Recent developments in osmotic dehydration.
Osmotic dehydration is an operation used for partial removal of water from foods such as fruits and vegetables. In this process, foods are placed in hypertonic (osmotic) solution. Three different mass transfer mechanisms occur in the osmotic dehydration; (i) water migration from food to the solution, (ii) solute migration from solution to food, and (iii) solute concerning product extracted to solution. Osmotically dehydrated fruits and vegetables are generally dried by hot air flow. In recent years, osmotic dehydration has been combined with various methods such as the high hydrostatic pressure, high electrical field pulses, gamma irradiation, ultrasound, vacuum and centrifugal force. These new combination methods increase mass transfer and drying rate and foods by increasing the cell membrane permeability. The operation time in the combined methods is shorter than that in traditional osmotic dehydration, causing further energy saving. In this study, recent advances in osmotic dehydration will be reviewed.
Effect of Pulsed Electric Field and Osmotic Dehydration Pretreatment on the Convective Drying of Carrot Tissue
The influence of pulsed electric field (PEF) and subsequent centrifugal osmotic dehydration (OD) on the convective drying behavior of carrot is investigated. The PEF was carried out at an intensity of E = 0.60 kV/cm and a treatment duration of t PEF = 50 ms. The following centrifugal OD was performed in a sucrose solution of 65% (w/w) at 40°C for 0, 1, 2, or 4 h under 2400 × g. The drying was performed after the centrifugal OD for temperatures 40–60°C and at constant air rate (6 m3/h). With the increase of OD duration the air drying time is reduced spectacularly. The dimensionless moisture ratio Xr = 0.1 is reached for PEF-untreated carrots after 370 min of air drying at 60°C in absence of centrifugal OD against 90 min of air drying after the 240 min of centrifugal OD. The PEF treatment reduces additionally the air drying time. The total time of dehydration operations can be shortened when OD time is optimized. For instance, the minimal time required to dehydrate untreated carrots until Xr = 0.1 is 260 min (120 min of OD at 40°C and 140 min of drying at 60°C). It is reduced to 230 min with PEF-treated carrots. The moisture effective diffusivity D eff is calculated for the convective air drying based on Fick's law. The centrifugal OD pretreatment increases drastically the value of D eff . For instance, 4 h of centrifugal OD permitted increasing the value of D eff from 0.93 · 10−9 to 3.85 · 10−9 m2/s for untreated carrots and from 1.17 · 10−9 to 5.10 · 10−9 m2/s for PEF-treated carrots.
ENERGY CONSUMPTION FOR REFRIGERATED, CANNED, AND FROZEN PEAS
The energy inputs at different stages in the total food cycle of peas were estimated for the market modes: refrigerated, frozen, and canned. The energy accounting showed for refrigerated 3,368; for canned 3,637; and for frozen 3,281 Btu/2.8-oz serving. Because the energy consumption for each market mode is of the same order of magnitude, there is little reason for the consumer to select on bases other than availability, taste preference, and convenience. It was also found that energy for packaging, marketing, shopping, and in the home can be high depending on the market mode. Measures to reduce energy consumption are discussed for several sectors.