Some Important Horticultural Properties of Summer Apple Genotypes from Coruh Valley in Turkey

ABSTRACT

Coruh Valley located in Northeastern part of Turkey is accepted one of the 34 hotspots for plant biodiversity area by International Union for Conservation of Nature. In this study, 22 seed propagated summer apple genotypes were evaluated using a number of phenological, morphological, and biochemical markers. Phenological, morphological, and sensory traits were highly differed among genotypes. Harvest dates of genotypes were found quite variable ranging from 9 July to 8 August. Fruit weight were found between 81.3 and 125.4 g. Round, conic, and oblate were the common fruit shapes of genotypes. Fruit firmness and stalk length recorded in the range of 3.10–6.11 kg/cm² and 4.0–8.0 mm, respectively. High total phenols and antioxidant capacity were found for genotypes CVE 16 and CVE2. This study could help promote the commercialization of promising summer apple genotypes, which are rich in bioactive compounds for use in for nutraceutical purposes. CVE2 and CVE16 genotypes displayed superior traits as summer apple genetic resources, and they could be important for future breeding activities.

KEYWORDS:

• Early apples
• biochemical content
• classification
• pomology

Introduction

The apple has been among the most consumed fruits around the world and the amount of world apples production averages more than 80 million metric tons a year, the vast majority of which is produced by China (44.500.000 tons) and followed by USA (4.650.000 tons), Poland (3.605.000 tons), Turkey (2.926.000 tons) and India (2.872.000 tons). Overall, world more than half of apples are normally used as fresh fruit. Rest of the production is used for vinegar, juice, jelly, apple butter, canned as pie stock and apple sauce (Way and McLellan, 1989).

Turkey is a key country for global biodiversity because its location is the junction of three continents. Moreover, Turkey has complex topography and geomorphology. These geographical features account for a great variety of habitats and species, and, particularly, for an exceptionally rich flora. The global map of biodiversity hotspot gives perhaps the best insight on Turkey’s global importance for biodiversity. Three out of 34 biodiversity hotspots meet within Turkey: Caucasus, the Mediterranean and the Irano-Anatolian (Eyduran et al., 2015a; Serce et al., 2010; Sezen et al., 2015).

The Coruh Valley lies within the Caucasus ecological zone, which is considered by the World Wild Fund for Nature and by Conservation International as a one of the biodiversity hotspot in the world (IUCN, 2013). The valley is an important growing area with substantial plant diversity because of its traditional agriculture practices, geography and ecological diversity. Summer apple genotypes, which are an important local and traditional fruits in this valley, have not been replaced by national or international summer apple cultivars so far.

Summer apple trees and its fruits are important part of human life in this valley. Seed propagated summer apples are abundant in the majority villages of valley, and they shows variable size, shape, skin color and taste. They are among the most widely used summer fruits in the valley, and important sources of nutrition, and income for their users and villagers. In addition to their use as food, summer apples may also yield a range of processed products (vinegar, pickle, jam etc.). Summer apple trees also thrive in diverse environments, such as agroforestry and urban landscapes, fallows, natural lands, and plantations (Abaci and Sevindik, 2014; Corumlu, 2010).

Summer apples are an overlooked class of apples that come into season in late July and early August. They’ve got yellow, red, green, purple skins, and intense flavors-much tarter and savorier than their autumnal counterparts. Autumn apples, on the other hand, are harvested in September and October, and many varieties can be stored for months.

The phenology, morphology, and biochemical contents of fruits are affected from various factors. More particularly, the environmental conditions and its genotype structure have significant effects (Akin et al., 2016; Butiuc-Keul et al., 2019; Ersoy et al., 2018; Eyduran et al., 2015b; Gecer et al., 2020; Reig et al., 2015; Senica et al., 2019). Apple fruits are extremely rich in important antioxidants, flavonoids, and dietary fiber (Drogoudi et al., 2008; Kschonsek et al., 2018; Wojdylo et al., 2008). The phytonutrients and antioxidants in apples may help to reduce the risk of developing cancer, hypertension, diabetes, and heart disease (Chai et al., 2012; Hyson, 2011; Muraki et al., 2013).

To increase the quality of the summer apples, it is important to study on phonological, morphological and biochemical variation in summer apple genotypes, but unfortunately, negligible work has been done on summer apples in spite of fact that lot of variability exist in summer apples for physiological and biochemical characters, which can be utilized for improving quality with high nutritive value. In fact, there were studies on autumn and winter apples in literature and indicating great variability for most of the morphological and biochemical parameters. Reig et al. (2015) evaluated the accession variability based on agronomic, morphological and fruit quality traits under the Ebro basin climatic conditions of 80 accessions [Malus x domestica Borkh] from the apple germplasm collection at the Experimental Station of Aula Dei (CSIC-Zaragoza, Spain). However, for summer apples the studies were scarce.

Thus, this paper describes some important horticulture characteristics of seed propagated summer apples.

Materials and Methods

Plant Materials

In this study, twenty two summer apple genotypes (Named from CVE1 to CVE22) were used. The fruits from each genotype were harvested in the periods when the fruits reach the commercial maturity stage in 2018. The fruit samples picked homogenously and morphological characteristics (fruit weight, fruit firmness, shape, color, stalk length, taste, juiciness, and aroma) were done on 30 fruits after harvest. Biochemical characteristics were done on fruits that were stored at refrigerator −20°C until their laboratory analyzes were done. Ripening time of genotypes were classified according to D.U.S guideline as: Very early ripening (18 May–27 June), early ripening (28 June–17 July), early-mid-ripening (18 July-27 July) and mid ripening (28 July– 6 August). Fruit weight (g) were measured with a digital scale sensitive to 0.01 g (Scaltec SPB31). Fruit firmness was determined with nondestructive Acoustic Firmness Sensor (Aweta B.V., The Netherlands) expressed as kg/cm². The skin ground and over color were determined by observation and comparison. The shape was determined by dividing fruit length by fruit width. Soluble solids content (SSC) were determined by extracting and mixing one drop of juice from the each fruit into a digital refractometer (Kyoto Electronics Manufacturing Co. Ltd., Japan, ModelRA-250HE) at 22°C. Vitamin C (Ascorbic acid) was quantified with the reflectometer set by using RQFlex (Merck Company, Darmstadt, Germany) and expressed as mg/100 g. Titratable acidity was determined by titrating 10 mL of 1:10 diluted apple pulp (10 g) with 0.1 M NaOH. A trained panel of five experts evaluated the sensory features (taste, juiciness and aroma) of fruits for each genotype.

A trained panel of five experts evaluated the sensory features (taste, juiciness and aroma) of fruits for each genotype. The 0 to 9 bipolar hedonic scale just described was used to rate overall liking of taste, juiciness and aroma which was rated on a unipolar 0 to 9 intensity scale, where 0 = not detectable, 1 = just barely detectable, 3 = slight, 5 = moderate, 7 = intense and 9 = extremely intense. The term ‘aromatics’ was used to denote all flavor components not covered by sweetness and sourness; no specific aromas were expected to be identified.

Analysis of Organic Acids

The samples collected were kept at deepfreeze (−20° C) until the time of analysis. In the research, for the extraction of organic acids, the method developed by Bevilacqua and Califano (1989) was modified and used. 5 g was taken from the fruit samples obtained and transferred to centrifuge tubes. These samples were homogenized by adding 20 mL 0.009 N H₂SO₄ (Heidolph Silent Crusher M, Germany). Then, it was mixed on the agitator (Heidolph Unimax 1010, Germany) for 1 hour and centrifuged at 15000 rpm for 15 min. The aqueous part which was separated at centrifuge was filtered from first coarse filter paper, then 0.45 µm membrane filter (Millipore Millex-HV Hydrophilic PVDF, Millipore, USA) for two times and finally SEP-PAK C₁₈ cartridge. The organic acids were analyzed in HPLC device (Agilent HPLC 1100 series G 1322 A, Germany). In HPLC system, Aminex HPX – 87 H, 300 mm x 7.8 mm colon (Bio-Rad Laboratories, Richmond, CA, USA) was used and the device was controlled with the computers including Agilent package program. DAD detector in the system (Agilent, USA) was set to 214 and 280 nm wavelengths. In the study, 0.009 N H₂SO₄ filtered at 0.45 µm membrane filter was used as mobile phase.

Total Phenolic Content

Total phenolic were detected with Folin-Ciocalteu assay. 10 g of flesh+peel were centrifuged at 6000 rpm after homogenized in 40 ml ethanol solution. After, diluted (1/10) 1000 μl Folin-ciocalteu and 800 μl Na₂CO₃ solution was added upon supernatant. After 2 h, incubated examples were read at 750 nanometer wavelength in spectrophotometer. Water–ethanol mixture was used as blank. Gallic acid is used as a standard in the calculation (Spanos and Wrolstad, 1992). Results are expressed mg GAE/100 g fresh weight base.

Antioxidant Capacity

Antioxidant capacity was determined using DPPH method. Fruit juice samples were obtained by pureed and filtered. Samples were homogenized by centrifuge. 950 μl 0.1 N DPPH (1,1-diphenyl-2-picrylhydrazyl) solution was added upon 50 μl supernatant. Then it was read against the blank at 515 nm wavelength spectrophotometer (Bakhshi and Arakawa, 2006; Rezaeirad et al., 2013). The results were expressed as μmol trolox equivalents (TE) per 100 g.

Statistical Analysis

All data were analyzed using SPSS software and procedures. Analysis of variance tables were constructed using the Least Significant Difference (LSD) method at p < .05.

Results and Discussion

Phenological Trait

Harvest dates of summer apple genotypes are shown in Table 1. Harvest dates of genotypes were found quite variable ranging from 9 July (CVE1) to 8 August (CVE16) (Table 1). According to D.U.S scale, harvest date of genotypes were classified as early ripening (CVE1, CVE5, CVE8, CVE14, CVE15, CVE17, CVE18, CVE19 and CVE21), early-mid-ripening (CVE4, CVE9, CVE10, CVE11, CVE12, CVE13 and CVE22) and mid ripening (CVE2, CVE3, CVE6, CVE7, CVE16 and CVE20). Hajnajari et al. (2019) reported that 53 hybrids of summer apples were individuated according to D.U.S scale as very early, early, mid-early and mid-ripening fruits.

Table 1. Some phenological and pomological characteristics of summer apples

Genotypes	Fruit weight (g)	Harvest dates	Fruit shape	Fruit ground color	Fruit over color	Fruit firmness (kg/cm^2)	Stalk length (mm)
CVE1	81.3 ge*	9 July	Oblate	Green	Green	5.80 ab	5.7 bc
CVE2	88.7 fg	6 August	Round	Yellow	Red	5.15 b	6.3 ab
CVE3	111.4 c	30 July	Conic	Green	Purple	6.11 a	4.7 bc
CVE4	83.39 g	23 July	Conic	Yellow	Red	4.92 bc	4.3 bc
CVE5	101.7 de	15 July	Round	Green	Green	3.10 d	7.1 ab
CVE6	117.1 bc	4 August	Round	Yellow	Purple	3.02 de	5.9 bc
CVE7	95.4 ef	2 August	Oblate	Red	Red	3.41 cd	6.0 b
CVE8	93.3 ef	12 July	Round	Yellow	Yellow	4.54 bc	7.4 ab
CVE9	103.4 de	18 July	Oblate	Green	Green	3.18 cd	8.0 a
CVE10	120.3 ab	23 July	Conic	Green	Red	4.78 bc	7.8 ab
CVE11	92.6 ef	27 July	Oblate	Green	Purple	4.01 cd	6.5 ab
CVE12	90.6 f	25 July	Conic	Green	Pink	4.22 bc	4.9 bc
CVE13	100.2 de	20 July	Round	Green	Red	4.57 bc	4.5 bc
CVE14	80.7 ge	16 July	Oblate	Yellow	Pink	5.12 b	6.0 b
CVE15	104.2 d	16 July	Conic	Green	Red	5.74 ab	5.5 bc
CVE16	125.4 a	9 August	Conic	Green	Pink	4.11 c	5.0 bc
CVE17	95.8 ef	16 July	Round	Red	Red	3.37 cd	5.3 bc
CVE18	118.6 b	11 July	Oblique	Green	Pink	3.92 cd	4.2 bc
CVE19	97.2 e	12 July	Oblate	Green	Red	3.55 cd	4.0 c
CVE20	113.2 bc	2 August	Conic	Yellow	Purple	4.70 bc	4.8 bc
CVE21	108.5 cd	16 July	Round	Green	Green	3.80 cd	4.0 c
CVE22	115.8 bc	20 July	Round	Green	Green	4.40 bc	4.6 bc

*Same letters in same column indicate statistically significant differences (p < 0.05) among the genotypes

Morphological Traits

In the study, fruit weight of summer apples greatly varied among genotypes and statistically significant differences among genotypes were observed (p < .05). The highest average fruit weight was obtained from CVE16 genotypes as 125.4 g, and followed by CVE10 as 120.2 g while the lowest value was observed in genotype CVE14 as 80.7 g (Table 1). In literature there were limited data on fruit weight of summer apples. Hajnajari et al. (2019) conducted a study in Iran on summer apples and they reported that 31 promising hybrids of summer apples had fruit weight between 11.47 g and 98.50 g. In Turkey fruit weight of 16 local apple cultivars from Van and Bitlis provinces were found between 20.9 and 139.3 g (Ozrenk et al., 2011). Balta and Kaya (2007) reported fruit weight between 32.29 g and 138.25 g in local apple cultivars from Eastern Anatolia region in Turkey. Serdar et al. (2007) found great variability among local apple cultivars in northeastern part of Turkey ranged from 54.3 g to 206.0 g. Kaya et al. (2015) reported fruit weight between 43 and 310 g among 37 apple selection from Van lake basin in Turkey. In another Mediterranean area, Reig et al. (2015) also reported wide range of fruit weight values (from 77.6 g to 265.8 g) on 80 local apple accessions evaluated.

Round, conic and oblate fruit shapes were common in summer apple genotypes (Table 1). Among 22 genotypes, 8 genotypes had round, 7 genotypes had conic, 6 genotypes had oblate and 1 genotypes had oblique fruit shape. Kaya et al. (2015) reported conic, round, oblate and cylindiric fruit shapes among 37 apple selection from Van lake basin in Turkey.

The summer apple genotypes had in general green and yellow ground skin color However over skin color were diverse (green, red, purple, yellow and pink). Ozrenk et al. (2011) reported yellow and green ground color and yellow, green and red over color in local apple cultivars. Kaya et al. (2015) studied on 37 local apple genotypes and reported yellow and green ground color. They found great variability on over color which were red, pink, yellow and green. Similar results were found by Reig et al. (2015), even some local apples with orange red over color.

Fruit firmness of summer apple genotypes were between 3.41 kg/cm² (CVE5) and 6.11 kg/cm² (CVE3) (Table 1). Ozrenk et al. (2011) reported fruit firmness between 3.9 and 6.2 kg/cm² in local apple cultivars, which supports our findings. Karlidag and Esitken (2006) have determined the fruit firmness values of the local apple cultivars grown in upper Çoruh valley in the range of 3.70–5.25 kg/cm². However, Kalkisim et al. (2016) determined the fruit firmness between 11.38 and 17.08 kg/cm² in local apple cultivars, while the average value of fruit firmness was obtained as 13.79 kg/cm².

The stalk length of summer apple genotypes is shown in Table 1. There were statistically significant differences among genotypes (p < .05). The stalk length of genotypes varied from 4.0 to 8.0 mm. Aygun and Ulgen (2009) found stalk length of different Demir apple types in Turkey were between 6.60 and 11.10 mm. Gundogdu et al. (2018) studied on 10 local genotypes in western part of Turkey and they reported stalk length between 6.48 and 10.44 mm. Reig et al. (2015) reported these values between 6.3 and 24.0 mm in apples.

Sensory Analysis

Sensory analysis (fruit taste, juiciness and aroma) is shown in Table 2. Fruits of summer apple genotypes had sweet (10 genotypes), sweet-sour (6 genotypes), sour (4 genotypes) and tart (2 genotypes). In terms of juiciness, 10 genotypes had low, 7 genotypes had moderate and 5 genotypes had high juiciness characteristic. Seven genotypes had high aroma, 9 genotypes had moderate aroma and 6 genotypes had low aroma characteristics. Gundogdu et al. (2018) studied on 10 local genotypes in western part of Turkey and they reported that 5 genotypes had sour, 3 genotypes had tart and 2 genotypes had sour taste. They also found that the majority of genotypes had low juiciness characteristics. Hajnajari et al. (2019) conducted a study in Iran on summer apples and they reported that based on the results of the sensory evaluation they found that the genotypes had diverse taste and aroma characteristics. Phenolic compounds play a decisive role in nutritional quality and sensory characteristics such as taste and aroma, color, odor, bitterness and astringency of apples (Hampson et al., 2004; Way et al., 1990). Kalkisim et al. (2016) determined that local apple cultivars had equal sweet, sour and tart fruit taste.

Table 2. Sensory characteristics of summer apples

Genotypes	Sensory features
	Taste Juiciness Aroma
CVE1	Sweet	Low	High
CVE2	Sweet	Low	Moderate
CVE3	Sour	Moderate	Moderate
CVE4	Sour	Moderate	Moderate
CVE5	Sour	High	Low
CVE6	Sweet	High	High
CVE7	Sweet-Sour	Low	Moderate
CVE8	Tart	Low	High
CVE9	Sweet	High	Moderate
CVE10	Sweet	Moderate	Moderate
CVE11	Sweet	Moderate	High
CVE12	Sweet-Sour	Low	Moderate
CVE13	Sweet-Sour	Low	Low
CVE14	Tart	Moderate	Low
CVE15	Sweet-Sour	Low	Low
CVE16	Sweet-Sour	High	Moderate
CVE17	Sweet	Low	Moderate
CVE18	Sweet	Low	Low
CVE19	Sour	Moderate	High
CVE20	Sweet	Moderate	High
CVE21	Sweet	Low	Moderate
CVE22	Sweet-Sour	High	High

Organic Acids

Organic acid content of 22 summer apple genotypes are shown in Table 3. As indicated in Table 3, we found statistically significant differences among the summer apple in terms of malic, succinic, oxalic and tartaric acid contents (p < .05). However there were no statistically significant differences on oxalic acid content among genotypes. The dominant organic acid was malic acid for all genotypes. Malic acid followed by citric acid, succinic acid, oxalic acid and tartaric acid (Table 3). Malic acid were found between 2.56 and 3.54 mg/100 ml with the genotype CVE17 had the highest value. The highest citric acid content was determined at CVE2 genotype as 0.65 mg/100 ml and lowest content was determined at CVE7 genotypes as 0.15 mg/100 ml. Succinic, oxalic and tartaric acid content of genotypes ranged from 0.10 to 0.40 mg/100 ml, 0.09 to 0.30 and 0.08 to 0.40 mg/100 ml, respectively (Table 3). Gundogdu et al. (2018) studied on 10 local genotypes in western part of Turkey and they reported that malic acid was the dominant and found between 2.06 and 4.62 mg/100 ml. They reported citric, succinic, oxalic and tartaric acid content between 0.15 and 0.57 mg/100 ml, 0.18 and 0.51 mg/100 ml, 0.16 and 0.33 mg/100 ml, and 0.04–0.17 mg/100 ml, respectively indicating similarities with our results. Organic acids important not only for human health but also for fruit flavor. In particular malic acid, citric acid and tartaric acid make significant contributions to the human health in various aspects such as strengthening the immune system, preventing the renal calculi, eliminating the oral diseases, decreasing the poisoning risks caused by the toxic metals, beautifying and strengthening the skin and decreasing the fibromyalgia symptoms (Abraham and Flechas, 1992; Penniston et al., 2007). Wu et al. (2007) and Petkovsek et al. (2007) determined that the highest organic acid in apple fruits was malic acid and organic acid content quite variable among apple cultivars.

Table 3. Organic acid contents in summer apples (mg/100 g)

Genotypes	Malic	Citric	Succunic	Oxalic	Tartaric
CVE1	3.11 ab*	0.28 bc	0.40 a	0.22^NS	0.10 bc
CVE2	2.80 bc	0.65 a	0.15 bc	0.10	0.15 bc
CVE3	2.56 c	0.40 ab	0.25 b	0.18	0.22 ab
CVE4	3.20 ab	0.30 ab	0.10 c	0.14	0.30 ab
CVE5	3.31 ab	0.36 b	0.27 ab	0.20	0.15 bc
CVE6	2.90 bc	0.25 bc	0.12 bc	0.25	0.34 ab
CVE7	3.00 b	0.15 c	0.31 ab	0.30	0.20 b
CVE8	2.80 bc	0.33 bc	0.35 ab	0.22	0.08 bc
CVE9	3.20 ab	0.54 ab	0.40 a	0.30	0.11 bc
CVE10	3.44 ab	0.50 ab	0.18 bc	0.17	0.22 ab
CVE11	3.18 ab	0.45 ab	0.15 bc	0.20	0.30 ab
CVE12	3.22 ab	0.42 ab	0.25 b	0.25	0.10 bc
CVE13	3.16 ab	0.20 bc	0.31 ab	0.20	0.08 bc
CVE14	2.95 bc	0.30 bc	0.20 bc	0.28	0.40 a
CVE15	3.04 b	0.22 bc	0.17 bc	0.09	0.18 bc
CVE16	3.37 ab	0.26 bc	0.15 bc	0.14	0.20 b
CVE17	3.54 a	0.34 b	0.25 b	0.17	0.12 bc
CVE18	2.85 bc	0.51 ab	0.32 ab	0.25	0.15 bc
CVE19	2.94 bc	0.55 ab	0.30 ab	0.20	0.10 bc
CVE20	3.02 b	0.20 bc	0.24 b	0.18	0.08 c
CVE21	3.15 ab	0.25 bc	0.28 ab	0.11	0.16 bc
CVE22	3.50 ab	0.30 bc	0.35 ab	0.15	0.20 bc

*Same letters in same column indicate statistically significant differences (p < 0.05) among the genotypes

SSC, Titratable Acidity, Vitamin C, Total Phenolic Content and Antioxidant Capacity

All analytical data on SSC, titratable acidity, vitamin C, total phenolic content and antioxidant capacity from the 22 summer apple genotypes are summarized in Table 4. There were statistically significant differences (p < .05) among genotypes for SSC, titratable acidity, total phenolic content and antioxidant capacity.

Table 4. Biochemical characteristics of summer apples

Genotypes	SSC (%)	Acidity (%)	Vitamin C (mg/100 g)	TPC (mg GAE/100 g)	AA (μmol TE/100 g)
CVE1	11.2 ab*	0.31 bc	7.2^NS	72.0 e	59.1 e
CVE2	8.7 g	0.19 c	5.4	130.7 ab	122.3 ab
CVE3	8.5 g	0.61 bc	6.2	110.4 bc	104.1 bc
CVE4	9.0 f	0.69 bc	6.0	95.4 cd	98.2 bc
CVE5	9.5 e	0.74 b	5.5	90.8 d	85.3 cd
CVE6	11.5 a	0.52 bc	6.0	122.4 b	120.6 ab
CVE7	11.0 b	0.62 bc	4.6	114.6 bc	107.3 bc
CVE8	10.7 bc	1.32 a	4.2	75.6 de	62.1 de
CVE9	9.8 de	0.40 bc	5.7	111.5 ab	101.4 bc
CVE10	10.0 d	0.25 bc	6.0	101.4 cd	95.8 bc
CVE11	10.5 c	0.30 bc	5.1	109.2 bc	97.7 bc
CVE12	9.4 ef	0.40 bc	5.4	106.5 c	87.2 cd
CVE13	11.2 ab	1.02 ab	4.9	88.2 de	79.4 cd
CVE14	10.7 bc	1.21 ab	4.7	85.1 de	76.1 d
CVE15	9.7 de	0.85 ab	4.0	80.2 de	70.3 de
CVE16	10.1 cd	0.92 ab	5.1	138.1 a	127.2 a
CVE17	10.8 bc	0.28 bc	4.9	98.3 cd	93.5 c
CVE18	11.3 ab	0.34 bc	4.3	79.1 de	62.7 de
CVE19	9.7 de	1.02 ab	5.0	76.2 de	65.3 de
CVE20	10.1 cd	0.49 bc	5.4	118.6 ab	110.1 b
CVE21	11.4 ab	0.52 bc	5.2	90.7 d	87.6 cd
CVE22	10.5 c	0.79 ab	4.3	96.2 cd	93.0 c

*Same letters in same column indicate statistically significant differences (p < 0.05) among the genotypes

SSC content was the highest at CVE6 genotypes as 11.5% while the lowest value was obtained from CVE4 genotypes as 9.0%. In general SSC content was high in late ripened genotypes such as CVE2, CVE6, CVE16 and CVE 20 whereas early ripened genotypes such as CVE1, CVE8, CVE18, CVE19 and CVE21 had the lowest SSC content (Table 4). Ozrenk et al. (2011) reported SSC content between 10.0 and 15.4% among local apple genotypes in Turkey. Karlidag and Esitken (2006) determined SSC content between 9.10 and 13.80% in the local apple cultivars. Balta ve Uca (1996) determined SSC content between 10.80 and 12.40% among summer apple genotypes grown in eastern Anatolia region in Turkey. Karadeniz et al. (1996) and Corumlu (2010) reported SSC content among local apple cultivars between 10.0–17.1% and 9.3–16.7%, respectively. Polat and Caliskan (2007) studied on SSC content and found that Ak, Golden Dorset and Anna had SSC content as 12.83, 12.95, and 13.33%, respectively. Reig et al. (2015) reported these values between 10.0 and 18.1% in local apples.

Titratable acidity values of summer apple genotypes were found between 0.19 and 1.30% (Table 4). Cripps and Richards (1993) used Pink Lady, Golden Delicious and Lady Williams apple cultivars and they found great variability among culticvars in terms of titratable acid content, which was 0.90, 0.32, and 0.83% for Pink Lady, Golden Delicious and Lady Williams cultivars, respectively. Kaya and Balta (2007) also indicated a great variability on titratable acid content among apple cultivars, which were between 0.07 and 1.57%. Serdar et al. (2007) studied on local apple cultivars and they stated that titratable acidity ranged from 0.2 to 1.3% which indicating similarities with our results.

Vitamin C content was the highest in CVE1 as 7.2 mg/100 ml while it was the lowest in CVE15 summer apple genotype as 4.0 mg/100 ml (Table 4). However there were no significant differences among summer apple genotypes for vitamin C content. This results indicating that summer apples could be placed vitamin C poor fruit group. In fact in general apples are not rich vitamin C compared to vitamin C rich fruits such as kiwifruit, orange, currants etc. Polat et al. (2018) reported vitamin C content between 17 and 26 mg/100 g among local apple genotypes in Mediterranean part of Turkey. Abaci and Sevindik (2014) reported vitamin C in local apples ranging from 5.2 to 17.2 mg/100 g. Lee et al. (2003) also indicated that apple fruits are vitamin C poor fruits and vitamin C content of apple cultivars varied from 9.0 to 16.6 mg/100 g. Markowski et al. (2009) reported vitamin C content between 5.1 mg/100 g (cv. Judor) and 7.3 mg/100 g (cv. Ariane) in French apple cultivars. Loncacic and Pilizota (2014) studied on Golden delicious and Gold Rush apple cultivars to determine biochemical content. They found vitamin C between 4.75 and 8.42 mg/100 g. L-Ascorbic Acid also called vitamin C, is an essential antioxidant molecule in plant and animal metabolism and also functioning as a cofactor in many enzymes (Gallie, 2013). Fresh fruits and vegetables are the major sources of this vitamin C, therefore increasing its concentration will have an important impact in human nutrition. Ascorbate deficiency in developed countries has registered a decrease throughout time. Average Requirement (AR) of 90 mg/day of Vitamin C for men and 80 mg/day for women, and a Population Reference Intake (PRI) of 110 mg/day for men and 95 mg/day for women, has been established by the European Food Safety Authority (EFSA Panel on Dietetic Products and Nutrition and Allergies, NDA, 2013). Vitamin C content of apples in general relative low and belongs to genetic background and also cultivation conditions and environmental also affects on it (Abaci and Sevindik, 2014).

The summer apple genotypes significantly differed each other in terms of total phenolic content (Table 4). The genotype CVE16 had the highest value (138.1 mg GAE/100 g), and followed by CVE2 (130.7 mg GAE/100 g) and CVE20 (118.6 mg GAE/100 g) while the genotype CVE1 had the lowest value (72.0 mg GAE/100 g). Previous studies conducted on apple cultivars in different parts of the world indicate big differences among cultivars. Vrhovsek et al. (2004) reported total phenolic content in apple cultivars between 66 and 212 mg GAE/100 g. Abaci and Sevindik (2014) also found great variability on total phenolic content on apples ranged from 46.9 to 112.2 mg GAE/100 g. These results on phenolics contents support the thesis that the main source of variation was fruit genotype rather than environment conditions (Loncacic and Pilizota, 2014). Wolfe et al. (2003) reported total phenolic content as 159, 130, 120, and 119 mg of gallic acid equivalents/100 g of flesh + peel for Rome Beauty, Golden Delicious, Idared, and Cortland apple cultivars, respectively. Our results were comparable with above all results.

The antioxidant capacity of summer apples is given at Table 4. The antioxidant capacity of CVE16 genotypes was highest (127.2 μmol TE/100 g), and followed by CVE2 (122.3 μmol TE/100 g) and CVE6 (120.6 μmol TE/100 g) (Table 4). The antioxidant capacity of the CVE1 genotype (59.1 μmol of vitamin C equivalents/g) were significantly lowest than the all the other genotypes. Different researchers were informed the results for total phenolic in apple. Kevers et al. (2011) reported antioxidant capacity among apples as 110.1–491.7 μmolTE/100 g fresh weight basis. Wolfe et al. (2003) found that Rome Beauty apples had the highest antioxidant activity (131 μmol of vitamin C equivalents/g) when compared to that component of the other apples (72, 84, and 67 μmol of vitamin C equivalents/g) for Idared, Cortland, and Golden Delicious, respectively. Those values close to our results indicating importance of our summer apple genotypes human health point of view.

Conclusion

According to phenological observation, pomological and biochemical analysis the summer apple genotypes CVE10, CVE16 and CVE18 had the highest fruit weight. CVE2 and CVE16 had the highest total phenolic content and antioxidant activity and CVE1, CVE18 and CVE19 were found important for earliness. In the light of findings obtained in this research, it is thought that promising genotypes have the potential to be candidate for developing new summer apple cultivars for future breeding activities.