Novel analytical methods based on real-time quantitative polymerase chain reactions by use of new reference molecules were validated in interlaboratory studies for the quantitation of genetically modified (GM) maize and soy. More than 13 laboratories from Japan, Korea, and the United States participated in the studies. The interlaboratory studies included 2 separate stages: (1) measurement tests of coefficient values, the ratio of recombinant DNA (r-DNA) sequence, and endogenous DNA sequence in the seeds of GM maize and GM soy; and (2) blind tests with 6 pairs of maize and soy samples, including different levels of GM maize or GM soy. Test results showed that the methods are applicable to the specific quantitation of the 5 lines of GM maize and one line of GM soy. After statistical treatment to remove outliers, the repeatability and reproducibility of these methods at a level of 5.0% were <13.7 and 15.9%, respectively. The quantitation limits of the methods were 0.50% for Bt11, T25, and MON810, and 0.10% for GA21, Event176, and Roundup Ready soy. The results of blind tests showed that the numerical information obtained from these methods will contribute to practical analyses for labeling systems of GM crops.

The quality of starch-containing foods is significantly impaired by contamination with small amounts of α-amylase, which hydrolyzes the starch and causes viscosity loss. We examined the effect of different temperatures and times on inactivation of α-amylase in starch-containing foods. Model foods containing a known amount of human salivary α-amylase (HSA) were incubated at temperatures from 60 to 80℃ for 30 min. In the case of a 3% starch suspension incubated at 70℃, it took 10 min before the viscosity loss ceased, by which time the viscosity was halved. In 0.1 − 3% starch suspensions at pH 5.5, the inactivation of HSA could be described by a first order kinetic model. The presence of starch decreased the inactivation rate constant by decreasing the Arrhenius frequency factor. To prevent viscosity loss by α-amylase contamination in starch-containing foods, the inactivation time and temperature should be increased with increasing concentration of starch.Keywords: α-amylase, inactivation, thermostability, starch-containing food, viscosity *To whom correspondence should be addressed. E-mail: k-koyama@housefoods.co.jp IntroductionEffective use of starch in the food industry requires a thorough understanding of the enzymatic properties of amylase and the degradation behavior of starch. The increase in viscosity of starch-containing foods is largely due to the gelatinization of starch during heating. Viscosity is an important quality factor for thickened foods, such as soups, stews and curries that contain 5% or less starch. If a trace amount of amylase contaminates starch-containing foods, it can hydrolyze the starch and cause viscosity loss. Possible sources of amylase contamination include honey, spices, grains, fermented food, human saliva left on a tasting spoon and enzyme-containing dishwashing detergent.To prevent viscosity loss by non-thermophilic amylase contamination, starch-containing foods need to be heated to inactivate the amylase. However, using more heat than is necessary will reduce the freshness of the food. Food manufacturers have empirically found that heating at approx. 80℃ results in amylase inactivation.The thermostability of amylase increases in the pres-