JULIANA CONEGERO

Título da Dissertação: PHYSICOCHEMICAL CHARACTERIZATION AND HYGROSCOPIC BEHAVIOR OF LYOPHILIZED MANGABA PULP POWDER

Orientador: Prof. Dr. Antonio Roberto Giriboni Monteiro

Data da Defesa: 08/07/2016

RESUMO GERAL

INTRODUCTION. The mangaba is a fruit that comes from the mangabeira (Hancornia speciosa Gomes), that has a pleasant taste and aroma, it is also a fruit with high nutritional value. This fruit have been used to raw material for the production of various food products: juices, ice creams, and jellies. And its commercial value is increased and need of preservation of mangaba for this purpose. Significant amounts of vitamin C in certain fruits from the Cerrado, e.g., the mangaba. Due to the high perishability of the mangaba in natura, it as verified the need for preservation methods to maintain its characteristics, with the maintenance of its quality. The advantage of drying process for the fruit pulp industry, which makes possible a longer storage time and the concentration of the raw material constituents. Lyophilization is a drying method that preserves volatiles compounds responsible for the flavor food and preserving its nutritional values. During the lyophilization, the water of the product passes directly from the solid state (frozen) to the gas state by the sublimation process. In this drying method, it is possible to add drying adjuvants such as maltodextrin, which leads to a decrease in the hygroscopicity of the obtained powders from juices and pulp fruit.The analysis of hygroscopic equilibrium isotherms makes possible the prediction of chemical, enzymatic and microbiological reactions since the hygroscopic behavior of the product is analyzed at different conditions of temperature and air humidity, and it is also possible to study more appropriate packages according to the obtained results. Different theoretical and empirical models, used by several authors, which allow the adjustment of the hygroscopic equilibrium curves of several products, both regarding water activity and air temperature, making possible to predict the behavior of adsorption isotherms. The higher accuracy of such mathematical models in relation to the water activity interval, besides the type of food analyzed.
AIMS. This study aimed to perform the physicochemical characterization of lyophilized mangaba pulp powder, as well as to analyze the hygroscopic behavior through the adsorption isotherm.
MATERIAL AND METHODS. Frozen pulps of mangaba, acquired from the industrial area of Natal (State Capital of Rio Grande do Norte, Brazil), were subjected to the lyophilization process. The drying, physicochemical characterization, and hygroscopic behavior analysis through isotherms, were carried out in the Laboratory of Food Quality Control and Drying of the Federal University of Ceará located in Fortaleza (State Capital of Ceará).
The lyophilization process was performed in a bench lyophilizer for 24 hours. The pH, titratable acidity, and soluble solids analyses were performed according to the Adolfo Lutz Institute (2008). The determination of ascorbic acid was carried out according by titration and the water activity analysis was performed using an AQUALAB 4TEV apparatus, calibrated with distilled water according to manufacturer's recommendations. The analyses were performed in triplicate. The moisture adsorption isotherm analysis was performed using the statistic gravimetric method, using saturated salt solutions in glass cells at ambient temperature (21ºC) to pack the lyophilized mangaba powders. After the equilibrium, determination of water activity at different temperatures, and moisture analysis in a vacuum oven, the weight measurements were performed in triplicate. The experimental data of adsorption isotherms were adjusted using the GAB, BET, Oswin, and Henderson mathematical models.
RESULTS AND DISCUSSION. The lyophilized mangaba pulp powder showed acidic characteristic with a pH of 3.14. This result contributed to the stability of the product, it makes it possible to inhibit other reactions related to food degradation. By analyzing different matrices
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of mangaba, other authors obtained results ranging from 3.62 to 4.39. The titratable acidity was 1,95 mg/100g.The high content of soluble solids here inside 99 °Brix may be related to the addition of maltodextrin to the dehydration process and the concentration of solids in the pulp, which is a characteristic of drying processes. The ascorbic acid content obtained in the present study, 55.97 mg/100g, is higher than the level recommended for daily intake, according to brazilian legislation, although it is lower than the content reported in other studies on analysis of lyophilized mangaba. The water activity value of 0.162, found herein for the lyophilized mangaba pulp powder, due to the lyophilization process, it is expected in these drying methods. Low levels of water activity are found in dehydrated food. An increase in the equilibrium moisture content with the increase in water activity is observed in the isotherm analysis. Same authors report this increase is a characteristic of amorphous powders, like the powders evaluated in this study. An increase in the equilibrium moisture content was observed with the increase of temperature and the porosity and food soluble compounds contribute to increasing the moisture content.At a relative humidity of 80%, the lyophilized mangaba pulp powder shows a higher gain of moisture, demonstrating that this relative humidity is the limit value to store this product without the occurrence of undesirable physical reactions.Regarding the obtained curve, we identified a type III and ''J'' shape curve, the flatter area in its first section, it is typical of food rich in sugars and solutes. Henderson was the best model to describe the hygroscopic behavior of the studied product since it showed the best characteristics, with the parameters ''a'' and ''b'' in accordance with the standard value, relative errors lower than 10%, and high retention coefficient values (R) and values close to 1.Other authors mention the use of the Henderson equation to calculate the isotherms of materials with water activity ranging from 0.10 and 0.75, such as grains, cereals, and fruit.
CONCLUSIONS.The lyophilized mangaba pulp powder obtained in this study showed appropriate characteristics, especially regarding low values of the water activity, pH and titratable acidity. The high soluble solids content is characteristic of dehydrated food ascorbic acid, and titratable acidity, with values expected for dehydrated food, with addition of carrier agent, besides being a source of Vitamin C. Of the applied mathematical models, Henderson presented the best adjustment at the analyzed temperatures of 25,30,35 and 40 °C.
Keywords: isotherm, sorption, hygroscopicity, dehydration.

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