Phenolphthalein indicator

Citrullus colocynthis (CC) fruits were collected from Wadi Hanifa in the Al-Diriyah region (Riyadh, Saudi Arabia) in February 2021. N-hexane (purity ≥ 99% (GC), Honeywell^®, Seelze, Germany) was used as a solvent. Methanol (purity 99.8% (GC), Sigma Aldrich^®, Steinheim, Germany), acetone (purity ≥ 99.5%, Sigma Aldrich^®), aqueous hydrogen peroxide (30 wt.%, Sigma Aldrich^®), glacial acetic acid (purity ≥ 99.8%, Fisher^®Chemical, Loughborough, UK), sulphuric acid (95–98%, Panreac^®, Barcelona, Spain), hydrochloric acid (37%, Panreac^®), diethyl ether (purity ≥ 99.8%, Sigma Aldrich^®), and anhydrous magnesium sulfate (purity ≥ 98%, Panreac^®) were used as supplied. The reagents were required for the determination of hydroxyl and acid value such as potassium hydroxide (purity as KOH ≥ 85%, Loba Chemie^®, Maharashtra, India), ethanol absolute (purity ≥ 99.97%, CHEM-LAB^®, Zedelgem, Belgium), n-butanol (purity ≥ 99%, Loba Chemie^®), pyridine (purity ≥ 99.5%, Loba Chemie^®), acetic anhydride (purity ≥ 99.7%, VWR^®, Fontenay-sous-Bois, France), and phenolphthalein indicator (purity ≥ 99%, Loba Chemie^®). The materials required for film formation, such as BYK-333 as a surface tension reducer, were purchased from Al-Azzaz Chemicals company (Riyadh, Saudi Arabia) and 3HDI isocyanurate from Sigma Aldrich (Sigma Aldrich).

Titratable acidity (TTA) was determined, as described by Rajković et al. (2007 (link)). About 10 ml of brine solution from spontaneously and controlled fermented Ss and Sv was mixed with 10 ml of distilled water in a conical flask. The mixture was titrated with 0.1N NaOH using two drops of phenolphthalein indicator (LOBA Chemie, India) to a persistent pink end. TTA was calculated in terms of LA anhydrous as follows: $$\mathrm{TTA}(\%)=0.09\times \mathrm{Titer}(\mathrm{ml})$$