**1. Introduction**

Several vegetables are limited to some regions; consequently, they are not well known and are little consumed in other regions of Brazil, and many of them contain higher levels of micro and macro nutrients when compared to conventional vegetable [1,2]. Studies show that there is a large amount of vegetables that are little explored and known in the country, and their scientific dissemination can contribute to food security. [1]. Jambu (*Acmella oleracea*) is an abundant vegetable in the Northern region of Brazil, where its different plant organs (flowers, leaves and stems) are consumed in preparations of typical foods of the Amazon region and as traditional medicinal herb in the treatment of diseases of mouth and throat [2–4].

The species *Acmella oleracea* is investigated for several applications, including evaluation of larvicidal activity of different crude extracts of leaves, as well as antioxidant and immunomodulatory properties, and many studies have focused on its use for centuries in the treatment of oral pain due to its analgesic properties [4–6].

Jambu is a perishable vegetable and requires post-harvest treatment in order to prevent and minimize losses that occur during its marketing, seeking to reduce to a minimum the losses of the active ingredients of interest and compounds aimed at adding flavor or aroma to food [7,8]. Conservation processes include artificial drying by hot air convection, one of the oldest used methods [9].

**Citation:** Gomes, F.P.; Resende, O.; Sousa, E.P.d.; Célia, J.A.; de Oliveira, K.B. Application of Mathematical Models and Thermodynamic Properties in the Drying of Jambu Leaves. *Agriculture* **2022**, *12*, 1252. https://doi.org/10.3390/ agriculture12081252

Academic Editor: Bengang Wu

Received: 31 July 2022 Accepted: 16 August 2022 Published: 18 August 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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The temperature and drying time must be appropriate for each vegetable, in order to preserve its physical characteristics, nutritional and sensory properties. It is necessary to use drying techniques that better preserve the qualities of the food [10].

The foam mat drying process in can be carried out on liquid or semi-liquid foods, the foam is incorporated by means of aeration with a foaming agen<sup>t</sup> and then dried [11]. Due to the foam structure, which generates a larger area exposed to the drying air, there is a higher mass transfer rate and shorter dehydration time [12].

Drying of agricultural products can be organized in several ways in which drying kinetics data can be represented by theoretical, semi-theoretical and empirical mathematical models [13]. The drying kinetics process presents important information about the characteristics of the typical drying behavior, heating, the period of fast drying due to the constant rate and the falling rate periods [14]. Drying curves are extremely important for the development of processes and equipment sizing; from the curves it is possible to estimate the necessary drying time of a certain amount of products and the time for production, obtaining an estimate of energy expenditure that reflects in the processing cost and influences the final price of the product.

Therefore, *Acmella oleracea* is a plant of commercial interest, due to its pharmacological properties, but there are few studies assessing its processing and application of conservation methods [15,16]. Thus, the objective of the present work was to perform the drying kinetics of jambu leaf mass and jambu leaf mass with foam, at different temperatures (50, 60 and 70 ◦C) in a thickness of 1.0 cm. determine thermodynamic properties and evaluate its physicochemical characterization.

#### **2. Material and Methods**

#### *2.1. Obtaining of Raw Material and Drying*

Jambu vegetable were collected on octuber the 2020 on a family farm in the municipality of Macapá, AP (0◦0126.0 South and 51◦0653.5 West of Greenwich), and the experiment it was made at the Food Laboratory of the Federal Institute of Amapá-IFAP (0◦0512.3 North and 51◦0531.0 West of Greenwich).

Jambu leaves were washed in chlorinated water, sanitized (solution composed of 2.5% sodium hypochlorite, for 15 min) and crushed (without adding water, for 2 min) in processor to obtain a homogeneous mass.

The foam was prepared by the mixture and aeration for 15 min in a domestic mixer (Mundial Chantilly, São Paulo, Brazil) of the mass of jambu leaves, 1% of a stabilizing agen<sup>t</sup> (Super Liga Neutra®) combined with 2% of an emulsifier (Emustab®). The mass of leaves and the foam were subjected to thin-layer convective drying.

Drying was carried out in a forced air circulation oven (Lucadema), at temperatures of 50, 60 and 70 ◦C and air velocity of 1.0 ms<sup>−</sup><sup>1</sup> (measured in a digital anemometer Homis Mod 489). The materials (mass of leaves and foam) were spread evenly in rectangular stainless steel trays (25.5 × 13.5 cm), forming a thin layer of 1.0 cm thickness measured with a digital caliper (King Tools).

During drying, the trays were weighed at regular intervals until they reached constant mass. The experiment was carried out in triplicate. The dehydrated material was removed from the tray with a spatula and crushed in a household food processor (Black Decker, Brazil) for 1 min to obtain the powder, which were subsequently stored in laminated packaging composed of two layers (Pet-Low-density polyethylene terephthalate and metallized PET-metallized polyethylene terephthalate).
