Interrelations of α- and β-amylase activity with starch, sugars, and culinary and nutritional quality attributes in sweetpotato storage roots

BACKGROUND Little information is available on α- and β-amylase activity and their associations with starch, sugars and other culinary qualities in sweetpotato. The objective of this study was to assess sweetpotato storage root α- and β-amylase activity in relation to starch, sugars, β-carotene content and storage root flesh color.

RESULTS α- and β-amylase activity (α-AA and β-AA) were assayed from a Tanzania (T) x Beauregard (B) genetic mapping population in their uncured (raw), cured and stored (~ 11 weeks) forms during 2016 and 2017. The Ceralpha and Betamyl methods, with modifications to suit a high-throughput microplate assay format, were used to quantify α-AA and β-AA, respectively. Storage root dry matter, starch, glucose, fructose, sucrose, and β-carotene content were predicted using near infrared reflectance spectroscopy (NIRS). There was little relationship (r2 = 0.02–0.08, p-value ≤0.05 in 2016 and r2 = 0.05–0.11, p-value ≤0.05 in 2017) between α-AA and β-AA. We observed negative linear associations between α-AA and dry matter content and generally no correlations between β-AA and dry matter content. β-AA and sugars were weakly positively correlated. β-AA and β-carotene content were positively correlated (r = 0.3–0.4 in 2016 and 0.3–0.5 in 2017).

CONCLUSIONS Generally, the correlation coefficient for amylase enzyme activity and sugar components of storage roots at harvest increased after curing and during post-harvest storage. This study is a major step forward in sweetpotato breeding by providing a better understanding of how α- and β-amylase activity are inter-associated with several culinary quality attributes.