Gas chromatography with flame ionization detection (GC-FID) has often been used to quantify fatty acids in fish. This study validated the common method for determining omega-3 fatty acids (DHA and EPA) in the raw and cooked warm-water fish, selayang, using GC-FID for subsequent evaluation on EPA and DHA retention using the Weibull model. The EPA and DHA were separated using a high-polarity capillary GC HP-88 column (60 m length, 0.25 mm ID, 0.2 μm DF) with a total run time of 45.87 min. The method was validated in linearity, precision, accuracy, specificity and sensitivity based on ICH requirements. In addition, it was found that the method had a high recovery rate (>95%) and good precision (RSD ≤ 2%) with overall RSDs ranging below 0.001% for both omega-3 PUFA. In conclusion, this method identified and quantified fatty acids and omega-3 accurately and precisely and can be used effectively for routine FAME analysis in fish samples.
Natural clays have recently been proven to possess antibacterial properties. Effective natural antimicrobial agents are needed to combat bacterial contamination on food contact surfaces, which are increasingly more prevalent in the food chain. This study sought to determine the antibacterial activity of clays against the food-borne pathogens Salmonella Typhimurium ATCC 14028 and Staphylococcus aureus ATCC 13565. Soils were processed to yield leachates and suspensions from untreated and treated clays. Soil particle size, pH, cation-exchange capacity, metal composition and mineralogy were characterized. Antibacterial screening was performed on six Malaysian soils via the disc diffusion method. In addition, a time-kill assay was conducted on selected antibacterial clays after 6 h of exposure. The screening revealed that Munchong and Carey clays significantly inhibit Salmonella Typhimurium (11.00 ± 0.71 mm) and S. aureus (7.63 ± 0.48 mm), respectively. Treated Carey clay leachate and suspension completely kill Salmonella Typhimurium, while S. aureus viability is reduced (2 to 3 log10). The untreated Carey and all Munchong clays proved ineffective as antibacterials. XRD analysis confirmed the presence of pyrite and magnetite. Treated Carey clays had a higher soluble metal content compared to Munchong; namely Al (92.63 ± 2.18 mg/L), Fe (65.69 ± 3.09 mg/L) and Mg (88.48 ± 2.29 mg/L). Our results suggest that metal ion toxicity is responsible for the antibacterial activity of these clays.
This study evaluates anti-biofilm activity of four extracts from marine fungi; Penicillium citrinum PR1T4, Sarocladium strictum PP2L4, Aspergillus sydowii PR3T13, and Aspergillus spp. PR5T4 against Staphylococcus aureus, Listeria monocytogenes (ATCC 19115), Escherichia coli, and Salmonella typhi (ATCC 14028). The ability of bacterial cells to adhere, detach, and form biofilm on stainless steel surface were examined and ethyl acetate extract of the fungal culture (15 mg/ml) were tested for anti-biofilm activity for 3, 6, 9, 12, and 15 days. E. coli showed the highest ability to adhere (>8 log CFU/cm 2 ) and lowest detachment (<4 log CFU/cm 2 ) after 24, 48, and 72 hr. Extract PP2L4 had the highest anti-biofilm activity against S. typhi (1.70 6 0.04 log CFU/cm 2 ). Fungal extracts, bacteria, and incubation period were significant factors and their interactions were significant. The results showed that marine fungal extracts are important natural sources for anti-biofilm agents that have high potential as food-contact surface sanitizers. Practical applicationsBiofilm removal from food contact surfaces has been one of the greatest challenges for food industry. There have been efforts to explore natural agents with anti-biofilm properties. This study showed that marine-derived fungal extracts significantly reduced the number of attached cell on stainless steel discs and, therefore, is potential candidates for anti-biofilm agents. Special attention would be given to the fungal isolate (S. strictum PP2L4) that presented a promising activity against the gram-negative S. typhi. As the active fungal extracts were unable to completely remove the adhered bacterial cells, optimization is recommended to increase probability of isolating active compounds capable for complete biofilm removal. The active compounds could be used in sanitizer formulation and applied on various food-contact surfaces (e.g., stainless steel and plastic) at food related industries such as in institutional food service kitchens as well as home kitchens.
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