DRYING CHARACTERISTICS OF PAWPAW (CARICA PAPAYA) SEED AND THE EFFECT OF PROCESSING FACTORS ON THE NUTRITIONAL/PHYSICOCHEMICAL PROPERTIES OF PAWPAW SEED OIL

Abstract

ABSTRACT Pawpaw (Carica papaya) seeds, often treated as agricultural waste, are a rich source of oil (25–34%) and contain valuable bioactive compounds such as benzyl isothiocyanate, phenolics, and flavonoids. This study investigated the drying characteristics of pawpaw seeds and examined how heating and expression temperatures affect the yield and quality of the extracted oil. The study employed a 2×3×3 factorial experimental design to evaluate the effects of drying methods (oven-drying at 40, 50, and 60°C; ambient air-drying) and expression temperatures (180, 200, and 220°C) on oil yield and quality. Ripe and unripe pawpaw seeds were collected, cleaned, and dried to determine moisture content and drying kinetics. Oil was extracted using an electric press, and the yield was calculated. The oil was analyzed for physicochemical properties (saponification value, free fatty acids, peroxide value, iodine value, pH, pour point, refractive index, specific gravity), proximate composition (moisture, protein, ash, carbohydrates, energy), and phytochemical content (total phenols, flavonoids). Drying kinetics were modelled using moisture ratio (MR), drying rate (DR), and effective moisture diffusivity (Deff). Oil quality parameters were assessed using standard Association of Official Agricultural Chemists (AOAC) and American Society for Testing and Materials (ASTM) methods. Results showed that oven-drying at 60°C significantly reduced drying time, but it also risked degrading heat-sensitive compounds. Ambient air-drying was slower but preserved more bioactive components. The Midilli-Kucuk model best described the drying behaviour. The highest yields were obtained from ripe seeds that were air-dried and expressed at 200°C (37.14%). Unripe seeds required higher expression temperatures (220°C) to achieve comparable yields (34.28%). Overheating (>200°C) reduced yields due to thermal degradation. Oil from seeds dried at 50°C showed good quality, with low free fatty acids (0.91%) and peroxide value (1.62 meq O₂/kg), v

indicating stability. Its high viscosity (45.2 mPa•s) makes it suitable for cosmetic use. In contrast, oil from ripe seeds dried at 60°C and expressed at 220°C had the highest saponification value (223.13 mg KOH/g), iodine value (73.51 g I₂/100g), and refractive index (1.47). These values suggest the oil contains short-chain fatty acids ideal for soap making, has good unsaturation levels beneficial for skin care, and a molecular structure suitable for cosmetic and pharmaceutical applications. Phytochemical analysis revealed that higher retention of phenols (301.11 mg/100 mg) and flavonoids (99.30mg/100mg) occurred. In air-dried samples. The study showed that drying and expression temperatures significantly (p < 0.05) influenced pawpaw seed oil yield and quality, with oven-drying at 50°C combined with expression at 200°C providing the best balance between efficiency and oil quality for ripe seeds, while unripe seeds require higher expression temperatures and ambient air-drying, though slower, preserves bioactive compounds better. These findings provide a foundation for optimizing industrial-scale pawpaw seed oil extraction, promoting sustainable utilization of this underutilized by-product.