Fruit Quality Traits of Six Ancient Apple (Malus domestica Borkh) Cultivars Grown in the Mediterranean Area

ABSTRACT

Today, ancient cultivars have been considered obsolete and replaced, leading to a dramatic loss of genetic diversity. In this trial we examined the quality of the six ancient apple cultivars: Bommino, Gelato, Miliadeci, Rotolari, Turco, and Virchiata. Fruit was submitted to the determination of physicochemical traits and a sensory profile was defined by a trained panel using 20 attributes. We also detected biometric data using a specific descriptor list. Obtained data showed interesting physicochemical and sensory traits among the observed cultivars. ‘Rotolari’, ‘Bommino’, and ‘Gelato’ should be used in breeding programs and revaluated for a placement on specific local markets.

KEYWORDS:

• Malus domestica
• germplasm
• biodiversity
• physicochemical traits
• sensory analysis

Introduction

The apple (Malus domestica Borkh) is a deciduous tree cultivated worldwide, from Northern Europe to the tropics, because it adapts well to different climates (Janick and Moore, 1996; Pereira-Lorenzo et al., 2008). It is considered the most important fruit crop of the Rosaceae family in the world for its diffusion and production (Food and Agriculture Organization of the United Nations, 2011). About 70.9 million tons of apples were grown worldwide in 2014, and China produced almost half of this total, followed by the United States and Turkey (United States Department of Agriculture (USDA), 2015). Apples are mainly used for fresh consumption, while those of minor quality are prepared for canning (Ercisli, 2004). In recent years the apple market in Italy is oriented towards a cultural standardization, through 4–5 apple varietal groups (Farina and Di Marco, 2009); on the other hand, a relaunching of this sector could be possible through the breeding programs using the characteristics of the ancient apple cultivars. In fact, these cultivars are often characterized by interesting traits, such as chemical and mechanical properties (Guiné et al., 2009, 2010), aromatic components (Wang et al., 2007), sensory parameters (Bignami et al., 2003; Farina and Mossad, 2011), nutritive values (Bounous et al., 2006; Guarrera et al., 2008), functional characteristics (Fallahi et al., 2007), disease resistance (Aldwinckle et al., 1999; Kellerhals et al., 2004), and particular adaptations to soil and climate (Du Zhongjun et al., 2002). In Sicily, apple cultivation is very ancient (Nicosia, 1735) and it is witnessed by local genotypes selected for growing fairly remotely. Many of these ancient cultivars are localized as isolated exemplars, in particular in the mountainous inland areas, in family gardens, or intensive orchards, where there is a limited usage of agricultural resources. Many of these, even if they are well adapted, have been considered obsolete and replaced, leading to a dramatic loss of genetic diversity. In Sicily, this is true in the areas of Etna district (Continella et al., 2007; Guarrera et al., 2008) and of Madonie mountains (De Michele, 1992). The preservation of plant genetic diversity has involved the establishment of genetic resource conservation programs (Urrestarazu et al., 2012). The identification of these germplasms is an important strategy to evaluate genetic resources of great value for the local environments (Fideghelli, 2007) and regional traditions (Inglese and Caruso, 2006), and this is crucial for the potentiality of these fruits for market, industrial transformation, and breeding programs. Due to this, valorization and conservation of apple genetic resources were carried out in many countries, such as France (Laurens et al., 2004), Spain (Pereira-Lorenzo et al., 2008), Turkey (Ercisli, 2004), and indeed Italy (Lo Bianco and Farina, 2012).

The aim of this trial was to analyze the qualitative characteristics of six old cultivars of Sicilian germplasm. Both physicochemical parameters and sensory profiles were defined. In fact, fruit attributes were evaluated by a trained panel test and through instrumental measurements due to explain each sensory attribute reducing variations among individuals (Abbott et al., 1984; Harker et al., 2002).

Materials and methods

The trial was conducted in a commercial orchard near Caltavuturo (Palermo) (37° 49ʹ N and 850 m a.s.l.) in central Sicily, Italy. The examined cultivars belonged to the following ancient local cultivars: Bommino, Gelato, Miliadeci, Rotolari, Turco, and Virchiata.

Three 8-year-old trees per each cultivar were selected. Trees were grafted on M9 rootstock and planted in a North–South direction with an inter-trees spacing of 1.5 m and 4 m between rows. Fruits were collected at commercial ripening in the second half of October using starch pattern index as maturity indexes. A 30-fruit sample for each tree (90 fruits per cultivar) was submitted to physicochemical analyses for the determination of fruit weight (FW), longitudinal diameter (LD), transversal diameter (TD), total soluble solids content (SSC), tritatable acidity (TA), SSC/TA ratio, starch state (SS), flesh firmness (FF), ground color index (GCI), and percentage of overcolor (OP).

Digital images were used to determine percentage and intensity of overcolor. In particular, we used an algorithm based on MATHLAB 6.0 (The MathWorks, Inc., Natick, MA, USA) that converts images from RGB to CIE L*a*b* format, extracts the fruit from the image (removing the image background), separates the total fruit area into two sub regions, cover color (closer to red) and ground color (closer to green) according to an adjustable green–red threshold, and quantifies color characteristics of each region as the weighed distance of each pixel in the image from pure green (ground color) or pure red (overcolor). The output is an index for the overcolor ranging from 0 (no red) to 1 (red). Percentage of overcolor was calculated dividing the number of pixels of the red region by the number of pixels of the entire fruit area.

Starch state was analyzed by Lugol’s iodine, compared to reference cards (Eurofru, CTIFL, France) and expressed with a 10-point scale (1 = highest presence of starch; 10 = no starch).

They also detected biometric data using a specific descriptor list adapted from IBPGR (Watkins and Smith, 1982) and UPOV guidelines (International Union for the Protection of New Varieties of Plants, 2005) to discriminate the different cultivars. In particular, the following were evaluated: General shape (GS), ribbing (RI), depth of stalk cavity (DS), width of stalk cavity (WS), depth of eye basin (DB), width of eye basin (WB), length of stalk (LS), thickness of stalk (TS), skin color (SC), hue overcolor (HO), overcolor tipology (OT), and flesh color (FC).

The sensory profile (UNI 10957, 2003) was defined on a subsample of 10 fruits per tree per cultivar by a panel of 10 judges (5 female and 5 male) that were trained to recognize the qualitative that would be assessed. All panelists were trained at Catania University and have a wide expertise in sensory evaluation of foods and, in particular, in fruits (Farina et al., 2011; Guarrasi et al., 2011; Liguori et al., 2014). In a preliminary meeting, 20 attributes were generated on the basis of frequency of citation (>60%), as listed below: one for appearance (color uniformity), six for odor (apple, vegetal, honey, fruit, almond, off), three for tastes (acid, sweet, bitter), four for rheological (juiciness, consistency, crunchiness, doughness), six for flavor (apple, vegetal, honey, fruit, almond, off). The evaluations were carried out from 10:00 to 12:00 am in individual booths with controlled illumination and temperature. The study was carried out during three different sessions; samples were evaluated in triplicate. In each session, panelists tested all cultivars under study; the sample order for each panelist was randomized and water was provided for rinsing between apple samples. The judges evaluated the intensity of each attribute by assigning a score between 1 (absence of the sensation) and 9 (extremely intense). A computerized data collection program was used (FIZZ, Software Solutions for Sensory Analysis and Consumer Tests, Biosystemes, Couternon, France).

The physicochemical and sensory data were tested for differences between the cultivars using the one-way analysis of variance (ANOVA; general linear model) using SYSTAT procedures. The differences between cultivars were tested with Tukey’s high significance difference (HSD) test at the 0.05 significance level.

Results and discussions

The analysis of pomological traits showed a wide variability (Tables 1 and 2). Commercial size is variable with interesting values in ‘Miliadeci’, ‘Turco’, and ‘Bommino’, whereas the smallest fruit were observed for ‘Gelato’, ‘Rotolari’, and ‘Virchiata’. FF was adequate for all cultivars, but Turco, Bommino, and Gelato showed the lowest values. This indicates the difficulties to introduce these cultivars on the GDO market. Bommino exhibited the highest values of GCI, followed by Rotolari; whereas the cultivars, Gelato and Miliadeci, showed the lowest values. ‘Gelato’ and ‘Miliadeci’ have no cover color while ‘Turco’ has the highest value. The higher values of SSC/TA ratio were observed in ‘Rotolari’ followed by ‘Bommino’ and ‘Gelato’. ‘Turco’, ‘Virchiata’, and ‘Miliadeci’, although they had an adequate SSC, had the highest TA.

Table 1. Pomological traits of the six apple cultivars in the trial.

Cultivar	FW^z (g)	LD (mm)	TD (mm)	LD/TD	FF (kg/cm^2)	GCI	OP (%)
Bommino	150.6b^y	74.6a	57.6b	1.3a	7.0c	0.970a	91.7b
Gelato	132.3c	68.4b	54.5b	1.2a	9.9a	0.877d	—
Miliadeci	201.5a	76.1a	65.3a	1.2a	6.5d	0.851d	—
Rotolari	112.5d	64.4b	55.7b	1.2a	9.3a	0.949b	44.6d
Turco	168.7b	75.0a	62.1a	1.2a	7.1c	0.928c	96.8a
Virchiata	77.49e	57.7c	46.5c	1.2a	8.0b	0.938bc	72.5c

^zAbbreviations: FW, fruit weight; LD, longitudinal diameter; TD, transversal diameter; FF, flesh firmness; GCI, ground color index; CP, percentage of over color.

^yThe values marked with different letters in the same column indicate significant differences (p ≤ 0.05).

Table 2. Physicochemical parameters of the six apple cultivars in the trial.

Cultivar	TA^z (g l^–1 malic acid)	SSC (°brix)	SSC/TA	SS
Bommino	11.50c^y	14.4b	1.2b	7
Gelato	10.77c	14.3b	1.3b	7
Miliadeci	14.23b	12.8c	0.9c	7
Rotolari	10.06c	16.0a	1.6a	7
Turco	22.10a	16.6a	0.8c	7
Virchiata	22.10a	12.3c	0.5d	7

^zAbbreviations: TA, tritatable acidity; SSC, total soluble solids content; SS, starch state.

^yThe values marked with different letters in the same column indicate significant differences (p ≤ 0.05).

Legal standards for the edible quality of apples have been in place in many apple-growing regions of the world (Harker et al., 2008) through a numerical lower limit for commercial size, diameter or fruit weight (Reg. CE n.85/2004), soluble solids or starch content (WSDA, 1999), or descriptive standards (Grange, 1976). About this, ‘Virchiata’ produced very small fruits that did not reach the standard for the fresh market (Dalpiaz et al., 2005) because they showed an inferior size in respect to the second commercial size for apple fruit (Reg. CE n.85/2004). The other cultivars have the size characteristics of the most diffused commercial apple varietal groups.

The descriptor list indicates a great variability among the cultivars (Table 3). The GS genotypes showed a variability of fruit features that varied from globose to rounded and only in one case cylindrical or conical. RI was absent because the diameter was circular for all cultivars except for Gelato and Rotolari, which were moderate. Four cultivars presented medium DS (Bommino, Gelato, Miliadeci, and Turco), while two cultivars (Rotolari and Virchiata) presented high DS. Most cultivars showed medium WS except for Rotolari (narrow) and Virchiata (broad). The same traits were observed for the DB that was medium for most cultivars except for Miliadeci and Virchiata (shallow), whereas the WB was medium for four cultivars (Bommino, Gelato, Miliadeci, and Turco), broad for Virchiata and narrow for Rotolari. LS was short for three cultivars (Gelato, Rotolari, and Virchiata), long for Turco, and medium for Bommino and Miliadeci. Four cultivars had a TS (Gelato, Miliadeci, Rotolari, and Turco), whereas one (Bommino) short and Virchiata thin. SC is green in two cultivars (Miliadeci and Rotolari) and green-yellow in Bommino, Gelato, Turco, and Virchiata. HO is absent in ‘Gelato’ and ‘Miliadeci’, red in ‘Virchiata’, red-brown in ‘Bommino’ and ‘Turco’, and red-orange in ‘Rotolari’. OT is uniform in ‘Rotolari’ and ‘Turco’, absent in ‘Gelato’ and ‘Miliadeci’, while in ‘Bommino’ is little strips and in ‘Virchiata’ is large strips. FC is green in three cultivars (Gelato, Miliadeci, and Turco) and white in the others.

Table 3. Biometric traits of the six apple cultivars in the trial.

Cultivar	GS^z	RI	DS	WS	DB	WB	LS	TS	SC	HC	CT	FC
Bommino	Rounded	Absent	Medium	Medium	Medium	Medium	Medium	Short	Green-yellow	Red-brown	Little strips	Green
Gelato	Cylindrical	Moderate	Medium	Medium	Medium	Medium	Short	Medium	Green-yellow	Absent	Absent	White
Miliadeci	Globose	Absent	Medium	Medium	Shallow	Medium	Medium	Medium	Green	Absent	Absent	White
Rotolari	Conical	Moderate	High	Narrow	Medium	Narrow	Short	Medium	Green	Red-orange	Uniform	Green
Turco	Globose	Absent	Medium	Medium	Medium	Medium	Long	Medium	Green-yellow	Red-brown	Uniform	White
Virchiata	Globose	Absent	High	Broad	Shallow	Broad	Short	Thin	Green-yellow	Red	Large strips	Green

^zAbbreviations: GS, general shape; RI, ribbing; DS, depth of stalk cavity; WS, width of stalk cavity; DB, depth of eye basin; WB, width of eye basin; LS, length of stalk; TS, thickness of stalk; SC, skin color; HO, hue overcolor; OT, overcolor tipology; FC, flesh color.

Regarding the results of the sensory analysis (Table 4), the observed cultivars differ significantly only for the descriptors: Color uniformity, Apple odor, Almond odor, Acid, Sweet, Consistency, and Honey flavor. In particular, Color uniformity ranged from 3.5 for ‘Virchiata’ to 7.0 for ‘Gelato’.

Table 4. Sensory profiles of the six observed apple cultivars as evaluated by a trained panel.

Descriptors	Bommino	Gelato	Miliadeci	Rotolari	Turco	Virchiata
Color uniformity	5.1cb^z	7.0a	6.4ab	4.9bc	6.0ab	3.5c
Apple odor	5.3abc	6.7a	4.7c	4.8bc	6.3ab	4.9bc
Vegetal odor	3.9	5.7	4.7	5.2	4.5	5.1
Honey odor	3.2	4.1	3.1	4.7	3.8	2.4
Fruit odor	4.2	4.1	3.4	4.4	4.5	4.0
Almond odor	1.9c	3.8ab	2.1c	3.9a	2.7abc	2.2bc
Off odor	2.7	1.4	2.1	2.1	1.9	1.9
Acid	2.5bc	2.6bc	4.2a	1.7c	3.6ab	4.8a
Sweet	6.0a	6.3a	3.8c	6.5a	5.7ab	4.1bc
Bitter	1.7	2.5	3.0	2.2	2.2	2.8
Consistency	4.6bc	5.6abc	6.6a	4.9bc	4.2c	6.1ab
Crunchiness	5.4	5.9	6.5	5.3	5.6	6.1
Sponginess	3.8	4.1	4.3	4.7	4.7	3.1
Juiciness	4.5	4.9	3.5	5.0	5.9	4.0
Apple flavor	5.4	6.3	5.0	4.7	6.3	4.6
Vegetal flavor	3.4	4.1	4.1	4.0	3.4	4.7
Honey flavor	4.0ab	4.2b	2.2bc	4.9a	3.1abc	2.0c
Fruits flavor	3.3	4.1	3.5	4.3	3.4	3.8
Almond flavor	2.6	2.9	2.1	3.2	2.6	1.9
Off flavor	2.4	1.4	2.4	2.0	2.0	2.6

^zThe values marked with different letters in the same column indicate significant differences (p ≤ 0.05).

The mean scores show that the descriptor Apple odor samples ‘Gelato’ and ‘Turco’ have the greater intensity, while ‘Miliadeci’ has the lower intensity.

The judges expressed a low result of Almond odor for ‘Bommino’ and ‘Miliadeci’, whereas a high value for ‘Gelato’ and ‘Rotolari’. On the other hand, this last cultivar reached the highest value of Consistency. For the descriptor Acid, ‘Miliadeci’ and ‘Virchiata’ had the greater intensity, but on the other hand, they had the lesser intensity of the descriptor Sweet.

The cultivars Miliadeci and Virchiata have the highest value of the descriptor Consistency while Turco has the lower intensity. Rotolari has the highest intensity of the descriptor Honey flavor, while the cultivar Virchiata has the lowest intensity.

Conclusions

Instrumental and sensory analysis allowed to characterize the six different cultivars and to assess the overall quality of the fruits. Obtained data showed a large variability of physicochemical and sensory data among the observed cultivars. In conclusion, Rotolari, Bommino, and Gelato were the cultivars with the best physicochemical characteristics and the highest sensory appeal. They showed an interesting balance between soluble solids and acidity and also a good perception of odor and flavor descriptors. There should be a re-evaluation of these fruits for placement on specific local markets. At the same time, these cultivars showed interesting traits and they could be used in breeding programs. A conservation and evaluation activity of these ancient cultivars’ ecotypes could conserve the regional biodiversity and implement the consumer needs that are oriented towards local products.