Laban rayeb and yoghurt : sensory, rheological, chemical and microbiological properties

Abstract EN

This investigation was run to study some sensory, rheological, chemical and microbiological properties of some fermented dairy products sold in Assiut city, Egypt.

The products were represented in Laban Rayeb and yoghurt, in which 100 samples (each product 50 samples) were collected randomly from different dairy shops distributed in Assiut city.

The sensory evaluation was depend on 3 main attributes as visual (including color and free whey), texture (including firmness, creaminess, viscosity, mouth feel, consistency and smoothness) and flavor (including taste and aroma), moreover, the resultant of the 3 main attributes were expressed in the overall acceptability (OAA).

Syneresis was used for the rheological properties.

The chemical analysis was run through the percentages of titratable acidity (TA), fat, total solids (TS) and hence solids-non-fat (SNF) and moisture.

The microbiological examination was done through counting of coliforms, fecal coliforms, E.

coli, Enterococci, Staphylococcus aureus, Clostridium perfringens, yeasts and molds.

The obtained results revealed that the sensory quality of the examined products was slightly good although 66 % of Laban Rayeb samples and 78 % of yoghurt samples had a relatively high score ranged from 5 to 9 according the 9 points hedonic scale.

The average values of syneresis from Laban Rayeb and yoghurt samples were nearly similar as 10.4 and 10.429 ml, respectively.

The chemical analysis of Laban Rayeb revealed the average values of TA as 1.21 %, fat as 3.01 %, TS as 11.30 %, SNF as 8.29 % and moisture as 88.70 ; and for yoghurt the average values of TA as 1.20 %, fat as 3.34 %, TS as 14.02 %, SNF as 10.68 % and moisture as 85.98 %.

For both Laban Rayeb and yoghurt, the highest % of samples contaminated with microorganisms was by molds as found in 92 and 60 % of the samples, respectively ; followed by yeasts as found in 68 and 24 %, Enterococci in 30 and 28 %, coliforms in 28 and 22 %, Staph, aureus in 6 and 8 %, fecal coliforms in 4 and 2 %, respectively; while E.

coli and CI.

perfringens could not detected.

In conclusion, the examined products were of a good chemical analysis when compared to the international standards; while, the microbiological quality was lower than the level required by the Egyptian and international standards in most of the examined samples.

The public health significance and economic importance of the different microbial contaminants, as well as, the recommended hygienic measures for production of high quality Laban Rayeb and yoghurt were discussed.