The adaptation of lactic streptococci for growth with their homologous bacteriophage was studied through the addition of bacteriophage filtrate to skim milk medium inoculated with Streptococcus lactis or Streptococcus cremoris. Both S. lactis and S. cremoris attained their adaptability for growth with their homologous bacteriophage after 5 and 2 transferes, respectively, and did not lose it after a storage period of 30 days at 0 degree C.
The main objective of the present paper is to study the impact characteristics of unidirectional polypropylene fiber (PPF)/polyester composite laminate. The PPF/polyester composite laminate was fabricated using the hand lay-up technique with fiber volume fraction of 30.28% and thickness of 6.2 ± 0.05 mm. The impact fracture characterization technique used is the notched Izod impact test. The failure modes of the impacted test specimens were investigated. Two-parameter Weibull distribution was used to analyze statistically both the absorbed impact energy and the impact strength of the studied composite in order to obtain the scatter values in the experimental test results. Also, a failure probability curve has been obtained to calculate the impact strength of PPF/polyester composite at different desired levels of failure probability. This curve can be used by the design engineers.
Pure cultures of S. luctis, S. cremoris, S. diacetilucris and S. thermophilus were cultivated on soymilk medium containing 3 % lactose and skim milk medium which were infected or not infected with bacteriophage. The cultures were incubated for 24 h at the optimum temperature of each organism. The growth, lactic acid production and activity of each culture were periodically examined. The growth and the acidity development of the cultivated cultures on soymilk medium infected with bacteriophage increased gradually during the incubation period, whereas the cultures grown on skim milk infected with bacteriophage showed less growth and acid production. Moreover, the growth and the rate of lactic acid production of the cultures cultivated on soymilk medium were higher than those of the cultures grown on skim milk medium (control). Therefore, soymilk medium containing 3 % lactose could be recommended as a protective medium against bacteriophage infection for lactic acid starter.
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