Impact of packaging materials on the quality attributes of potato ( Solanum tuberosum L . ) during storage

A comprehensive study was planned to identify best packaging material for the variety “Lady Rosetta” which has a higher market demand. Three different packaging materials (i.e. jute, polypropylene and cotton bags) shown as T1 (control), T2 (Jute packaging), T3 (Polypropylene net bags) and T4 (Cotton packaging) were used. Physico-chemical (weight loss, total soluble solids, pH, starch and sugars) and functional attributes (ascorbic acids and total phenolic contents) were investigated at 15 days interval during storage (25±2C). The processing performance of stored potato was also assessed in terms of chip crispiness, flavor and color. The physico-chemical parameters investigated revealed an increased weight loss during storage in all samples, however, lower weight loss in polypropylene net bags with a significant difference at P ≤ 0.05. Similarly, total soluble solids increased throughout storage in with a minimum mean value in T3, however a decline observed in pH values with significant difference (P ≤ 0.05). Starch content reduced in the stored samples, while glucose content and total sugars increased significantly (P ≤ 0.05) in all samples. Maximum increase was observed in T1 and minimum in T3. Total phenolic contents showed a slight increase, while ascorbic acid reduced during 105 days storage in all samples. Superior processing results were obtained for the polypropylene stored samples followed by jute and cotton bags. The overall results revealed that polypropylene packaging was found best in maintaining tuber quality attributes up to 105 days during ambient storage. Thus, it is suggested that polypropylene net bags may be used for storage of potato as packaging material.


Introduction
Potato (Solanum tuberosum) is a member of Solanaceae family and is a perennial herbaceous plant.Potato was cultivated previously in Latin America, Argentina, Chile, Colombia, Bolivia and Peru.It is supposed that the potato cultivar has been derived from wild species originated in South America [1].Potato production throughout the world is about 364,808,768 tons in 2014 and its demand in the international market is increase [2].Potato has more than 4000 known varieties [3] few of the most standard varieties found in Pakistan are red peeled (Asterix, Barna, Courage, Desiree, Lady rosetta etc and white peeled (Agria, Desi, Diamont, Hemes and Sante etc) which yields on large scale and use for culinary purpose and in industry for processing [4].In Pakistan potato is commonly cultivated vegetable crop in an area of 184972 hectare with annual production of 3392885 tons [5].Pakistan has multiple seasons for its growth with a large area under cultivation but the export remained only 50,000 tons annually sharing 0.5% export globally.Gilgit-Baltistan is rich in production of class potato [6].Its annual production on Gilgit-Baltistan is estimated about 134031 metric tons (MT).
Local consumption is about 17632 MT and the sale in market is 105921 MT with 10479 MT losses due to unsuitable packaging, diseases etc.The cultivated area is 8526 hectares which is increasing per year as it is main cash crop of the province [7].Potato is rich in carbohydrates and starch is the key component which is a main source of energy and also a good source of lysine protein [8].A hundred grams of potato provides 90 kcal energy [9].Potatoes are the main source of vitamin B6 [10].Potato is low in cholesterol with high potassium and significant antioxidants that protects human beings against circulatory diseases and cancer [11].
Potato is semi delicate crop and store in low temperature to protect from germination and to confirm their regular supply whenever required.Low temperature potato storage is related with low temperature sweetening and is unsuitable in processing potato varieties [12].Storage of potato in low temperature results in enzymatically hydrolysis of insoluble starch into soluble glucose, fructose and sucrose [13].Tuber sweetening loss its market value due to formation of acrylamide which turn brown its fried products and bitter in taste [14].There are high losses of potato in storage that significantly effects the farmer's economy.Packaging material used for potatoes is the effective operation which determine its storage quality.Packaging systems can be improved using low temperature storage [12].Frazier [15] used inhibitors and or suppressants to increase storage while ethylene scavengers [16] and irradiation as integrated management to reduce postharvest damages.The packaging materials treated by means of sheets, cloaks, bags, or more solid containers retain different features that regulate gas interchange between the inner and outer packaging environment [17].In Pakistan large bags made of jute are use in potato industry which has carrying capacity of 100 kg generally used to stock potato tubers after harvest.Hence an advance engineered packaging methods such as by using polyethylene, polypropylene, polystyrene and wound preventing corrugated cartons are essential to fulfill the basic food safety standard measures [18].Usage of poor packaging material deteriorates physical properties of potato such as freshness, tuber integrity and nutritional quality of tubers.Moreover there is not such study conducted regarding packaging material of potato in this region.Therefore keeping in view the specified problem a study was conducted to investigate the best packaging method for potato with the objectives to analyze the effect of different packaging material on quality and shelf life of stored potato; to identify suitable packaging material for extended storage life of potato; to analyze physico-chemical attribute of potato tubers during storage and to investigate chips quality of stored potato.

Materials and Methods
Physico-chemical and processing attributes of a commercial potato variety was chosen for evaluation because of the recent increasing in their production and contribution to the processing industry in Pakistan.This variety was harvested from potato research farm Naltar Gilgit in October 2014 and was immediately transferred to the Food Technology Department, Karakoram International University Gilgit, where the trials were carried out.The tubers were graded into homogenous lots of > 50 mm length, sorted for the exclusion of damaged, diseased and sunburned tubers afterward placed between 15-20 o C for suberization for one week.

Packaging trial
Potatoes were packed in different packaging materials of same size (30 cm × 40 cm) and perforations (10%) procured from local market.The set of treatments included T1 = Control T2 = Jute packaging (JP) T3 = Polypropylene net bags (PP) T4 = Cotton packaging (CP) 5 Kg of potato tubers were placed in each replication and 5 kg tubers were maintained in each treatment for per day analysis.In total 60 Kg potatoes were placed in each treatment later subjected to different physico-chemical and processing analysis at 15 days intervals respectively.

Weight loss
The weight loss (%) in different treatments during storage interval was find out by weighting the samples using digital balance (OHAUS, Model TS4KD Florham Park, NJ, USA).

Glucose
The Glucose test strips method was employed to test Glucose content which was imported from Snack Food Association (Arlington Virginia USA).The change in color was correlated with the color chart and the values were recorded in percentage (%).

Ascorbic acid
The ascorbic acid concentration was find out by titrametric technique using

Potato chips quality evaluation
In the experiment the potato tubers were processed into potato chips.In order to determine organoleptic evaluation twenty five students with the faculty members of Department of Food Technology selected as judges because they were the habitual consumers of potato chips.The judges graded chips according to their preferences for Crispiness (CRP) and Flavor (FLV) by using five point hedonic scale as described by [20].The Color (COL) of the chips was compared with British Potato Council (BPC) Frying color chart and the values were showed as approximate L-values.

Statistical analysis
Results obtained were subjected to statistical analysis by considering the varieties and packaging material as variation source, using two-way analysis of variance (ANOVA).Levels of significance at P ≤ 0.05 were determined by least significant difference test (LSD).

Effect on weight loss (%)
The general trend was an increase in weight loss (%) in all treatments; however the rate of weight loss was slower in packaged potato, as compare to control during the storage period (Table 1).Treatment means of packaged potato showed significant difference.Data on weight loss revealed significant differences between all the storage means.The interaction between treatment means and storage intervals showed maximum weight loss (%) in T1 and minimum in T3 at the end of storage.T1 (3.17%) showed maximum weight loss meanwhile polypropylene packaging (T3) Effect on total soluble solids Data pertaining to the total soluble solid (TSS) in potato exhibited general increasing during the storage period.The increase in total soluble solid was more pronounced in T1 as compare to rest of treatments (Table 2).Treatment means indicated minimum retention of total soluble solid in T2, followed by T3 and T4 with significant difference recorded between them.Storage interval means showed significant difference in total soluble solid with minimum value during the 0 day storage period and maximum retention was observed in case of 105 days storage period.Although nonsignificant interaction between treatment means and storage intervals means became significant after the 15 days storage .
Total soluble solid accumulation in all the packaging materials was steady during the early weeks of storage, which progressively increased with the increasing in storage duration.Maximum retention of total soluble solid value estimated in control (6.32 brix o ) followed by T3 (

Effect on starch
The variation in starch contents in response to different packaging material showed steady initial increased followed by progressive decline during the storage period (

Effect on glucose
The effect of different packaging materials on glucose contents showed steady increase throughout the storage period however, the rate of increase in glucose contents varied with the type of packaging material (Table 6).Treatment means showed significant difference in stored potato with T1 124.52 mg/100g retained maximum while T3 77.17mg/100g retained minimum glucose contents.Storage interval means also revealed significant difference with maximum value recorded in the last 105 days while minimum during first 15 days storage.The interaction between storage intervals and treatments revealed less significant difference at the start of storage however significant difference have been recorded at the later stages of storage.Steady increase in glucose contents had been observed in potato during storage however the increase was more pronounced in case of control.The rate of increase in glucose level in control started by the 45 days and gradually increased up to 251.12 mg/100g by the end of storage.Rapid increase in glucose contents had been recorded in cotton packaging by 60 days.Least

Effect on ascorbic acid
In response to different packaging systems the ascorbic acid was among the parameters, which decrease with the increase in storage time (Table 7).The decrease was highly significant in control as compare to all other treatments.Treatment means showed maximum ascorbic acid retention in T3 (24.02mg/100g) followed by T2 (

Effect on total phenolic contents
Total phenolic contents (TPC) showed initial decreasing trend which started to increase at the end of storage period (Table 8).Considerable decline in total phenolic contents was observed in control as compare to packaged potatoes.Treatment means showed significant difference in total phenolic contents in response to different packagings.T3 (138.44mg/GAE/100g d.w.) maintained maximum total phenolic contents followed by T2 (142.85 mg/GAE/100g d.w.) and T4 (145.25 mg/GAE/100g d.w.)While minimum were observed in T1 (154.75 mg/GAE/100g d.w.).Storage interval means expressed significant difference with maximum determined in 60 days storage while minimum estimated in 0 days interval (141.04 mg/GAE/100g d.w.).The interaction between treatments and storage intervals showed maximum total phenolic contents in T3 (157.75mg/GAE/100g d.w.) and during 105 days storage.
Total phenolic contents are bioactive compounds responsible for various significant physiological processes like enzyme activity, nutrient uptake, protein synthesis [45].They acts as substrate in potato browning mediated through the activities of poly phenol oxidase enzymes and molecular oxygen followed by subsequent melanin formation [46].High retention of total phenolic contents during storage is attributed to low poly phenol oxidase and momentous anti-oxidant activity in potatoes [11].During storage total phenolic contents in potato continued to increase [47] till the onset of poly phenol oxidase activity.The presence of ample molecular oxygen in control caused significant decline in total phenolic contents as compare to other treatments.Our results indicated that packaging materials in general polypropylene in particular curtail the decline in total phenolic contents as compare to control which are also in line with the findings of [48].

Effect on chip flavor
Chips flavor (CFL) estimated as scores recorded by the judges showed an initial increase and eventual decreasing trend in all the treatments during the storage (Table 9).The treatment means exhibited maximum chips flavor scores recorded in T3 (4.26)followed by T2 (3.99), T4 (3.75) and minimum found in T1 (3.65).The means of storage intervals showed maximum chips flavor during the mid-storage intervals while minimum were articulated during the start and end of the storage.The interaction between storage intervals and treatments showed minimum (2.72/5.00)and maximum (4.61/5.00)scores in T1 and T2 respectively during storage.In general chips flavor scores increased in all the treatments after 30 days storage which started to decline after 60 days storage in most of the treatments.Potatoes Flavor is the sensory impression of food detected by the blend of taste and smell senses.It is the overall resultant impression derived by the taste buds in mouth and aroma detected by olfactory epithelium in nose.Flavor evolution in potato chips is primarily attributed to the oil uptake and corresponding volatile formations during thermal processing [49].In the present study generally chips flavor scores were found in consistent with the other quality attributes in potato chips.The maximum chips flavor scores were identified in polypropylene net bags and jute packaged potatoes as compare to control.

Effect on chip crispiness
Chip crispiness (CCR) scores showed a steady increase followed by final decrease in all the treatments however the rate of decrease in chip crispiness scores was found lower in packaged potatoes as compare to control (Table 10).Treatment means revealed significant difference in all the treatments and were also found statistically dissimilar at 5% level of significance.
Storage interval means showed initial increase in chip crispiness scores which remained persistent during the most of storage time and found minimum during the end of storage.The interaction between treatments and storage intervals showed maximum chip crispiness scores in T3 (

Conclusions
In this study three packaging material (cotton, jute and propylene net bags) were tested against potato tuber to maintain quality during storage.From the results it was concluded that propylene net bags showed efficient packaging material followed by jute.So it is recommended that propylene net bags may be used as a packaging material for potato tuber during storage.Moreover the "Lady Rosetta" found as superior processing variety for potato manufacturing owing to its appropriate size and shape, high dry matter and reducing sugar with best processing performance.

Acknowledgment
The author is thankful to Department of Agriculture and Food Technology, Karakoram International University for providing fund and lab facility.The writer also thankful to his supervisor for assistance and support.The author specially acknowledge Mr. Babar Hussain for helping in preparing the manuscript.
most of other treatments at the end of storage.Chip color is the most important quality parameter sternly related to the consumer perception for the product acceptance[52].Potato chip color is the consequence of Maillard reaction primarily related to the presence of reducing sugars, protein, frying temperature and duration[53].In addition the chip color value is an important index of toxic acrylamide formation in potato during high temperature processing[54].Chip color values in the present investigation were quantified on the basis of approximate L-values as described in fry color chart by British Potato Council (BPC, UK).L * is the luminance having colorimeteric value ranges between 0 (Black) to 100 (Light) however the L-value for potato chips color presented in the fry color chart ranged between 65 (Grade-I) to 49 (Grade-V).In general the chip color values remained statistically similar in response to most of the packaging applications however found minimum in control as compare to all other treatments.Since the frying temperature and duration remained constant factors in potato processing thus presence of reducing sugars being the major determinant of chip color values during storage.Potato with low reducing sugar contents retained maximum chip color value as happened in packaged potatoes during storage.The correlation between reducing sugar contents and potato chip color has also been reported by different researchers like [39, 40, 55].
Conceived and designed the experiments: S Ali & A Hussain, Performed the experiments: T Abbas, Analyzed the data: T Abbas, SW Hussain & Z Hasnain, Contributed reagents/ materials/ analysis tools: I Fatima, Q Zehra & Y Abbas, Wrote the paper: B Hussain, R Alam & Z Hussain, Corresponding author: B Hussain.

Table 1 . Effect of different packaging materials on weight loss (%) during storage
0.3580 z 0.8687 u 1.7580 p 2.0620 m 3.9860 h 6.5763 b 9.8090 a 3.1773 A T2 0.00 b 0.4847 x 0.7877 v 1.1140 s 1.9783 o 2.9890 k 4.5893 e 5.9850 c 2.2410 C T3 0.00 b 0.3250 a 0.6287 w 0.9370 t 1.4643 q 2.4910 l 3.4933 i 4.3847 g 1.7155 D T4 0.00 b 0.3883 y 0.7833 v 1.1850 r 1.9873 n 3.2743 j 4.5657 f 5.8137 d 2.2497 B 0.00 H 0.3890 G 0.7671 F 1.2485 E 1.8730 D 3.1851 C 4.8062 B 6.4981 A All the means with different letters are significant at p ≤ 0.05 b

Table 2 . Effect of different packaging materials on total soluble solids (Brix o )
o ) packaging, while minimum accumulation observed in T2 (5.94 brix o ) at the end of 105 days storage.Overall different packaging's retained lower total soluble solid accumulation as compared to control.Changes in total soluble solid are directly related with the hydrolytic conversion of insoluble starch polymers into soluble sugars during the post-harvest period [29].In general conversion of starch into sugar is an important index of ripening in most of climacteric fruits.

Table 4 . Effect of different packaging materials on starch (%)
19.22 d 19.02 f 18.25 j 17.24 m 17.22 m 16.34 q 16.01 s 17.86 D T2 19.60 b 19.62 b 19.34 c 18.54 g 18.54 g 18.02 l 17.24 m 17.02 o 18.49 B T3 19.60 b 20.16 a 19.23 d 18.34 i 18.43 h 18.46 h 18.35 i 18.25 j 18.85 A T4 19.60 b 19.13 e 19.05 f 18.12 k 18.05 l 17.12 n 16.45 p 16.14 r 17.96 C 19.60 A 19.53 B 19.16 C 18.32 D 18.06 E 17.71 F 17.09 G 16.85 H All the means with different letters are significant at p ≤ 0.05 b

Table 5 . Effect of different packaging materials on total sugar (mg/100g).
848.94 G 861.38 F 875.23 E 885.03 D 893.03 C 917.97 B 945.22 A All the means with different letters are significant at p ≤ 0.05 H

Table 7 . Effect of different packaging materials on ascorbic acid (mg/100g)
25.33 d 23.63 h 23.07 k 22.07 m 20.12 q 18.05 r 15.64 s 21.86 D T2 27.00 a 25.13 e 24.88 f 23.55 h 23.32 i 23.13 jk 22.16 m 21.56 n 23.84 B T3 27.00 a 26.12 b 25.55 c 25.13 e 23.26 ij 22.34 l 21.33 o 21.45 no 24.02A T4 27.00 a 25.44 cd 24.34 g 23.12 jk 22.05 m 21.46 no 21.06 p 20.16 q 23.08 C 27.00 A 25.50 B 24.60 C 23.72 D 22.67 E 21.76 F 20.65 G 19.70 H All the means with different letters are significant at p ≤ 0.05 a

Table 8 . Effect of different packaging materials on total phenolic contents (mg GAE/100g d.w)
117.54 G 124.44 F 136.50 D 145.32A 144.05 B 140.59 C 135.55 E All the means with different letters are significant at p ≤ 0.05 H

Table 11 . Effect of different packaging materials on Chip Color (L-value)
All the means with different letters are significant at p ≤ 0.05