A procedure was developed for simultaneous determination of 21 synthetic antibacterials in fish and meat products by high performance liquid chromatography with a photodiode array detector. The antibacterials were extracted with acetonitrile-0.2% metaphosphoric acid (7:3), followed by liquid-liquid partition with dichloromethane. High performance liquid chromatography was carried out on a TSK-gel ODS-80Ts column using gradient elution with acetonitrile-sodium dihydrogenphosphate. The recoveries of antibacterials from fish and meat products spiked at 1.0μg/g were over 70% except in the cases of sulfisomidine and carbadox. The detection limits were 0.05-0.10μg/g for each antibacterial except thiamphenicol (0.25μg/g).
An analytical procedure was developed for the determination of nine volatile halogenated organic compounds (VHCs), i. e., chloroform, bromodichloromethane, dibromochloromethane, bromoform, 1, 1, 1-trichloroethane, 1, 1, 2-trichloroethane, 1, 1, 2, 2-tetrachloroethane, trichloroethylene and tetrachloroethylene, in food samples. The method employs a purge and trap procedure with collection on ORBO-100 (graphite carbon), commonly used for air sampling tubes for solvent desorption. Ten grams of food sample, 40ml of purified water, 0.5ml of phosphoric acid and 5 drops of silicone were placed in a color comparison tube (sample tube). Nitrogen as the purge gas was initiated at a flow rate of 100ml/min for 15min with the sample tube held at 40°C in a water bath. Trapped VHCs were extracted from the graphite carbon absorbent with 5ml of hexane by shaking for 20 seconds. The extract was analyzed by gas-liquid chromatography with an electron capture detector using a DB-624 column (0.32min i. d.×30m). Quantitation limit of the nine VHCs were as follows: chloroform 2ppb; bromodichloromethane 0.2ppb; dibromochloromethane 0.2ppb; bromoform 0.5ppb; 1, 1, 1-trichloroethane 2ppb; 1, 1, 2-trichloroethane 3ppb; 1, 1, 2, 2-tetrachloroethane 0.5ppb; trichloroethylene 0.2ppb; tetrachloroethylene 0.2ppb. The recoveries of VHCs added to five kinds of food samples were 70.0-99.5%. Using the proposed method, 25 samples of commercial products were analyzed. Four VHCs were detected as follows: chloroform ND (below quantitation limit) -45.3ppb, bromodichloromethane ND-20.3ppb, dibromochloromethane ND-3.7ppb, 1, 1, 1-trichloroethane ND-2.7ppb. Bromoform, 1, 1, 2-trichloroethane, 1, 1, 2, 2-tetrachloroethane, trichloroethylene and tetrachloroethylene were not detected.
During the period from January to October 1992, a total of 214 samples (100 raw pork, 94 raw chicken and 20 carp) obtained in Ibaraki prefecture were examined for the presence of Aeromonas. It was found that 42 (42%) of 100 raw pork samples, 30 (32%) of 94 raw chicken samples and 13 (65%) of 20 carp were contaminated by some Aeromonas. The population of Aeromonas in contaminated samples was mostly below 102cfu/g. Attempts to identify the isolates by the biochemical method (phenospecies) revealed that 26 (19%) of 137 isolates belonged to Aeromonas hydrophila groups, 5 (2.3%)to A. caviae, 59 (27.5%) to A. sobria groups, and 4 (1.9%) to A. jandaei; the rest 10 (4.7%) were untypable. On the basis of genetic classification by DNA-DNA hybridization in microdilution wells, 13 of 26 A. hydrophila group isolates were reidentified as A. hydrophila. Eight of 87 A. sobria group isolates were identified as A. sobria and 74 as A. veronii biotype sobria. All of 7 A. jandaei isolates hybridized with the type strain. One each of the 10 untypable isolates hybridized with A. sobria and A. veronii biotype sobria. All of the isolates were investigated for hemolytic activity to rabbit and sheep erythrocytes, and cytotoxicity to HeLa 229 cells. Many strains showed both activities in A. hydrophila groups, A. veronii biotype sobria and A. jandaei, suggesting that these activities were associated. In A. caviae and A. sobria, many strains lacked these activities.
Changes in freshness indexes, sensory evaluation and bacterial flora were examined for minced meat of mackerel (Scomber japonicus) stored at 5°C after pressurization at 2, 000atm for 60min. Control samples were stored at 5°C without pressurization. Bacterial counts were decreased by 80% after pressurization, and bacterial growth was retarded for 4 days. Changes in bacterial flora of minced meat caused by pressurization were observed. Bacillus, Moraxella, Pseudomonas I/II and Flavobacterium, which had been found before pressurization, disappeared after pressurization, while coryneforms, Staphylococcus and Micrococcus, became dominant during the storage after pressurization. After spoilage, Ps. I/II predominated in both samples. Changes in pH, VBN, TMA and amines were related to bacterial growth. There were no significant differences in the K-value or the amount of lactic acid between control and pressurized samples, but lipid oxidation was advanced in pressurized samples at the early stage of deterioration. From freshness indexes and sensory evaluation, the shelf-life of pressurized samples was judged to have been rolonged by about 4 days.
In order to judge whether carmine, an aluminum (Al)-lake, had been used as a color, the Al concentration in commercial canned cherries and cherries in canned fruit cocktail was determined by ICP atomic emission spectrometry with an ultrasonic nebulizer. Al concentration in cherries not colored or cherries labeled as containing a food color without Al was 0.1-0.4μg/g, while that in cherries in which the use of carmine was suspected from the labeling was about 1μg/g. The Al concentration in cherries colored with cochineal extract and alum was ca. 4μg/g. Thus, the determined Al concentrations were consistent with the labeling of the products. Consequently, Al level may be used as a screen to judge whether carmine has been used as a color for canned cherries. In the case of a product with a higher Al content, it is necessary to check the manufacturing process of the product.