Quality Characteristics of ‘Dongchul’ Persimmon (Diospyros kaki Thunb.) Fruit Grown in Gangwondo, Korea

Abstract

Persimmon has long been established as one of the major fruits in Korea. The southern parts of Korea were traditionally the pocket areas for good persimmon production; however, rising temperatures have gradually rendered the southern regions unsuitable for successful harvest. Ecology of fruit growing areas affects the productivity of various types of crops, including fruit trees such as persimmon. The quality characteristics of the fruit of persimmon cv. Dongchul grown in Gangwondo, which lies in the northern part of South Korea, were investigated. Different physicochemical, nutritional, and antioxidant properties of fruit were evaluated to assess the locational effect on the quality of persimmon fruits grown in Gangwondo. The results of this study showed that persimmon cv. Dongchul grown in Gangwondo maintains many of the physicochemical (4.33% crude protein and 4.32% crude fiber), nutritional (total mineral content: 461.51 and vitamin C content: 15.28 ㎎/100 g), and antioxidant properties (polyphenol content: 633.1 ㎎ gallic acid equivalent/100 g) those are found in other three commercial cultivars ‘Daebong’, ‘Kyengsan Bansi’, and ‘Sangju Doongsi’ grown in Korea. Overall results of this study imply that ‘Dongchul’ cultivar of persimmon could commercially be grown in Kangwondo, Korea.

Introduction

Persimmon (Diospyros kaki Thunb) is one of the most important fruits and has been cultivated from ancient times in Korea (Seo et al., 2013). Consumption of persimmon fruit is considered beneficial to various physiological functions, including protection against oxidative stress-related diseases; it has antimutagenic and anticarcinogenic properties as it is a valuable source of various biologically active compounds (Suzuki et al., 2005). It is rich in antioxidants such as catechins, which are known to have anti-infective, anti-inflammatory, and antihemorrhagic properties, and gallocatechins (Kim et al., 2006). Persimmon fruits are an abundant source of minerals, amino acids, flavonoids, sugars, carotenoids, tannins, terpenoids, vitamins A and C, and others. The anticarcinogenic properties of persimmon are attributed to the high contents of β-carotene and vitamin A in the fruits (Funayama and Hikino, 1979).

Persimmon has long been established as one of the major fruits in Korea (Kang and Ko, 1997). The area under fruit cultivation has almost doubled in the past 20 years and persimmon has become the most widely grown fruit crop in Korea (Song et al., 2005). The southern parts of Korea were traditionally the pocket areas for good persimmon production; however, rising temperatures have gradually rendered the southern regions unsuitable for production of fruits such as pears, peaches, grapes, and sweet persimmons, the cultivation of which has continuously shifted northwards (Kim et al., 2010). Change in climatic conditions of fruit growing area affects not only the growth of fruit trees but also fruit quality, harvest time, and fruit storage. Climate change in Korea has been proceeding at a rate that is faster than the global average rate (Kim et al., 2010).

Kim et al. (1988) established marginal regions for safety cultivation of non-astringent persimmons and, at that time, found that southern parts of Korea, including Cheonnam, Kyeongnam, and Kyeongbuk, were the most suitable areas for non-astringent persimmon production. Since then, the climate conditions have changed, and today persimmon is grown successfully in the northern parts. ‘Dongchul’ is one of the widely grown persimmon cultivars in commercial plantations in Korea. Currently, little is known about the quality characteristics of persimmon cv. ‘Dongchul’ cultivated in Gangwondo, which lies in the northern part of South Korea. Therefore, the objective of this study was to investigate the quality characteristics of the persimmon fruit cv. Dongchul, grown in Gangwondo. Production potential of ‘Daebong’, one of the commercial cultivars of persimmon in Kangwondo, was taken as reference for evaluating that of ‘Dongchul’. Both the cultivars are of astringent type.

 

Materials and Methods

Plant material and cultivation area

In the present study, persimmon (Diospyris kaki Thunb.) cv. Dongchul, grown at Yangyang-gun, Gangwondo, South Korea, was studied for investigating the quality characteristics. Yangyang-gun (38°4′0″N, 128°37′0″E; average sea level 100 m) lies in northern part of South Korea. The average weight of ‘Dongchul’ persimmon fruits in Kanwondo was 185.19 g and the yield was 148-185 ㎏ per tree which is quite acceptable for commercial production. The physiochemical properties of the fruit of ‘Dongchul’ were compared with three other commercial cultivars, ‘Daebong’, ‘Kyengsan Bansi’, and ‘Sangju Doongsi’ grown at Yangyang-gun, Gangwon-do in Korea. The fruits were harvested at commercial maturity stage in November of 2013, and were transported to the laboratory within 6 h of harvest. The fruits were washed with tap water to remove all the foreign matters of the surface, and were allowed to surface dry at room temperature. On the same day of harvest the fruits were peeled off using knife and kept for freeze drying without pre-treatment with any chemicals. The freeze dried fruit samples were considered for further analysis.

Chemicals and reagents

Folin-Ciocalteu reagent, gallic acid, 1,1-diphenyl-2-pricryl-hydrazyl (DPPH), and pyrogallol were purchased from Sigma Chemical Co. (St. Louis, MO, USA). All the reagents used in the study were of analytical grade.

Proximate composition analysis

Proximate compositions were determined following standard methods of AOAC (1995): moisture content (AOAC method 950.46), crude protein (AOAC method 928.08), lipid (AOAC method 991.36), fiber (AOAC method 985.29), ash (AOAC method 920.153), and carbohydrate contents (AOAC method 995.13) in persimmon fruit samples.

Quantification of vitamins C and E

Vitamin C content was determined according to standard methods of AOAC (1990 method 984.26).

Vitamin E was analyzed following the modified method of Aaran and Nikkari (1988). Fruit samples (2 g) were minced and mixed with 3 ㎖ of absolute ethanol, 3.1 ㎖ of 10% pyrogallol solution (w/v, in ethanol), and 0.1 ㎖ of 90% KOH (w/v). For saponification, the mixture was incubated at 65℃ for 30 min. After cooling, the sample was mixed with 4 ㎖ of distilled water and 3 ㎖ of hexane. After centrifugation (1400 × g, 3 min), the hexane layer was repeatedly washed with distilled water until the color of the water was not changed by phenolphthalein reagent. The remaining water in the hexane solution was removed using Anhydrous Na2SO4. The hexane solution was evaporated at 75℃ and absolute ethanol (2.5 ㎖) was used to dissolve vitamin E. The sample solution (0.5 ㎖) was mixed with 0.1 ㎖ of 2% FeCl3 solution (w/v, in ethanol) and 0.1 ㎖ of 0.5% 2,2-dipyridyl solution (w/v, in ethanol), and 1.8 ㎖ of absolute ethanol. The absorbance of the final solution was measured at 520 ㎚. ɑ-Tocopherol (20 ㎎/㎖) in 100 ㎖ of absolute ethanol was used for the standard.

Quantification of organic acids

Organic acid concentrations were measured using HPLC (Ashoor and Knox, 1982). One milliliter of ultrapure water (Milli-Q water purification system, Millipore Australia Pty Ltd., New South Wales, Australia) for every milligram of organic acid was used to prepare standards of pure organic acids (malic, citric, fumaric, succinic, and oxalic acids) as well as standard mixtures (of all acids) for calibration curves at various final concentrations. Samples were prepared by extracting freeze-dried samples (5 g) in distilled water (25 ㎖). The samples were flushed with nitrogen and centrifuged at 1660 × g for 15 min. One milliliter of sample was added to 9 ㎖ of distilled water and left overnight at room temperature. The samples were filtered through a 0.22 ㎛ syringe filter (Millipore, Billerica, MA, USA). Conditions for the HPLC were as follows: detector, M996 (Waters, Milford, MA, US); refractive index detector (RI, model 410; Waters); mobile phase, 0.005 M H2SO4 in water; column, PL Hi-Plex H (Agilent Technologies Inc., Santa Clara, CA, USA), 300 × 7.7 ㎜; column temperature, 65 ℃; flow rate, 0.6 ㎖/min; injection volume, 10 ㎕.

Quantification of free sugars

Free sugar content was analyzed following the method of Genard and Souty (1996). Each sample (5 g) was added to 10 ㎖ of distilled water and homogenized using a homogenizer (Ultra-Turrax T-25, IKA-Labortechnik, Staufen, Germany). The volume of the sample was adjusted to 20 ㎖ by adding distilled water and then centrifuged at 16000 × g for 30 min. The collected supernatant was filtered through a cartridge (Sep-Pak C18, WAT023501, Waters) and a 0.45 ㎛ syringe filter (PVDF, Whatman, Tokyo, Japan). Free sugars were quantified by HPLC (Model 9300, Younglin Co., Anyang, Korea) consisting of a refractive index detector (Triathlon M730D, Younglin Co.), a column heater set at 85℃, and Sugar-Pak (6.5 × 300 ㎜, Alltech, Staten Island, NY, USA); the mobile phase was deionized-distilled H2O delivered at 0.5 ㎖/min. The glucose, fructose, sucrose, and sorbitol obtained from Aldrich Chemical Co. Inc. (Milwaukee, WI, USA), were used as reference sugars for identification; mannitol was used as an internal standard. Free sugar content was expressed as ㎎/100 g sample.

Determination of mineral composition

A fraction of the sample (0.5 g) was placed in a cup and treated with 15 ㎖ of nitric acid. The solution was diluted with distilled water (2 ㎖). Mineral concentrations were determined using an inductively coupled plasma atomic emission spectrometer (ICP AES, Varian Vista Inc., Victoria, Australia) (Skujins, 1998).

Determination of amino acid profile

The amino acids profile was analyzed following the procedure of Je et al. (2005) with some modifications. One gram of freeze-dried sample was hydrolyzed with 6N HCl (10 ㎖) in a sealed-vacuum ampoule at 110℃ for 24 h. The HCl was removed from the hydrolyzed sample on a rotary evaporator and the volume was adjusted to 5 ㎖ with 0.2 M sodium citrate buffer (pH 2.2). The sample was passed through a cartridge (C-18 Sep-Pak, Waters) and filtered through a 0.22 ㎛ membrane filter (Millipore, Billerica). Amino acids were determined in an automatic amino acid analyzer (Biochrom-20, Pharmacia Biotech, Uppsala, Sweden).

Color value measurement

Values for L* (lightness: 100 score for white and 0 for black), a* (redness, + or greenness, -), and b* (yellowness, + or blueness, -) in dried samples were measured using a Chromameter (CR-300, Minolta Corp., Osaka, Japan). A Minolta calibration plate (YCIE = 94.5, XCIE = 0.3160, YCIE = 0.330) and a Hunter Lab standard plate (L* = 82.13, a* = -5.24, b* = -0.55) were used to standardize the instrument with D65 illuminant (Kim et al., 2013). Color was measured randomly on 3 areas of samples and the average was calculated.

DPPH radical scavenging activity

Scavenging activity of the sample extract was measured with DPPH radicals according to the method of Blois (1958) with some modifications. A DPPH solution was prepared in ethanol at a concentration of 4 × 104 M. A 0.1 ㎖ aliquot of extract was mixed with 2.9 ㎖ of DPPH solution and the mixture was incubated in the dark at room temperature for 30 min. After incubation, absorbance was recorded at 516 ㎚ using a spectrophotometer (Opron 3000, Hanson Technologies Co. Ltd., Seoul, Korea). The inhibitory percentage of DPPH radical in samples was calculated according to Shyu and Hwang (2002) as follows:

Scavenging effect (% inhibition) = [(A0 - (A - Ab))/A0] × 100

where, A0 is the absorbance of DPPH without sample (control), A is the absorbance of the sample and DPPH, and Ab is the absorbance of the sample without DPPH (blank).

Determination of total phenolics

Total phenolics (TP) were determined using the Folin-Ciocalteu method (Zheng and Wang, 2001). The absorbance was measured at 725 ㎚ using a spectrophotometer (HP 8452A diode-array, Hewlett-Packard Co., Palo Alto, CA, USA). Gallic acid was used to prepare a calibration curve. The total phenol contents were expressed as gallic acid equivalents (㎎ GAE/100 g of sample), and values are reported as mean values of triplicate analyses.

Tannin content

Tannin content was examined with a modified Prussian Blue assay method (Graham, 1992; Price et al., 1988). A 0.1 ㎖ of sample extract was added to 3 ㎖ of distilled water, centrifuged at 10000 × g for 15 min, and the supernatant was collected. Phenolics were determined in the supernatant by adding 1 ㎖ of 0.016 M K3Fe (CN)6 followed immediately by addition of 1 ㎖ of 0.02 M FeCl3 and vortexing (KMC-1300V, Vision Scientific Co. Ltd., Bucheon, Korea) the mixtures. After 15 min, absorbance was measured at 700 ㎚ using a spectrophotometer (HP 8452A diode-array, Hewlett-Packard Co.). The phenolics content was expressed as tannins content (Park, 1999).

Statistical analysis

Data were subjected to analysis of variance (ANOVA) using Molecular Evolutionary Genetics Analysis (MEGA) software 4.0 (Analytical Software, Tucson, AZ, USA). Differences between means at p≤0.05 were analyzed using the Tukey test. Average values of duplicate measurements of two samples were considered for statistical analysis unless otherwise mentioned. Each sample was composed of 10 fruits of each cultivar.

 

Results

Proximate composition

The proximate composition of ‘Dongchul’ persimmon was comparable with that of other three cultivars, ‘Daebong’, ‘Kyengsan Bansi’, and ‘Sangju Doongsi’ (Table 1). The moisture and carbohydrate contents in ‘Dongchul’ persimmon were not significantly different from those of other three cultivars. The crude lipid (1.8%) of ‘Dongchul’ was significantly higher than those of other cultivars; however, crude fiber (4.32%) and ash (12.09%) contents were significantly lower in ‘Dongchul’ persimmon. Crude protein content in ‘Daebong’ (3.99%) was significantly low as compared to other three cultivars.

Table 1.zQuoted values are the means ± SD of duplicate experiments. Different letters in the same row followed by average values are significantly different at p ≤ 0.05.

Vitamin and tannin content

The persimmon fruit of ‘Dongchul’ contained significantly high amount of vitamin E (2.79 ㎎/100 g) as compare to ‘Kyengsan Bansi’ (1.79 ㎎/100 g), ‘Sangju Doongsi’ (1.55 ㎎/100 g), and ‘Daebong’ (0.12 ㎎/100 g). However, vitamin C content was not significantly different among ‘Dongchul’ (15.28 ㎎/100 g) and ‘Daebong’ (13.99 ㎎/100 g), ‘Kyengsan Bansi’ (14.12 ㎎/100 g), and ‘Sangju Doongsi’ (13.58 ㎎/100 g). The tannin comprised 0.824%, 0.906%, 1.107%, and 1.201% of fruit in ‘Sangju Doongsi’, ‘Dongchul’, ‘Kyengsan Bansi’, and ‘Daebong’ on a dry weight basis, respectively.

Mineral content

Potassium was the most abundant element found in all four cultivars ‘Dongchul’, ‘Sangju Doongsi’, ‘Kyengsan Bansi’, and ‘Daebong’ (413.23, 407.72, 401.32, and 400.21 ㎎/100 g, respectively), whereas the amount of Cu was the lowest (0.09, 0.08, 0.08, and 0.08 ㎎/100 g, respectively). Total mineral content of ‘Dongchul’ (461.51 ㎎) was higher than those of other three commercial cultivars (Table 2). Elements As, Pb, Cd, and Hg were not detected in dried fruit sample of either cultivar.

Table 2.zND: Not detected.yQuoted values are the means of duplicate experiments.

Free amino acids content

The amounts of amino acids play a vital role in determining the nutritional qualities of fruits, vegetables, and food products (Basarova and Janousek, 2000). Twenty-two free amino acids were evaluated in four persimmon cultivars (Table 3). Among these 22 free amino acids, citrulline content was the highest (172.95, 161.12, 170.21, and 171.33 ㎎) followed by homocysteine (41.81, 40.18, 39.12, and 40.11 ㎎), phosphoserine (35.06, 34.12, 34.11, and 35.00 ㎎), glutamic acid (32.58, 30.12, 31.00, and 31.98 ㎎), serine (15.77, 17.22, 16.66, and 16.99 ㎎), aspartic acid (14.08, 13.01, 13.69, and 14.00 ㎎), carnosine (13.24, 12.98, 12.99, and 13.20 ㎎), and valine (12.24, 12.00, 12.01, and 12.21 ㎎/100 g) in ‘Dongchul’, ‘Daebong’, ‘Kyengsan Bansi’, ‘Sangju Doongsi’, respectively). Seventeen amino acids (1-Methylhistidine, 3-Methylhistidine, Alanine, Ammonium chloride, Anserine, Asparagine, Cystathionine, Cystine, Histidine, Hydroxyproline, Lysine, Methionine, Phenylalanine, Taurine, Urea, α-Aminoadipic acid, α-Aminobutyric acid, and β-Aminoisobutyric acid) were not detected in either cultivar. Total free amino acid content was higher in ‘Dongchul’ (410.39 ㎎/100 g) than in other three cultivars (Table 3).

Table 3.zQuoted values are the means of duplicate experiments.

Organic acid and free sugar content

The predominant organic acid was malic acid which was significantly high in ‘Daebong’ (813.0 ㎎/100 g) and ‘Kyengsan Bansi’ (800.2 ㎎/100 g) than in ‘Dongchul’, (704.0 ㎎/100 g) and ‘Sangju Doongsi’ (703.1 ㎎/100 g). However, the other three organic acids citric, fumaric, and succinic were not significantly different among four cultivars (Table 4).

Table 4.zQuoted values are the means ± SD of duplicate experiments. Different letters in the same row followed by average values are significantly different at p ≤ 0.05.

Amount of three free sugars fructose, glucose, and sucrose were higher in ‘Daebong’ (6.12, 11.92, and 0.18 g/100 g) than in ‘Dongchul’ (5.14, 10.67, and 0.12 g/ 100 g), ‘Kyengsan Bansi’ (6.00, 10.69, and 0.15 ㎎/100 g), and ‘Sangju Doongsi’ (6.08, 10.12, and 0.17 ㎎/100 g); however significant difference was found only for sucrose.

Color value and antioxidant properties

The color (lightness, redness, and yellowness) value of the fruit was measured using a Hunter Lab Miniscan colorimeter (Hunter Associates Laboratory, Inc., Reston, VA, USA). There was no significant difference in color values of ‘Dongchul’ and other three cultivars.

DPPH radical scavenging properties and total polyphenol content reflect antioxidant properties. DPPH radical scavenging capacity of ‘Dongchul’, ‘Daebong’, ‘Kyengsan Bansi’, and ‘Sangju Doongsi’ fruit were 75.97, 70.12, 71.77, and 72.00%, respectively. The total polyphenol content of ‘Dongchul’ (633.1 ㎎) was higher than that of other three cultivars (‘Daebong’, ‘Kyengsan Bansi’, and ‘Sangju Doongsi’ (531.1, 582.1, and 596.8 ㎎ GAE/100 g, respectively).

 

Discussion

The values for protein and ash contents in ‘Dongchul’ persimmon are higher than those previously reported by Celik and Ercisli (2008). The difference in composition of persimmon fruit must be due to the cultivar variation (Moghaddama et al., 2013; Mratinic et al., 2011; Jin and Song, 2012). Vitamin C content in the cultivar Hachiya grown in Turkey was 12 ㎎ 100/g of fruit (Celik and Ercisli, 2008). The amount of vitamin C found in the present study is in agreement with the study of Mowat and George (1994), whereas the tannin content is significantly higher in ‘Dongchul’ than in ‘Sangju Doongsi’ but lower than those of ‘Daebong’ and ‘Kyengsan Bansi’. The difference in tannin content may be due to differences in cultivar since pomological properties of fruit are strongly affected by the genotypes (Moghaddama et al., 2013; Mratinic et al., 2011). The vitamin C and tannins in the fruit are major factors determining persimmon fruit nutritional value and quality. Celik and Ercisli (2008) also found higher concentration of potassium in the persimmon fruit compared with other elements. In a study of Lee et al. (2012), the amounts of aspartic and glutamic acids were the highest among seventeen detected amino acids. The contents of these two amino acids were not much different to those found in the present study, and slight variation in their content might be due to the genotype. Lee et al. (2012) and Verberic et al. (2010) reported similar values, except for succinic acid, which they did not detect in the fruit juice of 11 persimmon cultivars. Earlier studies have shown that organic acids and sugars are associated with the aroma and sensation of sweetness in various fruits (Colaric et al., 2005) and are responsible for retaining the quality and nutritional value in food products (Ashoor and Knox, 1982). Specifically, organic acids have a protective role against various diseases because of their antioxidant activities (Valentão et al., 2005). Results of this study for free sugar content are similar to those reported in previous studies (Lee et al., 2012; Veberic et al., 2010). Changes in fruit color are closely related to an increase in sugars and a decrease in firmness. Color value is considered an important maturity index (Testoni, 2002) and consumers’ preference (Bolek and Obuz, 2014) for persimmon fruits. DPPH radical scavenging assay is widely used for evaluating the antioxidant capacity of plant extracts. It is superior to other similar essays, because it is unaffected by certain side reactions, including metal ion chelation and enzyme inhibition that do happen in other essays with free radicals such as the hydroxyl radical and superoxide anion (Yildirim et al., 2000). The DPPH radical scavenging potential of ‘Dongchul’ found in this study was higher than that of the cultivar Triumph (Park et al., 2006). The polyphenol content of persimmon fruit determined in this study is in the range of other persimmon cultivars (Jang et al., 2010; 2011). Phenolic compounds are considered to provide antioxidant properties to food products, crops, vegetables and natural plants (Abeysinghe et al., 2007; Maksimovic et al., 2005; Rice-Evans et al., 1995). Therefore, higher total polyphenol content in ‘Dongchul’ than in other three commercial cultivars signifies the potentiality of its commercial cultivation in Gangwondo as antioxidant rich cultivar.

The fruit of ‘Dongchul’ grown in Gangwondo, which lies in the northern part of South Korea and is a new area for its commercial production, contained many of the physicochemical, nutritional, and antioxidant properties those are found in other three commercial cultivars commercially grown in Korea. The nutrient contents of ‘Dongchul’ persimmon fruit were not found deteriorated irrespective of its cultivation in new agro-climatic zone, although the climate change has affected the persimmon growing areas in Korea. Overall results of the present study indicate that ‘Dongchul’ persimmon could commercially be grown in Gangwondo, Korea.