Characterisation of proteins in camel milk, the effect of heat treatment on physicochemical and functional properties related to yogurt

Abstract

Camel milk plays a central role in the food supply of Eastern African and Middle Eastern countries (e.g. Kenya, Somalia, Saudi, and Ethiopia), home to the majority of the world’s camel population. Raw, and traditionally fermented camel milk has become increasingly commercialised and consumed in urban areas. This has led to an increased interest in the processing of camel milk for the urban market, with skimmed camel milk casein and whey powders soon to be commercialised, in a manner similar to the already widely available bovine dairy powders. However, little information is currently available concerning the effects of different processing methods (e.g. thermal treatment) on camel milk fractions. Currently there are no camel milk derived products, such as yoghurt or cheese, available in local Saudi supermarkets. Furthermore, the abundance of bioactive substances in camel milk have been reported to have useful effects; one of the most prominent is the anti-diabetic benefits revealed by in vivo studies. However, the presence of insulin in camel milk still remains to be proven. The aims of this thesis are twofold. The first area (Chapters 2, 3 and 4) describe the effect of heat treatment on camel milk components and their functional properties in an oil and water emulsion, and in yoghurt. In order to test these functional properties, camel skimmed milk, whey and casein were prepared and freeze dried. The key novel findings include: skimmed milk that had been heat treated and freeze dried showed significantly improved functionality for use in emulsions and yoghurts, whereas heat treated whey did showed no significantly enhanced functional properties. Furthermore, non-heated freeze dried casein significantly enhanced curd formation in yoghurt, and resulted in a smooth texture. Two fermented yoghurts were developed containing heat treated skimmed milk powder or casein with similar textural properties to bovine milk commercial yoghurt, that were acceptable in taste and texture, as determined by an independent study for sensory evaluation. The second area of this study (Chapter 5) concerned the characterisation of insulin in camel milk. As it was confirmed by previous studies that the presence of high concentration of insulin in camel milk comparing to bovine milk. Key findings were that no protein with a characteristic molecular weight similar to bovine or human insulin (5.8 KDa) could be detected using Western Blotting; however, a 62 KDa protein showed consistent immune reactivity. ELISA results showed high immune reactivity in camel whey. An in vivo assay showed biological insulin like activity in camel milk, but the validity of the assay still needs to be confirmed.