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Opis: In our graduation seminar, we studied the effects of extended maceration of grape mash on polyphenol extraction in white wine production. Data from the literature show that grape variety plays an important role in the influence of the skin contact procedure on the extraction of phenolics. The polyphenol content of Chardonnay was improved by 24-hour cryomaceration of the mash at 8.0°C and 6.0°C, whereas no such effect was observed at 4.0°C. In the case of Malvasia, the maximum amount of caftaric and caffeic acid was obtained after 21 days of post-fermentation maceration at 16.0°C. These findings underscore the potential of controlled maceration to enrich white wines with greater complexity and antioxidant capacity. However, polyphenols are very susceptible to oxidation, especially during the initial stage of grape processing, leading to the formation of brown pigments and an amber color in such wines, which may also occur during the aging process if the phenolic-rich white wine is not sufficiently protected by other antioxidants. The changes in phenolics during prolonged maceration or aging of vintage white wines are not yet well understood. Further research is needed to elucidate the chemical reactions and transformations of polyphenols during prolonged skin contact and aging in order to develop targeted approaches to produce high-quality white wines with prolonged maceration of the mash with desirable sensory and health-promoting properties.
Ključne besede: polyphenols, white wine, skin contact, winemaking procedures
Objavljeno v RUNG: 19.08.2024; Ogledov: 559; Prenosov: 0
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Opis: A number of indigenous yeast strains isolated from vineyard / cellar-associated samples and non-vineyard sites, from forests with oak trees (a known habitat where Saccharomyces species resides) from existing in-house yeast collection and from ZIM culture collections (Slovenia) were screened for enzymatic activities with enological importance. The yeasts were screened for glycosidase enzymes connected to terpene aroma release, the β-lyase activity responsible for the volatile thiol release, and sulfite reductase activity involved in off-flavours. Yeast strains that showed positive results for qualitative and quick detection of glucoside hydrolase activity on plates were selected for further studies. The glucoside hydrolase activity of 20 selected strains belonging to 15 different species was quantitatively characterized by determinations of the activity on pNPG. All strains demonstrated hydrolase activity, especially strain H. uvarum 116 which showed the highest value of specific activity 6.32 mU/mg for cell-associated activity and T. delbrueckii Sut 94 with highest value of specific activity 1.36 mU/mg for extracellular activity. Increased growth of tested yeast on medium containing substrate S-methyl-L-cysteine indicated β-lyase activity, and by this approach a moderate activity was recorded throughout our tested strains with immense intraspecific inconsistency. Noticeable H2S production was observed in P. manshurica strain whereas, H. uvarum, L. thermotolerance, S. bayanus and S. cerevisiae demonstrated weak/slight H2S-producer strains in our study. Therefore, our screening indicates the importance of strain selection for enological application due to intraspecies differences, as well as the introduction of non-Saccharomyces yeast starters with interesting potential to enhance wine aroma.
Ključne besede: wine yeasts, non-Saccharomyces, enzymatic activities
Objavljeno v RUNG: 08.05.2023; Ogledov: 1605; Prenosov: 0
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Opis: Different analytical methods were tested and optimized for the determination of four biogenic amines (BA) histamine, putrescine, cadaverine and tyramine produced by grape-associated lactic acid bacteria (LAB). Autochthonous LAB were isolated from ‘Refošk’ grapes belonging to Slovenian-Italian Karst region as they represent a potential pool of beneficial LAB starter bacteria for improving the typicality and quality of wine. Six isolated strains were screened by multiplex PCR, of which four strains were positive for BA-forming genes (MKBT-49, MKBT-282, MKBT-568, MKBT-570). The production of BA was evaluated by thin-layer chromatography (TLC), high-performance liquid chromatography coupled to diode array detection (HPLC-DAD) and enzymatic method. The HPLC-DAD results showed that strain MKBT-49 (tyrdc+) had high tyramine production (386.6 ± 0.14 mg/L), which was confirmed by TLC. The ability to produce putrescine was confirmed in strain MKBT-282 by PCR, HPLC-DAD (16.4 ± 1.72 mg/L), and TLC. Histamine-producing ability was detected in strain MKBT-570, with a concentration below the limit of detection of the HPLC-DAD (<0.2 mg/L), while the other two methods were not sensitive enough for confirmation. This study shows that the production of BA can detected in native LAB and that relatively simple method such as TLC can be used effectively for the initial screening.
Ključne besede: grapes, wine-like matrices, biogenic amines, autochthonous lactic acid bacteria, analytical methods
Objavljeno v RUNG: 03.01.2022; Ogledov: 2449; Prenosov: 9
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Opis: The packaging is often a way of product communicating with its' consumer. Nowadays there are tons of different styles and ways to label the product to attract new customers. For every market, there is a certain way of packaging and developing a brand of the products due to the difference of the culture, lifestyle and habits. Our work aimed to determine the preferences of Chinese female consumers on various styles of Slovenian wine labels. Slovenian wines are still a rare guest on the shelves of the Chinese market. Thus, this research work gives us an opportunity of finding the best way of entering the market with a product from an unknown wine-producing country for the public and establish the brand. Due to the lack of information in this particular section, we have conducted an online survey to collect more precise data. Therefore, within the questionnaire we have used 5 wine labels from different Slovenian wine cellars with completely diversified design and styles, to compare customer's preferences. With the obtained online questionnaire it can be concluded that Chinese female consumers are most attracted to the whole package of the wine design from the wine's glass bottle, to its' shape as well as certain color preferences of the wine labels.
Ključne besede: packaging, wine label, brand, Slovenian wine label, Chinese market, Chinese female consumers
Objavljeno v RUNG: 15.03.2021; Ogledov: 4003; Prenosov: 183
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Opis: Lactic acid bacteria (LAB) are naturally present in grapes, musts and wines. During malolactic fermentation, besides the beneficial conversion of L-malic to L-lactic acid, LAB can form also other compounds like biogenic amines (BAs). BAs are formed through decarboxylation of corresponding amino acids, through the action of enzymes. Consumption of food containing BAs can lead to food poisoning such as histamine poisoning. Histamine, the most studied BA, is known to cause headaches, oedema, vomiting. In the last years, BAs associated pathways have been described as strain dependent and not as species dependent. Because of the high variability of microorganisms to decarboxylase amino acids, the detection of bacteria that have the possibility to transform precursor amino acid into BAs is very important in order to estimate the risk of BAs accumulation in wines. Since in previous years during project AGROTUR I we detected the higher BA content in some wines, we decided to focus on the presence of BA-producing LAB in Refošk grapes and wines. Therefore, during AGROTUR II project LAB collection of autochthonous lactic acid bacteria was set-up by isolating LAB from Refošk grapes and wines, originated from the grape growing cross-border region Karst (Slovenia). Over 600 isolates were obtained using MRS medium with added cycloheximide and 2% tomato juice. In parallel, also selective enrichment was performed using MRS medium described above with additionally added 5% ethanol. BA-producing LAB were primarily detected in microtiter-plate format using the decarboxylase screening medium with added amino acids (histidine, lysine, ornithine or tyrosine), which enable us to identify histamine-, cadaverine-, ornithine and tyrosine-producing LAB. Selected representatives from each BA-producing LAB groups were further on confirmed with chromatographic analysis (HPLC) and molecular methods (multiplex PCR method). BA-producing LAB were in majority represented by thyramin-producers, thereafter followed cadaverine-producers, with putrescine and histamine producers being the least presented. This screening of the BA-producing LAB is also incorporated in our on-going accurate selection of LAB starters for potential production of Refošk wines.
Ključne besede: biogenic amines, lactic acid bacteria, refošk, grape, wine
Objavljeno v RUNG: 22.01.2020; Ogledov: 4028; Prenosov: 0
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