Impact of Shelf Life on Content of
Primary and Secondary Metabolites in Apple
(Malus domestica Borkh.)
Robert Veberic, Valentina Schmitzer, Maja M. Petkovsek, and Franci Stampar
Abstract: In this study, we evaluated the changes in apple fruit quality during shelf life. After a month of cold storage,
apples of cultivars “Jonagold” and “Golden Delicious” were exposed to ambient temperatures for 21 d, with subsequent
sampling every 3 or 4 d. Fruit firmness, changes in amounts of sugars, malic acid, and phenolics were observed during
shelf life. Chemical analyses were done with HPLC-PDA system. An interchange between various sugars was noticed, but
in general, the sum of sugars remained at the same level. The content of malic acid remained stable or dropped, resulting
in sweeter fruit. Levels of phenolics were more constant in the pulp of both cultivars analyzed, while in the peel, the
changes were more pronounced. In the pulp, a peak in the content of hydroxycinnamic acids and flavanols was noticed
on the 2nd or 3rd sampling and afterwards, the amounts remained constant. In the peel an initial decrease of all analyzed
phenolic groups was observed in both cultivars, however it was more pronounced in “Jonagold.” It can be concluded that
changes in primary and secondary metabolites are not the main reason for the lower quality of fruit exposed to ambient
temperatures. On the other hand, fruit firmness might be the limiting factor for shelf life duration.
Keywords: color, firmness, organic acids, phenolics, sugars
Practical Application: In our study, we were able to show that various quality parameters react uniquely to exposure to
Introduction
The attractiveness of fruit to consumers is determined by visual attributes that include appearance, size, uniformity, color, and
freshness, as well as nonvisual attributes such as taste, aroma, flavor, firmness (texture), nutritional and health value. Among these
attributes, firmness and aroma appear to be the most important
for consumers (Awad and de Jager 2002).
Apart from vitamins and minerals, apples also contain other
phytochemicals, which are the important constituents of the fruit.
The group of phenolics has been a particular focus of several studies
in recent years. Consumers are becoming more interested in the
content of these health-promoting compounds in fruit because of
their antioxidant activity (Gil and others 2002). The importance
of consuming whole fruit, including apple peel, has also been
underlined because in general, the content of phenolics in the peel
can be several times higher than that in pulp of the fruit (Mikulic
Petkovsek and others 2007; Lata and others 2009). The reason
for this involves high quantities of certain groups of flavanoids,
like flavonol glycosides, catechins, and chlorogenic acid (Escarpa
and Gonzalez 1998). In particular, phenolics in apple skin have
shown a much higher contribution to the total antioxidant and
antiproliferative activities of the whole apple than those in apple
MS 20100463 Submitted 4/28/2010, Accepted 8/1/2010. Authors are with Dept. pulp (Wolfe and others 2003).
of Agronomy, Biotechnical Faculty, Univ. of Ljubljana, Chair for Fruit, Wine and
Several studies have dealt with the evaluation of changes in
Vegetable Growing, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia. Direct inquiries
fruit
composition during short- or long-term storage. Patterns
to author Veberic (E-mail: [email protected]).
of change in the content of organic acids, carbohydrates, and
On European as well as world fruit markets, apples represent an
important produce available year around. This is possible owing to
the different ripening periods in the northern and southern hemispheres as well as to excellent apple storability and sophisticated
storage conditions. During storage at reduced oxygen concentrations and low-temperature conditions, the general appearance
of stored apples can be maintained for a long period of time
(Brackmann and others 1994). It is well known that during inappropriate storage, apples can lose some of their quality as a result
of metabolic degradation, respiration, and synthesis processes. The
storage regimes and storage time have been optimized for minimal
losses due to physiological disorders and maximum retention of
firmness, juiciness, and sweetness (Varela and others 2008). Particularly at higher temperatures, such as those in supermarkets and
ambient temperatures in consumers’ homes, internal and external
fruit quality might be affected by the changed conditions (Matthes
and Schmitz-Eiberger 2009).
R
2010 Institute of Food Technologists
doi: 10.1111/j.1750-3841.2010.01823.x
C
Further reproduction without permission is prohibited
Vol. 75, Nr. 9, 2010 r Journal of Food Science S461
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ambient temperatures. The most dramatic change was noticed in fruit firmness, which might be the limiting factor for
the practical duration of shelf life. On the other hand phenolics, as the health-beneficial constituents in the flesh and peel
of apples, did not change dramatically during shelf life. This information is important for nutritionists as well as for the
consumers and specialists in fruit storage and handling.
Shelf life and apple quality . . .
phenolics during storage are variable. Roth and others (2007)
reported that the sucrose content in apples decreased during storage, while glucose and sorbitol contents increased. Piretti and
others (1994) found that epicatechin, quercetin glycosides, and
procyanidins in “Granny Smith” generally decreased during storage. Similar results were reported for “Boskoop” apples, where
a decrease in the content of catechin, epicatechin, and phenolic
acids was observed (Mosel and Herrmann 1974). In contrast, some
researchers found that the content of phenolics increased during
storage (Burda and others 1990; Napolitano and others 2004). The
majority of researchers, however, reported that no change in the
content of simple phenolics (mainly chlorogenic acid), flavonoids,
and anthocyanins occurred during storage (Awad and de Jager
2000; Golding and others 2001).
Even though many studies have been performed during storage,
little information is available about the changes in fruit quality
during shelf life. In available literature, the impact of shelf life was
mostly followed up to 2 wk and only few quality parameters were
considered. After storage, apples are normally kept in stores until
they are sold, and then for some additional time they are left at
ambient temperatures in consumers’ homes. The changes—not
only in firmness and sugars and organic acids content but also
in wide range of phenolics—could be of great importance for
consumers, particularly if the health benefits of fruit are affected.
Such an approach will provide additional knowledge about the
changes in fruit quality after cold storage, and the data could be of
use for a variety of nutritional studies.
Materials and Methods
nates. In this system of color representation, the L ∗ value corresponds to a dark-bright scale and represents the relative lightness
of colors with a range from 0 to 100 (0 = black, 100 = white).
The a∗ and b∗ scales extend from −60 to 60, where a∗ is negative
for green and positive for red and b∗ is negative for blue and positive for yellow. The hue angle (h◦ ) is expressed in degrees from
0 to 360, where 0 = red, 90 = yellow, 180 = green, and 270 =
blue.
S: Sensory & Food
Quality
Extraction and determination of sugars and organic acids
Primary metabolites (sucrose, glucose, fructose, sorbitol, and
malic acid) were analyzed from the whole edible part of the fruit.
For each cultivar, five repetitions per sampling date were carried
out (n = 5); each repetition included one fruit. Ten grams of fruit
for extraction were homogenized in 50 mL of bi-distilled water
using Ultra-Turrax T-25 (Ika-Labortechnik, Staufen, Germany)
and left for 30 min at room temperature. After extraction, the homogenate was centrifuged (Eppendorf 5810 R Centrifuge, Hamburg, Germany) at 12000 rpm for 7 min at 10 ◦ C. The supernatant
was filtered through a 0.45-mm cellulose ester filter (MachereyNagel, Düren, Germany), transferred into a vial, and 20 μL of
the sample was used for analysis. The analysis of sugar (fructose,
glucose, sucrose, and sorbitol) and malic acid content was carried
out using high-performance liquid chromatography (HPLC) from
Thermo Separation Products equipment. The separation of sugars
and sorbitol was carried out using a Rezex RCM-monosaccharide
column (300 × 7.8 mm; Phenomenex, Torrance, Calif., U.S.A.)
operated at 65 ◦ C from Phenomenex. The mobile phase was bidistilled water, and the flow rate was 0.6 mL/min; the total run
time was 35 min, and a refractive index detector was used to
monitor the eluted carbohydrates as described by Dolenc-Sturm
and others (1999). Organic acids were analyzed with HPLC using
an Aminex HPX-87H column (300 × 7.8 mm; Bio-Rad, Hercules, Calif., U.S.A.) associated with a UV detector set at 210 nm
as described by Dolenc-Sturm and others (1999). The column
temperature was set at 65 ◦ C. The elution solvent was 4 mM sulphuric acid in bi-distilled water at a flow rate of 0.6 mL/min. The
duration of the analysis was 30 min.
Plant material
This experiment was carried out in 2008. For the experiment,
fruits of “Golden Delicious” and “Jonagold” were taken from controlled atmosphere cool storage after 1 mo of storage. Fruit samples were exposed to ambient temperatures to mimic conditions
in stores and in consumers’ homes. The fruits were subsequently
sampled every 3rd or 4th day after exposure to ambient temperatures of 22 ◦ C (Table 1). At each sampling date, five fruit samples
were taken for analysis. Fruit firmness was measured, and the tissue
was frozen in liquid nitrogen and stored at −20 ◦ C for subsequent Extraction and determination of phenolic compounds
extraction and analysis of sugars, organic acids, and phenolics.
The apples were peeled with a mechanical peeler, and the peel
was separated from the pulp. The extraction of samples (peel and
Firmness and color measurement
pulp separately) was made as described by Escarpa and Gonzalez
The measurement of fruit firmness (Chatillon penetrometer (2000). The samples of 10 g of pulp and 5 g of peel were extracted
equipped with 11 mm probe) and skin color (in the case of with methanol containing 1% of 2.6-di-tert-butyl-4-methylphenol
“Golden Delicious”) was done immediately after sampling. Five (BHT) in a cooled water bath using sonification. BHT was added
fruit samples of each cultivar were used for measurements. Apple to the samples to prevent oxidation during the extraction. The
color was measured using the Minolta CR-10 Chroma portable samples were extracted with 10 mL of solvents for 1 h, 10 mL
colorimeter (Konica Minolta, Osaka, Japan) with C illuminant. for 30 min, and then 5 mL for 30 min. The extracts were then
Fruit chromaticity was recorded in Commission Internationale combined to a final volume of 25 mL. After centrifuging at 10000
d’Eclairage (CIE) parameters L ∗ , a∗ , and b∗ color space coordi- rpm for 10 min at 4 ◦ C, the supernatants were filtered through
a 0.45 mm membrane filter (Macherey-Nagel), prior to injection
into the HPLC. The phenolic compounds were analyzed on a
Table 1–Sampling dates and corresponding days of shelf life.
Shelf life (days after exposure to Thermo Finnigan Surveyor HPLC system, using a diode array
detector at 280, 350, and 530 nm. The hydroxycinnamic acids
Sampling
Dates
ambient temperatures)
(chlorogenic and caffeic acids) and the monomeric flavanols (cat1st
26 Nov
0
echin, epicatechin) were detected at 280 nm, while the flavonols
2nd
30 Nov
4
(quercetin rutinoside, quercetin rhamnoside, quercetin glucoside,
3rd
3 Dec
7
4th
6 Dec
10
and quercetin galactoside) were estimated at 350 nm and cyani5th
10 Dec
14
din galactoside at 530 nm. The spectra of the compounds were
6th
13 Dec
17
also recorded between 200 and 600 nm. The column used was a
7th
17 Dec
21
Phenomenex Gemini C18 (150 × 4.6 mm 3 μm; Phenomenex)
S462 Journal of Food Science r Vol. 75, Nr. 9, 2010
Shelf life and apple quality . . .
Chemicals
Malic acid was purchased from Merck (Darmstadt, Germany).
Fructose, glucose, sucrose, sorbitol, and acid were obtained
from Fluka (Buchs, Switzerland). For determining the phenolic
peaks, standards acquired from Sigma-Aldrich (Steinheim, Germany) (rutin, chlorogenic acid), Roth (Karlsruhe, Germany) ((+)catechin), and Fluka ((−)-epicatechin, quercetin-3-rhamnoside,
quercetin-3-galactoside, quercetin-3-glucoside, caffeic acid) were
used; and methanol was acquired from Sigma-Aldrich. Water was
bi-distilled and purified with the Milli-Q system (Millipore, Bedford, Mass., U.S.A.).
Statistic analysis
The data were analyzed with the Statgraphics Plus 4.0 program
(Statgraphics, Herndon, Va., U.S.A.) using one-way analysis of
variance. The differences between sampling dates for an individual
cultivar were tested using the Duncan test at the 0.05 significance
level. The means and the standard errors of the means are also
reported.
Results and Discussion
Fruit firmness and color measurement
Instrumental measurements of fruit firmness and texture have
become important tools of fruit quality assessment. In these tests,
a penetrometer is the most widely used device to assess fruit firmness. In our research, “Golden Delicious” showed higher values in
fruit firmness than “Jonagold” (Table 2). In both cultivars, firmness decreased during shelf life, resulting in softer and mealier fruit
at the end of the trial.
For a high-sensory estimation by the consumer, the firmness of
“Golden Delicious” fruit should not be lower than 5.5 kg cm−2
at the time of consumption (Lafer 2006). In our research, this was
the case at the 1st three sampling dates. Later, the firmness of the
fruit decreased to 4.75 kg cm−2 .
Konopacka and others (2007) reported that in panel testing
of cultivars, “Jonagold” scored very low when the fruit firmness
was below 4 kg cm−2 . In our case, firmness above this value was
maintained only at the 1st two sampling dates. We assume that
beyond this date, the fruit would be less acceptable to consumers.
Consumers worry that “old,” stored apples get “mealy” if kept
at home, which in many cases is true, since apple texture can
deteriorate during cold storage, resulting in softness and mealiness. Varela and others (2008) studied consumer acceptability, and
descriptive sensory analyses for storage periods of up to 28 d at
20 ◦ C indicated that the greatest quality loss in stored “Fuji” apples
was associated with increased mealiness, a perceived overripe taste,
and an alcoholic taste and odor.
Color measurements were done only on “Golden Delicious”
apples (Table 2). The main purpose of these measurements was
to monitor the changes from green ground color to yellow as a
result of chlorophyll degradation. This was not done on “Jonagold” apples, since the major part of the fruit was covered with
red blush, and any changes in the green ground color would be influenced by the red blush. In the case of “Jonagold,” we measured
anthocyanins, which are causing the red blush of apples.
As expected, the color parameters (L ∗ , a∗ , b∗ ) increased during
shelf life, indicating degradation of chlorophyll and exposure of
yellow pigments. L ∗ increased from 66.4 at the exposure to 69.1
indicating lighter hues in the fruit. a∗ increased from −1.8 to
8.5, where negative values represent green and positive red. b∗
increased from 44.3 to 54.8, where higher values represent yellow
coloration. Owing to high b∗ values, apples had a bright yellow
coloration. Similar data for “Golden Delicious” were also reported
by Rutkowski and others (2008). Intensification of the yellow
coloration can also be seen from the hue value, which represents
the best predictor of sensory color perception. A hue angle with
a value of 90 indicates a yellow coloration, while 0 means red
coloration. In our case, the values decreased from 92.2 to 81.4,
indicating that yellow coloration intensified with shelf life.
Sugars, sorbitol, and malic acid
Regarding the amount of sugars analyzed, “Golden Delicious”
as a typical sweet apple cultivar, showed high amounts, while
“Jonagold,” as a less sweet-tasting apple, contained slightly less total
sugars (Figure 1). In 21 d after exposure to ambient temperatures,
the total content of sugar showed no considerable change between
sampling dates. Only limited data are available about the changes in
sugar content during prolonged shelf life of apples. In the study by
Mikulic Petkovsek and others (2009), the content of total sugars
changed only slightly during storage time. Similarly, Suni and
others (2000) reported that storage had only a minor effect on the
average content of sugars and acids in apple fruit.
If individual sugars are considered, more changes during shelf
life in both cultivars can be noticed. Regarding the content of
sucrose (Figure 2), an increase between the 1st and the 2nd
Table 2– Changes in colorimetric parameters of “Golden Delicious” apple peel and changes in fruit firmness for both cultivars
during shelf life (numbers 1 to 7 represent sampling dates). Average values ± standard errors are presented. Different letters in
columns denote statistically significant differences between sampling dates at P ≤ 0.05.
Date
1
2
3
4
5
6
7
a
L∗
66.42 ± 0.52
68.53 ± 0.57
70.75 ± 0.56
70.57 ± 0.51
71.35 ± 0.47
70.62 ± 0.62
69.10 ± 1.04
a∗
a
a
bc
bc
c
bc
ab
−1.79 ± 0.65
−1.42 ± 0.56
1.60 ± 0.81
4.26 ± 0.88
7.35 ± 0.56
9.22 ± 0.95
8.45 ± 1.21
b∗
a
a
b
c
d
d
d
44.30 ± 0.67
45.24 ± 0.56
48.09 ± 0.74
51.76 ± 0.50
52.93 ± 0.64
55.29 ± 0.66
54.80 ± 1.23
Fruit firmnessa
“Jonagold”
h◦
a
a
b
c
cd
e
de
92.16 ± 0.91
91.83 ± 0.72
88.21 ± 0.94
85.38 ± 0.95
82.63 ± 0.65
81.35 ± 0.59
81.35 ± 1.07
d
d
c
b
a
a
a
4.43 ± 0.17
4.22 ± 0.23
3.85 ± 0.13
3.53 ± 0.09
3.37 ± 0.11
3.67 ± 0.15
2.95 ± 0.18
d
cd
bc
b
ab
b
a
Fruit firmnessa
“Golden
Delicious”
5.68 ± 0.21
5.83 ± 0.15
5.45 ± 0.13
4.98 ± 0.13
5.23 ± 0.23
4.92 ± 0.22
4.75 ± 0.32
c
c
bc
ab
abc
ab
a
Firmness is expressed in kg/cm2 .
Vol. 75, Nr. 9, 2010 r Journal of Food Science S463
S: Sensory & Food
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operated at 25 ◦ C. The elution solvents were 1% formic acid in
bi-distilled water (A) and 100% acetonitrile (B). The samples were
eluted according to the linear gradient described by Marks and
others (2007), with an injection amount of 20 μL and a flow
rate 1 mL/min. The phenolics were identified by comparing their
UV–Vis spectra and retention times. Quantification was achieved
according to concentrations of the corresponding standard. The
concentrations were expressed in milligram per kilogram of fresh
weight.
Shelf life and apple quality . . .
Figure 1–Changes in the sum of total sugars during
shelf life (numbers 1 to 7 represent sampling
dates) expressed in g kg−1 FW. Average and
standard error are presented. JG = “Jonagold,”
GD = “Golden Delicious.” Different letters denote
statistically significant differences between
sampling dates for individual cultivars at P ≤ 0.05.
Figure 2–Changes of sucrose content during shelf
life (numbers 1 to 7 represent sampling dates)
expressed in g kg−1 FW. Average and standard
errors are presented. JG = “Jonagold,” GD =
“Golden Delicious.” Different letters denote
statistically significant differences between
sampling dates for individual cultivars at P ≤ 0.05.
S: Sensory & Food
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Figure 3–Changes of glucose content during shelf
life (numbers 1 to 7 represent sampling dates)
expressed in g kg−1 FW. Average and standard
errors are presented. JG = “Jonagold,” GD =
“Golden Delicious.” Different letters denote
statistically significant differences between
sampling dates for individual cultivars at P ≤ 0.05.
S464 Journal of Food Science r Vol. 75, Nr. 9, 2010
Shelf life and apple quality . . .
also reported by Ackermann and others (1992) and Roth and
others (2007). The sugar with the highest content in apple fruit
was fructose (Figure 4). If only the 1st and the last sampling dates
are compared, there were no significant changes in its content in
the case of “Jonagold.” On the other hand, “Golden Delicious”
showed some increase in the fructose content after 21 d at room
temperature. The improvement in the content was about 18%.
However, oscillations were present in the content in both cultivars
during shelf life, probably owing to metabolic activity in the fruit.
Similarly, Mikulic Petkovsek and others (2009) noticed an increase
in the fructose content in the “Golden Delicious” cultivar, while
in many other cultivars in their study this was not the case. The
content of sorbitol, a sugar alcohol, decreased during shelf life; and
again an increase at the end was measured. However, the difference between 1st and last sampling dates was insignificant in both
cultivars (data not shown). Since sorbitol represents only a small
part of the total sugar content, the oscillations in its quantity are
of lesser importance.
Malic acid is the main acid in apple fruit and has an important influence on the sour taste of apples. In cultivars with low
Figure 4–Changes of fructose content during
shelf life (numbers 1 to 7 represent sampling
dates) expressed in g kg−1 FW. Average and
standard errors are presented. JG = “Jonagold,”
GD = “Golden Delicious.” Different letters
denote statistically significant differences
between sampling dates for individual cultivars
at P ≤ 0.05.
S: Sensory & Food
Quality
sampling dates can be observed, while a steady decrease during
the remaining shelf life can be seen. This was noticed for both
cultivars. Twenty-one days after exposure, “Jonagold” had about
40% less sucrose and “Golden Delicious” about 25% less sucrose
compared to the 1st sampling date. The rise in the amount of
sucrose on the 4th day after exposure to ambient conditions was
probably the result of starch degradation, although starch content
was not measured. As fruit ripen, starch is degraded and sugar content increases, providing the sweetness associated with changing
fruit taste (Blanco and others 1992). Thammawong and Arakawa
(2007) studied the degradation of starch in two apple cultivars and
noticed that starch degradation after harvest seems highly related
to climacteric and physiological changes in fruit, such as increased
ethylene production and respiration rate. Even more starch degradation related is glucose, the content of which generally rises in
both cultivars during the shelf life of fruit (Figure 3). When the
changes between 1st and last sampling dates are considered, glucose content increased by 18% and 47% in “Golden Delicious”
and “Jonagold,” respectively. An increase in glucose content in
the fruits of “Elstar” and “Jonagold” cultivars during storage was
Figure 5–Changes in malic acid content during
shelf life (numbers 1 to 7 represent sampling
dates) expressed in g kg−1 FW. Average and
standard error are presented. JG = “Jonagold,”
GD = “Golden Delicious.” Different letters
denote statistically significant differences
between sampling dates for individual cultivars
at P ≤ 0.05.
Vol. 75, Nr. 9, 2010 r Journal of Food Science S465
Shelf life and apple quality . . .
amounts of malic acid, the sweet taste becomes predominant. In
the case of the “Jonagold” cultivar, the content of malic acid decreased between the 1st and last sampling dates; meanwhile, in
“Golden Delicious” the 1st and last sampling dates exhibited similar amounts of malic acid (Figure 5). In both cases, a slight increase
with a maximum on the 3rd or 4th sampling dates was noticed. In
studies by Ackermann and others (1992), Roth and others (2007),
and Mikulic Petkovsek and others (2009), the content of malic
acids decreased during storage. Malic acid is the main substrate for
respiration; therefore, its content decreases during storage, particularly when high-oxygen content is present (Roth and others
2007).
Phenolic compounds
Hydroxycinnamic acids. In this group, the content of the
chlorogenic and caffeic acids was analyzed. Their sum is shown
in Figure 6. Approximately 85% is represented by the content of
chlorogenic acid, which is a caffeic acid derivate. It is interesting
that, contrary to other phenolics, the content of chlorogenic acid
is high in peel as well as in pulp. This was already demonstrated in
previous research (Veberic and others 2005). Regarding changes
in content during shelf life, the analyzed hydroxycinnamic acids in
pulp showed a peak at the 2nd sampling date, and after that a more
or less constant amount till the end of shelf life was recorded. Awad
and de Jager (2000) reported a constant level of chlorogenic acid
in apple peel during 2 wk of shelf life although their experiment
conditions differed in several points. They have examined the peel
of cultivars “Elstar” and “Jonagold,” the latter also being the case
of our study. On the contrary, in our experiment on “Jonagold”
apple, an increase in the levels of hydroxycinnamic acids in peel
was measured on the 2nd sampling date similar to that of the
pulp. In the skin of both cultivars, an increase in the concentration
of hydoxycinnamic acids can be observed in the 2nd part of the
shelf life. The increase in total phenols during storage could be
a result of ethylene activity. This hormone stimulates the activity
of phenylalanine ammonia lyase, the key enzyme in biosynthesis
of phenolic compounds, with the consequent accumulation of
phenolic constituents (Ritenour and others 1995). At ambient
temperatures, ethylene production is higher, thus stimulating the
biosynthetic pathway of phenolic compounds (Napolitano and
others 2004).
Flavanols. In the case of flavanols, the sum of catechin and
epicatechin is presented (Figure 7). Higher values were noticed
in the sum of both constituents in the fruit peel compared to
pulp. Values in the skin followed a similar pattern in both cultivars. After the decrease of flavanol concentration in the peel at
the beginning of the shelf life, their increase was again noticed
on later sampling dates. In the apple pulp, a pattern similar to
the case of the hydroxycinnamic acids could be observed. The
flavanols showed an increase at the 2nd or 3rd sampling, followed
S: Sensory & Food
Quality
Figure 6–Changes in the sum of the analyzed hydroxycinnamic acids (chlorogenic and caffeic acids) in the apple peel (left) and pulp (right) during shelf
life (numbers 1 to 7 represent sampling dates) expressed in mg kg−1 FW. Average and standard errors are presented. JG = “Jonagold,” GD = “Golden
Delicious.” Different letters denote statistically significant differences between sampling dates for individual cultivars at P ≤ 0.05.
Figure 7–Changes in the sum of the analyzed flavanols (catechin and epicatechin) in the apple peel (left) and apple pulp (right) during shelf life (numbers
1 to 7 represent sampling dates) expressed in mg kg−1 FW. Average and standard errors are presented. JG = “Jonagold,” GD = “Golden Delicious.”
Different letters denote statistically significant differences between sampling dates for individual cultivars at P ≤ 0.05.
S466 Journal of Food Science r Vol. 75, Nr. 9, 2010
Shelf life and apple quality . . .
other hand, lacks the ability to accumulate anthocyanins in high
amounts. During shelf life, the concentration of idaein decreased
rapidly in the beginning of shelf life and stabilized on the 17th day
after exposure of fruit to ambient temperatures (Figure 9). In the
study by Ju and others (1996), a decrease in anthocyanin amount
was also noted during 7 d of shelf life especially in the case of lessripe fruits. The authors discuss that high content of anthocyanins
is important for preventing the onset of scald during shelf life.
After 1 wk of shelf life, a slight decline in the content of cyanidin galactoside was also reported by MacLean and others (2006).
However, both-mentioned research studies followed anthocyanin
response during 1 wk of shelf life and therefore no stabilization in
the amount of idaein in apple peel has been reported contrary to
data obtained in our study that was carried out for longer period.
Conclusions
In the present study with a broad tracking of the changes in
several quality parameters—ranging from appearance and firmness to the content of primary and secondary metabolites—we
were able to demonstrate that various parameters react uniquely
to a prolonged exposure to ambient temperatures. Regarding the
Figure 8–Changes in the sum of the analyzed
flavonols (quercetin rutinoside, quercetin
rhamnoside, quercetin glucoside, and quercetin
galactoside) in the apple peel during shelf life
(numbers 1 to 7 represent sampling dates)
expressed in mg kg−1 FW. Average and standard
errors are presented. JG = “Jonagold,” GD =
“Golden Delicious.” Different letters denote
statistically significant differences between
sampling dates for individual cultivars at P ≤
0.05.
S: Sensory & Food
Quality
by a constant rate till the end of shelf life. In the study of MacLean
and others (2006), in the apple skin of “Red Delicious” after
1 wk of shelf life no changes in the levels of flavanols were noticed. They however claim that an increase in certain group of
phenolics could be due to ethylene-stimulated up-regulation of
transcription factors of enzymes involved in the phenylpropanoid
pathway.
Flavonols. Flavonols are presented as a sum calculated from
the concentrations of quercetin rutinosid, quercetin glucoside,
quercetin galactoside, and quercetin rhamnoside. Quercetins are
mainly located in apple skin and found only in traces in apple pulp
(Figure 8). Therefore, only the results for apple peel are presented.
Similar to other phenolic groups, there is a considerable decrease
in the group of flavonols at the beginning of shelf life, with a peak
in its 2nd part. In the study of Awad and de Jager (2000), constant
rates were reported with no evident peak after 2 wk of shelf life.
Idaein. Idaein (cyanidin galactoside) is a typical anthocyanin
in apple skin. All other anthocyanins are present only in minor
amounts. Idaein content was measured only in “Jonagold,” where
it is responsible for the formation of the red blush covering the
major part of the first quality apples. “Golden Delicious,” on the
Figure 9–Changes in the amount of cyanidin
galactoside—idaein in the apple peel of
“Jonagold” cv. during shelf life (numbers 1 to 7
represent sampling dates) expressed in mg kg−1
FW. Average and standard errors are presented.
Different letters denote statistically significant
differences between sampling dates at P ≤ 0.05.
Vol. 75, Nr. 9, 2010 r Journal of Food Science S467
Shelf life and apple quality . . .
primary metabolites, an interchange between individual sugars
was noticed, but total levels remained similar, while the content
of malic acid remained at the same level or dropped, thus making the fruit sweeter. Phenolics showed different patterns in fruit
peel and in pulp. They were more constant in the pulp, while the
changes in their content were more pronounced in the peel. On
the basis of our results, it is, however, difficult to say that the fruit
in consumers’ homes lose the health-beneficial constituents in the
flesh and peel of apples during shelf life. In intact cells of apples,
phenolics are located in the vacuoles and protected from enzymes
causing oxidation and therefore remain stable also at ambient temperatures. Similarly, the system of synthesis of phenolics remains
intact and responsive. The most important change was noticed in
firmness, which might be the limiting factor for the practical duration of shelf life. When the fruit becomes too soft, consumers’
acceptability drops rapidly, as has already been demonstrated in
other studies.
Acknowledgment
This work is part of program Horticulture nr P4-0013-0481,
funded by the Slovenian Research Agency.
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