KOH-Catalysed Methanolysis of Pawpaw Seed Oil: Taguchi Screening, Independent Confirmation and Product Characterisation

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Pawpaw processing generates a seed residue containing an extractable non-food oil. KOH-catalysed methanolysis of pawpaw seed oil was investigated using a four-factor, three-level Taguchi L9 array. Reaction time (45–65 min), temperature (40–60 °C), KOH loading (0.5–2.5 wt.%) and methanol-to-oil molar ratio (6:1–12:1) were evaluated using recovered ester-rich product yield as the response. Screening yields ranged from 80.3 to 98.8 wt.%. Temperature and KOH loading accounted for 46.50% and 42.05% of the corrected L9 variation, respectively, compared with 11.26% for methanol-to-oil ratio and 0.19% for time. The selected condition, 45 min, 60 °C, 2.5 wt.% KOH and a 12:1 ratio, gave 98.10 ± 0.44 wt.% in three independent confirmation runs, 0.70 percentage points below the additive estimate. FTIR bands at 1741.98, 1432.8 and 1195.22 cm−1 showed the expected ester and methyl-associated functional groups. GC-MS showed diagnostic m/z 74 and 87 ions and tentative assignments to several fatty-acid methyl esters. This study demonstrates an efficient screening and confirmation framework for converting discarded pawpaw seeds into an ester-rich renewable-fuel product.