Vasiliki P. Oikonomopoulou

Structural Properties of Dried Potatoes, Mushrooms, and Strawberries as a Function of Freeze-Drying Pressure

The structural and thermophysical properties of freeze-dried agricultural products (potatoes, mushrooms, and strawberries) were investigated to determine whether these properties were affected by freeze drying conditions. The true density of freeze-dried products was measured with a helium stereopycnometer, and apparent density was obtained by measuring their geometric characteristics. Porosity and pore size distribution were also measured with a mercury porosimeter. The mechanical properties of freeze-dried agricultural products were obtained using a universal testing machine. Dried products were equilibrated in saturated salt solutions of constant water activity and scanned with a differential scanning calorimeter (DSC) for the evaluation of glass transition temperature. Simple mathematical models were developed in order to correlate the structural and mechanical properties with process conditions. The apparent density and mechanical properties of freeze-dried products increased with the applied freeze-...

Novel Aspects of Formation of Food Structure during Drying

The acceptance of processed or minimally processed food products by consumers is highly dependent on several quality and nutritional attributes as well as their organoleptic characteristics. Shelf-life is an additional factor that influences consumer behavior. Moreover, consumers now demand high-value food products that are healthier and have high nutritional value. The quality, nutrition level, and perception of processed foods is governed, among other attributes, by the structure of the dried product. Hence, examination of the structure of dried foods is of significant importance. Dehydration methods have a great impact on the structural properties of most food products. The effect of various dehydration methods on shrinkage and porosity of dried foods is discussed in this article following a comprehensive review of the available literature. Novel drying processes and combination of various conventional drying methods are discussed with regard to their expected impact on food structure. Finally, aspects of food formulation during diverse drying processes and recommendations for future research are presented.

Effect of osmotic dehydration of olives as pre-fermentation treatment and partial substitution of sodium chloride by monosodium glutamate in the fermentation profile of Kalamata natural black olives

This study examined the effect of osmotic dehydration of Kalamata natural black olives as pre-fermentation treatment in combination with partial substitution of NaCl by monosodium glutamate (MSG) on the fermentation profile of olives. Osmotic dehydration was undertaken by immersing the olives in 70% (w/w) glucose syrup overnight at room temperature. Further on, three different mixtures of NaCl and MSG with/without prior osmotic dehydration of olives were investigated, namely (i) 6.65% NaCl - 0.35% MSG (5% substitution), (ii) 6.30% NaCl - 0.70% MSG (10% substitution), (iii) 5.95% NaCl - 1.05% MSG (15% substitution), and (iv) 7% NaCl without osmotic dehydration (control treatment). Changes in the microbial association (lactic acid bacteria [LAB], yeasts, Enterobacteriaceae), pH, titratable acidity, organic acids, sugars, and volatile compounds in the brine were analyzed for a period of 4 months. The final product was subjected to sensory analysis and the content of MSG in olives was determined. Results demonstrated that osmotic dehydration of olives prior to brining led to vigorous lactic acid processes as indicated by the obtained values of pH (3.7-4.1) and acidity (0.7-0.8%) regardless of the amount of MSG used. However, in non-osmotically dehydrated olives, the highest substitution level of MSG resulted in a final pH (4.5) that was beyond specification for this type of olives. MSG was degraded in the brines being almost completely converted to γ-aminobutyric acid (GABA) at the end of fermentation. Finally, the sensory assessment of fermented olives with/without osmotic dehydration and at all levels of MSG did not show any deviation compared to the control treatment.

Influence of Structure on Saltiness and Sweetness of Dehydrated Food Products

Pore structure of foods influences the quality and texture of dehydrated food products. The development of food products with different pore structures and its effect on the sensory characteristics of the products were investigated. Potatoes and bananas were osmotically pre-treated using salt and sucrose solutions, respectively, and dehydrated with various drying methods, such as air drying, freeze drying, and vacuum drying, in order to obtain different pore structures. Simple mathematical models were developed in order to correlate the structural properties with process conditions. Depending on the drying method, porosity varied from 5% to 75% for potatoes and from 15% to 60% for bananas. Porosity was higher for the samples that were freeze-dried at lower pressures, followed by samples freeze-dried at higher pressures and, finally, vacuum- and air-dried samples. The surface areas of the dried samples varied between 0.961 and 3.040 m2/g, which are typical values for dehydrated foods. Freeze-dried potatoes and bananas were found to be saltier and sweeter (Score 6.5–7.8), respectively, than air- and vacuum-dried products (Score 4.8–5.8). Bananas and potatoes with the highest porosity and the highest specific surface areas presented more intense taste, providing the opportunity of reducing the levels of salt and sugar of the produced products without affecting the salty or sweet taste.

Physical and Sensory Properties of High Added Value Rice Extrudates

Rice extrudates enriched with freeze dried carrot powder were produced using a twin screw extruder, operated at various conditions of screw speed (150–250 rpm) and temperature (140–180 °C). Different carrot concentrations (5–10 %) were added in rice flour and the mixtures were equilibrated at three moisture contents (14–20 %). A comprehensive understanding of the effect of process conditions and material characteristics on structural, textural, and sensorial properties of the produced extrudates was examined in the present study. Simple mathematical power models were used in order to correlate properties with extrusion conditions. According to regression analysis, moisture content and carrot concentration increment led to the production of denser extrudates, while a temperature and a screw speed rise significantly decreased apparent density. Expansion ratio showed a negative relationship with moisture content, carrot concentration, and temperature. In addition, textural properties were inversely related to expansion ratio, indicating the increased crispness of highly expanded products. Finally, sensory analysis indicated that increased moisture content and carrot concentration were highly correlated with loss of crunchiness and low sensorial porosity, while extrusion temperature and screw speed caused the opposite effect.