METHODS OF ASSESSING THE SPORICIDAL EFFICIENCY OF AN ULTRA-HIGH-TEMPERATURE MILK STERILIZING PLANT. II. EXPERIMENTS WITH SUSPENSIONS OF SPORES IN MILK

SUMMARY: The sporicidal efficiency of an ultra-high-temperature (UHT) milk processing plant has been tested using spores of a strain of Bacillus subtilis in milk. With the inoculum and volume of milk adjusted to obtain a countable number of survivors by a conventional dilution counting method, a temperature of 130·5° with the minimum time setting of the plant was found necessary to give a destruction of 99·99999%. This temperature was lower than that found previously (135°) for spores suspended in water and evidence is produced to support the suggestion that UHT milk may be inhibitory to the germination and/or subsequent growth of heated spores.     

METHODS OF ASSESSING THE SPORICIDAL EFFICIENCY OF AN ULTRA-HIGH-TEMPERATURE MILK STERILIZING PLANT. III. LABORATORY DETERMINATIONS OF THE HEAT RESISTANCE OF SPORES OF BACILLUS SUBTILIS IN WATER AND IN MILK

SUMMARY: Thermal death curves for spores of Bacillus subtilis 786 have been determined in water and in milk. Generally a non-logarithmic order of death was observed. Numbers of survivors were lower in milk than in water, suggesting that there may be inhibitory factors in UHT sterilized milk which affect the germination and/or subsequent growth of heated spores.
The thermal death curves for spores suspended in milk yielded Q₁₀ values of about 30 in the range 110–120°. This is higher than the figures previously reported in the literature for R. subtilis spores. Spores of a number of strains of B. subtilis were compared with strain 786 and all gave high Q₁₀ values.
The results obtained in this work have been used to predict the destruction of spores at higher temperatures in a UHT plant (Burton et al. 1958). The calculated values agree well with the results obtained in the plant by Franklin et al. (1958).     

THE INFLUENCE OF ELECTROLYTES ON THE CATAPHORETIC CHARGE OF COLLOIDAL PARTICLES AND THE STABILITY OF THEIR SUSPENSIONS : I. EXPERIMENTS WITH COLLODION PARTICLES.

1. When collodion particles suspended in water move in an electric field they are, as a rule, negatively charged. The maximal cataphoretic P.D. between collodion particles and water is about 70 millivolts. This is only slightly more than the cataphoretic P.D. found by McTaggart to exist between gas bubbles and water (55 millivolts). Since in the latter case the P.D. is entirely due to forces inherent in the water itself, resulting possibly in an excess of OH ions in the layer of water in contact and moving with the gas bubble, it is assumed that the negative charge of the collodion particles is also chiefly due to the same cause; the collodion particles being apparently only responsible for the slight difference in maximal P.D. of water-gas and water-collodion surfaces. 2. The cataphoretic charge of collodion particles seems to be a minimum in pure water, increasing as a rule with the addition of electrolytes, especially if the cation of the electrolyte is monovalent, until a maximal P.D. is reached. A further increase in the concentration of the electrolyte depresses the P.D. again. There is little difference in the action of HCl, NaOH, and NaCl or LiCl or KCl. 3. The increase in P.D. between collodion particles and water upon the addition of electrolyte is the more rapid the higher the valency of the anion. This suggests that this increase of negative charge of the collodion particle is due to the anions of the electrolyte gathering in excess in the layer of water nearest to the collodion particles, while the adjoining aqueous layer has an excess of cations. 4. In the case of chlorides and at a pH of about 5.0 the maximal P.D. between collodion particles and water is about 70 millivolts, when the cation of the electrolyte present is monovalent (H, Li, Na, K); when the cation of the electrolyte is bivalent (Mg, Ca), the maximal P.D. is about 35 to 40 millivolts; and when the cation is trivalent (La) the maximal P.D. is lower, probably little more than 20 millivolts. 5. A reversal in the sign of charge of the collodion particles could be brought about by LaCl₃ but not by acid. 6. These results on the influence of electrolytes on the cataphoretic P.D. between collodion particles and water are also of significance for the theory of electrical endosmose and anomalous osmosis through collodion membranes; since the cataphoretic P.D. is probably identical with the P.D. between water and collodion inside the pores of a collodion membrane through which the water diffuses. 7. The cataphoretic P.D. between collodion particles and water determines the stability of suspensions of collodion particles in water, since rapid precipitation occurs when this P.D. falls below a critical value of about 16 millivolts, regardless of the nature of the electrolyte by which the P.D. is depressed. No peptization effect of plurivalent anions was noticed.     

AN ANATOMICALLY PRESERVED POTONIEA WITH IN SITU SPORES FROM THE PENNSYLVANIAN OF ILLINOIS

Specimens preserved in coal balls collected from the Herrin (No. 6) Coal in Illinois reveal the internal structure of the pteridosperm pollen organ long known as the compression fossil, Potoniea. Cylindrical sporangia are concentrically arranged in a campanulate body and the end of each sporangium projects freely from the distal face of the organ. Pollen is trilete and without a distal germinal aperture. The exine is structureless and has a separable, perine-like layer adorned with orbicules.     

RAPID ENUMERATION OF CLOSTRIDIAL SPORES IN RAW MILK SAMPLES USING AN IMPEDIMETRIC METHOD

Late spoilage of cheese is due to gas formation during lactic acid fermentation by spore-forming, gram-positive, anaerobic clostridia of the species Ciostridium tyrobutyricum, Clostridium butyricum and Clostridium sporogenes. Since small numbers of such clostridial spores readily cause considerable losses in cheese production, spore numbers of fewer than 100 spores/liter must be determined reliably. Until recently, the only reliable method available was the time-consuming (7 days) and cumbersome Most Probable Number Method (MPN). The objective of this study was to examine the feasibility of using impedance technology as an alternative method for the enumeration of clostridial spores. Three to fifteen replicates of 7.5–12.0 mL samples were tested using an impedimetric method with and without the addition of Oxyrase to generate anaerobic conditions within the impedance measurement cells. Results were obtained in less than 48 h. Data derived from the rapid impedance method were statistically comparable to those obtained using the reference method (MPN).     

分层供水施磷对春小麦光合性能及水分利用率的影响

利用自制的植物生长装置研究了春小麦在不同土壤湿度和碳素水平的组合方式对作物光合及水分利用的影响。结果表明。在上干下湿的水分条件,表层施磷处理其光合曲线呈单峰,而整体湿润下不管磷的施用部位,其光合曲线呈双峰。这种变异多是非气孔限制下环境因子与植株体作用而致。     

人工生态系统净化水质模型研究

建立了自来水厂取水口附近的人工生态系统水质模型、研究在水面面积、水生植物放养密度、取水量等改变条件下,取水口处水质的变化特征。这一模型可应用于确定人工生态系统水面积面积,水生植物放养密度等值,以达到满足自来水厂取水口处水质的要求,对模型参数适当确定后,可应用于其它水域。