The potential of asymmetric flow field-flow fractionation hyphenated to multiple detectors for the quantification and size estimation of silica nanoparticles in a food matrix

This work represents a first systematic approach tothe size-based elemental quantification and size estimation ofmetal(loid) oxide nanoparticles such as silica (SiO2) in a realfood matrix using asymmetric flow field-flow fractionationcoupled online with inductively coupled plasma mass spectrometry(ICP-MS) and multi-angle light scattering (MALS)and offline with transmission electron microscopy (TEM)with energy-dispersive X-ray analysis (EDAX). Coffeecreamer was selected as the model sample since it is knownto contain silica as well as metal oxides such as titania at themilligramme per kilogramme levels. Optimisation of samplepreparation conditions such as matrix-to-solvent ratio,defatting with organic solvents and sonication time that mayaffect nanoparticle size and size distribution in suspensionswas investigated. Special attention was paid to the selection ofconditions that minimise particle transformation during samplepreparation and analysis. The coffee creamer matrix componentswere found to stabilise food grade SiO2 particles incomparison with water suspensions whilst no significant effectof defatting using hexane was found. The use of samplepreparation procedures that mimic food cooking in real lifewas also investigated regarding their effect on particle sizeand particle size distribution of silica nanoparticles in theinvestigated food matrix; no significant effect of the watertemperature ranging from ambient temperature to 60 °C wasobserved. Field-flow fractionation coupled to inductivelycoupled plasma-mass spectrometry (FFF-ICP-MS) analysisof extracts of both unspiked coffee creamer and coffee creamerspiked with food grade silicon dioxide, using differentapproaches for size estimation, enabled determination ofSiO2 size-based speciation. Element-specific detection byICP-MS and post-FFF calibration with elemental calibrationstandards was used to determine the elemental composition ofsize fractions separated online by FFF. Quantitative data onmass balance is provided for the size-based speciation ofthe investigated inorganic nano-objects in the complexmatrix. The combination of FFF with offline fractionationby filtration and with detection by ICP-MS and TEM/EDAXhas been proven essential to provide reliable information ofnanoparticle size in the complex food matrix

Effects of calcium chloride and sodium hexametaphosphate on certain chemical and physical properties of soymilk

Soymilks with sodium hexametaphosphate (SHMP) (0% to 1.2%) and calcium chloride (12.50, 18.75, and 25.00 mM Ca),were analyzed for total Ca, Ca ion concentration, pH, kinematic viscosity, particle diameter, and sediment after pasteurization. Higher added Ca led to significant (P <= 0.05) increases in Ca ion concentration and significant (P <= 0.05) decreases in pH. At certain levels of SHMP, higher concentrations of added Ca significantly increased (P <= 0.05) kinematic viscosity, particle diameter, and sediment. Increasing SHMP concentration reduced Ca ion concentration, particle diameter, and dry sediment content, but reduced kinematic viscosity of samples (P <= 0.05). Adding SHMP up to 0.7% influenced pH of soymilk in different ways, depending on the level of Ca addition. When the pH of Ca-fortified soymilk was adjusted to a higher level, ionic Ca decreased as pH increased. Ihere was a negative linear relationship between the logarithm of ionic Ca concentration and the adjusted pH of the soymilk. Ionic Ca appeared to be a good indicator of thermally induced sediment formation, with little sediment being produced if ionic Ca was maintained below 0.4 mM