Reported β‐glucanase activity by amyloglucosidases used in starch determination might lead to significant overestimates of starch concentration in plant tissue. To test this hypothesis, two amyloglucosidases and a porcine α‐amylase were evaluated using four starch and three β‐glucan preparations. The enzymes were also used to estimate starch concentration of alfalfa (Medicago sativa L.) roots and tall fescue (Festuca arundinacea Schreb.) and orchardgrass (Dactylis glomerata L.) stem bases. Release of reducing sugars by the α‐amylase was consistent with 95 to 98% hydrolysis of starch to maltose, and <3% hydrolysis of β‐glucans. The widely used amyloglucosidase from Rhizopus gave 89 to 93% hydrolysis of starch, but also 35 to 83% hydrolysis of β‐glucans. Hydrolysis with α‐amylase gave calculated starch concentrations for the grasses which were not significantly different from zero, but the Rhizopus enzyme gave starch estimates of 32 and 52 g kg−1 for tall fescue and orchardgrass, respectively. The amyloglucosidase from Aspergillus gave intermediate results. Neither amyloglucosidase should be used to estimate plant starch concentration.
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James M. Fedders (1990) studied this question.