Czech Journal of Food Sciences, 2002 (vol. 20), issue 2
Beta-galactosidase activity in psychrotrophic microorganisms and their potential use in food industry
P. Karasová, V. Spiwok, Š. Malá, B. Králová, N.J. Russell
Czech J. Food Sci., 2002, 20(2):43-47 | DOI: 10.17221/3508-CJFS 
Twenty-one psychrotrophic resp. psychrophilic bacterial strains were screened for presence of b-galactosidase activity which showed 8 of them. b-Galactosidase activity of these strains was determined for 2 substrates - synthetic substrate (ONPG) and lactose - and also temperature profile of this enzyme was measured. b-Galactosidase from Arthrobacter sp. C2-2 not only proved the typical properties of cold-active enzyme, but it also preferred lactose as a substrate. Therefore, it was chosen for further isolation and purification and was found that it contains two b-galactosidase isoenzymes. One of them had strong preference for lactose and was...
Inhibition of Aspergillus niger DMF 0801 by monoacylglycerols prepared from coconut oil
Z. Řiháková, V. Filip, M. Plocková, J. Šmidrkal, R. Červenková
Czech J. Food Sci., 2002, 20(2):48-52 | DOI: 10.17221/3509-CJFS
The objectives of the present study were to test the antifungal properties (inhibition of radial growth, inhibition of the mould spore germination) of lauroylglycerol and mixtures of monoacylglycerols synthesised from coconut oil (MIX-I and MIX-II) against Aspergillus niger DMF 0801. The content of monoacylglycerols in lauroylglycerol, MIX-I and MIX-II was 99.9% (w/w), 97.7% (w/w) and 75,1% (w/w), respectively. The content of 1-lauroylglycerol in MIX-I and MIX-II was calculated from the content of lauric acid and content of monoacylglycerols. The inhibition of the radial growth of Aspergillus niger DMF 0801 by lauroylglycerol was...
Optimisation of indirect competitive ELISAs of a-, b-, and k-caseins for the recognition of thermal and proteolytic treatment of milk and milk products
M. Vítková, P. Rauch, L. Fukal
Czech J. Food Sci., 2002, 20(2):53-62 | DOI: 10.17221/3510-CJFS
Polyclonal antibodies were raised against six immunogens (three native and three thermally treated casein fractions: a+b-casein, k-casein and whole casein). Using these antibodies the procedures of an indirect competitive enzyme immunoassay (ELISA) were constructed, optimised and characterised for determination of each immunogen. It was found that ELISA of caseins is very specific without any interferences of whey proteins and with proportionally low cross-interactions between caseins. Detection limits for a-, b-, and k-caseins and whole casein were 110, 49, 58 and 505 ng/ml, respectively. The coefficient of variation was lower than 12% in intra-assay...
A simple method for determination of deoxynivalenol in cereals and flours
F. Kotal, Z. Radová
Czech J. Food Sci., 2002, 20(2):63-68 | DOI: 10.17221/3511-CJFS
An effective and fast method for determination of deoxynivalenol (DON) in cereals and flours has been developed. The immunoaffinity column was used for the isolation of DON from wheat, corn, rice and flour extract. The determination was carried out by using the HPLC/UV method. The limit of detection was 0.02 mg/kg. The recoveries for the assay range 0.1 to 2 mg/kg were generally higher than 80%, ranging from 83 to 96% with an average relative standard deviation of 3.8%. The trueness of the method using the DON test - HPLC column was established by use of certified reference material CRM 379. The certified value was 0.67 mg/kg. The result obtained from...
The conformability of two equations for bacterial growth in pork
M. Miyahara, T. Matsumoto, H. Sakurai, P. Pipek
Czech J. Food Sci., 2002, 20(2):69-73 | DOI: 10.17221/3512-CJFS
Pork is now distributed as cut meat, which increases the chance of contamination with bacteria. The rate of bacterial growth can be expressed by an exponential function. In order to find how the number of contaminating bacteria increases, we compared two functional equations for a growth curve. They are logistic: Yt = K (1 + m e-at) (1) and Gompertz: log Yt = log K + (log a)bt (2) equations (where Yt = the number of bacteria at the time t in min, m and a = coefficient, e = natural logarithm,...
Chemical and biochemical changes during microwave treatment of wheat
J. Kaasová, B. Hubáčková, P. Kadlec, J. Příhoda, Z. Bubník
Czech J. Food Sci., 2002, 20(2):74-78 | DOI: 10.17221/3513-CJFS
The effect of microwave (MW) heating on the changes in wet gluten content, Gluten Index, Falling Number and amylographic characteristics was studied in sprouted wheat grain. Different moistures of wheat in two ranges of 10-11% and 15-17% and two end temperatures of MW heated samples (60 and 80°C) were applied to wheat samples. Falling Number and Gluten Index increased with increasing absorbed energy during MW heating, whereas gluten content decreased. Amylographic maximum increased due to a-amylase inactivation progressively with increasing absorbed energy as well. The greatest relative changes occurred when the end temperature of MW heated samples...
Changes in Egg Volatiles during Storage
J. Adamiec, M. Doležal, K. Míková, J. Davídek
Czech J. Food Sci., 2002, 20(2):79-82 | DOI: 10.17221/3515-CJFS
The quality of eggs is tightly associated with freshness. New possibilities for the determination of egg freshness were studied. The volatile compounds of eggs and their changes during storage were followed. Three methods for extraction of volatiles were compared: dynamic headspace (Purge and Trap), static headspace (Solid Phase of Microextraction - SPME) and extraction according to Likens-Nickerson by simultaneous distillation-extraction (SDE) with diethyl ether as organic solvent. The extracts were analysed by GC/FID. The volatiles in an extract obtained by SDE method were identified by GC-MS. The extract includes aldehydes, alcohols, acids and esters....
Authenticity of 100% orange juice in the Czech market in 1996-2001
M. Voldřich, P. Skálová, F. Kvasnička, P. Cuhra, M. Kubík, P. Pyš
Czech J. Food Sci., 2002, 20(2):83-88 | DOI: 10.17221/3514-CJFS
Commercial orange juices samples obtained from the Czech market were analysed in the years 1996-2001. The quality and authenticity of samples was evaluated according to the Code of Practice of AIJN (selected main analytical criteria were followed - K+, Na+, Ca2+, Mg2+, citric, isocitric and malic acid, citric acid/isocitric acid ratio, glucose, fructose, saccharose, sorbitol, formol number, flavonoid glycosides - according to Davis and HPLC procedure, refractive index and other). The approach of producers to the quality and authenticity of juices developed during the years of observation. The main cases of adulteration in 1996 were as follows: (i)...