Low thresholds for salt and dashi taste in usukuchi shoyu and combined effect of usukuchi shoyu and dashi on the enhancement of saltiness (salt reduction)

Abstract

Light-colored soy sauce (Usukuchi shoyu) is usually used for seasoning boiled dishes (Nimono). Although Usukuchi shoyu contains more NaCl by about 2% than Koikuchi shoyu, many Nimono cooked with Usukuchi shoyu contain less NaCl than those cooked with Koikuchi shoyu. Thiscooking phenomenon of Usukuchi shoyu is experientially well known, and called as "Usukuchi shoyu paradox". In this paper, we studied the mechanisms of Usukuchi shoyu paradox by two organoleptic evaluation methods. Firstly, we determined the discrimination threshold of saltiness in two kinds of shoyus, and the concentration of NaCl ineach shoyu was significantly discriminated at 0.92% and at 0.95% in Usukuchi shoyu (p<0.05), and at 0.92% and at 0.97% in Koikuchi shoyu (p< 0.001), respectively. Furthermore, dried bonito soup stock (Katsuo-dashi) was significantly discriminated at 1.00% and at 1.25% in Usukuchi shoyu (p<0.01), and at 1.00% and at 1.50% in Koikuchi shoyu (p<0.05), respectively. Also, the discrimination threshold ofthe taste of seaweed soup stock (Konbudashi) was less concentrated inUsukuchi shoyu than in Koikuchi shoyu. Secondly, the enhancing effectof saltiness was determined with probit method when Katsuo-dashi, Usukuchi shoyu and Koikuchi shoyu were combined. Sample 1 was prepared as a combination of 4% of Usukuchi shoyu and 3% of Katsuo-dashi, and the saltiness of sample 1 was equivalent to 0.90% NaCl solution when the NaCl concentration of sample 1 was 0.872%. Sample 2 was prepared as a combination of 4% of Koikuchi shoyu and 3% of Katsuo-dashi, and the enhancing effect of saltiness was not confirmed. Although 4% of Usukuchi shoyu, 4% of Koikuchi shoyu, and 3% of Katsuo-dashi did not show the enhancing effect of saltiness individually, the 95% confidential limits reinforced that only the combination of Usukuchi shoyu and Katsuo-dashi enhanced saltiness. In conclusion, the mechanism of Usukuchi shoyu paradox was suggested as follows : Usukuchi shoyu had a lower threshold for saltiness, which makes it easier to adjust appropriate saltiness required for Nimono and a combination of Usukuchi shoyuand Katsuo-dashi enhanced saltiness. Therefore, Nimono cooked with Usukuchi shoyu would be palatable with less salt.