Impact of hydrolyzed lactose by ?2-galactosidase enzyme on the physicochemical and organoleptic properties of fermented camel milk

摘要

The present study was conducted to evaluate the influence of lactose hydrolysis by using two different strategies (by addition of ?2-galactosidase (HA-LACTASEa?￠) before fermentation of camel milk to get hydrolyzed camel milk as substrate that included three levels of lactose-hydrolyzed milk (LHM) 25, 50 and 90% or together with the starter cultures during fermentation (co-hydrolysis)) on the microbiological, physicochemical and sensory properties of fermented camel during manufacturing and the storage period of 21 days at 5?oC. In general, the results showed a significant (P0.05) reduction in fermentation time with an increase in the level of lactose hydrolysis. The co-hydrolysis fermented milk exhibited a significant (P0.05) decrease in the fermentation time (279 min) in comparison to control treatment (452.5 min). After 6 h of the incubation period, the viable cell counts were more outstanding in the co-hydrolysis and LHM 90% fermented milk, about 1 log cycle higher than other treatments. The mean values of pH were a highly significant (P0.05) dropped in co-hydrolysis and LHM 90% samples and reached to pH 4.6 in 6 hours, whereas the control, LHM 25 and 50% samples reached to the near of the same degree of pH in 8 hours of the fermentation process. Furthermore, the higher amount of exopolysaccharide (EPS) was found in co-hydrolysis fermented milk 262.3 mg/kg followed by LHM 90% 250.3 mg/kg, while control, LHM 25 and 50% treatments had the lowest amount of 178.3, 185.3 and 197.7 mg/kg, respectively. The higher amount of EPS in co-hydrolysis and LHM 90% treatments caused a concomitant increase of the apparent viscosity and a signi???cant (P0.05) decreased in susceptibility to syneresis in comparison to other treatments. Moreover, the co-hydrolysis fermented camel milk had significantly (P0.05) higher ratings for all sensory characteristics and more liked than other treatments. Although the LHM 90% samples had a better rheological characteristic, the panelists rated as unacceptable because of the strong sweet taste. Results showed that the simultaneous addition of enzyme and starter together demonstrated to be a satisfactory strategy in making fermented camel milk with high quality in the texture and overall acceptability beside its beneficial properties as a functional dairy product.??