Stability of starch-proanthocyanidin complexes to in-vitro amylase digestion after hydrothermal processing.

Proanthocyanidins (PA) form poorly digestible complexes with starch. The study examined amylase degradation mechanism and hydrothermal stability of starch-PA complexes. Sorghum-derived PA was complexed with wheat starch, reconstituted into flour (10% gluten added) and processed into crackers and pancakes. In vitro digestion profile of the complexes and products were characterized. The starch-PA complexes retained more (34-84%) fragments with degree of polymerization (DP) > 6,000 after 120 min digestion than controls (0-21%). Debranching further revealed higher retention of DP 11 - 30 chains in the digested starch-PA complexes than controls, suggesting amylopectin complexation contributed to reduced starch digestion. Starch-PA complexes retained reduced digestibility (50-56% higher resistant starch vs controls) in the cracker, but not pancake model. However, removing gluten from the pancake formulation restored the reduced digestibility of the starch-PA complexes. The starch-PA complexes are stable to hydrothermal processing, but can be disrupted by hydrophobic gluten proteins under excess moisture conditions.

One-Step Fabrication of Stimuli-Responsive Chitosan-Platinum Brushes for Listeria monocytogenes Detection.

Bacterial contamination in food-processing facilities is a critical issue that leads to outbreaks compromising the integrity of the food supply and public health. We developed a label-free and rapid electrochemical biosensor for Listeria monocytogenes detection using a new one-step simultaneous sonoelectrodeposition of platinum and chitosan (CHI/Pt) to create a biomimetic nanostructure that actuates under pH changes. The XPS analysis shows the effective co-deposition of chitosan and platinum on the electrode surface. This deposition was optimized to enhance the electroactive surface area by 11 times compared with a bare platinum-iridium electrode (p < 0.05). Electrochemical behavior during chitosan actuation (pH-stimulated osmotic swelling) was characterized with three different redox probes (positive, neutral, and negative charge) above and below the isoelectric point of chitosan. These results showed that using a negatively charged redox probe led to the highest electroactive surface area, corroborating previous studies of stimulus-response polymers on metal electrodes. Following this material characterization, CHI/Pt brushes were functionalized with aptamers selective for L. monocytogenes capture. These aptasensors were functional at concentrations up to 106 CFU/mL with no preconcentration nor extraneous reagent addition. Selectivity was assessed in the presence of other Gram-positive bacteria (Staphylococcus aureus) and with a food product (chicken broth). Actuation led to improved L. monocytogenes detection with a low limit of detection (33 CFU/10 mL in chicken broth). The aptasensor developed herein offers a simple fabrication procedure with only one-step deposition followed by functionalization and rapid L. monocytogenes detection, with 15 min bacteria capture and 2 min sensing.