Effect of lactation stage and processing on characteristics of deer milk : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatu, New Zealand

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Interest in non-bovine milk consumption is growing, with scientific evidence for the unique benefits and the growing farming of non-bovine animals such as goat, sheep, and deer. The majority of studies have focused on cow milk and then followed by goat or sheep milk. Deer milk farming and detailed understanding of deer milk characteristics is a niche area of dairy farming that needs detailed exploration to understand whether it has the same processability when subjected to the standard dairy processing developed for cow milk. Along with the processing knowledge of deer milk, it is an interest of the dairy industry to understand how the lactation stage of deer affects the milk composition and its characteristics. This research aimed to understand the variation in milk composition with lactation stage of deer, and to investigate the milk characteristics along with different processing conditions to know its potential dairy products. Fresh deer milk samples were collected over the lactation period and the milk composition analysed, including fat, protein, and lactose content. The fresh milk was subjected to processing conditions most used in dairy industries such as 75°C/15 seconds with or without homogenization, and 95°C/5 minutes with homogenization. The seasonal and processing-induced changes in milk characteristics were analysed using conventional methods. The colloidal stability of deer milk was investigated in this study by using the different heating (time and temperature combinations) and homogenization conditions. The characteristics of reconstituted deer milk were also studied with the same processing conditions as used for fresh milk and compared with fresh deer milk characteristics. Deer milk was characterized by a higher content of macronutrients (fat and protein) and minerals compared to cow milk, and it was found that the protein distribution of deer milk was different from cow milk. The study showed that lactational stage of deer milk significantly impacted the fat, protein, minerals distribution in milk. Deer milk protein contained a significantly higher amount of β-casein and a lower amount of αs1-casein than cow milk. Deer milk formed stronger gels when inoculated with rennet or acidified than cow milk, but, like cow milk, heating improved the acid gel strength of deer milk. The behaviour of both fresh and reconstituted deer milk was almost similar after heat treatment as explained by milk physicochemical properties, but the gelation properties of rennet and acid gel made from reconstituted and fresh deer milk showed difference in terms of gel firmness and gelation time. The casein micelle size in deer milk was larger than micelles of cow milk. Heat treatment (95°C/5 min) increased the size of casein micelles in deer milk, and the effect was more pronounced as compared to micelles of cow milk, suggesting different mechanisms of casein micelle modification. Study of the colloidal stability of deer milk determined that the extent of whey protein denaturation and their association with casein micelles in deer milk increased with heating intensity like cow milk, but the kinetics of whey protein denaturation and their association with casein micelles differ in deer milk.
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