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Article

The Quality Assessment of Sour Cherries Dried Using an Innovative Simultaneous Osmotic–Microwave–Vacuum Approach Based on Image Textures, Color Parameters, and Sensory Attributes

by
Ewa Ropelewska
*,
Dorota Konopacka
and
Jan Piecko
Fruit and Vegetable Storage and Processing Department, The National Institute of Horticultural Research, Konstytucji 3 Maja 1/3, 96-100 Skierniewice, Poland
*
Author to whom correspondence should be addressed.
Agriculture 2024, 14(1), 54; https://doi.org/10.3390/agriculture14010054
Submission received: 5 December 2023 / Revised: 24 December 2023 / Accepted: 25 December 2023 / Published: 27 December 2023
(This article belongs to the Section Agricultural Product Quality and Safety)
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Abstract

:
Sour cherries are a perishable raw material, and their preservation is needed to extend their availability to consumers. Improving drying techniques is desirable to ensure the highest quality of products. This study aimed to determine image textures from color channels R, G, B, L, a, b, X, Y, and Z; color parameters L*, a*, and b*; the color difference (ΔE) of raw materials and dried fruit; and the sensory attributes of dried sour cherry products prepared using an innovative approach. Three sour cherry cultivars, ‘Nefris’, ‘Debreceni Botermo’, and ‘Łutówka’, were used in the experiment. Sour cherries were subjected to freezing and pit removal before drying. The simultaneous osmotic–microwave–vacuum drying was carried out in one process lasting an hour and combining osmotic dehydration using a 40 °Bx sucrose solution and microwave–vacuum drying at microwave powers of 100 W for 900 s, 300 W for 900 s, 250 W for 900 s, and 0 W for stabilization for 900 s and a pressure of 30 ± 2 hPa. After drying, the quality assessment of products was performed using non-destructive image analysis and color measurements, as well as sensory analysis, including non-destructively and destructively assessed attributes. The highest changes in textures occurred for the GHMean (histogram’s mean for color channel G) (from 30.69 to 22.64) and LHMean (histogram’s mean for color channel L) (from 66.93 to 59.07) of images of the cultivar ‘Łutówka’, and the smallest changes were found for the cultivar ‘Nefris’. Drying had a statistically significant effect on the color parameters of the ‘Debreceni Botermo’ and ‘Łutówka’ sour cherries. The value of ΔE was the highest (10.44) for ‘Debreceni Botermo’ and the smallest (1.98) for ‘Nefris’. All cultivars of dried sour cherries had very high values of overall quality, reaching 8.9 for ‘Nefris’ and ‘Debreceni Botermo’ and 8.8 for ‘Łutówka’. The ‘Nefris’ sour cherry was characterized by the highest value of flavor of 9.0. All dried samples were attractive in terms of their external appearance. The sensory parameters related to taste, texture, and crunchiness were also satisfactory. Innovative simultaneous osmotic–microwave–vacuum drying allowed for the obtainment of dried sour cherries with a high quality, including acceptable sensory attributes.

1. Introduction

The sour cherry (Prunus cerasus L.) is a popular fruit around the world due to its nutritional value, content of fibers, taste, sourness, and health-promoting properties [1,2]. It is rich in polyphenols, including flavonols, hydroxycinnamic acids, and anthocyanins [2,3]. Cherries have strong anti-inflammatory, antibacterial, antioxidant, anticancer, and antidiabetic activities [4]. The chemical properties of sour cherries can differ depending on the cultivar [5,6,7]. Moreover, the cultivation system can influence the chemical composition of particular varieties [8]. Sour cherries can be characterized by genetic diversity [9] and a high phenotypic variability [10,11].
Sour cherries are perishable, and the harvesting time and storage period of this fruit are limited because of a fast ripening process and a high respiration rate. Sour cherries can be eaten fresh, but due to the low sugar/acid ratio, they are most often processed, i.e., dried, brined, frozen, or used for the production of juices [4,12,13]. Most of the sour cherry cultivars are also suitable for the production of jams, jellies, concentrates, purees, or alcoholic beverages. Furthermore, sour cherry products can be ingredients of chocolate or other sweets. Generally, sour cherries are an important industrial fruit and a valued raw material for food production with the need to apply appropriate control and maintain the high quality of sour cherries subjected to processing [14].
Dried sour cherries are characterized by a long shelf life. Therefore, drying the fruit can ensure its availability out of season. Drying allows for food preservation due to water removal and, therefore, prevents the growth of microorganisms and decay. Dried sour cherries can be considered a healthy snack with preserved nutrients and bioactive compounds. Vacuum drying, due to the low drying temperature, high drying rate, and oxygen-deficient drying environment, is a desirable technique for fruit susceptible to damage. An advantage of vacuum drying is also energy savings [12]. These advantages are important compared with traditional convective drying using hot air. Convective drying requires high temperatures and relatively long times, which can result in a product deterioration in terms of nutrients, color, and shrinkage [4]. Microwave radiation as a non-ionizing radiation energy can alter the structural and functional properties of food ingredients. Microwaves are a fast heating source, directly affecting the food material and speeding up the drying rate and physicochemical reactions, as well as producing high-quality dried products [15]. Microwave drying has advantages over conventional techniques due to the reduction in processing times and lower amount of quality losses. The combination of microwave drying and vacuum conditions brings an additional advantage due to the reduction in the thermal oxidation of products. However, the inhomogeneity of a microwave field and the heterogenic structure of dried materials can result in hot spots and the overheating of some areas of the product despite the use of a vacuum or rotation [4].
Osmotic dehydration can be used to improve the quality of dried food products. It is usually considered a pretreatment before drying and involves the immersion of raw materials in hypertonic solutions to partially remove water due to the pressure difference between a hypertonic solution and the material. Osmotic dehydration has been proven to enhance the quality of processed fruit by favoring the retention of the color, texture, aroma, and nutritional composition. The application of only osmotic dehydration cannot provide a safe moisture content. Therefore, osmotically dehydrated products are not shelf-stable and should be further dried using vacuum, air, or freeze drying [2,11]. It was reported that freezing was a good pretreatment for osmotic dehydration and improved the mass transfer. Furthermore, the prefreezing of sour cherries with or without stones is common and the least invasive approach to their preservation. Osmotic dehydration can result in an increase in the water loss (WL) and solid gain (SG) with an increase in the time of the osmotic dehydration of frozen sour cherries [16]. Osmotic dehydration can be performed using carbohydrates such as sucrose to increase the sweetness of the fruit and enhance the sensory quality. It can increase the consumer acceptability of the sour cherry, which is rather limited for consumption as a fresh fruit because of its high acidity and astringency [2]. In the case of sour cherries, other pretreatment methods, for example, edible coatings or ultrasounds, can reduce the drying time and preserve the dried product quality [1]. However, novel approaches to drying sour cherries that ensure the highest quality and consumer acceptance are still desired.
In the present study, an innovative drying procedure combining osmotic dehydration and microwave–vacuum drying in one process was applied to the dehydration of sour cherries. The objective of this study was to determine the influence of the developed osmotic–microwave–vacuum drying on the texture parameters of images in color channels R, G, B, L, a, b, X, Y, and Z; color parameters L*, a*, and b*; the color difference (ΔE), and sensory attributes related to the appearance, aroma, color, texture, taste, and overall quality. The great novelty of this study was to compare the non-destructively and destructively assessed attributes of raw and osmotic–microwave–vacuum-dried sour cherries belonging to different cultivars. Furthermore, image textures from the individual color channels R, G, B, L, a, b, X, Y, and Z were used for the first time to assess the quality of sour cherry products obtained using osmotic dehydration and microwave–vacuum drying and provided reliable and objective results.

2. Materials and Methods

2.1. Materials

The research material consisted of different cultivars of sour cherries, ‘Nefris’, ‘Debreceni Botermo’, and ‘Łutówka’. The sour cherries were collected from the Experimental Orchard of the National Institute of Horticultural Research in Poland. The fruits were uniform in their size, color, and degree of ripeness. The sour cherries belonging to all cultivars were frozen in the laboratory freezer (Whirlpool Corporation, Benton Harbor, MI, USA) at a temperature of −29 ± 2 °C and stored in this form for several months. The pits were removed from sour cherries directly before drying experiments.

2.2. Drying Experiment

The sour cherries in their frozen form were subjected to an innovative drying technique combining osmotic dehydration and microwave–vacuum drying in one simultaneous process. The procedure was carried out according to the patent PL 236950 B1 [17] with slight modifications. The drying was performed with the use of a laboratory custom-made microwave–vacuum dryer (Promis-Tech, Wrocław, Poland). The Microwave–Vacuum Drying System is presented in Figure 1. The drying system comprised a polypropylene drying chamber, motor, microwave generator, control unit, and units for the measurements of temperature and pressure. For the experiments, the chamber was replaced with a glass container (jar) with a capacity of 2 L. A sample of 100 g of frozen sour cherries without pits was placed into a glass jar. Then, 60 g of a 40 °Bx sucrose solution prepared using sucrose and tap water was added as an osmotic solution. Sour cherries and the solution were mixed thoroughly before placing the jar into the dryer. Then, a process combining osmotic dehydration and microwave–vacuum drying was performed simultaneously in one device. The procedure was divided into 4 stages, including 3 stages of drying, the 1st stage at a microwave power of 100 W for 900 s, the 2nd stage at 300 W for 900 s, and the 3rd stage at 250 W for 900 s, as well as the 4th stage of stabilization for 900 s. The whole operation took an hour. The pressure during the drying was 30 ± 2 hPa and the temperature was below 60 °C. The used approach allowed the osmotic solution to penetrate the fruit and dry them in a continuous process. The experiments were performed in two technological repetitions (two processes of drying) for each sour cherry cultivar of ‘Nefris’, ‘Debreceni Botermo’, and ‘Łutówka’. After each process was finished, the samples were placed in closed plastic containers for further quality assessment, including image analysis, color measurement, and sensory analysis. The initial dry matter contents for the raw materials were equal to 16.3% for ‘Nefris’, 15.8% for ‘Debreceni Botermo’, and 12.3% for ‘Łutówka’. The final dry matter contents for dried products were 96.8% for ‘Nefris’, 92.1% for ‘Debreceni Botermo’, and 95.0% for ‘Łutówka’. All samples subjected to analysis were characterized by a water activity (aw) of 0.4.
The procedure of determining the influence of osmotic–microwave–vacuum drying on the quality of sour cherries is presented in Figure 2.

2.3. Image Analysis

Both raw materials and dried samples were subjected to image acquisition using the Epson Perfection V600 Photo flatbed scanner (Epson, Suwa, Nagano, Japan) and SilverFast Ai Studio 9 Scanner Software with Auto IT8 Calibration, version 9 (LaserSoft Imaging, Kiel, Germany). Sour cherries were placed without touching each other on the scanner glass, and a white background was used. Each photo included 15–20 fruits. The analysis was performed in 50 repetitions for each cultivar. The color images were saved at 1200 dpi in the TIFF file format. Before image processing, it was necessary to change the background of each image to black and to save the images in the bitmap (BMP) file format. The MaZda software, version 4.7 (Łódź University of Technology, Institute of Electronics, Łódź, Poland) [18,19,20] was used for the image processing to perform the image segmentation, regions of interest (ROIs) identification, and image texture extraction. The image segmentation was carried out using a manually determined brightness threshold of 10. The background was characterized by an intensity of 0. Each fruit was lighter from the background and was separated and considered as one ROI. The feature extraction was carried out for each ROI for images converted to color channels R, G, B, L, a, b, X, Y, and Z. Sample images of raw materials and dried fruit in selected color channels are presented in Figure 3.

2.4. Color Measurements

The color parameters L* (lightness, 0 (dark)–100 (light)), a* (green (−) –red (+)), and b* (blue (−)–yellow (+)) were measured with the use of the Konica Minolta CM-2600d portable spectrophotometer (Chiyoda, Tokyo, Japan). Before measurements, the Zero Calibration and White Calibration of the spectrophotometer were performed. For the color measurements, the CIE standard illuminant D65 and the observer 10° were used. The measurements were carried out in 30 repetitions for both the raw and dried sour cherries of each cultivar. In the case of each sour cherry cultivar, the color difference (ΔE) was determined using Equation (1):
Δ E = Δ L 2 + ( Δ a ) 2 + ( Δ b ) 2

2.5. Sensory Analysis

The sensory analysis of dried sour cherries was performed with the use of the Quantitative Descriptive Analysis (QDA) method in accordance with the procedure described in PN-EN ISO 13299:2016-05 [21]. The analysis was carried out with the use of ANALSENS computer software, version 5.0 (CogITos, Sopot, Poland) at the Sensory Analysis Laboratory of the National Institute of Horticultural Research in Skierniewice, Poland. All requirements specified in PN-EN ISO 8589:2010/A1:2014–07 [22] for sensory analysis laboratories were met. The test room for the sensory analysis of dried sour cherries included four sensory booths with computers and white light (6500 K). The sensory evaluation was performed by a team of 10 trained and experienced assessors. The evaluators were qualified in accordance with PN-EN ISO 8586:2014-03 [23]. Dried sour cherries were placed in plastic containers with a capacity of 40 mL with plastic lids. Each container with a few fruits was marked with a 3-digit code. Between the evaluation of individual samples, non-carbonated water was used as a taste neutralizer. The quality attributes related to the appearance, aroma, color, texture, taste, and overall quality were assessed. A list of all attributes with their boundary values is presented in Table 1. The values were marked on the unstructured linear scale, where 0 meant no intensity of the attribute and 10 was the highest intensity.

2.6. Statistical Analysis

The obtained results were statistically analyzed using STATISTICA 13.1 (Dell Inc., Tulsa, OK, USA, StatSoft Polska, Kraków, Poland) to determine the differences between the raw materials and dried sour cherries of the ‘Nefris’, ‘Debreceni Botermo’, and ‘Łutówka’ cultivars. The mean values of selected image texture parameters and color parameters were compared at a significance level of p < 0.05. The homogeneity of variance and normality of the distribution of variables were checked. Then, the Tukey’s test was applied.

3. Results

3.1. The Influence of Osmotic–Microwave–Vacuum Drying on Image Textures of Sour Cherries

It was observed that the applied drying procedure influenced the selected image textures of sour cherries. In this study, the changes in the texture HMean (histogram’s mean) for individual color channels R, G, B, L, a, b, X, Y, and Z of sour cherry images are presented (Table 2). Comparing the values of texture parameters between the raw materials and dried fruit belonging to the ‘Nefris’, ‘Debreceni Botermo’, and ‘Łutówka’ cultivars, osmotic–microwave–vacuum drying had a statistically significant effect on the image textures RHMean, GHMean, BHMean, LHMean, XHMean, YHMean, and ZHMean of all the sour cherry cultivars. The highest changes occurred in the case of the sour cherry ‘Łutówka’. This cultivar was characterized by a decrease in the values of the textures RHMean by 7.23 (from 54.60 to 47.37), GHMean by 8.05 (from 30.69 to 22.64), BHMean by 7.37 (from 32.25 to 24.88), LHMean by 7.86 (from 66.93 to 59.07), XHMean by 1.93 (from 6.90 to 4.97), YHMean by 1.93 (from 5.97 to 4.04), and ZHMean by 1.75 (from 4.93 to 3.18) after osmotic–microwave–vacuum drying compared to the raw material. In the case of the sour cherries ‘Nefris’ and ‘Debreceni Botermo’, osmotic–microwave–vacuum drying also resulted in a decrease in the image textures RHMean, GHMean, BHMean, LHMean, XHMean, YHMean, and ZHMean. However, the changes were slightly smaller. For textures aHMean and bHMean, no statistically significant differences were observed between the raw materials and dried sour cherries of any cultivars.

3.2. The Influence of Osmotic–Microwave–Vacuum Drying on Color Parameters of Sour Cherries

The osmotic–microwave–vacuum drying resulted in changes in the color parameters L*, a*, and b* of sour cherries (Table 3). Both raw materials and dried samples were characterized by low values of the color parameter L* and positive values of parameters a* and b*. It meant that the sour cherries were dark with a red and yellow color. The differences between the raw materials and dried fruit were statistically significant for cultivars ‘Debreceni Botermo’ and ‘Łutówka’. In the case of the sour cherry ‘Nefris’, no statistically significant changes were observed in any of the tested color parameters. The color difference (ΔE) was the highest (10.44) for the sour cherry ‘Debreceni Botermo’ and the smallest (1.98) for ‘Nefris’.

3.3. The Influence of Osmotic–Microwave–Vacuum Drying on Sensory Attributes of Sour Cherries

The values for the overall quality and flavor of the sour cherries ‘Nefris’, ‘Debreceni Botermo’, and ‘Łutówka’ are presented in Table 4, and individual parameters related to their appearance, aroma, color, texture, and taste are shown in Figure 4 and Figure 5. Generally, the sour cherries ‘Nefris’, ‘Debreceni Botermo’, and ‘Łutówka’ dried using an innovative simultaneous osmotic–microwave–vacuum approach were characterized by very high values of overall quality on the unstructured linear scale from 0 to 10. Dried samples belonging to ‘Nefris’ and ‘Debreceni Botermo’ reached an overall quality of 8.9. For the cultivar ‘Łutówka’, the overall quality of the dried fruit was slightly lower (8.8). Also, the flavor values were very high. Dried products belonging to all cultivars were considered palatable and aromatic. The highest palatability of 9.0 on the linear scale from 0 to 10 was observed for the dried sour cherry ‘Nefris’ (Table 4).
Firstly, the sensory attributes were assessed without the destruction of samples. The results of sensory analysis of whole dried sour cherries related to appearance, aroma, and color are presented in Figure 4. Considering the external appearance, all dried samples were attractive. Sour cherry samples belonging to ‘Debreceni Botermo’ were characterized by the most intense fruity smell (6.3), the most pleasant overall aroma (8.5), and the most uniform color (7.1). Sour cherries belonging to ‘Debreceni Botermo’ were also the most shiny (8.7) and sticky (8.8). Dried sour cherries belonging to ‘Nefris’ were the darkest (8.5), and dried samples belonging to ‘Łutówka’ were the lightest (5.0). A shape closest to a round one was observed for the samples. The surface stickiness was the smallest (5.7) for the dried fruit ‘Nefris’. All samples were characterized by an almost imperceptible off-odor and faintly imperceptible caramel aroma.
The sensory parameters related to taste, texture, and crunchiness determined destructively are presented in Figure 5. It was found that the dried sour cherry samples of the ‘Nefris’ cultivar were the most crunchy (7.0) and hard (4.8). They were characterized by an imperceptible bitter taste (0.0) and the least imperceptible caramel taste (0.4). Dried sour cherries of the ‘Nefris’ and ‘Debreceni Botermo’ cultivars had the most intense fruity taste values of 9.0 and 9.2, respectively, as well as the lowest values of astringent taste, 1.3 and 1.1, respectively. The sweetest (7.5) and the least sour (3.7) were the dried samples from the ‘Debreceni Botermo’ cultivar.

4. Discussion

The performed study confirmed the possibility of determining the quality of dried sour cherries using non-destructive image analysis and color measurements, as well as sensory analysis, including non-destructively and destructively assessed attributes. The changes in quality parameters were observed after the osmotic–microwave–vacuum drying of sour cherries and depended on the cultivar. The smallest changes in the image textures and color parameters of dried products compared to the raw materials occurred for the sour cherry ‘Nefris’. This cultivar was also characterized by the highest values of overall sensory quality due to its highly appreciated flavor. The obtained results stay in consensus with those reported by Konopacka et al. [11], who stated the sensory quality of osmo-convectively dried sour cherries strongly depends on the cultivar. Additionally, the appropriate selection of the sour cherry cultivar is important for the nutritional value of dried products. It was found that the cultivar ‘Nefris’ was the most suitable for osmo-convectively drying, resulting in a high quality, repeatable sensory attributes, and the pro-health properties of the dried fruit. However, vacuum–microwave drying can be more advantageous compared to convective drying. Wojdyło et al. [4] observed that the application of a short drying time, a low temperature, and the limited contact of the material with the oxygen present in the air allowed for the best maintenance of the bioactivity of dried sour cherries. The quality of vacuum–microwave-dried fruit was better than in the case of convective drying and competitive with freeze-dried products. A desirable content of phenolic compounds and anthocyanins, attractive color, and high antioxidant capacity were obtained. Šumić et al. [12] used the vacuum drying for frozen sour cherries. The authors found a vacuum pressure of 148.16 mbar and temperature of 54.03 °C to be the optimum conditions for vacuum drying to obtain the maximum content of anthocyanin, vitamin C, and total phenols; maximum antioxidant activity; and minimum aw and total color changes of dried sour cherries. Horuz et al. [24] reported that hybrid (microwave–convectional) drying increased the drying rate, reduced the drying time, and increased the content of vitamin C, total phenolic content, antioxidant capacity, and rehydration ability of sour cherries compared to the convectional drying. However, the values of the color parameters of the samples dried using hybrid (microwave–convectional) and convectional drying were similar. Both the microwave–convectional and convectional drying of sour cherries resulted in an increase in the color parameter L* and a decrease in color parameters a* and b* compared to fresh fruit.
Furthermore, a pretreatment before drying can influence the product quality and drying time. Nowicka et al. [16] obtained a high antioxidant activity and high content of polyphenols, as well as a large water loss/solid gain ratio, during osmotic dehydration using an apple concentrate as a pretreatment for frozen sour cherries. The best processing procedure for sour cherries combined osmotic dehydration with convective drying and vacuum–microwave drying. In the study performed by Siucińska et al. [13], an ultrasound pretreatment during osmotic dehydration had a neutral effect on the bioactive component retention of convectively dried sour cherries. Furthermore, a prolonged ultrasound treatment resulted in anthocyanin deterioration. According to Siucińska et al. [25], an ultrasound application during the osmotic pretreatment can result in a decrease in anthocyanin content and accelerate the loss of the antioxidant potential of stored convectively dried sour cherries. Simsek and Süfer [26] reported a reduced time for the microwave–hot air drying of white sweet cherries as a result of using 10% citric acid, 60% sucrose solutions, or a freezing pretreatment. In addition to osmotic dehydration, other pretreatment techniques can be used for sour cherries. Salehi and Inanloodoghouz [1] concluded that a pretreatment using edible coatings can reduce the shrinkage and color changes of convectively dried sour cherries. However, most of the available literature data included information on the use of a pretreatment as a separate step before drying. In contrast, in this study related to sour cherries, osmotic dehydration in a sucrose solution was applied during one simultaneous process with drying. In the previous study performed by Piecko et al. [27], the application of osmotic dehydration and vacuum–microwave drying in one process allowed for the obtainment of promising physicochemical properties in halved cranberries.
This study proved that an innovative approach to the osmotic dehydration and microwave–vacuum drying of sour cherries allowed a high quality of dried fruit to be maintained in terms of sensory attributes, image features, and color parameters compared to raw materials. The developed osmotic–microwave–vacuum drying can be of practical importance for preserving sour cherries without losing their quality. The application of the approach combining image analysis and machine learning provided a quick and objective assessment of the effect of drying on fruit. It can be used in further studies to compare raw materials and dried fruit, distinguish cultivars, and classify dried fruit using machine learning models based on image parameters. For the classification of dried fruits and fruit products, machine learning models were successfully applied, among others, by Przybył et al. [28], Przybył et al. [29], Bisri and Man [30], Baigvand et al. [31], and Raihen and Akter [32].
As reported in previous studies, the application of imaging allowed for the prediction of the fruit quality, including sensory attributes and physicochemical properties [33,34,35]. In view of the results of the above-mentioned studies, future studies can also be supplemented by determining the relationship between the image features, sensory attributes, and chemical properties of dried sour cherries and developing predicting models based on image parameters.

5. Conclusions

Sour cherries dried using an innovative simultaneous osmotic–microwave–vacuum procedure were characterized by a high quality. The osmotic–microwave–vacuum drying statistically significantly influenced the image texture parameters RHMean, GHMean, BHMean, LHMean, XHMean, YHMean, and ZHMean of all cultivars. The differences in the color parameters L*, a*, and b* between the raw materials and dried fruit were statistically significant for cultivars ‘Debreceni Botermo’ and ‘Łutówka’. The smallest changes were observed for ‘Nefris’. The sensory parameters were acceptable. The highest overall quality was found for ‘Nefris’ and ‘Debreceni Botermo’, and the highest value of flavor was indicated for ‘Nefris’. ‘Nefris’ dried sour cherries were also the crunchiest. Dried samples of ‘Nefris’ and ‘Debreceni Botermo’ were characterized by the most intense fruity tastes and the lowest values of astringent taste. Based on the obtained results, the usefulness of the approach involving non-destructive image analysis and color measurements and non-destructively and destructively assessed sensory attributes for the quality assessment of dried sour cherries was confirmed. The application of image analysis was promising. Image analysis combined with machine learning can be used in further studies for the development of classification models to determine the influence of osmotic–microwave–vacuum drying on the sour cherry quality in an objective manner. In further research, the correlation between the image parameters, sensory characteristics, and chemical properties of sour cherries can be determined.

Author Contributions

Conceptualization, E.R., D.K. and J.P.; methodology, E.R., D.K. and J.P.; software, E.R.; validation, E.R.; formal analysis, E.R.; investigation, E.R.; resources, E.R.; data curation, E.R.; writing—original draft preparation, E.R. and D.K.; writing—review and editing, E.R. and J.P.; visualization, E.R.; project administration, E.R. and D.K.; funding acquisition, D.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the research and development project ’An innovative device for producing dried fruit with high pro-health properties‘ (POIR.01.01.01-00-1073/21-00) financed by the European Regional Development Fund with the National Centre for Research and Development as an intermediate institution.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Microwave–Vacuum Drying System.
Figure 1. Microwave–Vacuum Drying System.
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Figure 2. A block diagram of an approach to determining the influence of simultaneous osmotic–microwave–vacuum drying on the quality of sour cherries.
Figure 2. A block diagram of an approach to determining the influence of simultaneous osmotic–microwave–vacuum drying on the quality of sour cherries.
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Figure 3. Exemplary images of raw and dried sour cherries in selected color channels R (a) and L (b).
Figure 3. Exemplary images of raw and dried sour cherries in selected color channels R (a) and L (b).
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Figure 4. Radar chart of the sensory analysis of dried sour cherries for attributes determined non-destructively.
Figure 4. Radar chart of the sensory analysis of dried sour cherries for attributes determined non-destructively.
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Figure 5. Radar chart of the sensory evaluation of dried sour cherries for parameters determined destructively.
Figure 5. Radar chart of the sensory evaluation of dried sour cherries for parameters determined destructively.
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Table 1. Sensory attributes and boundary values of the quality assessment of dried sour cherries using a profile method.
Table 1. Sensory attributes and boundary values of the quality assessment of dried sour cherries using a profile method.
Boundary Values
Attribute0—Minimum10—Maximum
External appearanceNon-attractiveVery attractive
Fruity smellImperceptibleVery intense
Caramel aromaImperceptibleVery intense
Off-odorImperceptibleVery intense
Overall aromaUnpleasant, irritatingVery pleasant
ColorBrightDark
Color uniformityNon-uniformUniform
GlossinessMatteGlossy
ShapeStrongly deformedClose to round
Surface stickinessDryVery sticky
Flesh textureVery hard Soft
Crunchiness No sound or short, quiet soundLong, loud sound
Fruity taste ImperceptibleVery intense
Sweet tasteImperceptibleVery intense
Sour tasteImperceptibleVery intense
Astringent tasteImperceptibleVery intense
Caramel tasteImperceptibleVery intense
Bitter tasteImperceptibleVery intense
Off-flavor ImperceptibleVery intense
FlavorEmpty, uncharacteristicRich, aromatic, palatable
Overall quality Poor quality, unharmonizedVery good quality, harmonized
Table 2. The changes in the texture HMean of sour cherry images in individual color channels as a result of osmotic–microwave–vacuum drying.
Table 2. The changes in the texture HMean of sour cherry images in individual color channels as a result of osmotic–microwave–vacuum drying.
SampleRHMeanGHMeanBHMeanLHMeanaHMeanbHMeanXHMeanYHMeanZHMean
‘Nefris’—raw material45.51 (8.18) a26.28 (2.97) a27.00 (4.35) a60.59 (4.61) a134.39 (2.79) a130.02 (1.27) a5.11 (1.09) a4.48 (0.77) a3.64 (0.77) a
‘Nefris’—dried 41.56 (3.87) b21.78 (2.09) b23.64 (2.29) b55.83 (2.57) b134.93 (1.26) a129.66 (2.29) a4.24 (0.65) b3.52 (0.55) b2.88 (0.52) b
‘Debreceni Botermo’—raw material49.81 (5.06) a31.19 (4.32) a32.24 (5.55) a65.37 (4.67) a134.12 (0.97) a129.53 (0.90) a6.40 (1.27) a5.81 (1.20) a4.98 (1.33) a
‘Debreceni Botermo’—dried 45.29 (10.18) b25.97 (11.50) b27.79 (11.02) b60.35 (11.05) b134.60 (2.65) a129.55 (1.25) a5.08 (2.85) b4.45 (2.84) b3.78 (2.76) b
‘Łutówka’—raw material54.60 (7.89) a30.69 (3.83) a32.25 (5.01) a66.93 (4.96) a136.07 (2.32) a130.43 (1.49) a6.90 (1.35) a5.97 (1.06) a4.93 (1.10) a
‘Łutówka’—dried 47.37 (9.88) b22.64 (10.32) b24.88 (9.80) b59.07 (9.61) b136.66 (3.35) a130.60 (1.95) a4.97 (2.82) b4.04 (2.85) b3.18 (2.79) b
a,b—the same letters in the columns for both the raw materials and dried fruit for one cultivar denote that there are no statistical differences. texture HMean—histogram’s mean; the first letter in the texture name denotes the color channel (R, G, B, L, a, b, X, Y, or Z). the parentheses—standard deviations.
Table 3. The changes in color parameters of sour cherries under the influence of osmotic–microwave–vacuum drying.
Table 3. The changes in color parameters of sour cherries under the influence of osmotic–microwave–vacuum drying.
SampleL*a*b*ΔE
‘Nefris’—raw material21.89 (3.64) a13.80 (6.33) a7.56 (3.47) a1.98
‘Nefris’—dried 21.85 (2.92) a12.02 (3.68) a6.69 (1.43) a
‘Debreceni Botermo’—raw material20.79 (3.13) a11.67 (2.32) a5.72 (2.09) a10.44
‘Debreceni Botermo’—dried 28.90 (11.28) b8.18 (2.23) b0.14 (1.62) b
‘Łutówka’—raw material21.99 (3.15) a13.60 (4.48) a6.89 (2.75) a6.30
‘Łutówka’—dried 27.04 (3.08) b16.95 (4.17) b5.18 (2.57) b
a,b—the same letters in the columns for both the raw materials and dried fruit for one cultivar denote that there are no statistical differences. L*, stated as L-star—lightness; a*, stated as a-star—red; b*, stated as b-star—yellow; the asterisks (*) are parts of full names and are pronounced star. the parentheses—standard deviations.
Table 4. The overall quality and flavor of sour cherries dried using osmotic–microwave–vacuum drying.
Table 4. The overall quality and flavor of sour cherries dried using osmotic–microwave–vacuum drying.
Dried SampleOverall Quality
(0–10)		Flavor
(0–10)
‘Nefris’8.9 (0.9)9.0 (1.0)
‘Debreceni Botermo’8.9 (1.2)7.6 (0.7)
‘Łutówka’8.8 (1.1)8.9 (0.6)
the parentheses—standard deviations.
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Ropelewska, E.; Konopacka, D.; Piecko, J. The Quality Assessment of Sour Cherries Dried Using an Innovative Simultaneous Osmotic–Microwave–Vacuum Approach Based on Image Textures, Color Parameters, and Sensory Attributes. Agriculture 2024, 14, 54. https://doi.org/10.3390/agriculture14010054

AMA Style

Ropelewska E, Konopacka D, Piecko J. The Quality Assessment of Sour Cherries Dried Using an Innovative Simultaneous Osmotic–Microwave–Vacuum Approach Based on Image Textures, Color Parameters, and Sensory Attributes. Agriculture. 2024; 14(1):54. https://doi.org/10.3390/agriculture14010054

Chicago/Turabian Style

Ropelewska, Ewa, Dorota Konopacka, and Jan Piecko. 2024. "The Quality Assessment of Sour Cherries Dried Using an Innovative Simultaneous Osmotic–Microwave–Vacuum Approach Based on Image Textures, Color Parameters, and Sensory Attributes" Agriculture 14, no. 1: 54. https://doi.org/10.3390/agriculture14010054

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