Viscosity behaviour of potato starch paste was measured with the Rapid Visco Analyzer (RVA, Newport Scientific, Warriewood, Australia). By reason of high viscosity properties of potato starch suspensions, starch concentration was reduced from 3.0 to 2.0 g starch weight (14% moisture) in 25 rnl distilled water. In view of Brabender viscograms a short temperature profile (13 min including heating, stable hot phase, and cooling) achieved the best results. Reproducibility of RVA-measurements was high as well with new canisters as with re-used ones. Coefticient of variation (?.Yo) was below 2%. A comparison of RVA and Brabender viscograrns pointed out a close correlation of r = 0.94 for both, the peak viscosityand the viscosity difference between peak and trough. Viskositatsmessungen von Kartoffelstslrke mit dem Rapid Visco Analyzer. Das Viskositatsverhalten von Kartoffelstlrkekleistern wurde mit dem Rapid Visco Analyzer (RVA, Newport Scientific, Warriewood, Australien) gemessen. Aufgrund der kraftigen Viskositatsauspragung der Kartoffelstarke wurde die Starkekonzentration von 3,O auf 2,O g Starke (14% Feuchte) in 25 ml destilliertem Wasser reduziert. Mit Blick auf das Brabender Viskogramm erzielte das kurze Temperaturprogramm (13 min einschliefilich Aufheiz-, stabiler HeiD-und Abkuhlphase) die besten Ergebnisse. Die Reproduzierbarkeit der RVA.Messungen war sowohl rnit neuen als auch mit gereinigten Mefieinsatzen hoch. So lag der Variationskoeffizient (soh) unter 2%. Ein Vergleich zwischen RVA-und Brabender Viskogrammen wies mit einem Korrelationseffizienten von r = 0,94 eine hohe Ubereinstirnmung sowohl bei der Spitzenviskositat als auch bei der Viskositatsdifferenz zwischen hochstem und niedrigstem Wert auf.
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Gomponents of variation for, and genetic correlations among, measures of milling and baking quality were estimated for 38 winter rye siiigle-erosses sown in three environments. Samples of grain were indirectly evaluated for baking quality via Ealling Number and Amylograph tests whereas direct assessments ot baking quality and milling yield were obtained from standardized Sourdough Baking tests and total flour release determinations, re.spectively. Estimates of genetic variation were large and highly significant (P<0.01) for all traits whereas those of genotype X environment interactions were much smaller and often non-significant. Broad-sense heritability estimates were very high, ranging from 0.64 to 0.96. Grumb elasticity, the most important direet measure of baking quality, was significantly correlated with falling number (r|, = 0.43) and Amylograph temperature at maximum viscosity (r^ = 0.55). The dough yield, loaf volume and total flour release, however, showed no relation with the indirect measures of baking quality. The crumb elasticity was correlated positively with flour release but negatively with dough yield and loaf volume. Selection for high falling number would be an effective indirect method of increasing crumb elasticity. E'nhancement ofthe tither baking and milling charactcri.stics would require direct mcasurcnieiits of the respective traits.
Phytic acid in food is considered to be responsible for a reduced bioavailability of essential dietary minerals; its detrimental effects can be diminished by hydrolysis with phytase during processing. The average phytic acid content was 8.18 mg/g and 3.44 mg/g and average phytase activity was 3.7 U/g and 2.6 U/g in rye kernels and in flour (Type 997, 1.09 ash content), respectively. Phytate and Phytase were about equally distributed between the two kernel halves (cross sections). During the early stages of germination (3 days) phytase activity did not change, and phytic acid content was reduced to 67%. After milling most of the phytic acid and phytase activity were found in the bran fractions. It is concluded that substrate and enzyme are present in the same kernel structures but separate within the cells. Cooking of ground rye caused a phytate hydrolysis which was the more effective 1.) the smaller the particle sizes were, 2.) the more water was added, and 3.) the longer phytase worked at optimum temperature. Extrusion cooking of the rye whole flour at up to 100 degrees C did not influence the phytic acid level but caused a 23% reduction at 170 degrees C. Phytase activity was reduced by 80% by extrusion cooking at 80 degrees C.
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