Vojtěch Kumbár

Fluid dynamics of liquid egg products

The rheological behavior of liquid egg products (egg yolk, egg white, and whole liquid egg) was studied using a concentric cylinder viscometer. Eggs of three poultry specimens were used: hen (Isa Brown), Japanese quail (Coturnix japonica), and goose (Anser anser f. domestica). Rheological behavior was pseudoplastic and flow curves fitted by the power law model (Herschel–Bulkley and Ostwald–De Waele). The meaning of rheological parameters on friction factors and velocity profiles during flow of liquid egg products in tube has been shown.

Study of rheology and friction factor of natural food hydrocolloid gels

Differences in the rheology and friction factor of natural food hydrocolloid gels were studied in this paper. The practical importance of the knowledge of the rheological parameters is quite evident. The experimental data were carried out using a concentric cylinder rotary viscometer. It was prepared 1% hydrocolloid solutions (hydrogels). Hydrogels of the natural gums extracted from the seeds of the plants and plant tubers have been used - carob gum (from the seeds of Ceratonia siliqua), guar gum (from the seeds of Cyamopsis tetragonoloba) and tara gum (from the seeds of Caesalpinia spinosa). Rheological behaviour has non-Newtonian pseudoplastic character and the flow curves were fitted using the Otswald - de Waele (power law) model and Herschel - Bulkley model. The hydrogels exhibit shear thinning behaviour. The meaning of the rheological parameters on the friction factors during flow of hydrocolloid gels in the tube has been shown. Information on time dependent behaviour of tested liquids has been also obtained. Time dependent curves were fitted by the Gaussian model. Preliminary results obtained for a constant shear rate showed the thixotropic and time-dependent behaviour of the hydrogels. These parameters can be especially used in much software dealing with a numerical simulation of the flow problems.

Effect of the loading rate on compressive properties of goose eggs

The resistance of goose (Anser anser f. domestica) eggs to damage was determined by measuring the average rupture force, specific deformation and rupture energy during their compression at different compression speeds (0.0167, 0.167, 0.334, 1.67, 6.68 and 13.36 mm/s). Eggs have been loaded between their poles (along X axis) and in the equator plane (Z axis). The greatest amount of force required to break the eggs was required when eggs were loaded along the X axis and the least compression force was required along the Z axis. This effect of the loading orientation can be described in terms of the eggshell contour curvature. The rate sensitivity of the eggshell rupture force is higher than that observed for the Japanese quail’s eggs.

Effect of storage duration on the rheological properties of goose liquid egg products and eggshell membranes

In practice, goose eggs are increasingly used and, therefore, the rheological properties have to be known for processing. The eggs of geese (Landes Goose, Anser anser f. domestica) were stored for one, 2, 3, 4, 6, and 8 wk at a constant temperature 4°C. First of all, the egg quality parameters were described in terms of egg weight, egg weight loss, egg shape index, yolk height, albumen height, yolk index, albumen index, and Haugh units. In the next step the rheological behavior of liquid egg products (egg yolk, albumen, and whole liquid egg) was studied using a concentric cylinder viscometer. Flow curves of all liquid egg products exhibited non-Newtonian shear thinning behavior. This behavior can be described using the Herschel-Bulkley model and for technical application using the Ostwald-de Waele model. The effect of the storage duration on the rheological behavior is different for the different liquid egg products. With the exception of very low shear rates, the viscosity of the egg yolk as well as of the whole liquid egg decreases with storage time. At lower shear rates there is a tendency toward increased albumen viscosity with storage duration. The storage duration also affects the mechanical properties of the eggshell membrane. This effect has been evaluated in terms of the ultimate tensile strength, fracture strain, and fracture toughness. All these parameters increased with the loading rate, but decreased during the egg storage. These mechanical phenomena should be respected, namely in the design of the egg model for the numerical simulation of the egg behavior under different kinds of the mechanical loading.

Relationship between viscosity and sugar content of must during ripening period of grapes

The relationship between dynamic viscosity and sugar content of the must is important indicator during the ripening of the vine grapes. For the experiment were selected and used only grape vine varieties. The grape vine varieties are divided into blue and white. The varieties of Blaufrankisch, Blauer Portugieser, and Cabernet Moravia were used in the blue varieties. Representatives of the white varieties were used Pinot Blanc, Pinot Gris, and Sauvignon. Country of origin was the Czech Republic, wine region Moravia (sub-region Slovacko). The grapes were collected and analyzed four times week after week during their ripening period. After grapes harvesting the individual berries were cut out of grape using the scalpel. These berries were then weighed and then the must was squeezed using a mechanical presser. Weight of berries, dynamic viscosity (in shear strain rate 100 s -1 ), sugar content, and density of must were measured and evaluated. From the values of berries weight it can be observed the variations in weight depending especially on the weather change - the water content in the berries. The observed sugar content did not change a lot during maturity, which can be explained by a more mature phase of the grapes. The results of viscosity and sugar content (for all varieties) demonstrate the viscosity dependence on the sugar content of must - with increasing viscosity of the must the sugar content of the must increase and conversely. The knowledge of the physico-mechanical properties os wine must is very important for for technocologists, producers, but also wine consumers.

Effect of additives to microbiological quality of yogurts

The objective of this work was to study the effect of addition chia flour, quinoa flour, nopal powder, apple fibre and bamboo fibre BAF 40 in yogurt to microbiological quality. Yogurts were made with 1, 3 and 5% of addition of these additives. The milk used for manufacturing was heated up to 85 °C for 5 min and flour, powder and fiber were irradiated for 20 min in three replicates. It was monitored: Lactic acid bacteria (LAB) - 72 hours at 30 °C (ISO 13721:1998) and yeasts and moulds - 5 days at 25 °C (ISO 21527-1:2009). During storage, the number of LAB was increased to match the initial concentration of yogurt with addition chia flour (concentration 1, 3, 5%) and quinoa flour (1%). The addition of nopal powder, apple or bamboo fiber to yogurt showed a tendency to decrease the number of LAB compared with its initial concentration. All samples were compared with the control yogurt without addition whatever flour, powder or fiber. The amount of yeasts and moulds was increased with the increasing addition of fiber in yogurts. The lowest amount of yeasts and moulds was in yogurt with the bamboo fiber. On the other hand the highest amount was in yogurt with chia flour.

Effect of different storage times on Japanese quail egg quality characteristics

The aim of this research was to monitor selected quality parameters of Japanese quails ( Coturnix coturnix japonica ) - the loss of egg weight, changing yolk and white index, Haugh units, egg yolks color. Quail eggs were stored for 0, 1, 2, 4, 6 and 8 weeks at 4 °C. The weight of the quail eggs ranged from 11.67 to 12.27 g. The ratio of the shell range 7.60 to 8.16 % (resp. 0.89 - 0.96 g), ratio of egg white from 59.33 to 62.10 % (resp. 6.31 - 6.66 g) and a ratio yolk of 30.13 - 32.88 % (resp. 3.68 - 3.91 g). The lost of egg weight ranged from 0.47 to 2.93 % during the quail eggs storage, corresponding to a weight loss of 0.26 - 0.58 g of the total weight of the eggs. The average values of the yolk index ranged from 42.67 - 48.53 % and the average values of the quail egg white index ranged from 6.77 to 11.35 %. The average Haugh units were set between 56.93 and 73.72. The color of quail egg yolk was determined using the La Roche scale with the most frequent value 3. During the quail eggs storage, a statistically significant difference was found with most of the quality traits observed.

Phthalic acid esters content in yoghurt with chia flour and bamboo fiber during storage time

Phthalic acid esters are plasticizers, they can migrate freely from plastic to their surroundings. They have negative health effects. European legislation sets specific migration limits for phthalic acid esters. In our study, we deal with two esters of phthalic acid, dibutylphtalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP). It was studied the effect of storage of four types of yoghurt on the concentration of phthalic acid esters. Yoghurts contained 1% chia flour, 5% chia flour, 1% bamboo fiber and 5% bamboo fiber. Yoghurts were stored in plastic cups, which contained both examined phthalic acid esters. Esters of phthalic acid were determined after 1 week of storage then after 2 weeks of storage and in the original raw material. Furthermore, the pH of the yoghurt was determined. The pH values ​​were correlated with phthalate concentrations: the correlation coefficient for DBP with a pH of -0.0265 and for DEHP with a pH of 0.3075. Mean concentrations of DEHP decreased over time, while DBP decreased for yoghurt with 1% chia flour, while in other cases they increased. The mean DBP concentrations in yoghurt were higher than the average concentrations of DEHP. Comparing the mean sample values ​​with t-test for dependent samples for yoghurt of the same type, when comparing the DBP or DEHP concentration in week 1 with the DBP or DEHP concentration at week 2, the mean values ​​were consistent. It can be noted that there was no increase in DEHP concentrations from cups to yoghurts, which was probably due to a lower concentration in cups than the DBP concentration. DBP concentrations increased in 3 of the 4 types of yoghurt. The determined pH in yoghurts did not differ significantly. Apparently a greater effect on the migration of phthalic acid esters will have in our case a different yoghurt consistency than pH. It would be appropriate to examine the effect of food density on the migration of phthalic acid esters. Likewise, it would be appropriate to examine the effect of pH but in the same food with different pH on the migration of phthalic acid esters.

Influence of sugar beet storage duration on root responseto non-destructive impacts

Abstract For the purpose of this paper, sugar beet roots were loaded by creating the impact of aluminium bars falling from different heights. The time history of the force at the contact between the sugar beet root and the bar was measured. The response of the sugar beet root to the impact was evaluated in terms of surface displacement. This displacement was measured using a laser vibrometer. The displacement was studied in the time and frequency domain during the postharvest period, up to 71 days after crop collection. The measured parameters describing the sugar beet response were significantly sensitive to the storage duration, namely in the frequency domain. Correlations between the storage duration and the main parameters of both the force and surface displacement were identified (p < 0.05).

Quality parameters of curd

The aim of this work was measurement of the curd firmness prepared by different volume of rennet solution and comparison of differences of curd firmness between these volumes. Further, it was observed the influence of different volumes of rennet up to thevolume of whey release, curd firmness, dry matter of curd and dry matter of whey. The composition of milk was determined according ISO and Czech state standard. Dry matter content (%) was determined by gravimetry, in drying oven at 102 °C to constant weight (ISO 6731:2010), the protein content (%) by Kjeldahl´s method (EN ISO 8968-1:2002), content of fat (%) by Gerber´s acidobutyrometric method (ISO 2446:2008), content of lactose by polarimetry, titratable acidity by titration Soxhlet-Henkel method, pH and calcium content in milk (g.L -1 ) was determined by complexometric titration with flueroxone as an indicator according to Czech state standart No 57 0530. For coagulation was used microbial rennet CHY-MAX R M 200. There were measured: curd firmness, rennet coagulation time, curd quality, volume of released whey, weight of curd, dry matter of curd and dry matter of whey. Different volumes of rennet solution had influence on curd firmness. Curd firmness (volume of rennet solution) had no significant influence on curd quality (five grade scale). Curd firmness had influence on volume of whey release (mL) out of the curd. With the increasing curd firmness s increased the volume of whey released from the curd. The volume of rennet solution had an influence on weight of curd. Curd dry matter raised with higher volume of rennet solution. Volume of added rennet solution had no statistically significant effect on the change of whey dry matter.