| Pleurotus pulmonarius,is characterized by its abundant yield,delicious taste,and high protein content,which surpasses that of most edible fungi.Moreover,it is rich in various amino acids,particularly umami-related amino acids such as glutamic acid and aspartic acid,rendering it a superior natural source of umami flavor.In this study,we employed liquid fermentation technology to produce a substantial amount of mycelium,utilized enzymatic hydrolysis technology and fungal co-culture technique to effectively release the umami substances present in the mycelium of P.pulmonarius,thereby promoting its application in umami flavoring products.The main findings of this research are as follows:（1）The preserved strain in our lab was identified to be the species of P.pulmonarius.The comparison of different treatment methods（no homogenization,homogenization,and microwaving）on the umami enhancement of P.pulmonarius mycelium indicated that homogenization treatment was the best,with the maximum equivalent umami concentration（EUC）value reaching 48.87 g MSG·100g-1on 5 d.Simultaneously,the accumulation of umami amino acids reached 4.72 mg·g-1.（2）Using EUC value,unami amino acids,and nucleotides as indicators,the optimal fermentation conditions for P.pulmonarius were determined to be:fermentation temperature of 30℃,initial p H of 6,inoculum size of 2%,and rotation speed of 150 r·min-1.Under these conditions,the EUC value was up to 91.86 g MSG·100g-1,1.88 times higher than before.By adding different concentrations of glutamate on the liquid fermentation of P.pulmonarius mycelium,along with the increase of glutamate concentration,the content of glutamic acid dropped rapidly to the lowest value(0.11 mg·g-1)at the concentration of 0.3 g·L-1,and the EUC value reached the maximum(69.75 g MSG·100g-1)at the concentration of 0.4 g·L-1,which was lower than the control group.（3）In order to further release the fresh flavor of P.pulmonarius,six different proteases(papain,neutral protease,flavor protease,acid protease,alkaline protease,and flavor protease were compared.The optimal conditions for flavor protease degradation were optimized as55℃,p H 7.5,with enzyme addition amount of 1000 U·g-1,and degradation time at 3 h,which resulted EUC value of 420.41 g MSG·100g-1,1.94 times higher than the unoptimized group and 4.58 times higher that the un-degraded one.（4）Due to the good degradation effect of flavor protease,Aspergillus oryzae possessing a enough flavor protease was selected to co-culture with P.pulmonarius to improve the content of unami.The optimal co-culture and fermentation conditions were 5 days of co-culture and fermentation time,3 days of inoculation interval,3%inoculation amount and2:1 inoculation ratio（P.pulmonarius:A.oryzae）.After optimization,the proteolytic enzyme activity achieved a level of 45.72 U·m L-1,while the maximum concentration of umami amino acids reached 6.18 mg·g-1.Additionally,the peak content of umami nucleotides was measured at 3.00 mg·g-1,and the maximal EUC value was ascertained to be 147.45 g MSG·100g-1.These results were 1.06,1.14,and 1.60 times higher than the unadded group(5.85 mg·g-1,2.64 mg·g-1,91.86 g MSG·100g-1),which achieved increases of 5.64%,13.64%,and 17.03%,respectively. |
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