Segregative interactions and competitive binding of Ca2+ in gelling mixtures of whey protein isolate with Na+ κ-carrageenan
Segregative interactions and competitive binding of Ca2+ in gelling mixtures of whey protein isolate with Na+ κ-carrageenan
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DOI：
10.1016/j.foodhyd.2008.03.007
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发表时间：
2009-03
影响因子：
10.7
通讯作者：
J. Harrington;E. Foegeding;D. Mulvihill;E. Morris
中科院分区：
文献类型：
--
作者：
J. Harrington;E. Foegeding;D. Mulvihill;E. Morris
用流变学和差示扫描量热法（DSC）研究了Na+κ-卡拉胶与乳清蛋白分离物（WPI）在pH 7.0下的胶凝混合物，并对混合物的各个组分进行了比较测量。WPI的浓度保持固定在10.0重量%，并且角叉菜胶浓度在0.05- 3.0重量%的范围内变化。Ca 2+阳离子，其先前已显示在诱导κ-角叉菜胶的凝胶化中特别有效，作为CaCl 2引入。大多数实验中使用的CaCl 2浓度为8 mM，但也研究了其他浓度。在45°C下以溶液状态制备混合物，并且没有显示相分离或络合物形成的证据。通过储能模量G′的低振幅振荡测量监测流变学变化，在（i）冷却（1 ℃/min）并保持在5 ℃，以在非凝胶化WPI存在下诱导角叉菜胶的凝胶化;（ii）加热并保持在80 ℃，以解离角叉菜胶网络并诱导WPI的凝胶化;（iii）冷却并再次保持在5°C，以得到两种成分均凝胶化的复合网络;和（iv）重新加热至80°C以解离角叉菜胶网络。凝胶结构进一步通过在每个保持期结束时的蠕变恢复测量和在WPI热凝胶化之前和之后在5°C下的扭转测量来表征。在8 mM CaCl_2中，10.0wt%WPI的存在促进κ-卡拉胶在冷却过程中的早期凝胶化，并将DSC中的无序-有序转变移向更高的温度。这些变化归因于与非凝胶WPI的分离相互作用。然而，所得到的网络比单独由κ-角叉菜胶形成的网络弱，这可追溯到Ca 2+阳离子与WPI的结合。在较高浓度的CaCl 2下，其中Ca 2+阳离子的可用性不再是κ-卡拉胶凝胶化的限制因素，分离相互作用的效果可以被视为凝胶强度的增加。在加热使WPI凝胶化时，κ-卡拉胶的存在导致DSC中聚集体的较早出现和在较短时间内形成网络，这可以类似地通过响应于与无序卡拉胶的分离相互作用而增强的变性WPI的自缔合来解释。随着角叉菜胶浓度增加至10.25wt%，凝胶强度的初始大的（约10倍）增加，随后在较高浓度下降低，这归因于WPI的过度聚集（初始沉淀）。随后冷却时观察到的G '变化幅度表明，κ-角叉菜胶在现有凝胶化WPI网络的孔隙内的凝胶化产生了双连续共凝胶结构。在冷却至5°C之前和之后在80°C下的模量的比较证明角叉菜胶网络的形成和解离不引起凝胶化WPI网络的破坏。
Gelling mixtures of Na+κ-carrageenan with whey protein isolate (WPI) at pH 7.0 have been studied rheologically and by differential scanning calorimetry (DSC), with comparative measurements for the individual constituents of the mixtures. The concentration of WPI was held fixed at 10.0wt% and carrageenan concentration was varied in the range 0.05–3.0wt%. Ca2+cations, which have been shown previously to be particularly effective in inducing gelation of κ-carrageenan, were introduced as CaCl2. The concentration of CaCl2used in most of the experiments was 8mM, but other concentrations were also studied. Mixtures were prepared in the solution state at 45°C, and showed no evidence of either phase separation or complex formation. Rheological changes were monitored by low-amplitude oscillatory measurements of storage modulus, G′, during (i) cooling (1°C/min) and holding at 5°C, to induce gelation of the carrageenan in the presence of non-gelled WPI; (ii) heating and holding at 80°C to dissociate the carrageenan network and induce gelation of WPI; (iii) cooling and holding again at 5°C, to give composite networks with both components gelled; and (iv) re-heating to 80°C to dissociate the carrageenan network. Gel structure was characterised further by creep–recovery measurements at the end of each holding period, and by torsion measurements at 5°C, before and after thermal gelation of WPI. In 8mM CaCl2, the presence of 10.0wt% WPI promoted earlier gelation of κ-carrageenan during cooling, and displaced the disorder–order transition in DSC to higher temperature. These changes are attributed to segregative interaction with non-gelled WPI. The resulting networks, however, were weaker that those formed by κ-carrageenan alone, which was traced to binding of Ca2+cations to the WPI. At higher concentrations of CaCl2, where availability of Ca2+cations was no longer a limiting factor in gelation of the κ-carrageenan, the effect of segregative interactions could be seen as an increase in gel strength. On heating to gel the WPI, the presence of κ-carrageenan led to the earlier appearance of an aggregation exotherm in DSC and to network formation at shorter times, which can similarly be explained by enhanced self-association of denatured WPI in response to segregative interactions with disordered carrageenan. An initial large (∼10 fold) increase in gel strength with increasing concentration of carrageenan to ∼0.25wt% was followed by a reduction at higher concentrations, attributed to excessive aggregation (incipient precipitation) of the WPI. The magnitude of the changes in G′ observed on subsequent cooling suggest that gelation of κ-carrageenan within the pores of an existing network of gelled WPI gives rise to a bicontinuous co-gel structure. Comparison of moduli at 80°C before and after cooling to 5°C demonstrated that formation and dissociation of the carrageenan network caused no disruption of the network of gelled WPI.