Effects of Freeze-Thaw Pretreatment Combined with Hot Air on Snake Gourd (Trichosanthes anguina L.)

Snake gourd is a seasonal vegetable with a high water content and medicinal value, but the short harvest period limits the large-scale application of snake gourd. Therefore, the effects of freeze-thaw pretreatment (FT) combined with hot air (HD) on the drying characteristics, active ingredients and bioactivities of snake gourd were investigated. The results showed that FT pretreatment reduced browning and shortened the drying time by 44%; the Page model was the best fit for describing the drying process. The polysaccharide contents (21.70% in alcoholic extract (TG1) and 44.34% in water extract (TG2)) and total phenol contents (1.81% in TG1 and 0.88% in TG2) of snake gourd pretreated by FT-HD were higher than those of snake gourd pretreated by the corresponding HD treatment. The FT pretreatment decreased the molecular weight of snake gourd polysaccharides and increased the molar ratio of glucose. The extracts pretreated by FT-HD showed greater chemical, cellular antioxidant capacity and α-amylase and α-glucosidase inhibition than those pretreated by HD. FT-HD can be recommended for achieving a short drying time and high quality of snake gourd and can be used for the drying of other fruits and vegetables.

Dried Beetroots: Optimization of the Osmotic Dehydration Process and Storage Stability

In this study, beetroots were osmotically dehydrated in sugar beet molasses. The input parameters of the drying process were varied: temperature (20 °C, 40 °C, and 60 °C), time (1 h, 3 h, and 5 h), and concentration of sugar beet molasses (40%, 60%, and 80%). Basic quality indicators were determined for the dried beetroot samples: dry matter content, water loss, solid gain, mineral and betaine content, and phenols and flavonoids, as well as antioxidant potential. After optimizing the results, favorable drying parameters were selected: temperature 60 °C, molasses concentration 70%, and processing time 5 h. According to the optimal drying conditions, the beetroots were dried and stored at 4 °C for 28 days. Half of the dried samples were coated with an edible biopolymer coating based on Camelina sativa oilcake, while the other half of the samples remained uncoated. The sustainability study aimed to confirm the effects of the biopolymer coating on the quality and sustainability of the osmotically dried beetroots.

Sustainable Utilization of Mushroom By-Products Processed with a Combined Osmotic Dehydration Pretreatment and a Hot-Air-Drying Step

Mushroom production and consumption are gaining increased interest due to their unique flavor and nutritional value. However, in the mushroom industry, large amounts of by-products are generated, which have a high negative environmental and economic impact. In this study, an osmotic dehydration process followed by hot-air-drying was applied to mushroom stems to produce dried mushrooms as the end product. The osmotic dehydration conditions (concentration of hypertonic solution, specifically, 10-30% maltodextrin and 20-40% oligofructose; a treatment time of 40-80 min; and a temperature range of 30-50 °C) were optimized using response surface methodology (RSM). The results showed that a four-factor three-level Box-Behnken experimental design was effectively implemented to evaluate the effect of the process parameters and identify the optimal osmotic dehydration conditions for producing osmotically dehydrated mushrooms. The main factor affecting mass transfer was the osmosis temperature, and the optimal conditions were found to be 38 °C, 40% oligofructose and 19.3% maltodextrin as the osmotic agents, and 80 min of immersion time. Moreover, the results showed that osmotic pretreatment, in the optimal conditions, significantly reduced the required drying time of the by-products compared to traditional hot-air-drying, especially at milder drying temperatures. Consequently, the required energy was also reduced by at least 40% at 50 °C.

Effect of Extraction Methods on the Antioxidant Potential and Cytotoxicity of the Combined Ethanolic Extracts of Daucus carota L., Beta vulgaris L., Phyllanthus emblica L. and Lycopersicon esculentum against Gastric Adenocarcinoma Cells

Frequent consumption of fruits and vegetables in the daily diet may alleviate the risk of developing chronic diseases. Daucus carota L. (carrot), Beta vulgaris L. (beetroot) Phyllanthus emblica L. (amla), and Lycopersicon esculentum M (tomatoes) are traditionally consumed functional foods that contain a high concentration of antioxidants, ascorbic acid, polyphenols, and numerous phytochemicals. This study assessed how three distinct preparation methods affect the phenolic, flavonoid, carotenoid, and ascorbic acid contents, antioxidant level, and cytotoxicity of the combined fruit extract. The fruit samples were taken in the ratio of carrot (6): beetroot (2): tomato (1.5): amla (0.5) and processed into a lyophilized slurry (LS) extract, lyophilized juice (LJ) extract, and hot-air oven-dried (HAO) extract samples. The sample extracts were assessed for their phytoconstituent concentrations and antioxidant and cytotoxic potential. The total phenolic content in LS, LJ, and HAO extracts was 171.20 ± 0.02, 120.73 ± 0.02, and 72.05 ± 0.01 mg gallic acid equivalent/100 g, respectively and the total flavonoid content was 23.635 ± 0.003, 20.754 ± 0.005, and 18.635 ± 0.005 mg quercetin equivalent/100 g, respectively. Similarly, total ascorbic acid content, carotenoids, and antioxidant potential were higher in the LS and LJ extracts than in HAO. Overall, the LS extract had a substantially higher concentration of phytochemicals and antioxidants, as well as higher cytotoxic potential, compared to the LJ and HAO extracts. The LS extract was tested in the MKN-45 human gastric cancer cell line to demonstrate its effective antioxidant potential and cytotoxicity. Hence, lyophilization (freezing) based techniques are more effective than heat-based techniques in preserving the phytoconstituents and their antioxidant and cytotoxic potential.

Drying and rehydration kinetics of peeled and unpeeled green apple slices (Granny Smith cv)

In this work, the kinetics of drying and rehydration of green apple slices peeled and unpeeled (Granny Smith cv) were studied. The apple slices were dried at 50, 60, and 70 °C, and after that, rehydrated at ambient (T_a) and boiling temperature (T_b). The drying kinetics were adjusted with the Dincer and Dost model, giving a good fit. Effective diffusivity (D_eff) and the convective mass transfer coefficient (h_m) were also determined, both coefficients increase with drying temperature, being 1.25 × 10^-9 m² s^-1 and 9.53 × 10^-7 m² s^-1 the highest values obtained for the peeled apple slices respectively. Peleg and Weibull models were adjusted to the rehydration experimental data obtaining a good fit (R² > 0.99). D_eff values increase significantly with rehydration temperature but take similar values between peeled and unpeeled samples. Acidity, pH, moisture content, solid soluble content, and equivalent diameter were determined to compare the fresh apple slices with those after dehydration and the post-rehydration process. The apple slices rehydrated at boiling temperature better preserved the characteristics of fresh samples due to the short immersion times in water, no significant differences were observed between peeled and unpeeled apples. According to the results, it is convenient to dry the apple slices unpeeled at 70 °C and rehydrate them at T_b.

Developing ultrasound-assisted hot-air and infrared drying technology for sweet potatoes

The influence of ultrasound (US) pretreatments combined with infrared (IRD) and hot-air (HAD) drying on drying kinetics, mathematical modeling, bioactive compounds (antioxidant activities, Vitamin C, phenolics, and flavonoid contents), qualitative properties (β-carotene, total carotenoids, color indexes, textural profile), enzyme inactivation, and exergetic analysis of sweet potatoes. The US pretreatment at 40 kHz combined with IRD and HAD (70 °C) significantly lessened the drying time and water contents. Besides, it did not affect the sweet potato's bioactive components and other quality-related attributes. The samples' activation energy (E_a) ranged from 17.60 to 29.86 kJ/mol for both dryers, with R² (0.999-0.9809). Control samples had the highest specific energy consumption (SEC) due to the extended drying period, whereas ultrasound (40 kHz) treated samples had the lowest SEC during HAD and IRD at 80 °C. The thermodynamic parameters indicated that increasing the drying temperature lowers the enthalpy and Gibbs free energy, while entropy resulted in negative values. HAD had better textural qualities (hardness and resilience). The US pretreatments followed by HAD or IRD may lead to an energy-efficient method with acceptable quality maintenance.

Role of dehydration technologies in processing for advanced ready-to-eat foods: A comprehensive review

Advanced ready-to-eat foods, which can be consumed directly or only need simple processed before consumption, refer to the products that processing with cutting-edge food science and technology and have better quality attribute. Cold chain and chemical addition are commonly used options to ensure microbial safety of high moisture advanced ready-to-eat foods. However, this requires freezing/thawing processing at high cost or has undesirable residue. Dehydration treatment has the potential to compensate those shortcomings. This article reviewed the positive effects of dehydration on advanced ready-to-eat foods, current application status of dehydration technologies, novel dehydration related technologies and the pathogenic bacteria control of products. It is observed that dehydration treatment is receiving increasing attention for ready-to-eat foods including space foods, 3 D-printed personalized foods and formula foods for special medical purposes. Recently developed drying technologies such as pulsed spouted microwave freeze-drying and infrared freeze-drying have attracted much interest due to their excellent drying characteristics. Finally, intelligent drying, dehydration-nano-hybridization and dehydration-induced multi-dimensional modification technology are some of the emerging R and D areas in this field.

Combining ethanol pre-treatment and ultrasound-assisted drying to enhance apple chips by fortification with black carrot anthocyanin

BACKGROUND

An interesting approach to improve dried foods nutritional properties, functionality, and sensorial attributes, is by taking advantage of pre-treatments for incorporating components into the food matrix. Based on this, this work studied the incorporation of black carrot anthocyanins in apple tissue by using ethanol (concentrations 0-300 mL L^-1 ) as a pre-treatment to ultrasound-assisted convective drying. Samples were pre-treated in acidified ethanol solutions, with and without anthocyanins, and then dried (50 °C, 1 m s^-1 ) by convective and ultrasound-assisted convective (21.77 kHz, 20.5 kW m^-3 ) drying. Both the drying process improvement and the obtained product properties were studied.

RESULTS

The anthocyanins did not influence the drying kinetics. In contrast, time reduction was > 50% by using both ethanol pre-treatments and ultrasound. Ethanol pre-treatments decreased the external resistance to mass transfer, while ultrasound decreased both internal and external resistances. The impregnation increased the anthocyanins (above 947%), which were retained after drying. Colour modifications after pre-treatments and after drying (L*, b*, h° decrease, and a* increase), and antioxidant capacity retention were observed in samples with anthocyanin addition.

CONCLUSION

The results point that ethanol pre-treatments and ultrasound application can accelerate drying, and through the natural colouring incorporation during pre-treatments, the nutritional properties of dried samples were better retained. © 2020 Society of Chemical Industry.

Techniques and modeling of polyphenol extraction from food: a review

There is a growing demand for vegetal food having health benefits such as improving the immune system. This is due in particular to the presence of polyphenols present in small amounts in many fruits, vegetables and functional foods. Extracting polyphenols is challenging because extraction techniques should not alter food quality. Here, we review technologies for extracting polyphenolic compounds from foods. Conventional techniques include percolation, decoction, heat reflux extraction, Soxhlet extraction and maceration, whereas advanced techniques are ultrasound-assisted extraction, microwave-assisted extraction, supercritical fluid extraction, high-voltage electric discharge, pulse electric field extraction and enzyme-assisted extraction. Advanced techniques are 32-36% more efficient with approximately 15 times less energy consumption and producing higher-quality extracts. Membrane separation and encapsulation appear promising to improve the sustainability of separating polyphenolic compounds. We present kinetic models and their influence on process parameters such as solvent type, solid and solvent ratio, temperature and particle size.

Optimization and Prediction of the Drying and Quality of Turnip Slices by Convective-Infrared Dryer under Various Pretreatments by RSM and ANFIS Methods

Drying can prolong the shelf life of a product by reducing microbial activities while facilitating its transportation and storage by decreasing the product weight and volume. The quality factors of the drying process are among the important issues in the drying of food and agricultural products. In this study, the effects of several independent variables such as the temperature of the drying air (50, 60, and 70 °C) and the thickness of the samples (2, 4, and 6 mm) were studied on the response variables including the quality indices (color difference and shrinkage) and drying factors (drying time, effective moisture diffusivity coefficient, specific energy consumption (SEC), energy efficiency and dryer efficiency) of the turnip slices dried by a hybrid convective-infrared (HCIR) dryer. Before drying, the samples were treated by three pretreatments: microwave (360 W for 2.5 min), ultrasonic (at 30 °C for 10 min) and blanching (at 90 °C for 2 min). The statistical analyses of the data and optimization of the drying process were achieved by the response surface method (RSM) and the response variables were predicted by the adaptive neuro-fuzzy inference system (ANFIS) model. The results indicated that an increase in the dryer temperature and a decline in the thickness of the sample can enhance the evaporation rate of the samples which will decrease the drying time (40–20 min), SEC (from 168.98 to 21.57 MJ/kg), color difference (from 50.59 to 15.38) and shrinkage (from 67.84% to 24.28%) while increasing the effective moisture diffusivity coefficient (from 1.007 × 10⁻⁹ to 8.11 × 10⁻⁹ m²/s), energy efficiency (from 0.89% to 15.23%) and dryer efficiency (from 2.11% to 21.2%). Compared to ultrasonic and blanching, microwave pretreatment increased the energy and drying efficiency; while the variations in the color and shrinkage were the lowest in the ultrasonic pretreatment. The optimal condition involved the temperature of 70 °C and sample thickness of 2 mm with the desirability above 0.89. The ANFIS model also managed to predict the response variables with R² > 0.96.

Enhancing carrot convective drying by combining ethanol and ultrasound as pre-treatments: Effect on product structure, quality, energy consumption, drying and rehydration kinetics

Ultrasound was combined with ethanol to improve different aspects of carrot convective drying, evaluating both processing and product quality. The ultrasound in water treatment resulted in cellular swelling and small impact on texture. Differently, the ultrasound in ethanol and ethanol treatments modified both carrot microstructure (cell wall modifications of parenchymatic tissue) and macrostructure (shrinkage and resistance to perforation). Pre-treatments with ultrasound in ethanol and ethanol improved the drying kinetics, reducing the processing time (~50%) and the energy consumption (42-62%). These pre-treatments also enhanced rehydration, whose initial rate and water retention were higher than the control. In addition, the carotenoid content was preserved after drying, for all the treatments. Any impact on shrinkage was observed. A mechanistic discussion, based on structural modification (microstructure and macrostructure) and physical properties of water and ethanol, was provided. As conclusion, this work not only described positive aspects of combining the technologies of ultrasound and ethanol as pre-treatments to convective drying, but also proposed mechanisms to explain the phenomena.