2.1. Effects of HWD and eucalyptus leaf on the weight loss
According to the results obtained, hot water dipping (HWD) alone or in combination with the Eucalyptus leaf (EL) provided significant influence on the prevention of weight loss (Fig. 1). Control fruits of current work were found to have an average 5.49% weight loss in 20 days of storage, where the fruits treated with the combination of HWD and EL were found to have a weight loss from 4.04–4.58%. This result showed that the both treatments provide significant influence in reducing the weight loss of Cyprus local mandarins. Fruit at the control treatment found to have 12.05% weight loss at the end of the experiments (60 days of storage). At that time, no significant difference was found among the other treatments. However, the least weight loss was obtained from the HWD + EL 55°C 3 min. Therefore, this result suggests that the Eucalyptus leaf can improve the efficiency of the hot water dipping.
2.2. Effects of HWD and eucalyptus leaf on the fruit firmness
Not surprisingly, results of current work showed that the fruit firmness had a decreasing trend during the postharvest storage of the mandarin fruits. Here, no significant difference was obtained among the control groups and other experimental treatments in 40 days of storage (Fig. 2). The extending storage showed that the control group is more sensitive to loosing fruit firmness. According to the results obtained, the fruit firmness of the control group decreased from 0.56 kg cm− 2 to 0.39 kg cm− 2 in 60 days of storage. At that time, fruit firmness of all other treatments was also decreased but it was significantly higher than the control group. Those findings suggest that the HWD and EL treatments provide significant efficacy in preventing the changes in fruit firmness.
2.3. Effects of HWD and eucalyptus leaf on the fruit visual quality
Visual quality is a very important parameter for the determination of the postharvest storage quality of fruits. Results of present study are meaningful in terms of the protection of the visual quality. The duration of hot water dipping and the Eucalyptus leaf extracts were also found to have significant influence on the visual quality. At the end of the storage duration, the best fruit quality was obtained from the HWD + EL, 55°C 2 min and HWD, 55°C 3 min (Fig. 3). No significant difference was measured for these two treatments.
2.4. Effects of HWD and eucalyptus leaf on the decay incidence
According to the results obtained, the first decay was observed 20 days after storage from the control treatment and the HWD 3 min treatment (Fig. 4.). The decay caused by pathogens found to have a continuous increase during storage and it was found to be higher than the other treatments. The HWD treatment was found to have significant influence on the prevention of the decay caused by pathogens. However, the most important result of present study is that the incorporation of the Eucalyptus leaf extracts into HWD, provided better control of the pathogens. According to the best of the Authors’ knowledge, this is the first report of the incorporation of a leaf extract into HWD. At the end of the experimental studies, the HWD + EL / 55°C 2 min treatment was found to have the highest influence on the control of pathogens. At the 60th day of storage (the end), the decay incidence was observed as 53.33% at the control treatment while the decay incidence was only 3.33% on the HWD + EL / 55°C 2 min treatment.
2.5. Effects of HWD and eucalyptus leaf on the juice content
Results about the juice content of the mandarin fruits showed that juice reduction mainly occurred after 40 days of storage. During the first days of the storage, the juice percentage of the all fruits showed slight increase (Fig. 5.). This increase in the juice percentage is thought to be due to the high weight loss from the fruit bark. According to the results obtained, the weight loss is higher at the fruit bark. Hereafter, the juice percentages of the all treatments were found to have a decreasing trend, parallel to the high weight loss of the fruits. At the 40th day of storage, lowest juice percentage was noted from the control treatment and it was followed by the HWD 55°C 3 min. Similar trend was continued after 40th day till the end, and the highest juice percentage was noted from the HWD 55°C 2 min, HWD + EL 55°C 2 min and HWD + EL 55°C 3 min. All of these results are in conjunction with the results about weight loss and fruit decay. To sum up, it can be concluded that the Eucalyptus leaf extracts has high potential for the protection of fruit weight and juice content.
2.6. Effects of HWD and eucalyptus leaf on the soluble solids concentration and titratable acidity
SSC of the mandarin fruits was found to have a declining trend from 20th day to 40th day, and a slight increase then after. The main reason is the huge weight loss after 40th day of storage (Table 1.). When comparing the treatments’ impact on the SSC, it was noted that the fruits treated with 3 min showed higher SSC loss as compared with the others. An important finding of current work was found to be about the titratable acidity (TA) contents of the mandarin fruits. The initial TA was measured as 6.6 g 100 g− 1, and it was decreased to a range of 2.2–2.7 g 100 g− 1 in 20 days of storage. This was about 200% decrease as compared with the initial contents. The final TA content of the fruits was found in a range of 1.2–1.4 g 100 g− 1 at the 60th day of storage. At that time, the higher TA content was observed from the HWD 3 min treatment. Findings of current work showed that the HWD treatment and eucalyptus leaf extract have significant influence on the TA contents of the fruits, but this was not so important as compared with the initial values. The SSC/TA ratio is an important indicator of the fruit flavour which significantly influences fruits’ acceptability and marketability. The increase in this ratio improves the fruits attractiveness for the consumers, but it is also a result in the postharvest changes. According to the results obtained, the SSC/TA ratio showed an increasing trend from the 20th day till the end. Within this increasing trend, the least increase (could be accepted as the most successful treatment) was noted from the HWD 3 min. This treatment was followed by the HWD + EL 2 min.
Table 1
Change in the mandarins’ SSC and TA contents in response to different treatments
Treatments
|
SSC
|
TA
|
SSC/TA
|
0 d
|
20 d
|
40 d
|
60 d
|
0 d
|
20 d
|
40 d
|
60 d
|
0 d
|
20 d
|
40 d
|
60 d
|
Control
|
11.6a
|
11.4a
|
11.6a
|
11.8a
|
6.6a
|
2.5bc
|
1.7b
|
1.3b
|
1.76a
|
4.58ab
|
6.71c
|
9.07a
|
HWD 55°C, 2 min
|
11.6a
|
11.0a
|
11.0ab
|
10.8b
|
6.6a
|
2.4c
|
1.3d
|
1.2c
|
1.76a
|
4.64ab
|
8.31a
|
8.80a
|
HWD 55°C, 3 min
|
11.6a
|
11.1a
|
10.4bc
|
11.2ab
|
6.6a
|
2.7a
|
1.9a
|
1.4a
|
1.76a
|
4.20b
|
5.61d
|
7.88b
|
HWD + EL 55°C, 2 min
|
11.6a
|
10.8a
|
10.5ab
|
11.1ab
|
6.6a
|
2.2d
|
1.5c
|
1.3b
|
1.76a
|
4.98a
|
7.17bc
|
8.34ab
|
HWD + EL 55°C, 3 min
|
11.6a
|
11.1a
|
10.0c
|
11.8a
|
6.6a
|
2.6ab
|
1.4d
|
1.3b
|
1.76a
|
4.35b
|
7.35b
|
8.90a
|
Means at the same measurement point with same letter or letters represents no significant difference according to the Duncan’s multiple range test (p < 0.05).
2.7. Effects of HWD and eucalyptus leaf on the ascorbic acid content
Similar to the results of SSC, the ascorbic acid (AsA) content of the fruits was also found to decrease in time. During the first 20 days of the storage, the AsA contents of the fruits treated with HWD or HWD + EL combination were all found to have an increasing trend, except the control treatment (Fig. 6.). The AsA content of the control fruits were all found to have continuous decreasing trend. Similar with the control treatment, other fruits were also found to have a decreasing AsA content during storage, after 20 days of storage. At the end of the experimental studies, the highest AsA content was noted from the HWD + EL treatments and no significant difference was obtained between the 2 min and 3 min treatments. The following highest AsA contents were noted from the HWD 2 min and HWD 3 min treatments. All were found to be significantly higher than the AsA content of the control treatment.