Bijan Choudhury

Study of lactic acid extraction with higher molecular weight aliphatic amines

Lactic acid extraction was studied with two extractants, trioctyl amine (TOA) and Aliquat 336, in three diluents (methylisobutyl ketone (MIBK), octanol and paraffin liquid). The effects of organic phase extractant concentration and aqueous phase pH on the extraction process were examined. Among the extractants, TOA was found to be a better extractant than Aliquat 336 in all the diluents. In experiments with 50% (v/v) TOA in methylisobutyl ketone, 79% lactic acid could be extracted (initial lactic acid concentration 86·96 g dm−3). MIBK had a profound effect on the extraction behaviour of TOA in comparison with octanol and paraffin liquid while none of the diluents affected the extraction with Aliquat 336. The extraction of lactic acid was favoured at low pH. The toxicities of TOA and the diluents to Lactobacillus rhamnosus NRRL B445 were also studied. While TOA was found to be highly toxic at the molecular and the phase level, the paraffin liquid was totally non-toxic. The extraction of glucose and yeast extract by TOA and the diluents used was found to be low, which thus enables the selective extraction of lactic acid.

Trends in bacterial trehalose metabolism and significant nodes of metabolic pathway in the direction of trehalose accumulation

The current knowledge of trehalose biosynthesis under stress conditions is incomplete and needs further research. Since trehalose finds industrial and pharmaceutical applications, enhanced accumulation of trehalose in bacteria seems advantageous for commercial production. Moreover, physiological role of trehalose is a key to generate stress resistant bacteria by metabolic engineering. Although trehalose biosynthesis requires few metabolites and enzyme reactions, it appears to have a more complex metabolic regulation. Trehalose biosynthesis in bacteria is known through three pathways – OtsAB, TreYZ and TreS. The interconnections of in vivo synthesis of trehalose, glycogen or maltose were most interesting to investigate in recent years. Further, enzymes at different nodes (glucose‐6‐P, glucose‐1‐P and NDP‐glucose) of metabolic pathways influence enhancement of trehalose accumulation. Most of the study of trehalose biosynthesis was explored in medically significant Mycobacterium, research model Escherichia coli, industrially applicable Corynebacterium and food and probiotic interest Propionibacterium freudenreichii. Therefore, the present review dealt with the trehalose metabolism in these bacteria. In addition, an effort was made to recognize how enzymes at different nodes of metabolic pathway can influence trehalose accumulation.

Nitrilase-catalysed conversion of acrylonitrile by free and immobilized cells of Streptomyces sp.

The biotransformation of acrylonitrile was investigated using thermophilic nitrilase produced from a new isolate Streptomyces sp. MTCC 7546 in both the free and immobilized state. Under optimal conditions, the enzyme converts nitriles to acids without the formation of amides. The whole cells of the isolate were immobilized in agar-agar and the beads so formed were evaluated for 25 cycles at 50°C. The enzyme showed a little loss of activity during reuse. Seventy-one per cent of 0.5 M acrylonitrile was converted to acid at 6 h of incubation at a very low density of immobilized cells, while 100% conversion was observed at 3 h by free cells.

Use of an osmotically sensitive mutant of Propionibacterium freudenreichii subspp. shermanii for the simultaneous productions of organic acids and trehalose from biodiesel waste based crude glycerol

Recently suitability of crude glycerol for trehalose and propionic acid productions was reported using Propionibacterium freudenreichii subspp. shermanii and it was concluded that presence of KCl in crude glycerol was the probable reason for higher trehalose accumulation with crude glycerol medium. To further improve trehalose production, an osmotic sensitive mutant of this strain (non-viable in medium with 3% NaCl) with higher trehalose yield was isolated. In mutant, trehalose yields achieved with respect to biomass and substrate consumed (391 mg/g of biomass, 90 mg/g of substrate consumed) were three and four times higher, respectively as compared to parent strain when crude glycerol was used as a carbon source. Other major fermentation products obtained were propionic acid (0.42 g/g of substrate consumed) and lactic acid (0.3g/g of substrate consumed). It was also observed that in mutant higher activity of ADP-glucose pyrophosphorylase was probably responsible for higher trehalose accumulation.

Suitability of crude glycerol obtained from biodiesel waste for the production of trehalose and propionic acid

Crude glycerol is a major by-product of the biodiesel manufacturing industry. Utilization of this by-product is an area of interest among biotechnologists and chemists. In particular, many thermo-chemical and biological methods are available for the conversion of crude glycerol into useful products. The objective of the present study was to determine the suitability of crude glycerol for trehalose (non-reducing sugar) and propionic acid productions by a food microbe, Propionibacterium freudenreichii subsp. shermanii. It was observed that crude glycerol obtained from biodiesel waste favoured higher yields of trehalose and propionic acid production as compared to pure glycerol. In crude glycerol medium, the maximum trehalose yield (based on substrate consumed) achieved was approximately 6.5 times higher as compared to pure glycerol medium. Similarly, the propionic acid yield obtained in crude glycerol medium was two times higher than in pure glycerol. Thus, this study clearly demonstrated the superiority of crude glycerol medium over pure glycerol medium for the simultaneous fermentative production of propionic acid and trehalose. It was also predicted that due to the presence of KCl in crude glycerol, the trehalose yield based on substrate consumed was increased significantly. It was also observed that 10 g l−1 of crude glycerol was the optimum concentration for fermentative production of trehalose and propionic acid.

Lactic acid fermentation in cell-recycle membrane bioreactor

Traditional lactic acid fermentation suffers from low productivity and low product purity. Cell-recycle fermentation has become one of the methods to obtain high cell density, which results in higher productivity. Lactic acid fermentation was investigated in a cell-recycle membrane bioreactor at higher substrate concentrations of 100 and 120 g/dm3. A maximum cell density of 145 g/dm3 and a maximum productivity of 34 g/(dm3…h) were achieved in cell-recycle fermentation. In spite of complete consumption of substrate, there was a continuous increase in cell density in cell-recycle fermentation. Control of cell density in cell-recycle fermentation was attempted by cell bleeding and reduction in yeast extract concentration.

Competitive adsorptions of nitrile hydratase and amidase on polyacrylonitrile and its effect on surface modification

In this study, enzymatic surface modification of polyacrylonitrile was studied using nitrile metabolizing enzyme of Amycolatopsis sp. IITR 215. During enzymatic treatment of polyacrylonitrile at pH of 5.8 and 7, it was observed that the conversion of cyano group to carboxylic acid at pH 5.8 was three times higher than at pH 7. This difference in enzymatic treatment efficiency was explained by studying the differences in adsorption profiles of nitrile hydratase and amidase on polyacrylonitrile at pH of 5.8 and 7. Adsorption profiles were determined by monitoring the unbound activities of these two enzymes in the supernatant. From the specific activity profiles of bound nitrile hydratase and amidase it was concluded that more specific binding of nitrile hydratase was observed at pH 5.8 as compared to pH 7. In case of amidase, optimum adsorption was obtained at pH 5.8 within 5h whereas in case of pH 7 it was obtained within 20 h. Thus at pH 7, sequential adsorption of nitrile hydratase and amidase was observed and this adsorption profile was similar to the Vroman effect reported during plasma protein adsorption at solid-liquid interface. Ideally, specific nitrile hydratase adsorption followed by sequential adsorption of amidase may enhance higher conversion of cyano group to carboxylic acid.

Biobleaching of nonwoody pulps using xylanase of Bacillus brevis BISR-062.

The efficiency of xylanase of Bacillus brevis BISR-062 as a prebleaching agent was evaluated on three nonwoody pulps at two different pH values (7.0 and 8.5). Crude xylanase was found to have an optimum temperature and pH of 65–70°C and 7.0, respectively. The stability of the enzyme was determined at two pH values (7.0 and 8.0), and it lost approx 50% of its activity at both values within 2 h at 50°C. However, the enzyme was found to be effective as a prebleaching agent only with rice straw pulp. A maximum brightness gain of 6 points was obtained with this pulp at pH 7.0. The strength properties of the rice straw pulp at pH 7.0 also improved as the result of enzyme treatment.

Enzymatic surface modification of polyacrylonitrile and its copolymers: Effects of polymer surface area and protein adsorption

Polyacrylonitrile (PAN) is a widely used polymer in the textile industry. PAN contains cyano groups on the surface due to which it possess low hydrophilicity and limits its application. Thus, there is a need to modify the functional groups on the surface of PAN for its industrial demand to improve moisture uptake, dyeability with ionic dyes, without affecting mechanical properties. A number of strategies such as chemical treatment, plasma treatment, enzymatic treatment etc. have been applied for the surface modification of polymer but enzymatic treatment are advantageous over plasma treatment and chemical treatment. In enzymatic treatment, reaction is limited to polymer surface only, and provides milder condition with less damage to polymer. In present study, it was found that enzyme system of Amycolatopsis sp.IITR215 was effective enzyme system for modification of surface nitrile groups of polyacrylonitrile. PAN powder was treated with the cell free extract of Amycolatopsis sp.IITR215 and it was found that the nitrile metabolizing enzymes of this strain were efficiently able to transform -CN to -COOH groups present on the surfaces of PAN powder. The formation of carboxyl group was quantified by ammonia released and dye binding assay. Further, confirmation of carboxyl group on polymer was done by FTIR and XPS. This study indicates that, specific adsorption of enzyme probably plays an important role in the enzymatic surface modification of polymer.

Potential Role of Halophile in Crude Glycerol Based Biorefinery

Biorefinery includes microbial fermentation processes which could utilize glycerol as raw material for the production of bio-derived building block compounds and polymers. The recent expansion in biodiesel market has resulted in a remarkable transformation in availability and subsequent cost of glycerol, which is generated at 10% of total biodiesel produced. Being produced in excess, crude glycerol price has suffered a major decline, thereby affecting the economics of biodiesel industry. Purification of crude glycerol for use in cosmetics and pharmaceutical industry increases the production cost and hence not considered as a viable option for disposal of such huge amount of glycerol, which also poses an environmental concern. Thus the crude glycerol based refinery concept is being explored whose objective should be to actualize technologies for valorization of waste glycerol. The major challenge thwarting the development of such biorefinery is obtaining microbial strains tolerant of crude glycerol along with its impurities. However, concentrated crude glycerol has rarely been used for microbial conversion to value-added products. High usage of portable water is required to dilute concentrated crude glycerol for crude glycerol based biorefinery. In this chapter, the recent attempts to explore microbial assimilation of glycerol has been summarized. Besides how halophiles can be considered as a viable alternative for valorization of crude glycerol is presented.