Orientador: Prof. Dr. Antonio Roberto Giriboni Monteiro

Data da Defesa: 21/02/2022

As a versatile, fast, high-productivity, and low-cost process, thermoplastic extrusion is widely used in the cereal industry for producing ready-to-eat foods such as snacks, instant noodles, soups, and breakfast cereals. This unit operation consists of forming and shaping a dough-like material by forcing it through a die. The quality of the final product is affected by the processing and raw material conditions. Cassava (Manihot esculenta Crantz) is a tuberous root widely consumed in tropical-climate countries, and it is the fourth-largest energy source in the diet of these regions, behind only rice, wheat, and corn. As it is easy to cultivate and a cheap source of carbohydrates, cassava is one of the most important crops in the world, especially in developing countries. But its shelf life is short, about three days post-harvest, which leads to a wide consumption in the form of flour, starch, and fermented products. Extruded products are usually rich in starch and have a high caloric value but are poor in micronutrients, fiber, and protein, challenging the extruded food industry to develop products with higher nutritional quality, lower caloric content, and keeping a pleasant taste. Several researchers are trying to meet this demand by reducing the sugar content and using food industry by-products that are cheap and rich in nutrients such as minerals, fiber, and antioxidants. From Stevia rebaudiana leaves, stems, and flowers, we obtain a safe, natural sweetener about 300 times sweeter than sugar, making it an excellent substitute for sucrose. It is also a source of bioactive compounds, fiber, and minerals that help to prevent and treat diseases such as obesity, diabetes, and cardiovascular disease.
This work aims to develop an extruded breakfast cereal based on cassava and ethanol pre-treated stevia leaves and characterize it chemically and sensorily.
We used granulated tapioca acquired in the local commerce of Maringá, PR, and stevia leaves provided by the Natural Products Center of the State University of Maringá (NEPRON) to prepare the breakfast cereals. The leaves were pre-treated with absolute ethanol to reduce undesirable flavors. We processed the breakfast cereals in the Cereal Technology Laboratory of the State University of Maringá by manually mixing granulated tapioca with pre-treated stevia leaves with standardized moisture by adding 10% water over the weight of granulated tapioca. We produced three breakfast cereal formulas, being F0 composed only of granulated tapioca, F1 of granulated tapioca and 1% stevia leaves, and F2 of granulated tapioca and 2% stevia leaves. The formulas were processed in an IMBRA RX50 extruder (INBRAMAQ, Ribeirão Preto, Brazil), featuring a single screw of 50 mm in diameter and 200 mm in length, using a matrix plate with two holes with 3 mm in diameter each. After extrusion, the breakfast cereals received sugar-based coating corresponding to 5% of the initial weight and were kept in polypropylene bags until the centesimal composition and sensory analyses. Moisture, ash, protein, and lipids content analyses were performed in triplicates. We estimated the carbohydrate content by subtracting the sum of the moisture, ash, protein, and lipid results from 100. Seventeen untrained testers evaluated sensory acceptance using a nine-point hedonic scale for taste, texture, and overall impression. The data underwent analysis according to the average of the numerical values obtained and the following classification: the acceptance region (between 6 and 9), indifference region (5), and rejection region (from 1 to 4). The data obtained from the sensory analysis test underwent statistical evaluation using the analysis of variance (ANOVA) method and Tukey's test at 5% significance using the Microsoft Office Excel 2019 software.
The incorporation of stevia leaves into tapioca breakfast cereals represented a significant increase in the centesimal composition of the extrudates. Only ash and lipid contents did not differ statistically between the formula with 1% stevia and the control. The moisture contents varied between 8.94% and 9.40%. The ash values were statistically equal between the formulas F0 and F1, respectively 0.11% and 0.19%, and F2 represented the highest ash content among all the formulations, 0.19%. Similarly, there was no variation at the 5% level of significance between F0 and F1 for the lipid content, with the control formulation containing 0.3% of lipids, the formulation with 1% of stevia leaves containing 0.6% of lipids, and the formulation with 2% of stevia leaves containing 0.16% of lipids, differing only from F0. Adding stevia leaves raised the protein content among the formulas F1, F2, and the control F0 by 0.46%, 0.52%, and 0.30%, respectively. Carbohydrates were the main components of tapioca and stevia leaves breakfast cereals, varying between 89.73% and 90.63%, with significant reduction provided by incorporating stevia leaves in the formulas. The sensory analysis showed that adding 1% or 2% of stevia leaves did not result in significantly different scores given to the tapioca breakfast cereals, obtaining values between 5.71 and 5.82 for flavor, 5.29 and 6.29 for texture, and 5.53 and 6.29 for the global evaluation. Flavor attribute obtained the highest percentage in the acceptance region, above 64% for all formulas, followed by texture, with more than 58% in the acceptance region, and global evaluation with a minimum of 52% in this region. As for the formulas, F0 was the most well-accepted concerning texture and global evaluation, obtaining the same index as F2 concerning flavor. All formulas received less than 23.5% in the indifference region, and only the formula F1 received a percentage higher than 23.5% in the rejection region, with an index of 35.3%.
Incorporating 1% and 2% of ethanol pretreated stevia leaves significantly altered the centesimal composition of tapioca breakfast cereals. All the formulas were sensorially well accepted for the attributes of flavor, texture, and global evaluation, with no significant difference between the samples' averages, being predominantly classified in the region of acceptance. The breakfast cereal prepared with the addition of 2% stevia leaves obtained the lowest percentages in the rejection region and the highest protein contents, showing promise for the production of breakfast cereals.
Key words: breakfast cereal, tapioca, Stevia rebaudiana, extrusion, cassava.

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