Browsing by Subject "laktoosi"

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  • Ivars-Öhman, Maria (University of Helsinki, 1993)
  • Hedberg, Leena (Helsingfors universitet, 2017)
    The literature review of this master’s thesis dealt with the chemical and nutritional properties of lactose, lactose content in food and methods used for lactose determining. The aim of the experimental part of this thesis was to develop, validate and implement a sensitive and reliable method for determining residual lactose in different kinds of foods using high-performance anion-exchange chromatography and pulsed amperometric detection (HPAEC-PAD). The method was developed for MetropoliLab in response to an increased demand. The matrices chosen for validation were food products that were known to contain traces of lactose: lactose-free skimmed milk, whole milk, banana flavoured yoghurt and cottage cheese. Lactose was extracted in water from a homogenized sample. Proteins were precipitated with Carrez-reagents and the extract was then purified by solid phase extraction and filtration. A strong anion exchange column with quaternary ammonium ion groups was used to separate lactose from other compounds found in the foods and a pulsed amperometric detector equipped with a gold electrode was used for the detection of lactose. The biggest challenges were to remove all compounds interfering with the detection of lactose and to separate lactose from other compounds oxidized at the gold electrode. The sample preparation and the solvent gradient used showed good resolution for lactose. The method was found very sensitive and selective and the whole range of measurement up to 40 mg/100 g was linear. Repeatability, reproducibility and accuracy of results were good. The measurement uncertainty of the method was 11—22 %, depending on the sample matrix. The method development and validation were completed successfully using different kinds of dairy products as sample matrices. Validation for other food matrices was started immediately and the experiments have already shown some promising results indicating the method’s suitability for meat, bakery and convenience food products. In spite of the simple sample preparation step the method is time consuming when analysing large sample arrays and options to overcome it are necessary to examine.
  • Alakotila, Anni (Helsingin yliopisto, 2019)
    The literature section of this Master's Thesis focuses on cheese making process from milk composition to cheese ripening. In addition, the thesis investigates the effect of lactose standardization on lactic acid fermentation, sensory characteristics of the cheese and what biochemical changes the standardization causes during cheese ripening. The aim of the experimental part was to investigate the effect of standardization of the lactose content of cheese milk and how it will affect the ripening and final quality of Swiss -type cheeses. The effect of lactose content of the cheese milk, protein fraction used, pre-ripening time and ripening temperature was studied using statistical design of experiments (DOE). 16 test batches were manufactured according to factorial screening design. Water, cream and protein fraction were used to standardize the lactose content of the cheese milk. In addition, two center point experiments were performed with third protein fraction. The fat and protein content, dry matter, moisture of non-fat substance, fat in dry mater, lactose, lactic acid, acetic acid, propionic acid, butyric acid and the level of volatile organic acids and titrated free amino acids of cheese were analyzed during manufacturing and ripening. The lactose and lactic acid content of the cheese milk can be lowered by standardization of the lactose concentration. If set too low however, it is no longer beneficial for the lactic and propionic acid fermentation processes or to the quality of the cheese, as flaws in the fermentation process will start to occur. With lower levels of lactose content, less lactic acid and more propionic acid will form in the cheese. Pre-ripening creates beneficial environment for propionic acids and that can prevent cracking of the cheese. Cheese that has been ripened for too long in temperatures too high will have flaws in the fermentation process. Moreover, the statistical centre point tests show that the standardization of the protein level in the cheese milk is best to be done by using protein fraction U. Fraction U gave best results on average in the sensory evaluation.
  • Hjelt, Anniina (Helsingfors universitet, 2016)
    Stickiness of food powders is a major issue in food industry because it causes problems during processing and it deteriorates the perceptible quality. The literature review presents different stickiness testing methods and the reasons and mechanisms for stickiness. The aim of the experimental work was to investigate stickiness of milk powders. Five different spray-dried milk powders were studied. Powders were characterized by measuring the moisture content, water activity, particle size composition, surface fatty acid composition and water sorption. Stickiness was investigated with a viscometer and with penetration test. Glass transition temperatures (Tg) were also determined. The results were analyzed with the PLSR (Partial Least Squares Regression). LF WMP contained much more surface fatty acids (42.7 mg/g) than WMP (12.4 mg/g) though the bulk fat content was same in both powders. According to the BET-sorption models, lactose-free powders adsorpt more water than conventional powders. The glass transition temperatures were much higher in lactose-containing powders (RH 0 %, 84–87 °C) than in the lactose-free powders (RH 0 %, 32–40 °C). Fat content did not affect the Tg because fat is not a water adsorbing component. Critical relative humidity is for lactose-free powders from 6 to 10 % and for lactose containing powders 40 to 42 % at room temperature (25 °C). Viscometric method was used to determine stickiness curves. Lactose-free samples became sticky at much lower temperatures than lactose-containing samples. When comparing the Tg and Tsp of skim milk powders, Tsp was 11–17 °C higher then Tg in SMP and in LF SMP the difference was 34–51 °C. In the PLSR model the coefficient of determination R2 was 90.3 %, adjusted coefficient of determination R2 adj. was 80.7 % and the coefficient of prediction Q2 was 59.9 %. Only lactose content was important according to the variables important in projection (VIP) in the PLSR model. The experimental work indicated that viscometric method is an applicable way to determine powder stickiness curve. Glass transition temperature determination is also reasonable way to predict powders stickiness and sticky point temperature is slightly above the Tg. The study showed that sugar content affected more to stickiness than fat content.
  • Rauta, Janne (Helsingin yliopisto, 2019)
    Extrusion is a versatile thermomechanical food processing technology, and cereal based snack products made with extrusion are one of the most significant ready-to-eat products. The literature review covered extrusion process in general while the effect of different components of grain and milk powders in extrusion was examined more closely, and also different methods to evaluate the properties and the quality of extrusion products were examined. The objective of the experimental study was to study the effects of sugar content and composition as well as the effects of different milk protein and water contents of the mass on the properties (water content, expansion and hardness) and organoleptic quality of extrudates. Experiments were carried out by using twin-screw extruder and the main component of extrudates was a mixture of oat flour and waxy maize starch. Three different milk powders were used (one lactose-containing and two lactose-free skimmed milk powders) in experiments, so that the milk protein content of mass was 8, 10 and 12 % (from solids) and water content 14, 16 and 18 %. The effect of sugar composition (lactose vs. glucose/galactose mixture) and sugar content (lowering the milk sugar content to about 60 % from solids) in extrusion was also examined. The water content, hardness and expansion of extrudates were measured. In sensory analysis (n=6) the effect of different milk powders and water contents on extrudates were evaluated. More expanded and less hard extrudates were obtained by adding milk powder that contained lactose compared to lactose-free milk powders. Lowering the sugar content did not affect the properties of extrudates significantly. Increasing the milk protein content of the mass increased the typical positive features of extrudates when lactose-containing milk powder was used, but when lactose-free milk powders were used the effect was the opposite. Increasing the water content of the mass decreased the expansion and increased the hardness of extrudates. In sensory analysis the major differences were observed in the darkness of color and the diameter of the extrudates. According to the results of the present study it is possible to obtain extrudates with good structure using lactose-containing milk powder as well as lactose-free milk powder. However, lactose-containing milk powder may be a better alternative in extrusion compared to the lactose-free milk powder. It may be possible, to some extent, to lower the sugar content of the extrudates that contain lactose-free milk powders without compromising the structural and organoleptical quality of the extrudates.