Cary 100 uv visible spectrophotometer

The levels of secondary saffron metabolites (picrocrocin, safranal, and crocin) were measured according to ISO 3632‐2 (2010 ) using the Cary 100 UV‐Visible Spectrophotometer (Agilent Technologies, the USA). For this purpose, 500 mg of each sample was ground, and after transfer to a 1000 ml volume balloon, 900 ml of distilled water was added to it. It was then mixed with a magnetic stirrer for 1 h at a speed of 1000 rpm. The solution's volume was increased to 1000 ml with distilled water and stirred again to obtain a uniform solution. Twenty milliliters of the resulting solution was brought to a volume of 200 ml. The solution was filtered, and after obtaining a clear solution, the amount of absorption was recorded at wavelengths of 200 to 700 nm relative to the reference (distilled water). The results are obtained by a direct reading of the specific absorbance at three wavelengths, as follows:
Absorbance at about 257 nm (λ max of picrocrocin), 330 nm (λ max of safranal), and 440 nm (λ max of crocin) (ISO, 2010 ). $$A_{1\mathrm{cm}}^{1\%}=\frac{D\times 10000}{m\times (100‐w_{\mathit{MV}})}$$
A1cm1% is the absorbance at the maximum wavelength of secondary saffron metabolites for a 1 g/100 ml solution of test sample using a 1‐cm quartz cell; D is the specific absorbance; m is the mass, in grams, of the test portion; w_MV is the moisture and volatile matter content, expressed as a percentage mass fraction, of the sample.

The volume phase transition temperatures (VPTTs) of the NGs were determined by turbidimetry assay, i.e., by measuring the light transmittance (at 500 nm) of the NG solutions as a function of temperature. The NG solutions, with concentration equal to 1 mg/mL, were prepared by dissolution of the dry NG in either deionized water or fish water followed by 10 min sonication and filtration with 0.2 μm PTFE syringe filters. The measurements were carried out in a temperature range between 25 and 65 °C, at a rate of 0.5 °C/minute, using a Cary 100 UV-Visible Spectrophotometer (Agilent Technologies, Santa Clara, CA, USA) coupled with a temperature controller. The raw data were analyzed using Origin2018 software, which allowed the plotting and fitting of the transmittance-temperature data with the sigmoidal Boltzmann fitting. For each measurement, the VPTT was considered equal to the temperature at which the curve presented its inflection point, after verifying the accuracy of this fitting in terms of adjusted R² (≥0.99).