| Abstract |
Part (II) of the present work was conducted to study effect of using whey protein concentrate (WPC) on composition and quality of zabady of different fat content (section A) or on composition and some properties of the resultant soft cheese (section B) .The attained results can be summarized as follows:
Section (A):
Composition and quality of low-fat zabady (LFZ) and full-fat zabady (FFZ) made from Cow’s milk:
Decreasing fat content had insignificant effect on activity of yoghurt culture, whereas adding WPC showed an insignificant retarding effect in acidity development old LFZ milk. Effect of WPC was also recorded in case of making FFZ.
Adding WPC increased acidity values of both fresh and stored zabady, whereas its effect on pH was less pronounced.
Adding WPC significantly increased TS content in fresh and stored zabady. This effect was also true with acetaldehyde content.
TN and protein content significantly increased with increasing WPC added. NPN significantly also increased whereas NPN/ TN values insignificantly changes in LFZ with increasing WPC added but the values of FFZ significantly increased.
Fat was significantly lower in LFZ as compared to FFZ, whereas adding WPC had no effect in this respect. This effect was also observed in case of FFZ treated with increased amounts of WPC. This addition significantly decreased fat/TS. TVFA content was not affected by adding WPC.
Adding WPC significantly increased – in general – lactose and ash content. The first component decreased during storage whereas the second one increased.
Curd tension was significantly increased by increasing the amount of WPC added the opposite was recorded with respect to curd syneresis. The values of the first property increased, whereas the second one decreased – in general – with advancing storage.
Adding WPC greatly improved appearance, firmness and smoothness of the resultant zabady and prevented wheying-off with no adverse effect on flavour of zabady.
Composition and quality of non-fat zabady (NFZ) and low-fat zabady (LFZ) made from buffalo’s milk:
Adding WPC had no effect- in general- on activity of yoghurt during fermention period in spite of pH values were slightly higher in the presence of increased amounts of WPC.
Adding WPC had insignificant effect on increasing acidity and decreasing pH of the fresh and stored zabady.
TS significantly increased with increasing quantity of WPC added, whereas acetaldehyde content significantly increased in NFZ and insignificantly increased in LFZ as affected by increasing amount of WPC added. Both values in the stored zabady were always higher than those of the fresh samples.
TN, protein and NPN were significantly – in general – increased by increasing the amount of WPC added. This was true in the fresh and stored zabady which always had higher values. The changes in NPN/TN were not affected by adding increased amounts of WPC.
Fat content was insignificantly affected by adding WPC, whereas fat/DM insignificantly decreased with increasing the amount of WPC added, TVFA was not affected by adding WPC.
Adding WPC increased lactose and ash contents with different rates. The values in the stored zabady were less in case of lactose and more in case of acetaldehyde than those of the fresh zabady.
Adding WPC with increased amounts significantly increased curd tension and decreased curd syneresis. The first property increased on storage whereas the second one decreased.
Adding WPC- in general – improved the organoleptic properties of the resultant zabady especially improving appearance and preventing whey syneresis.
Section (B):
Effect of using whey protein concentrate on composition and quality of Domiati cheese containing different fat content:
Cheese from 5% salted milk and stored in refrigerator:
Adding WPC to cheese milk increased recoveries of fat, protein, lactose and TS in the resultant cheese and significantly increased yield of the fresh cheese and loss of cheese weight during pickling.
Adding WPC had insignificant effect on acidity and pH of the fresh or pickled cheese which increased and decreased during pickling respectively.
Adding WPC significantly increased TS of fresh and 15 days old cheese and the differences in 30 days old cheese were insignificant, whereas fat on dry matter significantly decreased in most cases with insignificant effect on TVFA.
Adding WPC significantly increased protein content of the fresh and 15 days old cheese and insignificantly increased SN/TN and NPN/ TN in the fresh cheese whereas the increase was almost significant in the pickled cheese.
Adding WPC had – in general – a significant effect on increasing lactose content and increasing effect on ash content, which decreased and increased respectively during pickling.
Adding WPC increased all the amino acids detected except Pro. and Arg. in fresh low fat cheese (LFCh). This addition increased Asp., Thr., Ser., Gly., Ala., Val., Met., Ile., Phe. and Arg. and decreased Glu., Pro., Leu., Tyr., His., and Lys. in fresh non-fat cheese (NFCh).
Adding WPC increased Asp., Thry., Glu., Ala., Val., Met., Ile., Leu., Phe., Lys. and Arg. in the pickled LFCh and decreased Ser., Pro., Gly., Tyr. and His.
Adding WPC increased all the amino acids detected in the pickled NFCh except Pro., Val., Ile., Lys. and Arg.
Adding WPC improved falvour and body and texture of the resultant-fresh and pickled cheese of different fat content.
Cheese from 10% salted milk and stored at room temperature:
Adding WPC increased recoveries of fat, protein, lactose and TS in the resultant cheese and significantly increased yield of the fresh cheese and decreased loss of LFCh weight and increased that of NFCh during pickling.
Adding WPC had insignificant effect on acidity and pH of the fresh or pickled cheese which increased and decreased in order during pickling.
Adding WPC increased TS and decreased values of fat / DM in the resultant cheese, whereas the differences in TVFA were insignificant.
Adding WPC increased values of SN/TN whereas the differences in NPN/TN were insignificant.
Adding WPC increased lactose content which gradually decreased during pickling. The same effect was recorded with ash content which increased during pickled.
Adding WPC increased Thr., Ser., Glu., Pro., Met., Ile., Leu., His. and Lys. and decreased Asp., Gly., Ala., Val., Tyr., Phe. and Arg. of the fresh LFCh. In the pickled LFCh, WPC increased only His. and Lys. and decreased the rest of the amino acids.
In fresh NFCh, using WPC increased Asp., Thr., Ser., Glu., Pro., Gly., Ala., Ile., Leu., Phe. and His. and decreased Val., Met., Tyr., Lys. and Arg. In the pickled NFCh, adding WPC increased Asp., Thr., Glu., Pro., Gly., Ala., Val., Met., Tyr., Phe., Lys. and Arg. and decreased the rest amino acids.
Adding WPC improved flavour and body and texture of the resultant fresh and pickled cheese.
In conclusion, adding WPC gave more richness for composition of Domiati cheese of different fat content and improved the organoleptic properties.
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