Browsing by Author "Lavoisier, Anais"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Effect of a Whey Protein Network Formed by Cold Gelation on Starch Digestibility
    (2019) Lavoisier, Anais; Miguel Aguilera, Jose
    Composite gels of whey protein isolate (WPI) and potato starch (PS) were formed by calcium chloride induced cold gelation to obtain microstructures where native starch granules were encased in the WPI network. Gels were then subjected to heat treatment and PS gelatinized inside the protein network. In vitro starch digestibility was investigated using the INFOGEST protocol to explore if the protein gel was able to protect gelatinized starch granules from enzymatic attack during digestion. This study was focused on the impact of gel particle size and protein concentration on glucose release from the matrix. Mechanical and rheological properties of the composite gels were also evaluated after heat treatment. Glucose release from the matrix was reduced until the intestinal step of the simulated digestion when gels were ground to a particle size of 1mm. When gels were cut to a particle size of 5mm glucose release was decreased until the end of the test. In this case, at the end of the digestion glucose release was reduced by 15.5 and 20.5% for composite gels with 8 and 10% WPI respectively, whereas no significant reduction was observed for the gel with 6% WPI. Therefore, the effect of the WPI network on starch digestibility depended on particle size and on protein concentration. Mechanical and rheological properties of the gels were related to starch digestibility: PS hydrolysis rate decreased with increasing hardness and elasticity of the gels. This work contributes to a better understanding of starch digestion in soft food matrices.
  • No Thumbnail Available
    Item
    Effect of cysteine addition and heat treatment on the properties and microstructure of a calcium-induced whey protein cold-set gel
    (2019) Lavoisier, Anais; Vilgis, Thomas A.; Aguilera, Jose Miguel
    A model gel of whey protein isolate (WPI) was prepared by cold gelation with calcium. This system was modified by the addition of free cysteine residues (Cys) at different steps of the process. The WPI cold-set gels obtained were then subjected to heat treatment at 90 degrees C. First, the effect of Cys addition on the heat-induced aggregation of WPI was studied through Atomic Force Microscopy (AFM) and infrared spectroscopy (ATR-FTIR), while Cys' effect on cold gelation was observed by AFM, Confocal Laser Scanning Microscopy (CLSM) and oscillatory rheology (amplitude sweeps). The impact of heating on the microstructure and the viscoelastic properties of the WPI cold-set gels were finally investigated through several techniques, including DSC, ATR-FTIR, CLSM, cryo-SEM, and rheological measurements (temperature sweeps). When added during the first step of cold gelation, Cys modified heat-induced aggregation of WPI, resulting in the formation of a denser gel network with a fractal dimension (Df) of 2.8. However, the addition of Cys during the second step of cold gelation led to the formation of highly branched clusters of WPI and a looser gel network was observed (Df = 2.4). In this regard, the use and limitations of oscillatory rheology and the "Kraus model" to determine the Df of WPI cold-set gels was discussed. The viscoelastic properties and the microstructure of the WPI cold-set gels were irreversibly modified by heating. Gels were stiffer, more brittle, and coarser after heat treatment. New disulfide bonds and calcium bridges formed, as well as H-bonded beta-sheets, all contributing to the formation of the final gel network structure.
  • No Thumbnail Available
    Item
    Starch gelatinization inside a whey protein gel formed by cold gelation
    (2019) Lavoisier, Anais; Miguel Aguilera, Jose
    Native potato starch (PS) granules were trapped within a whey protein network formed by cold gelation. Heat treatment of these composite gels induced PS gelatinization inside the protein network, which was studied with a DSC/hot-stage system and confocal laser scanning microscopy. Gelatinization inside the protein network was also indirectly followed by rheological measurements and mechanical properties of the composite gels measured before and after heat treatment. The presence of the protein network shortened the gelatinization by 3 degrees C, reduced the gelatinization enthalpy by 42% and significantly restricted granules swelling. The rheological and mechanical properties of the gels were influenced by PS swelling, depending on starch concentration. After reheating to 90 degrees C, the addition of 1% PS resulted in a weakening of the gel. However, the addition of 9% PS led to a reinforcement of the gel, probably due to the formation of an interpenetrating network between whey proteins and the gelatinized PS.