Influence of sweet potato age and storage on cooking quality parameters

Small-sized sweet potatoes are often sold as a specialty product, graded out from the main harvest, but they can also be intentionally achieved by harvesting much earlier than usual. Since these roots are biologically young, questions arise as to their ability to convert starch to maltose in a similar manner to the older, full-sized roots. Here we show that small sweet potatoes harvested 59 days post-planting had lower dry matter and starch than full-sized sweet potatoes (harvested 120 days post-planting), reflecting the active growth stage of the young root. The concentration of maltose produced during cooking (dry basis) was lower in the young sweet potatoes. However, the proportion of available starch converted to maltose through β-amylase activity was similar (60–65%). An eight-week postharvest storage at 15°C had no effect on β-amylase activity or the concentration of maltose produced on cooking. Total sweetness index (sucrose equivalents) in cooked tissue was lower on a fresh basis for young roots compared to full-sized roots but was not different when expressed on a dry basis, suggesting that the sweetness intensity of young roots could potentially be improved by introducing a water deficit prior to harvest, or cooking practices such as fan baking.