Some properties of frozen concentrated starters produced by continuous culture

Abstract

Frozen concentrated cheese starters were prepared from 7 Streptococcus cremoris and 2 Str. lactis strains by continuous culture. pH control with NH 4 0H and Ca(OH) 2 increased the yield of Str. cremoris strains as compared with NaOH, but the resultant cells were smaller and less active. Maximum yields for both species were obtained at a dilution rate of 0-6 and pH 6-3, but with Str. cremoris cell activity was reduced above pH 60.Degeneration in continuous culture was observed in the 2 Str. lactis strains, due apparently in one case to the action of a bacteriophage and in the other possibly to selection or to loss of adaptive enzymes.Concentrated starters retained full viability and activity when stored for 10-12 weeks at -110 °C, and 94% activity after storage for 4 weeks at -40 °C.Cheese made with the concentrated starters ripened normally and was comparable in quality with control cheese made with normal bulk starter.Cheese-making in Australia is mostly confined to the Cheddar variety and the starter cultures used are single strains of the mesophilic lactic streptococci.Two strains of Streptococcus lactis and 10 strains of Str. cremoris are currently used in the manufacture of Cheddar cheese in Australia. These strains have been selected because there is no evidence that they are phage-related. A daily rotation of such strains is advised to help control phage levels in the factory. The commercial development of frozen concentrated starters in Australia would therefore need to be based on the supply of a number of strains to allow for at least a 4-day rotation (Czulak, 1966) and some degree of preference by individual factories.Concentrated starters prepared from Str. lactis grown in continuous culture in a trypsin-digested whey medium gave promising results, but with Str. cremoris poor yields were obtained (Lloyd & Pont, 1970). As several Str. cremoris strains would be required for a 4-day starter rotation, we have attempted to improve their yields in continuous culture.Using a trypsin-digested milk medium, some of the more important parameters affecting the growth of Str. cremoris and Str. lactis in continuous culture were studied, particularly the yield and biological activity and storage stability of frozen concentrates. The results are presented in this paper .

Growth of a Mixed Species Lactic Starter in a Continuous “pH-Stat” Fermentor

“…The productivity could be increased further by using the chemostat principle with pH control outlined by Lloyd and Pont (17,18), but in this case the increased accumulation of inhibitors could have changed the bacterial balance unfavorably compared to the pH-stat. This, however, has to be further investigated.…”

“…This method, together with chemostats with or without pH control, has been used for continuous cultivation of lactic starters and starter bacteria (1, 5, 10, 12-14, 17-19, 27). Much of this work has, however, been done on single-strain starter bacteria (10,13,14,(17)(18)(19).…”

Cheese starters

“…Continuous culture appeared initially to be an economic method for the production of large amounts of cells, particularly in terms of space requirements, costs, suitability to automation and the possibility of obtaining more uniformly active cultures. However, continuous culture was found to require sterile media for successful operation and avoidance of contamination was both difficult and expensive to achieve in practice (445). Furthermore, continuous culture led in some cases to the accumulation of variant strains with lower acid-producing ability (in, 445) and increased phage susceptibility (446).…”

“…Furthermore, continuous culture led in some cases to the accumulation of variant strains with lower acid-producing ability (in, 445) and increased phage susceptibility (446). It is now generally accepted (445,447) that concentrated starters are best prepared from batch cultures. The main factors that have the greatest influence on cell yield and activity are:…”

CHALK CULTURE METHOD FOR PRESERVING BACTERIA CULTURES AND ITS APPLICATIONS1

“…Most of the Lactic acid concentrated cultures can be stored at -20 to -4OC for a short time, while lower temperature is used to store lactic acid concentrated cultures for a long time. The survival percentage of concentrated lactic acid streptococci cultures was 42% at -2OC, 93-99% at -4OC, and 100% at -1lOC (Lloyd and Pont 1973).…”