Hot Air Assisted Infrared Drying of Vegetables and Its Quality

Abstract

Hot air assisted infrared (IR) drying of potato and carrot is carried out and product quality is compared with hot air dried samples. The synergistic effect of hot air and IR during combined mode (hot air assisted IR) drying reduced the processing time by nearly 48% as compared to hot air drying alone, besides improving the quality of products. Higher rehydration ratio and lower browning index values are observed for combined mode dried products. Photomicrographs of dehydrated carrot and potato showed superiority of product structure for combined mode dried products. The IR dried carrot had higher (by 17%) retention of carotenoid than hot air dried sample. The processing conditions such as velocity and temperature of air affected the drying characteristics during combined mode drying. Higher values of effective diffusivity of water are observed with combined mode drying.

Drying characteristics and quality of shiitake mushroom undergoing microwave-vacuum drying and microwave-vacuum combined with infrared drying

“…5 and 6. The same effect of infrared combined with hot air drying was also reported by Vishwanathan et al (2010) for microstructure of dried carrots. Besides, Shih et al (2008) reported a sequential infrared and freeze drying for producing crispy strawberries.…”

“…Higher IR resulted in an increase in rehydration ratio, i.e., increasing 1 to 10 % and 2 to 20 % at IR of 100 W and 200 W, respectively, compared to that dried by MVD. Faster drying with infrared and quicker diffusion of water vapor from the mushroom might help the sample retains its porous structure, increasing its ability to absorb higher amount of water during rehydration (Nasiroglu and Kocabiyik 2009;Vishwanathan et al 2010). As a result, drying of shiitake mushroom by MVD at 267 W under 18.66 kPa provided a higher rehydration ratio than other MVD conditions.…”

“…9b-e). This is because the mushroom is heated rapidly by infrared and water evaporates more quickly resulted in puffing, retains its porous structure and develops large pores within the sample (Shih et al 2008;Nathakaranakule et al 2010;Vishwanathan et al 2010). This helps in increasing its ability to absorb more water during rehydration and thus resulted in a softer texture in agreement with the results shown in Figs.…”

“…Infrared drying has gained popularity as an alternative method for drying of fruits and vegetables. The main advantages of infrared drying are reduction in drying time, energy saving, high energy efficiency and high product quality, i.e., reduces color change, improves rehydration (Hebbar et al 2004;Vishwanathan et al 2010;Doymaz 2011;Zhang and Wang 2011). Food products, such as grapes (Caglar et al 2009;Ruiz Celma et al 2009), sweet potatoes (Doymaz 2011) and pineapple (Ponkham et al 2012) have been dried using infrared dryer.…”

“…Moreover, agricultural products with high moisture content can be dried using combination drying, as it provides synergistic effect. There are many studies on the application of infrared combined with other drying methods like hot air assisted infrared drying (Vishwanathan et al 2010;Ponkham et al 2012) and microwave combined with infrared drying (Sumnu et al 2005;Wang and Sheng 2006).…”