Uv 2500 spectrophotometer

Polysaccharides with triple-helical chain conformation can form complexes with Congo red (CR), and the maximum wavelength of the complexes is redshifted, compared with CR. Therefore, CR can be used to detect whether the triple helix structure of polysaccharides is destroyed. In accordance with the description by Hou [25 (link)], the CR test method was as follows: 2 mg CR was dissolved in 100 mL of water, to prepare the CR solution. Next, 10 mg of paramylon powder was dissolved in 1.0 mol/L NaOH solution, which was then diluted with distilled water, until the NaOH concentration was 0.1~0.5 mol/L. Equal volumes of CR solution with NaOH aqueous solution containing polysaccharides were mixed well, and distilled water was used as control. The mixture was immediately scanned with a Shimadzu UV-2500 spectrophotometer (Shimadzu, Kyoto, Japan) in the wavelength range of 200 nm~800 nm, and the maximum absorption wavelength was determined.

The soluble protein content of the okara beverages was determined using the Coomassie brilliant blue method (Sheih et al., 2014 (link)), with BSA (bovine serum albumin) used as the standard. The soluble protein content in the samples was expressed in BSA equivalents (mg/mL). Free amino acids were detected based on previous research methods with minor modifications (Liu et al., 2018 (link)), using glycine as the standard. Absorbance was measured at 570 nm using a UV‐2500 spectrophotometer (Shimadzu, Tokyo, Japan).

β-Lactamase activity in the S. algae clade isolates was evaluated. First, the isolate of interest was inoculated into LB broth (Becton Dickinson and Co.) and incubated for 24 h with shaking at 160 rpm and 37°C. After incubation, 10 ml of the culture medium was centrifuged at 3,500 × g for 15 min at 4°C. After the supernatant was discarded, the pellet was washed with 500 μl of phosphate-buffered saline (PBS) (pH 7.0) and recentrifuged at 13,000 × g for 1 min at 4°C. After resuspending the pellet in 500 μl of PBS, the crude enzyme solution was prepared by sonication and subsequent centrifugation at 13,000 × g for 30 min at 4°C. The protein concentration was measured by the Bradford method using bovine serum albumin (BSA) (Bio-Rad Laboratories, Inc., Hercules, CA) as a standard. The change in absorbance over time caused by the hydrolysis of β-lactam by β-lactamase was measured using a Shimadzu UV-2500 spectrophotometer (Shimadzu, Kyoto, Japan). The β-lactams used as the substrates for β-lactamase were adjusted to a final concentration of 100 μM in PBS. All reactions were performed in a Bandpass 10-mm cuvette with a total volume of 5 μl of enzyme added to 500 μl of substrate solution at 30°C.

The optical rotations were detected at 20°C using MCP 5100 digital polarimeter (Anton Paar, Graz, Austria). The UV data were recorded on a Shimadzu UV-2500 spectrophotometer (Shimadzu, Kyoto, Japan). The Chirascan CD spectrometer (Applied Photophysics Ltd., Surrey, UK) was used to acquire ECD spectra. 1D and 2D NMR spectra were recorded on a Bruker AVANCE III 500 M NMR spectrometer (Bruker BioSpin Corporation, Billerica, USA). UPLC-Q-TOF/MS analysis was carried out on a Waters ACQUITY UPLC system (Waters Corporation, Milford, USA) equipped with an AB SCIEX Triple TOF 5600 mass spectrometer with electrospray ionization source (ESI; Framingham, MA, USA). Silica gel (200–300 mesh, Qingdao Marine Chemical Inc., Qingdao, China), RP-C₁₈ silica gel (Merck KGaA, Darmstadt, Germany), and Sephadex LH-20 gel (GE Healthcare Bio-Sciences AB, Uppsala, Sweden) were employed for column chromatography (CC). High-performance liquid chromatographies (HPLCs) were performed on Agilent 1260 series (Agilent Technologies, Santa Clara, USA) with C₁₈ reversed-phase columns (YMC, Kyoto, Japan; 250 × 4.6 mm i.d., 5 μm, for analysis; 250 × 10 mm i.d., 5 μm, for separation).

Thickness of film was measured by digital external micrometer (Mitutoyo Co., Kawasaki, Japan) and the overall thickness was expressed as an average generated randomly from each film at 15 different points.
The transmittance (%) of the films was measured by a Shimadzu UV-2500 spectrophotometer (Tokyo, Japan). Film was cut into 1 × 4 cm rectangular pieces. Then the cut films were fixed to one side of a spectrophotometer cell. An empty cell was used as control. Three duplications were performed for each film to guarantee the accuracy. The transparency of sample was measured at 600 nm. Relative transparency, which was an approximation, was calculated according to Formula (1): $\mathrm{Transmittance}(\%)=(\frac{T_{600}}{\mathrm{d}})\times 100$
where T₆₀₀ is transparency of the film at 600 nm; d is the averaged thickness (mm).
A Minolta colorimeter (Cr 410, Konica Minolta, Tokyo, Japan) was used to measure the color parameters of the films with a standard white plate applied for calibration. The results were expressed according to the CieLab color system, where L* was 0 for black and 100 for white, a* represented red (+) to green (−), and b* values indicated yellow (+) to blue (−). The mean values were then calculated.

The synthetic product solution was diluted 20× with phosphate buffer solution (pH 7.0), and absorbance at 420 nm was measured using UV-2500 spectrophotometer (Shimadzu, Japan). All measurements were performed in triplicate. Distilled water comprised the blank sample.