Introduction

Apple is the most popular temperate fruit in the world because of its crispy texture and sweet taste. India is the 5th largest producer of apples in the world, where it is commercially grown in states of Jammu and Kashmir, Himachal Pradesh and Uttrakhand. Apples form an important part of human diet as they are a rich source of sugars, minerals, dietary fibre and functional compounds such as ascorbic acid and phenolics (Bondonno et al. 2017; Wu et al. 2007). The quality and consumer acceptability of apples is associated with their overall sensory appeal and chemical composition (Musacchi and Serra 2017; Alberti et al. 2017). Differences in the relative concentrations of individual components in different cultivars may occur depending on the fruit maturity, environmental factors, horticultural practices applied in the orchard and storage conditions (Musacchi and Serra 2017).

Sugars, organic acids and phenolic compounds, the major compounds in apple, impart taste characteristics, such as flavour, bitterness and astringency to the fruits (Mihailović et al. 2018). The sugar profiling of fruits can give valuable information on the quality of fruit juices extracted from them as it affects the sensory properties and nutritional value of the juices (Wu et al. 2007). The content of organic acids in the extracted apple juice not only influences the flavour but also the stability, nutritive value, acceptability and keeping quality of the juice. Besides their importance in flavour, acids are also important in the gelling property of pectin required in processed apple products. Phenolic compounds considered as anti-mutagenic, antioxidant, anti-inflammatory and anti-carcinogenic (Alberti et al. 2017), are associated with browning processes in apple, with a low level being more desirable. The type and concentration of phenolic compound in any fruit depends on its cultivar (Alberti et al. 2017; Ayaz and Kadioglu 1997). Furthermore, mineral composition of any fruit is equally important as minerals are considered essential in regulation of several body functions (Cindric et al. 2012). Some minerals may even affect the ripening behaviour and disease incidence in fruits.

Cultivar specific profiling of sugars, organic acids, phenolic compounds and minerals of apple cultivars grown in India have not been investigated till now. Hence, the present study was conducted to comprehensively analyze and compare the chemical composition of selected apple cultivars grown in Indian conditions. Based on the nutritional profiling, some of these cultivars may be found to be suitable for table consumption, juice production and/or for development of minimally processed apple slices.

Materials and methods

Sampling

Twenty two apple cultivars including five non-red viz., ‘Golden Delicious’, ‘Granny Smith’, ‘Winter Banana’, ‘Goldspur’ and ‘Starkspur Golden’ and seventeen red viz., ‘Royal Delicious’, ‘Top Red’, ‘Oregon Spur-II’, ‘Starkrimson’, ‘Well Spur’, ‘Red Chief’, ‘Super Chief’, ‘Red Gold’, ‘Royal Gala’, ‘Scarlet Spur-II’, ‘Scarlet Gala’, ‘Early Red-I’, ‘Gale Gala’, ‘Spartan’, ‘Vance Delicious’, ‘Silver Spur’ and ‘Red Delicious’ were procured from Horticulture Research Station, YSPUH&F, Seobagh, Kullu Valley, Himachal Pradesh, India. The orchard is located at a height of 1290 msl (31°58′56″ longitude and 77°7′48″ latitude). The apples were harvested in 2017 at commercial maturity, having starch pattern index (SPI) of 3.0. The starch pattern index (SPI) was determined according to the method of Fan et al. (1995) by immersing the cross section of apple in I2–KI solution. After harvesting and sorting, the fruits were packed in cartons, transported to New Delhi and stored at 2 °C with 80–90% relative humidity at the Division of Food Science and Postharvest Technology, ICAR-Indian Agricultural Research Institute, New Delhi, for further observations. The physical and nutritional attributes were determined in 10 randomly selected fruits of each cultivar.

Determination of physical attributes

Fruit weight and dimensions

Fruit weight was recorded with the help of an electronic balance (Make: Precisa 310 M, Adair Dutt & Co. Pvt Ltd., Calcutta). Measurement of the fruit dimensions of different cultivars of apple was done using a vernier calliper (Mityoto, Japan). To determine the average size of the fruits, three linear dimensions, namely length (L)—equivalent distance of the stem to the calyx, width (W)—the longest dimension perpendicular to L, and thickness (T)—the longest dimension perpendicular to L and W, were measured. The geometric mean diameter (Dg) and arithmetic mean diameter (Da) were calculated using the following equations (Mohsenin 1986):

$$ D_{g} = \sqrt[3]{LWT} $$
$$ Da = \left( {L + W + T} \right)/3 $$

Fruit firmness

Fruit firmness (expressed in Newtons) was determined using a texture analyzer (model: TA+Di, Stable micro systems, UK) with a pre-test speed of 2 mm/sec and test speed of 0.5 mm/sec and was defined as maximum force attained during puncture by 2 mm probe upto a distance of 5 mm.

Peel colour

Peel colour was determined using Hunter Lab System (model: Miniscan XE PLUS). The colour value was expressed as L*, a* and b* values where L* is a measure of lightness, positive values of a* indicate redness and negative values complement green. Positive values of b* are the vector for yellowness and negative for blueness.

Estimation of nutritional attributes

Soluble solid content (SSC), titratable acidity, total carotenoid, ascorbic acid content and antioxidant (AOX) activity

The soluble solid content (SSC) of samples was estimated using hand refractometer (0–50 °B, ATAGO make) and expressed as degree Brix (°B) at 20 °C. Titratable acidity, ascorbic acid and total carotenoid content of the apple fruits were determined as per the standard procedures and denoted as percentage (%), mg 100 g−1 pulp and mg kg−1, respectively (Ranganna 1999). Antioxidant activity (AOX) in the apple fruits was determined by the cupric ion reducing antioxidant capacity (CUPRAC) method (Apak et al. 2004), and expressed as μmol Trolox equivalent g−1 FW. One mL each of copper (II) chloride, neocuproine and ammonium acetate buffer (pH 7) were mixed with the alcoholic extract of the sample (100 µL) and the developed colour was measured after 30 min of incubation in a spectrophotometer (Spectra Max M2, Molecular Devices, USA) at 450 nm.

Sugars and organic acids

The sugars and organic acids were estimated by high performance liquid chromatography (Wu et al. 2007). Fresh sample of apple fruit (5 g) was homogenized in distilled water and filtered through 0.45 μm membrane filter. The filterate was injected in HPLC for analysis. Standards of sugars and organic acids were procured from Sigma-Aldrich. Waters high performance liquid chromatography consisting of binary pump model 515, 2414 refractive index (RI) and 2998 photodiode array (PDA) detector was used for all analysis. Sugars and organic acids in aqueous phase were quantified by using Aminex HPX-87H (Bio-Rad Laboratories, Hercules, CA) column operated with 5 mM H2SO4 as mobile phase at a flow rate of 0.5 mL min−1 with the oven temperature at 50 °C using both detectors in series (PDA @ 210 nm). The concentration of sugars and organic acids in the apple cultivars were expressed as g L−1.

Phenolic compounds

Extraction of phenolic compounds from fresh apples was carried out by following the procedure of Wu et al. (2007). Ten gram sample was extracted twice with 20 ml of ethyl acetate. The obtained fractions were pooled and evaporated to dryness and the residue was dissolved in 1.0 ml of methanol (HPLC grade). The resultant solution was filtered through a 0.45 µm membrane filter prior to HPLC analysis. A 20 µL volume of each sample was manually injected into the Water Alliance HPLC System (Waters Chromatography, Milford, MA). C18 column (5 µm, 4.6 × 250 mm) was used to estimate the individual phenolic components. The HPLC components include e2695 separation module and the 2996 photodiode array detector and the system was operated with Empower 2 Software (Waters Corporation). The mobile phase consisted of solvent A (water 0.1% formic acid), solvent B (acetonitrile 0.1% formic acid) with gradient programming of 100% A to 100% B and total run time of 55 min. and flow rate of 0.5 mL min−1. The phenolic compounds peaks were detected at 280 nm, and expressed as mL L−1.

Macro and micro elements

For estimation of macro and micro elements, fruit sample (1 g) was digested in a microwave digestion system (Anton Par: Multiwave ECO) with concentrated nitric acid (Suprapur grade, Merck, Germany) and diluted to 100 ml. The element concentrations were analyzed using ICP-MS with auto-sampling protocol (Perkin Elmer, Model: NexION 300 ICP-MS) and computed as mg 100 g−1 for macro elements and µg g−1 for micro elements.

Statistical analysis

The results were statistically evaluated by one way analysis of variance (ANOVA). The data were expressed as mean ± SEM of triplicate analysis. Significant difference amongst the means was determined by Duncan’s Multiple Range Test.

Results and discussion

Fruit weight, dimensions, firmness and peel colour

Physical characteristics of horticultural produce are important parameters for design of grading, conveying, processing, and packaging systems (Tabatabaeefar and Rajabipour 2005). Appearance of fruit is the first and one of the most purchasing driving trait that influence the consumers decision for consumption that is basically manifested by different external characteristics of fruit such as colour, size and shape. Dimensional attributes of various cultivars can be used in describing the fruit shape and cultivar descriptions (Beyer et al. 2002). Of the twenty two cultivars studied, more than 200 g fruit weight was observed for red cultivar ‘Oregon Spur II’ (202.68 g) which also had maximum geometric mean (77.23 mm) and arithmetic mean diameter (77.46 mm), indicating the bigger size of the fruits. In contrast, ‘Starkrimson’ had the least fruit weight (107.41 g), geometric mean (61.33 mm) and arithmetic mean diameter (61.74 mm) (Table 1). This variation in fruit weight might be due to varietal differences as every variety has specific shape, colour and size. Péroumal et al. (2017) have also reported that the average fruit weight of six mamey apple accessions significantly varied from one to another.

Table 1 Physical attributes of different apple cultivars
Full size table

Fruit firmness is one of the most important quality characteristics of any fruit which governs the consumer acceptability. Harker et al. (2008) have reported that acceptability of firmer apple fruits is always better. In the present work, a variation in fruit firmness amongst the apple cultivars was observed, which ranged from 10.32 N in red coloured big sized fruits of ‘Silver Spur’ to 14.0 N in non-red coloured ‘Winter Banana’ (Table 1). Average firmness of the twenty two cultivars was found to be 11.47 N. This variation in fruit firmness may due to different factors as the range of fruit firmness depends on variety, location, maturity stage and environmental factors (Ornelas-Paz et al. 2018; Musacchi and Serra 2017).

Skin colour in apple industry is fundamental as a sorting criterion for various genotypes. The colour of apple skin from green, yellow and red contributes to distinguish the genotypes. Commonly, the red colour is preferred while bright red apples and new alternative colours are recently receiving the consumer attention. In the present study, the intensity of red peel colour was higher in Gala cultivars (Hunter ‘a*’ value ranging from 27.45 to 30.59), giving them an edge over sensory appeal in comparison to other cultivars Table 1). Some non-red apple varieties such as ‘Golden Delicious (Hunter ‘b*’ value = 40.06) and ‘Granny Smith’ (Hunter ‘b*’ value = 41.17) exhibited higher hunter ‘b*’ values, representing yellow and/or green colour. Other varieties have shown differed Hunter a*/b* values, giving different shades of colour. Such difference in peel colour of the studied apple cultivars may be due genotypic variations and composition of pigments in respective varieties (Ma et al. 2017).

Soluble solid content and titratable acidity of the apple cultivars

Soluble solid content (SSC) comprises majorly of sugars followed by acids, vitamins and some minerals that are soluble in water. It is an important integrated index to assess the quality and sweetness of fruits that is pivotal for consumer acceptance. The soluble solid content (SSC) of the apple cultivars ranged from 10 °Brix (‘Red Delicious’) to 16.1 °Brix (‘Gale Gala’). In an earlier study, Jan et al. (2012) have reported lower soluble solid content for the five apple cultivars they studied with values in the range of 11.24–11.79%. Ma et al. (2017) also described genotype differences to be the main factor determining the soluble solid content in kiwifruits. The most popular and widely grown apple cultivars in India, ‘Golden Delicious’ (13.5 °Brix) and ‘Royal Delicious’ (13.2 °Brix) recorded good soluble solid content (Table 2).

Table 2 Composition of different apple cultivars
Full size table

Titratable acidity in fruits governs the overall taste of the fruit. A wide variation in titratable acidity was observed with higher values in all non-red cultivars. The maximum titratable acidity was recorded in non-red cultivars, ‘Winter Banana’ and ‘Starkspur Golden’ (0.67%) while minimum was observed in red cultivars, ‘Royal Delicious’, ‘Red Gold’, ‘Early Red-I’, ‘Spartan’ and ‘Red Delicious’ (0.27%) (Table 2). Average titratable acidity of the twenty two cultivars was 0.39%. A range of 0.50–0.56% titratable acidity has been previously reported in apples by Jan et al. (2012). Cultivars possessing high SSC and acidity can be considered good for apple juice concentrate production as reported by Wu et al. (2007).

Ascorbic acid, antioxidant (AOX) activity and total carotenoid

Ascorbic acid (vitamin C) is an important quality characteristic of apple fruit, specially desired for its antioxidant properties (Lata and Tomala 2007). The maximum ascorbic acid content was recorded in red cultivars, ‘Starkrimson’ (32.08 mg 100 g−1) and ‘Oregon Spur II’ (31.76 mg 100 g−1) whereas the least ascorbic acid was recorded in ‘Well Spur’ (19.38 mg 100 g−1) (Table 2). Our data on this attribute are lower than those reported by Jan et al. (2012) and have wider range than those reported by Joshi et al. (2007) who reported ascorbic acid in the range of 14.3–45.9 mg 100 g−1 and 10.27–12.49 mg 100 g−1, respectively in apples. This deviation in the values of ascorbic acid may be due to fact that we analyzed different varieties than those studied by them.

A great variability in antioxidant (AOX) activity existed among the studied apple cultivars, the maximum being in red cultivar, ‘Silver Spur’ (13.20 μmol Trolox equivalent g−1) and the minimum in non-red cultivar, ‘Granny Smith’ (2.64 μmol Trolox equivalent g−1). In a similar study, Wang et al. (2015) reported that the antioxidant activity was significantly higher for red-fleshed genotypes than for white-fleshed genotypes. Similarly, a wider range of AOX activity (7.7–22.6 μmol Trolox equivalent g−1) has been reported by Joshi et al. (2007) in apple cultivars. The difference observed among the genotypes studied in terms of antioxidant activity may probably be due to plant genotype because all plants were grown in the same location using similar horticultural practices.

The apple cultivars varied in total carotenoid content, the maximum being in red cultivar, ‘Red Chief’ (147.06 mg kg−1) and lower in ‘Early Red-I (29.03 mg kg−1), ‘Granny Smith’ (32.90 mg kg−1), ‘Super Chief’, ‘Gale Gala’ and ‘Silver Spur’ (38.70 mg kg−1) (Table 2). A high level of variability existed with respect to total carotenoids, which could be due to genetic differences among the cultivars. Earlier, Delgado-Pelayo et al. (2014) and Péroumal et al. (2017) have reported a similar variation in the total carotenoid content among different apple accessions.

Sugar and organic acid profiling

The quantity of sugars and organic acids in fruits is influenced by the genotype (Wu et al. 2007) and also by environmental factors and horticultural practices followed in the orchards (Hudina and Stampar 2006). Further, the sugar profiling of fruits is important as it governs the sensory properties and nutritional value of fruits. A great variation in terms of individual sugars was observed among the studied apple cultivars (Table 3). The predominant monosaccharide was found to be fructose that ranged between 10.85 and 67.55 g L−1. All analyzed apple cultivars showed a higher concentration of fructose as compared to sucrose and glucose. As suggested by Hecke et al. (2006), this may favour the intake of apples by diabetic patients, since high fructose level keeps the level of blood sugar constant. Earlier, Zhang et al. (2010) have also reported presence of fructose, glucose, sucrose along with sorbitol in apple fruits. Sucrose was observed to be present in small amount with an average of 20.40 g L−1. The highest contents were recorded in non-red cultivar ‘Granny Smith’ (48.90 g L−1) and lowest in red cultivar ‘Royal Delicious’ (9.85 g L−1) (Table 3). Recently, Mpaia et al. (2018) have also reported a wide variation in composition of sugars in eleven Kei-apple fruit accessions. In this study, we used twenty two apple cultivars that were grown at the same location with similar horticultural practices. The variation in sugars demonstrated that a genetic variability existed among the cultivars that might have contributed to the differences in the synthesis of sugars in these apple cultivars.

Table 3 Sugar content (g L−1) and organic acids in different apple cultivars
Full size table

Besides sugars, the organic acids present in the fruits also influence their taste and the consumption pattern. Low acidic fruits with appreciable sweetness are good for fresh consumption. Among the studied apple cultivars, all the non-red cultivars had a higher level of organic acids, with malic acid being the most predominant, followed by succinic acid and traces of citric and acetic acid (Table 3). Wu et al. (2007) have also reported the presence of malic, succinic and citric acid in apples. In the cultivars we studied, malic acid ranged from 4.40 g L−1 (‘Red Gold’) to 9.50 g L−1 (‘Starkspur Golden’) whereas succinic acid was found to be absent in cultivar ‘Starkspur Golden’ and maximum (5.10 g L−1) in ‘Red Delicious’ (Table 3).

Mineral analysis

Apples are considered a good source of dietary minerals. Among the major elements studied in different cultivars of apple fruits, K was the most abundant with an overall mean concentration of 795.14 mg 100 g−1 (Table 4). Maximum potassium concentration was observed in ‘Scarlet Gala’ (1142 mg 100 g−1) and minimum in ‘Winter Banana’ (550 mg 100 g −1). Earlier, Horsley et al. (2014) have reported a higher concentration of potassium in apple cultivars, however in contrast, Joshi et al. (2007) have reported a lower concentration (700 mg 100 g−1). The sodium, calcium and magnesium concentrations among different apple cultivars fell in the range of 9.70–70.20 mg 100 g−1, 14.20–90.37 mg 100 g−1 and 15.98–31.12 mg 100 g−1, respectively (Table 4). The average values for Na (23.70 mg100 g−1) in this study were higher than those reported by Fazli and Fazli (2014) and Ornelas-Paz et al. (2018), however the concentrations of calcium (14.20–90.37 mg 100 g−1) and magnesium (15.98–29.54 mg 100 g−1) recorded by us, were comparable with the data reported earlier by Joshi et al. (2007) and Ornelas-Paz et al. (2018) in apple fruits.

Table 4 Minerals content in different apple cultivars
Full size table

The micro elements also support many important functions in the human body. The average concentrations of investigated micro elements in the 22 apple cultivars were: Fe (2.04 µg g−1), Zn (0.64 µg g−1), Mn (0.16 µg g−1) and Cu (0.12 µg g−1) (Table 4). Among different apple cultivars studied, maximum Fe (6.14 µg g−1), Zn (2 µg g−1), Mn (0.28 µg g−1) and Cu (0.22 µg g−1) concentrations were recorded in ‘Red Chief’, ‘Scarlet Spur-II’, ‘Starkrimson’ and ‘Early Red-I’, respectively (Table 4). As far as the concentrations of the micro elements are concerned, our results are comparable with those demonstrated for apple fruits by Manzoor et al. (2012) and Ornelas-Paz et al. (2018).

Profiling of phenolic compounds

Besides playing a major role in enzymatic browning in apple, the phenolic compounds act as a source of dietary antioxidants that may reduce the risk of many chronic disorders, including cancer (Alberti et al. 2017). A higher absorption of phenols has been reported to lead to a reduction in heart disease and lower cholesterol levels (Craig and Beck 1999). Therefore, there has been a growing interest for using apples in functional food products, such as functional beverages and healthy snack products. In this study, chlorogenic acid was found to be the predominant phenolic compound with an average concentration of 28.42 mg L−1 (Table 5). The highest concentration of chlorogenic acid was found in non-red cultivar ‘Winter Banana’ (163.97 mg L−1) and lowest in cultivar ‘Granny Smith’ (3.69 mg L−1). Phloridzin dihydrate, the second highest phenolic compound in the apple cultivars averaged to 26.71 mg L−1, with the highest concentration being in ‘Silver Spur’ (67.40 mg L−1). In addition, traces of rutin, catechin and 3-hydroxy cinnamic acid were also found in some cultivars (Table 5). In a study, Łata et al. (2009) determined the total phenolic yield of 19 apple varieties, and reported that the concentration of the main phenolics (chlorogenic acid, catechin, epicatechin, phloridzin and rutin) varied significantly among the different apple cultivars. Carbone et al. (2011) have also reported chlorogenic acid to be the major phenolic compound in apple that ranged from 2.94 to 7.52 mg 100 g−1 in different genotypes Apples with low phenolic content with a correspondingly high SSC, as observed for the Gala cultivars in the present study, make them suitable for the production of light coloured juices as suggested by Wu et al. (2007).

Table 5 Phenolic compounds (mg L−1) content in different cultivars
Full size table

Conclusion

Overall, study demonstrated that cultivars grown under Indian conditions varied widely for physical and biochemical attributes. The studied twenty two cultivars also showed differences in values than those grown in other countries of the world. This variability may be attributed to the genetic factors and geographical locations.