Stability of ß-carotene microcapsules with Maillard reaction products derived from whey protein isolate and galactose as coating materials.

The stability of ß-carotene microcapsules using Maillard reaction products (MRPs) derived from whey protein isolate (WPI) and galactose as coating materials, was studied under the varying environmental conditions of temperature, pH, air, incandescent light, and ultraviolet (UV) light. Scanning electron microscopy showed that microcapsules prepared by WPI-galactose MRPs displayed a smooth and less concave-convex surface and that the particle size (D50) of the microcapsules made with WPI-galactose MRPs was smaller than those made with WPI-galactose mixture. The storage stability of ß-carotene microencapsulated in WPI-galactose MRPs was remarkably better than that of ß-carotene microencapsulated in the WPI-galactose mixture and that of ß-carotene crystal, in respect of temperature, pH, air, incandescent light, and UV light measurements. When the storage temperature was increased from 5 to 105 °C, the retention rate of ß-carotene microcapsules significantly decreased (P<0.05). When pH values were increased from 1 to 12, the ß-carotene retention rate of the microcapsules significantly increased and afterward decreased. Compared with the retention rate of ß-carotene microencapsulated in a WPI-galactose mixture, the retention rate of ß-carotene microencapsulated in WPI-galactose MRPs was at a maximum between pH 8 and 9. Under the actions of air, incandescent light, and UV light, the retention rates of ß-carotene microcapsules in WPI-galactose MRPs and WPI-galactose mixture, as well as in ß-carotene crystal, decreased significantly as the storage time increased (P<0.05). Therefore, the use of WPI-galactose MRPs as coating materials can aid in improving the storage stability of ß-carotene microcapsules.

Development of a test strip for rapid detection of lactoperoxidase in raw milk.

Traditional methods for detecting lactoperoxidase (LP) are complex and time-consuming, so a test strip was made based on the enzymatic reaction principle to enable quick and convenient detection of LP in raw milk. In this study 0.1 mol/L citric acid (CA)/0.2 mol/L disodium hydrogen phosphate (NaP) buffer solution (pH 5.0), 22 mmol/L 3,3',5,5'-tetramethylbenzidine (TMB), 0.6 mmol/L hydrogen peroxide (H2O2), and 0.5% Tween-20 or 0.3% cetyltrimethyl ammonium bromide (CTAB) were optimal for preparing a quick, sensitive, and accurate LP test strip. The coefficient of variation (CV) of the estimated LP concentrations ranged from 2.47% to 6.72% and the minimum LP concentration detected by the test strip was 1-2 mg/L. Estimates of active LP in sixteen raw milk samples obtained using the test strip or the TMB method showed a good correlation (r=0.9776). So the test strip provides a quick, convenient, and accurate method for detecting the LP concentration of raw milk.

Stability and cytotoxicity of angiotensin-I-converting enzyme inhibitory peptides derived from bovine casein.

This study investigated the effect of heat treatment combined with acid and alkali on the angiotensin-I-converting enzyme (ACE) inhibitory activity of peptides derived from bovine casein. The free amino group content, color, and cytotoxicity of the peptides were measured under different conditions. When heated at 100 °C in the pH range from 9.0 to 12.0, ACE inhibitory activity was reduced and the appearance of the peptides was significantly darkened. After thermal treatment in the presence of acid and alkali, the free amino group content of ACE inhibitory peptides decreased markedly. High temperature and prolonged heating also resulted in the loss of ACE inhibitory activity, the loss of free amino groups, and the darker coloration of bovine casein-derived peptides. However, ACE inhibitory peptides, within a concentration range of from 0.01 to 0.2 mg/ml, showed no cytotoxicity to Caco-2 and ECV-304 cell lines after heat treatment. This indicated that high temperature and alkaline heat treatment impaired the stability of bovine casein-derived ACE inhibitory peptides.