Influence of high hydrostatic pressure pretreatment on properties of vacuum-freeze dried strawberry slices

Effect of various different pretreatment methods on infrared combined hot air impingement drying behavior and physicochemical properties of strawberry slices

In current work, the effect of freezing (F), ultrasound (U), and freeze- ultrasound (FU) pretreatment on infrared combined with hot air impingement drying kinetics, cell ultrastructure, enzyme activity, and physicochemical properties of strawberry slices were explored. Results showed that FU pretreatment enhanced cell membrane permeability via forming micropores, altered water status by transforming bound water into free water and thus promoted moisture diffusivity and decreased drying time by 50% compared to the control group. FU pretreatment also extensively decreased pectin methylesterase enzyme activity and maintained quality. The contents of total phenols, anthocyanins, vitamin C, antioxidant activity, and a* value of dried strawberries pretreated by FU were extensively increased compared to the control group. U and FU pretreatments were beneficial for retaining aromatic components and organic sulfides according to e-nose analyses. The findings indicate that FU is a promising pretreatment technique as it enhances drying process and quality of strawberry slices.

Incorporation of ascorbic acid in chitosan-based coating combined with plasma-activated water: A technology for quality preservation of red grapes after simulated transportation

Red grapes possess multiple bioactivities but are highly susceptible to spoilage due to the lack of efficient preservation techniques. Plasma-activated water (PAW) treatment and the incorporation of antioxidants in bio-based coatings are promising methods for preserving produce. In this study, we tested a novel combination by incorporating ascorbic acid (AA) into a chitosan-based edible coating (CH) and combining it with plasma-activated water (PAW) treatment (CA-PAW) before simulating transport vibrations to extend the shelf-life of red grapes. The results from storage at 4 °C for 20 d indicated that the CA-PAW treatment reduced microbial counts by 2.62 log10 CFU/g for bacteria, 1.72 log10 CFU/g for yeasts and molds, and 1.1 log10 CFU/g for coliforms, in comparison to the control group treated with sterile deionized water. Total phenols and total flavonoid content were the highest observed, at 111.2 mg GAE/100 g and 262.67 mg RE/100 g, respectively. This treatment also inhibited water migration and erosion, and reduced damage to cell structure. Microstructural observations revealed that the CH coating on the surface of red grapes diminished the degradation of bioactive components. In conclusion, the CA-PAW treatment effectively inhibited the adverse physiological changes caused by vibration and mechanical damage to red grapes, maintained their nutritional and sensory qualities, and extended the shelf life by at least 8 d.

Ultra-high pressure treatment improve the content of characteristic aromatic components of melon juice from the view of physical changes

Introduction

The effectiveness of ultra-high pressure (UHP) technology in retaining the flavor of fresh fruit and vegetable juices has been acknowledged in recent years. Along with previously hypothesized conclusions, the improvement in melon juice flavor may be linked to the reduction of its surface tension through UHP.

Methods

In this paper, the particle size, free-water percentage, and related thermodynamic parameters of melon juice were evaluated in a physical point for a deeper insight.

Results

The results showed that the UHP treatment of P2-2 (200 MPa for 20 min) raised the free water percentage by 7,000 times than the other treatments and both the melting enthalpy, binding constant and Gibbs free energy of P2-2 were minimized. This significantly increased the volatility of characteristic aromatic compounds in melon juice, resulting in a 1.2-5 times increase in the content of aromatic compounds in the gas phase of the P2-2 group compared to fresh melon juice.

Construction of photocatalytic coating for alleviating the shriveling of postharvest fruit cucumber after simulated transportation

The shriveling of fruit cucumber was commonly occurred during supply chain, photocatalyst exposed to UV light can endow the coatings with ethylene removal capacity to reduce the respiration of fruit and water loss. The study developed a novel photodynamic technology responsive photocatalytic coating with exceptional ultraviolet (UV) photocatalytic degradation of ethylene ability to decay the shriveling of postharvest fruit cucumber during supply chain. This coating involved the integration of Carbon dots (CDs)-loaded nano ZnO and the skillful selection of pullulan (Pul) and apple pectin (AP) matrix. The CDs/ZnO coatings boasted an impressive array of photocatalytic degradation of ethylene and adhesion properties, including high ethylene removal rates of 32.04 % in 60 min UV light stimulation. The decrease of cell-wall strength, degradation of the cell wall polysaccharides and water loss resulted in cucumber shriveling. Compared with CK sample, after UV-CDs/ZnO coating treatment, the higher firmness and cell wall polysaccharides were found in cucumbers with lower cell wall degrading enzymes activities, weight loss and water movement, which was associated with the decrease of respiration and ethylene accumulation. The UV-CDs/ZnO coatings possessed promising potential for alleviating the shriveling of postharvest fruit cucumber and applications in fruits preservation in the future.

Dehydration-rehydration vegetables: Evaluation and future challenges

In this review, the rehydration kinetics model, the quality factors affecting of vegetables during rehydration process, the future challenges and development direction of rehydration process were comprehensively analyzed. Based on the fitting equation for the change in moisture content during rehydration, a suitable rehydration model can be selected to describe the rehydration process of vegetables. Optimal pre-treatment, drying and rehydration methods were selected by considering quality, energy consumption and environmental aspects, and new technologies were developed to improve the quality characteristics of rehydrated vegetables. It is necessary to classify vegetables according to their shape and type to establish the criteria of rehydration processing through mathematical modeling. Industrial production from pre-treatment to product packaging will be precisely adjusted through process parameters. Furthermore, improvements the quality of rehydrated vegetables can be considered in terms of the structural and compositional aspects of the cell wall and cell membrane.

Non-thermal treatments of strawberry pulp: The relationship between quality attributes and microstructure

The relationship between quality attributes and microstructure in strawberry pulp after pasteurization (PS), ultrasound (US), electron beam irradiation (EB), and high pressure (HP) treatments was investigated. The results showed that US treatment decreased the viscosity to the lowest by 80.15% and increased the a* value, cloudy stability, and contents of titratable acid, total soluble solid, organic acids, total phenols, total flavonoids, and total anthocyanins (TAC), as well as its antioxidant capacity, due to the decrease in particle size, the destruction of microstructure, and the release of intracellular compounds. US and EB treatments could maintain the volatile compounds. The greatest deterioration in TAC and volatile compound content was found in the pulp treated with PS and HP treatments. HP treatment was beneficial to the enhancement of apparent viscosity, organic acids, and soluble sugar. These results provided insights into the enhancement of quality attributes in strawberry pulp due to the microstructure change.

Comparison of high pressure and thermal pasteurization on the quality parameters of strawberry products: a review

Strawberry (Fragaria ananassa) is rich in bioactive compounds with high antioxidant activity. High pressure processing (HPP) is an efficient alternative to preserve these bioactive compounds in terms of microbial inactivation and shelf-life stability. This review compares the effects of pasteurization methods using high pressure or thermal pasteurization (TP) on the quality parameters of various strawberry-based products. To summarize, most of the high pressure-treated products are microbiologically stable and showed minimum degradation of thermolabile compounds than TP-treated ones. However, some studies reported that high pressure did not have an advantage over TP especially in the preservation of phenolic phytochemicals during storage. The insufficient enzyme inactivation and high residual activity of enzymes after high pressure treatment could cause anthocyanins degradation thus affecting the product quality. Overall, this review could be valuable to potential processors in evaluating the effective commercialization of high pressure-treated strawberry products.

Effect of Trehalose on the Physicochemical Properties of Freeze-Dried Powder of Royal Jelly of Northeastern Black Bee

Trehalose is known for its effect of improving the stability of freeze-dried foods. In this work, vacuum freeze-drying (VFD) technology was employed to prepare northeast black bee royal jelly into lyophilized powder and a novel method mixing trehalose into royal jelly is successfully developed to enhance the free radical scavenging ability and the nutrition stability of royal jelly lyophilized powder. The effects of different trehalose content (0, 0.1, 0.3, 0.5, 0.7 and 0.9 wt.%) on the physicochemical properties of lyophilized royal jelly powder were studied. With systematic analysis, it was found that the incorporation of suitable trehalose content in lyophilized royal jelly powder can reduce the loss of the protein, total sugar, total flavone content during the VFD process and enhance the total phenolic antioxidant capacity, solubility, angle of repose, and bulk density of the royal jelly powder. Finally, lyophilized royal jelly with 0.5 wt.% trehalose is selected as the suitable addition content which exhibits the best radical scavenging ability as well as the lowest hygroscopicity. From the perspective of sensory evaluation, all royal jelly lyophilized powders with trehalose are acceptable.

Emerging drying techniques for food safety and quality: A review

The new trends in drying technology seek a promising alternative to synthetic preservatives to improve the shelf-life and storage stability of food products. On the other hand, the drying process can result in deformation and degradation of phytoconstituents due to their thermal sensitivity. The main purpose of this review is to give a general overview of common drying techniques with special attention to food industrial applications, focusing on recent advances to maintain the features of the active phytoconstituents and nutrients, and improve their release and storage stability. Furthermore, a drying technique that extends the shelf-life of food products by reducing trapped water, will negatively affect the spoilage of microorganisms and enzymes that are responsible for undesired chemical composition changes, but can protect beneficial microorganisms like probiotics. This paper also explores recent efficient improvements in drying technologies that produce high-quality and low-cost final products compared to conventional methods. However, despite the recent advances in drying technologies, hybrid drying (a combination of different drying techniques) and spray drying (drying with the help of encapsulation methods) are still promising techniques in food industries. In conclusion, spray drying encapsulation can improve the morphology and texture of dry materials, preserve natural components for a long time, and increase storage times (shelf-life). Optimizing a drying technique and using a suitable drying agent should also be a promising solution to preserve probiotic bacteria and antimicrobial compounds.

Effects of carboxymethyl cellulose/pectin coating combined with ultrasound pretreatment before drying on quality of turmeric (Curcuma longa L.)

Turmeric is an herb with multiple bioactive substances and health benefits. Drying is one of the most important steps of its processing and sales. In order to obtain high-quality turmeric products, we used five different pretreatment methods to treat turmeric prior to pulse-spouted microwave vacuum drying (PSMVD), including carboxymethyl cellulose coating (CMC), pectin coating (P), ultrasound (US) and their combination (CMCUS or PUS). The effect of different pretreatments on the drying kinetics, quality attributes and microstructure of turmeric were evaluated. Results showed that the US pretreatment had the shortest drying time (60 min), while coating treatment did not significantly affect drying rate. Dried turmeric with coating pretreatment had lower rehydration ratio and water adsorption capacity compared with individual ultrasound treatment. Carboxymethyl cellulose coating protected bioactive substances better than pectin coating. Moreover, CMCUS pretreatment showed significantly lower total color change, higher curcumin content, total phenols and flavonoid content as well as antioxidant capacity in all dried samples. Microstructure observation showed that the polysaccharide coating covering the surface of turmeric might reduce the degradation of bioactive compounds. Therefore, the CMCUS pretreatment before PSMVD of turmeric was recommended due to the efficiency and quality protections.

Effects of High Hydrostatic Pressure Combined with Vacuum-Freeze Drying on the Aroma-Active Compounds in Blended Pumpkin, Mango, and Jujube Juice

A combination process of completely non-thermal processing methods involving high hydrostatic pressure (HHP) and vacuum-freeze drying (VFD) for producing a new snack from fruit and vegetable blends was developed, and the effect of the process on flavor quality was investigated. The HHP-VFD treatment did not significantly reduce volatile compound contents compared to single HHP or VFD. Gas chromatography-olfactometry showed that HHP-VFD raised the contents of floral-like volatile compounds (e.g., β-ionone) compared to the untreated sample. Sensory evaluation analysis confirmed that the overall liking was unchanged after the HHP-VFD treatment. The HHP-VFD combined treatment is effective in maintaining the flavor and extending shelf life, and is convenient for the portability and transportation of ready-to-drink juice.

Ultrahigh Pressure Facilitates the Acylation of Malvidin and Chlorogenic Acid to Increase the Stability and Protective Effect of Malvidin Derivatives on H2O2-Induced ARPE-19 Cells

We explored the effects of ultrahigh-pressure technology and chlorogenic acid on the color stability and structure-activity relationship of malvidin (MV). Experimental conditions were optimized through single-factor experiments and response surface analysis at a pressure of 300 MPa, mass ratio of MV to chlorogenic acid of 1:3.64 (w/w), and time of 5 min. Compared with MV, MV derivatives showed higher stability and in vitro antioxidant activity. X-ray diffraction analysis, UV-vis spectroscopy, Fourier transform infrared spectroscopy, high-performance liquid chromatography, and mass spectrometry were conducted to determine the structures of MV derivatives for the first time. Ultrahigh pressure facilitated acylation of chlorogenic acid and MV and produced four new MV derivatives. Analysis of the effect of malvidin-3-O-6-(acrylic acid-(2-hydroxy, 4-carboxy-cyclohexanol) ester)-guaiacol (Mv3ACEC) on ARPE-19 cells exposed to H₂O₂ by RNA transcriptome sequencing showed that Mv3ACEC simultaneously inhibited various inflammatory and apoptotic signal transduction pathways, exerted a synergistic effect, and partly inhibited cell apoptosis through the MAPK signaling pathway. Therefore, the results show that ultrahigh pressure will cause acylation of chlorogenic acid and MV to produce four new MV derivatives, and MV derivatives protect ARPE-19 cells from H₂O₂-induced oxidative stress.

Effect of Osmotic Pretreatment Combined with Vacuum Impregnation or High Pressure on the Water Diffusion Coefficients of Convection Drying: Case Study on Apples

The paper presents water diffusion coefficients as providing a significant contribution to the creation of a comprehensive database and knowledge of weight variation during the drying process of raw plant materials that is used for modelling the technological process and designing innovative products. Dehydration is one of the most widely used methods for improving the stability and durability of fruit and vegetables because it reduces water activity and microbial activity, and minimises the physical and chemical changes during storage. The considerable impact of pressure on heat exchange and weight during the convection drying process of osmotically pretreated apples is demonstrated. The course of the drying curves and the drying rate is determined by the use of pressures of 0.02 and 500 MPa. Varied pressure applied during osmotic impregnation significantly influences the value of the diffusion coefficient: the average determined for the entire course of the drying curve and the average determined in the intervals of the reduced water content. The lowest values of the average water diffusion coefficient are obtained for apples preboiled under overpressure conditions and, at the same time, the determined diffusion coefficients in the water content are characterised on the drying curve by a clearly decreasing course until the reduced water content reaches approximately 0.2.

Effect of multi-mode dual-frequency ultrasound pretreatment on the vacuum freeze-drying process and quality attributes of the strawberry slices

The effects of osmotic pretreatment assisted by ultrasound in different frequency modes before vacuum freeze-drying (VFD) on moisture migration and quality characteristics of strawberry slices were investigated. The frequency modes are single-frequency modes under 20, 40 kHz (SM-20, SM-40), and dual-frequency under 20/40 kHz including sequential mode (SeDM) and simultaneous mode (SiDM). The quality characteristics of dried strawberry products including rehydration, hardness, color, flavor, total anthocyanins, total phenols, vitamin C content, and active antioxidant components (DPPH and -OH) were determined. Results showed that drying time of the strawberry slices irradiated by ultrasound was reduced by 15.25%-50.00%, compared to the control samples. Besides, dual-frequency ultrasound shortened the drying time more than single-frequency ultrasound. The drying time of SeDM was the shortest. In addition to vitamin C content, the quality characteristics including rehydration, hardness, color, flavor, total anthocyanins, total phenols, and antioxidant activity of dried strawberry products pretreated by SeDM were significantly (p < 0.05) better than those of control and other pretreated samples. It can be concluded that the SeDM was an effective pretreatment method to produce high-quality vacuum freeze-dried strawberry products.

Evaluation of infrared assisted freeze drying for strawberry snacks: drying kinetics, energy efficiency and quality attributes

Feasibility of infrared assisted freeze drying (IRAFD) was evaluated for production of the strawberry snacks. Infrared (IR) radiation provided the driving force of ice sublimation during freeze drying (FD). Different IRAFD conditions were tested, including the continuous IRAFD-1.6 kW/m² and IRAFD-1.6 kW/m² at different weight reductions (20%, 40%, and 60%). Conventional FD had a total drying time of 691 ± 19 min, whereas continuous IRAFD significantly reduced the drying time to 309 ± 32 min. Continuous IRAFD also reduced the amount of consumed electrical energy by 42% compared to that of FD. A long duration of IR radiation produced a soft texture in the snacks. Drying kinetics were analyzed using various models, including the Page model, exponential model, and Henderson and Pabis model. The Page model provided the best fit to the experimental drying curve. This study showed the potential of IRAFD in producing value-added fruit snacks with good textural quality and efficient use of energy.

Effect of ultrasonic pretreatment monitored by real-time online technologies on dried preparation time and yield during extraction process of okra pectin

BACKGROUND

Ultrasonic pretreatment is a novel physical method that can be used in the extraction process of okra pectin. Real-time online monitoring technologies were introduced in time and frequency domains when okra was pretreated. Preparation time of dried okra and yield of okra pectin were studied; and physicochemical properties of okra pectin were analyzed at the optimum ultrasonic parameter.

RESULTS

Results showed that ultrasonic intensity of sweeping-frequency ultrasonic (SFU) pretreatment was stronger than that of fixed-frequency ultrasonic pretreatment (FFU). SFU pretreatment (60 ± 1 kHz) at 30 min had a strong ultrasonic voltage peak of 0.05387 V and signal power peak of -6.62 dBm. The preparation time of dried okra was 160 ± 14.14 min in the pretreated group, 44.83% lower than control without SFU pretreatment. The intercellular space was 56.03% higher than control. Water diffusion coefficient increased from 1.41 × 10^-9 to 2.14 × 10^-9  m²  s^-1 . Monobasic quadratic equations were developed for the monitored ultrasonic intensity and pectin yield. Compared to control, extraction yield (16.70%), pectin content (0.564 mg mg^-1 ), solubility (0.8187 g g^-1 ) and gel strength (30.91 g) were improved in the pretreated group. Viscosity decreased, and values of G' and G″ crossing at 63 rad s^-1 revealed the viscoelastic behavior and the beginning of viscous behavior with a sol state.

CONCLUSION

Decrement of dried preparation time and increment of yield were achieved by ultrasonic pretreatment during the extraction process of okra pectin, and the relationship of ultrasonic intensity monitored by real-time online technologies and yield was given. © 2021 Society of Chemical Industry.

Recent Trends in Pretreatment of Food before Freeze-Drying

Drying is among the most important processes and the most energy-consuming techniques in the food industry. Dried food has many applications and extended shelf life. Unlike the majority of conventional drying methods, lyophilization, also known as freeze-drying (FD), involves freezing the food, usually under low pressure, and removing water by ice sublimation. Freeze-dried materials are especially recommended for the production of spices, coffee, dried snacks from fruits and vegetables and food for military or space shuttles, as well as for the preparation of food powders and microencapsulation of food ingredients. Although the FD process allows obtaining dried products of the highest quality, it is very energy- and time consuming. Thus, different methods of pretreatment are used for not only accelerating the drying process but also retaining the physical properties and bioactive compounds in the lyophilized food. This article reviews the influence of various pretreatment methods such as size reduction, blanching, osmotic dehydration and application of pulsed electric field, high hydrostatic pressure or ultrasound on the physicochemical properties of freeze-dried food and drying rate.