Marybeth Lima

The effects of ohmic heating frequency on hot-air drying rate and juice yield

Ohmic pretreatment of fruit and vegetable samples has been shown to increase hot-air drying rate, shift desorption isotherms, and increase juice yields over raw samples or those pretreated with conventional or microwave heating. The frequency of alternating current has been found to alter heat and mass transfer properties. In this study, the hot-air drying rate of yam and the juice yields of apples were compared using a 60 Hz sine wave and a 4 Hz sawtooth wave to determine if lowering the frequency would result in additional improvements to these processes. The 4 Hz sawtooth wave resulted in a faster hot-air drying rate of yam cylinders than the 60 Hz sine wave. The drying rates of the 4 Hz pretreated samples were significantly greater during most of the drying process, with the most pronounced differences occurring during intermediate stages of drying. The electric field strength affected the drying curves in the range tested at 4 and 60 Hz. Apple juice yield was improved by ohmic pretreatment, with 4 Hz sawtooth samples yielding significantly greater quantities than the 60 Hz sinusoidal pretreatment. Due to increased electrical conductivity at 4 Hz, pretreatments at this frequency require considerably less time than pretreatments at 60 Hz The efficiency of mass transfer processes appears to be significantly dependent on waveform and frequency of alternating current. These phenomena could have useful applications for food processing.

Microwave assisted extraction of biodiesel feedstock from the seeds of invasive Chinese tallow tree.

Chinese tallow tree (TT) seeds are a rich source of lipids and have the potential to be a biodiesel feedstock, but currently, its invasive nature does not favor large scale cultivation. Being a nonfood material, they have many advantages over conventional crops that are used for biodiesel production. The purpose of this study was to determine optimal oil extraction parameters in a batch-type and laboratory scale continuous-flow microwave system to obtain maximum oil recovery from whole TT seeds using ethanol as the extracting solvent. For the batch system, extractions were carried out for different time-temperature combinations ranging from 60 to 120 degrees C for up to 20 min. The batch system was modified for continuous extractions, which were carried out at 50, 60, and 73 degrees C and maintained for various residence times of up to 20 min. Control runs were performed under similar extraction conditions and the results compared well, especially when accounting for extremely short extraction times (minutes vs hours). Maximum yields of 35.32% and 32.51% (by weight of dry mass) were obtained for the continuous and batch process, respectively. The major advantage of microwave assisted solvent extraction is the reduced time of extraction required to obtain total recoverable lipids, with corresponding reduction in energy consumption costs per unit of lipid extracted. This study indicates that microwave extraction using ethanol as a solvent can be used as a viable alternative to conventional lipid extraction techniques for TT seeds.

Continuous microwave-assisted isoflavone extraction system: Design and performance evaluation

The purpose of this research was to design, test, and optimize a continuous microwave extraction method using temperature and residence time during and after microwave exposure as optimizing parameters for extraction of major isoflavones (genistin, genistein, daidzin, and daidzein) from soy flour. The extraction yield of four isoflavones at different heating temperatures (55 and 73 degrees C) and extraction times (0, 4, 8, 12, and 16 min) were investigated and compared with yields provided by a conventional solvent extraction method. The microwave prototype consisted of multiple, commercially available, batch-type, house-hold microwave units placed on top of each other in series to impart a continuous operation. The optimum parameters for microwave-assisted extraction of isoflavones were 73 degrees C for 8 min using a 3:1 ethanol-to soy flour ratio. At these parameters, the total yield of isoflavones extracted doubled, while the amount of oil extracted was 12%. Continuous microwave-assisted solvent extraction is a viable method for extraction of soybean isoflavones at relatively short residence times and high throughput.

A critical comparison of methyl and ethyl esters production from soybean and rice bran oil in the presence of microwaves.

Transesterification of vegetable oils (from soybeans and rice bran) into methyl and ethyl esters using a batch microwave system was investigated in this study. A critical comparison between the two alcohols was performed in terms of yields, quality, and reaction kinetics. Parameters tested were temperature (60, 70 and 80°C) and time (5, 10, 15 and 20 min). At all tested conditions, more than 96% conversion rates were obtained for both ethanol and methanol. Use of microwave technology to assist the transesterification process resulted in faster reaction times and reduced catalyst requirement (about ten-fold decrease). Methanol required lower alcohol:oil ratios than normally used in conventional heating, whereas ethanol required higher molar ratios. All esters produced using this method met ASTM biodiesel quality specifications. Methanol performed better in terms of performance and costs, while ethanol may have some environmental and safety benefits.

Microwave-Assisted Extraction of Soybean and Rice Bran Oil: Yield and Extraction Kinetics

Microwave-assisted solvent extraction has the potential to replace traditional solvent extraction of oils and fats from a variety of feedstock. The purpose of this study was to optimize oil extraction parameters for a batch microwave system from two feedstocks: soybeans and rice bran. Solvent-feedstock mixtures were exposed to microwave radiation for different time-temperature combinations ranging from 60°C to 120°C for up to 20 min with simultaneous magnetic stirring. The solvent (ethanol) to feedstock ratio used was 3:1. After extraction, solid-liquid separation was performed in a vacuum filter, and ethanol was evaporated from the filtrate in a vacuum centrifuge. Results showed that the oil yield changed with temperature and achieved a maximum value in a relatively short time (order of minutes). Continuous exposure after this time did not increase the oil yield. The results compared well with traditional solvent extraction, especially when accounting for the extremely short extraction times (min vs. h). Maximum oil yields of 17.3% and 17.2% at 20 min and 120°C were achieved by microwave extraction as compared to 11.3% and 12.4% using control extraction for soybeans and rice bran, respectively. The major advantage of microwave-assisted solvent extraction is the reduced time of extraction required to obtain ~95% of total recoverable oil, with corresponding reduction in energy consumption costs per unit of oil extracted.

LONGITUDINAL SURVEY OF FEMALE FACULTY IN BIOLOGICAL AND AGRICULTURAL ENGINEERING

Female faculty in biological and agricultural engineering (BAE) were surveyed in 1998 to examine their professional experiences, motivations, and insights. Approximately 7% of all BAE faculty were women in 1998, and the total number of women in the population was 57. Results, based on a 61% response rate, showed that 60% of the population was at the assistant professor rank. Respondents reported that BAE departments provided a supportive environment and believed that the attraction of women to BAE was due to its emphasis on biological systems, as well as biological engineerings relative newness and lack of long-standing stereotypes of male dominance. Full results of the original survey were published in the Journal of Women and Minorities in Science and Engineering in 2000. We re-surveyed the population of women in BAE in 2006 because we believe that longitudinal data on this population will provide interesting insights into this group and its experiences in the profession, and may suggest ways to increase female representation among engineering faculty. The population is now comprised of 89 women and represents approximately 11% of BAE faculty. Approximately 85% of all women in the original 1998 survey population are included in the current population. Reasons given by those exiting the population include staying in academia but moving to non-BAE departments such as chemical engineering or bioengineering, being promoted to academic leadership positions without retaining primary BAE status, or pursuing other non-academic professional opportunities. Forty-nine percent of the population are now assistant professors, and the number of BAE full professors increased from 10% in 1998 to 19% in 2006. A significant number of women BAE faculty have engineers and/or faculty members within their immediate families; two respondents are second-generation women engineers. The reported self-confidence level of women faculty is 65%, the same as the 1998 survey. Ninety-five percent of respondents act as mentors to others (up from 72% in 1998). Eighty-four percent of respondents do not feel that they have experienced space inequities, and 73% do not believe they have experienced salary inequities. Lack of support for dual-career couples and other family issues were mentioned by 48% of respondents as issues that could be addressed to improve the climate for women faculty in BAE; these issues were mentioned more often in 2006 than in 1998.

Microwave-assisted Transesterification of Soybean and Rice Bran Oil to Biodiesel

Microwave-assisted transesterification of oils offers the advantages of shorter reaction times, a lower alcohol/oil ratio, reduced catalyst consumption and an energy efficient operation. The purpose of this study was to optimize transesterification parameters for a batch microwave system using refined soybean and rice bran oil in the presence of two different alcohols namely methanol (predominantly used) and ethanol (safer alternative). Sodium hydroxide at 95% were achieved under all experimental conditions tested. Experimental results concluded that methanol was more suitable solvent than ethanol for biodiesel production. The biodiesel thus obtained was analyzed using various ASTM standards to determine if it met the required standards.