Ranjana Prakash

Selenium bioaccessibility and speciation in biofortified Pleurotus mushrooms grown on selenium-rich agricultural residues

Cultivation of saprophytic fungi on selenium-rich substrates can be an effective means to produce selenium-fortified food. Pleurotus florida, an edible species of oyster mushrooms, was grown on wheat straw from the seleniferous belt of Punjab (India) and its potential to mobilize and accumulate selenium from the growth substrate was studied. Selenium concentration in biofortified mushrooms was 800 times higher compared with control samples grown on wheat straw from non selenium-rich areas (141 vs 0.17 μg Se g(-1) dry weight). Seventy-five percent of the selenium was extracted after in vitro simulated gastrointestinal digestion and investigation of the selenium molecular fractions by size exclusion HPLC-ICP-MS revealed that proteins and any other high molecular weight selenium-containing molecule were hydrolyzed to peptides and low molecular weight selenocompounds. Analysis of the gastrointestinal hydrolysates by anion exchange HPLC-ICP-MS showed that the bioaccessible selenium was mainly present as selenomethionine, a good bioavailable source of selenium, which accounted for 73% of the sum of the detected species. This study demonstrates the feasibility of producing selenium-biofortified edible mushrooms using selenium-rich agricultural by-products as growth substrates. The proposed approach can be used to evaluate whether selenium-contaminated plant waste materials harvested from high-selenium areas may be used to produce selenium-biofortified edible mushrooms based on the concentration, bioaccessibility and speciation of selenium in the mushrooms.

Aerobic microbial manufacture of nanoscale selenium: exploiting nature’s bio-nanomineralization potential

The potential of the environment to yield organisms that can produce functional bionanominerals is demonstrated by selenium-tolerant, aerobic bacteria isolated from a seleniferous rhizosphere soil. An isolate, NS3, was identified as a Bacillus species (EU573774.1) based on morphological and 16S rRNA characterization. This strain reduced Se(IV) under aerobic conditions to produce amorphous α Se(0) nanospheres. A room-temperature washing treatment was then employed to remove the biomass and resulted in the production of clusters of hexagonal Se(0) nano-rods. The Se(0) nanominerals were analyzed using electron microscopy and X-ray diffraction techniques. This Bacillus isolate has the potential to be used both in the neutralizing of toxic Se(IV) anions in the environment and in the environmentally friendly manufacture of nanomaterials.

Optimization of medium and process parameters for the production of lipase from an oil-tolerant Aspergillus sp. (RBD-01).

Extracellular lipase production by Aspergillus sp. (RBD‐01) was monitored by modulating pH of the growth medium, ambient temperature for growth, source of nitrogen and percentage of carbon (virgin cottonseed oil). This strain was observed to be viable and produces lipase even up to 50% oil as a main carbon source. Maximum lipase activity of 21.8 U/ml was obtained with 50% (v/v) oil acting as the main carbon source and peptone (0.5% w/v) as nitrogen source. The optimum pH and temperature for enzymatic activity were observed to be 7.5 and 35 °C, respectively. The observations are of significance due to limited reports on use of 50% of oil as the main carbon source while obtaining significant lipase activity of 21.8 U/ml. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Bioaccessibility of selenium from Se-rich food grains of the seleniferous region of Punjab, India as analyzed by instrumental neutron activation analysis

In the present study, selenium (Se) bioaccessibility was measured in rice and maize cultivated in seleniferous soil of India using in vitro gastric (GA) digestion and gastro-intestinal (GI) digestion methods. The concentration of bioaccessible Se was determined by instrumental neutron activation analysis (INAA). The total Se was observed to be about 58.0 mg kg−1 and 29.0 mg kg−1 in flours of rice and maize, respectively. Total Se content in maize flour sample after GA and GI digestions were approximately 9.5 mg kg−1 and 15.0 mg kg−1, respectively; and in case of rice samples, the levels were about 32.0 mg kg−1 and 38.0 mg kg−1, respectively. The results indicate that the bioaccessibility of GI digestion (51% in maize and 65% in rice) was higher compared to GA digestion (32% and 52% in maize and rice, respectively). In addition, the bioaccessible levels of Se were significantly more in case of rice compared to maize.

Transesterification of used edible and non-edible oils to alkyl esters by Aspergillus sp. as a whole cell catalyst.

Aspergillus sp. (MTCC 5436), isolated from contaminated clarified butter was used as a whole cell catalyst for transesterification of oils from different sources. The strain was observed to be tolerant and grow in 90% oil as carbon source. Oils of Jathropa, karanj and spent cottonseed were used as carbon sources in the study. The product, alkyl ester, was characterized and quantified using 1H‐NMR. The strain was observed to facilitate transesterification in an oil:minimal medium with the ratio of 70:30 resulting in a 98% conversion of oil to ethyl esters within 48 h at 28 °C and 120 rpm. The physico‐chemical characteristics of the ethyl ester (>98%) at 70% oil as carbon source were similar to the standards specified for biodiesel as per standards of American Society for Testing and Materials (ASTM) and Bureau of Indian Standards (BIS), India. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Selenium Mobilization by Pseudomonas aeruginosa (SNT-SG1) Isolated from Seleniferous Soils from India

Selenium (Se) is a metalloid required at trace concentrations for normal metabolic activities of the cell. The bioavailable forms viz., selenate and selenite have been found in localized high concentrations in seleniferous environments. Studies are in progress on bacterial strains that were isolated from one such location in the North-West region of Punjab, India. A facultative anaerobe, identified as Pseudomonas aeruginosa by 16S rRNA gene homology, was isolated from the rhizosphere of crop plants from this region and was examined for selenium mobilization potential in the presence of selenium oxyanions. The isolate was observed to reduce 53 and 21% of sodium selenite and selenate to elemental selenium, respectively, and volatilize 4.7 and 5.1% within 72-hour duration. This is one of the few selenium tolerant aerobic bacteria isolated and reported from tropical seleniferous soils from India, and the first to show volatilization potential. These organisms are being considered for bioaugmenting Se-impacted soils for enhanced Se mobilization and removal.

Whole cell catalyzed esterification of fatty acids to biodiesel using Aspergillus sp.

Abstract Powdered biomass of Aspergillus sp. (RBD01) was used to carry out esterification of long chain fatty acids for biodiesel production. Dry biomass of Aspergillus sp. at 20% (w/w) with respect to the fatty acid was able to completely esterify oleic acid to ethyl ester at 35°C, in 36 h, with step wise addition of alcohol. Similar conditions also resulted in yield of 64.5% and 58% of ethyl ester from stearic acid and palmitic acid, respectively. However, the presence of methanol resulted in 87.5%, 71% and 41% of methyl ester from oleic, palmitic and stearic acid. Furthermore, it was found that the efficiency of biomass decreased by only 10% with its repeated use up to four cycles.

Effect of frying time on free fatty acid generation and esterification rate in Aspergillus sp.-catalyzed transesterification of cottonseed oil

Abstract The present study was carried out to examine the effect of different frying times of edible oil on the extent of transesterification catalyzed by the whole-cell biocatalyst, Aspergillus (RBD01). Cottonseed oil was chosen as a conventional and cost-effective edible oil used commercially in India. The results showed that increased frying time of the oil decreased the extent of the transesterification reaction and hence alkyl ester production. Nearly complete (>98%) transesterification to ethyl alcohol was observed with used oil containing a free fatty acid (FFA) content of 3.7%, whereas beyond an FFA content of 4.0% the yield was reduced. Biocatalyzed hydrolysis (in the absence of the ethyl alcohol acceptor) of used frying oil resulted in decreasing yield of FFA from 84.0% to 27.6% with increasing frying time. With fried oil capable of a hydrolysis yield of 82–41% FFA, transesterification reactions were nearly complete. With the lower hydrolysis yields of 38–27% FFA, the transesterified ethyl ester yield decreased to 61–51%. These observations indicate that factors other than the presence of FFA and moisture influence the biocatalytic transesterification of used cooking oils.

Fuel properties of blend and biodiesel generated from acid oil using whole cell biocatalyst

ABSTRACT Biodiesel was generated through whole cell catalyzed transesterification of acid oil, to the extent of up to 92%. The fuel properties of biodiesel (B100) and its blend (B20) were determined and compared with standard biodiesel as per American Society for Testing and Materials (ASTM) standard (ASTM D6751). B100 and B20 showed good pour point of −26°C and −29°C, respectively, indicating their operation viability in colder environment. Other properties of biodiesel are quite similar to petroleum diesel and ASTM standard. The results of this study reveal the potential use of acid oil as feedstock for generation of fuel grade biodiesel through biocatalyzed transesterification.

Selenium fortification and pro/anti oxidant responses in Allium cepa (onion) cultivated in Se supplemented soils.

Native plantlets of Allium cepa (onion) were cultivated in selenium (Se)-supplemented soils to observe dose- and time-dependent uptake and associated pro/anti-oxidant activity. Allium plantlets were grown in soils supplemented with Se at 2.5, 5.0 and 7.5 mg kg −1 as selenite (Na 2 SeO 3 ) and selenate (Na 2 SeO 4 ) for 40–120 days. The effect of different concentrations of Se oxyanions on the growth and accumulation profile in plants in relation to glutathione peroxidase activity and thiobarbituric acid reactive substances was studied. Total Se concentrations in plantlets were determined by instrumental neutron activation analysis. The accumulation of Se in plant was observed to be dose dependent in the case of selenite, but, no definite correlation between accumulation levels and exposed concentration was observed. The changes in pro/anti-oxidant properties were observed to be dependent on the accumulation of Se in plant.