# Improved Food-Processing Techniques to Reduce Isoflavones in Soy-Based Foodstuffs
## 3 Results
### Isoflavones Recovery  
The pre-selection results, as described in Section 2.6.3, highlighted evidence of polyphenol retentions ranging from 30% for acrylic resins to 40-60% for conventional styrene resins,  
Figure 4: Comparisons between the ELISA and the Folin–Ciocalteu methods for isoflavone content determination: (**A**) in soybeans, a lack of correlation; (**B**) in water, the presence of correlation; (**C**) between IF removal from soybeans (ELISA) and polyphenols in water (Folin–Ciocalteu), the presence of correlation. Error bars are SEM. the performance depending on the pores' volumes, diameters, and specific surface areas, as shown in Figure S6 in the Supplementary Materials. Remarkable performances were obtained with functionalized resins recently developed by DUPONTTM and SUN RESINTM, with polyphenol reductions over 95%. The various resins tested were all effective in trapping IFs; some of them, such as VPOC resins 1064, Relite EXA 90 and Optipore SD-2, made it possible to lower the water's residual IF content below the ELISA's limits of quantification. They correspond to resins with pore diameters between 5 and 10 nm and a styrene-divinylbenzene (DVB) base. Unlike the first two references mentioned, the Optipore SD-2 resin also fixed almost all polyphenols, probably because of its functionalization with an amine group. Consequently, the choice of the resin to be tested at pilot scale went naturally towards the one most effective for trapping organic compounds present in water, which was Optipore resin SD-2. However, it was likely that the adsorbed compounds would be difficult to desorb due to its functionalization. Thus, a second resin had to be selected in order to satisfy to both the most effective trapping and an adequate desorption. The candidate resin which appeared to fulfil these two constraints simultaneously was Amberlite(r) FPX 66. It is a non-grafted resin of the same base (styrene-DVB), from the same supplier, which ended up being very effective in trapping IFs (98.7%), even if it trapped only 50% of the total polyphenols. All polyphenols were recovered from Amberlite(r) FPX 66 resin by a 50:50 water:ethanol mixture, whereas even with 100% ethanol, only 40% were recovered from the OptiporeTM SD-2 resin. Concerning the total IFs, the trend is the same and it can be noted that GEN was less readily eluted than DAI, as shown in Figure 5B. A 70:30 water:ethanol mixture did not have sufficient eluting strength in both cases, and a minimum of 50% and 100% alcohol was required for Amberlite(r) FPX-66 and OptiporeTM SD-2 resins, respectively. Tests on OptiporeTM SD-2 resin showed that the polyphenol content of the first filtrate was low (4 mg/L), which confirms the IF-trapping yields obtained in the jar test. The exhaustion of the resin was gradual and only partial, since after filtration of 32 times the bed volume, the suspended matter was only 17 mg/L, which corresponds to a 62% reduction in total polyphenols. The OptiporeTM SD-2 resin fixed 223 mg of polyphenols, i.e., a fixing capacity of 1.05 mg/g, without reaching its maximum saturation capacity. For the IFs (44% GEN, 56% DAI), a quantity of 5.73 mg (i.e., 0.027 mg/g) was fixed without reaching saturation. Figure 5: Isoflavones adsorption (**A**) and desorption (**B**) from Amberlite FPX 66® resin. The curves (**A**) represent progressive isoflaves leaking from the resin. * w and e refer to water and ethanol, respectively. Regarding the Amberlite(r) FPX66 resin, during the filtration of 20 bed volumes, the polyphenol content fluctuated between 20 and 25 mg/L, and the reduction yields for polyphenols ranged between 44 and 56%, in line with the results of the jar test. In total, the Amberlite(r) FPX 66 resin fixed 112 mg of polyphenol, i.e., a fixing capacity twice as low (0.52 mg/g) as Optipro(tm) SD-2 resin, without reaching its maximum saturation capacity. For IFs, the assay results showed that the Amberlite(r) FPX 66 resin was less selective, since resin exhaustion appeared after passage of, at most, 16 bed volumes for DAI and GEN.