Abstract not available

Abstract not available

Abstract not available

Caffeine significantly repressed MMC induced $his\sp{-}$ reversion of wild type strains of Salmonella typhimurium in the standard plate reversion assay at high concentrations of MMC but not at low concentrations of MMC. The decrease in MMC induced revertants by caffeine was found to be accompanied by a decrease in the number of surviving cells. The incidence of MMC induced reversions with respect to the number of viable cells was increased by the addition of caffeine to culture media even though cell death was increased. Caffeine potentiated MMC induced cell death in S. typhimurium strains proficient in excision repair but not in excision repair deficient strains. Caffeine was more effective in wild type strains than in $recA\sp{-}$ or $polA\sp{-}$ strains. The presence of the resistance plasmid pKM101 did not alter the effectiveness of caffeine. Caffeine was found to potentiate the formation of crosslinks by MMC and to inhibit the removal of crosslinks induced by MMC in S. typhimurium strains proficient in excision repair but not in a excision repair deficient strain. The extent of the potentiation by caffeine of the formation of crosslinks in various strains correlated well with the potentiation by caffeine of MMC induced cell death. It is suggested that the potentiation by caffeine of MMC induced cell death is primarily due to the inhibition by caffeine of excision repair of crosslinks. Caffeine slightly increased the induction of recA gene expression by MMC in a wild type strain of Escherichia coli (but not in a uvrA strain) and the induction of umuC gene expression in both the wild type and uvrA strains. Among the SOS genes, recA and umuC genes are known to be involved in mutagenesis. The results of this study indicate that the apparent antimutagenic activity of caffeine on MMC induced mutations is due to the potentiation by caffeine of MMC induced cell death. Caffeine was found to potentiate MMC induced cell death primarily by inhibiting excision repair of interstrand DNA crosslinks induced by MMC. Caffeine may increase the rate of MMC induced mutations rate by inhibiting an error-free repair process (excision repair) and/or by increasing the induction of error-prone SOS functions.

Coat proteins from mature spores of two enterotoxin-positive (Ent$\sp+$) and two enterotoxin-negative (Ent$\sp-$) strains of Clostridium perfringens were solubilized using 50 mM dithiothreitol and 1% sodium dodecyl sulphate at pH 9.7, and alkylated using 110 mM iodoacetamide to prevent aggregation. SDS-PAGE patterns of solubilized spore coat proteins from different strains of C. perfringens show that the Ent$\sp+$ strains have similar major polypeptides (34- and 19-kDa). The Ent$\sp-$ strains also have similar coat protein composition (28- and 19-kDa major protein) distinct from that of the Ent$\sp+$ strains. The spore coat proteins seem to be synthesized under similar genetic control among strains of C. perfringens regardless of their ability to produce enterotoxin. The aggregation of enterotoxin in the presence of SDS did not occur at concentrations below 15 $\mu$g/ml. Enterotoxin was not a major structural component of the coat fraction of C. perfringens spores. But two enterotoxin-related proteins (34- and 48-kDa) were found in the solubilized spore coat protein of Ent$\sp+$ strains while only the 48 kDa enterotoxin-related protein was found in the spore coat fraction of Ent$\sp-$ strains. The possible precursor of enterotoxin (48-kDa) was detected in sporulating cell extracts of all seven strains of C. perfringens tested (NCTC 8239, NCTC 10240, ATCC 3624, ATCC 3626, FD1, 2498, 748) and in the vegetative cell extracts of four of these (NCTC 8239, FD1, 2498, 748). However enterotoxin itself was present in only Ent$\sp+$ strains (NCTC 8239, NCTC 10240). There was no clear relationship between the enterotoxin synthesis and the spore coat protein production even though netropsin and distamycin study showed that the syntheses of both were closely related to sporulation process of C. perfringens. In the absence of caffeine, netropsin and distamycin unexpectedly stimulated sporulation of C. perfringens NCTC 8679 grown in D sporulation medium although the majority of sporulating cells were defective.

This study investigates the interplay of naturally occurring pro- and antioxidants during deep-fat frying. The study has significance to the food industry because knowledge of these interactions are important for maintaining the sensory and nutritional quality of fried food. Antioxidant protection was observed in an oil blend of sunflower, olive and butteroil when used for potato frying, reflecting the presence of butteroil. Fractionation of butteroil and incorporation of these fractions into heating studies showed enhanced stability in the liquid fraction. Carotenoids and tocopherols may be responsible for this protection since these natural antioxidants are present in butteroil and are known to migrate to the liquid phase during fractionation. When butteroil was blended with sunflower oil and stored at 37$\sp\circ$C no antioxidant activity was observed, suggesting that the high temperatures of frying may also be necessary in the observed protection, i.e. through the production of malliard reaction products. When the oil blend was used to fry cod and analyzed for oxidation by polymer formation, the oil showed less polymers than expected, in comparison to the extensive oxidation reported by change in dielectric constant and fatty acid analysis. Subsequent studies suggest that polymers produced during the frying of cod may preferentially bind to the fish protein. When the cod was freeze-dried prior to frying, the fish was shown to protect the oil against oxidation. Lipid and non-lipid solid fractions of the fish exhibited antioxidant protection under similar conditions. This suggests that phospholipids and protein, the primary components of the lipid and solid fractions, respectively, may be responsible for this protection. Enhanced stability of sunflower oil was also observed when commercial amino acids and phospholipids were incorporated and heated at 185$\sp\circ$C. The oxidative process of oils during deep-fat frying can be very complex. A wide variety of factors must be considered when determining the oxidative stability of a frying system. The competitive role of pro- and antioxidants potentially present in both the oils used for frying and the food substrates being fried can greatly influence the frying system and ultimately affect the quality of the food product.

Probiotics die over time during processing, storage and digestion, resulting in reduced health benefits to the consumer. Microencapsulation of microorganisms is an effective way to improve probiotic viability by restricting cell exposure to extreme conditions through the gastrointestinal tract until release in the colon. In this work, appearance and survival of encapsulated probiotic species from two genera was explored. Lactococcus lactis and Bifidobacterium longum were suspended in calcium alginate microbeads by spraying droplets of alginate-probiotic mixture into calcium chloride solution. This produced uniformly shaped transparent microbeads with high encapsulation yield. Encapsulating Lactococcus lactis extended viability during dry room temperature storage. Encapsulating Bifidobacterium longum revealed high variation between eight different strains from subspecies longum and infantis. Coating alginate particles with chitosan did not improve viability and, viability of free and encapsulated bifidobacteria decreased when exposed to simulated gastric and intestinal conditions. Data from these studies suggest microencapsulating probiotic cells is an invaluable process to extending cell viability. Future research should optimize current formulations to improve encapsulation yield and cell survival during processing, storage, and gastrointestinal transit.

Lipid oxidation is a major challenge faced by the food industry since it causes loss of quality in lipid containing foods which results in a decrease of shelf life. In order to delay the oxidation in lipids, food industries make use of antioxidants such as EDTA (ethylene diamine tetraacetic acid), BHA (tbutyl-4-hydroxyanisole), BHT (t-butyl-4-hydroxytoluene), and TBHQ (tert-butyl-hydroxyquinone). However, these antioxidants are chemically synthesized and consumers desire simpler and cleaner labels without artificially synthesized antioxidants. Also, artificially synthesized antioxidants such as t-butyl-4-hydroxyanisole (BHA) can cause cancer in humans. Previous studies have shown that phospholipids such as phosphatidylethanolamine (PE) and phosphatidylcholine (PC) affect the activity of nonpolar antioxidants such as -tocopherol in bulk oils. PE when added to stripped soybean oil containing 100 M of -tocopherol was able to improve oxidative stability of the oil. However, PC decreased the activity of -tocopherol or had no effect. HPLC demonstrated that tocopherols were regenerated by PE which explains its synergism with - tocopherol. This study evaluated the effect of -tocopherol with varying levels of PE in stripped soybean oil. vi Additionally, antioxidant activity of -tocopherol has been shown to increase with increasing PE/PC ratio in lecithin. This study also examined the possibility of converting PC to PE in egg lecithin which will can be further used with -tocopherol. The enzyme phospholipase D was used for the conversion since it has been shown to have transphosphatidylation activity with phospholipids. The synergism of the modified lecithin with -tocopherol was analyzed in stripped soybean oil as well as in commercially refined oils. KEYWORDS: phospholipid, antioxidant, lipid oxidation, tocopherols, lecithin.

No description available.

No description available.