Effect of Convective and Vacuum–Microwave Drying on the Bioactive Compounds, Color, and Antioxidant Capacity of Sour Cherries

Effect of microwave and oven drying processes on antioxidant activity, total phenol and phenolic compounds of kiwi and pepino fruits

Kiwi and pepino fruits are most valuable fruits as they contains substantial amounts of nutrients and bioactive compounds. These fruits exhibited several health potentials such as antioxidant, antiinflammatory, antiobesity, antihyperlipidemia, and anticancer properties. However, studies on the effect of microwave and conventional drying methods on the antioxidant activity and bioactive compounds of kiwi and pepino fruits are limited. Therefore, this study was conducted to assess the effect of microwave and oven drying methods on antioxidant activity, total phenolic, and phenolic compounds of kiwi and pepino fruits. Drying of the fruit samples was carried out using conventional (70 °C for 20 h) and microwave (720 W for 3 min) ovens. 1,1-diphenyl-2-picrylhydrazyl scavenging and colorimetric Folin-Ciocalteu assays were used to assess the antioxidant activity and total phenolic contents, respectively, of fresh and dried fruits. Both drying methods significantly (p < 0.05) decreased the moisture contents of both fruits compared to untreated controls. Concomitantly, drying methods also enhanced (p < 0.05) antioxidant activity and total phenolic content of both fruits with the highest improvement being observed for microwave-dried fruits compared to untreated controls. In addition, a significant increase was observed in catechin and 1,2-dihydroxybenzene content of kiwi and pepino after drying process. However, microwave drying method reduced the amount of 3,4-dihydroxybenzoic acid in kiwi (ranging from 34.120 to 9.350 mg/100 g) and pepino (varied from 33.414 to 15.445 mg/100 g). Generally, the highest antioxidant activity and phenolic contents were reported in microwave oven dried samples, followed by samples dried in oven and fresh fruits. The results revealed that microwave drying could be more useful in fruit drying than conventional drying. In addition, dried kiwi and pepino fruits contains substantial quantities of phenolic compounds with high antioxidant activity compared to fresh fruits, and thus they are considered as healthy food.

Qualitative and Quantitative Evaluation of Heat-Induced Changes in Polyphenols and Antioxidant Capacity in Prunus domestica L. By-products

Plum pomace, an agro-industrial waste product has received attention due to the worldwide popularity of plums. During convection, the content of flavan-3-ols decrease, except drying at 90 °C, whereas the content of i.e., chlorogenic, 3-p- and 4-p-coumaroylquinic acids, quercetin rutinoside, and galactoside was observed to increase along with the increase in process temperature. The highest content of all identified polyphenols was found in plum pomace powders obtained using a combination of convective at 90 °C and microwave vacuum drying (MVD) at 120 W, whereas the highest retention of the group consisted of phenolic acids, flavonols, and anthocyanins was noted when CD 70 °C/MVD 120 W was used, pointing to a strong influence of the type of polyphenols on their changes caused by drying. The correlations between TEAC ABTS and the sum of flavonoids (r = 0.634) and anthocyanins (r = 0.704) were established. The multiple regression analysis showed that polyphenol content was more strongly affected by drying time than by maximum temperature, whereas antioxidant capacity was more influenced by maximum temperature of sample than by drying time.

Influence of Different Drying Techniques on Phenolic Compounds, Antioxidant Capacity and Colour of Ziziphus jujube Mill. Fruits

This study was to present the effect of different parameters of combined methods of drying such as vacuum-microwave (VMD: 480, 120 W), hot air (CDD: 70, 60, 50 °C) and combined methods as pre-drying by CD and finish drying by VMD (CD-VMD: 60 °C + 480/120W) in order to avoid a rapid increase in temperature at the critical moisture content of ca. 1 kg/kg dm (dry mass). Control samples were prepared by freeze-drying (FD). Drying kinetics, including the temperature profile of dried material, as well as on some quality factors of the finished product as phenolic compounds, antioxidant capacity, and color were evaluated. The increase in air temperature during CD as well as the increase in material temperature during VMD deteriorated dried product quality in terms of the content of phenolic compounds, antioxidant activity and color. Dried jujube fruits have a long shelf life and therefore may be a fine alternative to fresh fruit all year round.

Effect of heat- and freeze-drying treatments on phytochemical content and fatty acid profile of alfalfa and flax sprouts

BACKGROUND

Fresh sprouts are healthy foods, low in fats and high in phytochemicals, but have a short shelf-life, hence the need for processing methods that preserve their nutritional value. This work was aimed at evaluating the effect of heat-drying (HD) and freeze-drying (FD) on the phytochemical and fatty acid profiles of alfalfa and flax sprouts, as compared to fresh material.

RESULTS

Both FD and HD reduced the phytochemical contents compared to fresh sprouts. FD better preserved phytoestrogens, phytosterols and total tocols compared to HD. However, phytoestrogen and tocol content remained quite high also in HD. The fatty acid profile was affected only by sprouts species, with higher amounts of α-linolenic acid in flax and linoleic acid in alfalfa sprouts.

CONCLUSIONS

This work demonstrates that drying does not severely compromise the nutritional value of sprouts and provides a valid support for the choice of the drying method depending on the compound to be preserved, and taking into consideration the different cost of the methods. In addition, sprout powder is easy to handle and, due to its low volume, does not imply a decrease of feed consumption and energy intake, which is relevant in its use as a supplement in human and animal feeding. © 2019 Society of Chemical Industry.

Drying of Phyla nodiflora Leaves: Antioxidant Activity, Volatile and Phytosterol Content, Energy Consumption, and Quality Studies

Drying is an important process in the preservation of antioxidants in medicinal plants. In this study, leaves of Phyla nodiflora, or commonly known as frog fruit, were dried using convective drying (CD) at 40, 50, and 60 °C; vacuum-microwave drying (VMD) at 6, 9, and 12 W/g; and convective pre-drying followed by vacuum-microwave finish drying (CPD–VMFD) at 50 °C and 9 W/g. Drying kinetics of P. nodiflora leaves was modelled, and the influences of drying methods on the antioxidant activity, total phenolic content, volatile and phytosterol contents, energy consumption, water activity, and color properties were determined. Results showed that drying kinetics was best described by modified Page model. VMD achieved highest drying rate, whereas VMFD considerably reduced the drying time of CD from 240 min to 105 min. CPD–VMFD was the best option to dry P. nodiflora in terms of retaining volatiles and phytosterols, with lower energy consumption than CD. Meanwhile, VMD at 6 W/g produced samples with the highest antioxidant activity with 2,2′-Azinobis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and ferric reducing antioxidant power (FRAP) value of 11.00 and 15.99 µM Trolox/100 g dw, respectively.

Effect of dehydration techniques on bioactive compounds in hawthorn slices and their correlations with antioxidant properties

Hawthorn fruits are rich in nutrients and antioxidant compounds. Dehydration is the major processing and preservation method for hawthorn fruits. The rates of moisture loss; polyphenol, flavonoid and triterpenoid acid contents; and antioxidant activities and their relationships were investigated in hawthorn slices that were dried by four dehydration techniques (microwave drying, solar drying, hot air drying and freeze drying) under different operation conditions. The results showed that both the drying method and the processing parameter affected the antioxidants. Microwave drying and hot air drying at high temperatures (≥ 80 °C) resulted in the degradation of the polyphenols, flavonoids and triterpenoid acids in the hawthorn slices. These antioxidant compounds were best preserved by freeze drying and hot air drying at 60 °C. Epicatechin and chlorogenic acid were the major phenolic compounds identified in this research, and these compounds were significantly affected during processing. The antioxidant activities of the hawthorn fruits were significantly related to the total polyphenol, flavonoid and triterpenoid acid contents. Hot air drying at proper temperatures could be suitable for hawthorn slice dehydration processing that conserves the antioxidant properties of the fruit.

Antidiabetic, Anticholinesterase and Antioxidant Activity vs. Terpenoids and Phenolic Compounds in Selected New Cultivars and Hybrids of Artichoke Cynara scolymus L

The aim of the study was to analyze the chemical composition of new artichoke cultivars and hybrids and to assess their potential health-promoting properties. Polyphenols, carotenoids and chlorophylls were identified by liquid chromatography-photodiode detector-mass spectrometry/quadrupole time of flight (LC-PDA-MS/QTof) and quantified by ultra performance liquid chromatography-photodiode detector (UPLC-PDA). Sugar and organic acid profiles were prepared, and antioxidant capacity (ABTS, FRAP and ORAC) and in vitro antidiabetic (inhibition of α-amylase and α-glucosidase) and anticholinesterase (inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)) potentials were evaluated. The analyses revealed a highly varied content of bioactive compounds and great health-promoting potential significantly depending on a cultivar. The content of polyphenolic compounds ranged from 1681.49 (“Sambo”) to 3638.91 (“Symphony”) mg/100 g of dry weight (DW). “Blanca de Tudela” contained the highest amounts of carotenoids and chlorophylls (3761.91 mg/100 g DW) and exhibited high ABTS and ORAC capacity. Inhibition of antidiabetic enzymes was significant in cvs. “Symphony” and “Calico”. Additionally, all tested cultivars and hybrids turned out to be effective inhibitors of neurodegenerative enzymes.

HS-SPME Analysis of True Lavender (Lavandula angustifolia Mill.) Leaves Treated by Various Drying Methods

True lavender (Lavandula angustifolia Mill.) is a widely used flavoring and medicinal plant, which strong aroma is mainly composed of linalool and linalyl acetate. The most valuable parts of the plant are the flowers, however leaves are also abundant in volatile constituents. One of the main factors responsible for its quality is the preservation procedure, which usually comes down to a drying process. For this reason an attempt to verify the influence of various drying methods (convective drying, vacuum-microwave drying and combined convection pre-drying with vacuum-microwave finishing drying) on the quality of true lavender leaves was carried out by determination of the volatile constituents profile by solid-phase microextraction (SPME) coupled with GC-MS technique. Total essential oil (EO) content was also verified. The study has revealed that the optimal drying method is strongly dependent on the purpose of the product. For flavoring properties convective drying at 60 °C is the most optimal method, while the best for preserving the highest amount of EO is vacuum-microwave drying at 480 W. Furthermore, SPME analysis had shown that drying may increase the value of true lavender leaves by significantly affecting the linalool to linalyl acetate to camphor ratio in the volatile profile.

Corinthian raisins (Vitis vinifera L., var. Apyrena) antioxidant and sugar content as affected by the drying process: a 3-year study

BACKGROUND

Corinthian raisins or Corinthian currants are dried grape products that account for approximately 3% of dried vine fruit production worldwide. Greece is the major Corinthian raisin producer. In this study Corinthian raisins were produced by applying two traditional drying methods, i.e. sun and shade drying. The drying process effect on the raisin phytochemical and sugar content was assessed; samples obtained over three consecutive crops were evaluated to prevail over climatic condition variations.

RESULTS

Total phenolic, flavanol, and anthocyanin content were higher in Corinthian raisins dried under shade as compared with the sun-dried ones; individual anthocyanidin-3-O-glucosides were also qualitatively and quantitatively higher under shade drying in most cases. Differences were observed in Corinthian raisin phytochemical content among the crop years evaluated. The drying process applied did not discriminatively affect the sugar content of Corinthian raisin.

CONCLUSION

Drying under shade was proven superior to sun drying with respect to Corinthian raisin phytochemicals and could be considered as an appealing drying method for the production of dried raisins and perhaps other dried fruits. © 2018 Society of Chemical Industry.

Innovative technologies for producing and preserving intermediate moisture foods: A review

Intermediate moisture foods (IMF) or semi-dried foods (SDF) have gained more attention worldwide having features very similar to fresh food products, but with a longer shelf life. This review presents the recent developments in novel technologies and methods for the production and preservation of IMF. These include new drying methods, using agents to reduce water-activity, innovative osmotic dehydration technologies, electro-osmotic dewatering, thermal pasteurization, plasma treatments (PT), high pressure processing (HPP), modified atmosphere packaging (MAP), edible coating, active packaging (and energy efficiency, improve quality and extend the shelf life of the final food AP) and hurdle technologies (HT). Innovative methods applied to producing and preserving IMF can enhance both drying products. Yet more systematic research is still needed to bridge knowledge gaps, in particular on inactivation kinetics and mechanisms related to thermal and non-thermal pasteurization technologies for control of pathogens and spoilage micro-organisms in IMF.

Microwave-dried or air-dried? Consumers' stated preferences and attitudes for organic dried strawberries. A multi-country investigation in Europe

Non-thermal food processing technologies are becoming more important in the organic food sector because, beyond preserving the organic feature, they could offer organic products with additional benefits in terms of enhanced nutritional content and healthiness as well as better sensory properties that could satisfy the more complex demands of organic consumers. Berries have a well-known health benefits and show increasing market shares in European markets while dehydration can increase the food convenience in terms of extended shelf-life. This study investigates for the first time organic consumers' stated preferences, attitudes and individual differences for a non-thermal organic processing technology. Specifically, we investigated consumers' preferences for organic dried strawberries varying in drying technology used, such as the most conventional (i.e. thermal) air drying and the most innovative (i.e. non-thermal) microwave drying, origin, price levels, and nutrient contents in three European countries: Norway, Romania and Turkey. Data from a total of 614 consumers were collected through an online choice experiment. Results show that on average consumers prefer organic dried strawberries produced with air drying technology that have national origin, with natural nutrient content and at low price, but country and individual differences are identified. Consumers who showed least rejection for microwave dried products are young, mostly from Norway and have higher positive attitudes towards new food technologies. Consumers who showed most rejection for microwave dried products are older, mostly from Turkey and have higher positive attitudes for organic, natural and ecological products. Organic producers who adopt microwave drying might better inform consumers about the characteristics, the process and highlight the nutritional benefits of such technology. Finally, this research informs policy makers about the need to define and regulate more clearly microwave drying as an organic technology, as well as to regulate labelling to ensure that consumers are not misled and correctly informed about the new technology.

Consumers' Opinion on Dried Pomegranate Arils to Determine the Best Processing Conditions

Consumers' preference is essential to improve processed food products quality, but small companies sometimes lacks knowledge or tools to develop consumer studies. The aim of the present study was to investigate consumers' insight to recommend the best drying methodology for pomegranate arils. With the aim of providing information that industry can correlate to the drivers of liking, descriptive sensory characteristics, and volatile compounds of the samples were determined and related with consumers' responses. A total of 19 volatiles of dehydrated pomegranate arils were determined using solid-phase microextraction and gas chromatography-mass spectrometry. Partial least square regression (PLS) results indicated that consumers overall liking was positively correlated with "pom ID", "sweet", and "fruity" attributes, and also volatile compounds of the esters family. Overall liking was negatively correlated with the "off-flavor" and "burnt" attributes, related to the furan compounds family. Penalty analysis indicated that the sample corresponding with the current commercial product needed improvement on the "pom ID", "fruity", and "sweetness" parameters. All the samples processed using the proposed new drying techniques were more liked than the commercial sample, highlighting a sample dried using pre-osmotic dehydration in Wonderful concentrate pomegranate juice. PRACTICAL APPLICATION: Consumers' preference is essential to improve processed food products quality, but small companies sometimes lack knowledge or tools to conduct consumer studies. The present study provides useful information to understand consumers' preferences of a healthy product such as pomegranate dehydrated arils. Also, the link of physico-chemical and sensory tools is clearly described, providing information about possible sensory quality indicators.

The Influence of Drying Method on Volatile Composition and Sensory Profile of Boletus edulis

The objective of this study was to evaluate the influence of different drying methods on aroma and sensory profile of Boletus edulis (cepe). The drying methods tested were convective drying (CD), freeze-drying (FD), vacuum microwave drying (VMD), and a combination of convective predrying and vacuum microwave finish-drying (CPD-VMFD). Fresh and dried cepe volatiles, analyzed by SPME and GC-MS, showed the presence of 53 volatile compounds, most of them present in all dried samples but with quantitative variation. The major volatile compounds in fresh and dried cepe were 1-octen-3-ol (3405 µg 100 g−1·db), 3-octanone (429 µg 100 g−1·db), and hexanal (355 µg 100 g−1·db). The results showed that drying of cepe mushrooms caused major losses of aroma compounds; however, the highest content of volatile compounds and the highest intensity of most of the key positive sensory attributes were found in samples after (i) CD at 80°C (3763 µg 100 g−1·db), (ii) CD at 70°C (3478 µg 100 g−1·db), and (iii) CPD at 60°C and VMFD at 480/240 W (2897 µg 100 g−1·db).

Effects of different drying methods on the bioactive compounds and antioxidant properties of edible Centaurea (Centaurea cyanus) petals

Abstract The present study aimed to evaluate the effects of hot-air convective drying, shade drying and freeze-drying on the bioactive compounds and antioxidant activity of Centaurea ( Centaurea cyanus L.) petals, as well as on several of their physicochemical properties. All the dried samples showed different appearances as compared to fresh petals, with lower titratable acidity, lower carotenoids and hydrolysable tannins contents, and greater antioxidant activity. Of the drying methods, shade drying presented the highest values for monomeric anthocyanins, flavonoids, hydrolysable tannins, total reducing capacity and antioxidant activity. By contrast, greater losses were observed as a result of hot-air convective drying. Thus shade drying is a highly promising process that should be considered as a suitable drying method for Centaurea petals.

Sour Cherry By-products: Compositions, Functional Properties and Recovery Potentials - A Review

Sour (tart) cherry is an industrial fruit where a considerable amount of by-products remain after processing. Sour cherry by-products consist of pomace (skin and flesh) and seeds (pit, stone) which remain after the fruit juice and IQF processes. Sour cherry pomace is characterized with a high content of phenolic compounds and the seed constitutes a high oil yield with beneficial effects on human health because of their antioxidant, antimicrobial, and anti-inflammatory properties. There has been a great interest in sour cherry by-products due to the increasing production rate of sour cherry worldwide and the increasing efforts on seeking bioactive compounds from natural sources as functional food. Thus, there have been a number of studies regarding the sour cherry pomace and sour cherry seed, especially in the last five years. The present review summarizes the chemical, biological, functional, and technological properties of the sour cherry pomace and sour cherry seed with their current and potential applications.

Phenolic content and some physical properties of dried broccoli as affected by drying method

Broccoli samples ( Brassica oleracea) with an initial moisture content of 82.87% (wb) were dried using microwave technology (18, 36, and 54 W/g). Convective drying was used as a control group. The dependent variables investigated in the study were phenolic content, color, rehydration capacity, and microstructure of broccoli samples. Moreover, the best fitting thin layer model to the experimental moisture ratio was determined. The phenolic contents were found as 892.4, 740.6, and 759.8 mg gallic acid/100 g dry matter for fresh, convective dried, and microwave (MW) dried at 54 W/g broccoli samples, respectively. The total phenolic content of samples dried at 54 W/g was closest to fresh samples compared to other MW power intensities and convective drying. A similar result was obtained for color values too. L*, a*, and b* of microwave-dried samples at 54 W/g were comparable to fresh broccoli. Another important result obtained from the study was the insignificant effect of drying conditions on rehydration capacity. In addition, it was found that microwave power had a positive effect on drying time; as the microwave powers applied were compared, the shortest drying time was reached at 54 W/g. When the process durations of microwave drying and convective drying were compared, it can be reported that a much lower process time for microwave drying was obtained with respect to convective drying. Drying in microwave oven has reduced the drying time by 49-52%. In the light of the results obtained, it may be declared that it is possible to produce high-quality dried broccoli samples in a very short time by using microwave drying at 54 W/g.

Effect of freeze, microwave-convective hot air, vacuum and dehumidified air drying on total phenolics content, anthocyanin content and antioxidant activity of jamun (Syzygium cumini L.) pulp

Jamun (Syzygium cumini L.) pulp-skin paste was dried using four drying methods viz., microwave-convective hot air drying (MCD), freeze drying (FD), vacuum drying (VD), and dehumidified air drying (DAD) at different conditions. Except for FD, the drying temperatures of MCD (1, 2 and 3 W/g power density), VD (60, 160 and 260 mm Hg pressure) and DAD (1, 1.5 and 2 m/s of air velocity; 20% RH) were varied from 40 to 70 °C. The dried pulp-skin flakes were analysed for total phenolics content [TPC, gallic acid equivalent (GAE)], monomeric anthocyanin content [MAC, malvidin-3-glucoside (M3G)] and antioxidant activity [AA, butylated hydroxyanisole (BHA)]. This study aimed on selection of the best drying method based on the retention of the above functionalities. Compared to the fresh sample, TPC and AA of the dried samples increased for all the methods, whereas MAC showed mixed response. With the retention of 31.52 mg GAE, 11.99 mg M3G and 28.63 mg BHA per gram of dried sample (on dry basis), MCD (70 °C, 1 W/g) was selected as the most suitable method based on statistical analyses.

Effect of Microwave Vacuum Drying on the Drying Characteristics, Color, Microstructure, and Antioxidant Activity of Green Coffee Beans

The aim of this study is to investigate the effect of microwave vacuum drying (MVD) on the drying characteristics and quality attributes of green coffee beans. We specifically focused on the effective moisture diffusion coefficient (D_eff), surface temperature, glass transition temperature (T_g), water state, and microstructure. The kinetics of color changes during drying, total phenolic content (TPC), and antioxidant activity (DPPH, FRAP, and ABTS) were also characterized. Microwave power during MVD affected the porosity of coffee beans, their color, TPC, and antioxidant activity. The Allometric 1 model was the most suitable for simulating surface temperature rise kinetics. Thermal processing of green coffee beans resulted in increased b*, L*, ΔE, and TPC values, and greater antioxidant capacity. These findings may provide a theoretical reference for the technical improvement, mechanisms of flavor compound formation, and quality control of dried green coffee beans.

The Influence of Convective, Microwave Vacuum and Microwave-Assisted Drying on Blueberry Pomace Physicochemical Properties

The effect of hot air convective drying (HACD), microwave-vacuum drying (MWVD) and combined drying (HACD + MWVD) on the drying kinetics, bioactive compounds and color of blueberry pomace was evaluated. Drying time of blueberry pomace ranged from 0.6 to 6.7 h and moisture diffusion coefficients ranged from 7.94 × 10–8 to 1.83 × 10–7 m2/s. Drying caused degradation of total polyphenolics (TP) (39–76%), monomeric anthocyanins (21–77%) and antioxidant capacity values (24–76%). Drying time was shortened even by 91%, when MWVD was used instead of HACD. MWVD of blueberry pomace resulted in the smallest, while HACD at 60°C in the greatest loss of bioactive compounds and antioxidant capacity. HACD at 60°C + MWVD allowed to obtain a product with a higher content of TP, monomeric anthocyanins and a stronger antioxidant capacity than HACD at 90°C + MWVD. Combination of HACD at 60°C with MWVD allowed for the shortening of HACD time by 75% as well as for hapering the chemical changes as compared to HACD at 60°C. Even when the combination of HACD at 90°C with MWVD shortened the drying time by 68%, it did not improve the retention of TP, monomeric anthocyanins and antioxidant capacity when compared to HACD at 90°C.

Volatile composition and sensory profile of shiitake mushrooms as affected by drying method

BACKGROUND

One of the best preservation method for long-term storage is drying. In this work, the influence of different drying methods on aroma and sensory profile of shiitake mushroom was evaluated. The drying methods tested were: convective drying (CD), freeze-drying (FD), vacuum-microwave drying (VMD), and a combination of convective pre-drying and vacuum-microwave finish-drying (CPD-VMFD).

RESULTS

The volatile composition of fresh and dried shiitake mushrooms was analysed by SPME, GC-MS and GC-FID, and showed the presence of 71 volatile compounds, most of them present in all dried samples but with quantitative variation. The major volatile compounds in fresh shiitake were 1-octen-3-ol (20.2%), 2-octanone (20.7%), 1,2,4-trithiolane (9.8%), and 1,2,3,5,6-pentathiepane (8.2%). Drying of shiitake mushrooms caused significant losses of C8 compounds and cyclic sulfur compounds, such as 1,2,4-trithiolane (V31) and 1,2,4,5-tetrathiane (V57). Samples dried at CD 80 °C implied a relative short drying time (120 min), had the highest contents of total volatiles (1594 μg 100 g^-1 ) and cyclic sulfur compounds (e.g. V57 126 μg 100 g^-1 ), and the highest intensity of most of the key positive sensory attributes, such as inner colour (7.0), fresh shiitake flavour (6.7), and sponginess (6.2).

CONCLUSION

The best dehydration methods, resulting in the highest total concentrations of volatile compounds and high intensity of key sensory attributes were FD (if vacuum and liquid nitrogen facilities are available) and CD at 80 °C (for companies with vacuum and liquid nitrogen facilities). © 2017 Society of Chemical Industry.

Effect of Osmotic Pre-treatment and Temperature Storage Conditions on Water Activity and Colour of Dried Apple

The cylinders of apples cv.Braeburnwere subjected to osmotic dehydration in a sucrose solution with the addition of chokeberry juice concentrate. After osmotic pre-treatment the pieces of apples were dried by two methods: freeze-drying and air-drying. The storage results of dried apples at temperature 25–45 °C for 7 and 12 months were satisfactory. Mass changes were very minor. During storage dried apples obtained by both methods exhibited microbiological stability even after 7 and 12 months of storage, due to the fact that the water activity did not exceed the value of 0.4. Under the influence of the technological processes application, as well as storage conditions, appearance changes in the samples occurred. Higher temperature of storage had an increase impact in colour changes of control samples (without osmotic pre-treatment) and also osmotically dehydrated into sucrose solution, mainly in the case of samples which had dried using freeze-drying. Previously immersed in chokeberry juice concentrate, dried apples had colour changes comes from colour of solution.

The Effect of Selected Fruit Juice Concentrates Used as Osmotic Agents on the Drying Kinetics and Chemical Properties of Vacuum-Microwave Drying of Pumpkin

The study examined the osmotic dehydration of pumpkin slices in chokeberry, flowering quince, and raspberry concentrated juices. Products obtained were subjected to vacuum-microwave finish drying (VMD). The objective of the study was to evaluate the drying kinetics and the chemical properties, that is, total polyphenolics content and antioxidant capacity of the vacuum-microwave-dried pumpkin products. The concentration and temperature of the juices were 40°Brix and 45°C, respectively. The pumpkin slices were pretreated in concentrated juices for 0.5, 1, 2, 3, and 6 hours. Vacuum-microwave finish drying was carried out at the power of magnetrons that ensured the maintenance of the safe temperature (below 90°C) of the slices measured with the use of infrared camera. The results of the study showed that the moisture content of samples during the pretreatment in concentrated juices was decreasing until the equilibrium stage. The logarithmic model was used to describe the drying kinetics of pumpkin during VMD. Osmotic pretreatment resulted in a decrease in colour coordinates, improved the antioxidant activity of dried product, and prolonged the duration of VMD.

Volatile composition and sensory profile of Cantharellus cibarius Fr. as affected by drying method

BACKGROUND

In this work, the influence of different drying methods on the aroma composition and sensory quality of chanterelle mushrooms (Cantharellus cibarius Fr.) was evaluated. The drying methods tested were convective drying (CD), freeze drying (FD), vacuum microwave drying (VMD) and a combination of convective pre-drying and vacuum microwave finish drying (CPD-VMFD).

RESULTS

Analyses of fresh and dried chanterelle samples by HS-SPME and GC/MS and GC-FID showed the presence of 39 volatile compounds at different concentrations. The most abundant compounds in fresh chanterelle were 1-hexanol (33.4 μg per 100 g dry basis (db)), 1-octen-3-ol (80.2 μg per 100 g db) and 2-octen-1-ol (19.3 μg per 100 g db). The results showed that fresh and dried chanterelle contained very low levels of aroma compounds; however, the highest contents of volatile compounds were found in samples after (i) CD at 80 °C (129 μg per 100 g db), (ii) CPD-VMFD at 70 °C-480/240 W (136 μg per 100 g db) and (iii) CPD-VMFD at 80 °C-480/240 W (136 μg per 100 g db).

CONCLUSION

The best dehydration methods, which resulted in high contents of volatile compounds and appropriate sensory quality, according to descriptive sensory analysis and PCA tools, were CD at 70 and 80 °C. Besides, these methods led to spongy dried mushrooms with high intensities of fresh, mushroom ID, with proper color and without intense shrinkage. © 2017 Society of Chemical Industry.