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Microbial transglutaminase (MTGase) is a commercial enzyme that has been applied to many protein containing foods to improve their textural property. The screening of MTGase-producing microorganisms from various sources might lead to the discovery of a new MTGase with different characteristics. This report demonstrates the use of a direct detection method for MTGase-producing bacteria grown on an agar plate by filter paper disc (FPD) assay. The principle of the assay is the formation of a red burgundy color by the hydroxamate-ferric complex. The color developed intensity was linearly correlated by the concentration of hydroxamic acid in the range of 0.1-0.8 μM and was visually scored at 4 levels: 0, 1, 2 and 3. Streptoverticillium mobaraense DSM 40847, a positive MTGase-producer, was chosen for the verification and improving of the proposed method. The colonies grown on the nutrient agar plate at 37°C for 24 h were covered with FPDs and 30 μl of substrates (CBZ-Gln-Gly and hydroxylamine). After incubation, 10 μl of the ferric-TCA-HCl solution was placed on the FPD. The optimal time taken to catalyze the formation of CBZ-Gln-Gly-hydroxamic acid by the MTGase and the time taken for the hydroxamate-ferric complex to form color were 180 and 60 min, respectively. Using this assay, 30 of 189 colonies isolated from wastewater and floating-floc samples showed MTGase-positive colonies which were well correlated to the quantitative screening of MTGase activity (R(2) = 0.9758). The results revealed that the FPD assay could be used for the qualitative screening of MTGase-producing bacteria.

Pathogenesis of neurological diseases is associated with free-radical-mediated inflammatory processes. Phenolic compounds, saponin, and γ-aminobutyric acid (GABA) are nutraceuticals with neuroprotective properties. Lentinus squarrosulus is a mushroom with high proteins low calories, and nutraceuticals. This research aimed to investigate the nutraceutical contents of total phenolic compounds, saponins, γ-aminobutyric acid (GABA), and antioxidant activity in this mushroom after drying and frying for snack production. The nutraceutical contents and antioxidant activity were measured by Folin–Ciocalteu method and 2,2-diphenylpicrylhydrazyl (DPPH) assay, respectively. The stability of these nutraceuticals was also determined after drying and deep frying mushrooms in preparation for snack production. Results showed that the mushrooms after drying at 50 and 60 °C until the moisture content was below 12 % (according to Thai Community Products Standard) had water activity (aW) of 0.52 to 0.59. The dried mushrooms had lower lightness, redness, and yellowness with the increased drying temperature (p ≤ 0.05). The total phenolic content of dried mushrooms was not significantly different from that of fresh mushrooms, but saponin, GABA, and antioxidant activity were higher than in the fresh samples.