Development of dried African nightshade products for post-harvest loss reduction and shelf-life extension in Tanzania

Abstract

African nightshade (ANS) is a luminary food plant, considered a cheap and potential dietary source for micronutrients and bioactive compounds. Lack of value addition on ANS, results to high availability of ANS during peak season and shortage in off-season was the great demand for developing dried products. This study evaluated the effects of drying techniques on nutritional (minerals & vitamin C) and anti-nutritional (oxalate & phytate) contents of Solanum scabrum (SS) and S. villosum (SV). Three methods of drying namely indirect solar drying (ISD), mixed solar drying (MSD), and open sun drying (OSD) were employed. Furthermore, blanching (85°C, 2 min) with and without 3% salt (NaCl) were used as pre-treatments for ANS. The effect of pre-treatment methods on nutrient retention and anti-nutrients removal was also recorded. From the results ISD was the most effective method for vitamin C (14.76% 19.2%), Ca (92.90%, 96.57%), Fe (77.88%, 71.54%), and Zn (86.94%, 90.09%) retention for both SS and SV leaves, respectively. On the other hand, all drying methods significantly reduced levels of oxalate (4.46% to 35.24% ) and phytate (52.12% to 85.55%). Pannelists rated dried ANS significantly ≤ 0.05 higher for texture, colour, taste, aroma, bitterness and overall acceptability. Shelf life studies of dried products were stable at ambient and refrigeration storage for a period of three months with no growth of bacteria, yeast and mold, with significance loss of Vitamin C under both conditions. The findings showed that the ISD best method for vitamin C, minerals retention and anti-nutritional reduction.