Survival of lactic acid bacteria species in Filipino donor milk subjected to different heating temperatures

Abstract

This study aimed to characterize the behaviors of a cocktail of lactic acid bacteria (LAB) isolated from human donor milk after subjecting to processing at different temperatures. The isolates (n = 12) were identified using 16S rRNA sequencing prior to the propagation and challenge studies. BLAST comparisons revealed that the isolates were Streptococcus spp., Lactobacillus spp., and Enterococcus spp. (% Identity 91.20–98.67%). At an initial inoculation level (8.0 log CFU/ml), the isolates exhibited a non-linear inactivation curve in all temperatures. In the initial logarithmic-linear phase, a decreasing D-value that ranged from 1.70 to 0.20 min was observed with increasing heating temperatures (55 °C, 57 °C, 60 °C, and 63 °C). Microbial load reduction in this initial phase (LR1) also increased (3.31–5.42 log CFU/ml). Moreover, the time necessary to reach LR1 (tLR1), prior to the inactivation curve inflection to tailing, generally decreased. During tailing, minimal to no additional microbial load changes were observed. Total reduction (TLR) increased (3.32–5.42 log CFU/ml), the time it took to reach TLR (tTLR) decreased (60.00–40 min), and the survivor population decreased (4.83–2.63 log CFU/ml) with increasing temperature. The study was able to establish the thermal challenging behaviors and kinetic parameters of a cocktail of lactic acid bacteria (LAB) in human donor milk with known composition and physicochemical properties. The inactivation kinetic parameters were determined from the curves and significantly varied with increasing heating temperature. This study provides a basis for evaluation and possible improvement of the Holder pasteurization (HoP) protocols for human donor milk, specifically temperatures below HoP that allow for keeping the milk biologically active without compromising quality.