Influence of foam-mat drying temperature of red jambo (Syzygium malaccense) Influencia de la temperatura de secado del jambo rojo (Syzygium malaccense) en la capa de espuma

The Brazilian cerrado is one of the richest biomes in the world, with native and exotic fruit species, but little explored. Given this diversity, stands out the red jambo, an exotic fruit with remarkable sensory characteristics, but highly perishable, with reduced shelf life. Foam-mat drying (FMD) is a technique that aids in the preservation of fruits, resulting in a powder product with desirable characteristics such as high porosity and rehydration capacity. In this sense, this work aimed to analyze the influence of drying temperature, besides evaluating the kinetics and mathematical modeling of experimental data. In addition, the physicochemical properties of fresh jambo pulp were determined and after the foam layer drying process. Drying was performed in an air circulation oven at 50, 60, 70oC, using a concentration of 4.5% (w/w) emulsifier. The Lewis, Midilli and Kucuk and Page mathematical models were adjusted to the experimental data, being the best fit obtained using the Midilli and Kucuk and Page models. Research, Society and Development, v. 9, n. 3, e40932382, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i3.2382 3 The fruit powders presented acidic pH (throne of 3.5), the vitamin C content decreased as the temperature increased (108.16; 88.58 and 62,16 mg at 50, 60 and 70oC , respectively) and ash content increased significantly in dry powder samples due to the addition of foaming agents.

The fruit powders presented acidic pH (throne of 3.5), the vitamin C content decreased as the temperature increased (108.16; 88.58 and 62,16 mg at 50, 60 and 70ºC , respectively) and ash content increased significantly in dry powder samples due to the addition of foaming agents. Keywords: Cerrado fruits; Mathematical modeling; Vitamin C.

Introduction
The Brazilian cerrado is one of the richest biomes in the world, with vast renewable natural resources, yet many native and exotic fruit species with nutritional potential and striking sensory attributes are still unexplored. These characteristics make these fruits promising for the development of healthy and innovative food products (Morzelle et al., 2015;Souza et al., 2012).
In this sense, drying is a technique that helps in the conservation of fruits, preserving nutrients and active and antioxidants compounds (Sogi et al., 2015). Among the drying methods, foam-mat drying (FMD) stands out, which consists of mixing the pulp or fruit or vegetable juice with a stabilizing agent in order to obtain a stable foam, dried at temperatures ranging from 50 to 80ºC. The dried product is ground at the end of the process originating a powder product. As main advantages, FMD provides a higher drying rate compared to conventional drying, due to its larger surface area exposed to the heated air, reducing the energy expenditure of the process, adding value to the product, as it increases its porosity and rehydration capacity. Thus, it is essential to study the proper conditions to obtain a quality final product. (Abbasi & Azizpour, 2016). Therefore, the present study aimed to analyze the influence of temperature and drying kinetics, as well as the physicochemical properties of jambo pulp after the foam-mat drying process.

Methodology
For the development of this work were used as raw materials the fruits of jambo, from the local market of Colíder, Mato Grosso, Brazil. Fruit processing and analysis were performed at the Chemistry Laboratory of the Mato Grosso State University (UNEMAT), Barra do Bugres, Mato Grosso, Brazil.
The fruits were selected according to the ripening stage, being cleaned in running water, manually pulped, and then stored under freezing at -18ºC in a commercial freezer for 24h.
Subsequently, the jambo pulp was ground and homogenized and for the preparation of foam were tested 4.0, 4.5 and 5% (w/w) of emulsifier, with the aid of a commercial mixer, for 8 minutes at full speed. The concentration of 4.5% (w/w) emulsifier was selected because it has better stability. The foam formed was distributed in Petri dishes and taken to a forced-air oven for drying under controlled temperatures.

Drying kinetics and mathematical modeling
Samples of 10g of foam were carefully spread in Petri dishes and placed in a forced-air oven (CienLab, CE-480, Brazil) at 50, 60 and 70 ° C. The dried pulp foams were removed from Research, Society and Development, v. 9, n. 3, e40932382, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i3.2382 5 the Petri dishes with the aid of a spatula, stored and identified according to material type, date and experimental conditions. Drying curves were established for the samples subjected to the described conditions, by following up the moisture loss recorded by varying the mass of the samples at time intervals of 15 minutes. Mass losses during drying were obtained with the aid of a semi-analytical balance (Shimadzu, AY220, Japan) accurate to 0.0001 g. The tests were prolonged until they reached equilibrium conditions (constant mass). The moisture ratio (MR) was determined according to Equation 1. To evaluate the behavior of moisture loss over time, semi-empirical models were used.
Considering the equilibrium humidity as the humidity reached when the drying rate is canceled, the moisture ratios (MR) were calculated. Therefore, the Excel program was used to perform the calculations and modeling. To represent the drying kinetics of jambo pulps dried by FMD, the mathematical models of Lewis (1921), Midilli and Kucuk (2002) and Page (1949) were used, as shown in Table 1.

Physicochemical analysis
Fresh Pulp and dried jambo powder were subjected to analyzes of gravity moisture content (method 014/IV), acidity content (method 310/IV), pH (method 014/IV) and ash content (method 364/IV) and vitamin C content (method 364/IV) according to the Adolf Lutz Institute handbook (2008). All analyzes were performed in triplicate.
The comparison of the means obtained in the physicochemical analysis was performed by applying the Tukey test (p <0.05) using the Statistica software, version 7.0.

Drying kinetics and mathematical modeling
The drying curves of the jambo pulp are shown in Figure 1 in the dimensionless form of moisture content (MR versus time). The dried jambo foams at 50, 60 and 70 ° C the time required to reduce the water content was 435, 345 and 270 min, respectively. Also, according to Brooker et al. (1992) the external conditions of air velocity, temperature and relative humidity directly affect the drying process. As expected, drying time was shorter when higher temperatures were applied, behavior caused by increased drying rate in view of the higher temperature gradient between air and foam, resulting in steeper curves due to higher heat transfer from air to material (Akpinar et al., 2003). Such temperature effect was also observed in the drying of banana foam (Falade & Okocha, 2012) yacon juice (Franco et al., 2015), uvaia (Branco et al., 2016;Rigueto et al., 2018) and mango (Lobo et al., 2017). Table 2 shows the parameters of the Lewis, Midilli and Kucuk and Page mathematical models, adjusted to the experimental data of the drying of the jambo foams, as well as the correlation coefficients and mean errors.
As can be seen in Table 2, the Page and Midilli and Kucuk models presented the best Research, Society and Development, v. 9, n. 3, e40932382, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i3.2382 7 adjustments in relation to the models employed. Still, the Midilli and Kucuk model presented the best correlation and the lowest estimated average error in most of the studied conditions. The Lewis model presented the lowest correlation and highest error in all the studied conditions in relation to the other models. According to Samapundo et al. (2007) values below 10% of relative mean error indicate good suitability for practical purposes, therefore, it is found that the proposed models are appropriate to describe the phenomenon of foam-mat drying of jambo pulp and also to determine the transition point between the constant and decreasing drying period.  Research, Society and Development, v. 9, n. 3, e40932382, 2020(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i3.2382 8 The use of alternative pretreatments to optimize the drying process has been objectified in several studies, as in Oliveira et al. (2010), who evaluated the influence of ultrasonic pretreatment before air drying to promote dehydration of jambo. The authors observed that during the ultrasonic treatment in distilled water, the fruit lost sugar. In addition, effective water diffusivity increased by about 28% after ultrasound, reducing total drying time by more than 27%. c) The increase in effective water diffusivity due to the application of ultrasound as a pretreatment was also reported by Fernandes & Rodrigues (2008), applying it to dehydration of jambo and other fruits, favoring the increase of sugar content.
Da Silva et al. (2016) evaluated the use of ultrasound, osmotic dehydration and vacuum as pre-treatments for melon drying and found that the use of ultrasound or a combination of ultrasound and vacuum improved the drying efficiency of this fruit and thus present themselves as an alternative. to traditional drying. Research, Society and Development, v. 9, n. 3, e40932382, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i3.2382 9

Physicochemical analysis
The evaluated parameters of the physicochemical characterization of fresh jambo pulp and powder produced from foam composed of frozen jambo pulp and 4.5% (w/w) Emustab, dehydrated at 50, 60 and 70 ºC, are presented in Table 3.  Augusta et al. (2010) physically and chemically characterized the peel and pulp of red jambo, highlighting the importance of physicochemical characterization to evaluate fruit quality and provide reliable information on its nutritional value, yield and shelf life.
The moisture, pH, ash and vitamin C parameters obtained for the fresh pulp of jambo (Table 3) approximate the characterization performed by Augusta et al. (2010). However, the application of heat commonly used in traditional dehydration processes was expected to cause changes in the physical and structural properties of dry products (Barbosa-Cánovas et al., 2005), which was observed in virtually all parameters determined for jambo dried pulp, except for the pH.
Moisture reduction achieved through the foam layer drying method is critical to hamper microbial growth and the development of physicochemical reactions (Zotarelli, 2014). Table 3 further shows that the drying process increased the total titratable acidity of the dried pulp compared to the fresh sample, which may be explained by the almost complete removal of the aqueous part of the pulp, causing the concentration of acids present in the fruit. Such phenomenon was also observed by Rigueto et al. (2018), using the same method for drying uvaia in the same temperature range as the present study.
The pH values ranged from 3.52 (fresh pulp) to 3.47 (drying at 70 °C), with values progressively regressing with increasing drying temperature. Also, it is noted (Table 3) that the pH of fresh jambo and the powder obtained at 50ºC showed no significant difference (p>0.05), such difference was observed from the dry powders at 60 and 70 ºC.
Ash contents did not differ statistically (p>0.05) between the three temperatures studied, there was only difference between fresh pulp (0.46%) and the powders (≅ 3%). This increase may be related to the presence emulsifier in powder samples obtained after foam-mat drying (Rigueto et al., 2018).
All the pulps submitted to the foam drying process presented higher vitamin C content than the fresh pulp, being observed an inversely proportional relation with the increase of the drying air temperature with the retention of vitamin C. Thus, 50 °C is the most suitable temperature for dehydration of jambo, aiming at higher levels of vitamin C. Chambers et al. (1996) explain that fruits subjected to low drying temperatures may favor the stabilization of ascorbic acid and, consequently, increase its vitamin content, while increased warming and luminosity may lead to the reduction of vitamins, as already reported by other authors who studied vegetables different (Fernandes et al., 2014;Mehta et al., 2007;Kadam;Lata;Pandey, 2005). Azevêdo (2010)  var. Hungarian). The authors found that vitamin C content also decreased with increasing temperature (from 50 ° C to 90 °C), but in contrast to the present study, fresh red pepper had a higher amount of vitamin C than red pepper submitted drying at 50 °C.

Conclusions
According to the obtained data, it is concluded that the increase of the drying temperature favored the reduction in the drying time of the jambo foams. Regarding mathematical modeling, the Page and Midilli and Kucuk models provided the best adjustments to the experimental drying data at the three temperatures studied.
In physicochemical analysis, the fresh jambo pulp showed acid character, with increase of acidity and ash after foam-mat drying. In addition, dried 50 °C jambo pulp showed higher vitamin C retention due to lower foam exposure temperature.