Growth patterns of Pseudomonas aeruginosa in milk fortified with chitosan and selenium nanoparticles during refrigerated storage.

Pseudomonas spp are considered a common milk-associated psychotropic bacteria, leading to milk deterioration during storage; therefore, our study aimed to study the distribution of Pseudomonas aeruginosa in raw milk and its associated products then studying the growth behavior of P. aeruginosa in milk after employing chitosan nanoparticles (CsNPs 50, 25, and 15 mg/100ml) and selenium nanoparticles (SeNPs 0.5, 0.3 and 0.1 mg/100ml) as a trial to control the bacterial growth in milk during five days of cooling storage. Our study relies on the ion gelation method and green synthesis for the conversion of chitosan and selenium to nanosized particles respectively, we subsequently confirmed their shape using SEM and TEM. We employing Pseudomonas selective agar medium for monitoring the bacterial growth along the cooling storage. Our findings reported that high prevalence of Pseudomonas spp count in raw milk and kareish cheese and high incidence percent of P. aeruginosa in ice cream and yogurt respectively. Both synthesized nanoparticles exhibited antibacterial activity in a dose-dependent manner. Moreover, CsNPs50 could inhibit the P. aeruginosa survival growth to a mean average of 2.62 ± 1.18 log10cfu/ml in the fifth day of milk cooling storage; also, it was noted that the hexagonal particles SeNPs0.5 could inhibit 2.49 ± 11 log10cfu/ml in comparison to the control P. aeruginosa milk group exhibited growth survival rate 7.24 ± 2.57 log10cfu/ml under the same conditions. In conclusion, we suggest employing chitosan and selenium nanoparticles to improve milk safety and recommend future studies for the fate of nanoparticles in milk.

Identification of novel antibacterial peptides isolated from a commercially available casein hydrolysate by autofocusing technique.

Autofocusing, as a simple and safe technique, was used to fractionate casein hydrolysate based on the amphoteric nature of its peptides. The antibacterial activity of casein hydrolysate and its autofocusing fractions (A1-10) was examined against Escherichia coli and Bacillus subtilis. The basic fraction A9 exhibited the highest activity with minimum inhibitory concentration (MIC) of 150 µg/mL, whereas casein hydrolysate showed MIC values ranging from 2000 to 8000 µg/mL. The antibacterial peptides in A9 were purified by using a series of size exclusion and reversed phase chromatographies. Three peptides exhibited the most potent antibacterial activity with MIC values ranging from 12.5 to 100 µg/mL. These peptides were generated from α(s2)-casein, α(s1)-casein, and κ-casein and identified as K165 KISQRYQKFALPQYLKTVYQHQK188, I6KHQGLPQEV15, and T136EAVESTVATL146, respectively. Therefore, the results revealed that casein hydrolysate had potent antibacterial peptides that could be isolated by autofocusing technique.