Valorisation of whey for lactose recycling products production = Sūkalu valorizācija laktozes pārstrādes produktu ieguvei

The doctoral thesis “Valorisation of whey for lactose recycling products production” was developed from 2016 to 2021. Experiments were carried out in the research laboratories of the Faculty of Food Technology, Latvia University of Life Sciences and Technologies; Dairy Innovation Institute, California Polytechnic State University (USA); Institute of Microbiology and Biotechnology, Latvia University; Faculty of Chemistry, Latvia University; Institute of Solid State Physics, Latvia University and J.S. Hamilton Baltic Ltd. The aim of the doctoral thesis was to improve the lactose hydrolysis process for obtaining glucose-galactose and oligosaccharide syrups. The hypothesis of the doctoral thesis – the two-stage fermentation increases the sweetness of glucose-galactose syrup. The hypothesis of the doctoral thesis has been confirmed by the defended thesis: 1. The presence of cations affects the β-galactosidase activity in the sweet and acid whey permeate. 2. The chemical composition and quality of whey affect the physical properties of lactose. 3. Enzymatic reactions affect the functional and sensory properties of syrups. The research objects – sweet and acid whey permeates, glucose isomerase, commercial β-galactosidases and glucose-galactose syrup. The following tasks were set to achieve the aim of the doctoral thesis: 1. To evaluate the effect of cation concentration to ensure the β-galactosidase activity in substrate. 2. To investigate the physical properties of whey lactose in order to better understand its behaviour. 3. To study the changes of monosaccharide concentration in the lactose hydrolysis, varying with the solids concentration of the substrates and enzyme units. 4. To assess the possibilities of glucose isomerase to increase the sweetness of glucose-galactose syrup. 5. To evaluate the sensory properties of the developed syrups. The novelty of the doctoral thesis: 1. The study of the relationship of lactose hydrolysis process in the formation of galacto-oligosaccharides and lactulose. 2. The combination of β-galactosidase and glucose isomerase increases the sweetness of glucose-galactose syrup. The economic significance of the doctoral thesis: 1. The studies have shown the possibility to obtain syrup that can be used as sugar and sweeteners replacer in the food industry and to produce functional products. 2. A technological solution for hydrolysis of lactose is proposed, comprehensively evaluating the physical properties of lactose, fermentation parameters and whey composition. The doctoral thesis consists of three chapters: Chapter 1 describes the composition of whey and the possibilities of using it. An overview of the chemical and physical properties of lactose, lactose hydrolysis methods, the application of β-galactosidases and the properties of glucose-galactose syrup are provided. Chapter 2 summarises the materials and methods used in the thesis. Chapter 3 provides a summary of the results obtained in the study, the properties of commercial enzymes in different cation concentrations, the stability of enzymes in the gastrointestinal tract model, methods for the determination of lactose, the properties of dehydrated permeates are evaluated. The influence of factors on the hydrolysis of permeates and the profile of the obtained sugars was analysed. Possibilities for lactulose synthesis are considered. Sensory analysis of glucose-galactose syrups and syrups obtained in the two-stage fermentation are given. During the PhD studies the author had an internship at the Dairy Innovation Institute California Polytechnic State University (USA), where the experimental work was done. Internship was provided by the Baltic – American Freedom Foundation (BAFF) and the Council on International Education Exchange (CIEE). The study was partly financed by the LLU programme “Strengthening Research Capacity at the Latvia University of Agriculture” grant (Contract No. 3.2.-10/2017/LLU/27) “The optimization of bioprocesses for lactose recycling products”. The study was partly financed by the doctoral studies grant “Transition to the new doctoral funding model at the Latvia University of Life Sciences and Technologies” (Contract No. 3.2.-10/90). The thesis is written in English, it consists of 111 pages, 32 tables, 41 figures, 3 appendixes, and 233 bibliographic sources.