In this study, the ‘yacon’ was dried using pulsed vacuum osmotic dehydration as pretreatment followed by vacuum drying (at different temperatures) or convective drying. The use of osmotic dehydration and vacuum drying had their influence evaluated concerning drying kinetics and quality of the final product, considering fructan retention, color, and water activity. Fick’s second law and Page’s equation were suitable for the fitting of drying evolution. It was observed that higher temperatures (60 °C) resulted in shorter drying time, higher diffusivity, and higher fructan retention when compared to 40 and 50 °C. The osmotic pretreatment and the vacuum drying differed in fructan retention (p ≤ 0.05). Moreover, the dried product, osmotically pretreated, presented a shorter drying time. The best condition was vacuum drying at 60 ºC, preceded by pulsed vacuum osmotic dehydration that resulted in fructan retention of approximately 38% in a quicker, higher diffusivity and lighter color product concerning the other tested conditions.

Predição de escoamento de ar em um secador tipo túnel: Avaliação do uso de placas de direcionamento de fluxo e de modelos de turbulência Prediction of air flow in a tunnel type dryer: Evaluation of the use of plates direction of flow and turbulence models

Tomato is one of the most cultivated vegetables, playing important role in the human feed. Due to its characteristics and composition, tomatoes present reduced shelf life, and preservative techniques are required. In this study, response surface methodology was used to optimize process conditions during the osmotic dehydration (OD) of tomato slices, through the desirability function. Optimization factors were absolute pressure (21-89 kPa), vacuum application period (7-15 min), and osmotic solution water activity (0.893-0.943), while investigated responses were sodium incorporation (NaI), water loss (WL), solid gain (SG), weight reduction (WR), and osmodehydrated product water activity (ODaw). The optimized conditions were achieved, and a further hot-air drying (HAD) was conducted at different temperatures and air velocities. During the OD, lower absolute pressure, and osmotic solution water activity led to lower NaI and higher WL and WR. Shorter drying time and higher diffusivity were obtained at higher temperature and air velocity, during the HAD. The dried tomato slices with sodium incorporation reduction were evaluated with regard to the final water activity, rehydration and color, in which no significant differences (p > 0.05) were observed between the treatments.

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RESUMO-A secagem convectiva de frutos de physalis (Physalis peruviana) foi realizada à temperatura de 60°C e velocidade de ar de 2 m.s-1 sem e com diferentes pré-tratamentos (congelamento rápido com nitrogênio líquido, congelamento lento). A secagem foi realizada até o teor de umidade final de 0,08 ± 0,02 kg.kg-1 (b.s). Aos dados de cinética de secagem foram aplicadas seis Equações empíricas (Page, Page Modificado, Logarítmica, Midilli, Wang & Singh e Parabólica). Dentre as Equações avaliadas, a Equação de Wang & Singh foi a que melhor se ajustou aos dados experimentais, com valores de R 2 maiores que 0,99.