Optimization and physicochemical characterization of citrus peel slice jam for sustainable food waste valorization / Wan Fatimah Wan Mohd Nowalid

Faculty of Industrial Sciences and Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang - 2026

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Food waste is a critical global concern with profound environmental, economic, and social implications. Citrus peel, a significant by-product of the citrus processing industry, is often discarded despite its richness in bioactive compounds. This research explores the valorization of citrus peel waste through the development and characterization of a novel citrus peel slice jam, offering a sustainable solution to food waste and aligning with global Sustainable Development Goals (SDG 12). The study primarily aimed to evaluate the effectiveness of osmotic dehydration as a pre-treatment method, optimize the jam formulation using statistical modeling, characterize its physicochemical and antioxidant properties, and assess sensory acceptability and shelf life. Citrus sinensis peel was subjected to osmotic pre-treatment and analyzed via UPLC-QTOF MS to determine changes in bioactive compounds. Multivariate analysis, particularly Principal Component Analysis, was used to evaluate compositional variation. Two-Level Factorial Design and Central Composite Design were employed to optimize the formulation, focusing on peel concentration, sugar, and pectin content. The optimized jam formulation (25% peel concentration, 1.0% citric acid, and 1.5% pectin) demonstrated significant physicochemical properties: pH 3.26, hardness 96.4 mJ, moisture content 29.9%, total phenolic content 3.02 mg GAE/g, and vitamin C 22.48 mg/100g. Antioxidant activity measured by DPPH assay showed 67.85% inhibition, indicating high functional potential. Shelf-life evaluation confirmed microbial stability up to 100 days of storage at ambient conditions, with total aerobic microbial counts and yeast or mould counts remaining within acceptable limits. Sensory analysis revealed high consumer acceptability, particularly for visual appeal, chewiness, and overall taste, supporting the market potential of the product. This research contributes to scientific knowledge on food waste upcycling, introduces a novel sliceable jam format inspired by cheese slices, and offers practical insights for the food industry. It presents a scalable, environmentally conscious approach to utilizing citrus waste, promoting sustainable food innovation and circular economy principles.