Evaluating of fruit quality formation by their qualitative parameters in the adaptation process of Asimina triloba at the agroecological conditions of the experimental base in Nitra.

The observations of the collection genotypes of Asimina triloba in the period 2017 were performed during mass fruiting. We have described 6 genotypes (referred as AzT-01 to AzT-06) of Asimina triloba.

Molybdenum reducing antioxidant power of samples was determined by the method of Prieto et al. (1999) with slight modifications. The mixture of the sample (1 mL), monopotassium phosphate (2.8 mL, 0.1 M), sulfuric acid (6 mL, 1 M), ammonium heptamolybdate (0.4 mL, 0.1 M) and distilled water (0.8 mL) was incubated at 90°C for 120 min, then rapidly cooled. The absorbance at 700 nm was detected with the spectrophotometer Jenway (6405 UV/Vis, England). Trolox (10 – 1000 mg.L^-1; R² = 0.998) was used as the standard and the results were expressed in mg.g^-1 Trolox equivalents.

The total polyphenol content was measured by the method of Singleton and Rossi (1965) using the Folin-Ciocalteu reagent. A quantity of 0.1 mL of each sample was mixed with 0.1 mL of the Folin-Ciocalteu reagent, 1 mL of 20% (w/v) sodium carbonate and 8.8 mL of distilled water. After 30 min in darkness, the absorbance at 700 nm was measured with the spectrophotometer Jenway (6405 UV/Vis, England). Gallic acid (25 – 300 mg.L^-1; R² = 0.998) was used as the standard. The results were expressed in mg.g^-1 gallic acid equivalents.

The total flavonoid content was determined by the modified method described by Shafii et al. (2017). An aliquot of 0.5 mL of the sample was mixed with 0.1 mL of 10% (w/v) ethanolic solution of aluminum chloride, 0.1 mL of 1 M potassium acetate and 4.3 mL of distilled water. After 30 min in darkness, the absorbance at 415 nm was measured using the spectrophotometer Jenway (6405 UV/Vis, England). Quercetin (1 – 400 mg.L^-1; R² = 0.9977) was used as the standard. The results were expressed in mg.g^-1 quercetin equivalents.

Total phenolic acids content was determined using the method of Farmakopea Polska (1999). A 0.5 mL of sample extract was mixed with 0.5 mL of 0.5 M hydrochloric acid, 0.5 mL Arnova reagent (10% NaNO₂ + 10% Na₂MoO₄), 0.5 mL of 1 M sodium hydroxide (w/v) and 0.5 mL of water. Absorbance at 490 nm was measured using the spectrophotometer Jenway (6405 UV/Vis, England). Caffeic acid (1 – 200 mg.L^-1, R² = 0.999) was used as a standard and the results were expressed in mg.g^-1 caffeic acid equivalents.

Basic statistical analyses were performed using PAST 2.17. Data were analysed with ANOVA test and differences between means compared through the Tukey-Kramer test (α = 0.05). Variability of all these parameters was evaluated using descriptive statistics. Level of variability determined by Stehlíková (1998).

In our study, the weight of Asimina triloba fruits (Figure 1) was in the range from 92.17 (AzT-02) to 149.31 g (AzT-03) (Table 1). Crabtree (2004) determined the fruit weight from 88.10 to 141.80 g, Donno et al. (2014) determined the fruit weight from 39.40 to 238.70 g. Investigations of Klymenko et al. (2017) established the range of fruits weight of variety from 39.40 to 238.70 g. In our experiments, the fruit length and diameter were determined in the range from 78.16 (AzT-06) to 108.83 mm (AzT-04) and from 44.80 (AzT-02) to 55.06 mm (AzT-03), respectively. The length and diameter of fruits was determined in the range from 61.98 - 91.16 mm and from 41.27 – 49.65 mm, respectively, by Donno et al. (2014), from 14.0 to 46.0 mm and from 7.0 to 20.0 mm by Szilagyi et al. (2016), from 49.25 to 135.00 mm and from 37.55 to 63.80 mm, respectively, by Klymenko et al. (2017). A number of fruits per cluster were identified in the range from 2 (AzT-03) to 8 (AzT-06).

Crabtree (2004) determined the average number of fruits from 1.8 to 3.0, Klymenko et al. (2017) determined the number of fruits per cluster from 2 to 7.

Morphological parameters of ranged seeds weight from 0.81 (AzT-01) to 1.35 g (AzT-03), seed length from 20.43 (AzT-05) to 26.03 mm (AzT-03), seed width from 10.88 (AzT-06) to 14.86 mm (AzT-03), seed thickness from 6.26 (AzT-06) to 7.71 mm (AzT-05).

Investigations of Klymenko et al. (2017) established the range of seeds weight, length, width and thickness of genotypes from 0.60 to 1.80 g, from 17.10 to 28.80 mm, from 10.86 to 16.46 mm, from 5.54 to 9.15 mm, respectively. Szilagyi et al. (2016) determined the weight, length, and width of the seeds in the range from 1.30 to 1.65 g, from 2.51 to 2.69 mm, from 1.30 to 1.36 mm, respectively. A number of seeds in fruit were identified in the range from 4 (Az-05) to 16 (Az-04). The number of seeds in the fruit was determined in the range from 5 to 12 by Klymenko et al. (2017).

The analysis of coefficient of variation showed the difference of variability of morphological signs between Asimina triloba samples. Data showed that the most variable important selection signs are the seeds weight from 7.40 to 35.71%, fruit weight from 14.84 to 32.95%, a number of fruits per cluster from 18.21 to 32.54% and a number of seeds in fruit 13.49 to 27.72%.

These results indicate the promise of breeding in this way of investigations. The stable signs are seed width from 7.06 to 9.81%.

The antioxidant activity of Asimina triloba genotypes evaluated by the DPPH method (Figure 2) ranged from 2.84 (AzT-01) to 7.04 mg TEAC.g^-1 (AzT-04). The degree of mean variability of parameters was confirmed by the variation coefficient (31.77%) in all the genotypes tested.

The antioxidant activity evaluated by the molybdenum reducing antioxidant power (Figure 3) varied from 97.25 (AzT-06) to 275.41 mg TEAC.g^-1 (AzT-03). The degree of mean variability of parameters was confirmed by the variation coefficient (35.07%) in tested genotypes.

Nam et al. (2017) from methanolic extracts fruits obtained with DPPH method found the antioxidant activity to be 4.18 mg.mL^-1. Donno et al. (2014) found the total antioxidant activity from 889.6 to 1519.6 mg.kg^-1. Kobayashi et al. (2008) in ripe fruits from 15.57 to 17.04 mmol TE.g^-1 FW. Antioxidant activity of Asimina triloba fruits could be influenced by the degree of maturity and cultivars (Kobayashi et al., 2008; Donno et al., 2014). Since there are differences in genotypes of Asimina triloba cultivars grown under different geographic and agroecological conditions, our results are difficult to compare with the previously reported.

The total polyphenol content (Figure 4) in Asimina triloba genotypes ranged from 22.13 (AzT-05) to 37.36 mg GAE.g^-1 (AzT-02). The variation coefficient (16.87%) confirms the high variability of the parameter.

In our mind, the differences between the present and previously conducted studies may be attributable to the plant geographical origin as well as the different methods of extraction.

The total flavonoid content (Figure 5) varied from 15.10 (AzT-05) to 32.02 mg.g^-1 QE (AzT-02). The variation coefficient (25.39%) supported the observations on high variability of this parameter.

The total phenolic acid content was found to vary significantly among the various Asimina triloba genotypes (Figure 6), which may be due to their different botanical and regional origins. The mean total phenolic acid of the studied fruits genotypes was 25.16 mg.g^-1 CAE, with the highest phenolic acid recorded by genotypes AzT-02 at 32.02 mg.g^-1 CAE, indicating its superior antioxidant potential. The variation coefficient (25.39%) supported the observations on high variability of this parameter. Kobayashi et al. (2008) found in ripe fruits the total phenolic content from 64.11 to 98.42 mg.g^-1 GAE.

Correlation analysis was used to explore the relationships between the individual polyphenols, phenolics, flavonoids compounds and antioxidant capacities (DPPH and MRP methods) measured for all fruit extracts from six Asimina triloba genotypes (Table 2). It was observed a strong linear correlation between the polyphenol and flavonoid contents (r = 0.976).