Mold-ripened cheese was prepared using a commercial starter culture combined with Monascus, and its physicochemical properties, free amino acids, microstructure and volatile flavor substances were evaluated. The results showed that the yield of cheese was 16.55%, and the protein, fat, calcium, water, and salt contents of the cheese were 18.03%, 33.40%, 376.67 mg/100 g, 44.47%, and 863.67 mg/100 g, respectively. During the ripening process, pH value first decreased, then increased and finally leveled off. The microstructure indicated that Monascus had a significant effect on the internal structure of mature cheese. A total of 23 free amino acids and 32 volatile compounds were identified by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). At the end of the ripening period (21 days), the content of free amino acids in mold-ripened cheese was increased by an average of 58.8 times over the beginning of ripening, and the types and contents of volatile compounds also changed significantly.

The optimization of medium components and culture conditions for improved spore production of Monascus purpureus M-4 in submerge culture was performed using a combination of one-factor-at-a-time (OFAT) method and response surface methodology (RSM). The OFAT results showed that potato extract powder and glucose were the optimal nitrogen and carbon source, respectively and that their optimal concentrations were 0.4 and 2.0 g/100 mL, respectively. The optimal culture conditions that provided the maximum number of spores were as follows: initial medium pH 6.72 (natural pH), medium volume in a 500-mL triangular flask 120 mL, concentration of added CaCO3 2.0 g/100 mL, number of passages 2, and culture time 72 h. Potato extract powder and glucose concentration as well as culture time were identified as main variables that influence spore production and their optimal levels were determined to be respectively 0.38 g/100 mL, 2.2 g/100 mL and 6.5 d using RSM. The highest spore number of (7.47 ± 0.15) × 106 CFU/mL was experimentally obtained under the optimized conditions, which was close to the predicted value (7.53 ± 0.31) × 106 CFU/mL. The average error between the predicted and experimental values was 0.79%. A 31.13-fold increase in spore number was achieved by the optimization. Besides, the spore-producing ability per unit volume of strain M-4 was greatly improved.