Effects of temperature, sonication time, and power settings on size distribution and extractability of total wheat flour proteins as determined by size-exclusion high-performance liquid chromatography

The size-exclusion (SE) HPLC profile of total protein extract obtained by s onication of flour samples at ambient temperature showed marked instability on reinjection. Instability was related to the presence of flour proteases that were inactivated by thermal treatment of flour samples at 60 degrees C. Extraction of flour protein by sonication was a function of ultrasonic e nergy (sonication time x power product) delivered to flour sample. As prote in solubility increased, the proportions of the earliest eluted SE-HPLC fra ctions (F1 and F2) increased. Oversonication of proteins evidenced by a dec rease in F1 amount at the benefit of F2 occurred below the sonication energ y level needed for total protein extraction. Ultrasonic energy level was ad justed to allow total protein extraction while limiting oversonication. The sonication procedure was applied on 27 flour samples of contrasting dough strength to extract total proteins. Absolute amount of protein extractable by sonication, determined from SE-HPLC area, was strongly correlated with f lour protein content. Very significant and equivalent relationships were fo und between alveographic W index and absolute amount of either unextractabl e protein extract or F1 of SE-HPLC profile from total protein extract.