International Journal of Food Engineering

Improving Nutritional Value of Dried Blueberries (Vaccinium corymbosum L.) Combining Microwave-Vacuum, Hot-Air Drying and Freeze Drying Technologies

Esteban I. Mej�a-Meza — Wed, 20 Aug 2008 13:39:48 PDT

Blueberries (Vaccinium corymbosum L.) were dried combining microwave-vacuum, hot-air drying and freeze drying technologies to retain their nutritional value. Polyphenol retention, total polyphenols, anthocyanins, and antioxidant activity were evaluated in dried blueberries. Glycoside compounds for ellagic acid, quercetin, and kaempferol exhibited a higher retention than phloridzin, and R- and S-naringin in dried blueberries following dehydration. Freeze and HA-MIVAC� dried blueberries had a higher retention of total polyphenols and anthocyanins. Freeze dried blueberries had higher antioxidant activity, followed by the combination of HA-MIVAC�, MIVAC� and HA drying methods. FD, HA-MIVAC� and MIVAC� treated blueberries had a higher retention of individual polyphenols than HA treated blueberries indicating that the nutritional properties of berries may be retained to a greater extent when these processes are employed.

Fruits & Vegetables Drying Combining Hot Air, DIC Technology and Microwaves

M. Al Haddad — Tue, 19 Aug 2008 20:57:12 PDT

Dehydration of fruits and vegetables is one of the most ancient and efficient preservation methods. The quality of the product and its cost depend mainly on the final stage of drying. In the present paper we analyze physical mechanisms occurring during drying throughout heat and mass transfer for defining an efficient and economic three stage drying process of hot air drying combined to a texturing stage by DIC (Instant Controlled Pressure Drop) and finally using microwave assisted by ambient temperature air dehydration.

Effect of Osmotic Pre-Treatment on the Air-Drying Behavior and Quality of Plum Tomato Pieces

Marianne S. Brooks — Fri, 15 Aug 2008 16:07:08 PDT

The air-drying behavior and quality of plum tomato pieces after pre-treatment with different osmotic solutions was investigated. Four pre-treatment solutions (comprised of salt, sugar and/or calcium lactate), three sample geometries (halves, quarters and eighths) and two air-drying temperatures (55 and 65�C) were studied. During osmotic pre-treatment, the moisture loss of the tomato pieces decreased with osmotic pressure. The proportion of skin to cut surface area was found to be important for osmotic moisture loss. As the percentage of cut surface area decreased (59.6%, 47.6% and 25.3% for the eighths, quarters and halves, respectively) and the percentage of skin on the sample increased, the percentage osmotic moisture loss also decreased. At an air-drying temperature of 55�C, the critical moisture content for storage (15%, wet basis) for the pre-treated halves, quarters and eighths was reached after 25-27, 15-18 and 9-12 hours, respectively. At 65�C, the critical moisture content was reached after 16-19, 9-13 and 6-8 hours, respectively. In both cases, the osmotic pre-treatment reduced the critical drying time. The reduction in moisture ratio over time was described by an exponential model (R² values ≥ 0.92). The specific drying rate increased with osmotic pre-treatment and was more affected by air-drying temperature than the type of osmotic solution, while the geometry of the samples had no significant effect. Air-dried samples with osmotic pre-treatment were closer to the color of fresh tomato than samples without pre-treatment.

Flow Behaviors of High Acyl Gellan Aqueous Solutions as Affected by Temperature, and Calcium and Gellan Concentrations

Yiqun Huang — Fri, 15 Aug 2008 16:07:04 PDT

Rheological behaviors of high acyl (HA) gellan are not well understood partially because of its relatively late commercialization compared to low acyl gellan. The objective of this study was to investigate the effect of temperature (5-30 �C), calcium (0, 1 and 10 mM) and gellan concentrations (0.0044-0.1000% w/v) on the flow behaviors of high acyl gellan aqueous solutions using rheological tests. Gellan solutions with 0 or 1 mM added Ca++ exhibited shear thinning behavior at gellan concentrations above 0.0125%. The influence of temperature on apparent viscosity (shear rate, 100 s-1) of gellan solutions can be described with an Arrhenius relationship. The apparent viscosity of gellan solution at low concentrations was more sensitive to temperature changes. The addition of Ca++ led to a decrease in flow resistance for a dilute gellan solution (<0.0125%), but an increased resistance for a relatively concentrated gellan solution (>0.0125%).