Shinjiro Tachibana

Purification and characterization of heterogeneous glucoamylases from Monascus purpureus.

Two forms of an extracellular glucoamylase, MpuGA-I and MpuGA-II, were purified to homogeneity from Monascus purpureus RY3410. The molecular weights of these enzymes were estimated to be 60,000 (MpuGA-I) and 89,000 (MpuGA-II). These enzymes were glycoproteins with a carbohydrate content of 15.0% (MpuGA-I) and 16.2% (MpuGA-II) respectively. The pH optima were 5.0 for both enzymes, and the optimal temperatures were 50 °C (MpuGA-I) and 65 °C (MpuGA-II). The K m values for soluble starch were calculated to be 4.0±0.8 mg/ml (MpuGA-I) and 1.1±0.2 mg/ml (MpuGA-II) respectively.

Biochemical aspects of red koji and tofuyo prepared using Monascus fungi

Red koji or red mold rice is prepared by growing a genus Monascus on steamed rice. For centuries, it has been used in Asia for the production of fermented foods including red rice wine and fermented tofu. Although red koji is an important source of various hydrolytic enzymes critical for food fermentation, information on the enzymatic properties in red koji has been limited. Hydrolytic enzymes produced by Monascus fungi may play important roles in ripening of tofuyo (Japanese fermented tofu) regarding the chemical and physical properties of the product. This review provides an introduction of red koji, its properties, and the application of hydrolytic enzymes, especially aspartic proteinases and carboxypeptidases from Monascus fungi. We also describe tofuyo and a novel fermented soybean protein food using a microbial action originating from red koji.

Heterogeneity of dehydrogenases of Stenotrophomonas maltophilia showing dye-linked activity with polypropylene glycols

Distinct enzyme activities were found in extracts from Stenotrophomonas maltophilia showing dye-linked oxidation of polypropylene glycols. The activities were induced when polypropylene glycols served as sole carbon and energy sources for the bacterium. In the logarithmic phase, most of the enzyme activities (88%) were found in the cytoplasm. In the stationary phase, more than half of the activities (54%) were found on the membrane, but significant activities were also distributed in the periplasm (34%) and the cytoplasm (12%). The enzyme activities differed from each other in their localization, time of induction in the growth cycle, specificity toward electron acceptor, and electrophoresis mobility.

Purification and characterization of cytoplasmic NAD+‐dependent polypropylene glycol dehydrogenase from Stenotrophomonas maltophilia

The oxidizing enzyme NAD(+)-dependent polypropylene glycol dehydrogenase (PPG-DH) was purified to homogeneity from the cytoplasmic fraction of Stenotrophomonas maltophilia grown on polypropylene glycol (diol type) 2000. The purified enzyme consisted of a homotetrameric protein (37 kDa subunit) with a molecular mass of around 154 kDa. The N-terminal amino acid sequence (25 residues) showed similarity to the sequences of NAD(+)-dependent secondary alcohol dehydrogenases and NADH-dependent reductases. The enzyme preferentially oxidized medium-chain secondary alcohols, di- and tri-propylene glycols and polypropylene glycols including those with secondary alcohol groups in their molecular structure. Consequently, the enzyme was classified into a group of NAD(+)-dependent secondary alcohol dehydrogenases.

Characterization and in vitro biological activities of Thai traditional fermented shrimp pastes

In this work, chemical and biological characteristics of two types of Thai fermented shrimp paste, Kapi Ta Dam and Kapi Ta Deang, at different fermentation periods and their raw materials were investigated. Kapi had low water activity and high proteins with high glutamic acid and lysine. Both Kapis, which had different sources, showed similar characteristics. The number of lactic acid bacteria in the products increased during the early stages of fermentation. Free α-amino acid contents in the products increased with the fermentation time. The water extracts from Kapi products showed strong antioxidative activities against ABTS+ radical, and ACE inhibitory activity but they did not exhibit antimicrobial activity against Staphylococcus aureus, Bacillus cereus, Escherichia coli and Salmonella Typhimurium. Biological activities in Kapi could be developed by fermentation process, enzymatic hydrolysis of proteins and non-enzymatic browning reactions. Kapi could, thus, serve as a potential source of natural bioactive substances.

Taste and chemical characteristics of low molecular weight fractions from tofuyo – Japanese fermented soybean curd

Tofuyo, a Japanese traditional food, is a fermented soybean curd manufactured in Okinawa region. Due to its original cheese-like flavor, the current study was designed to evaluate the sensory and chemical characteristics of three stepwise ultrafiltration fractions, using 10,000, 3000 and 500 Da membranes and further chromatographic fractions from tofuyo. The results showed that umami, sweet and salty were the characteristic tastes of all fractions, with umami intensity evaluated for the fraction with MW less than 500 Da (F-500) as the most prominent among the three fractions. Subsequent Sephadex G-25 SF fractions and RP-HPLC fractions were subjected to sensory and chemical analyses. The tastiest fraction contained sodium chloride, sugars, organic acids, umami and sweet free amino acids, at concentrations above their thresholds. The abundant presence of umami and sweet free amino acids with certain concentrations of sodium chloride and glucose might provide the typical savory taste of tofuyo.