Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Food Science and Technology

Major Professor

F. Ann Draughon

Committee Members

John R Mount, Dayrl Golden


The demand for safe and minimally processed food and "nutraceuticals" has created a market for natural antimicrobials. Limited studies have investigated herbal medicine's safety, inhibitory and lethality effect to pathogenic microorganisms and the antimicrobial efficacy of herbs in food model systems such as chicken. Our objectives were to evaluate the antimicrobial and mutagenic activities of commercial herbal extracts and to investigate the antimicrobial efficacy of herbs to spoilage and pathogenic bacteria in marinated chicken. Essential oils and/or herbal extracts of bilberry, black cohosh, cranberry, evening primrose oil, flax seed, garlic, ginko, ginseng, goldenseal, gotu kola, grapefruit oil, grapefruit seed (GSE), kava-kava, lemon balm, marjoram, milk thistle, oregano, pau d'arco, skullcap, hypericum, thyme, and valerian were evaluated for antimicrobial activity by the disc agar diffusion method. Mutagenicity of selected herbs was determined by the Ames test. The mutagenicity ratio (MR) was calculated based on # revertants/plate as compared to control (MR > 2.0 = strongly mutagenic). The minimum lethal concentration (MLC) was evaluated by the tube dilution method to determine toxicity prior to mutagenicity assay. Fresh chicken breasts were inoculated (~ log 6 CFU/g) with C.jejuni, S. Typhimurium, L. monocytogenes, and E. coli O157: H7. The following marinade treatments (base of water, salt, sodium phosphate, and citric acid; pH 4.5) were evaluated using fresh inoculated chicken breasts (20% marinade by weight of the chicken): control (no herbs), 0.3% of each GSE, oregano essential oil (ORG), thyme essential oil (THY), 1% dried oregano leaves (ORL), and combination of 0.3% of each GSE, ORG, and THY. APC and survival of pathogenic bacteria during storage at 4°C were determined at days 0, 3 ,6, 9,12, and 15. The most effective antimicrobial herbs were oregano (inhibition zone: 37-87 mm, MLC: <200-3125 ppm), thyme (inhibition zone: 42-87 mm, MLC: 200-1563 ppm), and GSE (inhibition zone: 15-66 mm, MLC: 200-6250 ppm). Bilberry, flax seed, milk thistle, pau d'arco, and scullcap were the least effective antimicrobial herbs against all bacterial pathogens. Hypericum, ginko, and goldenseal were strongly mutagenic (Average MR= 4.6, 3.4, and 2.1, respectively). Black cohosh, cranberry, gotu kola, GSE, kava-kava, pau d'arco, marjoram, oregano, and valerian showed various degrees of weak mutagenicity. ORE marinade was the least effective treatment in inhibiting all microorganisms. The GSE marinade reduced the APC and growth of C.jejuni, (<2 log CFU/g) but did not significantly inhibit S. Typhimurium, E. coli O157:H7, or Z. monocytogenes (P>0.05). THY, ORG, and the combination treatment significantly reduced microbial counts (P<0.05). The combination treatment was the most effective (P<0.05) in reducing APC and E. coli O157:H7, and was highly lethal (~ log 4 CFU/g reduction) to S. Typhimurium, C.jejuni, and L monocytogenes. The mutagenicity data show that some frequently used herbs may also be strong mutagens and thus potential carcinogens. Further genetic toxicology testing is warranted for concentrated herbal extracts such as hypericum, ginko, and goldenseal due to their growing popularity and mutagenicity in the Ames test. Our data suggest that selected herbs have powerful antimicrobial potency both in culture media and chicken marinade and may be used to increase the shelf life and safety of value-added poultry products.

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