Changes in Microbial Safety and Quality of High-Pressure Processed Camel Milk

Abstract

High-pressure processing (HPP) is used as a non-thermal approach for controlling microbial viability. The purposes of this study were to (i) establish the decimal reduction times (D-values) for pathogenic bacteria during 350 MPa HPP treatment,; (ii) evaluate the impact of 350 MPa HPP on total plate count (TPC), yeasts and molds (YM), and lactic acid bacteria (LAB) in camel milk; (iii) investigate the behavior of several spoilage-causing bacteria during storage at 4 °C and 10 °C for up to 10 d post-HPP treatment; and (iv) assess the effect of HPP on the protein degradation of camel milk. The D-values for L. monocytogenes, E. coli O157:H7, and Salmonella spp. were 3.77 ± 0.36 min, 1.48 ± 0.08 min, and 2.10 ± 0.13 min, respectively. The HPP treatment decreased pathogenic microorganisms by up to 2 to 3 log cfu/mL (depending on treatment conditions). However, HPP reduced TPC, YM, and LAB by <1 log cfu/mL, regardless of the length of pressure exposure. HPP treatment, even at extended holding times, did not significantly alter either the proteolytic activity or casein micelle structure in camel milk. This study highlights HPP as a promising non-thermal technique for enhancing the microbiological safety of camel milk.

Keywords: lactic acid bacteria; pathogens; proteins; spoilage causing microorganisms; total plate count; yeasts and molds.

Figure 1

Survival curve of (a) Salmonella spp. (R² = 0.960, correlation coefficient = −0.586), (b) L. monocytogenes (R² = 0.928, correlation coefficient = −0.402) with confidence and predication bands (dotted lines in camel milk samples) at 350 MPa, and (c) E. coli O157:H7 spp. (R² = 0.938, correlation coefficient = −0.433) at 300 MPa.

Figure 2

SDS-PAGE gel with the lanes representing the (1) marker, 350 MPa HPP treatment of camel milk, at (2) 0 min, (3) 1 min, (4) 2 min, (5) 3 min, (6) 4 min, and (7) 5 min, respectively.