proved sufficient to ensure efficient drying without compromising the quality of the MF. This study revealed the reaction mechanism of the rapid browning processing of MF, which has important guiding significance for the rapid processing of browning foods.

Vacuum-steam pulsed blanching: An emerging method to enhance texture softening, drying behavior and physicochemical properties of Cornus officinalis.

Vacuum steam pulsed blanching (VSPB) was employed as a novel blanching technology on Cornus officinalis to soften the tissue for subsequent coring and dehydration. The current work aims to explore its effect on mass transfer behavior, PPO inactivation, drying characteristics, physicochemical properties, antioxidant capacity, and microstructure of C. officinalis. Results showed that VSPB increased water loss, decreased solid gain, and increased weight reduction with increased blanching cycles. Besides, VSPB significantly changed physical properties and extensively reduced drying time which was attributed to the cell wall components dissolving and cell turgor pressure decreasing, also verified by observing microstructure alteration. PPO was completely denatured after blanching in 6 cycles, but phenolic compounds were still diffused or degraded. Notably, the content of flavonoids and antioxidant capacity significantly increased compared to fresh samples probably due to increased extractability caused by the disrupting cell structure. Besides, the carotenoids and ascorbic acid could be well preserved.

Comparative Study on the Influence of Various Drying Techniques on Drying Characteristics and Physicochemical Quality of Garlic Slices.

Effects of vacuum freeze drying (VFD), air impingement drying (AID), hot air drying based on temperature and humidity control (TH-HAD), pulsed vacuum drying (PVD), and medium- and short-wave infrared radiation drying (MSIRD) on the drying characteristics and physicochemical properties of garlic slices were investigated in the current work. Based on the experimental results, the Weibull model fitted the experimental results better (R2 > 0.99) than the Wang and Singh model. Samples dried with PVD showed the smallest color difference (ΔE*), better rehydration capacity and desirable reducing sugar content. In response to thermal effects and pressure pulsations, the cell walls gradually degraded, and the cell and organelle membranes ruptured. The allicin and soluble pectin contents of garlic slices treated with PVD were higher by 8.0-252.3% and 49.5-92.2%, respectively, compared to those of the samples dried by other techniques. VFD maintained a complete garlic slice structure with the minimum shrinkage and the best appearance. The MSIRD process produced the densest structure, and caused an additional loss of color and phytochemical contents. The findings in current work implied that PVD could be a promising drying technique for garlic slices.

Chemical and physical pretreatments of fruits and vegetables: Effects on drying characteristics and quality attributes - a comprehensive review.

Pretreatment is widely used before drying of agro-products to inactivate enzymes, enhance drying process and improve quality of dried products. In current work, the influence of various pretreatments on drying characteristics and quality attributes of fruits and vegetables is summarized. They include chemical solution (hyperosmotic, alkali, sulfite and acid, etc.) and gas (sulfur dioxide, carbon dioxide and ozone) treatments, thermal blanching (hot water, steam, super heated steam impingement, ohmic and microwave heating, etc), and non-thermal process (ultrasound, freezing, pulsed electric field, and high hydrostatic pressure, etc). Chemical pretreatments effectively enhance drying kinetics, meanwhile, it causes soluble nutrients losing, trigger food safety issues by chemical residual. Conventional hot water blanching has significant effect on inactivating various undesirable enzymatic reactions, destroying microorganisms, and softening the texture, as well as facilitating drying rate. However, it induces undesirable quality of products, e.g., loss of texture, soluble nutrients, pigment and aroma. Novel blanching treatments, such as high-humidity hot air impingement blanching, microwave and ohmic heat blanching can reduce the nutrition loss and are more efficient. Non-thermal technologies can be a better alternative to thermal blanching to overcome these drawbacks, and more fundamental researches are needed for better design and scale up.

High humidity hot air impingement blanching (HHAIB) enhances drying rate and softens texture of apricot via cell wall pectin polysaccharides degradation and ultrastructure modification.

The effects of high humidity hot air impingement blanching (HHAIB) over a range of application times (30, 60, 90, and 120 s) on drying characteristics, hardness, cell wall pectin fractions contents and nanostructure, as well ultrastructure of apricot were investigated. Results showed that HHAIB reduced drying time and decreased the hardness of apricot by 20.7%-34.5% and 46.57%-71.89%, respectively. The water-soluble pectin (WSP) contents increased after blanching, while the contents of chelate-soluble pectin (CSP) and sodium-carbonate-soluble pectin (NSP) decreased significantly (P < 0.05). The hardness and drying time were found to correlate inversely with the WSP content, but positively with CSP and NSP contents. Atomic force microscopy (AFM) detection showed the decomposition and degradation of pectin fractions during blanching. Additionally, transmission electron microscopy (TEM) observation indicated that the cell wall structure was degraded and middle lamella integrity was destroyed by blanching.

Effects of high-humidity hot air impingement blanching (HHAIB) pretreatment on the change of antioxidant capacity, the degradation kinetics of red pigment, ascorbic acid in dehydrated red peppers during storage.

Effect of high-humidity hot air impingement blanching on photochemical degradation kinetics (red pigments and ascorbic acid) and antioxidant capacity changes (2,2-diphenyl-1-picrylhydracyl, DPPH and total antioxidant capacity) of red pepper during 6-month storage at ambient temperature in dark was investigated. Ultrastructure of raw and blanched samples was also observed using a transmission electron microscope (TEM). Blanching followed by drying resulted in 63-85% and 33-59% reduction in red pigment and ascorbic acid content, respectively. The antioxidant capacity of samples was found to increase after drying. After 6-month storage, further breakdown of red pigment and ascorbic acid was observed. The red pigment degradation followed the first-order reaction kinetics; untreated samples displayed the most red pigment loss, while the Weibull model described well the ascorbic acid degradation kinetics. Ultrastructure observations explained why over-blanching can cause serious phytochemical degradation. The current findings indicate proper blanching pretreatment prevents phytochemicals degradation of dried pepper during storage.