Drying of Eggplants and Assessment of Product Quality

Abstract

Eggplants (Solanum melongena L.) are a rich source of nutrients like dietary fibre, vitamins, protein and and micronutrients. They also contain various phytochemical compounds such as phenolics, tannins and flavonoids. They are highly perishable due to their high moisture content. This study investigated the effect of pretreatment (sodium metabisulphite) and oven drying on quality attributes in terms of nutrients, phytochemical compounds, functional properties including the drying behavior of African eggplants. Samples were dried up to ~11% moisture. The fresh and dried samples were analyzed for total phenolic content, tannins content, flavonoid content and proximate composition using standard methods. The sensory acceptability of the fresh and dried eggplants was also investigated. Results from sensory analysis indicated that fresh eggplants were preferred to dried ones. Results for drying behavior showed that untreated eggplants dried faster than the pretreated ones. On fitting the experimental results for moisture ratio into different drying models, page model had the best fit for both the samples due to its highest R2 values (R2 = 0.9671, R2 = 0.9588 for the control and pretreated respectively). Pretreated eggplants showed improved rehydration capacity compared to untreated samples, possibly because sodium metabisulphite mitigated structural damage from heat-induced cell wall collapse and case hardening. Oven drying significantly altered eggplant nutrient composition, reducing moisture (91.14% to 11.25%) and enhancing storage stability. Protein and fat content reduced, possibly due to interactions with other food components limiting their extraction, while ash content and carbohydrate increased. Phytochemical changes included reduced phenolic/tannin content (likely from enzymatic oxidation and heat) but elevated flavonoids via cellular disruption. Drying conditions and pretreatment (e.g., sodium metabisulphite) require optimization to balance nutrient and phytochemical retention with other properties.