Journal of Applied Botany and Food Quality 89, 142 - 149 (2016), DOI:10.5073/JABFQ.2016.089.017
1Department of Food Technology, Pir Mehr Ali Shah, Arid Agriculture University Rawalpindi, Pakistan
2 Department of Agricultural Sciences, University of Haripur, Pakistan
3 Division of Plant and Soil Sciences, West Virginia University, Morgantown, USA
Transition in tuber quality attributes of potato (Solanum tuberosum L.)
under different packaging systems during storage
Kashif Sarfraz Abbasi1, Tariq Masud1, Abdul Qayyum2*, Sami Ullah Khan2, Asif Ahmad1,
Ayaz Mehmood2, Abid Farid2, Matthew A. Jenks3
(Received December 19, 2015)
* Corresponding author
Summary
The suitability of different packaging materials i.e. jute, nylon,
polypropylene, cotton, low density polyethylene, medium density
polyethylene, and high density polyethylene were studied for tu-
bers of the premium potato (Solanum tuberosum L.) variety “Lady
Rosetta”. After harvest, potato tubers were washed, sorted, graded,
cured, and subsequently stored in different packaging materials at
ambient temperature (25 ± 2 °C). Changes in quality attributes of po-
tato tubers under different packaging materials were studied on the
basis of their physico-chemical and functional parameters. Overall
results revealed that packaging materials had a significant (p ≤ 0.05)
effect on many important quality attributes. Generally, weight loss,
glucose and glycoalkaloid amounts, and polyphenol oxidase and per-
oxidase activities increased, while ascorbic acid contents decreased
with increasing storage time. Total phenolic contents and radical
scavenging activity showed a nearly parabolic trend during the sto-
rage period. Amongst the different packaging materials employed,
potatoes stored in polypropylene and low-density polyethylene pre-
sented the best overall retention of vital quality attributes during
63 days storage. However, the higher tensile strength of polypro-
pylene packaging made it a more durable and thus more effective
material for prolonged potato tuber storage, a characteristic having
clear advantages when used in typical marketing supply chains.
Introduction
Potato is the most highly produced non-grain staple crop in the
world, with one third of total production harvested in densely-popu-
lated developing countries, like China and India (PIC, 2008). As
such, it is critically important for world food security. Moreover, it
is considered the most important crop in South America, the second
most important crop in Europe, and fourth on a global scale, after
wheat, rice, and maize (MESSER, 2000). One of the greatest chal-
lenges to potato tuber production is storage after harvest and grea-
test quantity of potatoes is lost each year due to inadequate storage
conditions after harvest and during marketing. Once the potato tu-
ber is harvested, it is washed and then cured for storage. The curing
process leads to the potato tuber entering physiological dormancy
(PANDE et al., 2007), and modern commercial potato cultivars grown
for the processing industry often have shorter dormancy periods and
more susceptibility to storage disorders like sweetening, greening,
and others. There is still much work needed to establish appropriate
postharvest interventions to ensure optimum tuber storage (quality
and duration) to facilitate continuous supply (SUTTLE, 2007). Use of
suitable packaging systems extends the storage life of potato tubers
during transit, in part by slowing down the ripening process during
postharvest storage and marketing (SANCHEZ et al., 2003). In deve-
loping countries, the development of effective packaging materials
for perishable commodities like potatoes can have tremendous ad-
vantages over more expensive technologies like controlled atmos-
phere storage facilities, and/or irradiation treatments, as a means to
prolonged postharvest storage life. Besides improving food security
within country, improved packing strategies that extend commodity
shelf life create new options for long-distance shipping of produce
to more distant markets.
In many cases today, various packaging systems can be supplemen-
ted with low temperature storage (KYRIACOU et al., 2009), sprout
inhibitors/suppressants (FRAZIER et al., 2004), ethylene scavengers
(ABBASI et al., 2004), and irradiation (BLESSINGTON et al., 2007) as
part of an integrated strategy to minimize postharvest losses. The
packaging materials themselves are often processed as sheets, wraps,
pouches, or more solid containers having diverse barrier proper-
ties that modulate gas exchange between the internal and external
package atmosphere (HONG et al., 2003). Potato being an impor-
tant cash crop with substantial export potential could have a major
impact on farm incomes and foreign exchange earnings for the ex-
porting country. In developing countries such as Pakistan with a gro-
wing potato industry, large bags made of jute (a natural plant fiber,
Corchorus olitorius L.) with typical carrying capacity of 100 kg are
commonly used to store potato tubers after harvest. However, more
highly engineered packaging systems that utilize polyethylene, po-
lypropylene, polystyrene, various biodegradable plastics, and wound
preventing corrugated cartons and other cushioning materials, are a
necessity in many marketing systems to maintain compliance with
food safety standards and to compete on the basis of quality in the
international market. The quality of horticultural commodities is a
critical consideration in decisions made by producers, exporters, and
consumers, and the packaging system utilized plays a principle role
in determining quality attributes. The present study was designed to
identify an optimized packaging system for postharvest storage of
the potato variety “Lady Rosetta” at ambient temperature.
Materials and methods
Tubers of potato (Solanum tuberosum L.) variety “Lady Rosetta”
were harvested from the Potato Research Institute, Sahiwal (Punjab,
Pakistan). Tubers were transported the same day to the Postharvest
Technology Laboratory, Department of Food Technology PMAS-
Arid Agriculture University Rawalpindi, Pakistan. On the same day,
the tubers were washed, sorted and graded by size and then cured for
one week at temperatures between 15-20 °C before being sampled
for analysis here. Potato tubers were packed in different packaging
materials (30 cm × 40 cm bags) procured from Ms. Multi Packages
Ltd. (Lahore, Pakistan). The set of treatments included control,
jute packaging, nylon packaging, polypropylene packaging, cotton
packaging, low density polyethylene packaging (LDPE), medium
density polyethylene packaging (MDPE) and high density polyethy-
lene packaging (HDPE). One kg of potato tubers were used for each
replication, sampling from a total of 30 kg of potato tubers subjec-
ted to different physico-chemical assessments each week. All the
Changes in potato tuber quality under different packaging systems 143
packaged potatoes were stored at approximately 25 ± 2 oC and
70 ± 5 % relative humidity.
Weight loss
The weight loss (%) in different experiments at specified storage in-
tervals was determined by weighing the samples with digital balance
(OHAUS, Model TS4KD Florham Park, NJ, USA) and reported as
percent loss in sample weight based on initial weight.
Weight loss (%) = (Initial weight - Final weight / Initial weight) ×
100
Glucose content
Glucose quantity was determined using glucose test strips imported
from Snack Food Association, (Arlington Virginia USA). The color
change was correlated with a standard color chart, and the values
expressed in mg glucose 100 gm-1 sample. The tests were conducted
in triplicate per treatment.
Ascorbic acid content
Ascorbic acid (AA) quantity was determined using titrametric me-
thod by employing 2, 6, di-chlorophenol indophenol dye (redox dye)
as explained in (AOAC, 1990) method no. 967.21. A 10 g represen-
tative sample was placed in a beaker and brought up to volume with
100 ml 3 % phosphoric acid and filtered. 10 ml of filtrate was titrated
with the standard dye solution. The ascorbic acid contents (mg 100
g-1 dry matter) were quantified as:
Ascorbic acid = (Dye factor × Titration × Volume made up) / (Weight
of sample × Volume of filtrate) × 100
Dye standardization
Five milliliters of standard ascorbic acid solution was diluted with
five milliliter of metaphosphoric acid (3 %) and titrated with dye so-
lution until a pink coloration could be observed to endure for ten sec.
Dye factor was determined (mg ascorbic acid ml-1 of dye) as:
Dye factor (D.F) = 0.5 / Titration
Glycoalkaloid content
The total glycoalkaloids (TGA) were determined by the method de-
scribed by GRUNENFELDER et al. (2006). Ground lyophilized potato
tissue (500 mg) was extracted in 10 ml of 80 % ethanol at 85-90 °C
for 25 min. The extract were filtered and reduced to 3-5 ml on rota-
ry evaporator at 50 °C. Each extract was rinsed twice with 3 ml of
10 % (v/v) acetic acid and then centrifuged at 10000 g for 30 min at
10 °C. The pH of the supernatants was adjusted at 9.0 with NH4OH.
The extract was refluxed at 70 °C for 25 min followed by overnight
storage at 4 °C temperature. The extracts were centrifuged, and after
discarding the supernatants the resulting pellets were dissolved in
0.5 ml of 7 % (v/v) phosphoric acid and stored at -20 °C. The Total
glycoalkaloids were estimated by adding 200 μl of extract in 1 ml
of 0.03 % (w/v) in concentrated phosphoric acid. The contents
were allowed to settle for 20 min and absorbance was measured at
600 nm. TGA concentrations were quantified based on α-solanine
(Sigma-Aldrich) standard curve using a CE-2021, Spectrophoto-
meter (CECIL Instruments Cambridge, England) and expressed as
mg TGA 100 g-1 dry weight.
Phenolic content
Total phenolic content (TPC) in terms of gallic acid equivalent
(GAE) were carried out by Folin-Ciocalteu (FC) assay (LACHMANN
et al., 2008) with few modifications. Tubers randomly selected were
freeze dried and then extracted with 80 % ethanol. A total of 2 gm
extract was quantitatively converted into 100 ml volumetric flask
and adjusted with 80 % ethanol. In 5 ml of the sample slightly dilu-
ted with distilled water, 2.5 ml of FC and 7.5 ml of 20 % solution of
sodium carbonate were added. The contents were allowed to settle
for 2 hrs and absorbance was measured at 765 nm using a CE-2021,
Spectrophotometer (CECIL Instruments Cambridge, England). Total
phenolic contents were quantified by standard calibration curve de-
rived from the absorbance of known gallic acid concentration (10-
100 ppm). Results were articulated as mg gallic acid equivalents
(GAE) 100 g-1 dry weight.
Radical scavenging activity (RSA)
Antioxidant activity was measured as radical scavenging activity
(RSA) using methods described by SINGH and RAJINI (2004) that
involved electron transfer reaction based assay by employing free
radical 2, 2-diphenyl-1-picrylhydrazyl (DPPH). Five mg of freeze
dried potato extract was incubated with 1.5 ml of DPPH solution
(0.1 mM in 95 % ethanol). The reaction mixture was shaken and al-
lowed to stand for 20 min under ambient temperature. Absorbance
of the resultant mixture was determined at 517 nm against a blank.
The radical scavenging activity was determined as a decrease in the
absorbance of DPPH using the following equation:
Scavenging (%) = 1 - (Absorbance of sample at 517 nm / Absorbance
of control at 517 nm) × 100
Enzyme determination
Enzyme extraction was carried out by the method described by
YEMENICIOGLU (2002), with some modifications. Washed, peeled,
and diced potato tubers were placed under -20 °C before homoge-
nate preparation. 200 gm frozen potato tuber was homogenized with
300 ml acetone and 1 gm of polyvinylpolypyrrolidone (PVPP) in
waring blender. The resultant mixture was homogenized for 2 min
and then filtered through Whatman No.1 filter paper. Acetone pow-
der preparation was carried out by repeated extraction and evapo-
ration. The extraction mixture was prepared by mixing 0.4 g PVPP,
2 g acetone powder, and 50 ml of cold 8.8 % sodium chloride so-
lution. Extraction was completed at 4 °C temperature 3 hrs under
magnetic stirrer. The extract was filtered, centrifuged at 11000 g for
20 min, and then stored at -20 °C prior to quantification of enzyme
activity.
Protein extraction was carried out with the Lowry et al., (1951) me-
thod using bovine serum albumin (BSA) as standard. Protein stan-
dards of crude and partially purified extracts were prepared in 8.8 %
NaCl solution and deionized water respectively. All the assays were
carried out in triplicate. The enzyme activity was calculated as U
100 g-1 fresh weight, in spectrophotometric assay 1 U was defined as
0.001 change in absorbance min-1 ml-1 of enzyme extract.
Polyphenol oxidase assay
Polyphenol oxidase (PPO) activity was determined as described by
YEMENICIOGLU (2002). The reaction mixture contained 2 ml 0.01 M
sodium phosphate buffer (pH 7.0), 0.2 ml of 0.25 M catechol, and
0.3 ml enzyme extract to the total volume of 2.5 ml. The optical
density (OD) of the reaction mixture was determined spectrophoto-
meterically at 420 nm. polyphenol oxidase activity was calculated
by the change in OD over a period of thirty sec and expressed as U
100 g-1 fresh weight.
Peroxidase assay
Peroxidase (POD) estimation was carried out as reported by ABBASI
et al. (1998). Reaction mixture consisted of 2.1 ml, 15 mM NaKPO4
144 K.S. Abbasi, T. Masud, A. Qayyum, S.U. Khan, A. Ahmad, A. Mehmood, A. Farid, M.A. Jenks
buffer (pH 6.0), 0.3 ml 1 mM H2O2, 0.3 ml 0.1 mM guaiacol and
0.3 ml enzyme extract to the total volume of 3 ml. The optical den-
sity (OD) of the reaction mixture was determined spectrophotomete-
rically at 470 nm. POD activity was estimated by the change in OD
due to guaiacol oxidation over thirty sec time and expressed as U
100 g-1 fresh weight.
Statistical analysis
Data obtained as a mean of three replications were statistically ana-
lyzed by a two-factor factorial in Completely Randomized Design
(CRD) and treatments and storage interval means were compared
using a Duncan Multiple Range test using M-Stat-C statistical soft-
ware as described by STEEL et al. (1997).
Results
Weight loss
Tuber weight loss (%) occurred in all treatments over time; how-
ever, the rate of weight loss was slower in packaged tuber than non-
packaged controls during the storage period. Treatment means of
packaged potato tubers showed non-significant differences between
Jute and HDPE, Polypropylene and LDPE, while all other differed
significantly. Data on weight loss revealed significant differences
between all the storage interval means. The interaction between
treatment means and storage intervals showed maximum weight loss
(%) in control and minimum in LDPE at the end of storage. In ge-
neral potato packed in different polyethylene packaging materials
(LDPE, MDPE and HDPE) showed lesser weight loss as compared
to jute, nylon and cotton packagings (Fig. 1).
creased up to 333.5 mg 100 g-1 (0.333 %) by the end of storage. Non-
significant differences were recorded between LDPE and MDPE
packaging at the end of their respective storage periods, and attained
220 mg 100 g-1 and 215 mg 100 g-1 respectively. The least glucose
contents were estimated in polypropylene packaged potato with less
than 200 mg 100 g-1 (0.2 %) glucose contents throughout the storage
period (Fig. 2).
Fig. 1: Weight loss in potato tubers stored using different packaging mate-
rials was highest throughout the storage period when stored in po-
lypropylene and LDPE packages. Vertical bars show ±SE of means
(n-3). Interaction between storage intervals and packaging materials
was significantly different at p ≤ 0.05.
Glucose content
Glucose contents showed steady increase throughout the storage
period, with an observed impact of applied packaging materials.
Treatment means showed significant difference in stored potato
with control having maximum while LDPE having minimum gluco-
se over time. Maximum glucose contents were recorded in the last
week while minimum during the first week storage. The interaction
between storage intervals and treatments was less significant during
the early storage, but differed significantly with the progression in
the storage period. The prominent increase in glucose contents in
the non-packaged control started on the 28th day which gradually in-
Ascorbic acid content
In response to different packaging systems, ascorbic acid (AA) was
amongst the parameters that decreased significantly during the sto-
rage period. Treatment means revealed that the maximum AA reten-
tion was observed in LDPE and polypropylene packagings were also
found statistically similar at the 5 % level of significance. Potatoes
packaged in Jute, MDPE and LDPE also maintained higher AA con-
tents than the control. Storage intervals showed significant impact
in their AA contents with maximum and minimum values estimated
during the first and last weeks, respectively. The interaction between
storage intervals and treatments showed substantial AA retention in
packaged potato tubers as compared to controls. Amongst different
treatments, potato packed in polypropylene packaging and LDPE
packaging retained maximum AA contents by the end of storage
period. Minimum retention in AA contents was observed in con-
trol (15.6 mg 100 g-1) while maximum in polypropylene (19.97 mg
100 g-1) packaging and LPDE 19.2 mg 100 g-1) packaging by the end
of storage period (Fig. 3).
Glycoalkaloid content
Total glycoalkaloid (TGA) accumulation in terms of solanine equi-
valent increased during storage in all the treatments. Treatment
means revealed significant difference between the tubers in their
TGA contents for the various packaging materials. Maximum and
minimum TGA contents during the storage period were identified
in Control and HDPE packaging, respectively. Storage interval
means showed significant differences in their TGA contents, and
these were found to be maximal at the end of the storage period. Re-
sults expressed on dry weight basis showed increase in TGA content
in potato tubers during storage. However, in all treatments except
in control, the TGA levels remained under a safe limit i.e. 20 mg
100 g-1, as suggested by NEMA et al. (2008). In general, irrespective
of packaging types, considerable increase in TGA content started on
Fig. 2: Glucose content in stored potato tubers stored using different pa-
ckaging materials was lowest by the end of the storage period when
stored in polypropylene packages. Vertical bars show ±SE of means
(n-3). Interaction between storage intervals and packaging materials
was significantly different at p ≤ 0.05.
Changes in potato tuber quality under different packaging systems 145
the 28th day, which continued till the end of storage. Maximum in-
crease in TGA was about eight folds (7.50 mg 100 g-1 to 63.80 mg
100 g-1) in control at the end of storage as compared to six folds
(7.50 mg 100 g-1 to 47.20 mg 100 g-1) increase in tubers in the poly-
propylene packaging (Fig. 4).
GAE 100 g-1, 124.07 mg GAE 100 g-1 and 120.5 mg GAE 100 g-1
TPC, respectively, in contrast to lowest TPC i.e. 88.77 mg GAE
100 g-1 estimated in control (Fig. 5).
Fig. 3: Ascorbic acid content in potato tubers stored using different pa-
ckaging materials was highest by the end of the storage period in
polypropylene packages. Vertical bars show ±SE of means (n-3).
Interaction between storage intervals and packaging materials was
significantly different at p ≤ 0.05.
Fig. 4: Total glycoalkaloids (TGA) in potato tubers stored using different
packaging materials was highest in non-packaged controls by the
end of the storage period. Vertical bars show ±SE of means (n-3).
Interaction between storage intervals and packaging materials was
significantly different at p ≤ 0.05.
Phenolic content
Total phenolic content (TPC) initially showed a trend toward increa-
sing, followed by a decline till the end of storage period. Treatment
means showed significant difference in TPC in response to diffe-
rent packagings. Polypropylene and MDPE packagings maintained
maximum TPC while control had minimum phenolic content. The
interaction between treatments and storage intervals showed maxi-
mum TPC in control and polypropylene packaging on 28th and 49th
day of storage, respectively. In general, considerable increase in TPC
was observed in all treatments up to 42nd day, which subsequently
declined by the end of storage. This decline in TPC was more signi-
ficant in control, nylon, HDPE, and cotton packaged potatoes. After
63rd days storage, potato tubers stored in polypropylene, LDPE, jute,
and MDPE packaging retained 137.23 mg GAE 100 g-1, 130.23 mg
Radical scavenging activity
Radical scavenging activity (RSA) determined in terms of % inhi-
bition of DPPH showed slight increase initially, followed by a gra-
dual decrease during potato tuber storage. Treatment means showed
LDPE packaging maintained maximum activity followed by MDPE,
polypropylene and HDPE packaging, while control demonstrated
minimum activity. Potato storage in jute, nylon and cotton packaging
was found statistically similar, and retained moderate activities
throughout the storage period. Radical scavenging activity increased
during the first week and attained maximum levels by the second
week in all the treatments. In general, maximum RSA activity in
tubers occurred between 14-21 days storage, and then progressively
decreased after. A considerable reduction in activity was observed
in all treatments on the 28th day storage. Potato tubers packed in
polypropylene and polyethylene packaging exhibited substantial
RSA that retained substantial higher after the fourth week till the
end of storage period, with no significant difference between them.
The loss in RSA after 14th day till the end of storage in polypropy-
lene was 45.8 % - 23.8 % as compared to 48.0 % - 17.8 % in control
(Fig. 6).
Polyphenol oxidase activity
In response to different packaging materials, polyphenol oxidase
(PPO) activity in potato tubers generally increased with time. Treat-
ment means demonstrated maximum activity in control, while mini-
mum was recorded in polypropylene and LDPE packaging (statis-
tically similar at 5 % level of significance). Moderate PPO activity
was observed in jute and HDPE packaging (statistically similar at
5 % level of significance). Interaction between storage intervals and
treatments was significant with maximum activity estimated in con-
trol (68.5 U 100 g-1 fresh weight) at the end of the storage period.
In general, steady increase with no significant differences in PPO
activity were observed in all the treatments till 28th day, afterward
prominent increase was estimated in control till the end. Neverthe-
less, irrespective of different treatments the PPO activity increased
after the fourth week storage. Lowest PPO activity was observed in
polypropylene, LDPE and MDPE packaged potato tubers and were
found statistically similar during most of the storage period (Fig. 7).
Fig. 5: Total phenolic contents in potato tubers stored using different pa-
ckaging materials were highest at the end of the storage period when
stored in polypropylene packages. Vertical bars show ±SE of means
(n-3). Interaction between storage intervals and packaging materials
was significantly different at p ≤ 0.05.
146 K.S. Abbasi, T. Masud, A. Qayyum, S.U. Khan, A. Ahmad, A. Mehmood, A. Farid, M.A. Jenks
Peroxidase activity
Peroxidase (POD) activity in potato tubers showed a steady increase
in all the treatments during storage. However the increase was most
prominent in the control. Increased POD activity in potato tuber
was comparable to their PPO activity but observed at slower pace.
Treatments means revealed maximum POD activity in control and
minimum in LDPE packaging during the complete storage. Non-
significant difference was observed in jute and nylon packaging,
whereas, cotton and HDPE were also found to be statistically similar
during their storage period. In general, POD activity was maximum
and minimum during the last and first weeks, respectively. Maxi-
mum activity POD activity (32.40 U 100 g-1) was estimated in con-
trol and minimum (23.20 U 100 g-1) in LDPE packaging at the end
of storage. Polypropylene and MDPE packaging retained compara-
tively lower POD activity i.e. 23.43 U 100 g-1 and 26.47 U 100 g-1,
respectively, during the same storage periods (Fig. 8).
Discussion
As the potato tuber is one of the most important crops supporting
worldwide food security, its extended storage life at high quality is
the focus of much interest by growers, exporters, consumers, and
researchers. Weight loss by potato tubers during storage results in
significant post harvest losses. As an edible plant stem typically for-
ming underground, weight loss is primarily attributed to the water
loss that occurs through the outermost skin tissues during the pro-
cesses of respiration and sprouting (TESTER et al., 2005). The phe-
nomenon is thus considered as an important stability index for the
storage life assessment. Packaging systems confer barrier properties
to the physiological gaseous exchange of stored tubers and decrease
the rate of weight loss during storage (HONG et al., 2003). Different
types of packaging material assessed in the present study had a sig-
nificant impact on potato tuber weight loss during storage. Potato
tubers stored in different polyethylene packaging (LDPE, MDPE
and HDPE) showed increased percentage weight loss with the in-
crease in the thickness of polyethylene packaging, which might be
the reason behind increased weight loss in high density polyethylene
packaging as compared to those packed in low density polyethyle-
ne. Similar impacts due to thickness and permeability of packaging
materials have also been reported by RAKOTONIRAINY et al. (2001).
Application of polyethylene packaging in horticultural products like
potato tuber (ROSENFELD et al., 1995) and tomato (Solanum lycoper-
sicum L.) fruit (SAMMI and MASUD, 2007) have been shown to re-
duce weight loss during the postharvest storage. Use of polypropy-
lene packaging material has also been shown to effectively prolong
storage stability in sweet cherry (CONTE et al., 2009) and fresh cut
pineapple (CALDERON et al., 2008).
The hydrolysis of sucrose by the invertase enzyme leads to the
formation of glucose and fructose monomers within potato tubers
(KUMAR et al., 2004).The presence of either kind of sugars is highly
undesirable for tuber processing, as high glucose and fructose are
reducing sugars that have a negative effect on potato chip fry color.
In addition, high levels of these sugars are a safety concern due to
their active participation in toxic acrylamide formation at elevated
processing temperatures (MOTTRAM, 2002). The significant increa-
se in glucose contents we report here later in the storage period in
treatments like control, jute, nylon, cotton, and HDPE are likely due
to earlier sprouting and the associated depletion of carbohydrate re-
serves in the tuber (BLENKINSOP et al., 2002). By comparison, potato
tubers stored in polypropylene, LDPE, and MDPE packaging were
observed to delay the dormancy break relative to other materials, and
thus retained lower glucose contents at the end of the storage period.
The maximum glucose content was reported at the end of storage
period for the non-packaged control treatments was associated to
Fig. 6: Radical scavenging activity (RSA) in potato tubers stored using dif-
ferent packaging materials was highest by the end of the storage pe-
riod when stored in polypropylene. Vertical bars show ±SE of means
(n-3). Interaction between storage intervals and packaging materials
was significantly different at p ≤ 0.05.
Fig. 7: Polyphenol oxidase (PPO) in potato tuber stored in different pa-
ckaging materials was lowest by the end of the storage period when
stored in polypropylene and LDPE. Vertical bars show ±SE of means
(n-3). Interaction between storage intervals and packaging materials
was significantly different at p ≤ 0.05.
Fig. 8: Peroxidase (POD) in potato tubers stored in different packaging ma-
terials was lowest by the end of the storage period when stored in
polypropylene and LDPE. Vertical bars show ±SE of means (n-3).
Interaction between storage intervals and packaging materials was
significantly different at p ≤ 0.05.
Changes in potato tuber quality under different packaging systems 147
more rapid progress toward dormancy break at the end of the storage
period, similar to results of FAUCONNIER et al. (2002).
Ascorbic acid is the predominant vitamin in potato tuber and of
significant importance in the human diet. Depletion of ascorbic acid
has been implicated with reduced nutritional quality; therefore their
assured stability during storage has been a major concern of the post-
harvest technologists. HAGG et al. (1998) reported that AA content
significantly decreases during storage of potato tuber. The reduction
is ascribed to the oxidation of ascorbic acid into dehydro ascorbic
acid and afterward to diketo-gluconic acid. Being a water-soluble
vitamin and susceptible to oxidation, AA contents rapidly decrease
with increasing rates of respiration and water loss in storage. The
present study revealed continuous reduction in AA content in all
treatments, but especially then on-packaged controls. Our applica-
tion of certain packaging materials such as polypropylene and poly-
ethylene could be shown to significantly reduce the rate of water
loss from potato, and this was apparently associated with less oxida-
tion of ascorbic acid compared to the controls and other treatments.
The efficacy of modified atmosphere packaging in retention of high
AA contents has likewise been described in tomato by SAMMI and
MASUD, (2007).
Glycoalkaloids contents in potato tuber are attributed to their me-
dicinal and toxicological properties. Low quantities (below 15 mg
100 g-1 fresh weight) impart flavor and functional value, while high
quantities (above 20 mg 100 g-1 fresh weight) can impart bitter taste
and even may even cause death at excessive intake (28 mg 100 g-1
fresh weight) (MENSINGA et al., 2005). NEMA et al. (2008) repor-
ted that total glycoalkaloids (TGA) contents increased during the
storage under different packaging systems. He proposed that color,
type, and permeability of packaging material effect TGA formation
during storage. Similar observations regarding the effect of diffe-
rent packaging materials on TGA contents have been documented by
ROSENFELD et al. (1995). In addition, potato tubers produced high
level of TGA in the tubers close to sprouting stage, which confirmed
the previous findings of SENGUL et al. (2004).
Large amounts of phenolic compounds can cause tuber discoloration,
as phenolics act as a substrate in potato browning mediated through
the activities of polyphenol oxidase (PPO) in melanin formation
(ANTHON and BARRETT, 2002). However, a high amount of pheno-
lics during storage is attributed to low PPO and high antioxidant
activity in potatoes (LACHMAN et al., 2008). Previous studies have
revealed that the phenolics content in potato continued to increase
during storage period until the onset of PPO activity (MADIWALE
et al., 2011). The presence of ample molecular oxygen in control
likely caused a significant decline in total phenolics (TPC) as com-
pared to other potatoes stored in different packaging. Our results in-
dicated that packaging materials in general and LDPE and polypro-
pylene packaging in particular curtailed the decline in TPC relative
to control, similar as reported by GONZALEZ et al. (2004).
Fruits and vegetables, owing to their rich vitamins and poly pheno-
lic contents, possess significant radical scavenging activity that cor-
responds to their antioxidant potential (KONDO et al., 2004). These
antioxidants have the capacity to quench free radicals (peroxides,
super oxides, hydroxyl radicals) thus, protect the cellular structures
and proteins from membrane peroxidation and degeneration (DING
et al., 2002). In the present investigation, our observation of an
initial increase in radical scavenging activity (RSA) might be due to
the increase in total phenolic contents observed early in the storage
period, as was also reported by (PADDA and PICHA, 2008). Moreover,
minimum loss in RSA during the last three weeks of storage and
was associated with all packaged potatoes. Potentially, this is due
to the regeneration of antioxidant compounds like ascorbic acids in
potato to counter balance the increased free radicals produced during
senescence. Packaged potato expressed higher antioxidant activity
as compare to the non-packaged controls, which might be explained
by greater retention of ascorbic acids, phenolics and other functio-
nal compounds. This improved response at later stages of storage in
packaging was similar to previous reports of horticultural commo-
dity packaging reported by SONIA and CHAVEZ (2006) and DING
et al., (2002).
Polyphenol oxidase activity increases in potato due to the avail-
ability of substrate and its subsequent oxidation during storage. The
non-significant changes during the 1st month storage in most of the
treatments might be due to absence of physical damages and appro-
priate curing which was also observed by NOURIAN et al. (2003).
Prominent increase in the PPO activity in different treatments after
the 1st month till the end of the storage period might be associa-
ted with an increased substrate (polyphenol) oxidation. However,
packaging materials conferred barrier properties to substrate oxida-
tion resulted in low eventual activity as compare to control. In ad-
dition, increased PPO activity in potato during postharvest storage
has also been implicated with increased sprouting percentage and
accelerated senescence (ABBASI et al., 2015). In the present study, all
the packaging materials effectively maintained modified atmosphe-
ric conditions around potato better than the non-packaged control.
This resulted in lower moisture loss and limiting oxygen availability
for the polyphenol oxidations. The variation in PPO activity within
different packaging materials might be attributed to the difference in
their oxygen permeability, which was also observed by RAKOTONI-
RAINY et al. (2001). KADER (2002) also reported substrate inhibition
for PPO enzymes under modified atmosphere packaging, which led
to low PPO activity during storage just as we observed in the present
investigation.
Enzymatic browning in potato may cause substantial loss by dete-
riorating nutritional and sensorial attributes, and this is primarily
associated with the activities of peroxidase and polyphenol oxida-
se enzymes during storage (LOAIZA and SALTVEIT, 2001). Peroxi-
dase (POD), being thermally stable and omnipresent in all part of
the plant, has a wider range of substrate-based activity than PPO
(ANTHON and BARRETT, 2002). Increased POD activity is asso-
ciated with oxidation of phenolic compounds under physiological
stress leading to decay and loss of quality during storage (DING
et al., 2002). In addition, POD can also degrade natural antioxidants
and liberate damaging free radicals (ROJAS et al., 2008). Both these
processes, mediated through peroxidase activity, accelerate potato
browning and affect the ultimate postharvest storage life. AYDIN and
KADIOGLU (2001) reported increased POD activity in fruits and ve-
getables under stress conditions, and with progression in the physio-
logical stages from ripening through senescence, just as we observe
in the present study as affected by packaging material by the end of
storage period. Our results showed that different packaging materials
could maintain low POD activity in potato tuber as compare with
non-packaged controls at ambient temperature storage, presumably
due to lower available oxygen required for the oxidation of phenols
and peroxides. The increased POD activity by the end of the storage
period, particularly in the non-packaged controls, might be attributed
to the physiological stress associated with senescence and sprouting
in these tubers, as previously reported by AFIFY et al. (2012) and
ABBASI et al. (2015).
Conclusion
This study revealed that storage life in potato tubers was significant-
ly affected by different packaging materials. In general, weight loss,
total soluble solids, glucose, total sugars, glycoalkaloids, polyphenol
oxidase, and peroxidase increased during the storage period. Ascor-
bic acids decreased with the increase in storage time. Total phenolic
contents and radical scavenging activity of the stored tubers increa-
sed initially and then declined later in the storage period. Amongst
the different packaging materials studied here, the potato tubers
148 K.S. Abbasi, T. Masud, A. Qayyum, S.U. Khan, A. Ahmad, A. Mehmood, A. Farid, M.A. Jenks
stored in polypropylene and low density polyethylene packaging
showed best overall retention of vital quality attributes during 63rd
day’s storage. However, tensile strength of polypropylene packaging
made it advantageous for prolonged potato tuber storage, which
helps prevent potential losses during transit operations and shipping
during marketing.
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Address of the corresponding author:
E-mail: aqayyum@uoh.edu.pk
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