Colloids and Surfaces B: Biointerfaces
Colloids and Surfaces B: Biointerfaces
Colloids and Surfaces B: Biointerfaces
Protocols
a r t i c l e i n f o a b s t r a c t
Article history: It is essential to obtain a clear understanding of the foam-induced protein aggregation to reduce the loss
Received 23 March 2017 of protein functionality in foam fractionation. The major effort of this work is to explore the roles of foam
Received in revised form 11 July 2017 drainage in protein aggregation in the entire process of foam fractionation with bovine serum albumin
Accepted 16 July 2017
(BSA) as a model protein. The results show that enhancing foam drainage increased the desorption of
BSA molecules from the gas-liquid interface and the local concentration of desorbed molecules in foam.
Keywords:
Therefore, it intensied the aggregation of BSA in foam fractionation. Simultaneously, it also accelerated
Protein aggregation
the ow of BSA aggregates from rising foam into the residual solution along with the drained liquid.
Insoluble aggregates
Foam drainage
Because enhancing foam drainage increased the relative content of BSA molecules adsorbed at the gas-
Foam fractionation liquid interface, it also intensied the aggregation of BSA during both the defoaming process and the
BSA storage of the foamate. Furthermore, enhancing foam drainage more readily resulted in the formation of
insoluble BSA aggregates. The results are highly important for a better understanding of foam-induced
protein aggregation in foam fractionation.
2017 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.colsurfb.2017.07.040
0927-7765/ 2017 Elsevier B.V. All rights reserved.
R. Li et al. / Colloids and Surfaces B: Biointerfaces 158 (2017) 562568 563
Table 2
Morphologies, sizes and molecular weights of oligomers, soluble polymers and insoluble aggregates.
Morphology
Table 3
Effects of foam height (Hf ) on volumetric foamate owrate (Qf ), BSA surface excess ( BSA ), bubble radius (r32 ), and the relative content () and the mass ux (Qm ) of BSA
adsorbed at the gas-liquid interface in foam.
200 5.6 0.6a 1.13 0.12 106a 0.38 0.04a 51.6 5.2a 10.8 1.1 105a
400 2.3 0.3b 1.25 0.13 106a 0.51 0.05b 68.8 6.9b 9.1 0.9 105a
600 1.3 0.1c 1.43 0.15 106b 0.64 0.06c 77.2 7.3c 8.1 0.8 105b
800 0.6 0.1d 1.45 0.15 106b 0.85 0.08d 84.9 8.2c 6.2 0.7 105c
1000 0.3 0.1e 1.46 0.15 106b 1.12 0.11e 88.9 9.0c 4.7 0.5 105d
Fig. 2. Effects of foam height on production rates (A) and partition coefcients (B) of total aggregates, oligomers, soluble polymers and insoluble aggregates.
tribution coefcients (Kagg ) of total aggregates, oligomers, soluble ing Hf (P 0.05). It is suggested that enhancing the foam drainage
polymers, and insoluble aggregates. In this work, the total aggre- intensied the ow of the BSA aggregates into the residual solution
gates encompassed the sum of the oligomers, soluble polymers, with the drained liquid.
and insoluble aggregates. Our aim is to provide a clear understand- According to the work of Bee et al. [14], the decrease in the
ing of how foam drainage affects the aggregation of BSA in foam gas-liquid interfacial area could cause the aggregation of protein
fractionation. The results are presented in Fig. 2. molecules at the gas-liquid interface and the aggregates were read-
According to the work of Wiesbauer et al. [13], the pro- ily desorbed from the interface. From Table 3, the higher level of
duction rate of protein aggregates was essentially determined foam drainage corresponded to the larger decrease in the gas-liquid
by the change in the size of the gas-liquid interfacial area. In interfacial area, so more BSA aggregates, particularly soluble poly-
foam fractionation, at each Hf , the total gas-liquid interfacial area mers and insoluble aggregates, could be formed. Furthermore, the
initially generated by the gas distributor was the same, and, decrease in Qm should correspond to the desorption of BSA aggre-
nally, all the generated interfacial area decreased to zero in the gates from the gas-liquid interface. In addition, increasing the BSA
defoaming process. Then, the change of the gas-liquid interfa- concentration in an aqueous solution often enhanced the aggrega-
cial area was the same, so that ragg(totalaggregates) should exhibit tion of BSA [21]. By this analogy, increasing the BSA surface excess
no signicant changes with increasing Hf . In fact, Fig. 2A shows could more readily intensify the protein aggregation at the gas-
that ragg(totalaggregates) signicantly increased from (1.4 0.1) 105 liquid interface, because the adsorbed protein molecules possessed
to (3.8 0.4) 105 kg/h as Hf increased from 200 to 800 mm more unfolded structures than those in the bulk solution. Thus, the
(P 0.05). Specically, the great increase in ragg(totalaggregates) was increased BSA due to foam drainage also enhanced the aggrega-
mainly attributed to the signicant increases in ragg(solublepolymers) tion of BSA at the gas-liquid interface. The enhanced foam drainage
and ragg(insolubleaggregates) (P 0.05). The change of ragg(oligomers) also improved the aggregation of BSA in defoaming, the reasons
was insignicant (P > 0.05), so its contribution to the increase of for which are explained in the following subsection. As a result,
ragg(totalaggregates) was slight. The results indicate that the enhanced ragg(totalaggregates) increased with increasing Hf .
foam drainage intensied the aggregation of BSA in foam fraction- A higher level of foam drainage corresponded to a larger
ation, particularly the formation of soluble polymers and insoluble decrease in the gas-liquid interfacial area and a larger number of
aggregates. From Fig. 2B, the partition coefcients of all the BSA BSA aggregates formed in the rising foam. These aggregates were
aggregates signicantly decreased to lower than 1 with increas- readily desorbed from the gas-liquid interface and then owed into
566 R. Li et al. / Colloids and Surfaces B: Biointerfaces 158 (2017) 562568
Fig. 4. Effects of foam height on mass uxes and relative contents of total aggregates, oligomers, soluble polymers and insoluble aggregates in the foamate.
R. Li et al. / Colloids and Surfaces B: Biointerfaces 158 (2017) 562568 567
Fig. 6. Effects of foam height (Hf ) on the variations of relative contents of total aggregates (A), oligomers (B), soluble polymers (C) and insoluble aggregates (D) in the foamate
with time.
568 R. Li et al. / Colloids and Surfaces B: Biointerfaces 158 (2017) 562568
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