Analiza metaboličke aktivnosti bakterija mliječne kiseline i kvasaca u modelnim uzorcima kefira pripravljenim od kozjeg mlijeka i mješavina kozjeg i kobiljeg mlijeka na temelju promjena električne vodljivosti i otpora

The aim of this study was to analyse the metabolic activity of lactic acid bacteria and yeast based of changes in electrical conductivity and electrical impedance during fermentation of goat milk and mixtures of goat’s milk and mare’s milk (1:1, 1:2). As a result of fermentation, conductivity increased 1.4-fold. The conductivity of kefir prepared from goat and mare milk mixed at a ratio of 1:2 (6.210 Ω-3∙cm-1) was lower than that of the 1:1 mixture or of goat milk alone (7.242 Ω-3∙cm-1). A significant dependence of electrical conductivity and pH (0.970 ≤ r ≤ 0.993) was recorded during fermentation. The addition of mare milk to goat milk significantly slowed down the growth of LAB (Δλ = 0.8 h) and yeasts during kefir production.Cilj ovog istraživanja bio je ispitati metaboličku aktivnost bakterija mliječne kiseline i kvasaca na temelju promjena u električnoj vodljivosti i otporu izmjerenim tijekom fermentacije kozjeg mlijeka i mješavina kozjeg i kobiljeg mlijeka (1:1, 1:2). Uslijed fermentacije električna vodljivost povećala se 1,4 puta. Vodljivost kefira napravljenog od mješavine kozjeg i kobiljeg mlijeka u omjeru 1:2 (6,210 Ω-3∙cm-1) bila je manja u usporedbi s električnom vodljivosti kefira pripravljenog samo od kozjeg mlijeka (7,242 Ω-3∙cm-1), odnosno od mješavine kozjeg i kobiljeg mlijeka u omjeru 1:1. Tijekom fermentacije utvrđena je statistički značajna ovisnost između električne vodljivosti i pH vrijednosti (0,970 ≤ r ≤ 0,993). Dodavanje kobiljeg mlijeka kozjem mlijeku značajno usporava rast bakterija mliječne kiseline (Δλ = 0,8 h) i kvasaca tijekom proizvodnje kefira

Effects of Different Techniques of Malolactic Fermentation Induction on Diacetyl Metabolism and Biosynthesis of Selected Aromatic Esters in Cool-Climate Grape Wines

The effects of different malolactic bacteria fermentation techniques on the bioconversion of aromatic compounds in cool-climate grape wines were examined. During three wine seasons, red and white grape wines were produced using various malolactic fermentation induction techniques: Coinoculation, sequential inoculation, and spontaneous process. Volatile compounds (diacetyl and the products of its metabolism, and selected ethyl fatty acid esters) were extracted by solid phase microextraction. Compounds were identified with a multidimensional gas chromatograph—GC × GC-ToFMS with ZOEX cryogenic (N2) modulator. Sensory evaluation of the wines was also performed. It was found that the fermentation-derived metabolites studied were affected by the malolactic bacteria inoculation regime. Quantitatively, ethyl lactate, diethyl succinate, and ethyl acetate dominated as esters with the largest increase in content. The total concentration of ethyl esters was highest for the coinoculation technique, while the highest concentration of diacetyl was noted for the spontaneous technique. Controlled malolactic fermentation, especially using the coinoculation technique, can be proposed as a safe and efficient enological practice for producing quality cool-climate grape wines enriched with fruity, fresh, and floral aromas

Influence of green tea added to Cherry wine on phenolic content, antioxidant activity and alpha-glucosidase inhibition during an In vitro gastrointestinal digestion

Cherries are a good source of bioactive compounds, with high antioxidant activity as well as nutritional and therapeutic importance. In this study, cherry wines enriched with green tea infusion (mild and concentrated) were produced, and their biological properties were evaluated. During winemaking, the main vinification parameters (alcohol, reducing sugars, acidity, total polyphenol content) as well biological activity (antioxidant activity, alpha-glucosidase inhibition potential) were determined. An in vitro digestion process was also performed to evaluate the impact of the gastrointestinal environment on the biological stability of the wines, and to analyze the interactions of wine-intestinal microflora. The addition of green tea to the cherry wine significantly increased the total polyphenol content (up to 2.73 g GAE/L) and antioxidant activity (up to 22.07 mM TE/L), compared with the control wine. However, after in vitro digestion, a reduction in total polyphenols (53–64%) and antioxidant activity (38–45%) were noted. Wines fortified with green tea expressed a stronger inhibition effect on intestinal microflora growth, of which E. coli were the most sensitive microorganisms. The tea-derived bioactive compounds significantly increased the potential of alpha-glucosidase inhibition. The proposed wines could be a good alternative type of wine, with an increased polyphenol content and the potential to control the insulin response supporting therapy for diabetes