Poultry by-products are not often processed into high-value products. Rather than being transformed into meal for animal feed, a large quantity of chicken skin could be used to produce collagen, which is valued for its unique functional properties. The purpose of this research project was to extract and characterize collagen from chicken skin. Skins were first ground and then were heated to 40 or 60 degrees C to extract the fat. After mechanical separation, the collagen contained in the resulting solid phase was extracted with pepsin or ethylene diamine. Types I and III collagen were then isolated and characterized by SDS PAGE, antigen labeling, determination of tyrosine residues, and transmission electron microscopy. The total collagen content of the skin was recovered from the solid phase following heat treatment at 40 degrees C. Extraction yields varied with the solubilization process: 38.9% of the collagen content in the solid phase was extracted with pepsin and 25.1% with ethylene diamine. Ratios of type I to type III collagen fractionated using NaCl were 74.4:19.8% with pepsin and 62.4:31.7% with ethylene diamine. Characterization tests further revealed the presence of telopeptides solely on ethylene diamine-solubilized collagen. Chicken skin thus appears to be a good alternative source of high-quality collagen.

Bipolar membrane electroacidification (BMEA) has been developed previously (Bazinet et al., Report for the Canadian Electricity Association 9326 U 987, 1996; Bazinet et al., J. Agric. Food Chem. 1997, 45, 2419-2425, 3788-3794) and has been used for isoelectric precipitation of soybean proteins. The purpose of this study was to validate the feasibility of BMEA for the precipitation of milk casein and to investigate the effect of flow rate. High-purity isolates containing 1.23 and 2.00% ash and 85.4 and 91.6% total protein were obtained with flow rates of 0.2 and 1.2 gal/min. The molecular composition profiles of the isolates obtained by HPLC showed that only caseins were precipitated. However, except for protein precipitation curves, the flow rate did not influence the final composition and purity of the isolates. These results showed that BMEA is a new alternative process for the production of high-purity bovine milk casein isolate.

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This study evaluated the effect of protein hydrolysis by lactic acid bacteria during milk fermentation on the release of amino acids and peptides duing subsequently simulated peptic and pancreatic digestion. After digestion with trypsin, we compared the elution patterns of proteins and peptides obtained from unfermented milk and from milk fermented by Lactobacillus helveticus under pH control, using HPLC gel filtration and reverse-phase HPLC. The results indicate that milk fermentation affects the release of some amino acids during simulated gastrointestinal digestion and has a major impact on the modification of protein elution profiles obtained after digestion with trypsin. We conclude that proteolysis during fermentation may lead to the formation of novel peptides during gastrointestinal digestion.

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