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Articles by R.M.U.S.K. Rathnayaka
Total Records ( 4 ) for R.M.U.S.K. Rathnayaka
  R.M.U.S.K. Rathnayaka
  In most of the novel and traditional methods used in the examination of food samples for Salmonella, pre-enrichment of samples is used as a means of increasing the sensitivity and reliability. However, the influence of pre-enrichment of sample on some of those methods has not been studied. Furthermore, the effect of the conditions of the sample on the sensitivity of some of those methods are also not been studied. The aim of this research was to study the influence of pre-enrichment and the conditions of the samples on the detection sensitivity of one novel method Fluorescent in-situ Hybridization (FISH) and one traditional culture techniques (XLT-4 agar plates). To study the influence of enrichment, 60 pork sausage samples collected from 20 different food outlets were examined for Salmonella contamination by both methods with and without pre-enrichment. To study the effect of the conditions of food, collected samples were spiked with 107 cfu mL-1 Salmonella enterica culture and examined with and without pre-enrichment. Detection sensitivity of both methods was higher in pre-enriched fresh samples as well as spiked samples. FISH method was found to be more sensitive and less affected by the conditions of food, compared to culture method.
  R.M.U.S.K. Rathnayaka
  There is a growing trend towards the production of ready to use multifunctional foods which has nutritional and medicinal value as well as good sensory properties. On the other hands, microbial safety of those foods is a major concern in food industry. Treatments used to ensure microbial safety of foods can affect the medicinal, nutritional and sensory properties of food. Aim of this study was to evaluate the affect of two such treatments namely UV irradiation and thermal processing on some important properties of ready to serve tropical almond drink. Prepared tropical almond ready to serve drink samples were subjected to UV irradiation and three different heat treatments. Then microbial stability, antioxidant activity and sensory properties of those treated samples were evaluated comparatively to non-treated samples. Two properties tested in this study, namely microbial stability and antioxidant activity was found to be affected by both treatments tested. Sensory properties of the product were found to be affected only by thermal processing. Compared to non-treated and thermal processed tropical almond ready to serve drinks, UV irradiated tropical almond ready to serve drinks were found to be microbiologically more safe and with preserved sensory properties. Hence, UV irradiation was identified as a suitable method to treat tropical almond ready to serve drinks to ensure microbial safety over thermal processing.
  R.M.U.S.K. Rathnayaka
  Consumption of un-pasteurized fruit juices has increased in recent years due to their freshness and other attractive characters. Contamination of those by pathogenic microorganisms is considered as one of the major problems. Organic acid treatments, such as malic acid treatment, are used to control these contaminations. Aim of this study was to evaluate the antimicrobial activity of malic acid against Listeria monocytogenes, Salmonella enteritidis and Escherichia coli in Mango, Pineapple and papaya juices. Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) of malic acid against those bacteria were evaluated for all tested fruit juices which were stored at 5, 20 and 35°C. Antibacterial effect of malic acid was observed against all tested bacteria under all tested conditions. The antibacterial activity was depended upon the type of bacteria, type of fruit juice and storage conditions. Antibacterial effect was higher in high temperature storage than low temperature storage. High concentration of malic acid was needed for Papaya juice compared to other fruit juices to reduce microbial population by a same amount. E. coli was found to be more resistant to antimicrobial activity of malic acid compared to the other two bacteria. According to the results of this study, E. coli can be recommended as a test bacterium in testing organic acids to be used as food preservatives. Further, these tests should be carried out in refrigerated temperature to find out more effective organic acids, as the lowest antibacterial activity of malic acid was observed at 5°C in this study.
  R.M.U.S.K. Rathnayaka
  In the present study interaction between three lactic acid bacteria species and three food borne pathogenic bacteria species were studied. The objective of the study was to determine the effect of those interactions to the antimicrobial compound producing ability of lactic acid bacteria. Using the three lactic acid bacteria namely, Lactococcus lactis, Lactobacillus acidophilus and Lactobacillus casei and three pathogenic bacteria namely, Salmonella enterica, Escherichia coli and Listeria monocytogenes 56 different culture combinations were prepared and grown in a medium invented by de Man, Rogosa and Sharpe (MRS) broth. Then Cell Free Filtrates (CFF) containing antimicrobial compounds were obtained from all those cultures and tested for antimicrobial activity against the three pathogenic microorganisms. All Cell Free Filtrates (CFF) were found to be having antibiotic activity against tested three pathogenic bacteria. Antibiotic activity of Cell Free Filtrates (CFF) obtained from cultures contained both lactic acid bacteria and some pathogenic bacteria were significantly higher than cultures contained only lactic acid bacteria. However, this stimulating effect of pathogenic bacteria on antimicrobial compound production by lactic acid bacteria was different for different pathogenic bacteria. Stimulation by Escherichia coli was not observed and some times Escherichia coli shown to be reducing the antimicrobial compound production. Antibiotic activity was found to be higher in mixed cultures of lactic acid bacteria compared to individual cultures. Results of this study confirm the importance of using mixed cultures and effective stimulant bacteria in antimicrobial compound production by lactic acid bacteria.
 
 
 
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