6-Deoxy-l-glucose, 6-deoxy-l-altrose, and 6-deoxy-l-allose were produced from l-rhamnose with an immobilized enzyme that was partially purified (IE) and an immobilized Escherichia coli recombinant treated with toluene (TT). 6-Deoxy-l-psicose was produced from l-rhamnose by a combination of l-rhamnose isomerase (TT-PsLRhI) and d-tagatose 3-epimerase (TT-PcDTE). The purified 6-deoxy-l-psicose was isomerized to 6-deoxy-l-altrose and 6-deoxy-l-allose with l-arabinose isomerase (TT-EaLAI) and l-ribose isomerase (TT-AcLRI), respectively, and then was epimerized to l-rhamnulose with immobilized d-tagatose 3-epimerase (IE-PcDTE). Following purification, l-rhamnulose was converted to 6-deoxy-l-glucose with d-arabinose isomerase (TT-BpDAI). The equilibrium ratios of 6-deoxy-l-psicose:6-deoxy-l-altrose, 6-deoxy-l-psicose:6-deoxy-l-allose, and l-rhamnulose:6-deoxy-l-glucose were 60:40, 40:60, and 27:73, respectively. The production yields of 6-deoxy-l-glucose, 6-deoxy-l-altrose, and 6-deoxy-l-allose from l-rhamnose were 5.4, 14.6, and 25.1%, respectively. These results indicate that the aldose isomerases used in this study acted on 6-deoxy aldohexoses.
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
The esterified maltodextrins (EMs) are prepared by enzymatic esterification of maltodextrin DE of 16 with three fatty acids (C‐10, C‐12, and C‐16). Three EMs are maltodextrin decanoate (DE16_D), maltodextrin laurate (DE16_L), and maltodextrin palmitate (DE16_P). Their surface‐active properties and anti‐microbial activities are investigated with various concentrations (0–20% (w/w)). All EMs exhibit surface activity that depends on the chain length of the fatty acid. The anti‐microbial activities of EMs and native maltodextrin are evaluated against Escherichia coli, a Gram‐negative bacterium, and Staphylococcus aureus a Gram‐positive bacterium. DE16_L is the most effective at retarding E. coli growth. The minimum inhibitory concentration (MIC) of DE16_L is 5% (w/w). Cell numbers of E. coli tend to decrease as the concentration increases for native maltodextrin, DE16_D, and DE16_L. On the other hand, DE16_P enhances the available cells of E. coli and S. aureus as concentration increases. EMs and native maltodextrin do not clearly retard the growth of S. aureus. This investigation indicates that the chain length of the fatty acid and the concentration of EMs affects their anti‐microbial ability.
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
throughout Thailand sell products to local markets, as freshly made khanom jeen noodles are preferred by consumers (Kusano 2017). To meet increasing market demand, many of these small-to medium-sized producers now use mass-produced fermented rice flour products purchased from suburban factories, despite having previously prepared fermented rice flour themselves (Kusano 2017).Fermented rice flour used for making khanom jeen noodles is typically produced as follows: The rice materials are first soaked in water and then drained in a sieve container. Wet rice in the container is covered with a plastic sheet and left to stand overnight under ambient conditions to undergo solid-state fermentation. The rice is then washed with water and the same process is repeated for a few days. The fermented rice is then wet-milled and precipitated in an approximately 2% saltwater pool overnight to undergo liquid-state fermentation, after which the supernatant is replaced with fresh salt water. After a few days of liquid-
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