Lactoferrin: structure, function, thermal denaturation and digestion

The demand for foods possessing health benefits above and beyond calorie value is continuously increasing. In this context, lactoferrin (LF) has received considerable research attention because of its unique iron binding and delivering abilities. LF is a minor constituent of milk proteins which possesses antibacterial, antioxidant and anti carcinogenic characteristics in addition to its iron-binding ability. For these reasons, it is increasingly used as an important ingredient in many foods (e.g. infant milk formula) and pharmaceutical products (e.g., Acne care drugs). The functional properties of LF are highly dependent on its structural integrity. Since LF is sensitive to temperature and other chemical induced denaturation, the extraction, powder formation processes and processing parameters of LF and LF-containing products have to be optimised to minimise the undesired conformational changes (denaturation). The breakdown of structure and subsequent loss in the functional values of LF and LF-containing products in human digestive system also require systematic study. This understanding will help develop novel methods to best deliver LF to the targeted absorption sites in the human gastrointestinal tract in structurally and functionally stable form. Therefore, this study investigated the structure-function relationship of LF during thermal processing (convective air drying, spray drying and freeze drying) and digestion (in-vitro adult condition), and also studied its complex coacervation with sodium alginate (NaAlg) to preserve its structural integrity and functional properties and to slow down its premature digestion.

This study provides fundamental insights into the fact that the structural and functional properties of LF can be altered due to thermal, acidic and enzymatic stresses encountered during thermal processing and digestion. It also shows that the undesirable changes in structure and functions of LF can be reduced by optimising process parameters and forming complex coacervates as a more acid-stable matrix. Overall, this study paves a way for the production of structurally and functionally intact LF powders through spray and freeze drying process. The outcomes of this study help better utilisation of LF in high-value food products that aim to deliver LF through oral intake. The complex coacervation based approach, developed in this study to protect LF in gastric stage of digestion, can also be applied to other bioactive proteins.