Kinetics of Cucurbita moschata Puree Drying with Maltodextrin as Drying Aid

The objective of this research was to investigate the influence of maltodextrin addition of pumpkin puree drying as well as studied the drying kinetics. Several thin layer drying kinetics model comprised of Page, Lewis, Henderson Pabis, Two Term, Weibull as well as diffusion model were used to study the behavior of pumpkin drying. The puree drying was conducted by added 15% of maltodextrin on pumpkin puree. The drying temperatures were varied of 60-70 °𝐶 The research result show that temperature influence the pumpkin puree drying in which added with maltodextrin as the drying aid. Pumpkin puree drying with addition of maltodextrin performed at temperature of 70 °𝐶 for 150 minutes is considered as the relatively suitable condition as it gives low moisture ratio of 0.07. The thin layer drying kinetics, Midili, give good fittest to the experimental data followed by Page and Weibull. The effective diffusivity is in range of 5.3𝑥10 −4 − 7.3𝑥10 −4 m/s with the obtained activation energy is 30.36 kJ/mol.


INTRODUCTION
Longer shelf life, product variations and nutritious products are three main demands in nowadays food industry. Those demands lead to research and development in term of quality innovation in food engineering. Research and innovation on drying as one of preservation method are numerous and gaining interest since it intended to prolong food shelf life and provide varied products. Application of drying process also impacts on minimization of its transportation, storage, as well as packaging cost while preserving food nutrients from degradation is the biggest challenge of drying process [1], [2].
Drying aid such as maltodextrin is reported as a good physical barrier agent in which act in minimizing degradation reactions of bioactive molecules. The addition of maltodextrin was also reported retained food color of the dried product [2], reduce the stickiness of product and improve the flow characteristics of dried powder [3]. Maltodextrin is applied in production of tamarind powder [3], avocado pulp powder [2] and asparagus powder [4]. Those researches reported the beneficial of the application of maltodextrin in fruit and vegetables pulp drying thus the application of maltodextrin in other type of fruit and vegetables pulp drying is need to be studied.
Pumpkin (Cucurbita moschata), a seasonal crop indigenous to the central South America that belongs to the Cucurbitaceae family, is a potential material for food drying with the addition of maltodextrin as drying aid. Pumpkin pulp is dominated by moisture (75.8-91.33%) and has low content of proteins, fats, and carbohydrates [5], in which the protein and carbohydrate of pumpkin pulp are 0.2 -2.7% and 3.1-13%, respectively [6]. Due to its low carbohydrate, fat and protein content, pumpkin is prized for its low-calorie (30 kcal/100 g) and easily digestible characteristic [5]. Pumpkin pulp is also sources of dietary fiber, essential amino acids, phenolic compounds, minerals, flavonoids, carotenoids and vitamins [5]- [7]. βcarotene, vitamin A, vitamin B2, α-tocopherol, vitamin C, vitamin E are predominat vitamins found in pumpin [6], [7]. While alanine, arginine, aspartic acid, glutamic acid, histidine, leucine, isoleucine, glycine, lysine, methionine, phenylalanine, serine, threonine, valine and tyrosine are essential amino acids on pumpkin [6]. The bioactive compounds found on pumpkin lead to its numerous pharmacological such as antidiabetic, antibacterial, antitumor, anti-inflammatory, immunomodulation, antifungal, antihypertensive and antioxidant activities [6], [8]. The health benefits and the chemical composition of pumpkin lead to its broad applications. Pumpkin powder is utilized as pigment in confectionery, bakery, pasta, and dairy products [5].
Considering the benefits of the utilization of maltodextrin in puree drying and of the potential health benefits of pumpkin, herewith, the kinetics of pumpkin puree drying with maltodextrin as dryimg aid is presented.

Materials
Pumpkin was obtained from local market in Bandungan Kabupaten Semarang. The pumpkin fruits were washed, peeled and separated from the seeds. The fruits was then chopped and milled to form puree. Maltodextrin (Zhucheng Donxiao, ltd) with ash content of 0.6% was used in this research.

2.2.
Drying process 50 grams of pumpkin puree was mixed with 15% of maltodextrin and laid on pan with 0.2 cm of thichkness. The pan was then inserted into tray drier. The drying process was performed at temperature of 60-70° and the weight loss was recorded at interval of 10 minutes until constant weight of pumpkin puree was achieved. The moisture content of the fresh and dried samples was determined according to AOAC (1995). The drying rater was determined by the removal of moisture (dry basis) and represented in g/g -1 /min.

2.3.
Data analysis The moisture content data were used to calculate the moisture ratio (Eq 1).
Where 0 is the initial moisture content and is the moisture content at certain time.

2.4.
Thin layer drying kinetics The experimental data was used to validate the thin layer drying kinetics models (Table 1) and the RSS was calculated according to Eq 2. Table 1. Drying kinetics models

Effective Diffusivity
Galves et al. [9] mentioned that drying process of most food is take place during the falling rate period and the transport phenomena in that period can be described by Fick's second law of diffusion. Crank (1975) provide the solution for the diffusion equation for slab geometry with assumption that the moisture distribution in initial condition is uniform, the external resistance is negligible, the diffusivity is constant and the no shrinkage (Eq. 3).

RESULT AND DISCUSSION
Maltodextrin has been added as drying aid in drying process of several products such as in infrared drying of avocado pulp [2], freeze drying of Lactobacillus plantarum [10], and spray drying of soybean oil [11]. It was reported that together with sucrose and inulin, maltodextrin act as cryoprotectant, preservative and prebiotic in freeze drying process of L. plantarum, while maltodextrin provide a beneficial in avoiding the reduction of total polyphenols, total chlorophylls, and antioxidant activity as well as minimizing of lipid oxidation in avocado pulp [2], [10]. addition in pumpkin puree drying was evaluated in three different temperatures i.e. 60°, 65° and 70° and the moisture ratio profiles were depicted on Figure 1a. It can be seen that the decrease of moisture ratio of pumpkin puree drying at temperature of 70° with 15% of maltodextrin addition as drying aid is faster than the ones of 60 and 65°. It is also supported by the drying rate profile as shown on Fig  1b. The phenomenon is logic since the higher the temperature applied; the more energy involves and transferred to the drying system. Similar result is reported from the convective drying of Cucurbita moschata conducted by Potosí-Calvache et al. [12] who dried squash at temperature of 45-65°. They found that the higher the temperature applied the faster the dyring rate. Figure 1a show that pumpkin puree drying process at temperature of 70° for 150 minutes with moisture ratio obtained of 0.079 can be considered as the relatively best choice since prolong the drying time longer than 150 minutes the profile of the moisture content is asymptotic. The method applied here is also considered better than the drying applied on pumpkin puree without the addition of maltodextrin reported by Hartati et al. [13]. It was found prior this research that drying process at temperature of 70° for 165 minutes gave pumpkin powder with moisture ratio of 0,04. Furthermore, this drying process of pumpkin puree with addition of maltodextrin applied in this research can also be considered as a better method as compared to convective drying of pumpkin reported by Calvache et al. [12]. They reported that pumpkin flour moisture content of 6.34 ± 0.10% (db) was obtained from convective drying at temperature of 55°C, air velocity of 7 m.s-1, and drying time 390 min. Longer drying time of pumpkin puree was also reported by Caliskan and Dirim [14] who apply vacuum drying on pumpkin puree with puree depth of 3 mm, condenser temperature of -48 ºC, plate temperature of 30ºC, pressure of 13.33 Pa and drying duration of 8 hours. The process condition applied gave pumpkin puree powder with moisture ratio of less than 0,1 [14].
The drying process of pumpkin puree with maltodextrin addition was investigated for its kinetics by applied Lewis, Page Henderson-Pabis, Midili dkk, Two term, and Weibull models (Figure 2). It can be seen that Midili, Page and Weibull model presented good fits with the experimental data of moisture content. Moreover, from the RSS values (Table 2), Midili shows the lowest one compared to the others models. The RSS values of Midili models are in range of 0.02-0.006. It is interesting that the other two models, Page and Weibull, gave similar value of their RSS for the three temperature applied. It was mentioned by Buzrul [15] that Page Model has same fit as Weibull Model with low parameter. In case of conventional drying process of pumpkin puree, in which no addition of maltodextrin, Midili was also gave the highet fit with the experimental data [13].
The validation of thin layer kinetics models i.e. Lewis, Henderson-Pabis and Two Term, the kinetics rate constants are increase with the increase of temperature applied while for Page and Midili, the kinetics rate constant are showing deviation on temperature of 65°. The value of the kinetics constant for Midili are 1 10 −6 − 1,7 10 −5 1/min. Those values are higher than the ones obtained from the pumpkin puree drying at the same temperature range but without the addition of maltodextrin which in range of 9 10 −8 − 2,4 10 −7 1/min [13] 60-70°. From the value of the kinetics rate constant, it can be conclude that the addition of matodextrin fasten the drying process of pumpkin puree. The kinetics rate constant found in this research were slightly lower than the one obtained from freeze drying of pumpkin reported by Caliskan and Dirim [14]. They used Henderson Pabis model and kinetics rate constant of 9,36 10 −5 was reported [14].
Moreover, the effective diffusivity was also investigated in this research ( Figure 3). The obtained effective diffusivities are 5.3 10 −4 − 7.3 10 −4 m/s. From the plot of 1/ versus 1/ with the universal gas constant of 8.314 J/mol/K, the obtained activation energy is 30.36 kJ/mol. This activation energy value is higher than the activation energy of olive cake drying in which reported as low as 12.43 kJ/mol [9]. The activation energy found in this research was similar with the one obtained from convective drying of squash (Ea of 33.55 kJ/mol) at air velocity of 8 m/s [12].

CONCLUSION
The influence of maltodextrin addition in pumpkin puree drying was investigated in this research. Several thin layer drying kinetics model and diffusion based drying kinetics was used to studied the behavior of pumpkin drying. It can be concluded that temperature influence the pumpkin puree drying in which added with maltodextrin as the drying aid. Pumpkin puree drying with addition of maltodextrin performed at temperature of 70° for 150 minutes is considered as the relatively suitable condition as it gives low moisture ratio of 0.07. The thin layer drying kinetics, Midili, give good fittest to the experimental data followed by Page and Weibull. The effective diffusivity is in range of 5.3 10 −4 − 7.3 10 −4 m/s with the obtained activation energy is 30.36 kJ/mol.