Comparative Evaluation of Preservation Methods on the Microbiological and Proximate Indices of Onions (Allium cepa L.)

Onions (Allium cepa L.) are among the most widely utilized vegetables globally known for both their culinary and nutritional attributes. Despite their importance, onions are highly perishable and susceptible to quality degradation under suboptimal storage conditions, particularly due to fluctuations in humidity and temperature. This study evaluated the impact of three preservation techniques such as salting, drying, and freezing on the nutritional profile and microbiological safety of onion samples during storage. Fresh onions were processed into raw, salted, dried (as onion powder), and frozen forms. Proximate analyses were conducted to assess moisture, protein, ash, fat, fibre, and carbohydrate levels before and after storage. Standard microbiological procedures were used to determine total viable counts, coliforms, yeasts, and moulds, while microbial species were identified via morphological and biochemical characterization. Results showed a marked reduction in moisture content in dried onions, which correlated with increased concentrations of protein and carbohydrates. Salting significantly suppressed microbial proliferation, including coliform and fungal populations. Although freezing preserved initial moisture levels, it was associated with increased fungal activity, likely due to intermittent thawing. The most frequently isolated microorganisms included Pseudomonas spp. and Staphylococcus spp., as well as Penicillium, Rhizopus, and Aspergillus species. Overall, salting and drying proved most effective in enhancing shelf life and maintaining product quality.