2.5. Determination of pH and Titratable Acidity

The pH of WM and SM samples with fucoxanthin and their controls without fucoxanthin was determined throughout the four week storage period using an Accumet benchtop pH meter (Fisherbrand™ Accumet™ AE150, Fisher Scientific, Pittsburgh, PA, USA) at 22 °C. The reference buffers (4.00 and 7.00; Orion buffer solutions; Thermo Fisher Scientific, Pittsburgh, PA, USA) that were used for the calibration of pH meter and the analyzed milk samples were at room temperature (22 °C). The titratable acidity in the milk samples was determined according to the AOAC method No 947.05 [24]. Briefly, to each 20 mL sample of goat milk, a 40 mL of boiled and cooled distilled water was added. Phenolphthalein (1% w/v in 95% ethanol) was used as an indicator. The mixture was titrated with standardized 0.1 N NaOH until the first color change, which signals the endpoint (at pH 8.1–8.3), persisted for 30 s. One more drop of 0.1 N NaOH was added and the final volume of NaOH used for titration was recorded. The results were expressed in percentage of lactic acid. The pH and titratable acidity in the samples were determined in triplicate.