Significance and Impact of the Study: The use of Enterobacter ludwigii strain SK01 as a proteolytic bacterial starter culture improved the quality of khanom-jeen noodles. Compared with khanom-jeen noodles produced without E. ludwigii strain SK01, those produced using this strain showed increased tensile strength, breaking length, brightness and whiteness. These findings will be useful for the development of specific and controllable methods for producing khanom-jeen noodles with desirable texture and colour. AbstractKhanom-jeen are traditional Thai fermented rice noodles with a characteristic flavour and texture. Based on their ability to hydrolyse rice proteins, five strains of proteolytic bacteria were isolated from fermented rice flour used to produce noodles in Thailand. Enterobacter ludwigii strain SK01 showed the highest degree of rice protein hydrolysis among the five strains and was selected as a starter culture for khanom-jeen production. The viable count of micro-organisms, acidity, pH, and protein and starch contents were compared throughout the fermented rice production with and without the SK01 strain. The pH of fermented rice increased on the first day of solid-state fermentation and subsequently decreased to 3Á7-3Á8 under both conditions. The protein content of rice significantly decreased from 80 to 18Á2 AE 0Á5 mg g À1 and 26 AE 0Á6 mg g À1 during fermentation with and without the SK01 strain, respectively. The tensile strength, breaking length, brightness, and whiteness, which are important factors for the texture and appearance of khanom-jeen, were improved using the SK01 strain to ferment rice. The results of this laboratory-scale study indicated that the use of the proteolytic SK01 strain in fermented rice production can improve the quality of khanom-jeen noodles.Letters in Applied Microbiology ISSN 0266-8254

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From Thai fermented fish sauce (Nam-pla), 59 bacterial isolates of halophilic glutaminase-producing bacteria were isolated. The hydrolysis of glutamine served as the primary screening procedure. It was discovered that strain FF5302 was an influential producer of the extracellular halophilic glutaminase enzyme. The moderately halophilic bacterium Tetragenoccus muriaticus FF5302 was identified through sequence analysis of the 16S rRNA gene, phylogenetic tree analysis, and phenotypic identification before it was possible to determine the optimal nutritional and culture conditions for its halophilic glutaminase activity. The purpose of this research was to determine the optimal nutritional and cultural conditions for producing halophilic glutaminase activity in a stirred tank bioreactor with a volume capacity of 3 L. The production of halophilic glutaminase from strain FF5302 was investigated by optimizing various physicochemical parameters. Seven potential factors are generally considered in halophilic glutaminase production, namely NaCl concentration, initial pH, temperature, incubation time, nitrogen sources, carbon sources, and inoculum size. According to the findings, the amount of halophilic glutaminase in the inoculum had an effect on the growth and activity of the enzyme when it was present at a concentration of 5 % (v/v). It was also found that halophilic glutaminase showed the highest activity (87.4 U mL−1) of strain FF5302 in SGC liquid medium containing NaCl 20 % (w/v), pH 8.0, agitation at 200 rpm, and an aeration rate of 0.05 VVM at 37 °C for 120 h. The size of the inoculum influenced both the proliferation and activity of halophilic glutaminase in the inoculum. Consequently, T. muriaticus FF5302 possessed an exceptional capacity to synthesize halophilic glutaminase. Furthermore, the halophilic glutaminase enzyme from halophilic bacteria is a prospective option for usage in the food industry as an aroma and flavor enhancer. HIGHLIGHTS muriaticus FF5302 was exceptionally capable of producing halophilic glutaminase. In addition, the enzyme is a viable candidate for usage in the food industry as an aroma and flavor enhancer. Furthermore, this study could also be helpful and valuable in improving enzyme productivity at the bioreactor scale for various industrial applications. GRAPHICAL ABSTRACT

The Plackett-Burman’s experiemental design was used to efficiently select the key cultural parameters for the production of halophilic glutaminase by moderating halophilic bacterium Tetragenococcus muriaticus FF5302. Eleven variables were selected, which involved glutamine, peptone, yeast extract, glucose, fructose, KCl, MgSO4, NaCl, temperature, pH, and inoculum size, to identify the most significant variables affecting halophilic glutaminase production in 12 experimental trials. The results of the statistical analyses demonstrated that glutamine, pH, and temperature had significant effects on halophilic glutaminase production. The maximum halophilic glutaminase activity of 199.27 U mL-1 was observed after 120 h of fermentation. After Plackett-Burman’s design experiments, the glutaminase activity was found to be 2.28 folds increase compared to basal conditions. Thus, the cultivation of T. muriaticus FF5302 under the optimal condition could enhance the production of halophilic glutaminase enzyme effectively.