The influence of storage conditions on flavour changes in human milk
Introduction
Breastfeeding is increasingly encouraged in mothers due to a broad series of beneficial effects for the neonate (Calder et al., 2006, Koletzko et al., 2001). Furthermore, breastfeeding has been shown in a series of studies to contribute to social binding effects and learning processes (Marlier and Schaal, 2005, Mennella et al., 2004, Schaal et al., 2004).
However, modern lifestyle and the increasing working requirements or wishes of mothers, as well as a lack of adequate structures for combining bringing up children and pursuing a professional career can greatly interfere with routine breastfeeding. Increasingly, therefore, breastfeeding is not performed directly but rather milk is pumped and stored for later use (Terry, 2004). While most studies until now have indicated that especially freeze-storage does not result in the development of any potentially harming constituents, e.g., microbial or biochemical, we have shown in a recent study that human milk undergoes significant flavour changes after two months storage at −19 °C (Spitzer & Buettner, 2010). In the present study we aim at a more detailed sensory elucidation of the temporal dynamics of these flavour changes, specifically with regard to orthonasal and retronasal odour sensations. In addition, the observed effects for freeze-storage of human milk were to be compared to human milk that had been heated prior to storage, as well as to cow milk treated in the same ways as the human milk samples.
Section snippets
Chemicals
The following reference compounds were obtained from the suppliers shown: decanoic acid 98%, dodecanoic acid 98%, hexanoic acid 99.5%, octanoic acid 98% (Sigma–Aldrich, Steinheim, Germany), oct-1-en-3-one 97% (ABCR GmbH & Co. KG, Karlsruhe, Germany), dichloromethane p.a. (Th. Geyer GmbH & Co. KG, Renningen, Germany). The following compounds were purified by means of argentation chromatography according to the literature (Steinhaus, Wilhelm, & Schieberle, 2007): (E,Z)-nona-2,4-dienal, (E,Z
Sensory evaluation of unheated and heated human milk with and without storage
Orthonasal evaluation of fresh human milk in comparison to freeze-stored unheated milk showed that metallic, fishy, rancid and sweaty odour attributes developed relatively rapidly during storage [cf. Fig. 1a and b; Friedman ANOVA (N = 14, dl = 5) = 37.4, 24.9, 29.5 and 26.6, respectively; p < 0.01 in all cases]. These four attributes were detectable orthonasally after three months of freeze-storage (cf. Table 1), and became significantly perceived after four months of storage, amounting to medium or
Discussion
Our study shows that human milk is prone to sensory deterioration during storage at −19 °C, even at a relatively early stage of storage. Formation of metallic and fishy odour notes are most likely related to the observed increases in oxidation products from polyunsaturated fatty acids such as (Z)-octa-1,5-dien-3-one, tr-4,5-epoxy-(E)-dec-2-enal and related carbonyl compounds (cf. Fig. 6) (Belitz, Grosch, & Schieberle, 2004). Such odorants have been previously shown to induce fishy and metallic
Acknowledgements
This work was supported by the German Federal Ministry of Education and Research (BMBF). The authors are exclusively responsible for the contents of the publication. We are grateful to Prof. Horst-Christian Langowski and Fraunhofer IVV (Freising, Germany) for support of our scientific work. Furthermore we would like to thank Prof. Monika Pischetsrieder and Dr. Michael Czerny for fruitful scientific discussions. Finally, we gratefully acknowledge Dr. Imre Blank for providing the (E,Z,Z
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2019, Behavioural ProcessesCitation Excerpt :Although it is an important preparative step in the process of chemical analysis or behavioral bioassay of natural substrates, improving procedures to inhibit or attenuate evaporation or oxidization, storage imposes modifications on milk. Several studies on milk storage have already been carried out for human milk and the impact of heating, lyophilization or refrigeration/freezing on the sensory and chemical properties of milk have been described (e.g., Contador et al., 2015; Spitzer and Buettner, 2010, 2013; Spitzer et al., 2010; Sandgruber et al., 2012). For example, fatty acids in human milk are oxidized into compounds bearing metallic and fishy off-odors when milk is stored at −19 °C for 1–2 months (Spitzer et al., 2010), but not when milk is stored at −80 °C, even for 24 months (Sandgruber et al., 2012).
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