The objective of this work was use ethanol and perforations as simple approaches to improve the infrared drying and rehydration of potato slices. Perforations were performed to study the effect of promoting routes to capillarity flow, while ethanol was impregnated in the samples to evaluate the effect of Marangoni flow. All pretreatments reduced the drying time compared to control treatment. However, a great time reduction was observed with P + E pretreatment: The synergistic combination of both treatments increased the drying rate in more than four times, reducing both drying time and the necessary energy by 44%. The samples with perforations (P and P + E) increased their rehydration rate as well as the water retention capacity. However, the pretreated samples with ethanol shows poor rehydration properties. Possible mechanisms were discussed. These results show simple approaches to enhance food drying and rehydration.
The solid residue from pulp production of guava (Psidium guajava) represents around 30% of the raw
material. The drying of this residue on drier’ trays at 45, 50, 55, 60, 65 and 70 °C was investigated. After
drying, the material was ground in one of two types of mills: a knife or a hammer mill. Guava flour samples
were characterized according to their water absorption capacity (WAC), oil holding capacity (OHC),
emulsifying and foaming properties, lycopene, total carotenoids and phenolic compounds. The drying
curves show typical behaviour and five mathematical models (two-term exponential, Henderson and Pabis,
diffusion approximation, Page and logarithmic) were constructed. Of the models tested for the temperatures
applied in the experiment, only the Henderson and Pabis model, when adjusted to the experimental data
obtained at temperatures of 45 to 50 °C did not represent the drying kinetics of the guava processing solid
residue, with coefficients of determination of 0.9376 and 0.6905, respectively. The type of mill and the
drying temperature influenced the phenolic compounds, lycopene and total carotenoids. The WAC was
higher than the OHC for all drying temperatures, due to the high content of dietary fiber in this residue.
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