We determined the optimum pretreatment conditions such as pH and time for swelling duck feet and investigated the effects of the extracting method, such as water bath (WB), pressure cooker (PC), and microwave oven (MO), on quality characteristics of the duck feet gelatin for improving utilization of duck feet as a novel source of gelatin. The soaking solution of pH 1 among pH 1-14 with unit intervals was selected due to the highest yield. The quality characteristics of the gelatin tested were color, pH, gel strength, viscosity, and melting point. For the extracted gelatin with different methods, the CIE L*, a* and b* values were in the following order: MO>PC>WB (p<0.05), WB>PC>MO (p<0.05) and PC>MO>WB (p< 0.05), respectively. The gelatin extracted using WB showed the highest pH and that extracted using MO showed the lowest pH (p<0.05). The gel strength, viscosity, and melting point were the highest for MO (p<0.05). The gel strength and melting point were the lowest for PC (p<0.05). No significant difference was found in viscosity between the gelatins extracted using WB and PC (p>0.05). The quality characteristic of duck feet gelatin was affected by extracting methods, and MO extraction can be one of the effective methods for duck feet gelatin.

This study was conducted to determine the effect of duck feet gelatin concentration on the physicochemical, textural and sensory properties of duck meat jellies. Duck feet gelatin was prepared with acidic swelling and hot water extraction. In this study, four duck meat jellies were formulated with 3, 4, 5, and 6% duck feet gelatin, respectively. In the preliminary experiment, the increase in duck feet gelatin ranged from 5 to 20%, resulting in a significant (p<0.001) increase in the color score, but a decline in the hardness and dispersibility satisfaction scores. An increase in the added amount of duck feet gelatin contributed to decreased lightness and increased protein content in duck meat jellies. Regarding the textural properties, increase in the added amount of duck feet gelatin highly correlated with the hardness in the center (p<0.01, R2=0.91), and edge (p<0.01, R2=0.89), of duck meat jellies. Meanwhile, the increase in duck feet gelatin decreased the score for textural satisfaction; duck meat jellies containing 6% duck feet gelatin had a significantly lower textural satisfaction score, than those containing 3% duck feet gelatin (p<0.05). Furthermore, a significant difference in the overall acceptance of duck meat jellies formulated with 5% duck feet gelatin was observed, as compared to those prepared with 3% duck feet gelatin. Therefore, this study suggested that duck feet gelatin is a useful ingredient for manufacturing cold-cut meat products. In consideration of the sensory acceptance, the optimal level of duck feet gelatin in duck meat jellies was determined to be 5%.

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The objectives of this study were to determine the interaction between porcine myofibrillar proteins and various gelatins (bovine hide, porcine skin, fish skin, and duck skin gelatins) and their impacts on gel properties of porcine myofibrillar proteins. Porcine myofibrillar protein was isolated from pork loin muscle ( M . longissimus dorsi thoracis et lumborum ). Control was prepared with only myofibrillar protein (60 mg/mL), and gelatin treatments were formulated with myofibrillar protein and each gelatin (9:1) at the same protein concentration. The myofibrillar protein-gelatin mixtures were heated from 10°C to 75°C (2°C/min). Little to no impacts of gelatin addition on pH value and color characteristics of heat-induced myofibrillar protein gels were observed (p>0.05). The addition of gelatin slightly decreased cooking yield of heat-induced myofibrillar protein gels, but the gels showed lower centrifugal weight loss compared to control (p<0.05). The addition of gelatin significantly decreased hardness, cohesiveness, gumminess, and chewiness of heat-induced myofibrillar gels. Further, sodium dodecyl poly-acrylamide gel electrophoresis (SDS-PAGE) showed no interaction between myofibrillar proteins and gelatin under non-thermal conditions. Only a slight change in the endothermic peak (probably myosin) of myofibrillar protein-gelatin mixtures was found. The results of this study show that the addition of gelatin attenuated the water-holding capacity and textural properties of heat-induced myofibrillar protein gel. Thus, it could be suggested that well-known positive impacts of gelatin on quality characteristics of processed meat products may be largely affected by the functional properties of gelatin per se , rather than its interaction with myofibrillar proteins.

The objectives of this study were conducted to characterize pepsin-soluble collagen (PSC) extracted from bones (PSC-B), skins (PSC-S), and tendons (PSC-T) of duck feet and to determine their thermal and structural properties, for better practical application of each part of duck feet as a novel source for collagen. PSC was extracted from each part of duck feet by using 0.5 M acetic acid containing 5% (w/w) pepsin. Electrophoretic patterns showed that the ratio between α1 and α2 chains, which are subunit polypeptides forming collagen triple helix, was approximately 1:1 in all PSCs of duck feet. PSC-B had slightly higher molecular weights for α1 and α2 chains than PSC-S and PSC-T. From the results of differential scanning calorimetry (DSC), higher onset (beginning point of melting) and peak temperatures (maximum point of curve) were found at PSC-B compared to PSC-S and PSC-T (p<0.05). Fourier transform infrared spectroscopy (FT-IR) presented that PSC-S and PSC-T had similar intermolecular structures and chemical bonds, whereas PSC-B exhibited slight difference in amide A region. Irregular dense sheet-like films linked by random-coiled filaments were observed similarly. Our findings indicate that PSCs of duck feet might be characterized similarly as a mixture of collagen type I and II and suggest that duck feet could be used for collagen extraction without deboning and/or separation processes.