Preparation of Monascus fermented soybeans and their physiological properties

• Main Authors: Yu-Ling Lee, 李煜玲
• Other Authors: 毛正倫
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/57668164102416784660

博士 === 國立中興大學 === 食品暨應用生物科技學系 === 95 === Monascus has been already used on fermented foods for thousands of years due to it can produce sour, alcohol, ester and several hydrolysis enzymes. Recently, the secondary metabolites from Monascus are the major study due to it can produce a lot of bioactive materials, such as natural pigments of Monascus, γ-aminobutyric acid (GABA) and monacolin K. Soybeans and soy products are rich in isoflavones and are very common foods in oriental countries as a meat substitute. Many studies have shown that daily intakes of soy foods may help human to prevent certain cancers, lower plasma cholesterol, lower blood pressure and reduce the risk of coronary heart diseases. Both Monascus species and soybean contain functional components but in combination, solid-state fermentation of soybean matrix by Monascus species is a new area of investigation. Therefore, the objective of this study was to prepare Monascus fermented soybeans (MFS-31527 and MFS-31499) by using soybeans as a substrate and incubating Monascus pilosus BCRC 31527 and Monascus purpureus BCRC 31499. Then, the quality properties, storage stability, antioxidant properties, anti-inflammatory reaction, lower blood pressure and blood cholesterol abilities were evaluated. The optimal fermentation conditions depend on the higher monacolin K content and the lower citrinin content. Hence, the optimal condition for MFS-31527 was at pH 5.0, 25°C for 7 days with carbon and nitrogen sources being 5% maltose and 0.5% peptone whereas for MFS-31499 was at pH 5.0, 30°C for 6 days with carbon sources being 5% maltose. Isoflavones changed forms from glucoside to aglycone during the process of Monascus fermented soybeans. In the proximate composition, crude proteins were the major components in MFS-31499, MFS-31527 and soybeans. All three samples contain lower soluble sugar contents and were major in non-reducing sugar form, sucrose. MFS-31499 exhibited higher total free amino acids content than those in MFS-31527 and soybeans. In the 5′-nucleotide contents, MFS-31527 and MFS-31499 showed higher content than soybeans. Equivalent umami concentration (EUC) of MFS-31499, MFS-31527 and soybeans were 8.10, 38.57 and 6.00 g/100g. The total isoflavone content of MFS-31499, MFS-31527 and soybeans were 1190, 1074 and 1410 mg/kg, and MFS were major in aglycone forms whereas soybeans were major in glucoside forms. Overall, Monascus fermentation could produce more amino acids, 5′-nucleotides and aglycone form contents. Antioxidant properties of MFS-31499, MFS-31527 and soybeans are studied in the forms of ethanol, methanol, cold water and hot water extracts. The extracted yields of cold water and hot water showed higher than those of ethanol and methanol. EC50 value is defined as the effective concentration at which the antioxidant activity up to 50%. The methanolic extracts from MFS-31499, MFS-31527 and soybeans exhibited better antioxidant activities and their EC50 values were 1.82, 1.11 and 0.91 mg extract/mL, respectively. In reducing powers, the cold water extracts from three samples were better and their EC50 values were MFS-31499 (4.61 mg extract/mL) ~ MFS-31527 (4.61 mg extract/mL) > soybeans (8.91 mg extract/mL), respectively. In scavenging 1,1-diphenyl-2- picrylhydrazyl radicals ability, the methanolic extract from MFS-31499 and the hot water extracts from MFS-31527 and soybeans were better and their EC50 values were 1.80, 1.66 and 1.59 mg extract/mL, respectively. Cold water extracts from three samples showed better scavenging hydroxyl radicals ability whereas ethanolic and methanolic extracts showed no effects. Total phenols were the major antioxidant components of three samples, and Monascus fermentation could produce more total phenol contents. The cold water extracts of three samples showed lower cell viability than hot water extracts with LPS induced or without. With LPS induced, the macrophages viability lowered to 80% of control. In inhibiting NO production of LPS-induced macrophages, the hot water extracts exhibited higher inhibiting ability for three samples. At 500 μg/mL, the hot water extract from MFS-31527 showed better effectiveness to 86% inhibiting NO production ability. Both cold water and hot water extracts from three samples exhibited the reduction ability of NO production could not due to reduce iNOS enzyme activity. This part was used to feed the spontaneous hypertension rats (SHR) and compared with adding MFS-31499, MFS-31527 and soybeans on 0.5% cholesterol feed and 0.5% cholesterol feed as a control. The blood pressure and serum lipids (including total cholesterol, triglycerides, low density lipoprotein-cholesterol (LDL-C) and high density lipoprotein-cholesterol (HDL-C) of SHR were measured periodically. After feeding one week, the results showed lower systolic pressure in the descending order: MFS-31527 (23.77%) ~ MFS-31499 (21.55%) > soybeans (9.45%) > control (3.56%) whereas lower diastolic pressure in the descending order: control (21.38%) > MFS-31527 (7.29%) ~ MFS-31499 (1.63%) ~ soybeans (1.60%). After feeding six weeks, the mean blood pressures were reduced and in the descending order: MFS-31527 (25.61%) > MFS-31499 (12.89%) ~ soybeans (11.69%) > control (4.07%). As feeding period increased, all three samples reduced triglyceride contents increasingly. After feeding four weeks, total serum cholesterol contents of SHR for three samples reduced in the descending order: MFS-31499 (47%) > MFS-31527 (38%) > soybeans (29%) whereas serum LDL-C contents of SHR reduced in the descending order: MFS-31499 (75%) > soybeans (62%) > MFS-31527 (51%) > controls (-1.71%). As feeding period increased, MFS-31499, MFS-31527 and soybeans could increase the serum HDL-C contents of SHR. Overall, Monascus fermented soybeans compared with uninoculated soybeans exhibited that could increase the functional components, tasty quality, antioxidant activity, anti-inflammatory effects, lower blood pressure and blood lipid abilities.