Drying rates of Rubi grapes submitted to chemical pretreatments for raisin production

Abstract

-The objective of this work was to determine the most appropriated chemical treatment to be used to dry grapes cv. Rubi for raisin production. Drying curves for convective drying with air at 50 o C, in a tray drier, were obtained for grapes submitted to chemical pretreatments with different concentrations of potassium carbonate and olive oil, and different dipping times, according to factorial designs. Convective drying curves were also obtained for grapes pretreated in aqueous suspensions of soybean lecithin, at varied lecithin concentrations and dipping times. Page model was adjusted to the experimental drying curves, and the calculated drying times showed that the best pretreatment consisted in dipping grapes for 2 minutes in a 5% olive oil and 6% K 2 CO 3 emulsion, at 50 o C, which resulted in a drying time close to that of the pretreatment with 2.5% of olive oil, but with a lower consumption of this substance. In addition, the immersion of grapes in an aqueous suspension of 2% soy lecithin, at 50 o C, for 5 minutes, resulted in a total drying time slightly higher than the most effective pretreatment.Index terms: Vitis vinifera, drying kinetics, soybean lecithin, olive oil, dipping treatments. Taxas de secagem de uva Rubi submetida a pré-tratamentos químicos para a produção de passasResumo -O objetivo deste trabalho foi selecionar o pré-tratamento químico mais apropriado para a secagem de uvas cv. Rubi para a produção de passas. Foram obtidas curvas de secagem convectiva com ar a 50 o C, em um secador de bandejas, para uvas submetidas a pré-tratamentos químicos com diferentes concentrações de carbonato de potássio e azeite de oliva, e diferentes tempos de imersão, de acordo com planejamentos fatoriais. Também foram obtidas curvas de secagem convectiva, para uvas pré-tratadas em suspensões aquosas de lecitina de soja, em várias concentrações de lecitina e diferentes tempos de imersão. O modelo de Page foi ajustado às curvas de secagem experimental, e os tempos de secagem calculados mostraram que o melhor pré-tratamento consistiu na imersão das uvas por 2 minutos, em uma emulsão de 5% de azeite de oliva e 6% de K 2 CO 3 , a 50 o C, o que resultou em tempos de secagem próximos aos do pré-tratamento com 2,5% de azeite de oliva, mas com um menor consumo dessa substância. Além disso, a imersão das uvas em uma suspensão aquosa de 2% de lecitina de soja, a 50 o C, por 5 minutos, resultou em um tempo de secagem total apenas levemente superior ao do pré-tratamento mais efetivo.Termos para indexação: Vitis vinifera, cinética de secagem, lecitina de soja, azeite de oliva, pré-tratamentos químicos.

Effect of the pre-treatment and the drying process on the phenolic composition of raisins produced with a seedless Brazilian grape cultivar

“…This result was close to that reported in a study carried out by Bingol et al (2012), where a 50% drying time reduction at 60°C was achieved after applying a pretreatment of K 2 CO 3 (5%) and ethyl oleate (2%) to Thompson seedless grapes. In a study with Rubi grapes, using an immersion solution containing olive oil (0.5%) and potassium carbonate (6%) at 50°C, drying time was also reduced when compared to grapes that were pretreated with only 2.5% olive oil (Telis et al, 2006). These results show that the use of olive oil, in the pre-treatment of grapes, gives greater efficiency in dehydrating to get raisins.…”

“…In order to accelerate the drying process to produce raisins, various chemical and physical pre-treatments have been investigated and applied (Adiletta et al, 2016;Jairaj et al, 2009). In the chemical pretreatments, often, an alkaline solution such as potassium carbonate is combined with other components such as olive oil (Telis, Lourençon, Gabas, & Telis-Romero, 2006) or ethyl oleate (Bingol, Roberts, Balaban, & Devres, 2012;Gabas, Menegalli, & Telis-Romero, 1999). However, the presence of residues of additives in the raisins can lead to human health problems (Adiletta et al, 2016).…”

Influence of the concentration of polyols on the rheological and spectral characteristics of guar gum

“…where h is the apparent viscosity (Pa s), h 0 and h N are the zeroshear rate and the infinite-shear rate viscosity (Pa s), respectively, k CR (s n ) is relaxation time, _ g the shear rate (s À1 ), and n is dimensionless exponent. The quality of fit was evaluated from the determination coefficient (R 2 ) and from the root mean square (RMS) of the residues (Telis, Lourençon, Gabas, & Telis-Romero, 2006).…”

DETERMINAÇÃO DAS CURVAS DE SECAGEM EM CAMADA DELGADA DE PIMENTA DE CHEIRO (Capsicum chinense) A DIFERENTES TEMPERATURAS

“…Apesar do ajuste do modelo de Page ser satisfatório, R 2 > 0,99 para todas as temperaturas estudadas, verifica-se uma falta de ajuste no estágio final do processo de secagem, onde o modelo superestima os valores experimentais de razão do teor de água. Este fenômeno também foi observado por Telis et al (2006) em estudos realizados com uvas rubi. Para o modelo Logarítmico este fato não foi observado.…”