Selection of phage insensitive lactic streptococcal strains for use in cheddar cheese manufacture

Graduation date: 1980A survey was conducted of six North American cheese plants to\ud determine levels of bacteriophages present. Fifty-nine lactic streptococcal\ud host bacterial strains were utilized in the survey. Phage levels\ud were generally lower in plants employing modern manufacturing techniques\ud than in plants employing traditional manufacturing techniques; this\ud difference was attributed to the Streptococcus lactis strains in the\ud group. A majority of the phage insensitive strains were the same for\ud all plants; no correlation was found between phage sensitivity and acid\ud producing ability.\ud The insensitive strains from the survey were characterized as to\ud acid-producing ability, lysogeny and campatability for growth in\ud mixtures. These strains were used in formulating multiple strain\ud starter cultures of six strains which were used successfully on a\ud commercial basis in two cheese plants. Variability in cheesemaking\ud caused by instability of starter activity was considerably reduced by\ud the ability to intelligently manipulate strains in the starter. Manipulation\ud was made possible by monitoring starter activity and phage\ud development patterns in each plant. The feasibility of direct addition of whey to a multiple strain bulk\ud starter culture to continuously select for phage tolerant strains for\ud use in Cheddar cheese manufacture was also investigated. A simulated\ud cheesemaking test was used to estimate starter performance in the\ud factory environment. Fluctuations in starter performance indicated\ud that direct whey addition produced starter that was not suitably stable\ud for Cheddar cheese manufacture.\ud Results demonstrated the successful use of phage-insensitive strains\ud of lactic streptococci in formulating improved multiple strain starters\ud for Cheddar cheese manufacture in the United States