Optimisation of growth and storage conditions of lactic streptococci
| dc.contributor.advisor | Daly, Charlie | |
| dc.contributor.author | Lyne, John Gerard | en |
| dc.date.accessioned | 2023-05-04T13:18:43Z | |
| dc.date.available | 2023-05-04T13:18:43Z | |
| dc.date.issued | 1987 | en |
| dc.date.submitted | 1987 | |
| dc.description.abstract | The application of defined strain culture systems in the Irish Cheese Industry required detailed knowledge of culture preparation and preservation. Concentrated starters were prepared for strains of Streptococcus lactis and Streptococcus cremoris in a low lactose medium (2.5% milk solids) with external pH control. Initial studies indicated that doubling the level of yeast extract in the medium did not have a significant effect on specific growth rate or on final cell numbers. For most strains, final cell numbers at 22°C were greater than obtained in 10%.milk solids medium. Individual strains showed variable ability to maintain activity once the culture entered the stationary phase. When optimum conditions for cell harvesting had been established, individual strains were stored at refrigeration and sub-zero temperatures - both with and without cryoprotectants. Samples were assayed at various intervals for cell viability and culture activity. At -80°C most strains maintained activity and viability whether cryoprotectants were added or not. Strains which showed a decline in viability were best protected by glycerol with lactose being slightly less effective. At -20°C, the spent ferementation medium was not able to protect the strains from freezing or from frozen storage. Some strains lost activity without showing a decline in viability. With others, activity decreased at a rate corresponding to the loss in viability. For the former strains, subculturing at 21°C did not restore full activity but the latter cultures were able to regain full activity on sub-culture. The addition of glycerol and lactose prior to freezing aided in cell protection as did freezing at low temperature. However, the degree of protection was strain dependent. Some strains retained activity at refrigeration temperatures for up to 73 days, with all strains remaining active at 4°C for at least 14 days. One S. cremoris strain did not grow well under pHcontrol. A bacteriophage was detected in the culture, initially at low levels. The phage propagated and eventually lysed the culture. This occurred in milk based media which were pH controlled between pH values 6.0 and 7.3. Growth under pH controlled conditions at pH 5.5 did not cause phage release even though in separate experiments the phage was able to multiply at this pH. Inducing agents, such as U.V. and mitomycin-C failed to release lytic phage, nor were phage detected in broth or in phage-inhibitory media. Single strain isolates also exhibited phage release, even though these isolates differed from the parent strain in phenotype and phage typing. With the exception of one S. cremoris strain, conditions of culture growth, harvesting and storage were established. These have proved useful for the growth of lactic streptococci for commercial cheese making. | |
| dc.description.status | Not peer reviewed | en |
| dc.description.version | Accepted Version | en |
| dc.format.mimetype | application/pdf | en |
| dc.identifier.citation | Lyne, J. G. 1987. Optimisation of growth and storage conditions of lactic streptococci. MRes Thesis, University College Cork. | |
| dc.identifier.endpage | 207 | |
| dc.identifier.uri | https://hdl.handle.net/10468/14433 | |
| dc.language.iso | en | en |
| dc.publisher | University College Cork | en |
| dc.rights | © 1987, John Gerard Lyne. | en |
| dc.rights.uri | https://creativecommons.org/licenses/by-nc-nd/4.0/ | |
| dc.subject | Optimisation | |
| dc.subject | Growth | |
| dc.subject | Storage conditions | |
| dc.subject | Lactic streptococci | |
| dc.subject | Strain culture systems | |
| dc.subject | Irish cheese industry | |
| dc.title | Optimisation of growth and storage conditions of lactic streptococci | en |
| dc.type | Masters thesis (Research) | en |
| dc.type.qualificationlevel | Masters | en |
| dc.type.qualificationname | MSc - Master of Science | en |
