Vasiliki Evageliou

Influence of jet milling and particle size on the composition, physicochemical and mechanical properties of barley and rye flours

Finer barley and rye flours were produced by jet milling at two feed rates. The effect of reduced particle size on composition and several physicochemical and mechanical properties of all flours were evaluated. Moisture content decreased as the size of the granules decreased. Differences on ash and protein contents were observed. Jet milling increased the amount of damaged starch in both rye and barley flours. True density increased with decreased particle size whereas porosity and bulk density increased. The solvent retention capacity profile was also affected by jet milling. Barley was richer in phenolics and had greater antioxidant activity than rye. Regarding colour, both rye and barley flours when subjected to jet milling became brighter, whereas their yellowness was not altered significantly. The minimum gelation concentration for all flours was 16%w/v. Barley flour gels were stronger, firmer and more elastic than the rye ones.

Drying of Fennel Plants: Oven, Freeze Drying, Effect of Freeze-Drying Time, and Use of Biopolymers

Fennel plants were oven and freeze dried. The influence of freeze-drying time on the concentration of the two main components, trans-anethole and isoanethole, of its essential oil was evaluated. Drying time up to 15 h led to 50% reduction of moisture content with minor increase in volatile losses, whereas drying time greater than 15 h resulted in a dried product with an aroma profile closer to the fresh one. Moreover, starch solutions and gelatin gels were tested as surface barriers. Both led to reduction of aroma compounds losses, but their concentration and state seemed to have no effect on this behavior.

Limonene encapsulation in freeze dried gellan systems

The encapsulation of limonene in freeze-dried gellan systems was investigated. Surface and encapsulated limonene content was determined by measurement of the absorbance at 252nm. Gellan matrices were both gels and solutions. For a standard gellan concentration (0.5wt%) gelation was induced by potassium or calcium chloride. Furthermore, gellan solutions of varying concentrations (0.25-1wt%) were also studied. Limonene was added at two different concentrations (1 and 2mL/100g sample). Gellan gels encapsulated greater amounts of limonene than solutions. Among all gellan gels, the KCl gels had the greater encapsulated limonene content. However, when the concentration of limonene was doubled in these KCl gels, the encapsulated limonene decreased. The surface limonene content was significant, especially for gellan solutions. The experimental conditions and not the mechanical properties of the matrices were the dominant factor in the interpretation of the observed results.

The effect of sugars on the retention of ethyl butyrate by gellan gels

The effect of sucrose, glucose and fructose on the retention of ethyl butyrate by low acyl gellan gels was investigated by static headspace gas chromatography. The air/biopolymer partition coefficient (K) and percentage of retention (R%) were determined. When 5 g of sample were left to equilibrate at 37 °C for 24 h, the obtained results were explained in terms of gel rigidity, as increased rigidity resulted in increased aroma retention. Glucose showed the greatest aroma release among the sugars and resulted in either the same or increased aroma release with increasing concentration. Increasing concentrations of fructose and sucrose did not alter aroma release significantly. For 15 g of sample mass, sucrose exhibited the lowest partition coefficient values among the sugars. The two higher sucrose concentrations resulted in decreased coefficient values. For fructose and glucose, aroma retention decreased with increasing concentration. The percentage of retention values were positive for all sugars, throughout their concentration range and for both experiments.

Properties of flour films as affected by the flour's source and particle size

Wheat (W) and rye flour (R, R1 and R2) films were developed. The rye flours used differed in their particle size. R1 and R2 resulted from jet milling of the R flour at two different feed rates. The mean particle size of W, R, R1 and R2 flours was 173.87, 100.91, 54.59 and 35.66 μm, respectively. Glycerol was used as plasticizer at concentrations of 0.5, 0.7 and 1 g/g of flour. Films made from mixtures of flours (50:50 w/w) were also studied in the presence of 0.7 g glycerol/g of flour. Colour, moisture content, solubility, thickness, viscosity, microstructure and mechanical properties were assessed. In most cases the films were homogeneous. Film moisture content, thickness, opacity and mechanical properties were correlated to glycerol concentration. Particle size was found important for the mechanical properties. Wheat films were lighter ([L*] ≈ 49) and less opaque (135). For both single and composite films, moisture content varied from 24 to 35%, solubility from 43.5-58%, opacity from 135 to 371, thickness from 0.66-0.72 mm and mechanical strength from 0.68-1.7 MPa. All film-forming solutions exhibited shear thinning behaviour. Wheat flour dominated most of the studied properties in composite films. Rye films were more opaque, with relatively high solubility but greater mechanical strength.