Studies on the Fluorescence of Sake

Part 6. Characteristics of Fluorescence of Sake and Changes of the Fluorescence in Sake brewing

Abstract

Variations in the fluorescence spectra of sake were examined under various conditions. The fluorescence spectra of sake varied with the pH as shown in Fig. 1, the intensity being the strongest at pH 7. O. The effects of dilution or concentration of sake on its fluorescent spectra were shown in Figs. 2 and 3, in which the fluorescent intensity did not run parallel with thatof sake diluted or concentrated. The fluorescence of rice-koji extract was hardly changed before and after fermentation by yeast as shown in Table 1. The presence of visible colored substances in solutions changed the fluorescence as seen in Table 2.
The fluorescence of the single solution and the mixed solution of various kinds of fluorescent or non-fluorescent substances were compared with each other, including that of sakeadded with substances shown in Tables 3, 4, 5 and 6, and in Figs. 4 and 5. It seemed that the fluorescence spectra of the mixed solutions were similar to those shown by the strongest fluorescent substance contained. But the fluorescence intensity of harman was decreased by the coexistence of other fluorescent substances having the fluorescent spectra different from those of harman. One of these substances was ferulic acid.
The changes of fluorescence were estimated in every stage of sake-brewing process such as koji making, yeast culturing and fermentation of the main mash, as shown in Tables 7, 8, 9 and 10, and Figs. 6, 7 and 8. The fluorescent intensities at two kinds of spectral peaks, i. e., excitation maxima at 352 mμ for emission maxima at 405-410 mμ, and excitation maxima at 468 ma foremission maxima at 521 mμ, were increased with time in the process of koji making as compared with those in the process of yeast culturing and fermentation of mash. The results suggest that fluorescent substances were produced mainly with the growth of fungi, Aspergillus.
While it was formerly demonstrated by the authors that aflatoxin is not producedby industrial strains of Aspergillus in Japan, a method of removing aflatoxin from foods and drinks should be established, considering any accidental contamination of this substance. Thus, amethod shown in Figs. 9 and 10 was developed by using ordinary amount of active carbon which hasbeen used for a long time in the manufacture of sake.