Salt, EDTA and pH effects on rheological properties of Aspergillus niger mycelium suspension.

Ph.D. - Doctoral Progra

Rheological Behaviour of Bentonite—Apple Juice Dispersions

Rheological behavior of the bentonite-apple juice suspensions were experimentally determined within the range of the industrial clarification processes: shear rate 4.3 to 43.1 s-1, pH 4.0-5.0, temperature 10-50°C, bentonite concentration 0.66-2.66 g/L. The experimental data were described with the power law as: τ = Kγ1.56. Temperature effects on the consistency index K agreed with the Arrhenius expression. Although no trend was observed in variation of the Arrhenius model constants with bentonite concentration, these parameters agreed with the frequency factor-activation energy compensation relation

EFFECT OF THE LACTOPEROXIDASE SYSTEM ON THE ACTIVITY OF STARTER CULTURES FOR YOGURT PRODUCTION

The LP system in raw milk was activated by the addition of equimolar concentrations (0.25 mM) of hydrogen peroxide (H2O2) and thiocyanate (SCN) as KSCN and utilizing the inherent milk lactoperoxidase (LP). H2O2 and SCN- concentrations were determined during the experiments by using spectrophotometric methods and found to decrease to 1.5 mug/ml and 0.4 mug/ml respectively in 5 h. A relatively small amount of H2O2 was produced in the untreated milk which then was found to decrease. The activated sample, at the end of the 5 h period contained 10(9) cells/ml whereas the control sample contained 10(11) cells/ml. Lactic acid (LA) concentration inceased from 0.24 to 0.58% in the control after a slight delay of 1 h, whereas in the LP activated sample LA remained at a level 0.23 for 5 h. The activated LP system was found to delay the coagulation time and to strongly reduce the activity of starter cultures

Effects of Bentonite Combinations and Gelatin on the Rheological Behaviour of Bentonite – Apple Juice Dispersions

Rheological behaviour of bentonite – apple juice suspensions were experimentally determined at 25°C, within the shear rate range of 4.3 to 43.1 s−1with 0.90, 1.33 and 2.66 g/L bentonite mixtures and 0 to 0.25 g/L (on dry basis) gelatin concentrations. The mixtures consisted of 100%, 80%, 60%, 40% 20% and 0% Ca-bentonite and balance Na-bentonite combinations. The experimental data were described with the power law as τ =Kγ.1.56. The consistency index was related to the calcium, sodium and gelatin concentrations asK=K0+K1CαCa+K2CßNa+K3CϵG

Salt, EDTA, and pH effects on rheological behavior of mold suspensions

The effects of surface properties on the rheological behavior of Aspergillus niger suspensions were studied at pH 2-7, with the addition of 0-0.10 m NaH2PO4, NaCl, CaCl2, AlCl3, and EDTA at shear rates of 0-21.6 s-1. The structural network concept was used to discuss the consequences of cell-cell interactions on the rheological behavior. Analysis of the data indicated that the suspensions containing CaCl2 nearly always had the smallest shear stress at all the pH values, indicating that, unlike with the yeast suspensions, Ca2+ does not contribute to the specific bonding of the mold cells. At low pH and salt concentrations, NaH2PO4 was better than AlCl3 for promoting bond formation between the cells. When either the salt concentration or the pH was increased, AlCl3 became a better bond formation agent than NaH2PO4. EDTA removes the charged groups from surfaces and encourages cell-cell contact via hydrophobic interactions. The shear stress and consistency index increased while the flow behavior index decreased with EDTA concentration

Mixed culture growth kinetics of Streptococcus thermophilus and Lactobacillus bulgaricus

A simple microbiological technique was used to differentially enumerate growth of Streptococcus thermophilus and Lactobacillus bulgaricus in a mixed culture. The growth of the microorganisms in the mixed culture was satisfactorily simulated with a set of modified logistic equations. This simple model was valid for various initial biomass concentrations and their ratios. It did not need substrate or product data for simulation of biomass growth, which may simplify the calculations in fermenter design. It was shown that our model may also be regarded as a special case of a common mixed culture model: Volterra's competition analysis

Separation of bread wheat flours into starch and gluten fractions: effect of water temperature alone or in combination with water to flour ratio

Two different commercial bread wheat flours (BF‐I, 65% extraction and BF‐V, 86% extraction) were separated into gluten and starch milk by making a dough, allowing some time for maturation, dispersing the dough in water and wet sieving/washing. The effect of using of warm water (20–45 °C) for dough making and washing on separation was studied for BF‐I flour at 640 g kg−1 water to flour ratio of and 300 s maturation time, and the separation was found to improve with increase in temperature. The combined effects of water temperature (20–50 °C) and water to flour ratio (640–780 g kg−1 for BF‐I and 620–870 g kg−1 for BF‐V) were studied at 600 s maturation time. The quantities and dry matter contents of the gluten fraction and starch milk were measured; a sample of starch milk was centrifuged to obtain decantate, tailing and prime starch fractions, and the dry matter contents of each were determined. All the dried samples were also analysed for protein content, and the fractional recoveries of dry matter and protein in the gluten fraction, prime starch, tailings and decantate were calculated. The results indicated the optimum point for BF‐I flour to be the combination of optimum farinograph water absorption and 40 °C. BF‐V showed very poor separation behaviour within the ranges studied. At the optimum farinograph water absorption the use of warm water for dough making and 20 °C water for washing steps was also tried, but no significant improvement over the 20 °C results was obtained

Use of a spouted bed to improve the storage stability of wheat germ followed in paper and polyethlyene packages

Stabilization of wheat germ by heating in a spouted bed for 180–540 s with air at 140–200 °C was studied. The lipase activity decreased by 6–65%. Wheat germ processed at 200 °C for 360 s was ranked highest in sensory evaluation, described as having ‘a golden color’ and ‘nutty flavor’, and its lipoxygenase activity had decreased by 91.2%. This product and raw wheat germ were stored in paper, polyethylene and vacuum‐packed polyethylene pouches at 5 °C, room temperature (18–26 °C) and 40 °C, and the moisture contents, water activities, free fatty acid contents and peroxide values were followed for 20 weeks. The increases were faster in paper pouches than in the polyethylene ones; vacuum packaging in polyethylene did not bring about significant improvement. The peroxide values of raw samples exceeded 10 meq O2 kg−1 oil after 3–23 days while those of the processed samples stored at room temperature or 5 °C were still less than 10 after 20 weeks. The free fatty acid content and peroxide value changes were expressed by zero order kinetics, resulting in similar activation energies for the raw and processed samples