Secagem de ameixa pelo método de camada de espuma: otimização dos parâmetros e caracterização do produto

Abstract

Plum is a seasonal fruit with low durability after harvest, requiring the application of techniques that prolong the shelf life of this food. Among the methods that can be applied is the drying in foam mat that consists of the transformation of liquids or semi-liquids into a stable foam from the addition of a foaming agent and application of agitation so that there is the incorporation of air. In this work, the plum foam was produced from the addition of egg albumin and the drying was carried out in an air recirculation oven with a speed of 2 m/s. The study of the drying of the plum in a foam layer was divided into stages, the first part of which is the investigation of the effects of the process variables, whipping time and albumin concentration, on the physical, thermal properties and drying time in order to optimize the operational conditions for the production of plum foam, whose values found were 3% albumin concentration and 12 minutes of whipping time. In the next step, the influence of temperature and foam mat thickness on the moisture, water activity and drying time of the plum foam was evaluated in order to define the best operational condition for drying this fruit, being observed that the higher temperature and less foam mat thickness are more suitable for the process, since they provided the best results for powder moisture (2.690 g water/100 g dry powder), water activity (0.245), drying time ( 70 minutes) and average drying rate (0.0631 g water/g dry powder/min). The last phase of this work investigated the influence of temperature on the physical-chemical properties, bioactive compounds and antioxidant activity and performed a comparison of the powders obtained by foam mat at four temperatures with the powder obtained by freeze drying, since the latter is widely used. known as the method capable of preserving the original characteristics of the fruit. The experiments were carried out using the foam in the previously optimized process condition (3% egg albumin in the formulation, 12 minutes of whipping and 0.8 cm layer thickness) and four drying temperatures: 50, 60, 70 and 80 ° C. For lyophilization, about 280 grams of pure plum pulp was used, without the addition of egg albumin (it was not foamed). The analysis of the produced powders showed that the higher temperature (80 ° C) provided a product with low cohesion between the particles (1.153) and good fluidity (13.235%), in addition to low absolute density (0.637 g/cm³), important characteristics for particulate materials. All powders showed good solubility in the range of 75.737 and 76.842 g/100 g and low water activity (0.245 to 0.386). The phenolic compounds were not impacted by the process conditions, the antioxidant activity was favored by the temperature, but the amount of ascorbic acid and carotenoids was greatly reduced by the action of this variable. The lyophilized powder was more hygroscopic (33.410 g water/100 g dry solid), however with very good fluidity (11.944%) and low cohesion between the particles (1.136). The process proved to be very favorable for the conservation of phenolic compounds (221.820 mg gallic acid equivalent/100 g of the sample) and antioxidant activity. Based on the results and bearing in mind that the lyophilization process is costly, drying in a foam layer proves to be a viable and low-cost alternative to prolong and increase the availability of the plum on the market. This study showed that the operating conditions that provided the best results for both the drying process and the quality of the plum powder were the thickness of the foam layer at 0.8 cm and the temperature of 80 °C.