Screening Of Monascus Strains And Their Effects On Metabolites In Monascus Cheese

With the integration of Western food culture,the market for mold-fermented cheese in China has a gradual growth trend.For a premium mold-fermented cheese,the fermentation strain and processing process are key factors affecting its quality.Currently,Penicillium and white mold are mainly used for cheese ripening,but such products do not fully meet the taste preferences of most Chinese people.For example,blue cheese is spicy and pungent,while white mold cheese has a certain mold and mushroom flavor.Therefore,there is an urgent need to bring a mold-fermented cheese to the Chinese consumers that has attractive color,suitable taste,and is beneficial for health.Monascus has been used for more than 1000 years in food manufacturing and processing in China,such as red koji rice and red koji fermented bean curd.Monascus fermented products have been consumed for a long time.They are safe for consumption and have some beneficial substances.Therefore,Monascus has the potential to process cheese.This project conducted the screening of Monascus strains,studied the metabolic product characteristics of Monascus cheese,and determined the optimal ratio of dominant strains for cheese ripening.To screen for Monascus strains that can produce attractive color and excellent flavors in cheese,Monascus strains were isolated and purified from traditional fermented Monascus foods,and a mature process suitable for rapid flavor screening of Monascus cheese was developed.A sensory experiment was conducted to screen 15 purified strains and 10 Monascus strains provided by the laboratory.Finally,six dominant strains were obtained.Through DNA sequence alignment,they were confirmed as Monascus.Some Monascus strains have the characteristics of producing citrinin,or the ability of ripening cheese is weak.Some Monascus strains that have been used in traditional fermented foods have excellent flavor but produce citrinin,because their edible safety was neglected due to a lack of advanced analytical methods in the past.Six strains of Monascus with flavor advantages were used to prepare cheese samples by short-ripening technology,and the safety,functionality,physical and chemical indexes,texture and antioxidant properties were tested to analyze their impact on cheese quality.The results showed that Monascus strains BC20 and ZX-99 had both edible safety and cheese ripening ability.At the end of cheese ripening,the content of citrinin in cheese samples was lower than the national standard detection limit of 25μg/kg,far lower than the quantitative limit of 80 μg/kg,and the content of p H4.6soluble nitrogen was(40.99±0.90)% and(26.05±0.56)% respectively.Therefore,Monascus BC20 and ZX-99 can be considered for the processing and production of mature cheese.Monascus cheese BC20 and Monascus cheese ZX-99 were used as experimental groups,and commercially available blue mold cheese and white mold cheese were used as control groups.The low molecular weight metabolites involved in the four cheeses were analyzed by non-targeted metabolomics.Metabolites that were only enriched in the experimental groups(VIP﹥1,P﹤0.05,FC﹥2)and had no significant difference between the experimental groups(VIP ≦ 1,P ≧ 0.05)were considered as the characteristics of Monascus cheese.Among the 2510 metabolites identified in positive and negative ion modes,23 substances were preliminarily considered as characteristic metabolites of Monascus cheese.Eight of these substances,including cucurbitacin e,fusidic acid,quinapril,methyl dopa,orcinol,licoricesaponin h2,alfuzosin,and 25-desacetyl rifapentin have certain beneficial activities.In the four comparison groups between the experimental groups and the control groups,there were 10 identical differential metabolic pathways.The enrichment degree of the protein digestion and absorption pathway was relatively high,and the proportion of pathways related to amino acids was the largest.This indicated that protein and amino acids were both biologically important for Monascus cheese.Among the differential metabolites involved in these two pathways,the substance contents of propionic acid,DL-tyrosine,homoharringtonine,2-isopropylmalic acid,creatine,and succinic were significantly increased in the two Monascus cheeses(P﹤0.05).The metabolomics analysis of Monascus cheese can provide theoretical basis for the definition of Monascus cheese,the regulation of metabolic direction and the enrichment of beneficial metabolites.Usually,a single strain is used for industrial production,and the flavor and beneficial substances of the cheese produced are relatively single.The quality of the product can be improved through the combination of strains,so that cheese has the advantages of different strains in performance.The selected Monascus BC20 and Monascus ZX-99 were compounded into 3 combinations.The cheese processed by single and combined strains was analyzed by metabolomics.First,through the comparison of the metabolites of Monascus cheese BC20,Monascus cheese ZX-99,blue cheese and white cheese and the retrieval of relevant material information,the beneficial and significantly enriched metabolites of Monascus cheese BC20 and Monascus cheese ZX-99 were screened.Then,the enrichment of these substances in the cheese processed by the combined strains was analyzed.Finally,it is believed that D cheese(Monascus cheese,BC20: ZX-99=2:1)combines the beneficial substances enriched in both Monascus cheese BC20 and Monascus cheese ZX-99,such as riboflavin,isoleucine,γ-aminobutyric acid and other substances are expected to be used for industrial production.The discovery of Monascus which used for mature cheese provides more choices for the development of moldy mature cheese in the future,and also provides more reference for the development of cheese with oriental characteristics and biological functional dairy products.