BIOCHEMICAL AND FUNCTIONAL PROPERTIES OF SOFT BRINED CAMEL MILK CHEESE

Abstract

This dissertation work was aimed to investigate the biochemical and functional properties of soft brined cheese made from camel milk and it is composed of four different papers. The papers are a review article on camel proteins technological functionalities and three experimental papers. In the first experiment, operating parameters for camel milk gelation kinetics (i.e. pH, temperature, coagulant (camel chymosin) concentration and CaCl2 addition) to optimize the recipe for cheese making and the last two experiments are composed of biochemical and functional properties of brined camel milk cheese made with two levels of coagulant and ripened in two different levels of brine (NaCl %) for 60 days. The hydrolysis rate of camel milk kappa (κ)-casein was significantly (p < 0.05) increased with the increase of coagulant concentration from 55 IMCU L- 1 to 85 IMCU L-1, temperature from 30 to 40 °C and with reduction of milk pH from 6.6 to 6.0. In camel milk, chymosin induced gelation initiates after > 95 % of k-casein is being hydrolyzed. A shift in the onset of gelation was seen as a result of increase in temperature of gelation that promoted hydrophobic interactions during camel milk casein micelle aggregation. Reducing pH, increasing temperature and coagulant concentration has significantly (p < 0.05) decreased the gelation time of camel milk and also improved the rheological properties (i.e. tau (τ) and storage modulus (G´͚) of the gel; however, effect of salt addition was pH dependent. The composition of soft brined camel milk cheese changes in the first 20 days of ripening. Salt uptake increases with increase in ripening time, brine concentration and coagulant concentration. Cheeses made with 85 IMCU L-1 of coagulant resulted in higher proteolysis products during ripening. The soluble nitrogen fractions generated from cheeses increased during ripening. α-casein degraded in early stage of ripening but most of the peptides were steamed from β-casein. Both increase in NaCl and coagulant level affected the degradation of α and β-caseins as well as peptides generated from brined camel milk cheese in addition to ripening time. The texture properties (Young modulu’s and stress at fracture) of cheese increased with increase in salt-in-moisture of the cheese during ripening. However, using 85 IMCU L-1 coagulant concentration resulted a xvi softening to brined camel milk cheese internal structure. Volatile aroma compounds generated from soft brined camel milk cheese was affected by ripening time, concentration of NaCl and coagulant level. Individual volatiles formed during ripening increased with increase in coagulant concentration. Sour, salty and firm sensory descriptors describe soft brined cheese made from camel milk. In conclusion, camel milk gel development mainly determined by gelation temperature and using higher (85 IMCU L-1) chymosin concentration during cheese making leads to higher degradation of caseins and the volatile aroma compounds of caseins origin also influenced by coagulant concentration.