Development and optimization of processing techniques for intermediate moisture muskmelon chunks

Abstract Muskmelon (Cucumis melo ) fruit is a best source of vitamins, minerals, and bioactive components. Ingestion of high sugary drinks leads to numerous ailments such as diabetes mellitus, obesity, and tooth decay. This study intended at formulation of intermediate moisture food with various combinations of sugar and glycerol and same levels of potassium metabisulphite, potassium sorbate, calcium chloride, and citric acid. It was observed a gradual decrease in TSS (56.53–53.28), vitamin C level in all treatments with the passage of time. The declining trend in ascorbic acid (25.49–21.63 mg/100 g) content of muskmelon chunks was increased as a function of storage. Sensory results showed that there was declining trend in the scores obtained for color parameter, that is, L * from 60.23 to 55.98. The overall results showed that combination of different additives contributed best values (T3) for flavor (7.70), taste (8.15), vitamin C (25.60 mg/100 g), and pH (5.16) as compared to other treatments. Conclusively, developed chunks of treatment 3 are physicochemical and organoleptically considered best, as it is helpful to sustain life stability of muskmelon and enhance its marketability.

alternative to hot air drying Zhou et al. (2019). The preferences in terms of acceptance by the consumers for melons are due to texture, flavor, and sweetness intensity (Lester, 2006). The two major cultivated and approved muskmelon varieties are Ravi and T-96, which are famous for nice texture, aroma with good sweetness level varying from 8.00 to 14.00 °brix in Pakistan.
It has been reported that about 30%-50% of fruits and vegetables are wasted after harvesting during transportation, storage, and processing in developing countries (Alzamora, Tapia, & Lopez, 2000). During 2015-16, in Pakistan, the annual production of fruits and vegetables was 17.35 million tonnes (GOP, 2015-16).
The enzymes present in fruits and vegetables are polyphenol oxidase which is responsible for browning of cut surfaces to catalyze the oxidation of phenolic compounds (Whitaker & Lee, 1995). After harvesting, the life of cantaloupe is not more than 2 weeks and this is great loss in the form of crop and economic value (Solval, Sundararajan, Alfaro, & Sathivel, 2012). Drying is an old method of food preservation to increase the postharvest life through decreasing the bulk weight and water activity. Changes in color degradation, microbial growth, changes in texture, and loss in nutrients are commonly observed during storage of dried fruit products (Salunke, Bolin, & Reddy, 1991). In case of osmotic dehydration, the excess moisture is partially expelled from the food by placing it in hypertonic sugar sirup. The intermediate moisture level products are good in nutritional values, easily consumable, reduce cost of transportation, and storage (Asavasanti, Tantipaibulvut, Samaal, & Sanuksaen, 2018;Corzo & Gomes, 2004;Leistner, 1992). It is an important food preservation process to decrease the input cost of energy consumption, enhance the food quality and as a pretreatment slow down enzymatic reaction, preserve natural color, and volatile aromas (Pokharkar, Prasad, & Das, 1997;Torreggiani, 1993). The main purpose of this research project was to develop and optimize the processing techniques for intermediate level muskmelon chunks and to assess the shelf stability through quality and sensory evaluation during storage period.

| Chemicals reagents and glassware
The chemicals, reagents, and glassware used for analytical purpose were purchased from authorized dealers of Merck, Sigma-Aldrich, Riedel de Haen, and Pyrex from local scientific store market of Faisalabad, Pakistan.

| Muskmelon pretreatment and samples preparation
Muskmelon (C. melo) varieties, that is, Ravi and T-96, were procured from the research area of Vegetable Research Institute, Ayub Agricultural Research Institute Faisalabad, Pakistan. The samples for R&D studies were manually sorted from the diseased, injured, and bruised one. The selected healthy, uniform in shape samples were washed with fresh tap water and then manually removed the seeds, peeled and cut into small pieces with dimension, that is, 3.0 × 2.0 × 0.5 cm chunks with sharp knife. Before osmo dehydration; the muskmelon samples were dipped in 2.0% CaCl 2 for 15 min and drained.

| Procedure for osmo dehydration and storage
The sugar solutions of 30 °brix were prepared by adding the preservatives with and without glycerol according to the treatment plan (Table1). The pretreated samples were immersed in sugars solutions for 24 hr. After immersion in sugar solution for 24 hr, samples were removed and drained. Then, the samples were placed in dehydrator (tray dryer Model No. R-5A, commercial dehydrator systems, USA) at 60°C up to water activity (a w ) 0.60 monitored with water activity meter (Rotronic Hygropalm Model: A w -DIO, Rotronic Instrument Corp) throughout the drying process. After retaining the required level of moisture level through water activity meter, 50 g muskmelon chunks were packed in high density polyethylene bags, sealed, and stored at ambient storage condition of laboratory (25 ± 2°C). The prepared samples were given name as intermediate level muskmelon chunks in this research paper, which were evaluated after 1 month up to 3-month storage period with various analyses for quality and sensory attributes.

| pH
The pH of samples was determined by following method as given by Ranganna (1999) in which 20g sample was ground in distilled water (100 ml) and filtered it. The pH meter (Model: HI 2211, HANNA instruments) was calibrated with buffer solutions at 4, 7, and 10 at room temperature and noted the reading of filtrate from display.

| Total acidity
The acidity of samples was measured according to the method as explained by Ranganna (1999). Two gram grounded sample was taken in 10 ml distilled water and filtered it. Add two to three drops of phenolphthalein as an indicator in filtrate and titrated against 0.1N NaOH till light pink color end point, noted the titer value and calculated the total acidity. The obtained results were expressed in percentage.

| Vitamin C
The oxidized amount of vitamin C was calculated by adopting the titrimetric method Ranganna (1999) in which 2,6-dichlorophenolindophenol reagent reduction values were recorded. The results were expressed as mg/100 g loss in vitamin C during storage period.

| Color measurement
The color of intermediate moisture muskmelon chunks was determined at different storage intervals according to method explained by Rocha and Morais (2003) with a handheld tristimulus reflectance color meter (PCM/PSM model, Color-Tec). The color values were recorded using a CIE-L * a * b * uniform color space (−Lab), where color parameters showed lightness for L * while a * indicates redness on a green (−) to red (+) axis, and b * parameter for yellowness on a blue (−) to yellow (+) axis.

| Water activity
The water activity was measured by filling the sample cup of water activity meter (Rotronic Hygropalm Model: A w -DIO, Rotronic Instrument Corp) at room temperature. The results were expressed as water activity (a w ) of intermediate level muskmelon chunks.

| Textural analysis
The texture of muskmelon samples was measured by adopting the method as given by Piga et al. (2005) with minor modifications.
Puncture test was performed to measure the texture values with texture analyzer (Model: TA-XT2, Stable Microsystems) having capacity of 5 kg load cell equipped with texture expert program version 4.0.9.0 for analyzing the data. Intermediate level muskmelon samples were punctured to measure the firmness from external to internal surface tissue cells by placing the samples in the center beneath the needle probe. Before the performance of test, load cell and probe were calibrated and measured the puncturing force (g) against time (s).

| Statistical analysis
The collected data in replicated form were subjected to statistical analysis by using the software statistix 8.1 and compare the results through one-way ANOVA and CRD factorial to determine the level of significance, and the results were elaborated in means and standard deviations (SD) as mentioned by Saxena, Mishra, Chander, and Sharma (2009). The means with significant difference were presented as p < .05 and indicated with different letters.

| TSS
Total soluble solids undergo changes in muskmelon chunks due to moisture because they picked moisture and decreased significantly the TSS. Figure 1 indicates that at first month of storage, it ranged from 53.08d to 54.09c from T 1 to T 4 , with p ≤ .05. According to Beaulieu and Lea (2010), likewise pattern was observed during storage of muskmelon when dried as intermediate moisture food. These results are in accordance with Chen, Chan, and Li (2011) who analyzed melon powder for storage stability and checked its feasibility for further use.

| T.A. (%)
Titratable acidity plays a crucial role in the shelf life of any type of fruit or drink and inhibits growth of microorganisms in foods. Titratable acidity (%) changed slightly during storage ( Figure 1). Values ranged from 0.223b to 0.233a from T 2 to T 4 . Likewise, Souza et al. (2009)

| pH
pH has inverse relation with acidity in any medium as shown in Figure 2. The present study for muskmelon chunk also expressed the same pattern of pH. pH values depicted the range 5.188a to 5.188a from T 1 to T 4 . With the passage of time, pH showed a decreasing tendency and was 5.273a, 5.249b, 5.216c, and 4.986d for T 1 , T 2 , T 3 , and T 4 , respectively. This decrease may be due to in situ acid production in product. According to Beaulieu and Lea (2010), similar trend was elucidated during storage of muskmelon drink. Dhaliwal and Hira (2004) studied carrot-spinach and pineapple juices and expressed that 3-month storage cause decrease in pH. Likewise, Hussain, Zaib, and Ayub (2010) also observed that storage of apricot and apple blend showed slight decrease in pH.

| Ascorbic acid (mg/100 ml)
The vitamin C content is reduced significantly during storage interval.

| Texture
Muskmelon chunk hardness increases with the storage if packs are intact but when chunks pick moisture harness is reduced little bit. Calcium chloride increases hardness due to cross-links of carboxyl carbon with polyuronide chains and calcium ion. Sarolia and Mukherjee (2008) proved that texture of mango leather was improved by adding calcium chloride and did not change during storage to greater extent. According to Nchez-moreno, Plaza, Adeancos, and Pilarcano (2003) texture (viscosity) of orange juice can be maintained by adding calcium salts during subsequent storage. Moreover, Figure 3 shows that keeping quality of melon chunks greatly depends upon their texture during shelf periods. Softness in texture of melon was observed by Lamikanra and Watson (2009) who explained it due to loosening of cross-links in structure of melon but texture was improved by adding calcium sorbate.

| Water activity
Shelf life of any product depends upon water activity, so it is important to maintain it at specific level. Figure 4 shows that water activity of chunks was increased during storage due to slight pick of moisture during storage. According to study of Dhingra, Singh, Patil, and Uppal (2008), osmotic drying of fruit and vegetables water activity is lowered and maintained in storage if additives like glucose and humectants are added. Likewise, pattern was also observed by Rangana (2012) who analyzed and stabilized number of fruits during storage. Produced the similar results and proved this by using apple chunks.

| Sensory evaluation
Muskmelon chunks were evaluated organoleptically during

ACK N OWLED G M ENT
Authors are thankful to the Higher Education Commission and Punjab Agriculture Research Board for providing opportunity to work on this project.

CO N FLI C T O F I NTE R E S T
Authors declare that they have no conflict of interests.

S TATE M E NT O F D ECL A R ATI O N FO R H U M A N S U BJ EC TS
This study has no involvement of human or animal subjects.