High Pressure Processing of Human Milk for Improved Nutrient Retention and Microbial Safety
ABSTRACT Viazis, Stelios. High Pressure Processing of Human Milk for Improved Nutrient Retention and Microbial Safety. (Under the direction of Dr. Brian E. Farkas). Human milk is generally accepted as the optimal nutritional source for infants. Human milk banks govern and oversee the collection, pasteurization, and distribution of human milk to those in need. Currently, Low Temperature Long Time (LTLT) pasteurization (30 min, 62.5 degrees C) is used to assure the safety of banked human milk. Studies have shown that LTLT inactivates pathogens, but also degrades important biochemical components including secretory immunoglobulin A (SIgA) and lysozyme, two of the most noted antimicrobial compounds in human milk. The kinetics of high pressure processing (HPP) favor the reduction of pathogenic microorganisms with retention of nutritional quality. The objective of the first study was to investigate the effects of HPP on SIgA and lysozyme activity in human milk in comparison with LTLT pasteurization. Human milk samples were pressure processed at 400 MPa for 30 to 120 minutes and heat treated at 62.5 degrees C for 30 minutes. An indirect modified Enzyme Linked Immunosorbent Assay (ELISA) and a Micrococcus lysodeikticus turbidimetric assay were performed to measure the activities of SIgA and lysozyme, respectively. Human milk subjected to pressures of 400 MPa for 30, 60, 90, and 120 minutes retained 85.6, 87.1, 80.6, and 75.4% of SIgA activity respectively, while LTLT pasteurized milk retained 51.2% activity. There was a significant difference (p<0.05) between raw human milk, HPP samples, and heat treated samples. High pressure processing of human milk at 400 MPa for 30, 60, 90, and 120 minutes retained 106.9, 96.3, 96.3, and 95.8% activity of lysozyme respectively, while LTLT pasteurization retained 78.8% activity. There was a significant difference (p<0.05) between raw human milk and LTLT pasteurized samples but not with HPP samples. These findings suggest that HPP results in improved nutrient retention of human milk when compared to traditional thermal pasteurization. However, further research was needed to study the process with respect to microbial inactivation. The objective of the second study was to investigate the efficacy of HPP for inactivation of Listeria monocytogenes ATCC 19115, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923 and ATCC 6538, and Streptococcus agalactiae ATCC 12927 in human milk. Human milk samples donated by a local milk bank were pooled and inoculated with each pathogen (108-109 CFU/ml); 0.1% peptone buffer solutions were likewise inoculated to serve as controls. Each sample was subjected to 400 MPa at 21 to 31 degrees C for holding times that ranged from 0 to 50 min, depending on the organism, or to 62.5 degrees C for 0 to 30 min using the capillary tube method. Samples were plated on tryptic soy agar and appropriate selective media for enumeration. In all cases, LTLT pasteurization of all pathogens seeded into human milk resulted in complete inactivation within 10 min. In human milk and in 0.1% peptone buffer, a 6-log10 reduction was achieved after 30 min of HPP treatment for S. aureus ATCC 6538. After 30 min, S. aureus ATCC 25923 was reduced by 8-log10 and 6-log10 in human milk and buffer, respectively. Treatments of 4 min and 7 min resulted in complete inactivation of Strep. agalactiae in human milk and buffer respectively, while only 2 min was necessary for inactivation of L. monocytogenes in human milk (3.5 min for complete inactivation of L. monocytogenes in buffer). Although an 8-log10 inactivation of generic E. coli suspended in buffer was achieved after 10 min of HPP, only a 2-log10 reduction was observed in human milk after the same treatment time. These data suggest that HPP may be a viable alternative for pasteurization of human milk. Further research is needed to evaluate its efficacy in the inactivation of relevant viral pathogens and establish recommended processing times that result in reliable inactivation of all relevant pathogens.
Advisor:Dr. Brian E. Farkas; Dr. Lee-Ann Jaykus; Dr. Jonathan C. Allen
School:North Carolina State University
School Location:USA - North Carolina
Source Type:Master's Thesis
Date of Publication:08/04/2006