Aim:  The study aimed for the complete purification and recharacterization of the highly hydrophobic circular bacteriocins, gassericin A and reutericin 6. Methods and Results:  Gassericin A and reutericin 6 were purified to homogeneity using previously described method and reverse‐phase HPLC with an octyl column and eluents of aqueous acetonitrile and 2‐propanol. Mass analysis, N‐terminal sequencing and bacteriocin assay of the HPLC‐purified bacteriocins showed the two bacteriocins had identical seamless circular structures with the same m/z value (5651) of [M + H]+ and both had the same specific activity. d/l‐amino acid composition analysis using two distinct methods with the chiral fluorescent derivatization reagents (+)‐1‐(9‐fluorenyl)ethyl chloroformate and o‐phthalaldehyde/N‐acetyl‐l‐cystein revealed neither gassericin A nor reutericin 6 contained d‐alanine residues contrary to our previous results. Conclusion:  Purified gassericin A and reutericin 6 are chemically identical circular molecules containing no d‐alanine residues. Significance and Impact of the Study:  The HPLC conditions developed in this study will facilitate advanced purification and correct characterization of other highly hydrophobic bacteriocins.

Gassericin A (GA) is a circular bacteriocin produced by Lactobacillus gasseri LA39. In this study, GA‐containing concentrate was prepared using a cross‐flow membrane filtration device (30 kDa cut‐off) from the culture supernatant of Lb. gasseri LA39 cultivated in a cheese whey‐based food‐grade medium. The bacteriocin activity titer in the concentrate was 16 times as high as that of the culture supernatant and was completely maintained through each incubation at 4°C for 3 months, 37°C for 2 months, 60°C for 5 h, and 100°C for 30 min. The GA‐containing concentrate was used with glycine powder to make custard creams, and then four representative strains of custard cream spoilage bacteria (Bacillus cereus, Lactococcus lactis subsp. lactis, Achromobacter denitrificans and Pseudomonas fluorescens) were individually inoculated at c. 103 colony forming units/g in the custard creams. Throughout 30 days of incubation at 30°C, all of the inoculated bacteria were completely inhibited by the combination of 5% (w/w) of the GA‐containing concentrate and 0.5% (w/w) glycine. This is the first highly practical application of GA to foods as a biopreservative, and the concentration method and the bacteriocin concentrate would contribute to biopreservation of several foods.

Seismic pounding of a 14-story reinforced concrete building, Nuevo León, damaged in the 1985 Mexico Earthquake is investigated by means of dynamic finite element analyses and cyclic loading tests of columns specimens. The building consisted of three adjacent units connected with 100-mm wide expansion joints. It was thought that the poundings caused impact lateral forces and frictions that resulted in serious structural damage. This study attempts quantification of the impact lateral load by the following four steps.(1) Two kinds of seismic response finite element analyses of a single unit of the building are conducted with /without simplified contact modeling with joint elements to approximately estimate the overall structural behavior. (2) Cyclic load test of two column specimens that represent a column of the building. One of the specimens is a simple column while the other consists of four pounding units, to which the column contacts during loading. Comparison of the two specimens indicates that the contact induces additional lateral shear force to the column. (3) Repeated cyclic responses of the two specimens are computed by static finite element analyses. The contact and friction behaviors are classified into normal and shear components to develop a constitutive model to be implemented into the two-node joint element. (4) A finite element model of two partial building units connected with the two-node joint elements is subjected to seismic response analysis. The analysis result indicates that the pounding causes an impact load equivalent to 0.9% of the total weight of a building unit.