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.
APPLICATION OF RESPONSE SURFACE METHODOLOGY ( RSM ) TO THE STUDY OF MASS TRANSFER PARAMETERS OF OSMO-PRETREATED AND DRIED GREEN BELL PEPPER
Osmotic dehydration was carried out on fresh green bell pepper at different osmotic solution concentrations (5% (w/w), 10% (w/w), 15% (w/w), 20% (w/w) and 25% (w/w)) of common salt and osmotic process durations of 60 min, 90 min, 120 min, 150 min and 180 min at an average room temperature of 31  ̊C and the effect of osmotic dehydration factors was investigated on mass transfer parameters; water loss and solid gain. A temperature of 50 ̊C was used to dry all pre-treated samples to moisture content of about 7 % (wb) in a fabricated cabinet dryer and were further analysed for rehydration ratio and shrinkage. Response Surface Methodology (RSM) under central composite design in Design Expert 8.0.3 computer software package was used to design the experiment, analyse data and present all results with contour and 3-dimensional plots. Results showed that increase in osmotic process duration and osmotic solution concentration caused reduction in solid gain and increase in water loss to values in the range of 0% 0.3g/g, and 0.1% 0.3g/g respectively. Also, increase in osmotic process duration and osmotic solution concentration led to increase in shrinkage and reduction in rehydration ratio to values in the range of 40% – 60% and 2.0 -3.5 respectively. Further study should be done on modelling and optimization of the process.
New Sweet-Tasting C21-Pregnane Glycosides from Pericarps of Myriopteron extensum.
Ten novel C21 pregnane glycosides, extensumside C-L (1-10), were isolated as highly sweet-tasting substances from the edible pericarps of Myriopteron extensum (Wight) K. Schum by sensory-guided fractionation and purification. Their structures were determined through 1D and 2D NMR, such as HSQC, HMBC, 1H-1H COSY, HSQC-TOCSY, and ROESY, as well as other spectroscopic analysis combined with chemical evidence. These compounds shared the same aglycone, 3β,16α-dihydroxy-pregn-5-en-20-one, and contained the deoxysugar chain and the glucose chain which were linked to C-3 and C-16 of the aglycone, respectively. The sweetness potency was evaluated by a human sensory panel test and preliminary structure-taste relationship was discussed. The sweetness intensities of these compounds are between 50 and 400 times greater than that of sucrose. Furthermore, quantitation analyses of compounds 1, 3, 4, and 6 in different parts of M. extensum indicated that the concentrations of these sweet components in the pericarps are obviously higher than those in stems and roots.