Production of acid- vs. rennet-curd fresh cheese varieties

This bachelor thesis‘ focus is on the production and characterization of fresh cheese. Model samples of fresh cheese were produced on VUT Brno using purely acidic curdling (cream cheese culture – lactic acid), combined curdling (cream cheese culture + rennet) and acidic combined with heat curdling (acetic acid. 92 C) The samples were observed for their content of bound and free fatty acids, volatile (aromatic) substances and for their sensory quality. The goal was to determine the influence of the method of curdling on the observed factors. The fats were extracted from the samples using a mixture of diethyl ether and petroleum ether solvents. The fatty acids were esterified with acid to methyl esters under boron trifluoride catalysis and identified by the GC-FID method. In the cheese curdled by combined curdling, a greater amount of free fatty acids was detected compared to the other samples. No significant difference in the amount of bound fatty acids was observed. The greatest fatty acid content overall was observed in the cheese produced by acidic curdling. For identification and semi-quantification of the volatile (aromatic) substances, an HS-SPME-GC-MS method was used. 72 volatile compounds were identified in the samples. The percentual representation of different chemical groups varied significantly, the highest number of volatile substances was observed in the cheese produced by acidic curdling. Sensory evaluation was conducted using an evaluation scale as well as a ranking test. In all the observed indicators, the commercial sample was evaluated the best. The cheese produced by combined curdling was received rather negatively due to the sour taste. The second-best cheese was ranked to be the cheese produced by acidic curdling. The results show that the acidic curdling is the best for taste as well as aromatic substance and fatty acid content. If we, however, consider other factors such as the time taken, the cheese produced by combined curdling appears to be the best overall