Thermally induced -lactoglobulin ( -Lg) and sodium polypectate (SPP) composite gels or coagulum were formed at pH 6.5 and 3.5 and evaluated by dynamic rheological techniques and transmission electron microscopy (TEM). At pH 6.5, SPP-induced -Lg gelation, resulting in the formation of opaque -Lg/SPP and transluscent -Lg/SPP/CaCl 2 gels. Co-gelation of -Lg and SPP increased the storage modulus (G′) of -Lg/SPP/CaCl 2 gels during cooling, whereas ungelled SPP prevented further increases in G′ of -Lg/SPP gels. Irrespective of calcium cations, -Lg and SPP interacted at pH 3.5 to form a grainy white precipitate that coagulated on heating. At pH 6.5, TEM micrographs revealed a nonuniform distribution of -Lg aggregates in -Lg/SPP gels as opposed to a homogenuous -Lg/SPP/CaCl 2 gel matrix. At pH 3.5, however, micrographs indicated the formation of a curdlike -Lg/SPP coagulum that did not form a cohesive network structure. Overall, there is a potential for using pectates or other anionic polysaccharides to modify the gelling properties of whey proteins and subsequently expand whey utilization in diverse food applications.

Thermal aggregation p?operties of duck breast and leg salt-soluble proteins (SSP) were studied at pH 5.50, 5.75 and 6.00. At pH 5.50, a major iran&ion for breast was observed at 60.3"C and for leg at 41.8'C. At OH 5.75. maior transitions at 44.6 and 43.2"C were obtained, resp&tiveli,'for ihe breast and leg SSP. Three transitions at 46.0, 53.0 and 59.O"C were exhibited by breast SSP at pH 6.00, whereas only two major transitions at 47.4 and 54.O"C were identified in leg SSP. Changes in transition peak heights and shifts in transition temperatures as a result of pH changes indicated that, depending on fiber type, pH may enhance or suppress the aggregation behavior of specific constituents of the myosin/actomyosin complex, thereby altering the overall aggregation pattern of the protein preparation.

Gels were made by heating duck breast and leg myofibrillar protein suspensions (20 mg/ml; pH 5.50, 5.75 and 6.00) at a constant rate of 1C/min from 18C to 70C. After heating the suspensions to 70C at pH 5.50, breast proteins formed gels which were not different (p > 0.05) in strength from leg proteins. At pH 5.75 and 6.00, however, breast proteins formed significantly stronger gels than leg proteins. Increasing the protein suspension pH from 5.50 to 5.75 had no significant effect on the strength of leg protein gels, whereas the strength of breast protein gels more than doubled. A further increase in pH from 5.75 to 6.00 resulted in a three‐fold decrease in the strength of leg protein gels; no significant difference was observed for breast gels. Overall, pH 5.75 was suitable for forming strong breast and leg protein gels, whereas pH 5.50 and 6.00 were detrimental for gel formation of breast and leg proteins, respectively. Variations in the gelation behavior of duck breast versus leg protein gelation are characteristic of differences in fiber composition of the muscle types.

Aggregation of ␤-Lactoglobulin (␤-Lg) solutions, with and without sodium polypectate (SPP), was investigated at pH 6.5 and 3.5 by turbidity measurements and gel permeation chromatography during heating at 1ЊC/min. The ratio of ␤-Lg:SPP was maintained at 10:1. At pH 6.5, the transition temperature of ␤-Lg aggregation decreased linearly with the logarithm of ␤-Lg concentration. Irrespective of ␤-Lg concentration, SPP did not affect the rate of ␤-Lg aggregation during heating at pH 6.5. However, SPP influenced the formation of high-molecular-weight (HMW) ␤-Lg aggregates during heating at pH 6.5 was related to bulk macromolecular concentration. No thermal aggregation transitions were detected for ␤-Lg solutions at pH 3.5. SPP interacted with ␤-Lg at pH 3.5 to form a complex that precipitated on heating.