Drying of Albedo and Whole Peel of Yellow Passion Fruit

The use of waste has been the focus of attention of the agri-food sector, and a fruit with large amount of waste is the passion fruit. Its peel consists of albedo and flavedo, which can be used to manufacture flour, and some studies propose the need to remove the flavedo as well as to perform maceration. The objective of the present work was to study the drying process to produce flour from passion fruit albedo and whole peel, checking the influences of the flavedo removal and maceration steps, as well as the drying temperatures (70 and 80 oC). Yield after drying was calculated and it was shown to be low. Page, Silva et alii, Henderson and Pabis and Logarithmic mathematical models were fitted to the experimental data using LAB Fit software. The statistical indicators used to identify the best fit were coefficient of determination (R) and chi-square (χ). The Page model was the one that fitted best to the data, showing the best statistical indicators. Also, it can also be highlighted that the sample composed of peel without maceration and dried at 70 oC had the best results regarding the statistical indicators.


Introduction
Yellow passion fruit (Passiflora edulis) is among the agricultural products with wide popular acceptance and large quantity of wastes.Its peel represents almost all the waste and is composed of albedo (white part) and flavedo (yellow part).In general, in order to use passion fruit peel in food production, the material is macerated (immersed in water), a procedure which aims to reduce the bitter taste caused by the substance naringin present in its composition (Dias et al., 2011;Yamashita, 2017).
One of the alternative processes that can be used to reduce passion fruit wastes is drying, which can be carried out using artificially moved air, followed by flour production, which can be used in the formulation of other various types of food (Di Domenico et al., 2017;Machado et al., 2013).
Drying allows the determination of the drying kinetics, which tries to define the behavior of the dried solid material and depends on its specific properties, temperature, drying air speed and relative air humidity, represented by the drying curves and drying rate.Depending on the material to be dried, the drying process may require a very long time, which makes it difficult to obtain data for drying kinetics determination.Thus, mathematical simulation becomes fundamental to describe such behavior (Silva et al., 2015;Di Domenico & Conrad, 2015).
Given the above, this study aimed to conduct drying experiments at different temperatures using passion fruit albedo and whole peel with and without maceration, checking the influence of flavedo removal and maceration on the production of flour, besides calculating the mass yield of the samples after the process.

Material and Methods
Approximately 600 passion fruits (Passiflora edulis f.Flavicarpa) were purchased in the Paraíba state, at full maturity stage (completely yellow peel).Initially, the passion fruits were washed in running water and immersed where, X t : moisture content at time t, dry basis, d.b.; X e : equilibrium moisture content, d.b.; X o : initial moisture content, d.b.
Drying kinetics was described using the nonlinear regression models presented in Table 1.The equations of the models were used for treatment and fitting of the experimental data using LAB Fit Curve Fitting Software.
Table 1.Models used to describe passion fruit flour drying kinetics The evaluation criteria used to identify the best fit of the models to the experimental data were the determination coefficient (R 2 ) and Chi-square (χ 2 ), calculated by Equation ( 2): where, χ 2 : chi-square; X * exp,i : experimental moisture ratio; X * pre,i : moisture ratio predicted by the model; N: number of experimental data; n: number of coefficients and constants of the model.
Finally, eight samples were collected for physical-chemical analysis, as shown in Table 2.
Table 2. Nomenclature adopted for the samples after drying

Results and Discussion
The drying kinetics of yellow passion fruit albedo (white part) and whole peel was studied as influenced by the drying temperature and maceration process.The temperatures used in the drying were 70 and 80±1 °C and the times required for mass equilibrium as well as mass yield of the samples are described in Table 3.In all samples, the mass loss was very expressive after drying, as expected.2018) elaborated flour with the watermelon peel to produce cupcakes and obtained a lower yield than the peel and passion fruit albedo of this work, of only 5%, a value that approximates only the flour made with the macerated and dry albedo at 80 °C.Vieira et al. (2017) elaborated flour with melon bark also for cupcakes production and obtained a yield of 8.8%, lower only than that found in the flour obtained from the integral shell of dried passion fruit at 70 and 80 °C.Freitas et al. (2017) elaborated flours with green bananas of the varieties silver and nanicão for the production of honey loaves and they describe that the final yield of the flour was 17%, higher than those of this research, certainly because the authors used the pulp of the fruit.Santos et al. (2015) conducted eight treatments for the flour processing using different parts and maturation stages of the banana banana, being: a) green banana pulp; b) mature banana pulp; c) green banana peel; d) ripe banana peel; e) pulp plus bark of green banana; f) pulp plus ripe banana peel and g) pulp plus green banana peel without sanitizing with sodium hypochlorite and obtained yields of 39.4; 23.81; 8.67; 11.24; 23.34; 25.67 and 23.13% for flour a, b, c, d, e, f and g respectively, it was observed that when using the fruit pulp in the flour preparation the yields were higher.However, for the flours c and d (which were made with only peel), the results approximate the values of the dried passion fruit peel flour at 70 °C and the 80 °C.
In relation to the drying temperature, samples dried at 80 °C reached equilibrium in a shorter time than those dried at 70 °C.This is expected, due to the temperature increase of 10 ºC, which causes the water to evaporate faster from the samples (Baptestini et al., 2017;Corrêa et al., 2017;Ferreira & Pena, 2010).Regarding maceration, it was observed that this process contributed to accelerating the drying, possibly because the samples contain higher contents of free water.In addition, water in the maceration process causes bound particles to detach, facilitating mass loss.Silva et al. (2016), studying the production and characterization of passion fruit albedo flour for food use, observed that the kinetic equilibrium in macerated albedo drying was reached after 1290, 930, 690 and 570 min with the temperatures of 50, 60, 70 and 80 °C, respectively.These periods were shorter than those observed in the present study for albedo samples macerated at the same temperatures; double the time was required for the sample dried at 70 °C and an additional time of 210 min was required for the sample dried at 80 °C.This difference can be explained by the quantity of sample used by these authors in the drying (200 g) and the device used (tray dryer).
Ferreira and Pena (2010) and Spoladore et al. (2014) conducted drying experiments with passion fruit peel and also obtained equilibrium in shorter period.530 and 390 min were required for the temperature of 70 °C, whereas only 475 and 300 min were required for 80 °C, respectively.The mass used by Ferreira and Pena (2010) was 500 g, which once again reveals that the larger the mass used in the drying of a product, the longer the time required for it to reach equilibrium, considering that the material is arranged on the trays for drying with similar thicknesses.Spoladore et al. (2014) did not describe the mass used in their study, but it was probably even smaller.
Yield values were very low, ranging only from 5.94% for sample of albedo macerated and dried at 80 °C to 10.07% for the sample of peel dried at 70 °C.Such low yield was due to the high moisture content (89.77-94.24%).It was evident that samples dried at the highest temperature (80 °C) obtained lower yield, since water loss is higher in this case.The samples with highest yield are those of peels with no removal of flavedo (yellow part) and which had not undergone maceration.By contrast, the samples with lowest yield were those composed of only albedo and which had undergone maceration, indicating that this process contributed to mass loss in the product.Figure 5.

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Table 3 .
Drying times required for mass stabilization and mass yield of passion fruit albedo and peel samples after drying at 70 and 80±1 °C

Table 4
presents the parameters of the mathematical models of Page, Silva et alii, Henderson & Pabis and Logarithmic, respectively.