Uv 2101 spectrophotometer

The yeast growth was followed by periodic optical density measurement (640 nm) of the appropriately diluted culture samples in a Shimadzu UV-2101 spectrophotometer (Shimadzu, Kyoto, Japan) and by counting the colony-forming units in YPD plates after incubation at 30°C, for 48 h. Further, the yeast cell biomass was determined using 2 × 50 and 3×15 ml samples centrifuged in pre-weighed tubes for 10 min at 2300 × g, washed twice with sterile deionized water, dried for 24 h at 100°C, and stored in a desiccator before weighing.
To evaluate the viability of nitrogen-starved cells, a sample from each low-nitrogen fermentation was spread onto yeast carbon base (YCB, Difco) agar plates with 0.73 mg N l⁻¹ as amino acids: histidine.HCl (1 mg l⁻¹), methionine (2 mg l⁻¹) and tryptophan (2 mg l⁻¹). YCB was used to test the ability of yeasts to assimilate nitrogen by adding diverse nitrogen sources. The histidine, methionine and tryptophan concentrations were reduced to 10% of their original concentration in the yeast nitrogen base. This experiment was expected to detect viable cells in solid media without a nitrogen source.

Color intensity (CI) and hue were determined by the OIV method [35 ], total polyphenol index (TPI) was determined by Curvelo-Garcia method [36 ], total phenols, non-flavonoids and flavonoids were determined according to Kramling and Singleton [37 ]. Total anthocyanins were analyzed by SO₂ bleaching method, described by Ribéreau-Gayon et al., [38 ], colored anthocyanins (CA), total pigments (TP) and polymeric pigments (PP) were analyzed by the method described by Somers and Evans [39 (link)], and total tannins were determined by the LA method [40 ]. All samples were analyzed by a spectrophotometer (GENESYS^TM 10 series spectrophotometers). The absorption spectra of WW samples were recorded with a Shimadzu UV-2101 spectrophotometer (Shimadzu, Kyoto, Japan) scanned from a range between 380 and 770 nm, with 5 nm distance, using 1 cm path length quartz cells. Data were collected to determine L (lightness), a (redness), and b (yellowness) coordinates using the CIELab 1976 method. This allows reliable quantification of the overall color difference of a sample when compared to a reference sample (blank). Color differences can be distinguished by the human eye when the differences between $\Delta E_{ab}^{*}$ values are greater than two units, in accordance to Spagna et al. [41 (link)]. All analyses were performed in duplicate. Table 2 resumes the formulas used in this work.