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Amylolytic activities and starch reserve mobilization during the germination of quinoa
- Hager, Anna-Sophie, Mäkinen, Outi E., Arendt, Elke K.
- European food research & technology 2014 v.239 no.4 pp. 621-627
- Chenopodium quinoa, alpha-amylase, enzyme activity, fructose, functional properties, germination, glucose, grains, high performance liquid chromatography, imbibition, malting, nutritive value, pH, scanning electron microscopy, seeds, starch, water content
- Quinoa (Chenopodium quinoa) is a dicotyledonous plant producing perispermic seeds that is increasingly popular in the Western world due to its nutritional value. Germination can be used in food processing to alter the sensory, nutritional and functional properties of grains, and the increased enzyme activities may have beneficial influences in food applications. Knowledge about the germination of perispermic seeds is scarce. In this study, the development of amylolytic activities and subsequent changes in sugar profiles and starch content were followed in quinoa over a period of 72 h. The seeds germinated rapidly with radicle protrusion occurring 8 h after imbibition, when the seeds had reached a moisture content of 44 %. A low level of α-amylase activity (determined at pH 5.2 using blocked ρ-nitrophenyl-maltoheptaoside as substrate) was present in the embryo of non-germinating seeds, but emerged in the perisperm only after 24 h, followed by a sharp increase in activity in both tissues. The accumulation of glucose and fructose (determined with high pressure liquid chromatography) and the decrease in starch content (determined with an enzymatic assay) were observed after 24 and 36 h, respectively, indicating the onset of starch reserve mobilization. Overall, the levels of amylolytic activities remained very low compared with traditional malting cereals, suggesting the unsuitability of quinoa as a source of amylases in food applications. Scanning electron microscopy, used to visualize changes in starch granule morphology, showed mainly exocorrosion, suggesting a homogenous structure of the outer layers of quinoa starch.