Proizvodnja i ocena kvaliteta voćnog vina od sorti domaće šljive (Prunus domestica L.) | Production and quality assessment of fruit wines from native plum (Prunus domestica L.) varieties

The aim of this PhD thesis was to assess the possibility of using three native plum varieties, with different ripening periods (Ĉaĉanska rana, Ĉaĉanska lepotica and Poņegaĉa), as raw material for the production of fruit wines. Determined mechanical composition and chemical characteristics of fruit pomace and juice indicate that the Ĉaĉanska lepotica and Poņegaĉa are considered as better raw materials for the production of fruit wine compared to Ĉaĉanska rana. Optimization of fermentation conditions (temperature, pH, the duration of fermentation and the dose of pectolytic enzyme) was conducted. This step also included investigation of the different pectolytic enzymes use for the treatment of pomace and evaluated the impact of using different yeast strains, as well as the effect of different production microorganisms on the plum wine quality. It was found that, among the tested production microorganisms, Spriferm (S. cerevisiae) yeast gives the plum wine of best quality. Numerical optimization procedure resulted with the following values of the process parameters of plum wine fermentation: temperature 25 °C, pH value 3.5 and pectolytic enzyme dose of 0.5 g/100 kg. Under these conditions the obtained fitted models predict the ethanol yield of 7.5% v/v, glycerol yield 5 g/l, the wine yield of 48% (48 ml from 100 g of pomace) and the formation of 710 mg/l of methanol. Characterization of the produced plum wines included the determination of the most important ingredients: alcohol, acids, minerals, phenolic and aromatic compounds, as well as evaluation of their functional characteristics (antiradical, antimicrobial and antiproliferative activities). Finally, the possibility of reducing the methanol production in plum wine was estimated by applying different physico-chemical treatments of the pomace. Significantly higher efficiency of procedures that involve some form of heat treatment of pomace, compared to treatments which involve the use of certain oenological means, was observed.