Thermal condition of mate (Ilex paraguariensis) processing

ABSTRACT: The Ilex paraguariensis is a species native to Brazil, Paraguay and Argentine, valued by its positive effects on human health. Mate processing consists of the following stages: pre-drying (rapid drying at high temperature, known as sapeco operation), drying, and milling. In order to verify the current process and to propose future improvements to the mate processing, thermal and mass balance analysis were applied to industrial mate processing units. Results showed that the consumption of energy in sapeco and drying operations exceeds the calorific input necessary for these operations. These results verify the need for a change in the management of temperatures in the sapeco and drying stages of mate processing in order to optimize the consumption of energy, resulting in lower costs, with positive effects on the quality of the mate products.


INTRODUCTION
Ilex paraguariensis or mate is an arboreal plant and an ombrophile, belonging to the family Aquifoliaceae and the genus Ilex (RESENDE et al., 2000;MOLINA & MOLINA, 2004;OMAR, 2009).Today mate, yerba-mate or mate are common names used for the plant, as well as the product comprising exclusively the leaves and stems of I. paraguariensis.The production of mate uses management systems of natural and cultivated populations, the main producing and consuming countries being Brazil, Argentina and Paraguay.In Brazil, its cultivation extends through the states of Rio Grande do Sul, Santa Catarina, Paraná and Mato Grosso do Sul.In these states mate occupies a position of considerable social, economic and cultural importance since it is commercialized by small farmers (VIDOR et al., 2002;ANTONIAZZI et al., 2018).

FOOD TECHNOLOGY
Ciência Rural, v.53, n.10, 2023.Vieira et al. diuretic, hypocholesterolemic, anti-rheumatic, antithrombotic, anti-inflammatory, anti-obesity and antiaging (GORZALCZANY et al., 2001;SCHINELLA et al., 2005;MENDES & CARLINI, 2007;PANG et al., 2008;SILVA et al., 2008;PIOVEZAN-BORGES, 2016;ALVES et al., 2020).A growing number of publications on the functional properties of mate, through research carried out in the producing regions, and in developed countries, recommend the consumption of products derived from mate, widening the interest in other applications, such as medicines and cosmetics (GORZALCZANY et al., 2001;LUNCEFORD & GUGLIUCCI, 2005;SCHERER et al., 2006;HECK & MEJIA, 2007;MENDES & CARLINI, 2007).However, despite the growing consumption of mate and interest from the chemical and pharmaceutical industries, spread through investigations on the properties of this plant, the technological resources used in the industrialization of mate have been limited (Figure 1).As a consequence of this, it can be verified that there is a need to implement control of the production processes making them more efficient, reducing the exposure of the leaves to the smoke and also to the high heating temperatures which generate toxic compounds such as polycyclic aromatic hydrocarbons (CAMARGO & TOLEDO, 2002;ZUIN et al., 2005;VIEIRA et al., 2010).
No studies have been published to date describing the thermal map of the various stages of mate processing, which demonstrated the need for future studies and a bettering of the processes and energy saving.Thus, there is still a need for improvement in relation to the quality of the traditional products based on mate, since the processes of production and industrialization have evolved little and the quality attributes of the products must be evaluated.Improvements in the process, from sapeco to drying, can contribute to the safety of the final product, avoiding the formation of chemically undesirable compounds, such as: naphthalen, phenanthrene, benzo [g,h,i] c,d] pyrene (considered as carcinogenic compounds) (VIEIRA et al., 2008), collaborating to widening the spectrum of mate use, considering its proven medical properties.Success in improving the quality may lead to an increase in the demand for mate and in the added value of the product (BERTONI et al., 1992).
The consumption of mate on the market has progressively evolved; however, the product is commercially and industrially limited.The best possibilities for broadening the market seem to be offered by the modernization of the production, where technological adaptation and optimization of the processes are fundamental, besides the diversification of the products offered (CAMPOS et al., 1996;VIEIRA et al., 2008;MURAKAMI et al., 2011;BOAVENTURA et al., 2015).With the aim of monitoring the processing and defining the thermal map during the mate production, this study described the mate processing, including the thermal analysis of conventional processes of sapeco and drying and the establishment of a simplified energy balance for the production of mate.

Descriptions of the installations and thermal balance of mate processing
The exploratory-descriptive research was based on data collected in the town of Catanduvas located in the mid-western region of Santa Catarina State, through the collection of data related to the different stages involved in mate processing.
From the literature survey and field research (visits to four mate processing units located in the municipality of Catanduvas), carried out with around 10 collaborators, 10 coordinators and 5 processing unit owners, the data related to the stages involved in the mate processing were obtained.The power consumed in the sapeco and drying was calculated from the information of the processors, regarding the consumption of firewood to mate drying and sapeco steps.According to the properties of the wood used (low calorific power of pine in kJ/kg of firewood), calculated from the density of the firewood, the power consumed was determined.

Evaluation of temperature of mate processing
The evaluation of temperatures of mate processing was carried out at 15 points on the equipment (sapecador and dryer), at two mate processing units, with the use of an infrared thermometer (Raytek, model PhotoTemp MX6, temperature range from -30 to 900 o C, with the emissivity regulated in the equipment software, adjusted to the required measurements (Ɛ 0.80), with three measurements carried out at each point, keeping the equipment accuracy at 0.75%, spectral range in 1 a 1000 µm.The points monitored at the installations studied are shown in figure 2 (1-15).

Thermography
In order to evaluate the thermal environment to which the mate leaves are subjected thermographic images were used, taken with a thermographic camera (ThermoCam S 65 -Flir Systems, calibrated for up to 1500 o C), of the furnaces of two mate processing units.The temperature was monitored through the hot extremities of the objects (metal plate) inside the furnace, subject to the same radiation and convection to which the leaves are submitted.

Moisture determination
Moisture of mate leaves was determined by drying to constant weight at 105ºC (AOAC, 2005;BASTOS et al., 2006).

Description of the installations
The processing of mate has undergone little modernization over the years, still following the sample principle of rudimentary installations used by the Indians, and therefore there remains many aspects which need to be improved compared with other agroindustries.The mate processing units visited use the mechanized system and possess the same type of industrial installation to scorch and dry the mate.Two wood burning furnaces (1000 -1500 kg/hour of mate leaves) are used, interconnected with rotary drying cylinders.
The images of the mate processing stages collected at the processing units under study are shown in figure 3, which follow the same operational sequence as the mate processing.
The leaves and green stems of the mate are unloaded from trucks (Figure 3A) and spread on a conveyer-belt (Figures 3B and 3C), which transports the mate onto the furnace flames of the scorcher.During the sapeco the flame is maintained, generated from the wood burning (Figure 3D), and the leaves and stems are fed into the equipment falling through the flames (Figure 3E).After being submitted to high temperatures, the leaves and stems circulate inside a rotary drum (iron cylinder) (Figure 3F), which apart from the gyrating movement has internal fins to facilitate the exit of the scorched material (Figure 3G).In this first stage, the leaves undergo a pre-drying process, since they enter with approximately 60% moisture content and leave scorched with a moisture content of around 35%.
The objective of the sapeco is to remove the superficial moisture and inactivate enzymes (peroxidases and polyphenoloxidases) which cause plant biomass oxidation, turning the leaves dark and the taste unpleasant (VALDUGA, 2002;NABECHIMA et al., 2014).This production system is currently mechanized; however, it follows the same principles practiced by the Indians who, manually, passed in a fast manner the raw material of stems with leaves over the flames of a wood fire, suitable for this purpose.

Vieira et al.
After the sapeco, the leaves are collected at the end of the rotary drum in a transport system which sends them to the dryer (Figure 3H).The equipment used for the drying is similar to that used for the sapeco; however, it uses a milder flame in the furnace and dehydrate the leaves until they acquired a breakable and crisp texture.
The raw material enters the dryer with a moisture content of around 35 % and exits with approximately 6 %.Besides the mechanical rotary  Thermal condition of mate (Ilex paraguariensis) processing.
dryers (Figure 3H), there are also conveyer-belt dryers.According to ESMELINDRO et al. (2002), the main difference between the two types of dryers is related to the contact of the raw material with the smoke during the drying process.The rotary dryer is the system most commonly used in the Brazilian market, with low industrialization and installation costs, easy handling and with no risk of damage by fire (SCHIFFL, 1997, cited by BOUGARDT, 2000); however, it has the disadvantage of direct contact of the smoke with the product, which is not observed in the conveyer-belt dryer, since the contact is indirect, causing less damage to the raw material.
After drying, in the final process, the mate is triturated or fragmented in an iron or hardwood triturator called a soque (Figure 3I).This apparatus forms part of the typical production system, where the triturated mate is called cancheada, constituting, thus, the raw material for the production mills, particularly for the commercial types: tea, chimarrão and tererê.
The removal of wood as a heat source for the process would bring advantages in terms of the reduction of these compounds, as well as facilitate the control of the temperature to obtain a product with quality and homogeneity.Avoiding the direct flame and controlling the temperature can minimize the generation of PAHs both through the contact with combustion gases and the formation these pyrolysis compounds from superheating of the leaves.

Thermal balance of the mate processing
In interviews with the production managers and staff at the units, it was possible to collect data for a simplified energy balance, as presented in table 1.
Table 1 -Estimate of thermal yield for the mate sapeco and drying processes of four processing units located in the municipality of Catanduvas.
The thermal balance allowed it to be estimated that the sapeco stage is characterized by a higher expenditure of energy in the process and that only 20 -26 % of the energy is effectively consumed in the evaporation of water from the mate leaves.These results verified the need for immediate action, both for energy saving and temperature control to avoid the formation of compounds toxic to human health (PAHs), derived from the pyrolysis of the leaves and wood combustion gases.In comparison, the efficiency of combustion engines, for instance, despite being modern, is around 35 -40% (DAHHAM et al., 2022) and the mate processing would be around 50% efficient, despite being rustic.However, the restrictions on energy consumption from the environmental and economic point of view, require efforts both for the diagnosis and designing of new projects for more energy efficient mate processing.
The units visited do not use thermal insulation on the furnace surfaces, the transporting systems and the rotary drum.This leads to an important loss of heat from the system which could be avoided.

Evaluation of temperature of mate processing
Table 2 gives the temperature values reported in the mate processing stages in processing units.The two units evaluated had similar temperature values during processing, and the temperatures during sapeco are higher than those during drying, according to the literature (ESMELINDRO et al., 2002).
The residence time and the average temperature of the mate in the dryers are dependent on the operating characteristics of each one.In the rotary dryer the product remains in direct contact with the smoke for approximately 30 mins, with the temperature oscillating from 350 -370 °C, at the entrance of the dryer, and from 80 -82 °C at the exit; these values are similar to those reported by ESMELINDRO et al. (2002), which were an average of 350 ºC at the entrance and 110 ºC at the exit of the dryer.For the conveyer-belt dryer, little used in Brazil, the average time is 3 hours and the temperature varies between 90 and 110 °C.

Thermography
To evaluate the thermal environment to which the mate is exposed during processing, the temperature at the hot extremities of the objects (metal plate) inside the furnace was monitored.Table 3 gives the temperatures observed (thermographic camera) in the sapeco stage of mate processing at the four of mate processing units studied.
The temperature to which the leaves are submitted during sapeco lies at around 540 -620 ºC, differing from the literature which reports the average temperature at the scorcher entrance as being around 400 °C (ESMELINDRO et al., 2002).Some authors stated that the quality of the final product can be affected by a thermally inefficient treatment due to the exposure to temperatures lower than those recommended during sapeco, allowing residual enzymatic action or contrarily to exposure to high temperatures causing the burning of the product (ESMELINDRO et al., 2002;VIEIRA et al., 2010;NABECHIMA et al., 2014), besides the possibility for greater generation of polycyclic aromatic hydrocarbons.
This preliminary research about the thermal condition of mate (Ilex paraguariensis) processing, in addition to stimulating new research for the enhancement of functional properties, avoiding the formation of PAHs in mate, also contributed to alerting about the need for changes in industrial processes.Despite the positive scenario, based on the properties of mate, the vast majority of processors are unaware of or neglect these needs for changes that could bring even more benefits to the health of consumers and new business opportunities for importing countries that despite recognizing the benefits of mate, have strict control over the presence of PAHs.

CONCLUSION
Results of this study verify that improvements need to be made to the mate processing for which 80 % wastage of the energy produced occurs, along with high temperatures originating from this process.
It is shown with the use of evaluations with a thermographic camera and thermometry that the mate sector needs to change the sapeco and drying systems, in order to save energy and, consequently, better regulate the processing temperature, resulting in product improvement.
The design of a new process focusing on energy saving, the integration and improvement of the performance of all economic aspects in the processing and promotion of the product, and the production process of mate in the producing states, Table 3 -Temperatures prevailing during the mate sapeco process, evaluated with the aid of a thermographic camera, in the four mate processing units studied.

Figure 1 -
Figure 1 -Flowchart of the main stages of the mate industrialization process.Adapted from Valduga (1995).

Figure 2 -
Figure 2 -Temperature monitoring points in the mate processing stages (1 -internal wall of sapecador furnace; 2external wall of sapecador furnace; 3 -sapecador flame temperature; 4 -External wall of drum next to furnace; 5 -middle of external wall of drum; 6 -near end of external wall of drum; 7 -separator lid; 8 -mate at exit of sapecador; 9 -internal wall of drier furnace; 10 -external wall of drier furnace; 11 -drier flame temperature; 12external wall of drum next to drier furnace; 13 -middle of external wall of drum drier; 14 -near end of external wall of drum; 15 -separator l.
-Data to calculate thermal yieldA-