The effect of pasteurization on transforming growth factor alpha and transforming growth factor beta 2 concentrations in human milk

Abstract

Transforming growth factor alpha (TGF-α) and beta 2 (TGF-β2) are present in human milk and are involved in growth differentiation and repair of neonatal intestinal epithelia. Heat treatment at 56°C has been shown effective for providing safe banked donor milk, with good retention of other biologically active factors. The purpose of our study was to determine the effect of heat sterilization on TGF-α and TGF-β2 concentrations in human milk. Twenty milk samples were collected from 20 lactating mothers in polypropylene containers and frozen at -20°C for transport or storage. Before heat treatment by holder pasteurization, the frozen milk was thawed and divided into 1-mL aliquots. All samples were heated in an accurately regulated water bath until a holding temperature was achieved, then held for 30 minutes using constant agitation. Holding temperature ranged from 56.5°C to 56.9°C. The milk was then stored at 4°C overnight for analysis the following day. The concentration of TGF-α was measured by radioimmunoassay. Mean concentration ± SD of TGF-α in raw milk samples was 119 ± 50pg/mL, range 57 to 234. The mean concentration ± SD of TGF-α in heat treated samples was 113 ± 50pg/mL, range 51 to 227. TGF-α concentration was minimally affected by pasteurization, with an overall loss of 6.1%. Of 19 samples, 4 had increased and 15 had decreased concentrations after pasteurization (mean percent ± SEM: 94% ± 7% of raw milk, range 72%-107%). The concentration of acid-activated TGF-β2 was measured by enzyme-linked immunosorbent assay. Mean concentration ± SD of TGF-β2 in raw milk samples was 5624 ± 5038 pg/mL, range 195 to 15480. The mean concentration ± SD of TGF-β2 in heat-treated samples was 5073 ± 4646 pg/mL, range 181 to 15140. TGF-β2 survived with relatively little loss (0.6%): of 18 samples, 11 had increased and 7 had decreased concentrations after pasteurization (mean percent ± SEM: 99.4 ± 6.7% of raw milk, range 79%-120%). In conclusion, both TGF-α and TGF-β2 were well-preserved in whole milk after holder pasteurization at 56.5°C. The relative increase in growth factor concentration in some of the samples may be attributable to the release of that factor from the cellular and/or fat compartments into the aqueous fraction of human milk. These findings have implications regarding use of donor milk as an alternate source of growth factors and cytokines for the newborn gut when mother's milk is unavailable.