Y.L. Xiong

Thermal and dynamic rheological properties of wheat flour fractions

Abstract A commercial high gluten flour (HGF) was fractionated into prime starch (PS), tailing starch (TS), and gluten (G). Fractions were examined alone or in various combinations. Dynamic rheological properties of samples were measured in an oscillatory rheometer (strain 0.02; frequency 0.1 Hz) during heating at 1°C/min. Thermal characteristics of samples were determined by differential scanning calorimetry (DSC) at a heating rate of 10°C/min. The loss (G″) and storage (G′) moduli of PS and mixed G/PS, G/TS, and G/PS/TS increased after 60°C, reaching peak values (e.g. 81, 301, 313, and 3000 Pa in G′, respectively) around 75°C after which the moduli decreased. HGF showed a steady increase in G′ from 32 to 2490 Pa as temperature increased from 65 to 90°C, indicating continuous formation of elastic networks. Cooling increased G′ for G/PS/TS, decreased G′ for HGF, and produced no rheological transitions for all samples. TS and G alone did not exhibit appreciable viscoelastic responses to the heating and cooling temperatures. DSC measurements revealed a major endothermic transition in HGF. This transition, with a peak around 60°C, was due to starch gelatinization. The presence of G or TS resulted in reduced melting enthalpies of starch in the PS fraction. Gluten or TS fractions alone or in combination did not exhibit any endothermic transitions.

Textural and viscoelastic properties of pork frankfurters containing canola-olive oils, rice bran, and walnut.

Textural, rheological and microstructural properties of frankfurters made with 20% pork backfat, 20% canola or 20% canola-olive (3:1) oils, including rice bran (RB) and walnut extract (WE) as macronutrients (2.5%) were investigated. Textural parameters, including hardness, gumminess and rupture-force, were highly (P<0.05) influenced by the fat-oil composition. Addition of RB or WE in vegetable oil emulsions improved textural consistency (P<0.05). However, RB addition reduced gelling capacity, suggesting antagonistic interactions between fiber and oil droplets. Vegetable oil addition favored gel network formation, and, when combined with WE, showed the highest improvement of gel elasticity. These textural and gelling properties were corroborated by frankfurter micrographs, which revealed interactions between vegetable oils, RB, or WE with protein matrix and fat globules affecting these parameters. The results suggest that functional plant-derived ingredients can be valuable to the modification of frankfurter formulations for improved nutrition and as well as textural quality.

Effects of carrageenan on thermal stability of proteins from chicken thigh and breast muscles

Abstract Thermal stability of ground chicken meat and myofibrillar proteins mixed with κ-, ι-, and λ-carrageenan (CGN) at different NaCl concentrations was investigated with differential scanning calorimetry. Three transitions, characteristic of myosin head (63.3, 62.2°C), sarcoplasmic proteins/myosin tail (67.7, 68.6°C), and actin (78.3, 81.4°C), were observed for nontreated thigh and breast muscles, respectively. The influence of CGNs on the thermal transitions was dependent on salt concentrations. κ-CGN with 2.5% NaCl decreased (P

Postmortem proteolytic and organoleptic changes in hot-boned muscle from grass- and grain-fed and zeranol-implanted cattle☆

Abstract A total of 21 yearling steers (Angus sires × crossbreed dams) were allotted to three forage management systems: (a) pasture on Johnstone fescue (G); (b) grain on grass (GG); and (c) grain on grass with zeranol implant, a growth promoter (GGP). After approximately 150 days on experiment (May to October), three randomly selected steers from each dietary group were slaughtered, and composition, sensory characteristics and proteolytic changes of semimembranosus muscle were examined during postmortem storage at 2 °C. Overall, muscle chemical composition was not affected (P> 0.05) by dietary regimen with or without the implant. Grass-fed beef had a stronger (P ≤ 0.05) grassy flavor at 2 days postmortem and developed more (P ≤ 0.05) off-flavor after 10 days of aging than grain-supplemented beef. Postmortem storage generally improved beef tenderness. The implantation did not (P> 0.05) affect weight gain nor carcass yield. However, GGP beef was more tender (P ≤ 0.05) than G and GG beef after 2 days storage; a similar trend was observed in overall beef acceptability. Proteolysis of the muscle from the three forage systems was similar in that all showed major changes beyond 2 days postmortem with the disappearance of titin and troponin-T and the appearance of a 30 kDa component being most noticeable. These results suggest postmortem differences in beef palatability among the different nutritional treatments were not closely related to muscle composition and proteolytic degradation.

Viscoelastic properties of mixed dairy gels

Abstract Pure and mixed gels prepared from a whey protein isolate (WPI) and skim milk powder (SMP) by heating to 90°C at pH 4·3–4·6, with or without fat globules, were studied by mechanical testing. The testing involved compression to 20% deformation and oscillatory rheometry (storage and loss moduli, G′ and G″, respectively). Compressive stresses of mixed gels varied between 0·7 and 1·9 kPa. Gels containing WPI reached higher G′ values and had shorter gel-set times than those containing SMP. SMP based gels were more elastic than WPI based gels as revealed by the lower loss tangent ( tan δ = G″ G′ ) values achieved after 17 min (0·18–0·23 versus approx. 0·38, respectively). Addition of fat resulted in higher compressive stresses and shorter gel-set times but did not affect the initial gelation rate. Gels with different viscoelastic and mechanical properties were prepared with varying amounts of WPI, SMP and emulsified fat.