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- Karlsson, Camilla
(författare)
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Fouling and cleaning of solid surfaces. The influence of surface characteristics and operating conditions
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The severe fouling common in food processing puts high demands on equipment cleaning. Adsorption of the protein betalactoglobulin to solid surfaces and its subsequent removal were followed using in situ ellipsometry. Most experiments were done in a stirred cuvette. Additionally, a flow cell was designed, which was employed in some work. The characteristics of the surface were shown to influence protein adsorption and removal. While differences between chromium oxide and stainless steel were small, methylated silica showed significantly different adsorption, desorption during rinsing and cleanability. Near the betalactoglobulin denaturation temperature, rapid multilayer build-up was observed, and the importance of the bare surface properties appeared to decrease. On metal oxides, a lag phase preceded the build-up, while on methylated silica an initial phase of slower adsorption was seen. Prolonged adsorption times gave less desorption during rinsing from metal oxides. For methylated silica, increasing the betalactoglobulin residence time on the surface led to lower removal by the anionic surfactant SDS. Increasing the NaOH concentration gave enhanced cleaning rates and better cleanability of the stainless steel. Combining SDS with NaOH resulted in improved cleaning compared to if using the individual components. Adsorption and removal at high temperature resulted in lower cleanability compared to at room temperature, due to heat-induced alterations in the protein. No correlation was found between the bulk composition or the surface finish of the stainless steel and the fouling tendency or the cleanability. Differences in NaOH-induced protein removal were striking between surfaces subjected to different pretreatments. Passivated surfaces were less cleanable than surfaces pretreated with strong alkali or plasma-cleaned. After repeated fouling and cleaning without renewed pretreatment, differences decreased. While the cleanability of alkali-precleaned surfaces decreased when reused, changes for passivated surfaces were smaller. The initial betalactoglobulin adsorption in turbulent flow was found to be kinetically controlled. At the laminar flow rate, results indicated effects of both mass transport limitations and adsorption kinetics. No significant influence on rinsing or cleaning was evident, and effects on the amounts adsorbed were small. All NaOH concentrations tested caused significant protein removal, and the performance of the two highest concentrations was comparable.
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- Langton, Maud, et al.
(författare)
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Texture as a reflection of microstructure
- 1996
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Ingår i: Food Quality and Preference. - 0950-3293 .- 1873-6343. ; 7:42067, s. 185-191
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Tidskriftsartikel (refereegranskat)abstract
- The perception of texture has been correlated to the micro-structure of particulate whey protein gels. A full, two-level, factorial experimental design was used in which the processing conditions, pH, heating rate and addition of salt were used as design factors. The texture of the gels was analyzed by a sensory panel, and the microstructure was analysed by light and electron microscopy. The microstructure was quantified by using different types of image analysis. In this study of particulate whey protein gels, the test principles of analysing texture were divided into two groups: destructive tests and non-destructive tests. The micro-structural parameters can also be divided into two groups: overall network dimensions (pore size and particle size) and strand characteristics. The texture as measured with destructive methods was sensitive to overall network dimensions, whereas texture as measured with non-destructive methods was sensitive to the strand characteristics of particulate protein gels.
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- Persson, Hans, et al.
(författare)
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Binding of Cu2+, Zn2+, and Cd2+ to Inositol Tri-, Tetra-, Penta-, and Hexaphosphates
- 1998
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 46:8, s. 3194-3200
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Tidskriftsartikel (refereegranskat)abstract
- myo-Inositol hexaphosphate, the salt of myo-inositol hexaphosphoric acid (IP6), is a common constituent of many plant foods, such as cereals and legumes. IP6 interacts with mineral elements, influencing their bioavailability. Processed foods contain a mixture of different inositol phosphates, i.e., IP6 and its degradation products with five or less phosphate groups (IP5-IP1). The interaction of the lower inositol phosphates with mineral elements is not well-known. In this study, the interaction between metal ions (Cu2+, Zn2+, and Cd2+) and isolated fractions of inositol phosphates with 6, 5, 4 and 3 phosphate groups (IP6-IP3) was investigated by using a potentiometric technique. The study was performed at pH 3-7, which is the pH range in the upper part of the duodenum, where mineral absorption takes place. The inositol phosphate fractions studied had a pronounced binding capacity between pH 5 and 7. Thus, mineral complex formation with lower inositol phosphates is likely to occur in the duodenum, which would be important from a nutritional point of view. The mineral binding capacity as calculated per phosphate group was similar for IP6, IP5, IP4, and IP3, but the binding strength was lower for the lower inositol phosphates (IP4 and IP3). At increasing pH, within the range (pH 3-7), the metal complex formation generally began in the order copper, zinc, cadmium for all inositol phosphates indicating the same order of binding strength, i.e., Cu > Zn > Cd. For IP6 the difference was small between Cu and Zn.
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- Ståhl Wernersson, Eva
(författare)
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Some Fluid Dynamic Characteristics in the Scale-up of Rushton Turbine-Agitated Tanks
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Turbine-agitated tanks are used in chemical and biochemical applications to increase mixing which, in turn, affects the yield, productivity and product quality. The purpose of this work was to study the hydrodynamic influence on the scale-up of turbine-agitated tanks, commonly used in fermentation. Local turbulent flow parameters, the turbulent kinetic energy and the local energy dissipation rate, were related to the global scale-up parameters: the impeller tip speed, impeller diameter and power per unit mass, and to the local flow parameter, the calculated convective velocity. A system for turbulent velocity measurements was designed using constant-temperature anemometry as the measuring method. A split-film probe was used which enabled velocity measurements to be made in two directions simultaneously. Measurements were performed in three tanks of different geometries and sizes (0.75 m3, 12 m3 and 30 m3). Different operating conditions, in regard of power input per unit mass, were used, comparable both to commercial fermentation and bench-scale units. Several estimates and hypothesis for the convective velocity were evaluated. Different methods for calculating the local energy dissipation rate were compared for measurements performed both in the impeller region and the bulk region of the tanks. It was shown that there was a correlation between the local turbulent parameters, turbulent kinetic energy and energy dissipation rate, and the local flow parameter, the convective velocity Uconv, independent of the tank size, the tank geometry or position in the tank, which confirms the similarity of the flows at high turbulent Reynolds numbers. The similarity of the flow conditions at high turbulent Reynolds numbers was also evidenced by scaling of energy spectra in the space domain for tanks of different geometries, sizes and at different positions in the tanks. Correlations are given for the scaling of local flow parameters, the turbulent kinetic energy and the energy dissipation rate, in the impeller region of the tank, using global scale-up parameters. Long-term characteristics have been detected in the mean flow and in the turbulent flow in the impeller and bulk zones. Increasing the power supplied to a process affects the impeller region more than the bulk region, and therefore increases the turbulent mixing in the process. This was shown by the higher values of the slopes of turbulent parameters compared with global parameters.
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- Lindberg, Anne-Marie
(författare)
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Characterization of Aeromonas, Enterobacteriaceae, Pseudomonas, Bacillus and Lactobacillus spontaneously growing to high numbers in milk, minced meat, fish or cheese
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The spoilage flora of refrigerated raw and pasteurized milk was classified and identified by numerical phenotypic analysis. Isolations of bacteria were made at a defined spoilage stage, when the total aerobic count was 106-107 cfu per ml. The secondary flora of ripened Swedish and Norwegian cheeses was investigated by numerical analysis. Aeromonas and Enterobacteriaceae spp. isolated from the spoiling stage of refrigerated milk, fish and minced meat were identified by numerical methods and by a commercial identification system (Biolog). Enterobacteriaceae isolates were also classified using RAPD analysis. Aeromonas isolates were tested for possible virulence factors and Enterobacteriaceae isolates for the possession of genes coding for E.coli toxins and virulence factors. Gram-negative organisms spoiled 100% of raw milk samples, and 65% and 50% of pasteurized milk products stored at 5ºC and 7ºC, respectively. Five taxa of Pseudomonas were found to be predominate and it is suggested that recontamination of pasteurized milk originates from the raw milk flora. Bacillus cereus was isolated from 21% of pasteurized milk samples stored at 7ºC but was never recovered from milk stored at 5ºC. The average shelf-life of pasteurized milk was prolonged from 9.9 d to 16.6 d by lowering the temperature from 7ºC to 5ºC. The secondary flora of ripened cheeses was found to be dominated by phenotypic groups designated "Lactobacillus paracasei/casei complex". A cluster identified as Lactococcus lactis, was found to be related to cheeses of adequate quality. Aeromonas spp., especially A.hydrophila, were found in high numbers in 69% of fishes, 7.5 % of minced meat samples and 1.2% of pasteurized milk samples. Some of the food isolates clustered closely with clinical strains. Enterobacteriaceae spp. were found in high numbers in 100% of minced meat samples, 31% of fishes, and 6% of pasteurized milk samples. The predominating species were Hafnia alvei, Rahnella aquatilis and Serratia liquefaciens. The RAPD profiles were found to facilitate the identification of H.alvei isolates. E.coli st1 gene was found in four isolates of H.alvei, lt gene in one isolate of R.aquatilis, vt1 and eaeA in one of the st1 positive isolates and vt2 in two isolates of S.liquefaciens.
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- Eneroth, Åsa
(författare)
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Bacteriological Hygiene in the Production of Pasteurised Milk
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Critical contamination sites and sources for the Gram-negative psychrotrophs (GNP) of the taxa Pseudomonas, Enterobacteriaceae and Aeromonas, and the Gram-positive spore-forming (GPS) species Bacillus cereus, have been traced in the production line of pasteurised milk. Samples of raw and pasteurised milk from different sampling sites along the line were collected. After incubation at 7°C until the total aerobic plate count reached 106 to 107 cfu/ml, or the number of GPS exceeded 104 cfu/ml isolates were picked randomly and identified. All GNP present in the raw milk were properly killed during pasteurisation. A recontamination by GNP was observed in 40% of the consumer packages. This recontamination was focused to the filling procedure, and Pseudomonas was the dominating GNP in all packages. Environmental samples, as water from different water sources in the dairy plant, air collected by a RCS-sampler on water-agar strips, and empty, formed and sealed packages taken from the filling machines, were inoculated with sterile milk. GNP isolates were randomly picked and identified after incubation at 7°C. Samples of water and air collected in the immediate surroundings of the filling machine contained large numbers of GNP causing growth in refrigerated milk. GNP isolates from the milk samples and from the environmental samples were genomically typed by the PCR-based method Randomly Amplified Polymorphic DNA (RAPD). The RAPD-typing showed that there are many different RAPD-types involved in the recontamination of pasteurised milk. Several of the milk contaminating RAPD-types were found in condensed water on the filling nozzles, in waste-water at the bottom of the filling machine, and in air surrounding the filling machine. Some contaminating RAPD-types were present inside the filling machine over long periods, especially at the bottom of the filling machine. The effect on post-pasteurisation contamination by reducing the usage of water around the filling machine was studied. A clear link between the usage of water inside the machine and the frequency of consumer packages contaminated by GNP was found. B. cereus were involved in, and sometimes solely responsible for, the spoilage of pasteurised milk. The B. cereus infection can originate from heat-resistant spores present in the raw milk, but B. cereus can also enter the milk at the dairy plant. By using traditional microbiological methods and RAPD-typing, the pasteurised milk was once found to be contaminated by B. cereus while passing through one pasteuriser, and commonly found to be contaminated during the filling procedure.
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