Biomedical subjects

G S Raghavan

Publications and source records attributed to G S Raghavan.

7 recordsLinked to original sources

PubMed2001

Multivariate calibration for the determination of total azadirachtin-related limonoids and simple terpenoids in neem extracts using vanillin assay.

Two-component and multivariate calibration techniques were developed for the simultaneous quantification of total azadirachtin-related limonoids (AZRL) and simple terpenoids (ST) in neem extracts using vanillin assay. A mathematical modeling method was also developed to aid in the analysis of the spectra and to simplify the calculations. The mathematical models were used in a two-component calibration (using azadirachtin and limonene as standards) for samples containing mainly limonoids and terpenoids (such as neem seed kernel extracts). However, for the extracts from other parts of neem, such as neem leaf, a multivariate calibration was necessary to eliminate the possible interference from phenolics and other components in order to obtain the accurate content of AZRL and ST. It was demonstrated that the accuracy of the vanillin assay in predicting the content of azadirachtin in a model mixture containing limonene (25% w/w) can be improved from 50% overestimation to 95% accuracy using the two-component calibration, while predicting the content of limonene with 98% accuracy. Both calibration techniques were applied to estimate the content of AZRL and ST in different parts of the neem plant. The results of this study indicated that the relative content of limonoids was much higher than that of the terpenoids in all parts of the neem plant studied.

Benzaldehydes↗

PubMed2001

Influence of operating parameters on the use of the microwave-assisted process (MAP) for the extraction of azadirachtin-related limonoids from neem (Azadirachta indica) under atmospheric pressure conditions.

The use of the microwave-assisted process (MAP) for the extraction of azadirachtin-related limonoids (AZRL) from various parts of the neem tree was investigated under different operating conditions. The influence of microwave power, solvent, and irradiation time on the recovery of AZRL was studied. The efficiency of the microwave-assisted extraction (MAE) of the seed kernel, the seed shell, the leaf, and the leaf stem was compared to that of conventional extraction methods. The content of AZRL in the extracts was estimated with a vanillin-based colorimetric assay and a multivariate calibration technique. The results showed that the MAE technique can enhance the extraction of AZRL from different parts of neem possessing microstructures. Investigation of the influence of the solvent also indicted that the solvent used not only influences the efficiency but also affects the selectivity of the MAE.

Atmospheric Pressure↗

PubMed2001

A slotted waveguide applicator for continuous flow grain drying.

A slotted waveguide antenna was designed and developed with series slots cut on the broad side that constituted a popular means of coupling microwaves with grain for drying. The radiating characteristics of the slotted wave guide antenna mounted in a setup that simulated the coupling to a grain conveying tube were studied at a frequency of 2.45 GHz. The antenna consisted of a WR-340 waveguide made of copper. The effect of the slot inclination angle O, moisture content and the shape of the slots were investigated. The results indicated 55 degrees as an optimum slot angle for slots having a width of 13 mm and a length 58 mm. Slots with a width of 6 mm did not exhibit any regular behavior and the effect of O was not clearly identified.

Desiccation↗

PubMed2001

Microwave processing of maple sap to maple syrup and maple syrup products.

A study of the physical process of concentration of maple sap to maple syrup and preparation of maple syrup products by microwave heating is described. Duty cycles of 60, 75 and 100% were used for the microwave application. During the process, some of the drying kinetics are discussed, including the reduction of moisture content with time, the progress of the process in terms of increasing sugar concentration and the power absorbed. Obviously, the rate of water removal was higher in case of the higher duty cycles. The total time required for finishing the syrup was also dependent on the initial mass of the load and the initial sugar content. The products obtained were compared with commercial graded products for the quality and met the highest standards prescribed by the industry. The absence of heat damage or browning of the product was identified as a distinct advantage that could be derived from microwave processing of maple syrup.

Acer↗

PubMed2001

Microwave-assisted extraction of phenolic compounds from grape seed.

A microwave-assisted extraction technique was developed to optimize the extraction of phenolic compounds from grape seeds. The microwave power (300-150W) and time of extraction (20-200s) were varied during the optimization process. The polyphenol content of the resulting extracts were measured as mg of tannic acid equivalent per gram of crude extract (mg TAE/g of crude extract), using a Folin-Ciocalteau reagent. In general, neither the time nor the power had a significant effect on the overall % yield (average of 13.5%) and on the polyphenol content (392 mg TAE/g of crude extract) of the extracts. However, when the solvent polarity was changed by the addition of 10% water, the yield increased to 15.2% and the polyphenol content increased to 429 mg TAE/g of crude extract.

Antioxidants↗

PubMed1999

Extraction and colorimetric determination of azadirachtin-related limonoids in neem seed kernel.

A colorimetric method was developed for the determination of total azadirachtin-related limonoids (AZRL) in neem seed kernel extracts. The method employed acidified vanillin solution in methanol for the colorization of the standard azadirachtin or neem seed kernel extracts in dichloromethane. Through the investigation of various factors influencing the sensitivity of detection, such as the concentration of vanillin, acid, and the time required for the formation of color, optimum conditions were selected to perform the assay. Under the optimum conditions, a good linearity was found between the absorbance at 577 nm and the concentration of standard azadirachtin solution in the range of 0.01-0.10 mg/mL. In addition, different extraction procedures were evaluated using the vanillin assay. The HPLC analysis of the extracts indicated that if the extractions were performed in methanol followed by partitioning in dichloromethane, approximately 50% of the value determined by the vanillin assay represents azadirachtin content.

Colorimetry↗

PubMed1995

Dielectric properties of grapes and sugar solutions at 2.45 GHz.

Dielectric properties of grapes at 2.45 GHz were measured at moisture contents varying from 80 to 15% (wet basis) at temperatures ranging from 25-80 degrees C using the Open Ended Coaxial Transmission Line Technique. Both dielectric constant and loss factor decreased with decreasing moisture content. In low moisture samples these properties were found to be considerably influenced by higher temperatures. Dielectric properties of sugar solutions of varying concentrations (20-250% by weight in water) were also determined at different temperatures, and these values were compared to those of grapes of corresponding moisture concentration. Predictive models of the dieletric properties as functions of moisture content and temperature were generated using response surface methodology. The results are useful in estimating the volumetric heating of grapes by microwave energy, and these methods can be extended to sugar-based foods in general.

Electrochemistry↗