Assessment of different novel approaches to accelerate cheese ripening for a range of applications

The aims of this thesis were to investigate the potential of different methods to accelerate Cheddar cheese ripening, individually and in combination. The following approaches to accelerate Cheddar cheese ripening were evaluated; (a) addition of lactic acid bacteria adjuncts attenuated by microfluidization selected on their enzymatic and metabolic potential, (b) addition of entrapped lactococcal cell free extracts in yeast attenuated by microfluidization (c) inclusion of spray dried enzymemodified cheese to the Cheddar making process (d) use of elevated ripening temperatures and (e) combinations of the above approaches. Initially several strains of lactic acid bacteria were screened for key intracellular enzymes and metabolic activities pre- and post-attenuation in broth, and subsequently in a sodium caseinate model system for their ability to generate volatiles associated with cheese flavour. Based on these results, strains with the greatest potential were attenuated by microfluidization and used as adjuncts in a mini-Gouda type cheese system. These strains were used with a commercial starter consisting of two Lc. lactis and compared with a commercial adjunct consisting of Lactobacillus helveticus. Results indicated that one Lc. lactis strain (Z8) exhibited similar sensory characteristics to the commercial adjunct, which validated the experimental procedure used to select strains and the method of attenuation. Subsequently a cell free extract of a different lactococcal strain (AM2) also identified as having flavour potential was entrapped in attenuated freeze-dried yeast (Yarrowia lipolytica). This entrapment approach was successfully used as a vector to augment enzymatic and metabolic activity in Cheddar cheese production, without any adverse effect on cheese quality. In addition a hydrolysed substrate in the form of spray dried enzyme-modified cheese was also successfully incorporated into Cheddar cheese during manufacture to boost substrate availability for key enzymatic and metabolic activities associated with cheese flavour development. The inclusion of the enzyme-modified cheese enhanced flavour development and has potential in the development of fast-ripened ingredient type cheeses. The impact of elevated ripening temperatures on flavour development in cheeses was confirmed as increasing ripening temperatures from 8 to 12 o C, enhanced biochemical activity and thus flavour development over short ripening periods of less than 2 months. Cheddar type cheese were also produced enhanced flavour development using combinations of added adjuncts, entrapped cell free extract, added enzyme-modified cheese and elevated ripening temperatures. This study has highlighted that different practical approaches can be used to create enhanced diverse cheese flavours in a wide range of applications from model systems, natural and ingredient type cheeses.