Ultrasound Assisted Osmotic Dehydration as Pretreatment for Hot-air Drying of Carrot

Abstract

Ultrasound assisted osmotic dehydration (UOD) combined hot-air drying (AD) process was investigated in thisstudy. The influences of operation parameters such as ultrasonic energy density and solution concentration on weight reduction ratio (WRR) were discussed. The effects of UOD on the following AD of carrot slices were also studied.The results showed that ultrasonic energy density and solution concentration have positive and significant effects on WRR. Osmosis dehydration (OD) pretreatment without ultrasound assistance before AD has negative effects on the total processing time and the effective moisture diffusivity. Yet when ultrasound is applied, the increase of ultrasonic energy density could shorten dehydration time of the following AD process and total processing time. UOD prior to AD has positive effects on improving carotenoid content of product and reducing process energy cost. So it's definitely concluded that UOD pretreatment is an effective and complementary method for traditional AD process.Keywords: ultrasound, osmotic dehydration, hot-air drying, carrot IntroductionAt the present time, consumption of dehydrated food has experienced a noticeable increase in its demand on the market.Conventional dehydration methods based on hot-air drying (AD) are widely used in agricultural industry, but they are time-consuming and energy-intensive, and easily deteriorate the quality of the final products (Humberto et al., 2001;Cohen and Yang, 1995).Scientists and technicists are looking for emerging food processing technologies to enable the production of safer, fresher and better quality foods with longer life for local and export markets.Among emergent new technologies ultrasound dehydration is very promising (Garcia-perez et al., 2007;Fuente-Blance et al., 2006).Ultrasonic waves can produce a rapid series of alternative compressions and expansions, in a similar way to a sponge when it is squeezed and released repeatedly (Soria and Villamiel, 2010).The forces involved by this mechanism can be higher than surface tension which maintains the moisture inside the capillaries and microscopic channels of the fruit, and therefore accelerate moisture removal (Mulet et al., 2003). Ultrasonic waves can reduce viscosity (Greguss, 1963), minimize diffusion boundary layer thickness and remove moisture from solid liquid interfaces (Carcel et al., 2007a;Rodrigues and Fernades, 2007). Furthermore, changes in microstructure have been reported after ultrasonic treatments of fruits, which can additionally improve water removal (Fernandes et al., 2008a).Ultrasonic waves are often used to strengthen osmotic dehydration (OD) of food (Carcel et al., 2007b;Riera et al., 2004). Simal et al. (1998) strengthened OD with ultrasound technology, and concluded that both dewater rate and moisture removal ratio increase significantly compared with traditional OD process. Lenart and Auslander (1980) reported that moisture diffusion rate would increase with the rise of ultrasonic power.Yet Floros and Liang (1994) indicated that the rise of moist...

Effects of ultrasound-assisted osmotic dehydration as a pretreatment and finish drying methods on the quality of pumpkin slices

“…Also, the increase in WR of samples with increasing concentration of osmotic solution was not significant at 120 min of pretreatment time. Similar to our finding, Liu et al () reported that weight reduction ratio of carrot slices treated by ultrasound assisted osmotic dehydration in sucrose solution (60°Brix) at 50 °C rose rapidly during 30 min, and then, the rate of increase slowed down. It is also reported that the diffusion of the soluble molecules in solution to sample tissue add extra resistance to lower the water removal rate during later stages of osmotic dehydration process (Xin et al, ).…”

“…It was most reduced (39.5%) for the sample pretreated in the 60% sugar solution for 120 min. Similar to our finding, UAOD pretreatment prior to hot air drying was reported to reduce the drying time of strawberry, carrot, mirabella plum compared with direct hot air drying (Amami et al, ; Dehghannya et al, ; Garcia‐Noguera et al, ; Liu et al, ). One reason of the reduction in drying time may be that the samples subjected to UAOD treatment had lower amount of water that needs to be removed during hot air drying.…”

“…They stated that the effect of UAOD on the effective water diffusivity depends on the degree of cell breakdown. It is clear that the UAOD pretreatment parameters like ultrasonic energy density, osmotic concentration, treatment period are important factors influencing loss of water, sugar gain, effective water diffusivity, and consequently the final drying time (Fernandes et al, ; Garcia‐Noguera et al, ; Jambrak, Mason, Paniwnyk, & Lelas, ; Liu et al, ). For vacuum drying, while UAOD pretreatment in the 40% sugar solution for 40 and 80 min and in 60% sugar solution for 40 min did not provide a significant reduction in the drying time, increasing the pretreatment time to 120 min shortened the drying time by nearly 9.2–18.3%.…”

“…One of these pretreatment methods is the application of ultrasound assisted osmotic dehydration (UAOD). As a pretreatment, the effects of UAOD on quality parameters of hot air dried apple (Mierzwa & Kowalski, 2016), strawberry (Amami et al, 2017), rabbiteye blueberries (Stojanovic & Silva, 2007), carrot (Liu, Wu, Chong, & Miao, 2014), mirabelle plum (Dehghannya, Gorbani, & Ghanbarzadeh, 2016), beet snacks (Bromberger Soquetta, Schmaltz, Wesz Righes, Salvalaggio, & de Marsillac Terra, 2018), and color of freeze dried strawberries (Garcia-Noguera, Oliveira, Weller, Rodrigues, & Fernandes, 2014) were investigated in literature. It is seen that these studies concentrate more on the effect of pretreatment parameters on dried product quality and that mostly the hot air drying is preferred as the finish drying method.…”

Effects of osmotic pretreatment and frying conditions on quality and storage stability of vacuum‐fried pumpkin chips

“…However, UAOP reduced the moisture content and water activity of the fried chips significantly ( P < 0.05). The ultrasound pretreatment might have modified the microstructure and physical properties of the samples, which consequently enhanced the rate of water diffusion during frying (Liu et al ., ). The water activity of all the samples was less than 0.2, which was lower than those reported for vacuum fried banana chips (Sothornvit, ), carrot chips (Dueik et al ., ) and vacuum fried peas (Zhu et al ., ).…”