Influence of post-harvest application of chitosan on physico-chemical changes of apple fruit during storage

Apple due to its climacteric nature lose its quality very rapidly. Chitosan being a non-toxic biodegradable material can be used as coating material for fruits. It would be environmental friendly as compared to other chemicals. Therefore, this experiment was conducted to evaluate the optimum chitosan concentration for retaining the quality of apple fruits for longer time. The fruits were coated with three chitosan concentrations (0.5, 1.0 and 1.5%) along with a set of fruits treated with distilled water as control. The fruits when dried were kept in the laboratory at room temperature (18±2oC) for 80 days, to study the effect of chitosan concentrations against physiological attributes after every 20 days interval. Both chitosan and storage had significantly influenced all the quality attributes of apples. Fruits coated with 1.5% chitosan were more firm and had maximum juice content, titratable acidity and ascorbic acid with less weight loss, fruit juice pH, total soluble solids (TSS) and TSS-Acid ratio and these results were at par with the effect of 1.0% chitosan on the fruits. Regarding storage effect, the fruits analyzed after 80 days showed maximum losses in weight, firmness, percent acidity and Ascorbic acids while pH, TSS and TSS-Acid ratio were found maximum. The interactive effect between chitosan and storage was found non-significant for all the studied attributes. It was concluded from the experiment that apple fruits Cv. Lady William coated with 1.0% chitosan after harvesting maintains the quality attributes up to 80 days during storage at 18±2 oC and 56±2% RH.

Despite of losses in quantity, stored apples also have a serious problem of rapidly diminishing nutritional and textural quality [3].Softening of apple fruits is one of the most important problems all over the world.As apples are climacteric fruits, respiration and ethylene synthesis are the primary factors responsible for both qualitative and quantitative losses in the fruits after harvest [4].Postharvest losses are mostly concerned with harvesting techniques, storage conditions, transportation and improper handling which create surface injuries to the fruits that ultimately give way to microbial attacks and huge losses [5].The demand for quality and nutritious food for human consumption has motivated the researchers and attracted their attentions towards food preservation.Most of the scientists conducted experiments on coating materials to increase the shelf life of food commodities.Edible coatings being an efficient barrier to diffusion of gases (O2 and CO2) and resolving issues of aroma and moisture loss [6, 7] can be used to enhance shelf life and post-harvest quality of vegetables and fruits [8].Many researchers have suggested that edible coatings are safe and very effective in preventing perishable food product from deterioration by reducing dehydration, limiting respiration, enhancing texture, maintaining flavor and suppressing microbial growth [9].Chitosan a non-toxic compound produced by de-acetylation of chitin, collected from fungi and the exoskeleton of crustaceans and insects.It could be one of the best edible coating materials because of its outstanding capability to form an antifungal and antimicrobial film with biodegradability, biocompatibility and non-toxicity to human beings [10].It creates semi permeable membrane on fruit surface that regulates gaseous exchange and limit transpiration and ripening [11].Many scientists used chitosan as a surface coating and successfully increased the postharvest life and minimized decay incidence in many fruits, such as strawberry [12], peach [13] and table grape [14].Beside all these significances, the usage of chitosan as a surface coating is more worth full due to its reasonable cost, effectiveness, easy application and antimicrobial properties [15,16].Currently there is no report available on chitosan used as a surface coating on apple (Lady William) to retain its nutritional and textural qualities during storage for longer time.Keeping in view the importance of chitosan as a coating material, the current study was conducted to evaluate the optimum coating concentration of chitosan for apple fruits to maximize its postharvest life for longer storage.

Materials and methods
Apple fruits (cv.Lady William) were harvested at physiologically mature stage from the orchard in Mingora Research Station in Nov, 2016 and brought to the Horticulture Laboratory, The University of Agriculture Peshawar.The fruits having equal sizes and maturity with no abrasions were selected for the current study.Three chitosan concentrations (0.5, 1.0 and 1.5 %) were applied with the help of soft foam to the fruits while distilled water was treated to the fruits as control treatment.The fruits were stored for 80 days (18±2°C, 56%±2 RH) in the laboratory and data were recoded after every 20 days of interval.

Preparing chitosan solution
For preparing various concentrations of chitosan solution, each chitosan weighed for specific concentration was first dissolved in dilute acid (HCl) placed on magnetic stirrer for several minutes.After proper dissolution distilled water was added to obtain a desirable volume of the solution.Its pH was adjusted up to 7 by adding 0.1 N NaOH.

Statistical analysis
The recorded data were analyzed through Analysis of Variance (ANOVA) procedure for CR design with two factor factorial arrangement.In case data were found significant, means were compared by using Least Significance Differences (LSD) test at 5% level of significance.Statistical software Statistix (8.1) was used for computing ANOVA and LSD test [17].

Fruit weight loss
The data regarding fruit weight loss is shown in (Table 1).Chitosan concentrations and storage duration significantly affected weight loss of the fruits.In fruits, treated with distilled water, maximum weight loss (8.33%) was observed, followed by fruits treated with 0.5% chitosan concentration (6.86 %), however weight loss was minimum (5.43 %) in fruits treated with 1.5% chitosan concentration.The chitosan concentrations significantly declined weight loss during storage.This might be the reason that chitosan coating acts as a barrier to gaseous exchange and cell wall integration which slow down the evapotranspiration and finally the level of respiration in fruits [18].Current results are in agreement with [19] that apples coated with various concentration of chitosan showed reduction in weight loss of fruit as compared to un-treated fruits.Weight loss in fruits was consistently increased during storage.Fruit storage upto 80 days resulted in maximum weight loss (9.15%), followed by (8.50%) at 60 days of storage, while least weight loss (3.79%) was observed at 20 days of storage.Respiration and transpiration has a major role in weight loss of fruits during storage [20].Other studies also revealed that a steady increase in weight loss of apples was recorded during storage [21,22].TSS/acid ratio of the fruits was increased with storage duration.Maximum TSS/acid ratio (20.8) was noted at 80 days of storage, followed by (18.6) at 60 days of storage, while, the lowest TSS/acid ratio (13.5) was recorded in fruits at freshly harvested stage.The increased TSS/acid ratio in fruits during storage is due to degradation of ascorbic acid and increase in TSS [44].Another study revealed that increase in TSS/acid ratio during storage might be due to the hydrolysis of polysaccharides; conversion of starch into sugar [45].Also [46] examined a high TSS/acid ratio in 'Valencia' oranges with the passage of time.
Ascorbic acid (mg 100g -1 ) Highest ascorbic acid (14.0 mg 100g -1 ) was recorded in the fruits treated with 1.5% chitosan, which was at par with ascorbic acid 13.3 mg 100g -1 ) in fruits coated with 1.0% chitosan.The lowest value for ascorbic acid (11.9 mg 100g -1 ) was observed in control fruits.Chitosan coating reduces oxygen diffusion, slowing down the respiration rate, which ultimately delays the deteriorative oxidation reaction of ascorbic acid of fruit The ascorbic acid was decreased in fruits with storage intervals.Maximum ascorbic acid (14.8 mg 100g -1 ) was noted in freshly harvested fruits, followed by ascorbic acid (13.7 mg 100g -1 ) at 20 days of storage, while the minimum ascorbic acid (11.3 mg 100g Introduction Apple (Malus domestica) belongs to the family Rosaceae.It is native to Eastern Turkey [1].Apples being highly perishable in nature, there have been almost 25-40% postharvest losses during its marketing [2].

[ 47 ].
The post-harvest application of chitosan significantly reduced vitamin C losses during storage [48].Similarly, [49] observed better retention of vitamin C in edible coated sweet orange fruits.Similar effect was also observed in chitosan coated pear fruits [50].

Table 1 . Weight loss, Fruit firmness, Juice content, Juice PH, TSS, Titratable acidity, TSS/Acid ratio and Ascorbic acid of apple fruit as affected by chitosan concentration and storage duration
Fruit firmness (kg.cm -2 ) Chitosan coating significantly retained the fruit firmness.Highest fruit firmness (4.81 kg.cm -2 ) was recorded in fruits coated with 1.5% chitosan concentration closely followed by fruits treated with 1.0% (4.65 kg.cm -2 ), while lowest fruit firmness (4.01 kg.cm -2 ) was noted in fruits treated with distilled water.The retained firmness in apple fruits might be due to low rate of respiration caused by chitosan coating, acted as barrier to gaseous exchange along the fruit surface [23].The results of [19] are also in Alves VD & Moldao-Martins M (2013).Impact of chitosanbeeswax edible coatings on the quality of fresh straw-berries (Fragaria ananassa cv Camarosa) under commercial storage conditions.Food Sci Technol 52: 80-92.37. Hayat I, Masud T & Rathore HA (2005).Effect of coating and wrapping material on shelf life of apple.Inter J Food Safety 5: 24-34.38.Farooqi WA & Hall EG (1973).Effect of wax coating on apple and pears during storage and ripening.Aust J Exp Agric 13(2): 200.39.Wills RBH, Banbridge PA & Scott KJ (1980).Use of flesh firmness and other objective test to determine consumer acceptibility of delicious apple.