EFFICACIES OF ACETIC, LACTIC AND TWO MIXED ACIDS IN REDUCING NUMBER OF BACTERIA ON SURFACE OF LEARN MEAT

This study on sanitizing beef surfaces was designed to evaluate effects of mixtures of acetic, lactic, citric and ascorbic acids with individual solutions of acetic and lactic acids. Acetic acid (3%), lactic acid (3%), MA1 (2% acetic, 1% lactic, 0.25% citric and 0.1% L-ascorbic acids) and MA2 (2% lactic, 1% acetic, 0.25% citric and 0.1% L-ascorbic acids) solutions were applied to beef core samples of muscle inoculated with bacteria. Experimental variables were type, concentration and temperature of acid solutions and type of microorganisms. Overall, an increase in either acid concentration or treatment temperature decreased numbers of residual viable bacteria. Lactic acid solution was the most effective against S. typhimurium with a reduction of 2 log₁₀ at 70°C. For enterobacteria, acetic, lactic and MA2 solutions at 70°C resulted in a 1.5 log₁₀ reduction. MA2 was the most effective acid solution at both 45 and 70°C, whereas, lactic acid and the MA2 mixture did not differ in effectiveness at 20°C.     

Production of Enterotoxin-B in Cured Meats

SUMMARY— A variety of laboratory cured hams were inoculated with 10³−10⁶ cells of S. aureus strain S-6 and incubated at 10, 22 and 30°C anaerobically for up to 16 weeks. Enterotoxin-B was detected by gel-diffusion in hams with original pH over 5.30, up to 9.2% NaCl (brine) and 0.54 ppm undissociated nitrous acid. There was better toxin production at 30° than at 22° or 10°C. Toxin was detected at 10°C after at least 2 weeks incubation and in most samples after 8 weeks when pH was greater than 5.6. Toxic hams had more than 4 × 10⁶ cells/g. Contaminants were always less than 10⁵/g. Tween 80 inhibited toxin production at 30° but not at 10°C. Toxic hams looked normal even after 2 months incubation at 10°C.     

The microbiology of mixed salad containing raw and cooked ingredients without dressing

Growth of aerobic mesophilic bacteria in mixed salad without dressing, containing cooked sweet corn and raw endive, was similar to that of raw endive alone. At 9°C, sweet corn permitted the growth of the lactic acid bacterium Leuconostoc mesenteroides , whenever the bacterium was present on raw endive, whereas no growth of lactic acid bacteria was recorded on raw endive alone. Listeria monocytogenes , artificially inoculated in the samples, grew more in the mixed salad than in the raw endive alone, for products stored at 6°C and 9°C. Acidification of sweet corn to pH 5.0 was proposed to reduce the development of L. monocytogenes in the mixed salad to a level similar to that recorded in the raw endive alone. Acidification with citric acid reduced spoilage of sweet corn, whereas acetic acid caused necrosis on the leaves of raw endive.     

GROWTH OF STAPHYLOCOCCUS AUREUS AND ENTEROTOXIN A PRODUCTION IN FOODS CONTAINING POLYPHOSPHATES

Effects of pyro-, tripoly- and hexametaphosphates (0.5 and 1%, w/w) on growth of Staphylococcus aureus strain 196E and enterotoxin A (SEA) production were studied in cooked custard and beef at 22 and 30°C. No effect was observed in custard, where cell numbers/g increased from 10³ to 10⁸ and SEA reached 4.2 ng/g after 48 h at 22°C, irrespective of treatment. Cell numbers in cooked beef were ca. 10⁹/g after 48 h, and reduced numbers (by 1.5–2 log cycles) were found in samples containing 0.5 and 1% pyrophosphate during incubation at 22%, but not at 30°C. SEA concentrations in beef were 28 ng/g after 48 h at 22°C, and 93 and 184 ng/g after 24 and 48 h, respectively, at 30°C. SEA concentration correlated with amount of growth, and was nondetectable when cell numbers were ± 10⁶/g. Reduction of the meat pH by sodium acid pyrophosphate contributed to the observed inhibitory effect.     

Microbiological, physicochemical and organoleptic changes of shredded carrots stored under modified storage

The effect of initial head spaces of air, 4.9% CO₂/2.1% O₂/93% N₂ and 5% CO₂/95% N₂ on the microbial flora of shredded carrots was studied at 4 and 10°C. The microbial flora of shredded carrots comprised lactic acid bacteria, pseudomonads and yeasts. Lactic acid bacteria were the predominant organisms in all samples. The pH dropped during the storage of carrots and this was more pronounced at 10°C. The concentration of different organic acids such as lactic, acetic, tartaric, citric and succinic increased in all samples stored under modified atmosphere packaging conditions at both temperatures. The spoilage of carrots stored under 5% CO₂/95% N₂ was delayed, as indicated by the changes in their texture, colour and odour, compared with those samples stored under air or 4.9% CO₂/2.1% O₂/93% N₂.     

QUALITY LOSS of DOUBLE CONCENTRATED TOMATO PASTE: EVOLUTION of the MICROBIAL FLORA and MAIN ANALYTICAL PARAMETERS DURING STORAGE AT DIFFERENT TEMPERATURES

This study deals with nonsterile canning of double concentrate tomatoes (30° Brix) stored for 210 days at three different temperatures (4, 10 and 25C) in 200 kg drums. the evolving analytical composition (soluble solids, total solids, glucose, fructose, pH, total acidity, volatile acidity, citric acid, malic acid, succinic acid, hydroxymethylfurfural (HMF) and color parameters) that the product underwent during storage was dependent both on storage temperature and on different aerobic levels within the drum (top and bottom sections). the microbial profile (yeast, lactic acid bacilli and molds) was correlated with many important metabolites (D- and L-lactic acids, ethanol, acetic acid and diacetyl). the results indicate that the increase of these substances is dependent both on storage temperature as well as the oxygen tension within the drums.
Taken all together, the analytical findings offer a great help in evaluating the quality of semifinished tomatoes. We also found that lactic bacteria grow rapidly at 25C and after 15 days their number from both sampling areas in the drums (i.e., 10 cm below the sample surface and 15 cm above the bottom of each drum) is already greater than 10⁵ cfu/ml. At 10C, 30 days were needed to reach such a cell concentration, and after 45 days the level reaches 10⁷-10⁸ cfu/ml. By contrast, at 4C there were differences between top and bottom sampling areas. In the top area, 10⁵ cfu/ml was reached after 60 days, while for the bottom area this was reached after 120 days. Regarding yeast at 25C.     

Influence of probiotic Lactobacillus acidophilus and L. helveticus on proteolysis, organic acid profiles, and ACE-inhibitory activity of cheddar cheeses ripened at 4, 8, and 12 degrees C

ABSTRACT:  The influence of adjunct bacteria on composition of cheeses, organic acid profiles, proteolysis, and ACE-inhibitory activity during ripening at 4, 8, and 12 °C for 24 wk was investigated. cheddar cheeses were made with starter lactococci (control), Lactobacillus acidophilus L10, and starter lactococci (L10), and L. acidophilus L10, L. helveticus H100, and starter lactococci (H100). The counts of L. acidophilus in L10 cheeses remained at >10⁶ colony forming units (CFU)/g after 24 wk of ripening at 4, 8, and 12 °C. Concentrations of lactic, acetic, and propionic acids of the L10 and H100 cheeses were significantly higher than those of the control cheeses after 24 wk of ripening ( P < 0.05). Proteolysis of the cheeses was improved as the ripening temperature increased. Water-soluble nitrogen, trichloroacetic acid soluble nitrogen, and phosphotungstic acid soluble nitrogen of L10 and H100 cheeses were significantly higher than those of the control cheeses ( P < 0.05). Increase in ripening temperature from 4 °C to 8 and 12 °C increased the percentage of ACE inhibition. The IC₅₀ value among cheeses ripened at 4, 8, and 12 °C, however, was not significantly different ( P > 0.05). Hence, probiotic L. acidophilus L10 can be added into cheddar cheeses to improve proteolysis and ACE-inhibitory activity.     

Quenching Mechanism and Kinetics of Ascorbic Acid on the Photosensitizing Effects of Synthetic Food Colorant FD&C Red Nr 3

ABSTRACT:  The pH effect on the oxidative stability of ascorbic acid in the presence of food colorant FD&C Red Nr 3 during storage with or without light was investigated. The quenching mechanism and kinetics of ascorbic acid on the FD&C Red Nr 3 photosensitized oxidation in an aqueous system at 25 °C were also studied by measuring the degradation of ascorbic acid or depletion of headspace oxygen. Red Nr 3 had no influence on the oxidation of ascorbic acid under dark storage, but accelerated its oxidation rate under light storage. The oxidative stability of ascorbic acid decreased as the pH increased from 4 to 7 under light without FD&C Red Nr 3. The quenching rates of ascorbic acid on the singlet oxygen by measuring the degradation of ascorbic acid in the presence of Red Nr 3 under light storage were 1.53 ± 0.15 × 10⁸, 1.86 ± 0.25 × 10⁸, and 1.19 ± 0.12 × 10⁸ M⁻¹S⁻¹ at pH 4, 5.6, and 7, respectively.     

Factors controlling the growth of Clostridium botulinum types A and B in pasteurized, cured meats III. The effect of potassium sorbate

The growth of Clostridium botulinum types A and B spores, at 10¹ or 10³ per container, was studied in a pork slurry system containing nitrite (40 μg/g), sodium chloride (2.5, 3.5, 4.5% w/v) sodium isoascorbate (550 μg/g) at varying pH levels, with or without potassium sorbate (0.26% w/v), without heating and after two heat treatments (80°C for 7 min, and 80°C for 7 min + 70°C for 1 hr) followed by storage at 15, 17.5, 20 or 35°C for up to 6 months. At a given spore inoculum, potassium sorbate significantly decreased toxin production, as did increasing NaCl, decreasing pH or decreasing storage temperature. Heat treatment did not significantly affect spoilage or toxin production overall, but interacted significantly with some factors. The effect of sorbate was greater at 3.5% NaCl than at 2.5%, at pH values below 6.0, and at low storage temperature.     

Recipes for antimicrobial wine marinades against Bacillus cereus, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica

ABSTRACT:  We have evaluated bactericidal activities against Bacillus cereus , Escherichia coli O157:H7, Listeria monocytogenes , and Salmonella enterica of several antimicrobial wine recipes, each consisting of red or white wine extracts of oregano leaves with added garlic juice and oregano oil. Dose-response plots were used to determine the percentage of the recipes that resulted in a 50% decrease in colony-forming units (CFU) at 60 min (BA₅₀). Studies designed to optimize antibacterial activities of the recipes demonstrated that several combinations of the naturally occurring plant-derived ingredients rapidly inactivated the above mentioned 4 foodborne pathogens. We also showed that (a) incubation temperature affected activities in the following order: 37 °C > 21 °C > 4 °C; (b) varying the initial bacterial concentrations from 10³ to 10⁴ to 10⁵ CFU/well did not significantly affect BA₅₀ values; (c) storage of 3 marinades up to 2 mo did not change their effectiveness against Salmonella enterica ; and (d) polyphenolic compounds isolated by chromatography from red wine exhibited exceptional activity at nanogram levels against 2 strains of Bacillus cereus . These observations suggest that antimicrobial wine formulations have the potential to improve the microbiological safety of foods.     

Changes of Volatile Compounds, Lactic Acid Bacteria, pH, and Headspace Gases in Kimchi, a Traditional Korean Fermented Vegetable Product

ABSTRACT Headspace volatiles of Kimchi stored at 5 °C increased over a 7 d period by 20.0% and then decreased from 7 to 27 d by 8.3%. Forty volatile compounds including 18 sulfur compounds were identified in Kimchi. Lactic acid bacteria in Kimchi increased from 3.1 to 4.5 (1 × 10⁸cfu/mL) over a 17-d period and decreased by 40% from 17 to 27 d. As the storage time increased from 2 to 27 d, pH decreased from 4.3 to 3.8, headspace oxygen decreased from 14.3 to 1.3%, and headspace carbon dioxide increased from 27.7 to 45.3%. Enzymatic reactions and chemical oxidations in Kimchi explained the changes of volatile compounds, lactic acid bacteria, pH, headspace oxygen and carbon dioxide.     

Thermal Stability of the Pigments Hydroxysafflor Yellow A, Safflor Yellow B, and Precarthamin from Safflower (Carthamus tinctorius)

ABSTRACT Three major yellow pigments were isolated from safflower petals ( Carthamus tinctorius ) and characterized as hydroxysafflor yellow A (1), safflor yellow B (2), and precarthamin (3) by ¹H-NMR, ¹H-¹H COSY, ¹³C-NMR, HMQC, and HMBC spectral analysis. Thermal degradation reactions of 3 yellow pigments 1 to 3 at temperatures of 70 to 90 °C were carried out at different pH levels within the range of 3.0 to 10.0 by UV-vis spectral measurements. First-order reaction kinetics was observed for the degradation of safflower yellow pigments (1 to 3) at pH 3.0 and 5.0. Activation energies of thermal degradation of 1-3 at pH 5.0 were calculated as 17.0, 15.4, and 20.1 kcal/mol, respectively. At neutral and alkaline conditions, yellow pigments 1-3 did not follow simple first-order kinetics.     

Effect of irradiation and modified atmosphere packaging on the microbiological safety of minced pork stored under temperature abuse conditions

The safety of irradiated pork packed in 25% CO₂:75% N₂ and stored at abuse temperature (10 or 15°C) was assessed by inoculation studies involving Salmonella typhimurium, Listeria monocytogenes, Escherichia coli, Yersinia enterocolitica and Clostridium perfringens . Irradiation to a dose of 1.75 kGy reduced pathogen numbers to below the detection limit of 10² cells g^-1. When higher inoculum levels were used (10⁶ cells g^-1) irradiation at 1.75 kGy reduced pathogen numbers by 1 –>5 log₁₀ cycles depending on strain. Clostridium perfringens was the most resistant, and Y. enterocolitica the most sensitive of the pathogens studied.
In all cases when high numbers (10⁶ to 10⁷g^-1) of spoilage and/or pathogenic bacteria were present initially on the pork the meat appeared spoiled, and although irradiation reduced the number of microorganisms, the meat was still unacceptable from a sensory viewpoint after treatment.
It was concluded that the microbiological safety of irradiated, modified atmosphere packaged (MAP) pork is better than that of unirradiated MAP pork.     

The effects of different incubation temperatures on the acetaldehyde content and viable bacteria counts of bio-yogurt made from ewe's milk

Yogurt and bio-yogurt were manufactured from ewe's milk using a starter culture and a probiotic culture. Incubation was carried out at 37°C and 42°C until pH 4.6 was reached and the yogurts were stored at 4 +1°C for 14 days. Analysis after 1, 7 and 14 days showed that incubation temperature and storage time significantly influenced overall properties of the samples. During the storage, whey separation and pH decreased, but titratable acidity, lactic acid and volatile fatty acid contents increased. Viable bacterial counts in all bio-yogurts were above 10⁷ cfu g⁻¹ at the end of storage.     

EFFECT OF SEVERAL EXPERIMENTAL PARAMETERS ON COMBINATION OF RED KIDNEY BEAN (PHASEOLUS VULGARIS) α-AMYLASE INHIBITOR WITH PORCINE PANCREATIC α-AMYLASE

Purified red kidney bean (Phaseolus vulgaris) amylase inhibitor forms a 1:1 stoichiometric complex with porcine pancreatic α-amylase leading to complete loss of enzyme activity on starch. Rate of complex formation is pH dependent and is maximal at pH 5. The rate constants for complex formation, as measured by loss of amylase activity, were 2.85 × 10⁴ M^-1 sec^-1 at pH 6.9 (ionic strength of 0.918) and 2.55 × 10⁵ M^-1 sec^-1 at pH 5 at 30°C. At pH 6.9, rate of complex formation was 4.8 times faster at 0.918 ionic strength as compared with the rate at 0.138 ionic strength. At 30°C, pH 6.9 and ionic strength of 0.168 the dissociation constant of the enzyme-inhibitor complex was determined to be 3.5 × 10^-11 M. The rate constant for dissociation of the complex was calculated to be 8.7 × 10^-8 sec^-1 under the same conditions. The rate constant for complex formation, at ionic strength of 0.168, was 1.1 × 10⁴ M^-1 sec^-1 at 37⁰ and 9.77 × 10² M^-1 sec^-1 at 25.7°C. The calculated activation energy for complex formation is 39.5 kcal/mole suggesting a rate-controlling conformational change. Oxidation of the carbohydrate moiety of the glycoprotein inhibitor caused complete loss of activity. Maltose, a competitive inhibitor of α-amylase, bound as readily to the enzyme-inhibitor complex as to free α-amylase. Trypsinized α-amylase, although still able to bind to Sephadex, did not bind inhibitor. The experiments with maltose and trypsinized amylase suggest the inhibitor may not bind at the active site of α-amylase.     

Low Temperature Growth of Type E Clostridium botulinum Spores. 1. Effects of Sodium Chloride, Sodium Nitrite and pH

SUMMARY— The effects of pH and the addition of sodium chloride (NaCl) or sodium nitrite (NaNO₂) to trypticase-peptone-glucose (TPGI and trypticase-peptone-sucrose-yeast extract (TPSY) media upon spore outgrowth were investigated using seven Type E Clostridium botulinum strains. An inoculum of 1.0 × 10⁵ spores/ml was used and the pH was adjusted with hydrochloric acid to cover the range of 5.2 to 6.6. To define salt tolerance, NaCl was added to the media at intervals of 0.5% in the range of 2.0 to 5.0% and at 0.1% intervals in the 4.5 to 5.0% range. The effect of NaNO₂ was investigated with the addition of 100 and 200 ppm NaNO₂ to the media. Samples were incubated at 30, 15.6, 10, 7.2, 5.0 and 3.4°C. Outgrowth of all strains tested was inhibited at pH 5.2 at 15.6°C. Inhibition occurred at higher pH at lower temperatures. None of the strains showed outgrowth with 4.87% NaCl in the media at any of the incubation temperatures used. Addition of 100 and 200 ppm NaNO₂ to the media inhibited the outgrowth of the Minneapolis, 517, 26080 and A6247 strains but not the Kalamazoo and Seattle Forks strains.     

Effect of carbon dioxide on improving the keeping quality of raw milk

Fresh cows' milk samples were treated with CO₂ to give a calculated CO₂ content of 77mM. The treated samples as well as the control were stored at 7° and 20 ± 5°C for three days and analysed periodically. The increase in the total count as well as the counts of psychrotrophic, lactic acid and coliform bacteria during storage at 7°C was found to be inhibited by the addition of CO₂. The treated samples had higher titratable acidity and lower pH values than the controls but satisfied the clot-on-boiling test. The keeping quality of cooled milk can therefore be improved by the addition of CO₂.     

Microbiological, physicochemical and organoleptic changes in dry-salted olives of Thassos variety stored under different modified atmospheres at 4 and 20 °C

Microbiological, physico-chemical and organoleptic changes were studied in dry-salted olives, cv. Thassos, stored under different atmospheres (100% carbon dioxide and nitrogen, 40% CO₂/30%O₂/30%N₂ and air) at 4 and 20 °C for 180 days. The initial microbial flora comprised of yeasts, no lactic acid bacteria, enterobacteria, pseudomonads or Staphylococcus aureus were detected, as the low water activity/high salt content does not favour their growth. At 4 °C, the population of yeasts declined steadily throughout storage but to a different extent depending on the gaseous atmospheres. At 20 °C, there was an initial decline in yeast counts in all samples followed by a steady increase until the end of the storage period. The CO₂ atmosphere was most effective at keeping the number of yeasts low at both storage temperatures. All gas atmospheres prevented fungal growth at both temperatures apart from the samples stored in air. The pH, a_w and salt content of the olives did not change significantly throughout the storage period. The prevailing yeast species was the salt tolerant Candida famata . The organoleptic characteristics did not differ significantly among differently treated olives. However, increased rancidity and reduced fruit colour was observed in the samples stored at 20 °C.     

The influence of mash pre-aging on the development of the flavour-active compound, 4-hydroxy-2(or5)-ethyl-5(or2)-methyl-3(2H)-furanone (HEMF), during soy sauce fermentation

Inoculation of Zygosaccharomyces rouxii into a soy sauce mash free from lactic acid bacteria at 10⁶ cells mL⁻¹ resulted in the formation of the flavour-active compound HEMF over a number of days at 30°C. Delays in inoculation up to 14 days after production of the mash greatly increased the amount of HEMF formed and under some conditions concentrations in the commercial range were achieved without addition of any other microorganisms.     

Shelf Life and Microbial Quality of Fresh-cut Mango Cubes Stored in High CO2 Atmospheres

ABSTRACT: Fresh-cut'Carabao'and'Nam Dokmai'mango cubes were stored in air or in high CO₂ atmospheres (3%, 5%, and 10%) at 5 °C and 13 °C. Freshly sliced'Carabao'mango cubes had a lower respiration rate and total bacterial count and higher L-ascorbic acid content and firmness than'Nam Dokmai'mango cubes. The shelf life of fresh-cut mango, based on browning discoloration and water-soaked appearance, was 6 d at 5 °C and 4 d at 13 °C for'Carabao'and 2 d at 5 °C and less than 1 d at 13 °C for'Nam Dokmai'. High CO₂ atmospheres retarded the development of water-soaked'Carabao'cubes at 5 °C and 13 °C and'Nam Dokmai'cubes at 5 °C. Texture of'Carabao'cubes was enhanced by high CO₂, but ethanol and L-ascorbic acid contents were not affected at 5 °C and 13 °C. Total bacterial count was lower in'Carabao'cubes than in'Nam Dokmai'cubes during storage at both temperatures, and a 10% CO₂ only reduced the bacterial count on'Carabao'and'Nam Dokmai'cubes stored at 13 °C. Bacterial flora in'Nam Dokmai'mango cubes consisted mostly of Gram-negative rods assigned primarily to phytopathogenic bacteria such as Pantoea agglomerans and Burkholderia cepacia . The genera of bacteria isolated from cubes stored in 10% CO₂ were similar to those from cubes on the initial day.