EFFECTS of DIPPING and WASHING PRE‐TREATMENTS ON MICROWAVE DRYING of GRAPES

Abstract

The effects of different dipping pretreatments on microwave drying of grapes was studied in a multimode cavity. Grapes pretreated with 2% ethyl oleate in 0.5 % sodium hydroxide (NaOH) solution resulted in comparatively good quality raisins with lowest drying times. Pretreatment with 3% ethyl oleate in 0.5% NaOH solution led to similar product without any major advantage over the former. Grapes treated with 3% ethyl oleate in 2.5% potassium carbonate solution took longer time to dry. Grapes treated with only NaOH solution resulted in raisins of inferior quality in terms of color and appearance. The intelphase mass transfer coeficients also described the effect of these chemical pretreatments. Studies conducted on the effect of washing and time of holding afrer the pretreatment indicated that both of these factors had no influence on drying time. potential of dielectric heating with microwaves (MW) for drying of grapes has been reported (Tulasidas et al. 1993). Several pretreatments have been developed to reduce the drying time of grapes and to enhance the quality of raisins in terms of color and appearance. In most of the pretreatment methods, the fruits are first fumigated with sulphur dioxide to attain a concentration of

Drying kinetics of black grapes treated with different solutions

“…So, drying of black grape was hastened. A similar effect of ethyl oleate has been found in drying of agricultural products such as seedless grape, corn and apricot (Doymaz & Pala, 2002;Doymaz, 2004;Pala et al, 1993;Saravacos, Marousis, & Raouzeos, 1988;Suarez, Loncin, & Chirife, 1984;Tulasidas, Raghavan, & Norris, 1996).…”

Effect of dipping treatment on air drying of plums

“…Because, plums are covered naturally with a thin layer of (Bolin, Petrucci, & Fuller, 1975;Petrucci, Canata, Bolin, Fuller, & Stafford, 1974;Tulasidas, Raghavan, & Norris, 1996). Chemical pretreatment using a solution of ethyl oleate and sodium hydroxide, sodium carbonate were found efficient for grapes (Doymaz & Pala, 2002a;Ponting & McBean, 1970;Saravacos, Marousis, & Raouzeos, 1988), corn (Suarez, Loncin, & Chirife, 1984), apricot (Pala et al, 1996), and red pepper (Doymaz & Pala, 2002b).…”

Drying characteristics and drying quality of carrot using a two-stage microwave process

“…Several food products have been successfully dried by the microwave-vacuum application and/or by a combined microwave assisted-convection process. These authors included Kim and Bhowmik (1995) for plain yogurt, Yongsawatdigul and Gunasekaran (1996) for cranberries, Lin, Durance, and Seaman (1998) for carrot slices, Drouzas and Saravacos (1999) for model fruit gels, Al-Duri and McIntyre (1992) for skimmed milk, whole milk, casein powders, butter and fresh pasta, Bouraout, Richard, and Durance (1994) for potato slices, Tulasidas, Raghavan, and Morris (1996) for grapes, Funebo and Ohlsson (1998) for apple and mushroom, and Ren and Chen (1998) for American ginseng roots.…”