Valorization of Agricultural Waste into Nutrient-Rich Functional Powders: Proximate, Phytochemical and Microbial Assessment

Background: Agricultural waste generated from fruits and vegetables is often underutilized despite its potential as a source of valuable nutrients and bioactive compounds. This study aimed to evaluate the proximate composition, phytochemical profile, and microbiological quality of powders developed from selected agricultural waste materials to explore their potential as sustainable functional food ingredients. Methods: Agricultural residues, including cauliflower leaves, cauliflower stem, cabbage leaves, cassava peel, beetroot peel, white pumpkin seed, yellow pumpkin seed, banana peel, and orange peel were collected and processed into dried powders using standardized techniques. The prepared powders were analyzed for proximate composition, phytochemical characteristics, and microbial quality using standard analytical techniques. Results: Significant nutritional variations were observed among the developed powders. Cabbage leaf powder exhibited the highest carbohydrate content (61.58 g/100 g), while yellow pumpkin seed powder showed the highest protein (30.37 g/100 g) and fat contents (45.00 g/100 g). Cassava peel powder recorded the highest crude fiber content (15.41 g/100 g), whereas cauliflower leaf powder contained the highest ash content (15.50 g/100 g), indicating greater mineral availability. Phytochemical analysis confirmed the presence of bioactive compounds such as flavonoids, tannins, saponins, steroids, and alkaloids, highlighting their potential functional and therapeutic significance. Microbiological evaluation showed low total plate count (TPC) values ranging from 1.0 × 10³ to 2.8 × 10³ colony-forming units per gram (CFU/g), indicating acceptable microbial safety and storage stability. Conclusion: The findings demonstrate that agricultural waste materials can be effectively converted into nutrient-rich functional powders with promising nutritional, phytochemical and microbiological properties. Their utilization may support food waste valorization, development of sustainable functional food ingredients, environmental protection, and circular economy approaches.