Ivan Petelkov’s research while affiliated with University of Food Technologies and other places

Background: In recent years, increasing health awareness in consumers has motivated breweries to expand their beverage ranges with products with increased biological value. The aim of the present research was to develop probiotic wort-based beverages with grapefruit or tangerine zest essential oil addition. Methods: Wort was produced with 60% Pilsen malt, 20% Vienna malt and 20% Caramel Munich ІІ malt with and without the addition of 0.05% (v/v) grapefruit or tangerine essential oils. It was inoculated with the probiotic yeast strain Saccharomyces cerevisiae var. boulardii Y1. Fermentations were carried out at a constant temperature of 10°C for 5 days. The dynamics of the extract, the alcohol content and the concentration of viable cells were monitored daily. The total phenolic content, phenolic acid and flavonoid phenolic compounds were determined because of their antioxidant activity. The antioxidant activity was determined by radical scavenging assay (DPPH) and ferric reducing antioxidant power (FRAP). A descriptive organoleptic evaluation of the final beverages was performed. Results: The essential oils inhibited yeast growth to some extent at the beginning of the fermentation, even at a concentration of 0.05% (v/v), which resulted in lower alcohol content in the beverages with essential oil addition. Nevertheless, at the end of fermentation the concentration of viable cells was almost equal in all the beverages. Tangerine essential oil addition led to the highest content of phenolics, of which phenolic acids predominated. Therefore, the highest antioxidant activity of the beverage with tangerine essential oil can be ascribed to phenolic acids. The results of the sensorial evaluation also showed that the panel had preference towards the beverage with tangerine essential oil. Conclusions: The combination of essential oil and the probiotic yeast strain resulted in beverages with higher biological value than the beverages produced with the probiotic strain alone. The results obtained will be used for optimisation of process variables in the production of pilot-scale wort-based probiotic beverages with essential oil addition.

The combination of modified mashing method and arrested fermentation for the production of low-alcohol and non-alcohol beers was studied. Therefore, five regimes for fermentation of wort with reduced fermentable sugar content with top-fermenting yeast strain at low temperatures and pitching rates were investigated. According to the fermentation dynamic results the decrease in the fermentation temperature from 10 °C to 5 °C at pitching rate of 109 Colony Forming Units cm−3 ( CFU cm−3 ) led to significantly reduced concentrations of ethanol and secondary metabolites in beer. The temperature decrease from 10 °C to 7 °C at pitching rate of 107 CFU cm−3 resulted in a decrease in the alcohol concentration and increase in all the secondary metabolite concentrations except for the vicinal diketones concentration. Data show that yeast biomass does not grow at 5 °C and at inoculum concentration of 107 CFU cm−3, which makes fermentation impossible. Fermentation kinetics using Monod's model supplemented with product inhibition was also investigated. Up to 1.7 % of alcohol accumulates in the beer in some of the variants within 7 days. At low fermentation temperatures, yeast biomass utilizes part of the substrate to maintain its vital activity under stress fermentation conditions, which leads to a reduction in the amount of alcohol synthesized. The synthesis and reduction of the secondary metabolites was delayed compared to conventional beer fermentation. The sensory evaluation of the beers produced showed that the most appealing beer was the one produced at 10 °C and pitching rate of 109 CFU cm−3.

In the context of growing interest for functional foods and cosmetic products, emulsified products such as dressings or lotions have been proposed to deliver probiotics and plant extracts with interesting biological (e. g. anti-inflammatory) properties due to their daily consumption or application on skin, respectively. Besides these positive effects, emulsified products containing water are often prone to microbial growth justifying thus the addition of preservatives such as parabens in their formulation. Safety concerns regarding some synthetic preservatives have stimulated the development of natural antimicrobial ingredients (namely from plant or microbial origin) for the preservation of food or cosmetic products. Besides direct addition of antimicrobial biomolecules, the addition of living bioprotective bacteria such as probiotic lactic acid bacteria (LAB) is a promising approach. Franco-Bulgarian ESCAPE project ambition is to identify synergistic combinations of such probiotic LAB and plant extracts for the preservation of food or cosmetic emulsions. The methodology and the relevant scientific questions (application of hurdle technology principles, selection of plant extracts not affecting LAB growth/viability and antimicrobial activity, distribution of LAB and antimicrobial metabolites in the different phases of emulsions, effect of LAB and plant extracts on emulsions stability…) to tackle this objective are presented and discussed.

Three different kinetic models – Monod’s model, Monod’s model with substrate inhibition, and Monod's model with substrate and product inhibition were developed for studying of beer fermentation with free and immobilized cells at different main fermentation and maturation temperatures. The most accurate model was Monod's model with substrate and product inhibition. It showed that maturation temperature had no effect on primary metabolism but it affected significantly the secondary metabolites production. In regard to carbonyl compounds and esters, the increase in maturation temperature led to different trends for free and immobilized cells. Regarding the higher alcohols, the increase in maturation temperature resulted in increase in their yield coefficients for both immobilized and free cells. A sensory evaluation of beers produced with free and immobilized cells were also carried out and the results showed similar results for two beer types.

Low-alcohol beer can be obtained by physical and biological methods. The group of biological methods includes modification of the mashing regimes and changes in the fermentation process. The aim of the present work was to study two mashing regimes for low-alcohol beer production. The increase in the mashing duration at 50 °C led to a linear increase in the extract and the concentration of reducing and fermentable sugars in the wort. It was found that the rate of formation of reducing sugars was higher than that of the formation of fermentable sugars, which can be used for the optimization of the mashing process. The introduction of a pause at 77 °C did not lead to a substantial increase in the concentration of fermentable extract, but did lead to an increase in the total and non-fermentable extract. The available nitrogen content in the laboratory wort was in the range of 120–150 mg/dm3. As a result of conducting fermentation processes with the top-fermenting yeast strain Saccharomyces cerevisiae S-33, it was found that the combination of a small amount of fermentable sugars and a low fermentation temperature led to a beer being obtained that met the requirements for a low-alcohol beverage. Copyright © 2016 The Institute of Brewing & Distilling

A study on the kinetics of alcohol fermentation for the production of beer with free and immobilized Saccharomyces cerevisiae Safbrew S-33 cells was conducted using three kinetic models. The process was best described by Monod model with product and substrate inhibition. The kinetic parameters showed a less pronounced impact on ester and higher alcohol accumulation, and enhanced influence of immobilization on carbonyl compound dynamics in beer. The profile of substrate and product concentration changes in the capsules were determined as well.