Effect of Packaging Material on Shelf Life and Quality of Ware Potato Tubers Stored at Ambient Tropical Temperatures

Abstract

The effect of seven packaging materials (transparent perforated and non-perforated high-density polyethylene (HDPE) bags, black perforated and non-perforated low-density polyethylene (LDPE) bags, nylon gunny sacks, khaki bags and net bags) on post-harvest quality of tubers from three potato cultivars was evaluated. Data were collected on time and percentage of sprouting, weight loss rates and percentage tubers with greening and rotting. Packaging significantly reduced weight loss and rate of tuber greening but increased the rate of sprouting and decay incidences. Non-perforated PE bags were the most effective in reducing weight losses, recording losses of 0.7 to 0.9% after 32 days in storage while unpackaged tubers had weight losses of 11 to 12%. Tuber rotting was highest (60 to 66% of the tubers) in non-perforated PE bags. Greening was faster in non-packaged tubers recording 55 to 100% after 2 weeks in storage and showed high cultivar differences, but did not occur in black bags, whether perforated or non-perforated. Sprouting was complete by week 3 in all tubers packaged in non-perforated HDPE bags irrespective of cultivar. Although the non-perforated HDPE bag packaging prevented weight loss, its positive effect was counteracted by the high incidence of rotting and sprouting. Amongst the different materials evaluated, perforated low-density black PE bags were the best method for ware potato packaging due to low sprouting, reduced weight loss, low rate of tuber greening and reduced rate of tuber decay compared to other packaging materials. The study also indicated that the interaction between cultivars, packaging and storage period also affected shelf life of ware potatoes under ambient tropical conditions.

Full text

1 23
Potato Research
Journal of the European Association for
Potato Research
ISSN 0014-3065
Potato Res.
DOI 10.1007/s11540-018-9377-0
Effect of Packaging Material on Shelf Life
and Quality of Ware Potato Tubers Stored
at Ambient Tropical Temperatures
Richard Ombui Nyankanga, Winnie
Wanjiku Murigi & Solomon Igosangwa
Shibairo

1 23
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Effect of Packaging Material on Shelf Life
and Quality of Ware Potato Tubers Stored
at Ambient Tropical Temperatures
Richard Ombui Nyankanga
1
&
Winnie Wanjiku Murigi
1
&
Solomon Igosangwa Shibairo
2
Received: 10 May 2017 /Accepted: 27 April 2018
#European Association for Potato Research 2018
Abstract The effect of seven packaging materials (transparent perforated and non-
perforated high-density polyethylene (HDPE) bags, black perforated and non-
perforated low-density polyethylene (LDPE) bags, nylon gunny sacks, khaki bags
and net bags) on post-harvest quality of tubers from three potato cultivars was
evaluated. Data were collected on time and percentage of sprouting, weight loss rates
and percentage tubers with greening and rotting. Packaging significantly reduced
weight loss and rate of tuber greening but increased the rate of sprouting and decay
incidences. Non-perforated PE bags were the most effective in reducing weight losses,
recording losses of 0.7 to 0.9% after 32 days in storage while unpackaged tubers had
weight losses of 11 to 12%. Tuber rotting was highest (60 to 66% of the tubers) in non-
perforated PE bags. Greening was faster in non-packaged tubers recording 55 to 100%
after 2 weeks in storage and showed high cultivar differences, but did not occur in black
bags, whether perforated or non-perforated. Sprouting was complete by week 3 in all
tubers packaged in non-perforated HDPE bags irrespective of cultivar. Although the
non-perforated HDPE bag packaging prevented weight loss, its positive effect was
counteracted by the high incidence of rotting and sprouting. Amongst the different
materials evaluated, perforated low-density black PE bags were the best method for
ware potato packaging due to low sprouting, reduced weight loss, low rate of tuber
greening and reduced rate of tuber decay compared to other packaging materials. The
study also indicated that the interaction between cultivars, packaging and storage period
also affected shelf life of ware potatoes under ambient tropical conditions.
Potato Research
https://doi.org/10.1007/s11540-018-9377-0
*Richard Ombui Nyankanga
richardnyankanga@yahoo.com
1
Department of Plant Science and Crop Protection, University of Nairobi, Upper Kabete Campus,
P.O. Box 30197-00100, Nairobi, Kenya
2
Kibabii University, P.O. Box 1699-50200, Bungoma, Kenya
Author's personal copy

Keywords Decay .Greening .Packaging .Shelf life .Sprouting .Ware potato .Weight
loss
Introduction
Potato (Solanum tuberosum L.) is the second most important food crop in Kenya
grown by over 800,000 smallholders (NPCK 2015). The potato industry plays a
major role in the Kenyan economy as it employs about 2.5 million people
directly and indirectly (Abong and Kabira 2013). Most of the potato growers
rely on rainfall-fed production. Unfortunately, production is slowly declining due
to climate change and hence threatening food security (Mwaura 2009). The
problem is further aggravated by high post-harvest losses. Post-harvest losses at
the farm level are estimated at 12.8%, open market 24.4%, processing 12% and
supermarkets 25% (Kaguongo et al. 2014). On average, 19% of the total produc-
tion per hectare is lost every season (Kaguongo et al. 2014).) These losses have
been attributed to poor storage management, use of poor-quality packages, poor
handling and generally limited information (Kaguongo et al. 2014). Physical and
quality losses are due to premature and excessive sprouting, tuber greening, tuber
decay, transpiration and respiration. Sprouting leads to weight loss and loss of
marketable tubers and reduces the nutritional and processing quality of tubers
(Suttle 2003). Tuber greening occurs when tubers are exposed for an extended
period to light causing chlorophyll formation in leucoplasts. As a result, the
affected tubers are not marketable for food. Minimizing storage losses and
extending shelf life of tubers is very important in this era of food security
concerns. Modified atmosphere packaging (MAP) has been used extensively in
fruits and vegetables. This technique involves modifying the atmosphere to create
low O
2
and high CO
2
levels within the package atmosphere with the aim of
extending the shelf life (Beaudry 2000;Mangarajetal.2009). In addition to
atmosphere modification, MAP greatly improves moisture retention (Ben-
Yehoshua et al. 1983;Yumbyaetal.2014). Modified atmospheres are generated
through the natural process of respiration by the enclosed product which reduces
the oxygen concentration and increases the carbon dioxide concentration under
restricted gas exchange through the film barrier (Beaudry 2000). The effect of
these changes in gas composition varies with commodity but it generally reduces
respiration rate and susceptibility to pathogens (Kader et al. 1989; Gorris and
Peppelenbos 1992). Modified atmosphere created by polymeric film has been
reported to increase the storage life of fruits and vegetables through reduction of
water loss, ethylene production and respiration (Mathooko et al. 1993; Mathooko
2003). Packaging potato tubers in dark plastic bags has been proposed as a way
to reduce greening in retail markets (Pavlista 2001). MAP techniques have been
used as an alternative to refrigeration of fresh produce as they are inexpensive
and readily available. MAP is of interest in preserving ware potato quality,
especially in the tropics, where cool storage is expensive and not readily avail-
able. The objective of this research was therefore to investigate the effect of
packaging on the quality of ware potato tubers during short-term storage at
ambient temperatures.
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Materials and Methods
Plant Material
Certified tuber seeds of three genotypes, Shangi a short-dormancy cultivar and Asante
and Kenya Mpya both medium-dormancy varieties, were grown at the University of
Nairobi Kabete Field Station farm between April and July 2013 and between October
2013 and January 2014. Standard agronomic practices recommended for potatoes
including ridging, pest control, fertilization and weeding were utilized. Freshly har-
vested potato tubers free of any evident disease and without any signs of sprouting were
selected for packaging.
Packaging Treatments
Seven types of packaging materials were used in the experiment: black non-perforated
and perforated low-density polyethylene (LDPE) bag, clear/transparent non-perforated
and perforated high-density polyethylene (HDPE) bag, khaki bag, nylon gunny sack,
net/mesh bag and open trays as control. The perforated bags each had 20 holes of 3-mm
diameter covering 2% of total surface area of the bag. The treatments were laid out in a
completely randomized block design (CRBD) replicated three times. Each package had
20 tubers.
Data Collection
Data were collected on dormancy, sprouting, weight loss, tuber greening and
rotting. Dormancy period was recorded as number of days since harvesting to
when 80% of tubers had visible sprouts of 3 mm in length. Ten tubers from
each treatment were randomly sampled and observed initially at 7-day intervals
until one of the tubers produced the first sprout in each treatment, and then at
4-day intervals to accurately record the dormancy period. Sprouting was
expressed as a percentage of the number of tubers sprouted to the total number
per sample. Weight measurements were done at the beginning of the experiment
and every 4 days thereafter to determine the weight loss trend over 32 days of
storage. The decrease in weight was expressed as a percentage of the initial
weight, with weight including sprouts. Tuber greening was evaluated visually
and the number of green tubers within each package recorded. Any tuber
showing signs of a green colouration was considered to have greened. Evalu-
ations on tuber rotting were made visually by observing each tuber for any
signs of dry and soft rots and incidence was recorded as a percentage of the
total number of tubers in a sample. The number of rotten tubers within a
sample was recorded for 5 weeks.
Data Analysis
All data were subjected to analysis of variance using Genstat statistical program
(Genstat 2010). Mean differences among the treatments were separated by Tukey’s
least significant difference procedure at 5% level of significance.
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Results
Dormancy Duration and Sprouting
There was significant (p≤0.05) interaction between package type and cultivar. Non-
perforated black LDPE and clear HDPE bags significantly reduced dormancy of the
three cultivars compared to the other packaging and the control with the highest
reduction recorded for non-perforated clear HDPE bags (Table 1). In contrast, perfo-
rated black LDPE and clear HDPE bags significantly increased the dormancy of
cultivar Kenya Mpya as compared to the other packaging and control (Table 1).
Generally, tubers of cultivar Shangi had the shortest dormancy period irrespective of
the type of package. Kenya Mpya tubers packaged in perforated LDPE, perforated
HDPE and nylon gunnysack had longer dormancy period than those packaged in trays,
khaki bag, net bag and non-perforated black LDPE bag. Cultivars Asante and Kenya
Mpya packaged in nylon gunny sacks, perforated HDPE and perforated LDPE bags
had longer dormancy period than that of unpackaged control tubers (Table 1).
Tuber sprouting percentage differed significantly (p≤0.05)among packaging treat-
ments, storage duration and cultivars (Table 2). Sprouting of all genotypes commenced
in the second week of storage for tubers packaged in non-perforated HDPE bags.
Significant differences in sprouting percentage among tubers of the three cultivars
packaged in non-perforated HDPE bags were observed in week 2; thereafter, differ-
ences among cultivars were not observed (Table 2). Generally, sprouting was observed
earlier in cultivar Shangi in all the packages tested compared to Asante and Kenya
Mpya tubers. Tubers packaged in non-perforated LDPE bags had over 80% tubers
sprouted by weeks 4, 8 and 10 for cultivars Shangi, Asante and Kenya Mpya tubers,
respectively (Table 2). Sprouting of cultivar Asante and Kenya Mpya tubers packaged
in khaki bags, net bags, nylon gunnysack bags, perforated PE bags and the unpackaged
control tubers commenced at week 10. Generally, the percentage of sprouted tubers of
all the cultivars increased with increased storage duration. At the end of week 12, there
Tab l e 1 Effect of packaging on dormancy duration (days from harvest to end of dormancy) of three potato
cultivars in Kenya
Package type Cultivars
Asante Kenya Mpya Shangi
Control 78.3
abc
70.3
cd
40.0
f
Khaki bag 75.3
abcd
72.0
bcd
40.0
f
Net bag 74.7
abcd
72.0
bcd
36.0
fg
Non-perforated black LDPE bag 56.0
e
66.3
de
28.0
gh
Non-perforated clear HDPE bag 17.0
hi
19.0
hi
10.0
i
Nylon gunnysack 77.3
abcd
82.0
ab
35.0
fg
Perforated black LDPE bag 78.7
abc
84.0
a
36.0
fg
Perforated clear HDPE bag 84.0
a
83.7
a
33.0
fg
Means in rows and columns with different superscript letters indicate significant differences (p<0.05) in
treatment means based on Tukey’s protected least significant difference (LSD)
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were no significant differences in sprouting percentage among the packages as well as
among cultivars (Table 2).
Weight Loss
The least cumulative weight loss over 32 days in storage was observed in tubers
packaged in non-perforated HDPE and LDPE bags for all the cultivars with no
significant difference between the HDPE and LDPE bags (Table 3). High weight loss
was observed for unpackaged tubers recording 11.3, 10.7 and 11.5% weight loss for
cultivars Shangi, Asante and Kenya Mpya, respectively (Table 3). This was approxi-
mately 15.8, 14.3 and 13 times more weight loss than that of non-perforated HDPE and
LDPE bags. Net bag packaging also resulted in significantly higher weight loss than the
rest of packaging materials, namely 9.1, 10.3 and 10.7% weight loss for cultivars
Shangi, Asante and Kenya Mpya, respectively (Table 3). However, for cultivar Shangi,
it was slightly lower than that of non-packaged tubers. When the PE bags were
perforated, weight loss was significantly higher than when they were not perforated.
Nylon gunny sack and khaki bag packaging had moderate effect on weight loss. Weight
loss differed slightly among the cultivars, with Kenya Mpya having a higher total
weight loss compared to Asante in all of the packages tested (Table 3).
Weight loss during the 4-day measuring intervals decreased with storage time. The
tubers stored in non-perforated PE bags maintained the lowest weight loss trend among
the packaging materials throughout the experimental duration (Fig. 1). Weight losses
during the first 12 days of storage were high across all the treatments whereas
unpackaged tubers recorded the highest weight loss during the first 8 days in storage
(Fig. 1). Towards the end of experimental duration, the rate of weight loss trend became
similarly low and tubers packaged in khaki bags, net bags, nylon gunny sack and
control displayed a similar weight loss trend (Fig. 1) but were still significantly higher
than that of tubers packaged in PE bags. Despite heavy sprouting of tubers packaged in
non-perforated PE bags, it was also observed that tubers preserved their initial firmness
for a long period of storage, while non-packaged tubers significantly shrivelled.
Greening Incidence
Packaging reduced the frequency at which greening of tubers occurred (Table 4). The
most effective packages in reducing greening were perforated and non-perforated black
LDPE bags. In 5 weeks of storage, tubers packaged in black LDPE bags had no visible
green colouration. Greening was 100% in unpackaged tubers and tubers packaged in
net bags after 5 weeks. Khaki bags significantly lowered the number of green tubers
and at the end of storage, greening was 27, 43 and 50% for cultivars Asante, Shangi
and Kenya Mpya, respectively. At the end of 5-week storage, 100% greening was
observed for cultivars Shangi and Kenya Mpya, packaged in nylon gunny sacks, net
bags, perforated clear HDPE bags and the control. Generally, the number of green
tubers increased with storage time. The unpackaged tubers began forming visible green
colouration within 7 days of the experiment. The most susceptible cultivar was Kenya
Mpya with tubers recording 100% greening in 7 days. Asante tubers recorded signif-
icantly lower greening incidences in most packaging materials tested while Kenya
Mpya tubers recorded the highest (Table 4).
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Tab l e 2 Effect of packaging on percentage sprouted tubers of three potato cultivars for 12 weeks under ambient conditions in Kenya
Sprouting (%)
Type of package Cultivar Storage duration (weeks)
123 4 5 6789101112
Unpackaged(control) Asante 000 0 0 000066.777.891.1
KenyaMpya000 0 0 000086.795.695.6
Shangi 0 0 0 0 68.8 84.4 91.1 100 100 100 100 100
Khakibag Asante 000 0 0 00006068.9100
KenyaMpya000 0 0 000082.297.8100
Shangi 0 0 0 0 68.8 91.1 97.8 100 100 100 100 100
Netbag Asante 000 0 0 000075.68097.8
KenyaMpya000 0 0 000075.688.993.3
Shangi 0 0 0 0 82.2 86.7 93.3 100 100 100 100 100
Nylongunnysac Asante 000 0 0 000046.771.193.3
KenyaMpya000 0 0 000042.266.784.4
Shangi 0 0 0 0 82.2 88.9 93.3 100 100 100 100 100
PerforatedLDPEbag Asante 000 0 0 000035.657.897.8
KenyaMpya000 0 0 000044.457.880
Shangi 0 0 0 0 82.2 93.3 100 100 100 100 100 100
PerforatedHDPEbag Asante 000 0 0 00002048.980
KenyaMpya000 0 0 000035.66080
Shangi 0 0 0 0 86.7 91.1 100 100 100 100 100 100
Non-perforated LDPE Asante 0 0 0 0 0 0 0 86.7 91.1 95.6 97.8 100
Kenya Mpya 0 0 0 0 0 0 0 0 73.3 84.4 84.4 88.9
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Tab l e 2 (continued)
Sprouting (%)
Type of package Cultivar Storage duration (weeks)
123 4 5 6789101112
Shangi 0 0 24.4 82.2 100 100 100 100 100 100 100 100
Non-perforated HDPE Asante 0 55.5 100 100 100 100 100 100 100 100 100 100
Kenya Mpya 0 28.8 91.11 100 100 100 100 100 100 100 100 100
Shangi 0 86.6 100 100 100 100 100 100 100 100 100 100
LSD (5%) ns 7.49 8.53 12.91 10.61 5.93 3.60 4.47 5.67 17.47 16.44 8.22
LSD (p≤0.05): P 1.473
LSD (p≤0.05): C 0.902
LSD (p≤0.05): SD 1.804
LSD (p≤0.05): P × C 2.551
LSD (p≤0.05): P × SD 5.102
LSD (p≤0.05): C × SD 3.124
LSD (p≤0.05): P × C × SD 8.837
HDPE high-density polyethylene bag, LDPE low-density polyethylene bag, Ccultivar, Ppackage type, SD storage duration, ns not significant
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Tuber Decay Incidences
Rotting was not observed in tubers packaged in perforated LDPE bags, nylon gunny
sacks, net bags and control in open trays. During the 5 weeks of storage, decay was
greatest in tubers packaged in non-perforated HDPE bags with losses being ashigh as 60,
66.67 and 64.44% for cultivars Asante, Shangi and Kenya Mpya, respectively (Table 5).
Tubers packaged in non-perforated LDPE bags recorded the second highest rate of decay
followed by those packaged in khaki bags, while for tubers packaged in perforated HDPE
bags, decay was recorded for cultivar Kenya Mpya only (Table 5). In fact, there was no
significant difference in decay among tubers packaged in khaki bags and perforated
HDPE. There were no significant differences among the cultivars (Table 5).
Discussion
Dormancy Duration and Sprouting
Packaging tubers in clear, high-density non-perforated polyethylene bags resulted in an
early end to dormancy (Table 1), the highest number of sprouts per tuber, high sprout
length and thicker sprouts (data not shown). This will be attributable to changes within
the package especially relative humidity and gas composition. The increased relative
humidity coupled with increased carbon dioxide and low oxygen concentration and
rises in temperature are likely factors that contributed to the early termination of
dormancy and subsequent sprouting. High relative humidity effects on shortening tuber
dormancy and enhancing sprout growth have been reported (Craufurd et al. 2001;
Ezekiel et al. 2002;Shiwachietal.2003; Singh and Ezekiel 2003).
Atmospheric gas composition during storage has been shown to affect the tuber
dormancy period. Increased carbon dioxide concentration in combination with
Tab l e 3 Effect of packaging material on total percentage weight loss of ware potato tubers of three potato
cultivars after 32 days of storage at ambient temperatures in Kenya
Type of packaging material Weight loss (%)
Cultivars
Asante Shangi Kenya Mpya
Control (trays) 10.7
fg
11.3
g
11.5
g
Khaki bag 8.3
cde
7.9
cd
9.9
efg
Net bag 10.3
fg
9.1
def
10.7
fg
Nylon gunnysack 6.5
c
8.2
cde
7.4
cd
Perforated LDPE bag 3.2
b
4.2
b
4.0
b
Perforated HDPE bag 3.7
b
3.8
b
3.9
b
Non-perforated LDPE bag 0.8
a
0.8
a
0.9
a
Non-perforated HDPE bag 0.7
a
0.7
a
0.8
a
Values followed with different superscript letters in rows and columns are significantly different according to
Tukey’s protected least significant difference test (p<0.05)
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reduction of oxygen to a certain concentration has been associated with faster dorman-
cy break, increased number of sprouts and cell elongation (Coleman and Mclnerney
1997; Pinhero et al. 2009). In addition, a decrease in abscisic acid level within the
potato tubers at 60% carbon dioxide and 20% oxygen has been reported (Coleman and
McInerney 1997; Coleman 1998). In this study, high carbon dioxide concentration and
low oxygen concentration could have been achieved due to respiration of the tubers and
restriction of air movement out of the non-perforated polyethylene packages.
Cultivar Shangi
Cultivar Asante
Cultivar Kenya Mpya
0
1
2
3
4
5
6
7
8
4 8 12 16 20 24 28 32
Control
Khaki bag
net bag
Nylon gunnysack
perforated LDPE bag
perforated HDPE bag
Non-perforated LDPE bag
Non-perforated HDPE bag
Duraon of storage (days)
weight loss
(%)
0
1
2
3
4
5
6
7
8
4 8 12 16 20 24 28 32
Control
Khaki bag
net bag
Nylon gunnysack
perforated LDPE bag
perforated HDPE bag
Non-perforated LDPE bag
Non-perforated HDPE bag
Weight loss %
Duraon of storage (Days)
0
1
2
3
4
5
6
7
8
4 8 12 16 20 24 28 32
Control
Khaki bag
net bag
Nylon gunnysack
perforated LDPE bag
perforated HDPE bag
Non-perforated LDPE bag
Non-perforated HDPE bag
Weight loss %
Duraon of storage (Days)
Fig. 1 Effect of packaging material on weight loss trend per 4-day interval of ware potato tubers of three
cultivars stored for 32 days under ambient temperature in Kenya
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High temperatures are also known to promote sprout growth (Wustman and Struik
2007). It is speculated that limited permeability within non-perforated HDPE bags
could have resulted in slightly higher temperature than the surrounding ambient air. The
differences observed in sprout length, number of sprouts per tuber and sprout thickness
Tab l e 4 Effect of packaging on tuber greening (% tubers with green colour) for three cultivars during 5-week
storage under ambient conditions in Kenya
Package type Cultivar Storage duration (weeks)
12345
Unpackaged (control) Asante 36.7 55.0 78.3 100.0 100.0
Kenya Mpya 100.0 100.0 100.0 100.0 100.0
Shangi 51.7 100.0 100.0 100.0 100.0
Khaki bag Asante 0.0 1.7 6.6 15.0 26.7
Kenya Mpya 3.3 23.3 33.3 38.3 50.0
Shangi 0.0 5.0 5.0 16.7 43.3
Net bag Asante 15.0 40.0 53.3 91.7 100.0
Kenya Mpya 50.0 66.7 100.0 100.0 100.0
Shangi 38.3 55.0 100.0 100.0 100.0
Non-perforated black LDPE Asante 0.0 0.0 0.0 0.0 0.0
Kenya Mpya 0.0 0.0 0.0 0.0 0.0
Shangi 0.0 0.0 0.0 0.0 0.0
Non-perforated clear HDPE Asante 0.0 0.0 0.0 5.0 20.0
Kenya Mpya 0.0 6.6 16.7 43.3 60.0
Shangi 0.0 6.6 20.0 30.0 46.7
Nylon gunnysack Asante 1.6 20.0 33.3 48.3 61.7
Kenya Mpya 43.3 68.3 100.0 100.0 100.0
Shangi 26.7 50.0 70.0 75.0 100.0
Perforated black LDPE bag Asante 0.0 0.0 0.0 0.0 0.0
Kenya Mpya 0.0 0.0 0.0 0.0 0.0
Shangi 0.0 0.0 0.0 0.0 0.0
Perforated clear HDPE bag Asante 3.3 15.0 28.3 41.7 46.7
Kenya Mpya 56.7 70.0 100.0 100.0 100.0
Shangi 25.0 45.0 100.0 100.0 100.0
LSD (5%) 9.15 13.50 14.28 12.65 10.74
LSD (p≤0.05): C 1.88
LSD (p≤0.05): P 3.07
LSD (p≤0.05): SD 2.43
LSD (p≤0.05): C × P 5.32
LSD (p≤0.05): C × SD 4.20
LSD (p≤0.05): P × SD 6.86
LSD (p≤0.05): C × P × SD 11.89
HDPE high-density polyethylene bag, LDPE low-density polyethylene bag, Ccultivar, Ppackage type, SD
storage duration
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among cultivars can be attributed to their genetic differences (Struik 2007). Cultivar
Shangi, which exhibited a short dormancy period, gave long sprouts and also high
number of sprouts in every package type compared to Asante and Kenya Mpya. Similar
results have been reported by Carli et al. (2010) who found a negative correlation
between dormancy period and length of the longest sprout with shorter dormancy
clones recording longer sprouts and more sprouts per tuber than tubers with longer
dormancy periods.
Weight Loss
The post-harvest moisture content of vegetables is considered one of the most impor-
tant factors in maintaining their quality and shelf life. Post-harvest weight loss brought
about by water loss is a primary factor limiting post-harvest longevity in most vege-
tables. The acceptable weight loss in potato tubers is up to 10% since no visible
shrivelling takes place at this point (Mehta and Ezekiel 2010). In this study, non-
packaged tubers as well as tubers packaged in net bags lost more than 10% of their
weight during 32 days of storage. The tubers were shrivelled; hence, the market value
of these potatoes was greatly reduced.
Weight loss in stored tubers has been attributed to processes such as evaporation,
respiration and sprouting but the main contributing factor is evaporation (Mehta and
Ezekiel 2010). Sprouting results in a notably large increase in weight loss due to
increased moisture evaporation resulting from sprout growth (Singh and Ezekiel
2003). Contrary to literature, the results of this study found that the highest sprouting
rate, high sprout length and high number of sprouts did not result in increased weight
loss. This was due to packaging of tubers especially in non-perforated PE bags. The
remarkable reduction in weight loss observed in non-perforated PE bags will be linked
to a high relative humidity created within the package as well as the limited perme-
ability of the PE bags. The moisture evaporating from the tubers and sprouts
Tab l e 5 Effect of ware potato packaging on tuber decay (% decayed tubers) during 5-week storage under
ambient storage in Kenya
Type of package Decay (%)
Cultivar
Asante Kenya Mpya Shangi
Control 0.0
a
0.0
a
0.0
a
Khaki bag 4.4
ab
4.4
ab
4.4
ab
Net bag 0.0
a
0.0
a
0.0
a
Non-perforated LDPE bag 17.8
c
13.3b
c
15.6
c
Non-perforated HDPE bag 60.0
d
64.4
d
66.7
d
Nylon gunnysack 0.0
a
0.0
a
0.0
a
Perforated LDPE bag 0.0
a
0.0
a
0.0
a
Perforated HDPE bag 0.0
a
2.2
a
0.0
a
Means in rows and columns with different superscript letters indicate significant differences (p<0.05) in
treatment means based on Tukey’s protected least significant difference (LSD)
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condensed, creating a high in-pack relative humidity. Several studies have reported that
film packaging maintains a high relative humidity and reduces water loss (Chandran
2010; Rodov et al. 1995; Ben-Yehoshua et al.1983). Additionally, high relative humid-
ity has been reported to reduce transpiration from the produce, thereby reducing weight
loss, wilting, shrivelling and loss of firmness (Aharoni et al. 2007). Although the tubers
packaged in non-perforated PE bags had multiple sprouts, they appeared firmer than the
non-packaged tubers that had few sprouts. High weight loss in the non-packaged tubers
and those in net bags could be attributed to the high airflow rate around the tubers as
observed in other studies (Whitelock et al. 1994). Generally, permeability of packaging
material to moisture loss played a great role in weight loss. The more permeable a
material was, the more weight was lost. The small differences observed among cultivars
could be due to their genotypic differences in sprouting characteristics, skin surface and
tuber dry matter concentration. Cultivar Asante has high dry matter concentration
compared to Shangi and Kenya Mpya (NPCK 2015). Differences between cultivars
in skin surface permeability could result from differences in cuticle thickness (Lownds
et al. 1993). Also Gachango et al. (2008) attributed weight loss differences among
genotypes to differences in skin surface and the dry matter concentration of the tubers.
Ezekiel et al. (2002) reported that tuber weight loss differs by cultivars, storage
conditions and storage durations among other factors.
Tuber Greening
Greening affects the quality and palatability of potatoes. In this study, packaging the
tubers reduced the frequency at which greening occurred, probably due to lowering the
light transmission. The lowest numbers of greened tubers were recorded in tubers
packaged in black package (perforated and non-perforated) and the highest numbers of
greened tubers occurred in trays and net bags. Khaki bags, nylon gunnysack and clear
PE bags allowed some light transmission, resulting in greening (Table 4). Rosenfeld
et al. (1995) reported that greening of potato tubers packaged in different bags was
proportional to the amount of light allowed in. Additionally, their study found differ-
ences in glycoalkaloid levels in potato tubers packaged in materials with different light
transmission. Cultivar differences in greening were observed (Table 4). Asante tubers
recorded lower greening incidences in most packaging materials tested while Kenya
Mpya tubers recorded the highest. Cultivar differences in the degree of greening of
tubers exposed to light have been reported earlier (Percival 1999). Reeves (1988)found
that greening was less in russet compared to white cultivars. This is probably the reason
why cultivar Kenya Mpya, which has a cream-white skin colour, showed faster and
greater incidence of tuber greening, while cultivar Asante with a pink skin colour
recorded the least incidence of tuber greening. Differences in potato greening among
cultivars exposed to light have been reported to be an inherited genetic factor (Jakuczun
and Zimnoch-Guzowska 2006).
Tuber Decay Incidence
Tuber rot was heavier in non-perforated HDPE bags than in other packages. This may
have been due to high in-pack relative humidity. Moreover, water droplets condensed
on the tubers and inner film surfaces of the non-perforated PE bags could have
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contributed to the increased decay. Kader (2004) pointed out that having condensed
moisture on commodity surfaces could enhance decay development more than in-
creased relative humidity. Rodov et al. (2010) and Aharoni et al. (2007) suggested that
having condensed moisture on the commodity surface inhibits gas exchange and
enhances microbial growth. As much as high relative humidity is advantageous in
reducing weight loss, it is known to increase disease incidence. In this study, high
relative humidity leading to moisture condensation primarily caused increased decay in
addition to soft rot (Pectobacterium carotovorum). Tuber respiration in the non-
perforated packages could have depleted the oxygen supply. Due to the limited
permeability of the non-perforated HDPE bags, temperature inside the pack could have
been higher than the ambient temperature, hence contributing additionally to tuber
rotting. Temperatures above 28 °C are said to favour the growth of the pathogen
P. carotovorum and an increase in temperature increases the severity of the disease
(Singh et al. 2002). No tuber rotting was reported in unpackaged, net bags, perforated
bags and nylon gunny sacks. This was attributed to storage conditions that were dry,
thus not conducive for disease development.
In this study, non-perforated polyethylene bags were manifestly more efficacious in
preventing weight loss and maintaining a fresher looking tuber. However, these non-
perforated polyethylene bags reduced shelf life by promoting sprouting and tuber
decay. Perforation of the PE bags reversed the negative effect (excessive sprouting
and tuber decay) of non-perforated PE bags. Low-density black PE bags were the best
method for ware potato packaging due to low sprouting, reduced weight loss, low rate
of tuber greening and reduced rate of tuber decay compared to other packaging
materials tested.
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