Drying the grapes with electromagnetic radiation

Sultani is the most preferred grape variety for raisin production in Turkey. Traditionally, grapes are dried by direct exposure to sunlight under uncontrolled conditions. Spreading the bunches over the covers laid around or hanging the bunches on string racks are the common applications in sun drying of grapes. Traditional solar drying processes have many negative effects besides their benefits in terms of energy costs. Exposure to environmental conditions (i.e. dust contamination), microbial growth, nutritional deterioration and high labor costs can be considered as important disadvantages. Also, dependence on meteorological conditions may result in long process times and product quality deficiency. Innovative artificial drying systems, which operate at low operating costs and enable grape production in superior quality, are an important alternative in solving the problems mentioned. In this study, it was aimed to compare the grape quality of dried grapes dried by conventional methods and determine the effects of the different types of grains on the drying time and quality of the grains applied at different powers. Sultani variety grapes were immersed in a 5% K2CO3 solution and then dried up to 14% dry matter content in the dryer as well as adhering to the traditional method (on wire and floor display). The temperature and air velocity in the dryer were kept constant at 30˚C and 1.2 m / s respectively, and the infrared and ultraviolet lamps in the dryer were applied at three different levels: 600, 450 and 300 W. The drying time of the grapes was determined and the color, texture, shrinkage, particle density, free heap density, rehydration rate and microbial qualities (total mold / yeast) of the products were compared. The obtained data were analyzed statistically by one way analysis of variance. The water activities of grapes dried to 14% moisture content were below 0.6 and thus found to be microbiologically safe. Drying in the sun lasted 7 days in the ground show and 12 days in the wire show. The drying times of the grapes were found to be 19,75 hours, 49,41 hours, 68,25 hours respectively when the power of the lamps in the electromagnetic radiation dryer was 100%, 75% and 50% (600 W, 450 W and 300 W) respectively. The grape surface temperature is between 55-60˚C and the wire is measured between 35-45˚C. The 50% power is measured at 30-40˚C, 75% power at 40-50˚C and 100% power at 50-92˚C. Fresh grapes have an emissivity value of about 0.85, whereas dry grapes with a moisture content of 14% have an emissivity value of about 0.55. The product surface temperature during drying increased as L increased depending on the applied strength. EI100 (15,33 ± 1,38) has the highest L value. GKY (0,73 ± 0,68), GKT (0,89 ± 0,83), EI50 (0,78 ± 0,25) were close to each other because they dried at temperatures close to each other. EI75 (1,77 ± 0,23) and EI100 (1,41 ± 1,10) increase in temperature have higher a values. It was found to be low b value in GCF (0,14 ± 0,87) and GCT (0,24 ± 0,74) according to the dryer. In the dryer, EI50 (1,76 ± 1,77) has higher b value than EI75 (2,037 ± 0,39) and EI100 (0,913 ± 1,27). The highest color change (ΔE) was seen in EI100 (7,81 ± 1,02) at least EI75 (4,04 ± 0,31) followed by EI50 (6,10 ± 3,06). The highest and most acceptable hue value was observed at EI50 (78,9 ± 1,56), while the hue value decreased as the temperature increased in the dryer. Dried grapes were given EI50 (10,5-11) given the highest score by expertise. The lowest rehydration rate was found in EI100 (0,67 ± 0,02), which dried at the highest temperatures, and the highest rehydration rate was found in the GKT (0,78 ± 0,01), which dried in the lowest temperatures. The bulk density of raisins obtained as a result of all experiments is close to the recommended value of 0.6 g / mL or 0.6 g / mL. EI100 has the highest numerical value of particle and bulk density. Among the samples, the lowest shrinkage value is GKT (1,22 ± 0,31) and the highest shrinkage value is EI100 (1,31 ± 0,17). As the drying time increased, the hardness value increased. Dryers on the ground show a numerically higher hardness value than the samples dried on wire. In case of electromagnetic radiation, 100% power is the highest and 50% power is the lowest. There is no significant difference between the samples in terms of tackiness, flexibility, chewability. The increase in temperature and the drying time of the product increased the value of internal viscosity and gumminess. The highest internal viscosity value and gumminess value were found at EI100. In the analysis made after drying in the ground exhibit (1.6x104) and wire show (3.6x104), the total yeast content increased according to the raw material. In EI50, EI75 and EI100, mold yeast was not detected according to the raw material.