This study investigates the effect of extended rye scald fermentation times (12–48 h) on its biochemical properties and rye bread’s nutritional and sensory qualities. Traditional rye bread production in Latvia involves prolonged fermentation with lactic acid bacteria (LAB), a process that influences the bread’s acidity, sugar content, and concentrations of organic acids, fructans, and phytates. Scald fermentation was analyzed at intervals of 0, 12, 24, 36, and 48 h to monitor microbial activity, particularly LAB population dynamics. Organic acids and sugar profiles were analyzed using HPLC, while phytic acid and fructan concentrations were determined using the Phytic Acid Assay Kit (K-PHYT) and Fructan Assay Kit (K-FRUC). Sensory evaluation assessed attributes including aroma, sour and sweet taste, stickiness, and floury aftertaste. A rapid pH decrease and increased total titratable acidity (TTA) after 12 h confirmed scald’s suitability as a substrate for Lactobacillus delbrueckii metabolism. Lactic acid content increased 13.8-fold after 48 h. Combined scald and dough sourdough fermentation reduced phytic acid by 20% and fructans by 49%, improving mineral bioavailability. Extending fermentation beyond 24 h showed no significant differences in physicochemical parameters, although it improved sensory quality, reduced stickiness, balanced sweet–sour flavors, enhanced aroma, and minimized floury aftertaste.

In wholemeal bread production, scalding and fermentation contribute to the improvement of the structural characteristics of the dough and bread. The influence of fermented scald on rye and barley dough and bread structure formation was specified in this study. The microstructural analysis performed using a scanning electron microscope revealed the separation of phases during the fermentation of scalds. According to the storage G′ and loss G″ moduli, both scalds exhibited elastic character over viscous. The fermentation of barley scald increased both moduli and complex viscosity, while no substantial changes were observed in the fermented rye scald. The addition of fermented scald containing partially hydrolyzed starch and a fraction of water-soluble compounds contributed positively to the formation of a well-organized structure of dough fermented for 4 h. Fermentation substantially reduced the dough’s complex viscosity and moduli values, confirming the partial structure alteration leading to the viscous portion increase. The dough with fermented scald showed a significantly lower loss factor than the dough without fermented scald, indicating enhanced mechanical process ability. The most substantial weakening of the structure was observed for dough without scald. The addition of rye scald to the rye dough promoted the formation of fewer pores with relatively smaller specific volumes.

The technology of fermented rye bread in Latvia has a strong traditional value. Microorganisms play an important role in the fermentation process of sourdough bread, mainly due to lactic acid bacteria (LAB). Traditional rye bread in Latvia is prepared using scalded flour and sourdough. Total fermentation time can be from 6 till 48 hours, depending on the bakery. Usually sourdough contains two to five LAB species. One of the metabolites in sourdough produced by LAB is exopolysaccharide (EPS). It has been found that 20% of the analysed strains in sourdough are able to produce EPSs from sucrose — mainly fructans and glucans are produced. The exopolysaccha-rides produced by LAB are able to bind water, improving the quality of bread, increasing the volume, delaying staling of the bread, and thus extending the shelf life. Many studies have shown that EPSs produced by LAB can improve the growth of probiotics in the human body, thus improving the immune function. Of particular interest about possible prebiotic functions are EPSs produced by LAB. Long rye bread scalding fermentation technology can improve the texture, quality, and shelf life of bread, as well as functionally affect the human immune system.

Amylase activity in rye flour plays a crucial role in the production of rye bread. When preparing a scald in rye bread production, diastatic rye malt is utilized to augment the amylase activity of the rye flour. This study investigated the effects of the diastatic power (DP) and concentration of rye malt on the Falling Number (FN) and the rheological properties of rye flour. Additionally, it examined reducing sugars in the scalding process and fermentation. Mixolab results provided comprehensive data on dough properties at different temperature stages, highlighting significant changes in starch gelatinization and enzyme activity due to varying malt diastatic power and concentrations. The decline in the gelatinization index (C3-C2) indicated faster starch gelatinization with increased diastatic power. Adding rye malt significantly increased maltose content in the saccharified and fermented scald, promoting a favorable environment for lactic acid bacteria and yeasts. FN and Amylograph results showed that less active malt (DP 170, 179 °WK), at a 1.5% concentration, could achieve similar effects as the more active malt (DP 362, 408 °WK) at 0.5%. Adding rye malt to rye flour allows for the regulation of the flour’s rheological properties and FN, adjustable based on malt DP and concentration.

The doctoral thesis "The influence of rye malt and scald fermentation on rye bread production" was developed during the period from 2020 to 2025. The research was carried out in the laboratories of the Faculty of Agriculture and Food Technology at the Latvia University of Life Sciences and Technologies, In the Smart Technologies Division of the Biotechnology Scientific Laboratory, the Center of Food and Fermentation Technologies (TFTAK) in Estonia, Chopin Technologies in France, as well as at the bakery “Ķelmēni” (Rankas parish, Gulbene municipality, Latvia). The hypothesis of the doctoral thesis: a technologically stable and predictable production process for rye bread prepared with scald can be achieved by the precise addition of unfermented rye malt, considering its diastatic power, and by prolonged scald fermentation. Theses. 1. The addition of unfermented rye malt affects the technological properties of rye flour depending on its content and diastatic power, promoting sugar formation in the scald. 2. During prolonged scald fermentation, a reduction in sugar content and changes in the composition and concentration of acids produced by lactic acid bacteria occur. 3. Prolonged fermentation reduces the content of fructans and phytic acid in the fermented scald. 4. Extended scald fermentation improves the sensory properties of rye bread and reduces the content of fructans and phytic acid. Aim of the doctoral thesis: to evaluate the effect of the diastatic power of unfermented rye malt and the scald fermentation time on the microbiological and chemical parameters of the scald, the technological properties of the flour, and the sensory and chemical characteristics of rye bread. Research tasks. 1. To analyze the activity of the enzymes α-amylase and β-amylase in unfermented rye malt samples with different diastatic power. 2. To evaluate the effect of the content and activity (diastatic power) of unfermented rye malt on the enzymatic activity and technological properties of rye flour. 3. To develop a mathematical model for stabilizing the falling number of rye flour–malt mixtures. 4. To analyze changes in the sugar content of rye scald after saccharification and after 24 hours of fermentation. 5. To evaluate the dynamics of microbiota changes and acidity development in rye flour scald during prolonged fermentation. 6. To analyze changes in the chemical composition of rye flour scald during prolonged fermentation. 7. To analyze the chemical composition and sensory properties of rye bread prepared with differently processed scalds. The doctoral thesis is structured into three chapters. 1. Literature Review. This chapter compiles and analyzes the latest scientific literature on the chemical composition and enzymatic activity of wholegrain rye flour and their impact on the technological properties of the flour. Recent findings regarding the enzymatic activity of rye malt, characterized by the quality indicator diastatic power, are evaluated. As this indicator is insufficiently explained in the scientific literature in relation to bread production processes, it is important to understand its relationship with starch hydrolysis and the efficiency of scald fermentation. The chapter also describes different types of scald and summarizes information on the microbiological and chemical processes occurring in scalds and their influence on the chemical and sensory properties of bread. 2. Materials and Methods. This chapter presents the materials and methods used in the study, including the applied mathematical and statistical data analysis techniques. 3. Results and Discussion. The obtained results are compiled into three subchapters, structured according to the study design. The activity of diastatic rye malts is characterized, and the influence of malt activity and content on the physicochemical and technological properties of rye flour, including sugar formation during saccharification and fermentation, is analyzed. A mathematical model for stabilizing the falling number of rye flour–malt mixtures is developed. Changes in the microbiota and chemical composition of rye scald during prolonged fermentation (up to 48 hours) are evaluated, including the dynamics of sugars, organic acids, phytic acid, and fructans. The quality of rye bread prepared using scalds fermented for different durations is assessed by analyzing sugar and organic acid contents, sensory properties, and chemical changes. The results provide a basis for evaluating the significance of malt activity, content, and scald fermentation time in ensuring the stability and predictability of the bread production process. The study was conducted with the support of the Latvia University of Life Sciences and Technologies (LLU) program “Strengthening Scientific Capacity at LLU” within the project Z52 “Development of a Mathematical Model for Predicting Rye Flour Quality Using Unfermented Rye Malt' and the LLU program 'Implementation of Fundamental Research at LLU” within the scientific project G10 'Investigation of Exopolysaccharide Formation Dynamics During the Long-Time Fermentation of Rye Scald”.