Effect of pretreatment on physicochemical, microbiological, and aflatoxin quality of solar sliced dried ginger (Zingiber officinale Roscoe) rhizome.

Pretreatment of fruit and vegetables is necessary to reduce microbial proliferation and to preserve color of the produce. The effect of drying and pretreatment with potassium metabisulfite (KMBS) of concentrations 0.0%, 0.1%, 0.15%, 0.2%, and 1.0% and blanching at 100°C and 50°C using a tent-like concrete solar (CSD) dryer as compared to open-sun drying (OSD) of yellow ginger rhizomes was investigated using routine methods. The total color change and residual sulfur dioxide (SO2) were analyzed. KMBS reduced the yeast and mould load significantly from 3.6 × 104 ± 1.4 × 103 CFU/g in 0.0% (control) to <10 CFU/g in 1.0% KMBS and 100°C blanched fresh samples. Drying of the fresh samples for 5 days increased the yeast and mould load of all the treatments to as high as 1.15 × 105 ± 2.12 × 104 CFU/g for the 1.0% KMBS. Overall, the CSD had fewer microbial loads than the OSD but it was not significant. Aflatoxins and Salmonella sp. were not detected in any of the samples. The sulfur dioxide residue (SO2) for KMBS pretreated samples increased as the concentration of KMBS increased with the CSD retaining slightly higher amount than the OSD. The total color change index increased with increase in KMBS, and drying further increased the total color change index. On the whole, the blanched samples had the least color change among the pretreatments with 100°C CSD showing the least change among the dried samples.