Microwave (MW) vacuum dehydration using temperature to control the level of MW power demonstrated potential in improving the performance of the process. Product surface temperature measured by an infrared temperature sensor was used to control MW power at any level between 0 and 3 kW. Multiple linear regression analysis indicated an r 2 = 0.942 for prediction of final moisture content and r 2 = 0.985 for prediction of puffed character of grapes based on product temperature, time, specific energy, fresh fruit sugar, and fresh fruit moisture content. Temperature was found to be the most significant predictor. The elemental and compound contents of grapes dried using MW vacuum was compared to sun-dried raisins. The grapes dried using MW vacuum exhibited better preservation. Vitamin A was found in the MW-vacuum-dried grapes but none was detected in the raisins, and Vitamin C, thiamine, and riboflavin were also higher in the MW-vacuum-dried grapes than in the raisins.
: Microwave vacuum drying has been investigated as promising potential for high‐quality dried fruits. In this study, a batch microwave vacuum dryer was used to understand the effect of levels of microwave power on the drying characteristics and moisture content of grapes. Thompson seedless grapes were treated 1st for 30, 60, and 90 min at fixed levels of 500, 750,1000,1250, and 1500 W at a reduced pressure of 2.7 kPa and then treated by 3 staged microwave power levels: a higher level of power during the initial stages of dehydration and 2 subsequently lower levels of power applied as the moisture content decreased. A typical temperature profile was found during the drying process, linearly increasing at the start of drying, followed by a nearly constant value during the drying period while water was evaporating. The total specific energy estimated by the energy balance model was 0.97 to 1.01 W‐h/g of fresh grapes and agreed well with the experimental specific energy of 0.85 to 0.90 W‐h/g for the fixed power tests. The multiple regression results showed that the specific energy was the most influential parameter on the final moisture content of grapes both in fixed and incremental power levels. Further research is needed to further improve the process with high efficiency and good product quality using product temperature as a control measure. Keywords: microwave vacuum dehydration, specific energy, fruits, grapes
Pilot scale procedures were developed for the use of fatty acid ester emulsions to decrease the time to dry the Thompson seedless grapes to raisins. Both sun and mechanical drying were used in these experiments. Mechanically harvested grapes were dipped in a 1% or 2% fatty acid ester emulsion and dehydrated at drying times less than those required for the soda‐dipped raisins. Spraying grapes on the vine with a commercial ethyl ester mixture, which contained an emulsifier and added potassium carbonate, allowed the grapes to dry faster than the conventional sun drying procedures. These procedures produced light colored raisins of acceptable quality. In addition, these methods show savings by decreasing labor costs.
The amino acid profile of raisins indicated that of the 2.9g amino acids per 1OOg dry matter of raisins, arginine was present in the greatest concentration (25%), followed by proline and glutamic acid.
The potential for artificial ground water recharge by continuous flooding of dormant grapevines was evaluated in the San Joaquin Valley of California using the cultivar Thompson Seedless. The study was started in 1982 and was completed in 1985 after three complete flooding cycles during dormancy. An average daily rate of recharge of 80 mm/thy for a 32-day period each year was achieved through a clay loam soil. There were no adverse effects on the grapevines and yields in the flooded plots in any of the growing seasons following recharge periods. Yields were higher in the recharge plots than in the control plots in the last year of the study. We conclude that artificial ground water recharge by continuous flooding during grapevine dormancy is a viable recharge method. (KEY TERMS: ground water recharge; grapevines; water management; flooding.)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.