Processing methods affect phytochemical contents in products prepared from orange-fleshed sweetpotato leaves and roots.

Phytochemicals enhance human health by acting antagonistically on incidences of cancer and other chronic diseases. They are considered indispensable in a variety of nutraceutical, pharmaceuticals, and medicinal and cosmetic applications. This study evaluated the effects of common processing methods on inherent phytochemical content in the roots and leaves of orange-fleshed sweetpotato (OFSP) varieties called Kabode and SPK031. Yellosp and Whitesp, which are local sweetpotato varieties, were also included as check for roots and leaves, respectively. The sweetpotato products prepared for phytochemical analysis were boiling roots and leaves, frying chips and crisps, baking bread (for roots only), and fermenting and dehydrating leaves. Phytochemicals that were assessed included vitamin C, total phenolics and flavonoids, tannins, phytates, and soluble oxalates. Results indicated that retention of vitamin C was highest in boiled roots (85%-95%), followed by fries (71%-94%) and crisps (44%-76%), whereas the least retention was in bread (4%-11%) and leaves (0%-27%). Total phenolics, flavonoids, and antioxidant activity in leaves significantly (p < .05) varied with the type of processing. Higher retention of these phytochemicals was observed in processed roots but was lowest in bread. Boiling retained more than 100% of all carotenoids, while fermenting and drying the leaves retained 58-62 and 22%-48%, respectively. Frying retained more than 100% of the ß-carotene in the roots, while boiling retained 96%-100%. All processing methods significantly (p < .05) reduced antinutrients in leaves and roots. Fermentation of leaves had higher reduction of oxalates, tannins, and phytates, while boiling had the least effect. It is concluded that traditional boiling enhances phytochemical retention in roots but degrades most of them in leaves.

Effects of Acidification and Preservatives on Microbial Growth during Storage of Orange Fleshed Sweet Potato Puree.

Orange Fleshed Sweet Potato (OFSP) puree, a versatile food ingredient, is highly perishable limiting its use in resource constrained environments. It is therefore important to develop shelf-stable puree. A challenge test study was carried out to determine the effect of combinations of chemical preservatives and acidification on microbial growth in stored puree. Puree was prepared and treated as follows: control (A); 0.05% potassium sorbate+0.05% sodium benzoate+1% citric acid (B); 0.1% potassium sorbate+0.1% sodium benzoate+1% citric acid (C); 0.2% potassium sorbate+0.2% sodium benzoate+1% citric acid (D); 1% citric acid (E). Samples were inoculated with Escherichia coli and Staphylococcus aureus at levels of 5.2 x 109 cfu/100g and 1.5 x 109 cfu/100g, respectively, before being evaluated during storage for 10 weeks at prevailing ambient temperature (15-25°C) and refrigeration temperature (4°C). Total aerobic counts, yeasts, and molds were also evaluated. E. coli and S. aureus counts declined significantly (p<0.05) by 4 log cycles in all puree treatments except for control and puree with only citric acid. Total viable count, yeasts, and molds were completely inhibited except for puree with only citric acid. Combination of chemical preservatives and acidification is effective in inhibiting pathogens and spoilage microorganisms in sweet potato puree.