Nutritional characterization of apple as a function of genotype

Abstract

Twenty two apple cultivars grown in Himachal Pradesh, India were harvested at commercial maturity and analysed for different physical (fruit weight, fruit dimensions, firmness, color) and nutritional attributes (ascorbic acid, antioxidant activity, total carotenoid, sugars, organic acids, phenolic compounds and minerals). Cultivar ‘Oregon Spur II’ was found to have maximum fruit size and weight while the least was observed for cultivar ‘Starkrimson’. Quantitative differences were found in the nutritional profile among the cultivars with respect to all the above attributes. The ascorbic acid content ranged between 19.38 mg 100 g⁻¹ (‘Well Spur’) and 32.08 mg 100 g⁻¹ (‘Starkrimson’) while the antioxidant activity varied between 2.64 μmol Trolox equivalent g⁻¹ (‘Granny Smith’) and 13.20 μmol Trolox equivalent g⁻¹ (‘Silver Spur’). The highest total carotenoid was found in ‘Red Chief’ (147.06 mg kg⁻¹) while in ‘Early Red-I’ the total carotenoid was only 29.03 mg kg⁻¹. HPLC analysis for individual sugars, organic acids and phenolic compounds was carried out. Fructose (average 50.79 g L⁻¹) was the most abundant sugar. Malic acid (average 6.03 mg L⁻¹) predominated among the individual organic acids. Potassium (average 795.14 mg 100 g⁻¹) and iron (average 2.04 µg g⁻¹) were the predominant macro and micro elements, respectively. Chlorogenic acid was the major constituent among phenolic compounds.

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 (D_g) and arithmetic mean diameter (D_a) were calculated using the following equations (Mohsenin 1986):

$$D_g=\sqrt[3]{\mathit{LWT}}$$

$$Da=\left(L+W+T\right)/3$$

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

Cultivar	Fruit weight (g)	Fruit dimension (mm)				Firmness (N)	Colour
		Width	Length	Geometric mean diameter	Arithmetic mean diameter		L*	a*	b*
Non-red cultivars
Golden Delicious	133.40 ± 1.84k	69.71 ± 1.51ih	59.63 ± 0.34g	66.17 ± 0.71hij	66.35 ± 1.22ihj	11.25 ± 0.08edf	68.24 ± 1.10c	− 8.76 ± 0.03n	40.06 ± 0.48c
Granny Smith	175.00 ± 3.07d	73.86 ± 0.80ed	65.76 ± 0.17d	71.05 ± 0.79c	71.16 ± 0.80d	12.69 ± 0.10b	61.72 ± 0.66fe	11.40 ± 0.05o	41.17 ± 0.37b
Winter Banana	131.24 ± 0.21l	68.24 ± 1.08ijk	59.08 ± 0.60g	65.04 ± 1.17ikj	65.19 ± 0.63ikj	14.00 ± 0.24a	74.87 ± 1.09a	− 9.22 ± 0.07n	39.70 ± 0.14c
Goldspur	131.42 ± 1.38lk	70.49 ± 0.78ihg	60.56 ± 0.93feg	67.01 ± 0.76hifgj	67.18 ± 1.17igh	10.90 ± 0.08hgf	69.36 ± 0.94c	− 8.03 ± 0.08m	41.27 ± 0.26b
Starkspur Golden	134.04 ± 2.25k	71.79 ± 0.29ehgf	62.48 ± 0.61fe	68.54 ± 0.73dfge	68.69 ± 0.85eghf	10.53 ± 0.06hi	72.15 ± 0.82b	− 9.21 ± 0.09n	42.66 ± 0.52a
Red cultivars
Royal Delicious	165.32 ± 2.02feg	76.42 ± 0.51cb	68.21 ± 0.82cb	73.58 ± 0.86b	73.68 ± 0.40c	10.72 ± 0.16hgi	54.94 ± 0.06h	15.20 ± 0.13i	26.15 ± 0.07i
Top Red	170.30 ± 2.48d	78.50 ± 0.77b	72.02 ± 0.46a	76.28 ± 0.52a	76.34 ± 1.27ba	12.64 ± 0.05b	49.46 ± 0.39ji	18.24 ± 0.26hg	21.79 ± 0.27kj
Oregon Spur II	202.68 ± 1.23a	81.61 ± 0.15a	69.17 ± 0.68b	77.23 ± 1.27a	77.46 ± 0.24a	11.63 ± 0.13d	45.69 ± 0.81k	21.32 ± 0.21f	18.30 ± 0.16nm
Starkrimson	107.41 ± 1.70n	66.61 ± 0.51jk	51.99 ± 0.54h	61.33 ± 0.56l	61.74 ± 0.55l	10.37 ± 0.15i	54.31 ± 0.75h	15.56 ± 0.29i	22.60 ± 0.17j
Well Spur	168.82 ± 1.99e	72.50 ± 0.25egf	65.57 ± 0.60d	70.11 ± 0.91dce	70.19 ± 1.42edf	12.08 ± 0.22c	55.52 ± 0.06h	11.25 ± 0.06j	27.06 ± 0.45h
Red Chief	145.72 ± 0.84j	73.09 ± 1.69edf	65.39 ± 1.53d	70.43 ± 0.71dc	70.52 ± 0.44ed	12.33 ± 0.18cb	47.89 ± 0.85j	18.00 ± 0.12h	20.79 ± 0.06l
Super Chief	151.06 ± 2.05i	70.93 ± 0.74hgf	62.73 ± 0.48e	68.08 ± 1.31hdfge	68.20 ± 0.26eghf	11.09 ± 0.15egf	45.81 ± 0.13k	22.08 ± 0.27e	17.67 ± 0.25n
Red Gold	159.66 ± 1.30g	73.17 ± 0.95edf	62.29 ± 1.36fe	69.35 ± 0.78dfce	69.54 ± 0.39egdf	10.92 ± 0.17hgf	62.95 ± 1.12e	7.32 ± 0.09k	32.02 ± 0.25f
Royal Gala	195.82 ± 4.10b	72.86 ± 0.72egf	65.49 ± 0.45d	70.32 ± 0.72dc	70.40 ± 1.55ed	11.11 ± 0.01egf	63.19 ± 0.32e	27.45 ± 0.19b	29.83 ± 0.21g
Scarlet Spur-II	163.52 ± 1.43fg	71.25 ± 0.56hgf	62.56 ± 0.49fe	68.23 ± 0.68hdfge	68.35 ± 0.87eghf	11.45 ± 0.13ed	44.33 ± 0.64k	24.39 ± 0.39c	18.89 ± 0.14m
Scarlet Gala	134.96 ± 1.36k	69.77 ± 0.51ih	61.98 ± 0.40fe	67.07 ± 0.72hifg	67.17 ± 0.78igh	10.52 ± 0.23hi	60.87 ± 0.83f	27.94 ± 0.34b	33.42 ± 0.21e
Early Red-I	120.68 ± 1.01m	65.92 ± 0.39lk	62.28 ± 0.25fe	64.68 ± 0.69kj	64.71 ± 0.63kj	11.04 ± 0.13gf	47.89 ± 0.69j	18.00 ± 0.34h	20.79 ± 0.20l
Gale Gala	141.01 ± 2.21k	70.60 ± 1.14ihg	58.53 ± 0.87g	66.32 ± 1.25higj	66.58 ± 1.07ihj	11.46 ± 0.09ed	38.52 ± 0.69m	30.59 ± 0.42a	15.76 ± 0.16o
Spartan	157.35 ± 1.84h	75.40 ± 0.67cd	60.64 ± 0.95feg	70.12 ± 0.52dce	70.48 ± 0.16ed	12.39 ± 0.05cb	65.33 ± 0.51d	− 2.51 ± 0.04l	36.78 ± 0.17d
Vance Delicious	166.48 ± 1.96fe	68.42 ± 0.81ij	66.94 ± 1.38cd	67.92 ± 0.87hfge	67.93 ± 0.68ghf	10.44 ± 0.12i	50.78 ± 0.45i	18.70 ± 0.28g	21.71 ± 0.07k
Silver Spur	185.47 ± 1.91c	80.23 ± 0.70b	70.12 ± 0.76d	76.71 ± 0.60b	76.86 ± 0.26bc	10.32 ± 0.12i	41.8 ± 0.61l	23.55 ± 0.21d	13.79 ± 0.29p
Red Delicious	142.00 ± 2.99k	64.13 ± 0.95l	60.37 ± 0.60fg	62.85 ± 0.52lk	62.88 ± 0.55lk	12.35 ± 0.11cb	58.17 ± 0.63g	11.57 ± 0.19j	30.16 ± 0.66g
Average	154.04 ± 1.11	71.98 ± 0.48	63.14 ± 0.45	68.88 ± 0.48	69.03 ± 0.48	11.47 ± 0.08	56.08 ± 0.41	11.91 ± 0.13	27.83 ± 0.17

Results as mean ± SE of triplicate measurements. Means with same superscript in the same column are not significantly different

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

Cultivar	SSC (°B)	Titratable acidity (% malic acid)	Ascorbic acid (mg 100 g−1)	Total antioxidant (μmole Trolox g−1)	Total carotenoids (mg kg−1)
Non-red cultivars
Golden Delicious	13.50 ± 0.20c	0.54 ± 0.00fe	21.60 ± 0.33h	6.45 ± 0.06h	100.62 ± 0.75d
Granny Smith	12.00 ± 0.08g	0.54 ± 0.00b	20.00 ± 0.17i	2.64 ± 0.02n	32.90 ± 0.11p
Winter Banana	11.00 ± 0.11h	0.67 ± 0.00a	21.39 ± 0.27h	10.57 ± 0.19c	79.34 ± 0.46h
Goldspur	11.00 ± 0.09h	0.54 ± 0.00c	20.19 ± 0.24i	6.64 ± 0.08g	42.57 ± 0.66n
Starkspur Golden	12.50 ± 0.22f	0.67 ± 0.00ba	21.18 ± 0.25h	6.01 ± 0.10ij	44.51 ± 0.15m
Red cultivars
Royal Delicious	13.20 ± 0.17dc	0.27 ± 0.00j	21.18 ± 0.28h	5.56 ± 0.08kl	46.44 ± 0.60l
Top Red	12.70 ± 0.08fe	0.54 ± 0.00e	25.37 ± 0.08ed	7.11 ± 0.03g	90.95 ± 0.91e
Oregon Spur II	12.60 ± 0.02fe	0.47 ± 0.00hi	31.76 ± 0.70a	7.35 ± 0.12e	139.32 ± 1.24b
Starkrimson	12.50 ± 0.12f	0.56 ± 0.00i	32.08 ± 0.38a	5.71 ± 0.06kl	46.44 ± 0.96l
Well Spur	12.50 ± 0.09f	0.59 ± 0.00d	19.38 ± 0.28i	5.97 ± 0.09kj	83.21 ± 0.31g
Red Chief	14.40 ± 0.12b	0.42 ± 0.00k	24.92 ± 0.31e	9.33 ± 0.11d	147.06 ± 0.75a
Super Chief	13.20 ± 0.03dc	0.52 ± 0.00fe	23.77 ± 0.05f	7.27 ± 0.08f	38.70 ± 0.01o
Red Gold	12.50 ± 0.14f	0.27 ± 0.00hi	19.82 ± 0.32i	2.77 ± 0.02m	48.38 ± 0.46k
Royal Gala	14.30 ± 0.03b	0.64 ± 0.00j	26.18 ± 0.32d	5.76 ± 0.07kj	52.25 ± 0.32j
Scarlet Spur-II	11.90 ± 0.04g	0.48 ± 0.00h	22.59 ± 0.43g	6.21 ± 0.09ih	108.36 ± 1.15c
Scarlet Gala	13.20 ± 0.16dc	0.51 ± 0.00l	25.20 ± 0.20e	9.40 ± 0.06c	87.08 ± 0.88f
Early Red-I	11.10 ± 0.01h	0.27 ± 0.00hg	21.60 ± 0.40h	11.58 ± 0.14b	29.03 ± 0.29o
Gale Gala	16.10 ± 0.11a	0.62 ± 0.00m	27.17 ± 0.26c	5.11 ± 0.06l	38.70 ± 0.52o
Spartan	11.90 ± 0.07g	0.27 ± 0.00h	28.80 ± 0.41b	6.69 ± 0.08g	59.99 ± 0.90i
Vance Delicious	12.90 ± 0.16de	0.54 ± 0.00f	28.24 ± 0.29b	6.43 ± 0.07h	79.34 ± 0.36h
Silver Spur	12.10 ± 0.09g	0.47 ± 0.00i	27.09 ± 0.08c	13.20 ± 0.17a	38.70 ± 0.56o
Red Delicious	10.00 ± 0.08i	0.27 ± 0.00g	21.60 ± 0.08h	8.24 ± 0.11e	42.57 ± 0.23n
Average	12.60 ± 0.06	0.39 ± 0.00	24.14 ± 0.18	7.09 ± 0.05	67.11 ± 0.382

Results as mean ± SE of triplicate measurements. Means with same superscript in the same column are not significantly different

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

Cultivar	Sugars			Organic acids
	Glucose	Fructose	Sucrose	Malic acid	Succinic acid	Citric acid	Acetic acid
Non-red cultivars
Golden delicious	9.50 ± 0.11j	49.10 ± 0.41f	26.00 ± 0.18e	6.50 ± 0.03d	0.90 ± 0.01h	–	–
Granny Smith	10.50 ± 0.14h	10.85 ± 0.18k	48.90 ± 0.59a	6.60 ± 0.05d	3.35 ± 0.03b	5.10 ± 0.08b	0.65 ± 0.00a
Winter Banana	10.05 ± 0.08i	52.30 ± 0.40e	14.05 ± 0.09g	8.25 ± 0.06b	1.10 ± 0.01gf	–	–
Goldspur	22.50 ± 0.47b	54.60 ± 0.13d	12.75 ± 0.06g	7.20 ± 0.08c	0.85 ± 0.01ih	–	–
Starkspur Golden	9.85 ± 0.09ij	65.55 ± 1.17b	22.30 ± 0.27f	9.50 ± 0.11a	0.00 ± 0.00l	–	–
Red cultivars
Royal Delicious	17.00 ± 0.15c	48.05 ± 0.41f	9.85 ± 0.10l	5.50 ± 0.06hgi	0.15 ± 0.00k	–	–
Top Red	24.40 ± 0.49g	56.60 ± 0.43c	17.80 ± 0.34ih	6.10 ± 0.04e	1.10 ± 0.02gf	–	–
Oregon Spur II	25.15 ± 0.44ih	58.15 ± 1.06h	17.90 ± 0.16ih	5.90 ± 0.10f	1.45 ± 0.01e	–	–
Starkrimson	21.35 ± 0.26fe	51.40 ± 0.30h	16.75 ± 0.36ihj	5.35 ± 0.08i	1.15 ± 0.01f	–	–
Well Spur	16.80 ± 0.17d	47.85 ± 0.94g	17.15 ± 0.16ihj	5.50 ± 0.06hgi	1.55 ± 0.01d	–	–
Red Chief	20.45 ± 0.17d	57.55 ± 1.09h	24.80 ± 0.31e	5.70 ± 0.03g	1.45 ± 0.02e	–	–
Super Chief	26.70 ± 0.26m	57.05 ± 0.73c	17.05 ± 0.23ihj	4.90 ± 0.04j	1.40 ± 0.02e	–	–
Red Gold	12.50 ± 0.11e	52.20 ± 0.40e	29.90 ± 0.29c	4.40 ± 0.05l	0.55 ± 0.00j	–	–
Royal Gala	16.85 ± 0.09k	52.05 ± 0.52h	19.55 ± 0.17k	5.55 ± 0.06hg	1.40 ± 0.01e	–	–
Scarlet spur-II	20.40 ± 0.12c	48.00 ± 0.41g	23.15 ± 0.27f	4.65 ± 0.06k	1.60 ± 0.02d	–	–
Scarlet Gala	25.90 ± 0.25e	67.55 ± 0.20a	10.95 ± 0.08h	6.05 ± 0.11fe	1.55 ± 0.03d	–	–
Early Red-I	13.00 ± 0.02d	54.30 ± 0.62d	14.10 ± 0.20g	6.10 ± 0.04e	1.05 ± 0.01g	–	–
Gale Gala	11.40 ± 0.12l	51.65 ± 0.87h	23.90 ± 0.17f	5.90 ± 0.02f	0.80 ± 0.00i	–	–
Spartan	10.00 ± 0.15i	48.10 ± 0.34f	14.65 ± 0.09g	6.00 ± 0.07fe	1.85 ± 0.03c	–	–
Vance Delicious	24.50 ± 0.21d	59.90 ± 0.78h	22.20 ± 0.23f	5.40 ± 0.05hi	1.85 ± 0.00c	–	–
Silver Spur	23.25 ± 0.28f	54.85 ± 0.59dc	19.85 ± 0.19k	6.05 ± 0.02fe	1.90 ± 0.00c	–	–
Red Delicious	23.00 ± 0.18a	19.65 ± 0.24j	25.20 ± 0.36d	5.50 ± 0.02hgi	5.10 ± 0.05a	11.00 ± 0.10a	–
Average	17.96 ± 0.13	50.79 ± 0.36	20.40 ± 0.14	6.03 ± 0.03	1.46 ± 0.01	0.73 ± 0.01	0.03 ± 0.00

Results as mean ± SE of triplicate measurements. Means with same superscript in the same column are not significantly different

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

Cultivar	Macro-elements (mg 100 g−1)				Micro-elements (µg g−1)
	Na	K	Ca	Mg	Fe	Zn	Mn	Cu
Non-red cultivars
Golden delicious	54.50 ± 0.59c	936.00 ± 11.00c	15.74 ± 0.14n	17.37 ± 0.34kj	1.27 ± 0.01i	0.51 ± 0.02jk	0.13 ± 0.00k	0.07 ± 0.00p
Granny Smith	11.40 ± 0.14k	674.00 ± 12.26k	14.94 ± 0.24o	21.22 ± 0.32gf	1.10 ± 0.00j	0.77 ± 0.00d	0.12 ± 0.00lm	0.11 ± 0.00i
Winter Banana	16.30 ± 0.18i	550.00 ± 4.39m	18.07 ± 0.17l	17.23 ± 0.21k	0.93 ± 0.02k	0.25 ± 0.00n	0.08 ± 0.00o	0.09 ± 0.01m
Goldspur	9.90 ± 0.11l	1047.00 ± 16.44b	15.94 ± 0.17n	18.13 ± 0.21ij	1.13 ± 0.00j	0.50 ± 0.00k	0.20 ± 0.01d	0.14 ± 0.00e
Starkspur Golden	70.20 ± 0.58a	753.00 ± 8.69ijh	21.01 ± 0.44i	21.82 ± 0.25f	1.12 ± 0.00j	0.61 ± 0.01g	0.15 ± 0.00i	0.13 ± 0.00g
Red cultivars
Royal Delicious	19.30 ± 0.30g	618.00 ± 5.31l	19.94 ± 0.11k	21.41 ± 0.28f	1.26 ± 0.00i	0.86 ± 0.00b	0.16 ± 0.00ih	0.08 ± 0.00n
Top Red	57.00 ± 0.53b	868.00 ± 5.62d	26.39 ± 0.14f	23.86 ± 0.29d	1.55 ± 0.00h	0.82 ± 0.00c	0.13 ± 0.00lk	0.12 ± 0.00h
Oregon Spur II	19.40 ± 0.12g	810.00 ± 4.14e	19.55 ± 0.05k	21.89 ± 0.25f	1.31 ±  0.01i	0.53 ± 0.00ji	0.16 ± 0.00h	0.09 ± 0.00k
Starkrimson	41.20 ± 0.30d	696.00 ± 12.75k	42.21 ± 0.20c	31.12 ± 0.24a	2.56 ± 0.02d	0.80 ± 0.01c	0.28 ± 0.00a	0.09 ± 0.00lk
Well Spur	19.60 ± 0.17g	739.00 ± 7.90j	22.37 ± 0.18h	20.47 ± 0.25g	1.28 ± 0.01i	0.72 ± 0.00e	0.17 ± 0.00g	0.16 ± 0.00c
Red Chief	17.60 ± 0.01h	769.00 ± 3.38igh	17.55 ± 0.17ml	21.23 ± 0.17gf	6.14 ± 0.12a	0.13 ± 0.00o	0.17 ± 0.01g	0.15 ± 0.00d
Super Chief	11.70 ± 0.12k	887.00 ± 12.09d	23.01 ± 0.04g	23.30 ± 0.28ed	1.80 ± 0.02gf	0.54 ± 0.00i	0.14 ± 0.00j	0.11 ± 0.02j
Red Gold	19.80 ± 0.29g	782.00 ± 2.87fg	28.95 ± 0.15e	26.42 ± 0.35c	2.53 ± 0.01d	0.51 ± 0.00jk	0.23 ± 0.00b	0.12 ± 0.00h
Royal Gala	10.30 ± 0.08l	754.00 ± 8.01ijh	55.17 ± 0.25b	15.98 ± 0.14l	1.54 ± 0.00h	0.58 ± 0.00h	0.12 ± 0.00lm	0.09 ± 0.00lm
Scarlet Spur-II	11.30 ± 0.10k	614.00 ± 6.96l	31.98 ± 0.40d	29.54 ± 0.50b	3.52 ± 0.04c	2.00 ± 0.01a	0.22 ± 0.00c	0.18 ± 0.00b
Scarlet Gala	9.70 ± 0.09l	1142.00 ± 19.10a	14.20 ± 0.05p	17.73 ± 0.17kj	1.82 ± 0.00gf	0.66 ± 0.00f	0.11 ± 0.00n	0.09 ± 0.00m
Early Red-I	23.30 ± 0.21f	778.00 ± 10.82fgh	16.99 ± 0.28m	19.46 ± 0.17h	2.31 ± 0.01e	0.65 ± 0.00f	0.14 ± 0.00j	0.22 ± 0.00a
Gale Gala	11.70 ± 0.10k	748.00 ± 1.63ij	21.04 ± 0.21i	17.55 ± 0.25kj	1.87 ± 0.00f	0.51 ± 0.00jk	0.22 ± 0.00c	0.14 ± 0.00f
Spartan	33.10 ± 0.49e	795.00 ± 9.14fe	22.38 ± 0.13h	18.71 ± 0.26ih	1.78 ± 0.02g	0.38 ± 0.00m	0.19 ± 0.00f	0.15 ± 0.00d
Vance Delicious	22.80 ± 0.27f	886.00 ± 4.36d	90.37 ± 0.15a	29.25 ± 0.43b	4.33 ± 0.02b	0.87 ±  0.01b	0.19 ± 0.00e	0.11 ± 0.00i
Silver Spur	18.10 ± 0.24h	872.00 ± 7.75d	21.74 ± 0.07i	23.40 ± 0.24ed	2.33 ± 0.03e	0.40 ± 0.00m	0.12 ± 0.00lm	0.12 ± 0.00i
Red Delicious	13.30 ± 0.10j	775.00 ± 10.56fgh	20.94 ± 0.16i	22.93 ± 0.26e	1.32 ± 0.00i	0.45 ± 0.00l	0.16 ± 0.00ih	0.08 ± 0.00o
Average	23.70 ± 0.16	795.14 ± 5.47	26.39 ± 0.11	21.82 ± 0.16	2.04 ± 0.01	0.64 ± 0.00	0.16 ± 0.00	0.12 ± 0.00

Results as mean ± SE of triplicate measurements. Means with same superscript in the same column are not significantly different

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

Cultivar	Chlorogenic acid	Coumaric acid	Phloridzindihydrate	Rutin	Catechin	3-hydroxy cinnamic acid	Total
Non-red cultivars
Golden delicious	53.29 ± 0.47d	3.58 ± 0.03j	4.72 ± 0.00p	TR	TR	0.53 ± 0.00c	62.11
Granny Smith	3.69±0.06m	2.06±0.02m	22.11±0.12k	TR	TR	TR	27.89
Winter Banana	163.97±1.79a	9.32±0.10a	18.68±0.24l	TR	TR	0.74±0.00a	192.70
Goldspur	8.00±0.10k	1.11±0.01o	2.05±0.00q	0.46±0.00c	TR	TR	11.60
Starkspur Golden	67.76±0.36b	5.11±0.04e	13.23±0.20n	0.30±0.00f	TR	0.66±0.00b	87.06
Red cultivars
Royal Delicious	17.88 ± 0.40h	5.76 ± 0.06c	46.21 ± 0.12c	TR	TR	TR	69.84
Top Red	8.89±0.04k	3.39±0.04k	24.94±0.31j	TR	TR	TR	37.22
Oregon Spur II	7.75±0.09k	9.32±0.01a	30.46±0.40g	TR	TR	TR
Starkrimson	40.48±0.49e	6.08±0.06b	38.39±0.26d	0.50±0.00b	TR	TR	85.45
Well Spur	15.17±0.18i	4.03±0.04	35.23±0.24f	TR	TR	TR	54.43
Red Chief	27.23±0.28f	5.70±0.07c	65.34±0.26b	0.29±0.00g	42.44±0.51b	TR	140.99
Super Chief	15.44±0.02i	3.82±0.04i	35.60±0.40f	0.21±0.00h	TR	TR	55.07
Red Gold	10.34 ± 0.09j	1.01 ± 0.00o	16.85 ± 0.19m	TR	TR	TR
Royal Gala	17.99±0.09h	4.92±0.06f	5.67±0.01o	TR	TR	0.25±0.00e	28.81
Scarlet Spur-II	18.83±0.13h	4.74±0.05g	29.87±0.17hg	0.32±0.00e	TR	0.18±0.00f	53.93
Scarlet Gala	5.44±0.06l	1.90±0.00n	4.40±0.04p	TR	TR	0.11±0.00h	11.85
Early Red-I	7.75±0.09k	3.00±0.03l	37.48±0.46e	0.43±0.00d	45.71±0.70a	TR
Gale Gala	7.74±0.09k	1.99±0.04nm	2.37±0.04q	TR	TR	0.12±0.00g	12.22
Spartan	54.82±0.27c	3.90±0.04ih	26.79±0.13i	0.20±0.00i	TR	TR	85.71
Vance Delicious	22.84±0.54g	5.14±0.05e	29.38±0.35h	0.10±0.00j	TR	TR	57.46
Silver Spur	23.30±0.28g	5.53±0.06d	67.40±0.73a	0.65±0.00a	TR	TR	96.87
Red Delicious	26.68±0.24f	4.79±0.04gf	30.54±0.40g	TR	TR	0.36±0.00d	62.37
Average	28.42±0.26	4.37±0.03	26.71±0.17	0.16±0.00	4.01±0.10	0.13±0.00

Results as mean ± SE of triplicate measurements. Means with same superscript in the same column are not significantly different

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.