Physicochemical properties, microbial loads and shelf life prediction of solar dried mango (Mangifera indica) and pineapple (Ananas comosus) in Tanzania

Abstract

Solar drying seems to be a feasible technique for preserving and extending the shelf life of perishable fruits all year round in developing nations like Tanzania. However, there have only been a few studies on the effect of solar drying on the microbiological load and shelf-life stability of dried fruits. The purpose of this study was to examine the effects of solar drying techniques on the physicochemical properties, microbial loads, and shelf life of dried mango and pineapple. Fruits were properly cleaned, peeled, cut into 5 mm-thick slices, and dried in cabinet mixed-mode and tunnel dryers for 3 and 2 days respectively. The dried samples were packaged in high- and low-density polyethylene bags and stored at 28 °C for six months before being analyzed for moisture, aw, pH, and total bacterial and fungal loads using standard methods. Shelf life was predicted by kinetic reaction and regression analysis methods. Tunnel-dried samples had significantly (p < 0.05) lower moisture (14.0 ± 0.00–15.1 ± 0.36 g/100 g), water activity (0.45 ± 0.1–0.47 ± 0.01), pH (3.5 ± 0.15–3.6 ± 0.17), total plate count (TPC) (3.4 ± 0.09 log10 CFU g−1) and fungal loads (3.0 ± 0.1–3.1 ± 0.1 log10 CFU g−1) than cabinet-dried samples with higher values. The TPC values in all samples were below the maximum allowable limits (5 log10 CFU g−1), but the fungal loads were slightly above the limits (3 log10 CFU g−1). There were no coliforms in any of the samples. Additionally, shelf lives of 38.2–41.5 and 33.2–34.6 months were predicted for tunnel-dried and cabinet-dried samples respectively in terms of microbiological stability. Solar drying improves the physicochemical qualities, reduces microbial load, and extends the shelf life of dried fruits; hence, its application for fruit preservation combined with further studies to establish drying and storage conditions that would reduce the fungal loads to safe lower levels are recommended.