Effect of UV-C light, ozone and hydrogen peroxide pre-treatments on the drying rate of grapes and the raisin optical properties

CONTIGIANI, EUNICE; JARAMILLO- SÁNCHEZ, GABRIELA; POK, PAULA; CORONEL, MARÍA BERNARDA; GARCIA LOREDO, ANALIA; GONZALEZ, HÉCTOR L.; ALZAMORA, STELLA M.; GÓMEZ, PAULA

Texas

Congreso; Institute of Food Technologist Annual Meeting (IFT 2021); 2021

Institute of Food Technologist

Chemical dipping pre-treatments, commonly applied to accelerate the grape drying process in the commercial production of raisins, have the disadvantages of leaving harmful residual chemicals in the product and the environment. Therefore, this work aimed to evaluate novel alternative pre-treatments (UV-C light, ozone, and peroxide hydrogen) for enhancing grape drying rate. The impact of pre-treatments on the color of the dried grape was also analyzed. Seedless grapes cv. Italia were exposed to UV-C light (fluence: 27 kJ/m2; 30 min at 8 cm from two 15 W germicidal lamps), aqueous ozone (4.5 mg O3/L, 20 ± 1 °C; 30 min), and 1.0 % (w/v) hydrogen peroxide solution (pH = 3.0, 50 ± 0.1 °C; 10 min) before drying. Non-pretreated grapes were used as control. Grapes with and without pre-treatments (initial moisture content: 79-83 % (w.b.)) were subsequently dried in a laboratory scale forced hot air dryer at 60 ± 1 °C and 3 m/s air velocity, until their moisture content reached ~17 % (w.b.). Weight loss was recorded at 1-h intervals. The experiments were replicated twice. The color of dried grapes was recorded using a colorimeter.Grapes pre-treated with H2O2 showed no changes in the drying rate when compared to the control, while ozone-treated samples presented a slight reduction in the drying time of about 13 %. The most effective pre-treatment to enhance the drying rate was UV-C light, which allowed a reduction in the drying time of about 40 %. Previous microscopic studies revealed that UV-C light induces not only alterations in the epicuticular waxes but also causes disruption in the outer and inner tangential epidermal and subepidermal cell walls of grapes. UVC- pre-treated raisins showed also significant changes in the colorimetric parameters and functions (> L*, b* and chroma* values) as compared to the control and H2O2 and ozone- pre-treated samples, which were associated with a lower browning of samples. These finding suggest that UV-C light could be a suitable alternative pre-treatment in the drying process of grapes, reducing the drying time without leaving residues in the raisins and preserving better their optical properties.