Shelf life of Dragon Fruit (Hylocereus spp.) coated with chitosan -

Shelf life of Dragon Fruit (Hylocereus spp.) coated with chitosan

This study identified the synergistic effect of chitosan coating with different concentrations on the postharvest quality and shelf life of dragon fruits stored at ambient conditions. Dragon fruits were coated with 2 %, 3 %, and 4 % chitosan solution and stored at ambient temperature for 14 days. Changes in fruit’s physiological loss of weight (PLW), firmness, shelf life, total soluble solid (TSS), titratable acidity (TA), reducing sugars, total sugars, ascorbic acid as well as decay rate were periodically recorded. The results indicated that the chitosan coating with 4 % significantly reduced the decrease of PLW, firmness, TSS, TA, ascorbic acid content and partially inhibited decay.

Preparation of chitosan solution

After sorting and grading, healthy fruits were divided in to four equal lots. Chitosan solutions at concentrations of 2%, 3% and 4% were prepared in 1000 ml with 10 ml of acetic acid. The solution was followed by stirring using an overhead stirrer at a speed of 500 rpm for 20 min till a transparent solution is obtained. Fresh and fully matured uniform sized and disease-free dragon fruits were washed with tap water to remove the dirt and dust particles and dried at room temperature. The dipping treatment of chitosan coating to all the samples was done at ambient conditions for 10 minutes and stored at ambient temperature. The analysis of the fruits was done at every 2 days interval.

Experimental details:

T1 – Chitosan 2%, T2 – Chitosan 3%, T3 – Chitosan 4%, T4 – Control

Physiological loss in weight (%)

Physiological loss in weight (PLW) was determined by recording the initial weight of the fruits on the day of initiating experiment and subsequently at two days interval. The loss of weight in grams and in relation to initial weight was calculated and expressed in percentage.

Decay (%)

The percent decay (%) of fruits was calculated on the number basis by counting number of fruits decayed and total fruits at each storage interval.

Fruit firmness (Kg cm^-2)

Penetrometer was used to record the firmness of fruits and direct readings were obtained in terms of kg cm^-2. The sample fruits were subjected to penetrometer by pressing near the center of the fruit and direct reading on the scale was recorded at two days intervals.

Shelf Life (days)

Shelf life of the fruits was determined by recording the number of days the fruits remained in good condition in storage.

Total Soluble Solids (^o B)

Total Soluble solids were determined by using refractometer. The percentage of TSS was obtained from direct reading on the instrument.

Titratable acidity (%)

Titratable acidity (TA) Titratable acidity was determined by adding 2 drops of 0.1% phenolphthalein solution to 5 mL of fruit juice and titration against 0.1 N NaOH until the pH reached 8.1. The fruit juice was obtained by homogenizing 10 g of fruit pulp from a mixture of 4 fruit in a kitchen blender with 10 mL of purified water. The mixture was centrifuged at 5000 × g for 5 min and then filtered through a cheese cloth. The results were expressed as percentage of citric and l-lacticacids (mg/100 g of fresh weight) titrating sample against the Fehling solution (5 ml A+ 5 ml B) using methylene blue as an indicator and the titration was done till the appearance of brick red colour as in reducing sugars. The results were expressed in percentage.

Total Sugars (%), Reducing Sugars (%) and Ascorbic acid content (mg 100g-1) were estimated by standard methods

Results

Application of chitosan coating retarded the weight loss of dragon fruits during storage compared to the control. There was an added benefit to control of weight loss by increasing concentrations of chitosan from 2 to 4%. The lowest weight loss was found in 4% chitosan followed by 3 and 2% chitosan and then uncoated after 14 days of storage. The highest weight loss (10.56 %) was observed in untreated dragon fruits at the 8^th day of storage, whereas the lowest weight loss (1.56 %) was observed in fruits coated with 4% chitosan at the same day of storage. Among the chitosan concentrations, 4% resulted in the best in terms of controlling weight loss of dragon fruit during storage.

The effect of chitosan coating on the decay of dragon fruit stored at room temperature at different intervals, the percent decay values showed an increasing trend from the 2^nd day to 14^th day during storage. On the 2^nd and 4^th day of storage at ambient conditions, the fruits appeared fresh without any change on their surface. Hence percent decay values for chitosan coated fruits and control recorded (0). On the 8^th day of storage T4 -Control recorded the highest decay percent (20) followed by T1- Chitosan @ 2% (10), T2-Chitosan @3% (4) percent decay. While T3-Chitosan @4% (0) or no decay. A similar trend of increasing decay percent was observed up to the 14^th day of storage under ambient conditions. Among all the treatments, fruits treated with chitosan @ 4% showed minimum score.

Fruit firmness is often the first of many quality attributes judged by the consumer and is, therefore, extremely important in overall product acceptance. Dragon fruit suffers a rapid loss of firmness during senescence which contributes greatly to its short postharvest life and susceptibility to fungal contamination. Initial flesh firmness values were similar for control and coated samples. On the 2^nd day of storage uncoated dragon fruits began to show a gradual loss of firmness. On the 2^nd day, fruits treated with T3-Chitosan @ 4% recorded the highest value of firmness (6.04) followed by T2-Chitosan @ 3% (5.52), T1-Chitosan @ 2% (5.20) while the lowest firmness was recorded was noticed in T4 -Control (5.06). A similar trend of decreasing firmness of dragon fruits with the increase in storage period was observed up to 14^th day at ambient conditions. From the result, it is observed that the highest firmness was observed with fruits treated with Chitosan coated with 4%. Maximum deterioration and minimal degree of firmness indicate the maximum quality degradation. The highest firmness may be due to a low rate of respiration due to the application of surface coating which slowdowns the metabolic activity of fruits leading to retention of firmness in fruits.

The highest shelf life of (13.80 days) was recorded in T3-Chitosan @4% dragon fruit followed by T2-Chitosan @3% (10.60days), T1-Chitosan @2% (9.80 days) while the lowest shelf life was recorded in T4- Control (7.80 days). Dragon fruits treated with Chitosan 4% recorded the highest shelf life as chitosan coatings reduce shrinkage by reducing loss of moisture, transpiration and respiration losses thereby retaining the freshness of the fruits.

Total soluble solids increase with the storage period in room temperature up to the 6^th day and it starts decreasing from the 8^th day except for T3-Chitosan @4%. On the 2^nd day, of storage the highest TSS was recorded in T4- Control (15.56) which was followed by T1-Chitosan @2% (15.16) and the lowest TSS was noticed inT2- Chitosan@3% (14.36) which was statistically on par with T3 -Chitosan @ 4% (14.24). Hylocereus species with white flesh have higher soluble solids contents than those with red flesh fruit and the distribution of soluble solids in the fruit flesh is not homogeneous, the core part being richer in sugars than the peripheral part.

A large percentage of the soluble solids in dragon fruit are sugars mainly glucose and fructose that are central and are involved in cell respiration and synthesis and the third sugar is sucrose that is non-reducing by nature and presents relatively in smaller amounts. From the above results, it can be concluded that the fruits treated with Chitosan 4% recorded a slower increase in TSS.

The acidity of fruits decreases with the progress in the storage period. Titratable acidity (TA) values decreased in chitosan coated and uncoated fruit, with a significant difference after 14 days of storage. However, the maximum decrease in TA was recorded in the control fruit, while a slight decrease was observed in fruit treated with T3- Chitosan @4%.Titratable acidity of fruits decreases due to the increase of soluble sugars during ripening. This decrease was observed less in fruits coated with surface coating compared to control due to edible coatings.

Total sugars content increased with the storage period at room temperature from 1^st day to the 8^th day. The results of this study revealed that T3-Chitosan 4% was the best treatment, chitosan treatments formed a semi-permeable film around the fruit which suppressed ethylene production and restored TSS content in the fruit. Suppression of respiration also slows down the synthesis and use of metabolites resulting in lower TSS due to the slower hydrolysis of carbohydrates to sugars.

A similar trend was noticed with respect to reducing sugar content on the 6^th, 8^th, 10^th and 12^th day respectively. On the 14^th day of storage, except T3- Chitosan @4% all other treatments showed the end of shelf life. T3-Chitosan @4% recorded reducing sugar content (4.96). The total and reducing sugars were increased in all treatments. The raise in sugars may be due to conversion of starch into sugars during storage.

Ascorbic acid content in dragon fruit pulp gradually decreased during storage and this reduction was effectively inhibited by 3 and 4% chitosan coating. Dragon fruits coated with Chitosan 4% recorded the highest ascorbic acid content. The decreasing trend of ascorbic acid is less in chitosan coated fruits compared to control where there is a rapid decrease of ascorbic acid. This may be due to an increase in total soluble sugars in the fruits and it also suggests that the modified atmosphere created by chitosan coating suppresses the loss of ascorbic acid.

Conclusions:

In conclusion, the experiment conducted here indicated that the application of chitosan coating, Chitosan 4% recorded significantly higher results in terms of minimum PLW, decay percent and highest firmness, shelf life and quality parameter namely TSS,TA, sugars and ascorbic acid content. It was followed by T2-chitosan 3% in pink fleshed fruits for improving the postharvest quality and prolongs the shelf life of dragon fruits when stored at ambient condition

Future scope

Further studies can be conducted on the combined effect of chitosan and 1-MCP on postharvest quality and shelf life coupled with MAP packaging of dragon fruits.

Reference:

Prashanth, R., Kumar, A.K., Rajkumar, M. and Aparna, K., Studies on Postharvest Quality and Shelf Life of Pink Fleshed Dragon Fruit (Hylocereus spp.) Coated with Chitosan and Stored at Ambient Temperature.