Growth studies on the lactic streptococci: IV. Some observations on redox potential
Summary Redox potential changes at 30°C in anaerobic reconstituted skim-milk cultures of Streptococcus cremoris AM1 and AM2 and Streptococcus lactis ML8 have been investigated in batch cultures and continuous cultures maintained at constant pH by the addition of fresh medium. Str. lactis ML8 was more strongly reducing than either Str. cremoris AM1 or AM2. The positive Eh values which can arise in dense continuous cultures of lactic streptococci are not likely to affect either the lactic acid formation or proteolytic activity of the resultant bacterial concentrate. An electrolytic reduction cell is described which allows variations in redox potential in cultures to be controlled simply and effectively.
Growth studies on the lactic streptococci: III. Observations on continuous growth behaviour in reconstituted skim-milk
Summary The behaviour of Streptococcus cremoris AM1 and AM2, and Streptococcus lactis ML8 in continuous growth in reconstituted skim-milk medium under controlled conditions of pH has been investigated. At 20°C under aerobic conditions small quantities of oxygen were found to stimulate the growth rate of Str. lactis ML8 between pH 5·05 and 5·45. Growth between pH 5·45 and 6·35 became erratic due to the accumulation of hydrogen peroxide. Above pH 6·35 hydrogen peroxide could not be detected in the continuously growing culture and below pH 5·05 the growth rate of the culture was not affected by small quantities of oxygen. An effect of direct oxygen toxicity on growth, distinct from that of hydrogen peroxide accumulation, was observed over the limited pH range investigated. After 48 h growth in the presence of small concentrations of oxygen the effect disappeared. At 30°C under anaerobic conditions a region in the dilution rate curves was observed with Str. cremoris AM1 and AM2 and Str. lactis ML8 which suggested the occurrence of a growth-limiting component. This region of slow growth could be correlated with diminished soluble nitrogen values, and was eliminated by enrichment of the medium with soluble nitrogen. An unusual feature of the investigation was the dilution rates, indicative of extremely fast specific growth rates, experienced for Str. lactis ML8. It was thought unlikely that wall growth contributed appreciably to the dilution rate as a similar phenomenon was not observed with Str. cremoris AM1 or AM2.
Perceived job importance and job performance satisfaction of selected clinical nutrition management responsibilities.
A nationwide survey of clinical nutrition managers was conducted to assess perceived importance of selected job responsibilities and perceived performance satisfaction of those job responsibilities. A questionnaire was developed to achieve the study objectives, validated by an expert panel, and pilot-tested prior to data collection. All members of the American Dietetic Association's Clinical Nutrition Management dietetic practice group (N=1,668) were asked to rate the importance of selected job responsibilities and their satisfaction with those responsibilities using Likert-type scales with descriptions. Results revealed that clinical nutrition managers perceived all job responsibilities listed in the questionnaire to be important (ie, the mean score of each responsibility was >3.0 of a 4.0 scale). Respondents rated regulatory-related job responsibilities as most important and were most satisfied with their performance of these responsibilities. Following regulatory-related responsibilities, clinical nutrition managers perceived patient satisfaction and staff retention to be more important than other responsibilities. In general, clinical nutrition managers were more satisfied with their job performance for job responsibilities that they ranked as more important.