Comparison of low- and high-methoxyl pectin for the stabilization of whey protein isolate as carrier for lutein

Lutein (LUT) is a natural colorant and antioxidant that is found in vegetable sources such as marigold flowers and green leaves. Due to its instability under some environmental conditions, carrier materials are desirable to protect and incorporate this natural colorant into food products. Whey protein isolate (WPI) and pectin have been studied as a well-known system to entrap active compounds. The first part of this study evaluated the effect of total concentration (0.2 and 0.4%) and biopolymer ratio (3:0, 3:1, 3:2, 3:3, 2:3, 1:3 and 0:3) of the WPI:low methoxyl pectin (LMP) nanocomplexes (NCs). Subsequently, the influence of the type of pectin, including LMP and high methoxyl pectin (HMP) for the optimization of NCs was studied at different concentrations of pectin at ratios of 4:0, 4:1, 4:2, 4:3, 4:4 and 0:4 (WPI:LMP/HMP). Moreover, the loading of LUT into the NCs was investigated to assess its effect on the particle and stabilization properties. All NCs showed a stable particle size at pH 5.0 and precipited at lower pH values. NCs loaded with LUT at a ratio of 4:1 (WPI:LMP) and pH 5.0 showed the most stable system with a particle size of 204 ± 5 nm after 30 days. The binding properties showed a maximum binding constant (Kq) of 5.35 × 10¹³ M⁻¹ S⁻¹ at pH 7.0, which proves that this is the optimal pH condition to bind the LUT to the WPI.