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.