Drying of Seabuckthorn (Hippophae rhamnoides L.) Berry: Impact of Dehydration Methods on Kinetics and Quality

Convective hot air drying and freeze drying were investigated as potential dehydration processes to obtain powders of seabuckthorn fruit pulp. Halved seabuckthorn fruits were placed in a hot air dryer and dried at 1 m/s and at 50 or 60°C or freeze dried at less than 30 mTorr and at 20 or 50°C shelf plate temperature. An initial characterization of the seabuckthorn pulp (moisture, pH, soluble solid content, vitamins C and E, total phenolics, and carotenoids) was performed. Water loss, total phenolic compounds, total carotenoids, and vitamin C were determined at different processing times. Vitamin E was determined before and at the end of drying.

Freeze-drying kinetics were faster than air drying, probably due to lower moisture diffusion in the compact, sugary, and oily structure of the air-dried tissue. The temperature had an important impact on hot air–drying and freeze-drying kinetics. Drying method and processing times affected the remaining phenolic, carotenoid, and vitamin contents of seabuckthorn berries. Freeze drying was revealed as a superior method to obtain seabuckthorn powders because of the lower residual moisture content, the ease of grinding, as well as the better nutritional retention.     

陕西本土留兰香精油的成份分析

本文用GC法对陕西生产的本土留兰香精油与美国样品的组成成份进行分析,结果表明,陕西产的本土留兰香精油品质达到国际合格标准,与美国样品的品质接近。     

Effects of Four Different Drying Methods on the Quality Characteristics of Peeled Litchis (Litchi chinensis Sonn.)

Four different drying methods, namely, air drying (AD), microwave-assisted vacuum drying (MWVD), coupled microwave–hot air drying (MWAD), and freeze drying (FD), were studied, in terms of drying time, color, reducing sugar content, shrinkage, microstructure, and sensory evaluation. The drying rate of MWVD and MWAD were notably faster than that of AD and FD. The highest reducing sugar content was observed in MWAD, followed by MWVD. No significant differences were observed in reducing sugar between air-dried and freeze-dried products. FD had the best color and shrinkage among the other drying methods. The color and shrinkage of MWVD drying is close to the fresh litchis and much better than hot air and MWAD. Scanning electron microscopy (SEM) images showed that the MWVD and FD litchis have a porous structure, whereas AD and MWAD litchis have a compact structure. The sensory evaluation suggests that peeled litchis dried by the four studied drying methods are of a quality that is accepted by consumers.     

Effects of Different Drying Methods on the Quality Changes of Granular Edamame

In this article, the quality changes of the granular fruits and vegetables dried by vacuum microwave drying, freeze drying, hot air drying, and combined hot air-vacuum microwave drying are investigated, and the quality parameters compared on the basis of vitamin C and chlorophyll contents, shrinkage and rehydration capacity, color, texture, and microstructure changes. The quality parameters of products dried by vacuum microwave drying are slightly lower than those obtained by freeze drying, but much better than those obtained using conventional hot air drying. The quality characteristics of product dried by combined hot air-vacuum microwave are significantly improved compared to those simply hot air-dried.     

Effects of Different Drying Methods on the Quality Changes of Granular Edamame

In this article, the quality changes of the granular fruits and vegetables dried by vacuum microwave drying, freeze drying, hot air drying, and combined hot air–vacuum microwave drying are investigated, and the quality parameters compared on the basis of vitamin C and chlorophyll contents, shrinkage and rehydration capacity, color, texture, and microstructure changes. The quality parameters of products dried by vacuum microwave drying are slightly lower than those obtained by freeze drying, but much better than those obtained using conventional hot air drying. The quality characteristics of product dried by combined hot air–vacuum microwave are significantly improved compared to those simply hot air–dried.     

Freeze Drying of Saffron (Crocus sativus L.)

Saffron obtained from the dried stigmas of a flower scientifically known as Crocus sativus L. is considered to be the most precious and expensive agricultural product due to its labor-intensive harvest and post-harvest processing. The post-harvest processing such as dehydration and storage conditions determine stability, quality, and economical value of the final product. The contents of crocin (degraded carotenoids) and safranal (carotenoid oxidation products) are the key components that characterize color, taste, and aroma characteristics of saffron. In this work, the quality parameters such as crocin and safranal contents of commercial saffron that were obtained by using the freeze-drying method and natural sun drying were studied. The sarfanal contents of the samples dried in a freeze dryer were found to be five times higher than the safranal contents of the samples dried naturally under the sun, while crocin contents of the samples dried in a freeze dryer were about 40% higher than the crocin contents of the samples dried naturally under the sun. These encouraging results indicate that the freeze-drying process can be used effectively for dehydration of saffron by minimal loss of safranal and crocin contents.     

Foam-Mat Freeze Drying of Egg White—Mathematical Modeling Part II: Freeze Drying and Modeling

Foam-mat freeze drying is one of the promising methods of drying, which utilizes advantages of both freeze drying and foam-mat drying. Egg white with its excellent foaming properties makes a suitable candidate for foam-mat freeze drying. Experiments were conducted to study foam-mat freeze drying of egg white, in an effort to determine the suitability of this method. Xanthan gum (XG) at 0.125% concentration was used as stabilizer for foaming. The results showed that the addition of xanthan gum during foaming has a positive impact in reducing the total drying time and also produces excellent quality egg white powder. The addition of stabilizer also plays an important role in improving drying. Simple models were applied for determining drying time and diffusion coefficients during freeze drying.     

Effect of Different Drying Methods on the Quality of Jute (Corchorus olitorius L.)

The need to promote the use of indigenous vegetables is gaining momentum, as more of their quality factors (nutritive and medicinal) are unveiled through research. Quality factors are classified as quantitative (ingredients, weight); hidden (nutritive, toxic substances); and sensory (appearance, kinaesthetic, flavor). Organoleptically, vegetables are valued for their supreme flavors and aroma, crisp texture, attractive colors, and their overall appeal to human senses of smell, taste, touch, and sight. The retention of these characteristics in dried reconstituted vegetable is of great importance to human consumption. Fresh jute (Corchorus olitorius L.) leaves, which are used as indigenous vegetables in Kenya, were dried under shade, in the sun, by vacuum, and by freeze drying. The effect of the drying methods on the quality of the vegetables was then evaluated. Freeze-dried vegetable was found to have the best quality in terms of color, ascorbic acid content, and reconstitution characteristics.     

The Effects of Predrying Treatments and Different Drying Methods on Phytochemical Compound Retention and Drying Characteristics of Moringa Leaves (Moringa oleifera Lam.)

The most appropriate maturity stage of Moringa oleifera leaves was selected for drying based on phytochemical content, including quercetin and kaempferol. Desorption isotherms were developed and were best fit by the modified Henderson model. Prior to drying, samples were left untreated, blanched in boiling water, and blanched in NaHCO₃/MgO. The leaves were dried by hot air tray drying (TD) and heat pump–dehumidified drying air (HPD) at air temperatures of 40, 50, and 60°C. Alternatively, leaves were subject to microwave drying (MWD) at 150, 450, and 900 W and to freeze drying (FD). The moisture versus time data were fitted to five drying models. In general, a three-parameter model gave the best fit. The drying constant was related to the drying temperature or microwave power using an Arrhenius model. Effective moisture diffusivity (D _eff) increased with higher drying temperature, higher microwave power, or blanching treatments. Structural changes in the leaves after drying and upon rehydration were observed by scanning electron microscopy (SEM). Leaves blanched and dried using HPD at 50°C and fresh and dried using FD showed a partial breakdown of the tissue structure upon rehydration. HPD and blanching reduced the drying time by 8.3% and increased quercetin and kaempferol levels by 42.1 and 51.4%, respectively, compared to TD at 50°C. MWD provided the quickest drying followed by HPD and TD, respectively. HPD drying of M. oleifera after blanching resulted in relatively greater quality compared to TD and MWD.     

一种变种留兰香精油化学成分的研究

本文采用GC/MS法 ,研究了一变种留兰香精油的化学成分。鉴定出 39种化合物 ,主要成分为胡椒烯酮醚(30 .5 11) %、1,8-桉叶素 (2 8.791% )、烯 (9.986 % )、β -月桂烯 (8.4 81% )和 β -蒎烯 (4 .796 % ) ,而作为一般留兰香油主成分的香芹酮则未能检测到。     

Effect of Homogenization Pressure and Oil Load on the Emulsion Properties and the Oil Retention of Microencapsulated Basil Essential Oil (Ocimum basilicum L.)

The objective of this work was to evaluate the influence of oil concentration and homogenization pressure on the emulsion and particle properties during the microencapsulation of basil essential oil by spray drying, using gum arabic as the wall material. Experiments were planned according a 2² rotational central composite design. The independent variables were oil concentration with respect to total solids (10–25%) and homogenization pressure (0–100 MPa). Emulsions were analyzed for droplet mean diameter, stability, and viscosity, and particles were analyzed for oil retention, moisture content, particle size, and morphology. Emulsion viscosity was not affected by any of the independent variables. The increase in the homogenization pressure from 0 to 100 MPa resulted in smaller emulsion droplet size (down to 0.40 µm) and, consequently, higher oil retention (up to 95%). On the other hand, higher oil loads (25%) resulted in poorer oil retention (51.22%). Microencapsulation of basil essential oil using gum arabic as the wall material proved to be a suitable process to obtain powdered basil essential oil, presenting great oil retention with the use of lower oil concentration and higher homogenization pressure.     

A Comparative Study of Four Drying Methods on Drying Time and Quality Characteristics of Stem Lettuce Slices (Lactuca sativa L.)

This article presents experimental results and analysis of four drying methods, viz. hot air drying (AD), hot air-assisted radio frequency drying (ARFD), infrared drying (IRD), and microwave-assisted hot air drying (MAD), on color, microstructure, density, rehydration capacity, and texture after rehydration of stem lettuce slices (Lactuca sativa L.). The drying time required for these drying protocols was also compared. These four drying tests were conducted at fixed air temperature (60°C) and velocity (1 m/s), as well as identical sample load (300 g), bed depth (20 mm), and the power level for ARFD, IRD, and MAD, which was fixed at 4 W/g. The results showed that the drying time required for stem lettuce slices using ARFD was the shortest (120 min), followed by MAD (140 min) and IRD (180 min); AD required the longest time (360 min). Notably, ARFD yielded uniform drying and the quality of the dried samples using ARFD was also the best among these four drying methods.     

Effect of Drying Methods on Dyeing Capacity of Dyestuff Plant Materials

This article presents a study of the effect of drying methods on dyeing capacity of widespread European flora dyestuff plant materials. The natural colorants, derived from the selected plant materials, were applied on chemical pulp in order to examine their dyeability. In this work, three different drying methods were examined—the natural, the air-, and the freeze-drying method—in various conditions. The plant materials that were dried naturally show weak dyeing results in comparison with the air- and freeze-dried materials. Freeze drying significantly improved the dyeing capacity of dyestuff plant materials with high initial moisture content. On the other hand, air drying at low temperature and high relative humidity improved the dyeing capacity of plant materials with low initial moisture content.     

Effect of Four Drying Methods on the Quality of Osmotically Dehydrated Cranberries

Abstract

Partially dehydrated cranberries (osmotically dehydrated) were dried to low water contents using one of following four methods: hot air drying; microwave-assisted convective drying; freeze-drying; and vacuum drying. Quality evaluation was performed on all samples, including sensory evaluation (appearance and taste), texture, color, water activity, and rehydration ratio. Hot air drying produced dried cranberries with the best visual appearance while freeze-dried cranberries had the highest rehydration ratio. The other methods presented similar rehydration ratios. There was no significant difference in color measurements and water activity. Few differences in texture were found, except for freeze-dried cranberries, which had a lower toughness compared to the other drying methods including commercially available dried cranberries. Microwave-assisted to hot air drying rate ratios increased as the moisture content decreased.     

Drying Kinetics of Apple Tissue Treated by Pulsed Electric Field

The aim of this work was to study the influence of pulsed electric field (PEF) on the drying kinetics of apple tissue. Therefore, mathematical models that are commonly used in the literature were applied to describe the process. PEF treatment of the samples was carried out at an intensity of E = 5–10 kV/cm and 10–50 pulse numbers. Subsequently, the apples were convectively dried at 70°C and air velocity of 2 m/s. Based on electrical conductivity measurement, the cell disintegration index Z _p was computed. Midilli et al.'s(Drying Technology, Vol. 20, pp. 1503–1513, 2001) model was evaluated as the most adequate to describe the moisture transfer in PEF-treated and intact samples. PEF pretreatment induced a reduction in drying time of up to 12% when 10 kV/cm and 50 pulses were applied. For instance, after 60 min of drying, the dimensionless moisture ratio for PEF-treated (10 kV/cm, 50 pulses) samples was 0.18 compared to 0.26 for the untreated apples. The effective moisture diffusivity, calculated on the basis of the Fick's second law, was 1.04 × 10^?9 m/s for intact samples and from 1.09 × 10^?9 to 1.25 × 10^?9 m²/s for PEF-treated samples at 10 pulses at 5 kV/cm and 50 pulses at 10 kV/cm, respectively.     

Effect of Four Drying Methods on the Quality of Osmotically Dehydrated Cranberries

Partially dehydrated cranberries (osmotically dehydrated) were dried to low water contents using one of following four methods: hot air drying; microwave-assisted convective drying; freeze-drying; and vacuum drying. Quality evaluation was performed on all samples, including sensory evaluation (appearance and taste), texture, color, water activity, and rehydration ratio. Hot air drying produced dried cranberries with the best visual appearance while freeze-dried cranberries had the highest rehydration ratio. The other methods presented similar rehydration ratios. There was no significant difference in color measurements and water activity. Few differences in texture were found, except for freeze-dried cranberries, which had a lower toughness compared to the other drying methods including commercially available dried cranberries. Microwave-assisted to hot air drying rate ratios increased as the moisture content decreased.     

Comparison of the Retention of 6-Gingerol in Drying of Ginger Under Modified Atmosphere Heat Pump Drying and other Drying Methods

A heat pump dryer using normal air, nitrogen, and carbon dioxide was selected to dry sliced West Indian ginger (Zingiber officinale Roscoe) rhizome (3 mm in thickness). The drying characteristics were compared with each other and inert gas heat pump drying showed an improved effective diffusivity. Quantities of the main pungent principle (6-gingerol) of ginger, extracted from these dried samples, were determined by high-pressure liquid chromatography (HPLC). The evaluation included dried samples obtained by heat pump, modified atmosphere heat pump, freeze drying, and vacuum drying. Retention of 6-gingerol increased in the order of normal air drying, freeze drying, nitrogen drying, carbon dioxide drying, and vacuum drying. From this point of view, inert gas also showed a better retention of flavor compared to most other types of drying.     

Effective Diffusivity and Evaporative Cooling in Convective Drying of Food Material

This article presents mathematical models to simulate coupled heat and mass transfer during convective drying of food materials using three different effective diffusivities: shrinkage dependent, temperature dependent, and the average of those two. Engineering simulation software COMSOL Multiphysics was utilized to simulate the model in 2D and 3D. The simulation results were compared with experimental data. It is found that the temperature-dependent effective diffusivity model predicts the moisture content more accurately at the initial stage of the drying, whereas the shrinkage-dependent effective diffusivity model is better for the final stage of the drying. The model with shrinkage-dependent effective diffusivity shows evaporative cooling phenomena at the initial stage of drying. This phenomenon was investigated and explained. Three-dimensional temperature and moisture profiles show that even when the surface is dry, the inside of the sample may still contain a large amount of moisture. Therefore, the drying process should be dealt with carefully; otherwise, microbial spoilage may start from the center of the dried food. A parametric investigation was conducted after validation of the model.     

Qualitative and Quantitative Changes in the Essential Oil of Lemon Verbena (Lippia citriodora) as Affected by Drying Condition

The objective of this study was to evaluate the effect of drying air temperature and air flow rate on the quantity and quality of the essential oil of lemon verbena. A completely randomized design was applied with a factorial arrangement of two factors: temperature (30, 40, and 50°C) and air flow rate (0.5, 1, and 1.5 m/s). The leaves were harvested in full blooming stage and placed in the drying machine at different temperatures and air flow rates. The essential oil of leaves was extracted by hydrodistillation in a Clevenger apparatus and analyzed by gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS). The results showed that the interaction between different temperatures under various air flow rates had a significant effect on the content and chemical composition of the essential oil. Seventeen compounds were identified in essential oil of lemon verbena, of which geranial, neral, and limonene were the major components. The maximum oil content and majority compounds of essential oil were obtained at 50°C and a 0.5 m/s air flow. Finally, seven mathematical models of thin-layer drying such as correlation coefficient (R ²), sum of square errors (SSE), and root mean square error (RMSE) were evaluated and the modified Page model was found to be the best drying model for lemon verbena.     

Effect of Drying Methods on Quality of Pistachio Nuts

The effect of various methods of drying (sun drying, bin drying, vertical continuous drying, vertical cylindrical drying, and funnel cylindrical drying) on moisture content, lipid quality (peroxide value, thiobarbituric acid value, and free fatty acids), sensory attributes (firmness, sweetness, rancidity, roasted flavor, split shell, shell appearance, and overall palatability), and percent split shell of pistachio nuts (Pistacia vera L.) were studied. Sun drying and bin drying resulted in higher split shell percent on pistachio nuts than other drying methods. The different drying methods used in this study did not have any significant influence on the free fatty acids, peroxide value, and thiobarbituric acid of lipids in pistachio nuts. Drying significantly affected shell appearance and split shell. Overall, the bin drying method produced pistachio nuts with the best quality.