Sugar matrices in stabilization of bioactives by dehydration

Development of functional foods with bioactive components requires component stability in foods and ingredients. Stabilization of sensitive bioactive components can be achieved by entrapment or encapsulation of these components in solid food matrices. Lactose or trehalose was used as the structure-forming material for the entrapment of hydrophilic ascorbic acid and thiamine hydrochloride or the encapsulation of oil particles containing hydrophobic α-tocopherol. In the delivery of hydrophobic components, milk protein isolate, soy protein isolate, or whey protein isolate were used as emulsifiers and, in some cases, applied in excess amount to form matrices together with sugars. Dehydrated amorphous structures with bioactives were produced by freezing and freeze-drying. Experimental results indicated that: (i) lactose and trehalose showed similar water sorption and glass transition but very different crystallization behavior as pure sugars; (ii) the glass transition of sugar-based systems was slightly affected by the presence of other components in anhydrous systems but followed closely that of sugar after water plasticization; (iii) sugar crystallization in mixture systems was composition-dependent; (iv) the stability of bioactives was better retained in the amorphous matrices, although small losses of stability were observed for hydrophilic components above glass transition and for hydrophobic components as a function of water activity; (v) sugar crystallization caused significant loss of hydrophilic bioactives as a result of the exclusion from the continuous crystalline phase; (vi) loss of hydrophobic bioactives upon sugar crystallization was a result of dramatic change of emulsion properties and the exclusion of oil particles from the protecting structure; (vii) the double layers at the hydrophilic-hydrophobic interfaces improved the stability of hydrophobic bioactives in dehydrated systems. The present study provides information on the physical and chemical stability of sugar-based dehydrated delivery systems, which could be helpful in designing foods and ingredients containing bioactive components with improved storage stability.

Stabilisation of dehydrated nanoemulsions using sugar - protein matrices

There are numerous review papers discussing liquid nanoemulsions and how they compare to other emulsion systems. Little research is available on dried nanoemulsions. The objectives of this research were to (i) study the effect of varying the continuous phase of nanoemulsions with different carbohydrate/protein ratios on subsequent emulsion stability, and (ii) compare the physicochemical properties, lactose crystallisation properties, microstructure, and lipid oxidation of spray dried nanoemulsions compared to spray dried conventional emulsions having different water and sugar contents. Nanoemulsions containing sunflower oil (10% w/w), β-casein (2.5–10% w/w) and lactose or trehalose (10–17.5%) were produced following optimisation of the continuous phase by maximising and minimising viscosity and glass transition temperature (Tg’) using mixture design software. Increasing levels of β-casein from caused a significant increase in viscosity, particle size, and nanoemulsion stability, while resulting in a decrease in Tg’. Powders were made from spray drying emulsions/nanoemulsions consisting of lactose or a 70:30 mixture of lactose:sucrose (23.9%), sodium caseinate (5.1%) and sunflower oil (11.5%) in water. Nanoemulsions, produced by microfluidisation (100 MPa), had higher stability and lower viscosity than control emulsions (homogenization at 17 MPa) with lower solvent extractable free fat in the resulting powder. Partial replacement of lactose with sucrose decreased Tg and delayed Tcr. DVS and PLM showed that in powdered nanoemulsions, lactose crystallises faster than in powdered conventional emulsions. Microstructure of both powders (CLSM and cryo-SEM) showed different FGS in powders and different structure post lactose crystallisation. Powdered nanoemulsions had lower pentanal and hexanal (indicators of lipid oxidation) after 24 months storage due to their lower free fat and porosity, measured using a validated GC HS-SPME method, This research has shown the effect of altering the continuous phase of nanoemulsions on microstructure of spray dried nanoemulsions, which affects physical properties, sugar crystallisation, and lipid oxidation.