Further studies were made on effects of nitrate on dissolving of tin from an internal surface of can containing acid products. In order to investigate the behavior of nitrate contained in syrup for use in canned fruits, a canning experiment test of mandarin orange was conducted, using syrups containing various amounts of nitrate. Syrups in general for use in canned fruits contain rather a small amount of water (18%), so-called preparing water, in comparison with syrups intended for use in canned soft drinks. In this case, they contain water at the mate of 63%. With the increase of the amount of nitrate added to the syrup, the rate of detinning increased in the early stage of its storage (within 3 months). No significant changes regarding vacuum level, pH, organoleptic quality, etc. were found in the samples containing nitrate, indicating that nitrate attacked the metal directly without accompanying any reaction with the content. Water samples from wells of canning plants in a certain district of Japan were found to contain significant amounts of nitrate. It is recommended from the above results that the preparing water ought to be checked as for its nitrate content, and that water containing less than 5ppm of nitrate-nitrogen can be used for preparing the syrups.
Commercial preserved foods, frozen fish, shellfish and vegetables and dried fish and prepared products were investigated bacteriologically. Two strains of Vibrio parahaemolyticus were isolated from samples of frozen tuna-stick and salted, halfdried sillago. Three plasmacoagulase-positive strains of Staphylococcus aureus were present in frozen pampano, green peas and dried spaghetti. All of the samples had an average aerobic plate count of less than 213200 per g. From the fish meat samples separated aseptically and inoculated with strains of Vibrio parahaemolyticus and enterotoxigenic Staphylococcus aureus experimentally, the inoculated bacteria were reisolated after freezing and storage for three months at -20°C.
Enterococci were obtained from 410 samples (45.2%) of 906 various poikilothermal materials. Of these samples examined, enterococcal strains were isolated at fairly high level (70%) from intestinal contents of fish and insects, while they were not frequently detected from those of frogs, plants and soils. The bacterial counts of enterococci in certain samples tested were at the level from 103 to 105 per g. The classification method for enterococcus group reported by Shimazaki et al. was used in this stndy. According to biological properties, the majority of the isolated strains were identified as the type B-II (Str. faecium). Most of the remainders were classified as the type A-II (Str. faecalis and Str. faecalis var. liquefaciens), and only a few strains showing the beta-haemolysis were isolated. Furthermore, some strains among the isolated could not be clearly classified.
A vertical diffusion method for quantitative analysis of Nisin in canned food was discussed. Bacillus stearothermophilus IAM 1035 was used as test organisms for this study. Results obtained may be summarized as follows: 1. Dispense 9ml of nutrient agar (meat extract 0.5%, Polypeptone 1.0%, NaCl 0.5%, Agar-agar 1.5%, pH 7.0) in sterile 16mm×160mm cotton-stoppered tubes. Sterilize in an autoclave for 15 minutes at 121°C. 2. Spore suspensions of B. stearothermophilus are prepared in nutrient agar slants with incubation at 55°C for five to seven days until 80 per cent or more cells are in the spore state. Spores are suspended in sterile saline to give the desired concentration (6×106-6×105/ml), and heat-shocked for 10 minutes at 80°C before putting them into the test media. 3. An one ml portion of spore suspension is added to the test media which have been melted in water bath. After thoroughly mixing, the media are dispensed in sterile 5mm×75mm cotton-stoppered tubes and soiidified at vertical position in cold water. 4. The sample adjusted to pH 6.0 was stratified on the agar media and stored for 120 minutes at 30°C. 5. After incubation for 18 hours at 55°C, the length of inhibited zone is measured through a projector (×20) and read at the level of 0.01mm. The concentration of Nisin is obtained from the standard curve.
A rapid and semiquantitative determination method for dehydroacetic acid (DHA) in foods was studied. An adsorption technique for testing DHA to cation exchange resin soaked previously with titanium trichloride was characteristic. DHA adsorbed effectively by this resin from its aquous solution produced persistent reddish violet color, the reaction of which was not obstructed by most of other substances contained in foods except a few. 50ml of a sample solution was acidified by diluted hydrochloric acid to pH 1.0, in which 0.3ml of Dowex 50 precoated with titanium trichloride was added. The mixture was shaked in a flask for 5 minutes. The intensity of developed color on the resin was compared with those obtained by standard samples which were previously prepared from solutions containing known quantities of DHA; 0.5 to 3.0mg per 50ml water.
In the previous report the authors introduced a rapid detecting method for dehydroacetic acid (DHA), using cation exchange resin. In the present study, the method using anion exchange resin was investigated. In this method, DHA in an acidic aqueous solution prepared from a food was extracted by benzene and reextracted by alkaline solution, in which 0.3ml of anion exchange resin was added. This mixture was shaked for 15 minutes. After decanting the supernatant, 3ml of a TiCl3 solution was added. Blue coloration indicates the presence of DHA. DHA concentration range to be detected by this method was 0.2 to 1.5mg of DHA per 50ml of a sample solution and the color was retained for about 3 minutes. Several food preservatives, except sorbic acid, benzoic acid and salicylic acid, and food colors, except xanthene series did not interfere with the color reaction of DHA. This method seems to be simple and useful for the detection of DHA in various foods.
It was clarified that the trans type of 2- (2-furyl) -3- (5-nitro-2-furyl) -acrylamide (Furylfuramide) has two kinds of crystal form by infrared absorption spectra, differential thermal analysis and X-ray diffraction method. Crystals of new modification (α-form) were obtained as prisms by slow evaporation of ethanol solution and their IR spectrum was quite different from that of the usual crystals (β-form) which were obtained as thin needles by usual recrystalization from methanol or other organic solvents. Furthermore, it was observed that a transition from α- to β-form occurs at 140°C. Both crystal forms belong to monoclinic system, and their lattice constants and other crystallographic data were also determined.