3.2. Color (L, a, b, C, h°, ΔE)
Figure 3 and Fig. 4 give the results of fruit color values as L (lightness), a (redness), b (yellowness), C (chroma value), h° (hue angle) and ΔE (color difference) at the constant drying air velocity of 0.8 m.s− 1 for different drying air temperatures. Among the examined applications, it is stated that, while statistical differences are found insignificant in terms of L value, found significant in terms of a and b values. In addition, it can be said that increasing drying air temperature raised the a and b values statistically. Depending on the applications, L values ranged from 19.14 to 20.13, a value from 1.11 to 5.03, b value from − 1.30 to 2.98 (Fig. 3).
Statistical differences are found significant in terms of C value. The lowest color intensity (C) was in the fresh fruits with 1.85, while the highest value was measured at 80°C with 5.69. Therefore, it was found that, drying increased C value of the fruit. Statistically, the highest C value was found at 60, 70 and 80°C, respectively (Fig. 4).
It is seen that, h° value of the fruit in drying process was not affected by drying air temperatures. Nevertheless, the highest h° value was stated by 38.61; the lowest was stated at 80°C in the experiment. On the other hand, among the different drying air temperatures, there was no significant difference stated in terms of ΔE values. These values changed between 3.43 and 5.40 depending on different treatments (Fig. 4).
Consequently, all the applied treatments increased a, b, C values compared to fresh fruits. The highest a, b, C values were determined specifically at drying air temperature of 80°C.
Figure 5 and Fig. 6 give the results of fruit color values as L (lightness), a (redness), b (yellowness), C (chroma value), h° (hue angle) and ΔE (color difference) at constant drying air temperatures of 70°C and different drying air velocities. Statistical differences were found insignificant in terms of L value, changing between 19.45 and 20.16. All the tried different drying air velocity treatments increased a and b values compared to fresh fruits. As a matter of fact, the lowest a (1.11) and b (-1.03) values determined in fresh fruits. The highest a (5.12) and b (3.85) values were stated at drying air velocity of 1.2 m.s− 1 (Fig. 5).
Effects of the treatments on fruit color C values were found statistically significant (Fig. 6). All the applied drying air velocities increased C value compared to fresh fruits. Additionally, the highest C value was determined at 6.50 and 1.2 m.s− 1 drying air velocity. On the contrary, there was no significant difference in terms of h° value among the drying air velocity treatments. ΔE changed between 0.00 and 6.61 depending on the treatments. There was no significant difference in terms of ΔE values among the drying air velocity treatments (Fig. 6). There is one study about fruit color changes of processed chokeberry powders [12]. Sadowska et al. [12] stated the highest L (18.10), a (9.20) and b (4.57) values of chokeberry powders color via high energy air stream drying method in this study on which they compared freeze-drying, vacuum drying, convection drying. Besides L value is 15.05, a value is 4.75 and b value is 1.76 in convection drying (CD) method. Adak et al. [27] indicated that, increasing drying air temperature lowered the L, a, b and C values, but the h° increased small amount for infrared drying of strawberries. In the same research, it was also stated that regarding to the drying air velocity of 1.0 m.s− 1 was found as the best in terms of L, a, b, C, h° and ΔE values compared to the 1.5 and 2.0 m.s− 1 and increasing air velocity had led to decrease in lightness, color intensity but not the color which showed an increase. Samoticha et al. [25] indicated that, the drying process caused alteriations in the appearance and brightening of color and rised the contribution of yellow color in the fruits at higher levels.
As a consequence, all the applied drying air velocity treatments increased a, b and C values compared to fresh fruits. Particularly, 1.2 m.s− 1 drying air velocity stands out with high a, b and C values.
3.3. Antioxidant Activity, Total Anthocyanins, Total Phenolic Content
Effects of different drying air temperature under constant drying air velocity of 0.8 m.s− 1 on fruit biochemical features are shown in Table 1. As given in Table 1, significant statistical differences in terms of antioxidant activity, total anthocyanin (TAC) and total phenolic content (TPC) were determined.
Table 1
Effect of different air temperature, at air velocity 0.8 m·s− 1 on nutritional fruit quality characteristics of chokeberries.
Treatments | Antioxidant Activity A (mg TE /Kg) | Total anthocyanin content (TAC) B (mg Cyd-3-glu kg− 1) | Total phenolic content (TPC) C (mg GAE kg− 1) |
Fresh fruit | 1680.0 d | 66.04 c | 278.09 c |
50 oC | 2496.7 c | 52.15 c | 734.88 b |
60 oC | 2772.3 b | 106.79 ab | 873.15 a |
70 oC | 3105.6 a | 115.83 a | 918.52 a |
80 oC | 2906.9 ab | 81.60 bc | 877.47 a |
LSD%5 | 247.66 | 30.734 | 123.79 |
*Values in the same coloumn that are followed by different letters are significantly different (p < 0.05) using LSD comparison test. |
A The antioxidant activity was analyzed by DPPH assay according to the procedure of Fernández-León et al. (2013). Values were expressed as mg TE kg− 1. |
Antioxidant activity was analyzed using the DPPH assay described by Fernández-León et al. (2013). |
B Total monomeric anthocyanin content were calculated using a pH-differential method described by Wang and Xu (2007). Values were expressed as mg Cyd-3-glu kg− 1 by spectrophotometer. |
C The total phenolic content analyses were performed using the method described by Dincer et al. (2013). Values were expressed as mg gallic acid equivalents (GAE) kg− 1 by spectrophotometer. |
**The results based on as wet basis for fresh fruit and dry weight for dried fruits. |
In Table 1, all the applied drying air temperatures increased the antioxidant activity values in the dried fruits compared to fresh ones. Antioxidant activity in dried fruits varied from 48.61–84.80% depending on the drying process. In experiments, antioxidant activity was increased depending on the elevated heat level. In fact, the highest antioxidant activity was determined at drying air temperature of 70°C (3105.60 mg TE/kg FW), whereas antioxidant activity fell slightly at 80°C (2906.90 mg TE/kg FW). The total anthocyanin content showed differences among the different drying air temperatures. The highest total anthocyanin content was found at drying air temperature of 70°C (115.83 mg·Cyd-3-glu.kg− 1), however, this value decreased relatively at the other drying air temperatures. The lowest value for total anthocyanin content was observed at 50°C (52.15 mg·Cyd-3-glu.kg− 1). Total phenolic content (TPC) showed some significant differences depending on the drying air temperatures and the lowest TPC was seen in the fresh fruit. TPC increased statistically depending on the drying air temperature rises. The highest TPC was found at drying air temperature of 70°C (918.52 mg GAE kg− 1) (Table 1).
According to findings, drying air temperatures affected the biochemical content in a dramatic way. In fact, all the drying air temperatures increased antioxidant activity, total anthocyanin content and total phenolic content in dried fruits compared to the fresh ones. These findings were similar to Adak et al.’s [27] results. As a matter of fact Adak et al. [27] indicated that, infrared drying of strawberries increased antioxidant activity content of the fruits compared to fresh forms. In this study, specifically 70°C drying air temperature stands out in terms of this qualities.
Findings of this study were found different from Adak et al. [27] for strawberry drying in terms of total anthocyanin and phenolic contents. In fact, Adak et al. [27] stated that, heightened drying air temperatures caused a decline in total anthocyanin and phenolic contents, as well as antioxidant activity; therefore, drying at 60°C was found to be more beneficial than the others. Antioxidant activity, total anthocyanin and phenolic contents increased when the drying air temperature raised from 50 to 70°C according to current study. At 80°C, however, slight decrease was seen in these values.
Effect of different drying air velocities at constant drying air temperature of 70 oC on nutritional fruit quality characteristics of chokeberries were indicated in Table 2. As shown in Table 2, significant statistical differences were found in terms of all examined features among the treatments. In all drying air velocities, antioxidant activity was increased when compared to fresh fruits. In fact, the lowest antioxidant activity was found in fresh fruits (1680.0 mg TE.kg− 1) and the highest value was found at drying air velocity of 1.2 m.s− 1 (3140.00 mg TE.kg− 1). In other words, with the increased drying air velocity from 0.5 m.s− 1 to 1.2 m.s− 1, antioxidant activity in fruits increased (Table 2).
Table 2
Effect of different air velocity at air temperature 70 oC on nutritional fruit quality characteristics of chokeberries.
Treatments | Antioxidant Activity A (mg TE /Kg) | Total anthocyanin content (TAC) B (mg·Cyd-3-glu kg− 1) | Total phenolic content C (TPC) (mg·GAE kg− 1) |
Fresh fruit | 1680.00 b | 66.04 b | 278.09 b |
0.5 m·s− 1 | 2938.97 a | 117.67 a | 909.57 a |
0.8 m·s− 1 | 3105.64 a | 115.83 a | 918.52 a |
1.2 m·s− 1 | 3140.00 a | 105.31 a | 917.28 a |
LSD%5 | 241.200 | 26.132 | 118.910 |
*Values in the same coloumn that are followed by different letters are significantly different (p < 0.05) using LSD comparison test. |
A The antioxidant activity was analyzed by DPPH assay according to the procedure of Fernández-León et al. (2013). Values were expressed as mg TE kg− 1. |
Antioxidant activity was analyzed using the DPPH assay described by Fernández-León et al. (2013). |
B Total monomeric anthocyanin content were calculated using a pH-differential method described by Wang and Xu (2007). Values were expressed as mg Cyd-3-glu kg− 1 by spectrophotometer. |
C The total phenolic content analyses were performed using the method described by Dincer et al. (2013). Values were expressed as mg gallic acid equivalents (GAE) kg− 1 by spectrophotometer. |
**The results based on as wet basis for fresh fruit and dry weight for dried fruits. |
When the results examined in terms of total anthocyanin content, all the drying air velocities increased this value compared to fresh fruits. As a matter of fact, the lowest total anthocyanin content was stated in fresh fruits (66.04 mg Cyd-3-glu.kg− 1 FW). Total anthocyanin content decreased depending on the drying air velocity rise, however, that decrease statistically made no difference. These values varied between 105.31 mg Cyd-3-glu.kg− 1 FW and 117.67 mg Cyd-3-glu.kg− 1 FW depending on drying air velocities (Table 2).
The effects of all the applied drying processes on total phenolic content (TPC) of fruits were found statistically significant (Table 2). While the lowest TPC was stated in fresh fruit (278.09 mg GAE.kg− 1 FW), all the applied drying air velocities increased TPC compared to fresh forms. These values, also, varied between 909.57 mg GAE.kg− 1 DW and 918.52 mg GAE. kg− 1 DW (Table 2).
Current findings indicated that, at constant drying air temperature of 70°C with different drying air velocity treatments affected the biochemical content of fruits in a significant way compared to fresh ones. In fact, the lowest values of antioxidant activity, TAC and TPC were found in fresh fruits. Therefore, all the drying air velocity treatments from 0.5 m.s− 1 to 1.2 m.s− 1 can be suggested as their positive effects on biochemical fruit contents.
In this concern, some scholars have reported different results. The reason of these differences is the usage of different drying techniques and differently processed fruits.
In this regard, findings of this study was found partly similar to strawberry drying study Adak et al. [27]. Hence, these researchers stated that convective drying treatment increased biochemical content compared to the fresh fruits. Additionally, the researchers indicated that, increasing drying air velocity from 1 m.s− 1 to 2 m.s− 1 caused decrease in total anthocyanin and total phenol contents, but increase in the antioxidant activity. In this study, change of the drying air velocity did not affect the antioxidant activity, total anthocyanin and total phenol contents. Petkovic et al. [24] used 50, 60 and 70°C of convective drying temperatures for chokeberry powders and suggested 50°C in terms of bioactive components (anthocyanins, flavonoids, phenols) and total antioxidativity. They stated the results as the drying air temperature of 50°C had the highest ratio of total anthocyanins (376.89 ± 5.73 mg cyn-3-glu.[100 g dm]−1), total flavonoids (1037.19 ± 3.83 mg CE.[100 g dm]−1), phenols (1918.79 ± 3.26 mg GAE.[100 g dm]−1) and antioxidant activity (37.11 ± 0.28 mg TE.[100 g dm]−1). On the other hand, findings showed that, rising temperature increased the biochemical content. In fact, the highest values of antioxidant activity, total anthocyanin and total phenolic content are stated at 70°C drying air temperature.
Calin-Sanchez et al. [23] reported that, vacuum microwave and combined drying were found as the best two different drying techniques of black chokeberry fruit. This suggestion led to shorter drying time (40–70 min). Sadowska et al. [12] applied freeze, vacuum, convection and high energy air stream drying on chokeberry powders. According to their results, high energy air stream drying was the best method in terms of vitamin C (80.57 mg.[100 g dry matter]−1), polyphenol contents (2484.60 mg GAE.[100 g dry matter]−1), antioxidant activity (58.91 mmol Trolox.[100 g dry matter]−1), and anthocyanin (1035.51 mg.[100 g dry matter]−1 Cyanidin-3,5-digalactoside). In addition, Horszwald et al. [11] were stated that, there was a correlation between bioactive compounds and antioxidant capacity. In other studies, Samoticha et al. [25] indicated that, the highest content of bioactive compounds and antioxidant activity were found in freeze-dried samples, compared with fresh fruits. In addition, the rise in drying air temperature during convective drying as well as the increase in material temperature during microwave drying deteriorated the dried product quality in terms of the content of phenolic compounds, antioxidant activity and color.
As stated Ertekin et al. [37], the highest total phenolic content and total soluble solid content were attained at drying air temperature of 80°C for ‘Strawberry Camarosa’ and ‘Strawberry Festival’ in vacuum drying. The same investigators in another research, the highest total phenolic content was attained in infrared drying at 70°C for both strawberry cultivars [38].