This work aimed to experimentally study the drying behaviour of yacon tubers with and without steam blanching. Drying was carried out for 5 h and 30 min in a forced air dryer at 50°C, 60°C and 70°C. The results indicated that the shortest drying time was obtained at 70°C for blanched samples, and that the equilibrium water activity values were significantly lower for the blanched samples at all temperatures. The yacon dried without prior blanching showed lowest concentrations of reducing sugars when dried at 70°C, significantly lower than those dried at 50°C and 60°C. This indicates hydrolysis of the fructooligosaccharides at 70°C, a fact verified by the significant increase in reducing sugars content from 36.65 ± 0.54-44.10 ± 0.96% and reduction in the non-reducing sugars from 31.62 ± 0.55-26.18 ± 0.29%.

The inactivation of the enzymes polyphenoloxidase (PPO) and peroxidase (POD) and color loss with steam blanching, was studied. The yacon roots were washed and peeled, cut into 1.75 Ϯ 0.35-mm slices, and placed in wire baskets inside an autoclave generating steam at a temperature of 100C for 1, 2, 4, 6, 8 and 10 min. The best condition was with a time of 4 min, where it was possible to reduce the activity of POD and PPO by 84.62 and 83.76%, respectively, with losses of inulin, glucose and fructose of 30.69, 39.40 and 15.82%, respectively. Total color difference and browning index values changed when compared with original color of yacon roots. These changes were higher during the first 2 min and, after this time, these parameters did not change significantly. Principal component analysis of steam blanching times in yacon too revealed no significant differences starting from 4 min of blanching. PRACTICAL APPLICATIONSBlanching is a unit operation that is used in order to achieve inactivation of enzymes that produce the browning. This procedure is used as a pretreatment before pasteurization, sterilization, refrigeration and freezing. Either steam or hot water can be used to blanch food. However, prolonged hot water blanching results in considerable loss of soluble sugars because of leaching. Blanching can also be used to deactivate enzymes that cause depolymerizing of polysaccharides such an inulin. This fructan has prebiotic properties and is a dietary fiber. The aim of the present work was to study the deactivation of enzymes that produce changes of color using steam in yacon roots.

Yacon roots contain inulin, which has prebiotic properties and it may be used as sucrose or fat substitutes. However, inulin is very soluble in water. The loss of this important nutrient during blanching is caused mainly by diffusion or leaching, which might be diminished if blanching temperature -time conditions are correctly employed. The aim of this study was to determine the leaching of the sugars inulin, glucose and fructose, present in yacon roots, during hot water blanching under different time/temperature conditions. The samples were cleaned and peeled and cut into geometric forms of 1.75 ± 0.35 mm thick disks. A complete factorial experimental design was used, and the treatments of the samples were compared using the Tukey test. The results indicated that the time and temperature were significant in the dissolution of the sugars. The lowest inulin losses occurred at temperatures and times lower than 60 ºC and 3 minutes. For all temperatures, the lowest glucose and fructose losses were obtained at time lower than 3 and 5 minutes, respectively. Index terms:Glucose; fructose; prebiotic; response surface. RESUMOAs raízes de yacon contém inulina, o qual possui propriedade prebiótica e pode ser usado como substituto de sacarose ou gordura. Entretanto, a inulina é solúvel em água. As perdas desse nutriente durante o branqueamento são causadas, principalmente, por difusão ou lixiviação, o qual pode ser diminuído se as condições de tempo e temperatura são corretamente empregadas. Objetivou-se neste trabalho, foi estudar a lixiviação, durante o branqueamento em água quente em diferentes condições de tempo e temperatura, dos açúcares inulina, glicose e frutose presentes na raiz do yacon. As amostras foram previamente limpas, descascadas e cortadas na forma geométrica de disco de 1,75 ± 0,35 milímetros de espessura. Os resultados indicaram que o tempo e a temperatura foram significativos na dissolução dos açúcares. As menores perdas de inulina ocorreram à temperaturas e tempos menores que 60 ºC e 3 minutos, respectivamente, enquanto que as menores perdas de glicose e frutose, para todas as temperaturas, foram obtidas para tempos menores que 3 e 5 minutos, respectivamente.Termos para indexação: Glicose; frutose; prebiótico; superfície de resposta.