Abstract:

The molecular weight and content of soluble polypeptide in high-temperature soybean meal subjected to
Monascus purpureus fermentation were determined to ascertain whether denatured protein could be decomposed during
the fermentation process. The strain was mutagenized with ultraviolet light. The mutant strains were inoculated into hightemperature
soybean meal and screened twice for the highest yield of soluble polypeptides. The results showed that
proteins were decomposed in high-temperature soybean meal during Monascus purpureus fermentation, producing soluble
polypeptides with molecular weight of 7.8–20.1 kD. The yield of soluble polypeptide from fermented soybean meal after
120 h of fermentation was (13.41 ± 0.20) mg/mL, which was 3.60 times higher than that from the original soybean meal.
Monascus purpureus was irradiated by a 15 W UV lamp at a distance of 35 cm with stirring for 50 s, leading to a death
rate of (82.70 ± 2.20)%. The mutant 0501100 could produce relatively high yield of soluble polypeptide under these
conditions. The yield of soluble polypeptide from soybean meal fermented by the mutant strain 0501100 for 96 h was
(17.20 ± 0.18) mg/mL, which exhibited a 1.47- and 4.61-fold increase when compared with that obtained from the original
strain under the same fermentation conditions and the original soybean, respectively. Moreover, the fermentation time was
shortened and the mutant strain had a good genetic stability.

Key words: Monascus purpureus, high-temperature soybean meal, soluble polypeptide