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    Interactive effect of pre-fermentative grape freezing and malolactic fermentation on the anthocyanins profile in red wines prone to colour instability
    (Springer Nature, 2023-08-01) Darnal A; Poggesi S; Ceci AT; Mimmo T; Boselli E; Longo E
    The effects of pre-fermentative freezing of red grapes from Schiava variety and co-inoculation with lactic bacteria were evaluated on the profile of anthocyans of the musts and the finished wine. Peonidin-3-glucoside is the main anthocyanin in Schiava grape musts, but it was overcome by malvidin-3-glucoside at bottling. Grape freezing increased the extraction of all anthocyanins in the musts. However, the amount of all anthocyanins except peonidin-3-glucoside and malvidin-3-glucoside was lower in wines from frozen grapes than in control wines. Wines obtained with co-inoculation showed higher anthocyanin content than their respective controls. Petunidin-3-(6′′-p-coumaroyl)-glucoside, peonidin-3-(6′′-cis-p-coumaroyl)-glucoside and malvidin-3-(6′′-trans-p-coumaroyl)-glucoside were dramatically affected by the interaction of the two applied factors. Colorimetric hue (H*) was strongly correlated with peonidin-3-glucoside, and spectrophotometric tint (N) with malvidin-3-glucoside. Tint also showed a positive correlation with malolactic fermentation. Graphical abstract: [Figure not available: see fulltext.]
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    An improved MTT colorimetric method for rapid viable bacteria counting
    (Elsevier BV, 2023-11) Xu W; Shi D; Chen K; Palmer J; Popovich DG
    The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay has been employed in the analysis of bacterial growth. In comparison to experiments conducted on mammalian cells, the MTT bacterial assay encounters a greater number of interfering factors and obstacles that impact the accuracy of results. In this study, we have elucidated an improved MTT assay protocol and put forth an equation that establishes a correlation between colony-forming units (CFU) and the amount of formazan converted by the bacteria, drawing upon the fundamental principle of the MTT assay. This equation is represented as CFU=kF. Furthermore, we have explicated a methodology to determine the scale factor "k" by employing S. aureus and E. coli as illustrative examples. The findings indicate that S. aureus and E. coli reduce MTT by a cyclic process, from which the optimal reduction time at room temperature was determined to be approximately 30 mins. Furthermore, individual E. coli exhibits an MTT reduction capacity approximately four times greater than that of S. aureus. HPLC analysis proves to be the most accurate method for mitigating interferences during the dissolution and quantification of formazan. Additionally, this study has identified a new constraint related to the narrow linear range (0-125 μg/mL) of formazan concentration-absorbance and has presented strategies to circumvent this limitation.