Potassium hydroxide

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).

The β‐carotene was determined as described by Perez‐Lopez (2010 (link)) and Association of Official Agricultural Chemists (AOAC) (1980 ) with some modifications. Five grams (5 g) of the sample (raw, pickle, and relish products) in 1% butylated hydroxytoluene (BHT) (LOBA Chemie, India) was homogenized using a blender (Moulinex, China) for 5 min and placed into the falcon tube (BR Biochem, India). The homogenate was treated with 30 ml of solvent (50% hexane:25% acetone:25% ethanol) (LOBA Chemie, India) and then centrifuged at 4000 rpm at ambient temperature for 10 min. The supernatant was collected and filtered using Whatman No. 1 filter paper (Whatman International Ltd., India), and then was re‐extracted two times until the residue was colorless. The supernatant was combined, and the volume was recorded. The supernatant was saponified with 40% potassium hydroxide (LOBA Chemie, India) and left at ambient temperature for 12 h. The mixture was then transferred into the separating funnel and treated with the same volume of 10% w/v sodium chloride (LOBA Chemie, India) for removing moisture. The mixture was then shaken vigorously, and the upper phase was collected and dried over anhydrous sodium sulfate (LOBA Chemie, India). The β‐carotene content was estimated based on the standard curve of β‐carotene, and the result was expressed as mg/100 g (wet basis).

The materials used are manganese(ii) nitrate tetrahydrate (Mn(NO₃)₂·4H₂O, 99.99%, Sigma Aldrich), barium(ii) chloride dihydrate (BaCl₂·2H₂O, 99%, Loba Chemie), potassium permanganate (KMnO₄, 99%, Sigma Aldrich), strontium(ii) nitrate (Sr(NO₃)₂, 99.99%, Sigma Aldrich) and potassium hydroxide (KOH, 85%, Loba Chemie).