Control of vegetative micro-organisms in foods.
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Microbes share our food whether we want them to or not. We need to control microbial proliferation in foods in order to avoid spoilage, to enhance flavour and, most importantly, to reduce the risk of food-borne illness. A broad spectrum of interventions are available to control microbial growth, but the most widely used is temperature. The use of temperature to control metabolically active bacteria is discussed briefly in the context of current practices. The marketing and legislative climate has provided an impetus to develop an ever-widening range of systems for microbiological control. This short review highlights some of the problems associated with such novel control systems, including selection of new spoilage agents or food-borne pathogens, and the difficulties of monitoring the efficiency of microbial control in the light of a better understanding of bacterial physiology. (+info)
Enzymes currently used to tenderize meat are not substrate-specific, resulting in extensive myofibrillar protein degradation that often produces an undesirable texture. Bovine placental metalloproteases, which selectively hydrolyze connective tissue proteins while leaving myofibrillar proteins intact, may tenderize meat without causing texture problems. Therefore, our objective was to extract and crudely purify bovine metalloproteases from bovine placenta for possible use as tenderizers in meat systems. Enzymes were extracted from homogenized tissue and purified by ammonium sulfate precipitation. Samples were collected before (crude enzyme) and after gel filtration on a Sephadex G-100 column. Spectrophotometric analysis identified one major peak (filtered enzyme). Gelatin, casein, and type I acid-soluble collagen zymography were used to determine substrate specificity. Beef myofibrillar proteins were incubated with crude and filtered enzyme fractions, enzymes quenched, and substrate degradation visualized using SDS-PAGE. Active gelatinases and collagenases exhibiting molecular weights of 57 to 65 kDa were detected on zymograms. Banding patterns from crude enzyme indicated two enzymes with both gelatinase and collagenase activity and a third enzyme with gelatinase activity only. Banding patterns from filtered enzyme indicated two enzymes with both gelatinase and collagenase activity. Proteolytic activity was not detected with casein, actin, or myosin heavy-chain substrates. Due to specificity for collagen and gelatin, these enzymes may be capable of improving the tenderness of certain cuts relatively high in connective tissue, while avoiding myofibrillar protein hydrolysis. (+info)
Arabinoxylan fiber from a by-product of wheat flour processing behaves physiologically like a soluble, fermentable fiber in the large bowel of rats.
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Arabinoxylan is a major dietary fiber component of many cereals. Its physiological effects in the colon are largely unknown. This study examined the effects of an arabinoxylan-rich fiber (AX) extracted from a by-product of wheat flour processing in the rat colon compared with well-characterized soluble/rapidly fermentable and insoluble/slowly fermentable fibers. Rats were fed diets containing no fiber (NF) or 100 g/kg of total dietary fiber from AX, guar gum (GG) or wheat bran (WB) for 4 wk. Cecal mass and short-chain fatty acid (SCFA) pool were significantly higher while pH was significantly lower in the fiber-supplemented groups, particularly in the AX and GG groups. The pattern of SCFA production in the cecum was altered; AX fiber was a good source for acetate while GG and WB favored propionate and butyrate production, respectively. Fecal output was 7-, 6- and 5-fold higher, respectively, in the AX, GG and WB than in the NF groups (P < 0.01). All epithelial proliferation indices (crypt column height, number of mitotic cells/crypt column and mitotic index) differed significantly across the groups in a descending order of AX > GG > WB > NF. Distal mucosal dipeptidyl peptidase IV activities, which indicate cell differentiation status, were significantly lower in fiber-supplemented groups than in the NF groups. Distal mucosal alkaline phosphatase activities, induced as a response to injury or stress, were significantly higher for the AX and GG groups than for the NF or WB groups (P < 0.001). These results indicate that AX fiber behaves like a rapidly fermentable, soluble fiber in the rat colon. (+info)
Isolation of mycobacteria from frozen fish destined for human consumption.
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Mycobacteria were isolated from defrost water and tissue of sole (Solea solea), hake (Merluccius merluccius), cod (Gadus morhua), ling (Genypterus blacodes), and monkfish (Lophius piscatorius) on Lowenstein-Jensen medium after incubation at different temperatures. Samples of frozen fish were obtained under sterile conditions inside a refrigeration chamber (-18 to -22 degrees C) in a wholesale market from which these products are distributed to shops for retail sale and human consumption. (+info)
Protection from cholera by adding lime juice to food - results from community and laboratory studies in Guinea-Bissau, West Africa.
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Epidemiological studies have shown that food plays an important role in the transmission of Vibrio cholerae, and different foods have been incriminated in many epidemic outbreaks of cholera. Storing contaminated meals at ambient temperatures allows growth of V. cholerae. Some ingredients such as lime juice may inhibit the survival of V. cholerae in foods. During an epidemic caused by V. cholerae O1 in Guinea-Bissau in 1996, a case control study was conducted in the capital Bissau, the main affected region with an attack rate of 7.4%. Cases were hospitalized patients and controls were matched for area, gender and age. Lime juice in the sauce eaten with rice gave a strong protective effect (odds ratio [OR] = 0.31, 95% confidence interval [CI] = 0.17-0.56), and tomato sauce was also protective (OR = 0.36, 95% CI = 0.24-0.54). On the other hand, use of a bucket for storage of water in the house was associated with increased risk (OR = 4.4, CI = 2.21-8.74). Laboratory experiments to elucidate the inhibitory effect of different concentrations of lime juice on survival of V. cholerae in meals showed that V. cholerae thrives in rice with peanut sauce, but lime juice inhibited its growth. Since lime juice is a common ingredient of sauces, its use should be further encouraged to prevent foodborne transmission in the household during cholera outbreaks. (+info)
Effects of planting density and processing method on laboratory characteristics of grain sorghum for ruminants.
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Grain sorghum grown in 38-cm (high-density) or 76-cm rows (normal-density) was steam-flaked, harvested as high-moisture grain followed by rolling and ensiling, or dry-rolled. Chemical composition, enzymatic starch availability, CP insolubility, and IVDMD in a reduced-strength buffer were evaluated. High-density planting increased (P < .10) OM and starch concentration and decreased (P < .0001) CP concentration but did not affect (P > .10) P concentration, enzymatic starch availability, or CP insolubility. High-density planting resulted in lower (P < .10) in vitro ruminal culture pH at 6, 12, and 18 h of incubation when grain sorghum was processed by steam flaking, and lower (P < .10) IVDMD at 6, 12, and 18 h of digestion when grain sorghum was processed by dry rolling. Steam flaking decreased (P < .10) CP concentration and solubility and increased (P < .10) OM concentration. High-moisture ensiling decreased (P < .10) the insolubility of CP but did not otherwise seem to alter the chemical composition of grain sorghum relative to dry rolling. Starch was more available (P < .10), and DM was digested more rapidly and extensively (P < .10) in vitro, in steam-flaked sorghum followed by high-moisture sorghum. Based on these data, it seems that planting density primarily affected chemical composition of grain sorghum, whereas processing primarily affected CP insolubility and rate and extent of starch fermentation. (+info)
An examination of the possibility of lowering the glycemic index of oat and barley flakes by minimal processing.
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Differences in glycemic responses to various starchy foods are related to differences in the rate of starch digestion and absorption. In this study, the importance of the degree of gelatinization and the product thickness for postprandial glycemic and insulinemic responses to rolled oats and barley were studied in healthy subjects (5 men and 5 women). Thick (1.0 mm) rolled oats were made from raw or preheated (roasted or steamed) kernels. In addition, thin (0.5 mm) rolled oats were made from roasted or roasted and steamed (processed under conditions simulating commercial production) oat kernels. Finally, steamed rolled barley kernels (0.5 or 1.0 mm) were prepared. All thin flakes elicited high glucose and insulin responses [glycemic index (GI), 88-118; insulinemic index (II), 84-102], not significantly different from white wheat bread (P: > 0.05). In contrast, all varieties of thick oat flakes gave significantly lower metabolic responses (GI, 70-78; II, 58-77) than the reference bread (P: < 0.05). Thick barley flakes, however, gave high glucose and insulin responses (GI, 94; II, 84), probably because the botanical structure underwent more destruction than the corresponding oat flakes. We conclude that minimal processing of oat and barley flakes had a relatively minor effect on GI features compared with the more extensive commercial processing. One exception was thick oat flakes, which in contrast to the corresponding barley flakes, had a low GI. (+info)
Characterization of Leuconostoc gasicomitatum sp. nov., associated with spoiled raw tomato-marinated broiler meat strips packaged under modified-atmosphere conditions.
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Lactic acid bacteria (LAB) associated with gaseous spoilage of modified-atmosphere-packaged, raw, tomato-marinated broiler meat strips were identified on the basis of a restriction fragment length polymorphism (RFLP) (ribotyping) database containing DNAs coding for 16S and 23S rRNAs (rDNAs). A mixed LAB population dominated by a Leuconostoc species resembling Leuconostoc gelidum caused the spoilage of the product. Lactobacillus sakei, Lactobacillus curvatus, and a gram-positive rod phenotypically similar to heterofermentative Lactobacillus species were the other main organisms detected. An increase in pH together with the extreme bulging of packages suggested a rare LAB spoilage type called "protein swell." This spoilage is characterized by excessive production of gas due to amino acid decarboxylation, and the rise in pH is attributed to the subsequent deamination of amino acids. Protein swell has not previously been associated with any kind of meat product. A polyphasic approach, including classical phenotyping, whole-cell protein electrophoresis, 16 and 23S rDNA RFLP, 16S rDNA sequence analysis, and DNA-DNA reassociation analysis, was used for the identification of the dominant Leuconostoc species. In addition to the RFLP analysis, phenotyping, whole-cell protein analysis, and 16S rDNA sequence homology indicated that L. gelidum was most similar to the spoilage-associated species. The two spoilage strains studied possessed 98.8 and 99.0% 16S rDNA sequence homology with the L. gelidum type strain. DNA-DNA reassociation, however, clearly distinguished the two species. The same strains showed only 22 and 34% hybridization with the L. gelidum type strain. These results warrant a separate species status, and we propose the name Leuconostoc gasicomitatum sp. nov. for this spoilage-associated Leuconostoc species. (+info)