Effect of high hydrostatic pressure and heat treatment on antimicrobial protein stability, shelf-life, and rheological characteristics of donkey milk

2021-11
Köker, Alperen
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Donkey milk has been gaining popularity due to its beneficial properties and similarity to human milk, however, since heat treatment lead to phase seperation and nutritional losses, it is consumed raw, which may cause health risks and limit its shelf life. High hydrostatic pressure (HHP) is a non-thermal food processing technique in which microbial inactivation can be obtained with minimum effects on fresh like properties of food product. This study aimed to investigate the effects of HHP, and heat treatment on physicochemical and rheological properties, stability of proteins, microbial load, and shelf-life of donkey milk. Increasing processing pressure (200, 400, and 500 MPa) decreased microbial load, lysozyme, and lactoferrin contents significantly (p<0.05). Although HHP application temperatures of 25 °C and 35 °C had no significant effect (p>0.05) on microbial load, lysozyme, and lactoferrin loss, while at 45 °C, decreased these parameters significantly (p<0.05). By using different processing times similar values were obtained (p>0.05) in terms of microbial inactivation, lysozyme, and lactoferrin content. Even though heat treatment of donkey milk samples at 75 °C for 1 and 2 min resulted in sufficient microbial inactivation, high lysozyme and lactoferrin inactivation were observed. Total aerobic mesophilic bacteria (TAMB) counts of HHP-treated and heat-treated milk samples stored at 4 °C exceeded 5 log CFU/mL after 21 days of storage, in contrast to untreated milk stored at 4 °C in which TAMB count increased to 5.82 log CFU/mL after 7 days of storage. pH values were decreased and titratable acidity values increased within the storage period for all samples. Significantly higher flow consistency index (K) and significantly lower flow behavior index (n) were observed in heat-treated samples comparing with untreated and HHP-treated samples (p<0.05). The results suggest that HHP is a more suitable process than heat treatment for treatment of donkey milk since lower loss of valuable antimicrobial proteins with longer shelf-life is obtained by HHP.
Donkey milk, High hydrostatic pressure (HHP), Antimicrobial proteins, Microbial inactivation, Shelf-life
https://hdl.handle.net/11511/94948
Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats
A. Köker, “Effect of high hydrostatic pressure and heat treatment on antimicrobial protein stability, shelf-life, and rheological characteristics of donkey milk,” M.S. - Master of Science, Middle East Technical University, 2021.
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