Combined effect of hot water dipping and Cistus creticus L. leaf extracts on the storage quality of fresh Valencia oranges

Valencia oranges originally bred in southern California but were named after the city of Valencia in Spain. They are medium-sized oranges with a bright orange colour and finely textured rinds. They are very juicy with a sweet-tart flavour. Valencia oranges of the current research were purchased on-tree from a local grower located in Northern Cyprus and hand-collected by the researchers at the commercial maturity. Harvesting was performed when the fruits reached above 12% soluble solids concentration (SSC) and <3.0 g · 100 g⁻¹ citric acid. Valencia oranges were quickly transferred to the laboratory and hand-selected to provide uniform size and colour and to eliminate damaged and diseased fruits. Leaves of C. creticus L. subsp. creticus were then collected from Yeşilırmak village of Northern Cyprus.

The fruits of the current research were first separated into 10 groups with 125 fruits in each group. These groups represent the 10 treatments of current studies. Then, the 125 fruits were separated into 25 sub-groups with 5 fruits in each group. After the application of the postharvest treatments, each group was separately stored in cold rooms at 6.0 ± 1.0°C and 90–95% RH (relative humidity); and five sub-groups (totally 25 fruits) from each group (treatment) were removed from the cold rooms with 30-days interval for the measurement of quality parameters. The treatments of current study were as follows: (1) control [dipping in water at 25°C for 5 min;]; (2) HWD at 50°C for 5 min; (3) HWD + Additives (A) [Arabic gum (0.2%), potassium sorbate (0.05%), citric acid (0.05%) and vitamin C (0.05%)] at 50°C for 5 min; (4) Additives alone at 25°C for 5 min; (5) 1.0% C. creticus leaf + HWD + A; (6) 1.0% C. creticus leaf + A; (7) 0.5% C. creticus leaf + HWD + A; (8) 0.5% C. creticus leaf + A; (9) 0.5% C. creticus leaf + HWD; and (10) 0.5% C. creticus leaf. Detailed explanations of the treatments are given in Table 1.

Eight different quality parameters were regularly measured with 30-days interval during the 150 days of storage. Both the initial and final weights of each fruit were measured with an electronic scale (±0.01 g), and the values were used to calculate the weight loss in percentage (%) by following the standard ratio analysis. Then, the method of Fonseca et al. (2002) was used to measure the respiration rate (RR) of each replication (five fruits together) as the produced CO₂ (ml CO₂ · kg⁻¹ · h⁻¹). The standard method of Cao et al. (2011) was used to calculate decay incidence (DI) as a percentage by following the 0–3 scale and standard formula. The 0–5 scale of Silva et al. (2015) was then used to observe and score the visual quality of each fruit (0: worst, 5: best). The visual quality parameters included the observations about both browning and microbial decay.

A hand penetrometer with a probe diameter of 5 mm was used to assess the firmness (kg · cm⁻²) of orange fruits. The fruits were then half-cut and squeezed to obtain clear juice for further measurements. A hand refractometer was used to assess the fruit's SSC as % and the standard titration method with NaOH was followed for the determination of titratable acidity (TA – g · 100 g⁻¹ citric acid). Finally, the titrating with 2,6-dichlorophenol indophenols was followed for the assessment of AsA contents as mg · 100 g⁻¹ (Youssef and Hussien, 2020).

Raw data of each treatment at each measurement point were summarised in Microsoft Excel, and line figures were prepared with the means and standard deviations of the data. Hereafter, the raw data were analysed in SPSS 22.0 software to compare treatments with oneway analysis of variance (ANOVA), and the statistical separation of means from each other was then performed with Tukey's HSD test (p < 0.05).

The findings of the present study showed that, as usual, weight loss of the Valencia oranges increases during cold storage (Table 2).

Furthermore, findings showed that the highest weight loss was observed from the control treatment; and all other test applications are effective in preventing weight loss (Figure 1). Among the test treatments, Additives (A) alone had the least effect and no significant difference was noted among the control and Additives. At the first measurement point (30 days after cold storage), the highest weight loss was observed from the control treatment with 5.38% and the lowest weight loss was found to be 2.99% from the HWD + CC (0.5%) treatment. The same trend was continued till the end of the storage period, but the difference between the HWD + CC (0.5%) treatment and the others decreased. Thus, at the 150th day of storage, no significant difference was found among the HWD and C. creticus leaf extracts treatments and any of their combinations. Although no significant difference was noted for those of the test treatments, the best treatment in terms of the prevention of the weight loss was found to be HWD + CC (0.5%) treatment.

Figure 1

The general efficacy of the tested treatments on the firmness of orange fruits was found to be in conjunction with the efficacy of weight loss. However, some of the treatments were found to have lower efficacy on firmness than weight loss prevention. These treatments are the HWD, HWD + A and Additive (Figure 2). The firmness of orange fruits decreased during the storage, and at the end of the 150 days of cold storage, the lowest fruit firmness was noted from these four treatments (control, HWD, HWD + A and Additive), which varied from 0.54 to 0.57 kg · cm⁻². Furthermore, no significant difference was noted among the other six treatments (HWD + CC (1%) + A, CC (1%) + A, HWD + CC (0.5%) + A, CC (0.5%) + A, HWD + CC (0.5%) and CC (0.5%)). The fruit firmness of these treatments was found to vary from 0.65 to 0.69 kg · cm⁻². Results showed that treatments with C. creticus leaf extracts have higher efficacy than the other treatments. Thus, current findings reveal that the efficacy of the treatments on fruit firmness is due to the C. creticus leaf extracts.

Figure 2

Visual quality is an important parameter for the marketability of fresh horticultural products and is known to decrease during storage. As expected, the visual quality of the Valencia oranges showed a decreasing trend during the 150 days of cold storage (Table 2). In the beginning of the experiments, the fruits were all selected to have the best quality for each group of treatments (Figure 3). Thus, the initial quality of all treatments was 5.00. The visual quality of the control fruits showed the highest reduction during the first 30 days of storage and the visual quality score was decreased to 3.20. At the same time, the visual quality score of the fruits treated with Additives and CC (1%) + A was noted as 4.40. Similar to the fruit firmness, results suggested that the HWD treatment alone is not so effective in the prevention of the loss in visual quality. Moreover, the combination of HWD with Additives and/or C. creticus leaf extracts was noted to have a high influence on the prevention of quality loss. A similar trend was found to continue till the end of the experiments, and at the end of the studies, the highest visual quality score was noted from the CC (0.5%) + A treatment with a score of 3.40. This was found to be above the acceptable marketability quality score of 3.00. The visual quality score of the control fruits was recorded as 2.00 and was followed by the HWD treatment with a score of 2.20.

Figure 3

Pathogenic decay is so important for the protection of postharvest storability of fresh horticultural products. Elimination of the decay improves the storability and the acceptability of the products by the consumers. The present study resulted in meaningful findings for the elimination of the DI. It was noted that all test applications, even the Additives alone, are effective in the prevention of the DI. The increasing trend of the DI can be followed from Table 2 and/or Figure 4. DI of control fruits increased from 13.33% at day 30 to 48.00% at day 150 (Figure 4). It is clear from the results that about half of the fruits were lost during the 150 days of storage if they were not treated with any of the treatments. The second highest fruit loss (caused by DI) was noted from the Additives treatment as 22.67% and followed by CC (0.5%) with a DI of 18.67%. The findings of the present study revealed that the HWD application is effective in the prevention of the DI and the lowest DI score of 9.33% was noted from the combination of HWD with CC (1.0%) and Additives. However, no significant difference was noted with the other treatments, showing significant differences only with the control fruit.

Figure 4

Fruit SSC is an important internal quality characteristic for the consumers, which together with TA determines the fruit flavour. Present findings showed that the SSC content of the fruits had an upward tendency during the first 90 days of storage and then had a decreasing trend. The initial SSC of Valencia oranges was recorded as 12.08% and increased to 12.85% in 90 days of storage. The final SSC content of the mean of all treatments was 12.53% on the 150th day of cold storage (Table 2). On the other hand, the treatments were noted to have no significant influence on the fruit SSC. At the end of the 150 days of cold storage, the highest SSC was measured from the HWD + CC (0.5%) + A treatment with 12.94% and the lowest SCC was recorded from the similar treatment (HWD + CC (1%) + A) as 12.32% (Figure 5). However, as described above, no significant difference was noted among the treatments.

Figure 5

The TA content of the Valencia oranges was found to have a decreasing trend during cold storage (Table 2 and Figure 6). The initial TA content was 2.75 g · 100 g⁻¹ and it decreased to 1.52 g · 100 g⁻¹ in 150 days of cold storage. The TA of oranges was observed to be significantly affected by the different treatments (Figure 6). This significant influence had begun to be observed after 90 days of cold storage. At that time, the highest TA content (2.24 g · 100 g⁻¹) was noted from HWD + CC (0.5%) application and the lowest TA content (1.84 g · 100 g⁻¹) was observed from the control fruits. A similar trend was then continued till the end of the storage period. At the end of the 150 days of storage, the highest TA content was found to be 1.79 g · 100 g⁻¹ from the fruits treated with HWD + CC (0.5%). Results suggest that both the HWD and C. creticus leaf extracts are effective in delaying the reduction of TA and their combination provides the best results. Moreover, the Additives alone treatment was found to have a slight effect on delaying the decrease in TA, but the highest efficacy was noted from the combination of HWD and C. creticus leaf extracts, without the Additives.

Figure 6

AsA is among the most important quality parameters of Valencia oranges. It is so important for consumers because of its confirmed health benefits and high antioxidant activity. The AsA values of Valencia oranges in the present study showed a similar trend with SSC during the cold storage period (Table 2). It was noted to have an increasing trend during the first 90 days of storage and then it decreased. However, the final AsA content of the Valencia oranges was recorded as higher than the initial value. On the other hand, findings of current work showed that all test applications, alone or in combination, have a significant influence on the AsA content. As seen from Figure 7, the lowest AsA content was measured from the control oranges and was followed by the oranges treated with Additives. This treatment was followed by HWD and HWD + A treatments. Results also suggested that there is no any significant difference among the other treatments. At the 150th day of cold storage, the highest AsA content was noted from the HWD + CC (1%) + A and HWD + CC (0.5%) + A treatments with the same value as 65.41 mg · 100 g⁻¹.

Figure 7

RR is an important parameter determining the storage duration and quality of fresh horticultural products. Cold storage, HWD and coatings, alone or in combination, are known to reduce the RR and improve the storability of products. The findings of current work showed that RR has a decreasing trend during the first 90 days of storage and then increased. This trend is different from that detected for SSC and AsA contents and is explaining the changes in SSC and TA. The RR was noted to be higher in the control groups, which clearly explains the quality loss in these untreated fruits (Figure 8). All of the test treatments were found to be efficient in reducing the RR as compared with the control treatment. The highest influence was noted from the HWD + CC (0.5%), followed by the applications of CC (0.5%) + A and HWD + CC (1%) + A. All of these results suggest that the HWD is effective in reducing RR, but its efficacy is increasing with the Additives and/or C. creticus leaf extracts.

Figure 8