Date of Award
Doctor of Philosophy
There are concerns about using synthetic phenolic antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) as food additives because negative effects to human health have been reported. thus, a replacement of these synthetics by antioxidant extractions from various foods has been proposed. By the generation of more than eight thousand different phenolics, fruits and vegetables are the prime sources of natural antioxidants. The consumption of fruits and vegetables has been strongly linked with several health benefits, a result of their medicinal properties and high nutritional value. Antioxidants control and reduce the oxidative damage in foods by delaying or inhibiting oxidation caused by reactive oxygen species (ROHs); ultimately increasing the shelf-life and quality of these foods.Beta-carotene, ascorbic acid, and many phenolics play dynamic roles in delaying aging, reducing inflammations, and preventing certain cancers. Increasing the consumption of fruits and vegetables has been recommended by many agencies and health care systems. In order to extract, measure, and identify bioactive compounds from a wide variety of fruits and vegetables, researchers use many different techniques and methods. Ultrasonic assisted technique (UAE) is known to be one of the easiest extraction techniques because it uses common laboratory equipment such as ultrasonic baths and probes. In this technique, a smashed sample is mixed with the suitable solvent and placed into the ultrasonic bath while temperature and extraction time are controlled. Five experiments were conducted to study the effects of different ultrasonic parameters on the polyphenol and antioxidant content and antimicrobial activity of extracts from plants grown in southern Illinois. In the first experiment, ultrasonic treatments at different frequencies,temperatures, power levels, and exposure times were compared for their effects on the yield of total phenolics, total flavonoids and antioxidant activities of spinach extracts. The best conditions for extraction judged by yields were an ultrasonic frequency of 37 kHz, extraction time of 30 min, reaction temperature of 400C, and ultrasonic power of 50%. The mean yield (mg/100g), total phenolics (mg gallic acid equivalence/ g DW), flavonoids (mg/g DW), % DPPH free radical scavenging activity, and % ferric reducing antioxidant power were all high (64.88±21.84, 33.96±11.30, 27.37±11.85 , 64.18±16.69 and 70.25 ±9.68). In the second experiment, the study was designed to optimize ultrasonic-assisted extraction of lutein and β-carotene from spinach. Further, the identities and purity of the natural products in the TLC spots were assayed using matrix-assisted laser desorption/ionization time-off-light mass spectrometry (MALDI-TOF MS) analysis. The optimal UAE settings for output of lutein and β-carotene simultaneously from spinach extracts were an extraction temperature of 40 °C, extraction power of 40% (28 W/cm3) and extraction time of 16 min. UAE assisted extraction of carotenes from spinach can provide a source of lutein and β-carotene for the dietary supplement industry. In the third study, investigations of the effects of extraction parameters for UAE on antioxidant activity of peach and pumpkin extracts; and studying the chemical structures of samples before and after processing by Fourier transformed infrared spectroscopy were made. The optimal conditions for peach extracts were an extraction temperature of 41.53 ̊C, power of 43.99 % and time of 27.86 min for total phenolics. The optimal conditions for extractions of total phenolics from pumpkins were inferred to be a temperature of 41.45 ̊C, a power of 44.60 % and a time of 25.67 min. In the fourth study, TLC followed by Quantity-OneTM (Biorad) image analysis was used as a simple and rapid method for identification and quantification of compounds in complex mixtures. The results were consistent under optimal conditions among the experimental values and their predicted values. The MALDI-TOF MS technique was also applied for result confirmation. In the last experiments, UAE and Box-Wilson design were applied to optimize the extraction of antimicrobial activities from spinach extracts and to test their antimicrobial activities on both Gram-negative and Gram-positive bacteria. The spinach extracts exhibited antimicrobial activities against both bacterial pathogens with MICs in the 60-100 mg.ml-1 range. SEM showed that cells of the treated bacterial strains were damaged and showed structural defects compared to the controls. RAPD analysis of genomic DNA showed that the number and sizes of amplicons were decreased for the treated pathogens compared with non-treated strains.
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