Strawberry Slices Research Articles

Drying Strawberry Slices: A Comparative Study of Electrohydrodynamic, Hot Air, and Electrohydrodynamic‐Hot Air Techniques

ABSTRACTThe investigation encompassed an examination of the drying durations, modeling, and quality attributes (color, rehydration capacity, microstructural features, total soluble solid [TSS], and pH values) of strawberry slices subjected to diverse drying methodologies, namely electrohydrodynamic (EHD), EHD‐hot air, and hot air processes. Furthermore, 10 distinct thin‐layer drying models were applied, and their goodness‐of‐fit was assessed to identify the most suitable model for the drying process. This analysis encompassed applying two distinct temperatures (50°C and 55°C), and voltage levels (20 and 30 kV). The EHD method yielded the lengthiest drying durations for the strawberry samples, with hot air and EHD‐hot air drying techniques subsequent in descending order of drying time. The outcomes of the modeling analyses demonstrated that the thin‐layer drying behaviors of used drying methods were best described by the Midilli et al. and Wang and Singh models in terms of their goodness‐of‐fit. A decline in the L* values was noted with the elevation of temperature in the hot air drying method and with the escalation of voltage in the EHD drying. The minimum a* value was detected in the hot air drying method conducted at 55°C. The rehydration capacity of strawberry samples subjected to the EHD and EHD‐hot air combination drying methods (except 20 kV‐55°C) did not exhibit any statistically significant variation in response to different voltage settings. Although the structure of strawberry samples dried with 20 kV application was observed as smoother, cracks occurred on the product surface in other drying applications. In hot air and EHD methods, varying temperature and volt applications did not show a significant effect on TSS and pH values. As a result, it has been seen that EHD technology, which is a promising drying method used in this study, is a suitable method in terms of processing efficiency and consumer acceptability of dried strawberry products.

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.

Influence of Pretreatments and Freeze-Drying Conditions of Strawberries on Drying Kinetics and Physicochemical Properties

The aim of this study is to analyze the effects of pretreatments and drying temperature on the freeze-drying (FD) kinetics, ascorbic acid content, color changes, and antioxidant activity (AA) of strawberries. Experiments were performed at 20 °C, 40 °C, and 60 °C, with a constant pressure of 63 Pa in the FD chamber. The strawberry samples were cut into slices (CS) and pulped (PS) before drying. The drying kinetics was best described using the Midilli or logistic model depending on the strawberry grinding method used and the FD temperature. The FD of strawberries significantly increased the lightness, redness, and yellowness of the dried fruit. The FD temperature and pretreatment methods had little influence on the total phenolic content (TPC) and AA. The lowest TPC was found in strawberry pulps after dehydration at 60 °C, and the highest TPC was observed in strawberry slices dehydrated at the same temperature (18.54 and 22.04 mg of gallic acid equivalent per gram of dry mass, respectively). Furthermore, the ascorbic acid content in dried strawberries was higher for the samples freeze-dried at a higher temperature.

Electrohydrodynamic drying of fruit slices: Effect on drying kinetics, energy consumption, and product quality

The effect of electrohydrodynamic drying on the drying kinetics, energy consumption, and quality was studied for apple and strawberry slices with different thicknesses from 1 to 4 mm. Effective diffusivity and energy consumption were quantified via direct measurements, while visual quality attributes, such as color and shrinkage were determined through image analysis. It was found that effective diffusivity was independent of thickness, around 0.5×10-11 m2/s for apples and 0.24×10-11 m2/s for strawberries. The average specific energy consumption increased with the fruit thickness from 601.13 kJ/kg (1 mm) to 1433.83 kJ/kg (4 mm) for apple slices and from 1324.17 (3 mm) to 1756.71 kJ/kg (4 mm) for strawberry slices. The effect of EHD drying on apple color was significantly smaller than conventional hot-air drying. The impact of EHD drying on the shrinkage of apple slices was about 85%, and for strawberry slices, about 90%, which was higher than in hot-air drying. It can be concluded that EHD is effective for drying thin fruit slices due to the low energy consumption and better quality.

Influence of ethanol and ultrasound on drying, bioactive compounds, and antioxidant activity of strawberries (Fragaria × ananassa)

This study aimed to evaluate the use of ethanol (ET) and ultrasound (US) in convective drying of strawberry slices, as well as the effect on physicochemical, bioactive, and antioxidant parameters. For this, strawberry slices with a thickness of 0.005 m were pretreated with ET (in different volume fractions), US, and a combination of both. Drying kinetics were performed for control strawberry slices (without ET and US) and pretreated with 50% ethanol (ET50), 50% ethanol and ultrasonic (ET50US), 100% ethanol (ET100), and 100% ethanol and ultrasonic (ET100US) at a temperature of 60 °C. Empirical and diffusive models were fitted to the experimental data to describe the drying kinetics, and the fresh and dried slices were analyzed according to the parameters of water activity (aw), water content, total phenolic compounds (TPC), total anthocyanins (ATS), vitamin C and antioxidant activity (AA) (ABTS•+, DPPH•, and FRAP). The use of the ET100US combination provided an increase in the moisture transport process, higher drying rate, shorter process time (570 min), and reduction of aw to a safe value (aw <0.5), however, it sharply degraded the TPC, ATS, and AA. The ET50US pre-treatment even with a drying time of 690 min was the most efficient, since the values of TPC, ATS, and vitamin C suffered smaller reductions, where the AA varied in only 10.32%, 13.78% and 6.54% for the methods ABTS•+, DPPH•, and FRAP, respectively when compared to fresh strawberry. In this sense, it can be stated that the pre-treatment with 50% ethanol and ultrasound (ET50US) showed less reduction in the degradation of bioactive and antioxidant properties, and in the minimization of drying time for strawberry slices.

Effects of ultrasound and ultra-high pressure pretreatments on volatile and taste compounds of vacuum-freeze dried strawberry slice

The influences of ultra-high pressure (UHP), ultrasound (US) and their combination (UHP-US) assisted vacuum-freeze drying on volatile and taste compounds of strawberry slices were analyzed by GC-MS, HS-GC-IMS, HPLC, E-tongue as well as sensory analysis. Three pretreatments of vacuum-freeze dried strawberry slices could increase the concentrations of characteristic volatile compounds (hexanoates and 2,5-dimethyl-4-methoxy-3(2H)-furanone), especially UHP-US (P < 0.05) sample, the increase of compounds associated with floral, fruity and sweet notes. Meanwhile, these pretreatments would ameliorate the taste of dried strawberry slices, individual sugars (glucose and fructose) increased, while the organic acids (malic acid and citric acid) contents decreased, which was consistent with the result of E-tongue. On the other hand, the taste of US sample was better than other samples, the glucose and fructose content (sweetness) of US sample increased by 19.42%, 23.51%, respectively, whereas the malic acid content (sourness) was decreased for 5.03%. All in all, US pretreatment would help to better improve the critical flavors for vacuum-freeze dried strawberry slices.

Survival of Hepatitis A Virus on Two-Month Stored Freeze-Dried Berries

Imported berries have contributed to U.S. hepatitis A virus (HAV) infections. Minimal processing by freeze-drying is preferred by industry for preserving food quality, but virus inactivation by this process may be limited. This study investigated HAV survival on strawberries during 24-h freeze-drying followed by 22°C storage. The outer surfaces of strawberry slices were prepared and each inoculated with 5 to 6 log PFU HAV, air dried for 20 min, frozen for 1 h at -80°C, and freeze-dried for 24 h with radiant heating up to 36°C. Infectious HAV levels eluted from berry slices were quantified on FRhK-4 cells grown onto six-well dishes. Freeze-drying trials (n = 17) with radiant heating inactivated ≤1 log PFU per trial, although HAV inactivation was significantly (P < 0.01) greater at 36°C than at 15°C heating. Average HAV reduction rate on dried berries continuously decreased as storage time increased: 0.2-, 0.09-, 0.08-, 0.04-, 0.04-, and 0.03-log reduction per day at day 2, 7, 14, 28, 42, and 56, respectively, with the cumulated log reduction divided by storage days. Therefore, the best-fit regression for the total or cumulative virus reduction (Y) at any given day (X) is Y = 0.2882X0.4503 (r2 = 0.97), with a maximum 2.7-log reduction on berries throughout the drying and subsequent 2-month storage. HAV showed the greatest decline within the first 14 days of storage of dried berries (ca. 70% weekly reduction from its previous week's level), but the HAV reduction rates were still lower than that occurring on fresh produce.

Microbial inactivation and drying of strawberry slices by supercritical CO2

This work explores the feasibility to apply supercritical carbon dioxide (scCO2) to dry and increase the microbial safety of strawberries. Strawberry slices were dried at 10 MPa and 40 °C up to 6 h. The treatment was able to remove the 98% of the initial moisture content, corresponding to a weight loss of 90%. The method showed a limited inactivation power towards total mesophilic bacteria, while yeasts and moulds were under the detection limit of the technique (<10 log CFU/g). The process is efficient against different strains of pathogens (E. coli O157:H7, Salmonella spp. and L. monocytogenes), which were inoculated on the sample surface. Results highlight the potential of scCO2 drying as innovative food drying technology for the simultaneous drying and stabilization of the product without the use of high temperatures.

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.

Optical and thermal properties of edible coatings for application in solar drying

Solar drying is a sustainable process that may impact the quality of dried food. This is because, pigments contained in food are sensitive to sunlight, and exposure to ultraviolet radiation can affect them. We applied biopolymer-based coatings on strawberry, from hydro-colloidal solutions of Opuntia ficus indica-mucilage, fenugreek, xanthan gum, gum Arabic, and guar gum to evaluate their potential use as UV filters for solar drying of food. Thermal properties and the optical transmittance, absorbance and reflectance of the coatings were measured to assess their influence on food-sunlight interaction. During the drying experiments, the moisture content, total anthocyanins (TA), and total phenolic compounds (TPC) were measured. Optical and thermal properties are influenced by the biopolymer-based coatings. Also, the optical properties are influenced by the coating thickness. The differences in optical and thermal properties influence the drying process. Differences exist in the drying rate for strawberry slices with coating, compared with those without the coatings. In general, the TA and TPC content in the product are better preserved under solar drying than in control experiments done in a drying oven. A partial transmittance of solar UV radiation is recommended to obtain increased TA and TPC contents in the dried product.

Impact of ultrasound combined with ultrahigh pressure pretreatments on color, moisture characteristic, tissue structure, and sensory quality of freeze‐dried strawberry slices

The effect of pretreatments (ultrasound (US), ultrahigh pressure (UHP), and the combination (US-UHP)) on the color, moisture, tissue structure, and sensory quality of strawberry slices were investigated. US, UHP, and US-UHP pretreatment significantly increased the anthocyanin content and redness in the center section of strawberry slices, resulting in the increase of anthocyanin content by 0.62 mg/g, 1.01 mg/g, and 3.09 mg/g, respectively. Compared to the control, all pretreatments decreased the moisture content, and transverse relaxation time. The distribution of water become more uniform after pretreatment, and US, UHP, and US-UHP pretreatment decreased the total energy consumption by 12.52%, 29.90%, and 42.39%, respectively. The changes observed on the structure of the strawberry explained the effects of these pretreatments on the water diffusion and color change. Practical applications Freeze vacuum-dried fruit slices is currently increasingly popular with modern consumers due to their long shelf life and nutritional values with an attractive crispy taste. However, freeze vacuum drying is a long drying time, high energy, and cost-intensive process. The application of US-UHP technology is an effective method before food drying since the use of US-UHP pretreatment is used, as well shorter drying times are obtained, and consequently, lower the total energy consumption. The US-UHP improves color and sensory properties of strawberry slices, which can serve as a pretreatment method to process freeze vacuum-dried strawberry slices.

UV-C Treatment Applied Alone or Combined with Orange Juice to Improve the Bioactive Properties, Microbiological, and Sensory Quality of Fresh-Cut Strawberries

The effects of UV-C treatment (5.8 kJ m−2) alone and combined with the addition of orange juice on the bioactive properties, microbiological, and sensory quality of fresh-cut strawberries for 12 days at 0 °C were studied. During storage, the contents of ascorbic acid (AA), total phenols, flavonoids, and anthocyanins were enhanced in strawberry slices only treated with UV-C (UV slices), whereas ellagic acid slightly decreased in correlation with the antioxidant capacity. After 12 days of storage, AA level in UV slices was 10% higher than those in the other samples studied. In addition, UV slices showed higher contents of phenols (about 14%), flavonoids (about 23%), and anthocyanins (11–41%) than untreated slices during storage. However, fresh-cut strawberries UV-C treated and immersed in juice showed slight but significant AA decrease due to its oxidation to dehydroascorbic acid. Also, phenolic compounds decreased that was associated with their diffusion to the juice and correlated with the antioxidant capacity. Although both UV-C treatments alone and combined with juice immersion reduced microbial load, UV-C applied alone allowed obtaining the highest microbial reductions. After 8 days of storage, the most significant reductions were found, 1.4 log units for mesophilic bacteria and 1.3 log units for molds and yeasts. In addition, UV-C applied alone allowed maintaining firmness and obtaining a product with the best sensory quality throughout storage. Hence, the irradiation at 5.8 kJ m−2 applied alone was the most effective preserving treatment and may be useful to obtain a value-added product.

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

Effects of high hydrostatic pressure (HHP) (50, 100, 150, 200 and 250MPa) pretreatment on water mobility and distribution, drying duration, microstructure, color, cell wall fraction and tissue structure of strawberry slices were investigated. HHP significantly increased water mobility of the strawberry slices, resulting in the reduction of drying duration by 9-24%. As the pretreatment pressure was increased, redness value and anthocyanin content continuously increased, soluble pectin (SBP) content increased and then decreased, while the contents of protopectin (PTP) and cellulose decreased. After the HHP pretreatment, chromoplasts and moisture was distributed more uniformly in the strawberry slices. Microscopy images showed the formation of microscopic holes or channels in the matrix and the breakdown of tissue structure by HHP. Results suggested HHP pretreatment disrupted the integrity of the fresh strawberry which enhanced the drying efficiency and migration of the chromoplasts during the vacuum-freeze drying process.

Effects of ultrahigh pressure and ultrasound pretreatments on properties of strawberry chips prepared by vacuum-freeze drying

The present work investigated the influences of ultrahigh pressure (UHP), ultrasound (US) and their combination (UHP-US) as pretreatments on properties of vacuum-freeze dried strawberry slices. During vacuum-freeze drying, drying duration and total energy consumption of UHP sample, US sample and UHP-US sample was decreased. After the UHP or US pretreatments, a* value (redness), antioxidative substances (total anthocyanin content, total flavonoid content, total phenolic content, diphenyl picrylhydrazyl (DPPH), hydroxyl (–OH) radical-scavenging assay), hardness and cross-section areas of matrix in the dried slices were significantly (P < 0.05) increased. Transverse relaxation times and peak area corresponding to free water in the pretreated samples were obviously decreased, indicating lower mobility in the pretreated samples. As compared with UHP or US individually, UHP in combination with US increased those parameters more pronouncedly. Therefore, UHP and US are promising techniques for the vacuum-freeze drying processing of strawberry products.

The impact of proportion of different cut-fruits on respiration rate of fruit salad

Fresh fruit and vegetables present a unique challenge since these products continue to respire even after harvesting, resulting in a shelf life which is inversely proportional to the respiration rate. This study aimed to analyse the respiration rate of mixed fresh-cut fruit salad. The experiment was designed according to a simplex lattice method with three types of fruits (strawberry, pineapple chunks and apple slices). The total mass fractions of the three fruits in any given mixture was always unity. The three products were mixed in varying proportions according to a simplex lattice design and the respiration rate was measured at 5°C. The respiration rate varied from 4.1 to 16.4 mL of CO2 kg-1 h with a maximum value observed for strawberry, followed by apple slices and then pineapple chunks. Each individual fruit had a significant effect on the overall respiration rate of fruit salad. The binary mix of strawberry and pineapple showed a negative and significant impact whereas the ternary mix showed a positive impact on the respiration rate of fruit salad. The simplex lattice model developed, provided a good prediction of respiration rate of mixed fruit salad and could be applied to any other mixed fruits or vegetables once the respiration rate of the individual components is known.

Strawberry drying: Development of a closed-cycle modified atmosphere drying system for food products and the performance evaluation of a case study

ABSTRACTIn the present study, a closed-cycle modified atmosphere drying (CC-MAD) system was developed as an alternative drying technique to facilitate drying processes for agricultural commodities appropriate to highly humid and sunny regions with a better quality. An absorption dehumidifying system was designed for working pseudo-continuously with the most efficient absorbent in terms of moisture absorption, desorption rate, and capacity. The system, assisted by a solar panel for absorbent regeneration, was tested, while its optimum working condition was determined by strawberry drying. This unique process was comparatively carried out using hot-air and freeze-drying techniques in terms of processing time and final product quality. Strawberry slices (5 mm thickness) were dried successfully using CC-MAD. The optimum drying conditions of CC-MAD were determined as drying temperature of 60°C, drying air/gas velocity of 3 m/s and drying medium oxygen level of 9.47%. The loss of ascorbic acid was significantly reduced by CC-MAD technique. These losses were found to be 2.9, 6.9, 27.2, and 23.8% by freeze-drying, CC-MAD, hot-air drying, and hot-air drying combined with CC-MAD, respectively. The total monomeric anthocyanins loss was also significantly reduced by the CC-MAD technique (20.3%), in a similar way to that of freeze-drying (18.1%) in comparison with hot-air drying (40.4%). In addition, CC-MAD (12,446 kJ/kg fresh product at 4 h drying time) is three times more advantageous in terms of energy cost compared with freeze-drying (30492.8 kJ/kg fresh product at 24 h drying time) and six times faster in terms of drying time. This new drying system can be used as an alternative to freeze-drying in the drying of foods, especially in products sensitive to oxidation.

Ultraviolet light-C increases antioxidant capacity of the strawberry (Fragaria x ananassa) in vitro and in high-fat diet-induced obese rats.

Flavonoids and polyphenols from the strawberry and other fruits have been proposed to reduce the oxidative stress produced by the obesity and her complications. Moreover, it has been proposed that irradiation with UV‐C to strawberry may increase the antioxidant capacity of this fruit. The aim of the present study was to explore the effects of the UV‐C on antioxidant capacity of strawberry in vitro and in vivo. Strawberry slices were irradiated with ultraviolet light‐C (UV‐C) at 1.2 W/m2/16.5 min; then, the power antioxidant was isolated from the nonirradiated and irradiated strawberry slices into an organic phase, which was lyophilized to finally producing a nonirradiated strawberry extract (NSE) and UV‐irradiated strawberry extract (UViSE) powder. After the antioxidant capacity of both extracts were determined in vitro using the Trolox equivalent antioxidant capacity (TEAC) assay and in vivo using high‐fat diet‐induced obese rats. Our results demonstrated that irradiation with UV‐C to strawberry slices increased the antioxidants content, which was corroborated in vitro, where the antioxidant capacity of UViSE was higher than the NSE. However, in obese rats, the reduction in the oxidative damage by the UViSE and NSE were similar in peripheral tissues. Interestingly, the UViSE was better than the NSE to reduce the oxidative damage in brain. In conclusion, UV‐irradiation increases the antioxidants content of strawberry that is correlated with an increased antioxidant capacity in vitro, but in rats, this antioxidant capacity may be more effective in brain than in peripheral tissues.

Experimental and Numerical Investigation of Strawberry Drying

Strawberry drying was investigated experimentally and numerically in this study. In the experiments, samples of strawberry slices with 1 cm thicknesses were used to investigate the effect of the drying air velocity. 5-hour experiments were conducted for three different velocities (0.5, 1 and 2m/s) at 70°C air temperature. It was observed that increasing the drying air velocity up to 2 m/s decreased the drying duration by 17% on average. Moreover, the data obtained from the experimental study were compared to the numerical results. The results were found compatible with each other. Finally, the effect of air temperature and product thickness on drying was examined numerically.

Drying studies on peach and strawberry slices

AbstractDrying experiments were carried out on peach and strawberry slices using a laboratory scale tray dryer with chamber dimension 30 cm × 30 cm × 20 cm at temperatures of 50, 60, and 70°C for air flow velocities of 0.18, 0.22, and 0.26 m/s. The experimental data were found to fit well with the Page thin-layer drying model. Transport of water during drying was described by Fick’s second law of diffusion and the diffusion coefficients were 3.99, 5.37, and 7 × 10−10 m2 s−1 for peach and 5.39, 7.41, and 8.59 × 10−10 m2 s−1 for strawberry. Activation energy was determined to be 25.92 kJ/mol for peach and 21.49 kJ/mol for strawberry using Arrhenius-type equation.

Preparation of a Nanosilver Composite Plant Medium with Antimicrobial Capability through a Nontoxic Method

A nanosilver composite plant medium with a good antimicrobial capability was successfully prepared via a two-step method in this work. First, nanosilver particles were prepared in a silver nitrate (AgNO3) solution by using D-glucose as a reduction reagent at room temperature. The effect of AgNO3 concentration levels on the size of the nanosilver particles was investigated. The sedimentation activation energy of the nanosilver particles was also measured. Second, the solvent containing the nanosilver particles was added to a Murashige-Skoog medium (a plant growth medium used in the laboratory for the cultivation of plant cell cultures, which was invented by Toshio Murashige and Folke K. Skoog) to form a composite plant medium. The antimicrobial capability of the composite medium was investigated by cultivating in it some fresh strawberry slices. The results showed that the concentration level of AgNO3 significantly influenced the average size of the prepared nanosilver particles. When the AgNO3 concentration was increased from 1.0×10−3 mol/L to 4.0×10−3 mol/L, the average diameter of the nanosilver particles increased from 52 nm to 72 nm, and the sedimentation activation energy of the particles increased from −20.0 kJ/mol to −63.3 kJ/mol. Images from the transmission electron microscope showed that the size distribution of the particles was within narrow parameters. The results of sedimentation activation energy strongly supported the size results obtained from the TEM measurement. It meant that the preparation method could offer good control over the size and size distribution of the nanosilver particles. The cultivation experiments proved that the composite medium has a good antimicrobial capability. Since D-glucose is a nontoxic material, this method of preparing the composite MS medium with an antimicrobial capability was a ‘green’ method.