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Article

Wild Strawberry Fragaria vesca L.: Kinetics of Fruit Drying and Quality Characteristics of the Dried Fruits

1
Department of Thermal Technology and Food Process Engineering, University of Life Sciences in Lublin, 31 Głęboka St., 20-612 Lublin, Poland
2
Department of Biochemistry and Food Chemistry, University of Life Sciences in Lublin, 8 Skromna St., 20-704 Lublin, Poland
3
Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences (SGGW), Warsaw, Nowoursynowska 159c, 02-776 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Submission received: 17 September 2020 / Revised: 3 October 2020 / Accepted: 6 October 2020 / Published: 8 October 2020
(This article belongs to the Special Issue Progress in Food Processing)

Abstract

:
The aim of this study was to determine the effect of the temperature of convection and freeze–drying of wild strawberry Fragaria vesca L. fruits on the drying kinetics and on selected quality features of the dried fruits. The process of convection drying was carried out at the temperatures of 25 °C, 40 °C, and 60 °C, whereas freeze–drying was carried out at the temperatures of 20 °C, 40 °C, and 60 °C of the heating shelves and at the pressure of 63 Pa in the lyophilizer chamber. The drying kinetics were best described by the Midilli model for both drying methods. An increase of the drying temperature to 60 °C, for both convection drying and freeze–drying, resulted in a decrease of the total content of phenolic compounds and of the antioxidant activity of the dried fruits. An increase in the temperature of convection drying reduced the lightness of the dried fruits. However, during freeze–drying, these features changed little despite the increase in the drying temperature. The dried fruits with the highest brightness were obtained at a freeze–drying temperature of 60 °C. The method of freeze–drying is proposed as the best because of the resulting color, L-ascorbic acid retention, and antioxidant properties of the dried fruits.

1. Introduction

Wild strawberry (Fragaria vesca L.) is a perennial plant about 5–20 cm high, naturally occurring throughout the northern hemisphere. There are reports that it was already known by primitive people, and archaeological studies show that it was also eaten by apes [1,2,3].
In Poland, wild strawberries can be found all over the country and are also commonly grown in home gardens and allotment areas [2,4]. Despite the fact that well-yielding varieties of strawberries are available, there is no large-scale cultivation of this plant; only small plantations are found in France, Italy, Austria, and Poland [2].
Wild strawberry fruits are valued for their high nutritional content, taste, and dietary value and are a source of antioxidant and antithrombotic compounds essential for our body [5,6,7,8,9]. Their action consists in neutralizing reactive forms of oxygen, thus playing an important role in combating cancer and atherosclerosis [10]. These fruits have been used in folk medicine as a diuretic, an oversleptic agent, and to treat kidney and liver diseases as well as anemia [2,11]. Apart from monosaccharides and mineral salts, they contain the vitamins C, B, and K, carotene and tannins, pectin, phenolic compounds, flavonoids, and anthocyanins [2].
Wild strawberry fruits are harvested for home use, are used in the pharmaceutical and cosmetic industry, and, due to their specific aroma and taste, are used in confectionery and as an ingredient in jams and liqueurs [12,13,14].
A hybrid strawberry, also called pineapple strawberry or large-fruit strawberry, was created from the cross of the Chilean strawberry (Fragaria chiloensis L.) and the Virginia strawberry (Fragaria virginiana Duch.) [15,16]. This strawberry is commonly processed on an industrial scale and has gained the interest of scientists.
Both strawberry and wild strawberry fruits are susceptible to mechanical damage, have a short shelf-life, and therefore require refrigeration or heat treatment to extend the storage period [17,18,19,20]. All processing methods cause to a greater or lesser extent a decrease in product quality in relation to the raw material and require different amounts of energy. Freezing results in unfavorable changes in the quality of fruits at the thawing stage [21]; strawberries dried by the most popular convection method have a hard consistency and limited rehydration properties [22]. Freeze–drying, on the other hand, ensures the highest quality of the dried fruits [23].
Despite the facts that wild strawberries are characterized by better taste and aroma compared to strawberries and that their fruits in the form of dried fruits are generally available, the drying kinetics of these fruits has not yet been studied, and the influence of the drying method and the drying temperature on color changes and antioxidant properties of wild strawberries has not been determined. Therefore, the aim of this study was to analyze the parameters of freeze– and convection drying of wild strawberry fruits in relation to the kinetics of the drying process and selected quality characteristics of the dried fruits.

2. Materials and Methods

2.1. Material

Wild strawberry fruits (Fragaria vesca L.) came from a naturally growing population in the forest area of Lublin Province (eastern Poland). The raw material was obtained from bushes in full ripeness present in a single location, in June 2019. Selected on the basis of their size, ripe and undamaged fruits were subjected to convection drying immediately after harvesting. Fruits were purchased from (Group of Producers KLASA, Klementowice, Poland). The material intended for freeze–drying was frozen in a freezer chamber chest (Liebherr, GTL-4905, Nussbaumen, Switzerland) at −25 °C, in conditions of free convection.
The dry matter (DM) content of wild strawberry fruits was 13.40 g/100 g of raw material, determined in accordance with the Association of Official Analytical Chemists (AOAC), method 934.06, by drying the tested material at 70 ± 0.1 °C to a constant mass in a Pol-Eko dryer, SLW 53 STD (Wodzisław Śląski, Poland) [24].

2.2. Drying Method

The freeze–drying process was carried out in a lyophilizer Alpha 1-4 (Martin Martin Christ Gefriertrocknungsanlagen GmbH, Osterode am Harz, Germany) with a contact heat supply system, equipped with a scale adapted to work in the vacuum, recording the weight of the raw material during drying with an accuracy of ±0.1 g. The freeze–drying process was carried out at a constant pressure of 63 Pa and at a temperature of the heating shelves of 20 °C, 40 °C, and 60 °C. During freeze–drying, the conditions were selected so to obtain a minimum moisture content of 5%. Changes in the weight of the dried fruit samples were recorded during drying according to a described methodology [25].
Convection drying was carried out using a Promis-Tech dryer (Wroclaw, Poland), which enabled continuous recording of the fruit weight with an accuracy of ±0.1 g. This process was carried out at air temperatures of 25 °C, 40 °C, 60 °C, with a constant air flow of 0.5 m·s−1 under the dryer screen. The minimum temperature of convection drying was increased to 25 °C compared to freeze–drying, because our own research has shown that carrying out this process at 20 °C requires a long time and does not allow achieving the assumed final humidity of the dried fruits of 10%. For both methods of drying, the fruit samples weighed 100 g.

2.3. Modeling of the Drying Curves

To show the kinetics of the drying process, the reduced water content (MR) was calculated from the following formula:
M R = u t u r u 0 u r ,
where ut is the water content in the course of drying (kg H2O·kg DM−1), u0 is the initial water content (kg H2O·kg DM−1), and ur is the equilibrium water content (kg H2O·kg DM−1).
Since the value of ur is negligible compared to those of u0 and u, it was omitted. This simplification is widely used and has no major impact on the drying kinetics [26].
In order to select the best mathematical model describing freeze– and convection drying of wild strawberry fruits, seven equations commonly quoted in the literature were analyzed (Table 1).

2.4. Measurement of Color Coordinates

The color coordinates of the raw and dried materials were determined using the X-Rite 8200 spherical spectrophotometer (X-Rite, Grand Rapids, MI, USA) in the CIE L*a*b* colorimetric system, which allows determining the brightness L* and color changes from green to red (a*) and from blue to yellow (b*). The homogeneity of the samples was ensured by grinding the material to be tested before taking the measurements, using a GM-200 laboratory mill (Retsch, Düsseldorf, Germany).
On the basis of the experimentally determined color coordinates, the value of the total color difference (ΔE) with respect to the raw material, the color saturation (C), and the hue (HU) of the individual samples were calculated according to the following formulae:
Δ L = L * L 0 , *   Δ a = a * a 0 , *   Δ b = b * b 0 *
Δ E = ( Δ L * ) 2 + ( Δ a * ) 2 + ( Δ b * ) 2
C = ( a * ) 2 + ( b * ) 2
H U =   tan 1 b a
where L0*, a0*, and b0* are the color parameters of the fresh sample.

2.5. L-ascorbic Acid Determination

The content of L-ascorbic acid was determined during titration with the Tillmans method, which consists in the oxidation of L-ascorbic acid to dehydroascorbic acid in an acidic medium with a solution of 2,6-dichloroindophenol. Samples of the grinded raw material and dried fruits weighing 10 g (±0.01g) were quantitatively transferred to a beaker (50 mL); after adding 2% oxalic acid, the samples were kept in the dark for 15 min. The solution was then filtered through filter paper and brought to 100 mL in a volumetric flask, from which 10 mL of the filtrate was taken and titrated with 2,6-dichlorophenolindophenol solution until a pale pink color appeared, which lasted for 30 s. The total content of L-ascorbic acid was determined in mg/100 g (DM).

2.6. Total Phenolics Content and Antioxidant Activity

In order to determine the total content of phenolic compounds and the antioxidant activity of the raw material before and after drying, extracts from the tested samples were prepared according to a described methodology.
The total content of phenolic compounds was determined in methanolic extracts [34] and was expressed in mg of gallic acid per gram of dry matter (GAE/g DM) [35]. The antioxidant activity of the dried fruits was also determined using four methods based on chelating power (CHEL) [36], antiradical activities (ABTS (2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) free radicals [37], DPPH (2,2-diphenyl-1picyclohydrazil) free radicals [38], and reducing power (RED) [39]. The EC50 index was used to express the antioxidant activity of the obtained extracts [40].

2.7. Statistical Analysis of the Results

The results of the analyses concerning the kinetics of the freeze– and convection drying processes are presented as a mean of three repetitions, while the remaining analyses concerning the quality of the dried fruits included five repetitions. Experimental data were analyzed for variance at the significance level of α = 0.05; the Tukey’s test was used to determine the significance of differences between the mean values (Statistica 13, StatSoft). During the regression analysis of the drying kinetics, the determination factor (R2), the mean-square error (RMSE), and the values of the chi-quadrate test (χ2) were determined:
R M S E = i = 1 N ( M R i , p M R i , e ) 2 N ,
χ 2 =   i = 1 N ( M R i , p M R i , e ) 2 N n ,
where MRi,p is the predicted value of reduced water content; MRi,e is the experimental value of reduced water content; N is the number of measurements; and n is the number of parameters in the model equation.

3. Results and Discussion

3.1. Drying Kinetics

Changes in the reduced water content (MR) as a function of the duration of the process of freeze– and convection drying of wild strawberry fruits are summarized in Figure 1 and Figure 2. On the basis of the conducted research, it can be concluded that an increase in the drying temperature was accompanied by a decrease in the duration of the process for both analyzed drying methods. At a temperature of 40 °C, freeze–drying was slightly shorter, while at 60 °C, the time of convection drying was much shorter (by 80 min). Increasing the temperature from 20 °C to 60 °C shortened the freeze–drying time by about 40%. Increasing the convection drying temperature from 25 °C to 60 °C shortened the drying time by about 60%. The shortest time was observed in the case of convection drying at 60 °C, which was 250 min.
The results of the regression analysis of seven studied models used to describe the kinetics of freeze– and convection drying of wild strawberry fruits are summarized in Table 2 and Table 3. It can be concluded on the basis of the analysis of the obtained results that a good match of the experimental data was obtained for each of the analyzed models. The value of the coefficient of determination (R2) of the equations for both analyzed drying methods ranged from 0.9479 to 0.9999. The mean-square error (RMSE) and the value of the reduced test (χ2) were small, corresponding to 0.0035–0.0608 and 0.00001–0.00385, respectively. In order to standardize, the drying kinetics was modeled using the Midilli model, although slightly better model matching values were obtained using the Wang and Sing models for freeze–drying at 20 °C and 40 °C. For both drying methods, at the three analyzed temperatures, the Midilli model resulted in coefficients of determination (R2) in the range from 0.999 to 0.9999, and the highest mean-square error (RMSE) was 0.0099. Analyzing the results of other researchers, it can be seen that the Midilli model very often gave the best matching results among the empirical models used to describe the processes of freeze– and convection drying [41,42,43]. In the description of the kinetics of convection and freeze–drying of fruits and vegetables, good results are often obtained using the Page model. However, in the case of wild strawberry fruits, this model did not give such a good match to empirical data as the Midilli model.
The coefficients of equations of the analyzed models of kinetics of freeze– and convection drying of wild strawberry fruits are presented in Table 4 and Table 5.

3.2. Color Changes

The results regarding the color of the raw material and of the dried wild strawberry fruits are presented in Table 6. The material obtained after the drying process, regardless of the method, was characterized by a higher brightness (L*) compared to the raw material. In the case of convection drying, an increase in the temperature of the process resulted in a decrease in the brightness of the dried fruits, while during freeze–drying, the color changes were small in the whole temperature range; however, the brightest dried fruits were obtained at the temperature of the heating shelves of 60 °C. The strongest brightness of the freeze–dried fruits compared to the product obtained from convection drying may be related, among other factors, to the lower water content in the lyophilizate.
An increase in color saturation (C) of the dried wild strawberry fruits relative to the raw material was observed in the case of convection drying, while freeze–drying caused a decrease in color saturation. The temperature of the drying process had no statistically significant effect on (C) in the case of both freeze– and convection drying.
Both drying methods resulted in an increase in the hue (HU) of the dried material compared to the raw material. An increase in the drying temperature produced an increase in (HU) regardless of the dehydration method, with changes in this parameter being statistically significant only between the lowest temperature of freeze–drying and the highest temperature of convection drying. Dried wild strawberry fruits with the shade of color closest to that of the raw material were obtained as a result of freeze–drying at the lowest temperature of the heating shelves.
The total change in color of the dried fruits (ΔE) was smaller during convection drying, over the whole temperature range. In the case of freeze–drying, small changes of this parameter were noted, with an upward trend, with an increase in the process temperature, and the direction of the change was the opposite during convection drying. The higher values (ΔE) in the case of dried fruits obtained as a result of freeze–drying were associated, among others, with a greater difference in the brightness (L*) of the dried fruits compared to the raw material. Although the smallest total difference in color (ΔE) between the raw material and the dried material was recorded as a result of convection drying, the dried material obtained during freeze–drying was characterized by a color similar to pink, visually more attractive and probably more desirable for the consumer.
According to reports of researchers analyzing the drying process of strawberry fruits in relation to the wild strawberry, the unfavorable change in the color of the dried fruits is mainly due to the degradation of anthocyanins, which are unstable compounds, resistant to oxidation and thermal treatment [44,45]. The color of the dried fruits is also affected by pH, content of some metal ions, enzymes, and their associated decomposition reactions [46]. Some researchers found a decrease in the brightness of dried strawberry fruits relative to the raw material in the case of convection drying [47], other researchers showed the opposite result [48].

3.3. L-ascorbic Acid Changes, Total Phenolics Content, and Antioxidant Properties

The average content of L-ascorbic acid (AC) in fresh fruits of wild strawberry was 43 mg per 100 g of raw material, which corresponded to 304 mg per 100 g DM. According to other researchers, the content of L-ascorbic acid in the fruits of wild strawberry subjected to drying is similar to the average values of this quality marker in strawberry fruits [47]. The process of drying, regardless of the method and parameters, causes a decrease in the L-ascorbic acid content in the dried fruits. The highest content of L-ascorbic acid in dried wild strawberry fruits was recorded after freeze–drying at the lowest temperature of the heating shelves. An increase in the process temperature caused a decrease in L-ascorbic acid content, regardless of the drying method. In the case of freeze–drying, the loss of L-ascorbic acid compared to the raw material was about 13% at the temperature of of 20 °C of the heating shelves and reached a maximum of about 35% at 60 °C. The process of convection drying resulted in the degradation of L-ascorbic acid by about 78% at the air temperature of 60 °C (Table 7). The results of research concerning L-ascorbic acid content in dried strawberry fruits are inconclusive. As reported by Yurdugu [19], as a result of the freeze–drying process, the L-ascorbic acid content in dried strawberry fruits increased compared to the raw material.
The total content of phenolic compounds (TPC) in fresh wild strawberry was 20.5 mg GAE/g DM. Drying caused a decrease in TPC, but the higher the process temperature, the higher the decrease. Convection drying caused a higher decrease in the content of phenolic compounds compared to freeze–drying. TPC were in the range from 15.0 to 19.7 mg GAE/g DM in freeze–dried fruits and from 10.2 to 17.4 mg GAE/g DM in the convection-dried wild strawberry (Table 7). The antioxidant activity of the raw material before drying, measured by different methods, was as follows: 5.2 mg DM/mL (ABTS), 27.5 mg DM/mL (DPPH), 10.3 mg DM/mL, and 10.1 mg DM/mL (RED). Drying at 20 and 40 °C had little effect on the decrease of the antioxidant activity (increase of EC50 parameter). On the other hand, the higher process temperature tested (60 °C) already caused a significant decrease in the antioxidant capacity of the extracts obtained from the samples. The extracts from freeze–dried wild strawberries at the same drying temperature were usually characterized by slightly higher antioxidant activity compared to extracts obtained from convection-dried fruits. Such patterns were observed for each of the methods considered to assess the antioxidant activity (Table 7).
The literature lacks studies on changes in the antioxidant activity of wild strawberry fruits due to drying. Studies by many authors confirm that temperature, duration, and drying method have the greatest influence on the content of bioactive compounds and the antioxidant potential of dried fruits [45,46,47,49]. López-Ortiz et al. [44] analyzed changes in the content of bioactive compounds and their activity during convection drying of strawberry fruits at 40, 50, and 60 °C. They found that fruits dried at 40 and 50 °C were characterized by a similar decrease in total content of phenolic compounds and antioxidant activity. However, this decrease was already much higher at the drying temperature of 60 °C. Studies on the convection drying of strawberry fruits at 50 and 60 °C showed that the greatest decrease in antioxidant activity occurred during the first 100 min of the process [45]. Sadowska et al. [50] dried strawberry fruits by various methods (convection drying, freeze–drying, spray drying) and found that the smallest changes in the antioxidant activity and content of bioactive compounds occurred during freeze–drying, while the largest changes were observed after convection drying. Özşen and Erge [51] analyzed changes in the activity of bioactive compounds during the heating of wild strawberry pulp at 60–90 °C in a time from 0 to 80 min. They found that the longer the time and the higher the temperature of the process, the larger the losses of phenolic compounds and anthocyanins.

4. Conclusions

The drying kinetics of two drying methods of wild strawberries was described using the Midilli model, over the entire measuring range. The dried material obtained during freeze–drying was characterized by a color similar to pink, visually more attractive to the consumer, although the smallest total color difference (ΔE) between the raw material and the dried material was recorded as a result of convection drying. The highest content of L-ascorbic acid in dried wild strawberry fruits was recorded in the case of freeze–drying at the lowest temperature of the heating shelves. A drying temperature not exceeding 40 °C had a relatively small effect on the total content of phenolic compounds and on the antioxidant activity of the tested samples. Increasing the drying temperature to 60 °C caused significant drops in TPC and antioxidant activity. Freeze–drying carried out at the same temperatures as convection drying resulted in slightly lower losses of TPC and antioxidant activity compared to convection drying. The best-quality dried fruits were obtained by freeze–drying, with a temperature of the heating shelves not exceeding 40 °C.

Author Contributions

Conceptualization, A.K.; methodology, A.K.; D.D.; validation, S.R. formal analysis, D.D.; investigation, A.K., S.R., U.G.-D., and E.J.-T., data curation, B.B.; writing—original draft preparation, A.K.; D.D., and S.R.; writing—review and editing A.K. and D.D.; supervision, D.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

χ 2 chi-squared test
ABTSantiradical activity (ability to neutralize free radicals against ABTS)
ACL-ascorbic acid content
Ccolor saturation
CHELchelating power
DMdry mass
DPPHantiradical activity (ability to neutralize free radicals against DPPH)
HUcolor shade
MRreduced water content
RMSEroot mean square error
TPCtotal phenolics content
ΔEtotal change in color

References

  1. Maliníková, E.; Kukla, J.; Kuklová, M.; Balážová, M. Altitudinal variation of plant traits morphological characteristics in Fragaria vesca L. (Rosaceae). Ann. For. Res. 2013, 56, 79–89. [Google Scholar] [CrossRef]
  2. Dyduch, M. Poziomka-Niedoceniana roślina zielarska. Panacea 2008, 24, 26–27. [Google Scholar]
  3. Pawlaczyk, I.; Lewik-Tsirigotisa, M.; Capek, P.; Matulova, M.; Sasinkova, V.; Dąbrowski, P.; Witkiewicz, W.; Gancarz, R. Effect of extraction condition on structural features and anticoagulant activity of F vesca conjugates. Carbohydr. Polym. 2013, 92, 741–750. [Google Scholar] [CrossRef] [PubMed]
  4. Najda, A.; Dyduch-Siemińska, M.; Dyduch, J.; Gantner, M. Comparative analysis of secondary metabolites contents in Fragaria vesca L. fruits. Ann. Agric. Environ. Med. 2014, 21, 339–343. [Google Scholar] [CrossRef] [Green Version]
  5. Dyduch-Siemińska, M.; Najda, A.; Dyduch, J.; Gantner, M.; Klimek, K. The content of secondary metabolites and antioxidant activity of wild strawberry fruit (Fragaria vesca L.). J. Anal. Methods Chem. 2015, 2015, 831238. [Google Scholar] [CrossRef] [Green Version]
  6. Naemura, A.; Mitani, T.; Ijiri, Y.; Tamura, Y.; Yamashita, T.; Okimura, M.; Yamamoto, J. Anti-thrombotic effect of strawberries. Blood Coagul. Fibrinolysis 2005, 16, 501–509. [Google Scholar] [CrossRef]
  7. Cao, G.; Russell, R.M.; Lischner, N.; Prior, R.L. Serum antioxidant capa city is increased by consumption of strawberries, spinach, red wine or vitamin C in elderly women. J. Nutr. 1998, 128, 2383–2390. [Google Scholar] [CrossRef]
  8. Carlton, P.S.; Kresty, L.A.; Siglin, J.C.; Morse, M.A.; Lu, J.; Morgan, C.; Stoner, G.D. Inhibition of N-nitrosomethylbenzylamine-induced tumorigenesis in the ratesophagus by dietary freeze-dried strawberries. Carcinogenesis 2001, 22, 441–446. [Google Scholar] [CrossRef] [Green Version]
  9. Wang, S.Y.; Lewers, K.S.; Bowman, L.; Ding, M. Antioxidant activities and anticancer cell proliferation properties of wild strawberries. J. Amer. Soc. Hort. Sci. 2007, 132, 647–658. [Google Scholar] [CrossRef] [Green Version]
  10. Milivojevic, J.; Maksimovic, V.; Nikolic, M.; Bogdanovic, J.; Maletic, R.; Milatovic, D. Chemical and antioxidant properties of cultivated and Wild fragaria and rubus berries. J. Food Qual. 2011, 34, 1–9. [Google Scholar] [CrossRef]
  11. Witkowska, A.M.; Zujko, M.E.; Technologii, Z.; Żywności, T.; Medycznego, U.; Kierownik, B.; Witkowska. Aktywność antyoksydacyjna owoców leśnych. Bromat. Chem. Toksykol. 2009, 3, 900–903. [Google Scholar]
  12. Couto, J.; Figueirinha, A.; Batista, M.T.; Paranhos, A.; Nunes, C.; Gonçalves, L.M.; Marto, J.; Fitas, M.; Pinto, P.; Ribeiro, H.M.; et al. Fragaria vesca L. extract: A promising cosmetic ingredient with antioxidant properties. Antioxidants 2020, 9, 154. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  13. Almenar, E.; Hernandez-Munoz, P.; Lagarón, J.M.; Catala, R.; Gavara, R. Controled atmosphere storage of wild strawberry fruit Fragaria vesca L. J. Agric. Food Chem. 2006, 54, 86–91. [Google Scholar] [CrossRef] [PubMed]
  14. Strzelecka, H.; Kowalski, J. Encyclopedia of Herbalism and Herbal Medicine; PWN: Warsaw, Poland, 2000. [Google Scholar]
  15. Szczygieł, A.; Pierzga, K. Uprawa Truskawki; Hortpress sp z o. o.: Warsaw, Poland, 2004. [Google Scholar]
  16. Rochalska, M.; Orzeszko-Rywka, A.; Czapla, K. The content of nutritive substances in strawberries according to cropping system. J. Res. Appl. Agric. Eng. 2011, 56, 84–86. [Google Scholar]
  17. Moraga, G.; Martinez-Navarrete, N.; Chiralt, A. Compositional changes of strawberry due to dehydration, cold storage and freezing–thawing processes. J. Food Process Preserv. 2006, 30, 458–474. [Google Scholar] [CrossRef]
  18. Amami, E.; Khezami, W.; Mezrigui, S.; Badwik, L.S.; Bejar, A.K.; Perez, C.T.; Kechaou, N. Effect of ultrasound-assisted osmotic dehydration pretreatment on the convective drying of strawberry. Ultrason. Sonochemistry 2017, 36, 286–300. [Google Scholar] [CrossRef]
  19. Yurdugu, S. An evaluation of the retention of quality characteristics in fresh and freeze-dried alpine strawberries. J. Food Sci. Technol. 2008, 43, 865–870. [Google Scholar] [CrossRef]
  20. Núñez-Mancilla, Y.; Vega-Gálvez, A.; Pérez-Won, M.; Zura, L.; García-Segovia, P.; Di Scala, K. Effect of osmotic dehydration under high hydrostatic Pressure on microstructure, functional propertiesand bioactive compounds of strawberry (Fragaria vesca). Food Bioprocess. Technol. 2014, 7, 516–524. [Google Scholar] [CrossRef]
  21. Evans, S.D.; Brambilla, A.; Lane, D.M.; Torreggiani, D.; Hall, L.D. Magnetic resonance imaging of strawberry (Fragaria vesca) slices during osmotic dehydration and air drying. Lebensm. Wiss. Technol. 2002, 35, 177–184. [Google Scholar] [CrossRef]
  22. Alvarez, C.A.; Aguerre, R.; Gomez, R.; Vidales, S.; Alzamora, S.M.; Gerschenson, L.N. Air Dehydration of strawberries: Effects of blanching and osmotic pretreatments on the kinetics of moisture transport. J. Food Eng. 1995, 25, 167–178. [Google Scholar] [CrossRef]
  23. Hammami, C.; Rene, F. Determination of freeze-drying process variables for strawberries. J. Food Eng. 1997, 32, 133–154. [Google Scholar] [CrossRef]
  24. AOAC International. Method 934.06 moisture in dried fruits. In Official Methods of the Association of Analytical Chemists, 15th ed.; AOAC: Virginia, VA, USA, 1990. [Google Scholar]
  25. Rudy, S.; Dziki, D.; Krzykowski, A.; Gawlik-Dziki, U.; Polak, R.; Rózyło, R.; Kulig, R. Influence of pre-treatments and freeze-drying temperature on the process kinetics and selected physico-chemical properties of cranberries (Vaccinium macrocarpon ait.). LWT Food Sci. Technol. 2015, 63, 497–503. [Google Scholar] [CrossRef]
  26. Rayaguru, K.; Routray, W. Mathematical modeling of thin layer drying kinetics of stone apple slices. Int. Food Res. J. 2012, 19, 1503–1510. [Google Scholar]
  27. Demir, V.; Gunhan, T.; Yagcioglu, A.K.; Degirmencioglu, A. Mathematical modeling and the determination of some quality parameters of air-dried bay leaves. Biosyst. Eng. 2004, 88, 325–335. [Google Scholar] [CrossRef]
  28. Diamante, L.M.; Munro, P.A. Mathematical modelling of the thin layer solar drying of sweet potato slices. Solar Energy 1993, 51, 271–276. [Google Scholar] [CrossRef]
  29. Henderson, S.M.; Pabis, S. Grain drying theory. II. Temperature effects on drying coefficients. J. Agric. Eng. Res. 1961, 6, 169–174. [Google Scholar]
  30. Sarimeseli, A. Microwave drying characteristics of coriander (Coriandrum sativum L.) leaves. Energy Convers. Manage. 2011, 52, 1449–1453. [Google Scholar] [CrossRef]
  31. Wang, C.Y.; Singh, R.P. Use of variable equilibrium moisture content in modeling rice drying. Trans. ASAE 1978, 11, 668–672. [Google Scholar]
  32. Midilli, A.; Kucuk, H.; Yapar, Z. A new model for single-layer drying. Dry. Technol. 2007, 20, 1503–1513. [Google Scholar] [CrossRef]
  33. Soysal, Y.; Öztekin, S.; Eren, Ö. Microwave drying of parsley: Modeling, kinetics, and energy aspects. Biosyst. Eng. 2006, 93, 403–413. [Google Scholar] [CrossRef]
  34. Dziki, D.; Polak, R.; Rudy, S.; Krzykowski, A.; Gawlik-Dziki, U.; Różyło, R.; Miś, A.; Combrzyński, M. Simulation of the process kinetics and analysis of physicochemical properties in the freeze drying of kale. Int. Agrophys. 2018, 32, 49–56. [Google Scholar] [CrossRef]
  35. Singleton, V.L.; Rossi, A. Colorimetry of total phenolics with phosphomolybdic-phosphotungstics acid reagents. Am. J. Enol. Vitic. 1965, 16, 144–158. [Google Scholar]
  36. Gawlik-Dziki, U.; Dziki, D.; Nowak, R.; Świeca, M.; Olech, M.; Pietrzak, W. Influence of sprouting and elicitation on phenolic acids profile and antioxidant activity of wheat seedlings. J. Cereal Sci. 2016, 70, 221–228. [Google Scholar] [CrossRef]
  37. Re, R.; Pellegrini, N.; Proteggente, A.; Pannala, A.; Yang, M.; Rice-Evans, C. Antioxidant activity applying an improved ABTS radical cationdecolorization assay. Free Rad. Biol. Med. 1999, 26, 1231–1237. [Google Scholar] [CrossRef]
  38. Brand-Williams, W.; Cuvelier, M.E.; Berset, C. Use of a free radical method to evaluate antioxidant activity. LWT Food Sci. Technol. 1995, 28, 25–30. [Google Scholar] [CrossRef]
  39. Lisiecka, K.; Wójtowicz, A.; Dziki, D.; Gawlik-Dziki, U. The influence of cistus incanus L. leaves on wheat pasta quality. J. Food Sci. Technol. 2019, 56, 4311–4322. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  40. Rudy, S.; Dziki, D.; Biernacka, B.; Krzykowski, A.; Rudy, M.; Gawlik-Dziki, U.; Kachel, M. Drying characteristics of dracocephalum moldavica leaves: Drying kinetics and physicochemical properties. Processes 2020, 8, 509. [Google Scholar] [CrossRef]
  41. Mihindukulasuriya, S.; Jayasuriya, H. Mathematical modeling of drying characteristics of chilli in hot air oven and fluidized bed dryers. Agric. Eng. Int. CIGR J. 2013, 15, 154–166. [Google Scholar]
  42. Zarein, M.; Samadi, S.; Ghobadian, B. Kinetic drying and mathematical modeling of apple slices on dehydration process. J. Food Process. Technol. 2013, 4, 1–4. [Google Scholar] [CrossRef] [Green Version]
  43. Darici, S.; Sen, S. Experimental investigation of convective drying kinetics of kiwi under different conditions. Heat Mass Transfer. 2015, 51, 1167–1176. [Google Scholar] [CrossRef]
  44. López-Ortiz, A.; Méndez-Lagunas, L.L.; Delesma, C.; Longoria, A.; Escobar, J.; Muñiz, J. Understanding the drying kinetics of phenolic compounds in strawberries: An experimental and density functional theory study. Innov. Food Sci. Emerg. Technol. 2020, 60, 102283. [Google Scholar] [CrossRef]
  45. Méndez-Lagunas, L.; Rodríguez-Ramírez, J.; Cruz-Gracida, M.; Sandoval-Torres, S.; Barriada-Bernal, G. Convective drying kinetics of strawberry (Fragaria ananassa): Effects on antioxidant activity, anthocyanins and total phenolic content. Food Chem. 2017, 230, 174–181. [Google Scholar] [CrossRef] [PubMed]
  46. Shishehgarha, F.; Makhlouf, J.; Ratti, C. Freeze-drying characteristics of strawberries. Dry. Technol. 2002, 20, 131–145. [Google Scholar] [CrossRef]
  47. Askari, G.R.; Emam-Djomeh, Z.; Mousavi, S.M. An investigation of the effects of drying methods and conditions on drying characteristics and quality attributes of agricultural products during hot air and hot air/microwave-assisted dehydration. Dry. Technol. 2009, 27, 831–841. [Google Scholar] [CrossRef]
  48. Núñez-Mancilla, Y.N.; Pérez-Won, M.; Uribe, E.; Vega-Gálvez, A.; Di Scala, K. Osmotic dehydration under high hydrostatic pressure: Effects on antioxidant activity, total phenolics compounds, vitamin C and colour of strawberry (Fragaria vesca). LWT Food Sci. Technol. 2013, 52, 151–156. [Google Scholar] [CrossRef]
  49. Staniszewska, I.; Liu, Z.; Zhou, Y.; Zielinska, D.; Xiao, H.; Pan, Z.; Zielinska, M. Microwave-assisted hot air convective drying of whole cranberries subjected to various initial treatments. LWT Food Sci. Technol. 2020, 133, 109906. [Google Scholar] [CrossRef]
  50. Sadowska, A.; Świderski, F.; Hallmann, E. Bioactive, physicochemical and sensory properties as well as microstructure of organic strawberry powders obtained by various drying methods. Appl. Sci. 2020, 10, 4706. [Google Scholar] [CrossRef]
  51. Özşen, D.; Erge, H.S. Degradation kinetics of bioactive compounds and change in the antioxidant activity of wild strawberry (Fragaria vesca) pulp during heating. Food Bioproc Tech. 2013, 6, 2261–2267. [Google Scholar] [CrossRef]
Figure 1. Drying curves of the freeze–drying process of wild strawberry fruits.
Figure 1. Drying curves of the freeze–drying process of wild strawberry fruits.
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Figure 2. Drying curves of the air-drying process of wild strawberry fruits.
Figure 2. Drying curves of the air-drying process of wild strawberry fruits.
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Table 1. Equations applied to the drying curves.
Table 1. Equations applied to the drying curves.
Model NumberModel NameModel EquationReferences
1Newton 1 M R = exp ( k · τ ) [27]
2Page M R = exp ( k · τ n ) [28]
3Henderson and Pabis M R = a · exp ( k · τ ) [29]
4Logarithmic M R = a · exp ( k · τ ) + b [30]
5Wang and Singh M R = 1 + a · τ + b · τ 2 [31]
6MidilliMR = a exp (−k ∙ τn) + b ∙ τ[32]
7Logistic MR = b · ( ( 1 + a · exp ( k · τ ) ) 1 [33]
1k—Drying coefficient (min−1); a, b—Coefficients of the equations; n—Exponent; τ—Time (min).
Table 2. Analysis of models describing the kinetics of freeze–drying of wild strawberry fruits.
Table 2. Analysis of models describing the kinetics of freeze–drying of wild strawberry fruits.
ModelTemperature
20 °C40 °C60 °C
R2RMSEχ2R2RMSEχ2R2RMSEχ2
Newton0.9700.05260.002810.9690.05490.003080.9650.060.0037
Page0.9950.02120.000460.9970.01810.000340.9990.01230.00016
Henderson and Pabis0.9790.04390.001990.9790.04460.002080.9780.04680.00231
Logarithmic0.9980.01410.000210.9980.01530.000250.9950.02220.00054
Wang and Singh0.9990.00290.000010.9990.00650.000040.9980.01590.00027
Logistic 0.9980.01410.000210.9980.01530.000250.9950.02220.00054
Midilli0.9990.00990.000100.9990.00780.000060.9990.00630.00004
Table 3. Analysis of models describing the kinetics of air drying of wild strawberry fruits.
Table 3. Analysis of models describing the kinetics of air drying of wild strawberry fruits.
ModelTemperature
25 °C40 °C60 °C
R2RMSEχ2R2RMSEχ2R2RMSEχ2
Newton0.99980.0040.000020.99840.01060.000110.99430.0220.0005
Page0.99980.00390.000020.99850.01020.000110.99950.00640.00004
Henderson and Pabis0.99980.00380.000010.99880.00910.000090.9970.0160.00028
Logarithmic0.99980.00370.000010.99930.00730.000060.99760.01440.00023
Wang and Singh0.96020.05220.002820.94790.06080.003850.98120.03990.00172
Logistic 0.99980.0040.000020.99870.00960.00010.99940.00740.00006
Midilli0.99980.00360.000010.99920.00760.000060.99990.00350.00001
Table 4. Values corresponding to different models describing the freeze–drying process of wild strawberry fruits.
Table 4. Values corresponding to different models describing the freeze–drying process of wild strawberry fruits.
TemperatureEquationCoefficient
ak (min−1)nb
20 °CNewton 0.004581
Page 0.0006999921.337876
Henderson and Pabis1.0939740.004990
Logarithmic1.2286060.003301 −0.1964
Wang and Singh−0.003297 0.000003
Logistic−6.25637−0.00330 −5.09225
Midilli 0.0013861.191808−0.000125
40 °CEquationCoefficient
ak (min−1)nb
Newton 0.006255
Page 0.0009111.367605
Henderson and Pabis1.1025690.006863
Logarithmic1.2374890.004581 −0.194121
Wang and Singh−0.00451 0.000005
Logistic−6.37488−0.00458 −5.15147
Midilli 0.0015771.242171−0.000142
60 °CEquationCoefficient
ak (min−1)nb
Newton 0.007945
Page 0.0009211.430819
Henderson and Pabis1.1212150.008836
Logarithmic1.2315310.006216 −0.163777932
Wang and Singh−0.005726 0.000008
Logistic−6.10585−0.00622 −7.51954
Midilli 0.0012631.355914−0.0000931
Table 5. Values corresponding to different models describing the air drying of wild strawberry fruits.
Table 5. Values corresponding to different models describing the air drying of wild strawberry fruits.
TemperatureEquationCoefficient
ak (min−1)nb
25 °CNewton 0.006371
Page 0.0065660.994308
Henderson and Pabis0.9953100.006341
Logarithmic0.9962530.006286 −0.002644
Wang and Singh−0.004315 0.000005
Logistic15.471840.00653 0.06131
Midilli 0.0068480.984885−0.000008
40 °CEquationCoefficient
ak (min−1)nb
Newton 0.009089
Page 0.0083371.017652
Henderson and Pabis1.0209670.009282
Logarithmic1.0173650.009663 0.011738
Wang and Singh−0.005942 0.000009
Logistic21.901910.00948 0.04288
Midilli 0.0070341.0583790.000041
60 °CEquationCoefficient
ak (min−1)nb
Newton 0.015674
Page 0.0080761.152685
Henderson and Pabis1.0525340.016463
Logarithmic1.0607780.015683 −0.016418
Wang and Singh−0.010688 0.000028
Logistic1.7328450.020325 0.359499
Midilli 0.0071811.1849100.000057
Table 6. Effect of the drying method on the color of wild strawberry fruits.
Table 6. Effect of the drying method on the color of wild strawberry fruits.
MD *DTDimension of Color
L*CHUΔE
RM 35.89 ± 1.16 a**27.48 ± 1.15 b21.78 ± 1.25 a0
FD20 °C52.78 ± 0.30 e20.18 ± 0.28 a42.83 ± 0.91 b20.34 ± 0.18 c
40 °C53.54 ± 0.43 ef19.89 ± 0.52 a44.61 ± 0.94 c21.36 ± 0.58 d
60 °C54.04 ± 0.35 f19.87 ± 0.47 a45.29 ± 0.54 c21.89 ± 0.39 d
AD25 °C49.37 ± 0.43 d29.33 ± 0.43 c45.92 ± 0.22 c18.17 ± 0.34 b
40 °C47.14 ± 0.53 c29.40 ± 0.64 c45.92 ± 0.32 c16.60 ± 0.45 a
60 °C44.18 ± 0.44 b29.85 ± 0.47 c48.30 ± 0.69 d15.86 ± 0.59 a
* MD—Method of drying, DT—Drying temperature, RM—Raw material, FD—Freeze–drying, AD—Air drying, L*—Brightness, C—Color saturation, HU—Color shade, ΔE—Total change in color. ** The values designated by different small letters (a, b, c, d, e, f) are significantly different (α = 0.05).
Table 7. L-ascorbic acid content, total phenolics content, and antioxidant activity of wild strawberries.
Table 7. L-ascorbic acid content, total phenolics content, and antioxidant activity of wild strawberries.
MD *DTACTPCABTSDPPHCHELRED
(mg/100g DM)(mg GAE/g DM)(EC50; mg DM/mL)
RM 304 ± 4.08 d**21.5 ± 0.96 f5.2 ± 0.33 a27.5 ± 1.12 a10.3 ± 0.75 a10.1 ± 0.31 a
FD20 °C267 ± 4.44 a19.4 ± 0.58 e6.7 ± 0.42 b31.6 ± 2.23 bc11.5 ± 0.92 ab10.8 ± 0.26 ab
40 °C228 ± 3.26 b18.3 ± 0.62 d6.2 ± 0.27 b30.2 ± 1.78 b13.2 ± 0.67 bd11.6 ± 0.38 b
60 °C197 ± 3.75 c15.0 ± 0.69 b8.7 ± 0.61 c33.8 ± 1.07 c16.7 ± 0.42 ce13.2 ± 0.46 c
AD25 °C123 ± 3.42 e17.4 ± 0.4 c6.2 ± 0.56 b32.3 ± 1.78 c14.1 ± 0.51 d13.6 ± 0.54 c
40 °C101 ± 3.14 f15.6 ± 0.52 b6.5 ± 0.47 b33.7 ± 0.76 c12.7 ± 0.56 b14.3 ± 0.36 c
60 °C68 ± 3.21 g10.2 ± 0.36 a9.2 ± 0.51 c36.2 ± 1.29 d15.3 ± 0.47 c16.5 ± 0.22 e
* MD—Method of drying, DT—Drying temperature, RM—Raw material, FD—Freeze–drying, AD—Air drying, AC—L-ascorbic acid content, TPC—total phenolics content, ABTS—ability to neutralize free radicals against ABTS, DPPH—ability to neutralize free radicals against DPPH, CHEL—chelating power, RED—reducing power; ** The values designated by different small letters (a, b, c, d, e, f, g) are significantly different (α = 0.05).

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Krzykowski, A.; Dziki, D.; Rudy, S.; Gawlik-Dziki, U.; Janiszewska-Turak, E.; Biernacka, B. Wild Strawberry Fragaria vesca L.: Kinetics of Fruit Drying and Quality Characteristics of the Dried Fruits. Processes 2020, 8, 1265. https://0-doi-org.brum.beds.ac.uk/10.3390/pr8101265

AMA Style

Krzykowski A, Dziki D, Rudy S, Gawlik-Dziki U, Janiszewska-Turak E, Biernacka B. Wild Strawberry Fragaria vesca L.: Kinetics of Fruit Drying and Quality Characteristics of the Dried Fruits. Processes. 2020; 8(10):1265. https://0-doi-org.brum.beds.ac.uk/10.3390/pr8101265

Chicago/Turabian Style

Krzykowski, Andrzej, Dariusz Dziki, Stanisław Rudy, Urszula Gawlik-Dziki, Emilia Janiszewska-Turak, and Beata Biernacka. 2020. "Wild Strawberry Fragaria vesca L.: Kinetics of Fruit Drying and Quality Characteristics of the Dried Fruits" Processes 8, no. 10: 1265. https://0-doi-org.brum.beds.ac.uk/10.3390/pr8101265

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