Research background. Drying represents a viable unit operation for the preservation of food. Convective drying is the most used method for plant materials. However, it can result in negative changes in food nutrient composition, and other quality parameters, besides having high energy consumption. Pretreatments can represent an alternative to minimize these negative aspects of dried materials. This work aimed to evaluate the use of ethanol and ultrasound before pineapple convective drying and its effect on the product´s color, water activity, ascorbic acid, and total carotenoid contents. Experimental approach. For the pretreatment step, fruit samples were immersed in different ethanol concentration solutions, and experiments were carried out for 10 min with and without using ultrasound (25 kHz). Fruit samples were dried at 60 ºC. A control group (without the pretreatment step) was also dried in the same condition. Semi-theoretical models were used for drying data fitting, and the diffusional model was used to describe the moisture transfer and calculate the effective diffusivities. Water activity, ascorbic acid, total carotenoids, and color analyses were performed. Results and conclusions. The association between ethanol and ultrasound as a pretreatment reduced the drying time of pineapple. Higher effective moisture diffusivities were obtained when ethanol and ultrasound were performed before drying. The Two Term Exponential model presented the best fit for drying experimental data. In comparison to the fresh sample, the dried samples showed a darker color. The pretreatment with ethanol resulted in increased retention of the studied bioactive components. This study represents an improvement for the drying process, providing satisfactory results. Novelty and scientific contribution. Ultrasound and ethanol as a pretreatment to convective drying are promising. However, each food matrix has a typical structure and composition. Therefore, the application of the pretreatment in other products or using other conditions is still necessary to deeply understand and explain their effect on the process and the quality of dried products.

A velocidade de sedimentação de partículas finas pode ser aumentada por meio de agregação por coagulação, aglomeração ou floculação. A floculação direta de partículas coloidais não é suficiente para aumentar significativamente a velocidade de sedimentação, pois o floco ainda pode ter pequeno tamanho. Portanto, a desestabilização de sistemas coloidais passa pela necessidade de uma pré-agregação. Nesse trabalho comparou-se a influência de uma pré-agregação, com um surfatante - dodecilamina (DDA) e com um sal – cloreto de alumínio (hexa)hidratado (CAH), na floculação de partículas coloidais de dióxido de titânio com uma poliacrilamida hidrolisada (PAMH). Os resultados foram avaliados em termos de turbidez do sobrenadante e compactação final do sedimento. A pré-agregação, com um eletrólito ou um surfatante, melhora significativamente a floculação com PAMH. A DDA proporciona a formação de pré-agregados maiores, menor turbidez do sobrenadante e sedimentos mais compactos, quando comparado com o AlCl3.6H2O.