Microencapsulação de polpa de feijoa (Acca sellowiana) pelo processo de secagem por atomização (Spray Drying)

Abstract

Acca sellowiana, synonym Feijoa sellowiana, belongs to the Myrtaceae family. It is native to Brazil, but is widely cultivated in countries such as Colombia, the United States and New Zealand, where it has economic importance. Its fruits are aromatic and rich in bioactive substances that may contribute to the diet of the population. However, due to the rapid maturation and the difficulties in the prolonged storage, the application of post-harvest technologies is employed, among these the use of spray drying is highlighted as an alternative way to minimize loss through drying in order to preserve its quality.The objective of this work was to microencapsulate the feijoa pulp by spray drying and to evaluate the influence of drying air temperature, encapsulating agent concentration and type of agent (gum Arabic and maltodextrin) on the antioxidant, physical, morphological and thermal characteristics of the products microencapsulated. Feijoa fruits were evaluated for physical, physicochemical and antioxidant parameters. A simple 2³ factorial experiment was used to evaluate the drying conditions of the feijoa pulp and the independent variables were: inlet air temperature (90 and 150 ºC), concentration (10 and 30%) and type of encapsulating agent (gum arabic and maltodextrin). The total phenolic compounds were determined, identified and quantified. The profile of phenolic compounds was investigated by high - performance liquid chromatography (HPLC) microencapsulated pulp. The antioxidant activity was performed by different spectrophotometric methods (DPPH, ABTS and FRAP). The microcapsules were physically characterized and the color was determined by means of colorimetric analyzes. The microstructures formed were analyzed by scanning electron microscopy (SEM) and thermal degradation by thermogravimetry. The fruits presented yield of 53.19% (mass: fruit = 103.6 g, peel = 48.49 g, pulp = 55.10 g) and length / diameter ratio of 1.525 (length = 7.683 cm, diameter = 5.042 cm). The in natura pulp presented values of pH, ATT and SS of 3.32, 2.82 g, 100 g-1 and 14.50 ºBrix, respectively.The ascorbic acid content was 38.09 g 100 g-1. The bark, with a green coloration (h* =117.33) presented a texture strength of 10.64 N for epidermis rupture. The pulp has cream coloration (h* = 90.66) and soft texture (force for penetration of 0.63N).It was suggested as being the condition selected in the study the inlet air temperature of 150 °C, 10% encapsulating agent concentrationandmaltodextrin, to obtain powder rich in total phenolic compounds and antioxidant activity.Chromatographic analysis revealed the presence of rutin (46.13 and 75.87 μg g-1), catechin (18.59 and 97.07 μg g-1), quercetin (26.09 and 63.42 μgg-1) and trans-cinnamic acid (32.13 and 40.93 μg g-1). The humidity water activity, solubility, hygroscopicity and dissolubility values of the powders ranged from 4.61 to 15.40%, 0.143 to 0.443, 91.24 to 99.73%, 13.15 to 24.33%, and 140 to 378 s, respectively.Thus, feijoa pulp powder obtained by spray drying can be considered of quality, since it presented low moisture content, water activity and hygroscopicity, besides being considered solubility and fast rehydration time. Such characteristics are commonly described as important for powdered foods.The use of maltodextrin and gum Arabic as drying supporting promoted an increase in total solids and reduces the moisture content of the material to be dehydrated, to facilitate obtaining powders with lower moisture content. The use of higher temperatures in the drying process promoted rapid evaporation of the water and the film of the dehydrated material became dry and rigid, preventing the particles from shrinking.At some points in the image, it was possible to observe the adhesion of smaller particles on the surface of larger particles, forming agglomerates which demonstrates the absence of crystalline surfaces and is characteristic of amorphous products. There was variation in the color of the microcapsules evidenced by the value h* of 75.68 to 82.79 indicating tendency in the coloration between yellow and red.The microcapsules presented spherical shape of different morphologies with smooth to rough surface, and varied sizes (1.06 to 23.2 μm) desirable characteristics for the stability of the material. It was observed increase in thermal stability of the powders relative to the thermal degradation of the pulp in nature. The spray drying technology meets a point of storage, as well as nutritional importance as regards the maintenance of the bioactive compounds from the feijoa fruit.