Soba (buckwheat) noodles were made from soba (Fagopyrum esculentum) flour with konnyaku (Amorphophallus konjac) powder added as a binder. Three kinds of konnyaku powder were used: A, first-grade untreated powder; B, powder A treated with ethanol for 15 min; and C, powder A treated with ethanol and ultrasonic irradiation for 15 min. A konnyaku sol was prepared from each of these types of konnyaku powder to add to soba flour for making soba noodles.
The effect of each type on the quality and preservation of the noodles was studied. The best product was obtained by using soba flour containing 2% konnyaku powder. Changes in the rupture stress and rupture strain of the dough with time were very small, so that the dough did not require rising. The best results were obtained with soba dough containing konnyaku powder C which exhibited the best rupture characteristics and physical properties, the noodles being resilient to break age and the elastic properties being maintained after rising for 1 hr. Moreover, the soba noodles made with powder C were preferred more than those made with 100% soba flour and those containing powder A or B as determined by a sensory evaluation. Soba noodles incorporating konnyaku powder contain a large amount of dietary fiber, and we therefore expect the functional characteristics of the soba noodles to be enhanced. It is concluded that konnyaku powder treated ethanol and ultrasonic irradiation was best suited for use as binder in soba noodles.
After keeping the raw soba noodles in a refrigerator at 5°C for 3 days, the bacterial count increased from 10⁶ to 10⁷/g, while that of the boiled soba noodles decreased to a level of 10³/g.