Mixed Lactic Culture Research Articles

Antioxidant activity of essential oils from condiment plants and their effect on lactic cultures and pathogenic bacteria

ABSTRACT: Studies about preservative and antioxidant activity of essential oils have been encouraged in recent years, given their importance to food industry. The aim of the current study was to evaluate the antioxidant properties and antimicrobial activity of essential oils deriving from Syzygium aromaticum, Cymbopogon citratus and Lippia alba against lactic and pathogenic bacteria responsible for food-borne diseases. Essential oil antibacterial activity was assessed through disc diffusion and macrodilution tests conducted in a mixed lactic culture of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus (YF-L903) and of Escherichia coli (ATCC 8739), Staphylococcus aureus (ATCC 6538), Salmonella enterica (ATCC 6017) strains. Based on the chromatographic analysis results, the essential oils shown to be composed of eugenol (79.41%) which was the prevalent compound in S. aromaticum, geranial (31.89%), neral (24.52%) and β-myrcene (25.37%) in C. citratus, as well as of geranial (33.80%) and neral (25.63%) in L. alba. The observed antibacterial activity confirmed the dose-dependent effect of these three oils on all the assessed bacteria; there was halo inhibition at concentration 20μL mL-1. The essential oil of S. aromaticum presented better antioxidant activity, with IC50 equal to 5.76μg mL-1 and antioxidant activity index of 6.94, and it was considered strong (AAI>2.0) in comparison to the other evaluated oils. This essential oil also presented excellent antioxidant activity at concentrations lower than the one required to inhibit lactic cultures. Based in this outcome, the essential oil from S. aromaticum can be used as preservative agent in processed food whose formulation presents lactic cultures.

Assessment of the Anti-Microbial Activity of Dried Garlic Powders Produced by Different Methods of Drying

The anti-microbial activity of a range of garlic products including dried garlic powder produced by different methods, commercial garlic products, and garlic oil was determined against a range of selected bacteria. The bacteria included food borne pathogens, spoilage agents, and health-beneficial agents, namely Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, Bacillus cereus, and a mixed lactic culture consisting of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. The dried powders were produced using air-drying at both 60 and 80°C, vacuum-drying at 50 and 60°C, and freeze-drying at −20°C. In addition, five commercial products were tested, two of which are used as spices, and three as food supplements. Before testing, the moisture content of the dried garlic powders was raised to that of fresh garlic before drying. Garlic oil was used without any addition of water. In general, the results showed that the lactic culture was the most sensitive to the growth inhibitory active compound of garlic used in this study, followed by Staphylococcus aureus. In contrast Salmonella typhimurium and Bacillus cereus demonstrated the greatest resistance to garlic. Generally, fresh garlic produced the greatest inhibition followed by freeze-dried powder. The anti-microbial activity decreased with decreasing dried garlic powder concentration. The results showed that both drying temperature and time have major effects on retaining the active components responsible for the inhibition of microbial growth. The anti-microbial substances in the moist fresh garlic were also affected by moist-heating temperatures and time. Higher heating temperatures caused faster loss of anti-microbial activity. The decrease in growth-inhibition zones for moist-heated fresh garlic followed zero-order kinetics.

Microbial profiles during lactic fermentation of meat by combined starter cultures at high temperatures

Studies were conducted to stabilize minced meat and meat cubes with added salt and glucose by fermentation using mixed lactic cultures of Lactobacillus plantarum, Lactobacillus casei and Lactococci lactis. Microbial profiles were recorded. The study revealed that a desired pH of 4.0–4.2 can be achieved (within 24–36 h at 37 °C and 30–42 h at 30 °C), with a substantial reduction in coliforms, Escherichia coli, Staphylococcus aureus and Salmonella spp. The study demonstrated that the use of combined lactic cultures would enhance the fermentation process and preserve fresh meat for extended periods at high temperatures for further use in the development of specific products.

Biostabilization of Kefir with a Nonlactose-Fermenting Yeast

The biostabilization of kefir was studied using sequential fermentation of milk with a nonlactose-fermenting yeast culture and mixed cultures of lactic acid bacteria. To simulate kefir manufacturing, reconstituted skim milk containing three concentrations of glucose (0.4, 0.5 and 1.0%) was fermented first with the yeast culture, followed by lactic fermentation. The yeast fermentation produced ethanol, but the ethanol production did not continue during lactic fermentation with 0.4 and 0.5% of added glucose. However, some continued ethanol production occurred at 1.0% of added glucose. This pattern appeared to be extended to the refrigerated and room storage. During fermentation, all samples showed similar trends in pH reduction, but higher percentages of added glucose caused faster reduction in pH. The titratable acidity showed trends comparable with the pH changes. With 0.4% added glucose, the yeast culture containing Saccharomyces cerevisiae utilized 98% of the added glucose and produced 0.07% ethanol at 31°C during 16h; the mixed lactic cultures utilized 29% of the lactose at 22°C during the additional fermentation of 16h. Little change occurred during storage at 5°C for 7 d. The selected strain of Saccharomyces cerevisiae appeared to be effective in stabilizing kefir products during storage.

Production of quarg by ultrafiltration

The increased protein concentration in UF concentrate caused some problems in achieving the desired pH for quarg making when yogurt and mixed lactic cultures were used. Yogurt culture could ferment concentrated milk to a lower pH than the mixed culture. With the increasing concentration during UF, levels of total ash, calcium and phosphorus in the concentrate increased, but these increases were much lower at pH 4.6. Quarg obtained from UF concentrated sour milk was rated close to conventional quarg and had no bitter taste. A high heat treatment of milk before lactic fermentation and subsequent UF concentration resulted in a quarg with a smoother texture. Diafiltration of UF concentrated milk did not result in significant elimination of excessive calcium. The quality of the quarg was also poor with respect to taste, body and texture. Thus diafiltration would be of little use in quarg making.

Effect of addition of molasses and lactic culture on the fermentation pattern of buffalo dung

The effect of the addition of molasses—and inoculation with a mixed lactic culture and Dahi culture—on the fermentation pattern of buffalo dung wastelage was studied. The rate of fermentation increased with the addition of molasses. On addition of mixed lactic culture, the fall in pH was maximum and the lactic acid/total VFA ratio was highest. Coliform bacteria could not be detected in wastelage prepared with mixed lactic inoculum and Dahi cultures and Clostridial growth was restricted. The wastelages from lactic and Dahi cultures showed equally good aerobic stability after 20 and 40 days of fermentation.

Component Balance in Mixed Lactic Starters as Influenced by Preservative Procedures

Relative storage efficiency of freezing at −20C, lyophilization, and ultra-low temperature freezing (−196C) in maintaining the component-strain balance of mixed lactic cultures was evaluated. Liquid nitrogen freezing, followed by lyophilization and freezing at −20C, was the best preservative procedure for retaining the original strain balance and acid-producing ability of mixed lactic cultures.

Inhibitory Effect of Nisin upon Various Organisms1,2

Summary Two nisin-producing strains of Streptococcus lactis were found to vary in their ability to produce the antibiotic. In the milk medium containing 5% of nisin-broth, cell multiplication and acid production of two strains of Streptococcus thermophilus were delayed, but upon further incubation their total cell count and acid production were not affected appreciably. Nisin-broth did not inhibit three strains of S. lactis , two strains of Lactobacillus bulgaricus , two strains of S. thermophilus , a mixed lactic culture, and one strain each of Bacillus subtilis and Bacillus cereus . Nisin was not quite as inhibitory as several other antibiotics against the dairy cultures tested. Of 11 strains of Staphylococcus aureus Used, the antibiotic seemed to be active only against the coagulase-negative and weak coagulase-producing organisms. The data presented in this paper indicate that the antibiotic may be considered for use to inhibit certain staphylococci or lactic organisms. Additional work should be conducted to determine the applications of nisin and nisin-producing organisms in the dairy industry.

The Presence of Unidentified Chick Growth Factor Activity in Dried Whey Prepared with a Minimum of Bacterial Fermentation

DRIED whey products have been reported to contain unidentified growth factor activity for growing chicks by Hill (1948), Menge et al. (1949, 1952), Reed et al. (1951), Groschke (1950) and Petersen et al. (1953). Casein whey may be produced without bacterial fermentation by the addition of mineral acids to the milk. On the other hand, the production of a cheddar cheese-type whey employs a fermentation involving a heavy mixed lactic culture. Furthermore, the handling of liquid whey during commercial operations ordinarily is conducive to some microbiological fermentation prior to drying. Since certain fermented products also have been shown to contain unidentified factor activity for chicks by McGinnis et al. (1953), Edwards et al. (1953) and Lewis et al. (1953), a study was conducted to determine whether or not the unidentified chick growth factor activity of whey products is contingent on the fermentation involved in their production.An acid precipitated casein …