PhD: Study on the specific chemical and biochemical changes in the beaten cheese during ripening

Erhan Sulejmani
Department of Food Technology and Biotechnology, Faculty of Technology and Metallurgy, Ss. Cyril and Methodius University, Skopje, Macedonia
May, 2014
 

Abstract

Cheese is a biochemically dynamic product and undergoes significant changes during ripening. The process of cheese ripening is a long, complex and still incompletely biochemically studied. The objectives of this doctoral thesis were aimed to study the biochemical changes in the ripening process such as proteolysis, lipolysis, metabolism of lactose, lactate and citrate as well as the formation of volatile components responsible for flavor and aromatic characteristics of beaten cheese.

Beaten cheeses from different geographical areas from the Republic of Macedonia such as northeast, Polog, southwest, Pelagonia, Vardar and east region were investigated.

The overall composition, proteolysis, volatile compaunds and textural characteristics were determined. Mean values for gross composition were: 57-68% for dry matter, 25-38% for fat, 25-31% for protein and 2-8% for salt.
Proteolysis was followed by determining the amount of water soluble nitrogen fraction (WSN/TN) and 12 % trichloroacetic acid (TCA / TN) soluble fraction in relation to the total amount of nitrogen (TN). Different levels in the range of 10-33 % for the WSN / TN and 1-7 for TCA / TN were determined. The influence of beaten cheese origin on the total amount of free amino acids (TFAA) was statistically significant (p < 0.05). The degree of proteolytic degradation of casein was determined by applying urea polyacrilamid gel electrophoresis (Urea-PAGE) method, and by reversed phase high performance liquid chromatography (RP-HPLC). 65 volatile components: carboxylic acids (11), ketones (13), esters (16), alcohols (8), terpenes (12) and others (7) were identified using gas chromatography with mass spectrometry (GC-MS).

The influence of the process parameters on the manufactured ewe’s milk cheese in industrial (I) and traditional (T) conditions were studied. Higher levels of proteolysis were observed in (I) cheeses compared to (T) cheeses (p <0,05) during 180 days of ripening. Levels of residual β- and αs-caseins were 72,2 and 48,7%, respectively, in 180-day-old (T) cheeses. However, the residual levels were 52,8% for β-casein and 18,7% for αs-casein in (I) cheeses. A total of 7 volatile compounds were identified in ( I) industrial and (T) traditional ewes milk beaten cheese during 180 days of ripening. These compounds belong to different chemical groups including acids (14), ketones (5), esters (17), alcohols (15), aldehydes (4), terpenes (7) and miscellaneous (10). The amount of in total 17 volatile components depend statistically significant on the applied conditions of production, while 30 of the identified volatile components are statistically significant (p <0.05) influenced by the timing of ripening.