Aloe vera gel coating along with calcium chloride treatment enhance guava (Psidium guajava L.) fruit quality during storage

Guava (Psidium guajava L.) is one of the commercially important fruit having a perishable nature. In this study, the effectiveness of various concentrations of Aloe vera gel as an edible coating and Calcium Chloride were examined on post-harvest quality of guava fruit stored at 5±1oC for 35 days. Treated guava fruit samples were studied for physicochemical properties (Fruit firmness, phenol content, physiological weight loss, respiration rate, decay index, pH, TSS, titratable acidity, ascorbic acid content, sugar acid-ratio) and sensory attributes (colour and flavour score). All the quality attributes were significantly affected by both treatment and storage intervals. The interaction effect of both treatment and storage duration also significantly affected all quality parameters. Edible coating and low temperature storage had reduced decay and enhanced shelf life of guava fruit. Guava coated with 2% CaCl2 and 10% Aloe vera gel (labelled as GCA4) promisingly retained physico-chemical characteristics and also maintained the sensory attributes than all the other treatments performed and was found to be most effective treatment in maintaining the fruit quality attributes along with the shelf life extension for 35 day.


Introduction
Fruit surface coating is used as one of the best treatment to control the post-harvest losses and to extend the shelf life of fruits. Recently edible coating also known as bio preservation have been developed for preserving and improving the appearance of fruit. Such coating have beneficial effects on fruits like color improvement, prevent moisture loss percentage, delay weight loss, extending shelf-life reducing rate of respiration and protection against microbial decay [1]. Bio preservation is innovative method of preservation that has the ability to extend and enhance shelf life and safety of foods by the use of natural or controlled antimicrobial compounds. The use of bio preservation strategies instead of chemical preservation is userfriendly and has great potential if production and application techniques are fully investigated. Among the various biopreservative plants, the Aloe vera plant has a medicinal history due to its extensive disease and fruit preservation. It can prevent the loss of water and hardness, control the respiration rate and maturation, delay oxidative browning, reduce microbial reproduction and other parameters such as titratable acidity, soluble solids content, ascorbic acid content, firmness and decay rate [2]. In postharvest technology, bio preservation use plant based products used in food engineering to prolong shelf life of fruits and vegetables. Gel of Aloe vera depicted promising results and potential to be used as bio preservative for fruits and vegetables [3] and is widely used as consumable coating for increasing shelflife and delay ripening [4]. It has been also broadly reported that salts of calcium used in fruits help in keeping postharvest quality in order to reduce the problem of softening thus, reducing the ripening, respiration processes and the senescence [5-9]. In recent works 0.5-3% calcium salts concentrations are used by Bico et al.
[10]. Calcium as a firming agent and preservative in fruits and vegetable sector is used for quite long time [11]. Also it plays a significant role in maintaining cell membrane and turgour pressure. Moreover it reduces browning as it minimizes the leakage of polyphenyl oxidase (PPO) on the exposed surfaces of the fruits or vegetables [12]. When fruits are dipped in CaCl2 then their storage span is enhanced and firmness is also slow down [13]. Guava (Psidium guajava L.) is most attractive and tasteful fruit. As a desert fruit it is very sweet and fresh and can be consumed along with skin. Furthermore, it has the ability to produce best quality products like candies, concentrates puree, squash, paste, jams, juice, and jellies. Due to its commercial and nutritional importance the guava fruit is well thoughtout a man's fruit and called "apple of the tropics" [14]. Softening is one factor which eventually reduces its shelf-life because of climacteric characteristic and higher metabolic process [15]. Guava grown in Pakistan has shorter shelf life because of high moisture content present in it. Its shelf life cannot be extended easily with different techniques even when stored at cold environment. The main problems due to rapid ripening and softening is its sensitivity to fruit decay, low temperature and perishability, therefore effects the handling, storage and transport potential [16]. According to Toivonen and Deel [17], storage life of fresh fruits and post-cut quality it's totally dependent on cultivar, ripeness stage at harvest, processing technologies and storage environment. Though the use of calcium salts and Aloe vera gel has been widely used for keeping the quality of fruits during storage but very little is known about using Aloe vera gel along with the calcium salts as a postharvest reagent for keeping the quality of guava fruits. In the current study, guava fruit harvested at physiological maturity stage were stored for 35 days and the individual as well as combined effects of Aloe-Vera gel coating and CaCl2 were studied for the physicochemical and sensory attributes of guava fruit and their respective results for minimizing the postharvest losses.

Materials and Methods Guava fruits selection and treatment preparation
Guava fruits having identical size, shape and free from defects were harvested at physiological maturity from Malakandair farm, University of Agriculture Peshawar, Pakistan. The fruits were thoroughly washed with tap water and then air dried keeping under air fan overnight. The fruits were then cleaned with soft cotton cloth before treatment.  (Table 1).

Treating guava fruits with aloe gel and CaCl2
The guava fruits were treated with different concentrations of aloe gel and CaCl2 solution as prescribed in (Table 1) using Dip technique [20]. The guava fruits were divided into six lots symbolically expressed as GA0, GA1, GA2, GC3, GCA4 and GCA5 (Table 1). Guava fruit of the treatment GA1 were immersed in 10% Aloe vera gel while GA2 were dipped in 20% Aloe vera gel for 30 mints and GC3 were immersed in 2% CaCl2 for 3 minutes. Similarly, guava of treatment GCA4 were first dipped in 2% calcium chloride solution and then coated with concentration of 10% Aloe vera Gel for 30 mints respectively. Whereas GCA5 were treated with same concentration of 2% CaCl2 solution and addition of 20% Aloe vera Gel for about 30 minute. The treatment (GCA0) was left as a control without CaCl2 and Aloe vera coating treatment. Guava fruits after treating with different coating materials were dried with a fan blower. All the samples were then stored in refrigerator at around 0 to 5±1ºC. The process of data recording and lab analysis of guava fruit was carried out after each 7 days of interval for maximum of 35 days of storage period.

Analysis of physico-chemical properties
The treated stored guava fruits were characterized for various physicochemical properties on weekly basis. Fruit firmness and phenol content Fruit Firmness (kg/cm 2 ) of guava fruits was measured from the two opposite sides of the fruits using hand Penetrometer following the standard method as prescribed in AOAC [21]. Phenol content (mg/100 g) was predicted by the method followed by Rana et al. [22]. Physiological weight loss and respiration rate Physiological Weight loss (%) was measured by using the weighing digital balance using the formulae given below; The respiration rate was measured in μ mole of CO2 evolved/hour/ kilogram of fruit as described by

Sensory evaluation of stored guava fruits
The stored samples were organoleptically evaluated for colour and flavour by applying nine point

Results and Discussion Physico-chemical analysis
Results for the Physico-chemical analysis for all the studied parameters of stored guava fruits were significantly influenced by both treatment (GA0, GA1, GA2, GC3, GCA4 and GCA5) and storage intervals (0, 7, 14, 21, 28, 35 days). Means were separated by p < 0.05 followed by different alphabetic letters (Table 3a, b). Guava fruit firmness (kg/cm 2 ) and phenol content (mg/100g) Fruit firmness is the promising and important parameter in the post-harvest study to test the maturity level and softening of fruits. Correspondingly, Phenol content decrease during storage leading to the softening of the fruit and affects the fruit firmness. These could be an important quality variables having a direct association with ripeness of the fruits. In the present study, statistical analysis of data indicated that firmness of guava fruit was significantly (p < 0.05) influenced by both treatment and storage intervals. Fruit firmness (2.87 -2.89 kg/cm 2 ) and phenol content (60.1 mg/100g) was noted in fresh fruits at 0 days of storage which were reduced throughout storage time period. The maximum reduction in fruit firmness (0.71 kg/cm 2 ) and phenol content (15.9 mg/100g) was recorded in control fruits while the minimum reduction in fruit firmness (0.99 kg/cm 2 ) and phenol content (32.2 mg/100g) was recorded in fruits treated with 2% CaCl2 and 10% Aloe vera gel (labelled as GCA4) at 35 days of storage. This indicates that the fruit firmness ( Fig. 1) has been significantly retained by GCA4 with minimum reduction in phenol content (Fig. 2), up to 35 days of storage having less reduction as compared with the control and other treatments.
As observed in the present study, it was also reported in previous studies that during ripening process the firmness of fruits declined. The reason behind it is the conversion of insoluble proto pectins to much soluble pectin as well as the chain length of pectin material is shortened which ultimately increase the pectin esterase and polygalacturonase. The prominent activities of these enzymes that hydrolyze cell wall was declined by maximum level of CO2 and minimum level of oxygen which leads to keep the firmness in post-harvest storage duration. It was also reported previously that coating materials acts as a firming agent which delays the changes occur in structural polysaccharide like pectin and maintained the firmness of fruit for a long period during storage [25]. Oms-Oliu et al. [26] reported that coating of fruit retain the firmness for longer time and act as a barrier to prevent loss of nutrient and moisture. The results regarding the prevention of fruit firmness are in line with the findings of Akhtar et al. [27] worked on the shelf life extension of loquat fruit using CaCl2, and with Arowora et al. [28] studying the shelf life of oranges using Aloe vera gel as a coating material but CaCl2 with the combination of Aloe vera gel used in the present study appeared to be the best coating material for the retention of fruit firmness which is directly an indication of preventing fruits from ripening during storage.

Physiological
weight loss (%), respiration rate (μ mole CO2 release/hr/kg fruit) and decay index (%) Fruits start losing moisture contents soon after harvest due to higher respiration rate during storage and thus rapidly loss their weight and deteriorate. Results demonstrated that weight loss (Fig. 3), respiration rate (Fig. 4) and decay index (Fig. 5) in guava fruit was significantly affected (p<0.05) by both treatment and storage intervals and there is a significant difference exists among coated and uncoated fruits. The physiological weight loss and decay index of Guava fruits having the respiration rate (4.9 -5.5 μ mole of CO2 evolved/hour/ kilogram of fruit) at 0 days of storage continuously rose with increase in storage period. None of the guava fruit experienced any sign of decay during first 7 days having lowest physiological weight loss (3.4 -6.13 %) and respiration rate (7.7 -9.8 μ mole of CO2 evolved/hour/ kilogram of fruit), however the fruits start deteriorating after 7 days of storage. At  pH, TSS, titratable acidity, ascorbic acid, sugar acid ratio During preservation period of fruits, the post-harvest parameters like pH, total soluble solids (TSS), Titratable acidity, Ascorbic acid has a greater contribution in preserving the fruits from deterioration and early ripening and has a great relation among them. During the post-harvest life, pH and TSS increases whereas, the titratable acidity and ascorbic acids decreases. pH value increase due to the development of pectin and free acids [33] and TSS due to losses in water through respiration and evaporation and also hydrolysis of starch in storage duration [34]. Similarly, Titratable/ percent acidity and Ascorbic Acid/ Vitamin C content decreases in post-harvest storage due to metabolic activity organic acids and oxidation of Ascorbic Acid into dehydro ascorbic acid by enzyme ascorbic acid oxidase [35,36]. During storage, the coating materials forms a semipermeable layer around the fruits due to which it delayed ripening of fruit and slow down the respiration rate with reduction of consumption of acids. The losses in acids are greatly because organic acids are used as a substrate for respiratory metabolism and also as a carbon skeleton for the synthesis of new compounds during process of ripening. In addition, accumulation of sugars at the time of ripening contributes to decrease of acidity as a result of rise in TSS acid ratio [37]. In present study, pH (Fig. 6), TSS (Fig. 7), Ascorbic Acid (Fig. 8), Acidity (Fig. 9) and sugar acid ratio (Fig. 10) was significantly (p < 0.05) influenced by both treatment and storage intervals. At the initial day of storage, in Guava fruits, TSS (7.81 -7.85 o Brix) and pH (4.28 -4.87) was found in coated and uncoated fruits which increased during storage period while Ascorbic acid (187.51 -198.27 mg/100g) and Titratable Acidity (0.92 -0.98 %) was found in coated and uncoated fruits which decreased with the increase in storage period. Similarly sugar acid ratio was found (8.01 -8. 49) in all coated and uncoated fruits at 0 days of storage which also showed an increased trend during storage period. Maximum TSS (9.36 o Brix) and pH (4.61) was retained by 2% CaCl2 and 10% Aloe vera gel (labelled as GCA4) while maximum increased in TSS (11.05) and pH (6.74) was noted in controlled fruits at 35 days of storage. Similarly, the minimum decrease in ascorbic acid (155.8 mg/100g) and titratable acidity (0.74 &) was found in guava fruits treated with 2% CaCl2 and 10% Aloe vera gel (labelled as GCA4) as compared with the controlled fruits with maximum decrease in ascorbic acid (109.11 mg/100g) and titratable acidity (0.47 %) at 35 days of storage. Correspondingly the minimum increase in sugar acid ratio (12.65) was noted in maximum fruits treated with 2% CaCl2 and 10% Aloe vera gel (labelled as GCA4) and maximum increase in sugar acid ratio (23.51) in control fruits at 35 days of storage. Identical outcomes for the impact of edible coating were described by Ali [42]. Fruit coating slow down the respiration rate in fruits after harvest and therefore helps in maintaining Vitamin C for long duration [43]. The outcomes of the present study are also relevant to this study of El-Alakmy [44]. Sensory evaluation Results for the Sensory evaluation of stored guava fruits were significantly influenced by both treatment (GA0, GA1, GA2, GC3, GCA4 and GCA5) and storage intervals (0, 7, 14, 21, 28, 35 days). Judges score for the target parameters i.e. color and flavor were statistically analyzed. To confirm the scores for both color and flavor, the scoring for overall acceptability of the fruits were also counted and their means were separated by p < 0.05 followed by different alphabetic letters (Table 4). Colour and flavor score Data analysis revealed that color and flavor score of guava fruit was significantly (p <0.05) influenced by different treatments and storage intervals. Judges score for colour and flavour was (8.53 -8.81) at the initial day of storage which is considerably decreased during storage period. The final score for colour and flavour of stored guava fruits (3.81) was significantly retained by treatment of 2% CaCl2 and 10% Aloe vera gel (labelled as GCA4) while the lowest colour and flavour score (2.17) was recorded in control fruits at 35 days of storage (Fig. 11). Similar results for color flavor and overall acceptability were also reported by Hayat (1-9) (1-9) (1-9) GCA0 GA1 GA2 GC3 GCA4 GCA5 Points: Like/ Dislike; Scale: (9-Like Extremely), (8-Like very much), (7-Like moderately), (6-Like slightly), (5-Neither liked nor disliked), (4-Disliked slightly), (3-Disliked moderately), (2-Dislike very much), (1-Disliked extremely)