The
katsuobushi, an important product in Japan made from skipjack by a time-honored special method of drying, is truly a masterpiece from various points of view, and yet there remains some room for further improvement in its property. The occurrence of the so-called
shirata, for instance, along with which a piece of
katsuobushi under storage loses its original amber color to become ashy white with simultaneous moldering of its body, often gives rise to more or less serious drops in commercial value of this product.
As the amber color of
katsuobushi is to be due to the heme pigment in the muscle of skipjack as raw material, the said discoloration may surely be a change of this pigment de-veloping through a certain course. Some difficulties, however, stand in the way of approach to this course, because the muscle pigment already denatured as in a piece of
katsuobushi cannot be extracted with any sort of solvent to be directly measured. Also the known method of estimating the color tone of meat by measuring the light coming reflected by the meat fails to be availed in the case of
katsuobushi because of the extreme transparency of this product. The authors, now trying to extract with HCl-acetone the heme component after deriving it to hemin, found that the extract from an amber-colored normal portion of
katsuobushi alway contained the hemin thus formed but the extract from
shirata comprised no heroin (Fig. 4). This tells the absence of muscle pigment in the
shirata portion, suggesting the destruction of porphyrine ring into simpler pyrrole derivatives. WATTS
2) states in his lecture on the color change of meat products through oxidation that the porphyrine ring as the prosthetic group of heme pigment is attacked, opened and further led to derivatives more and more strongly reduced in the constituent pyrrole rings with corresponding change in color from yellow down to a colorless state. Since the authors confirmed on the other hand that chips of
katsuobushi are readily brought by aeration into a state of shirata (Figs. 5 and 6), the development of said ashy white with the formation of
shirata may perhaps be taken, in analogy to the case of other meat products described by WATTS, as a manifestation of an oxidative destruction of muscle pigment caused by the air that surrounds the
katsuobushi pieces.
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