Determination of in vitro isoflavone degradation in rumen fluid

Abstract

The aim of this study was to determine the degradation of dietary isoflavones in rumen fluid under 2 feeding regimens. The experiments were performed in vitro using a rumen fluid buffer system. The rumen fluid was taken from cows fed either a hay diet or a concentrate-rich diet (the diet consisted of 34.6% maize silage, 17.6% haylage, 12.8% alfalfa hay, and 35.0% supplemental mixture on a dry matter basis). As a source of isoflavones, 40% soybean extract (Biomedica, Prague, Czech Republic) at levels of 5, 25, 50, and 75 mg per 40 mL of rumen fluid was used. Samples of soybean extract were incubated in triplicate at 39°C for 0, 3.0, 6.0, 12.0, and 24.0 h in incubation solution. The metabolism of daidzein and genistein was faster under concentrate-rich diet conditions. In general, production of equol started after 3 to 6 h of incubation and reached the highest rate after approximately 12 h of incubation regardless of the type of diet or concentration of extract. In most of the experiments, production of equol continued after 24 h of incubation. Generally, equol production was greater under the hay diet conditions. Furthermore, experiments with higher amounts of added soybean extract revealed possible inhibitory effects of high levels of isoflavones on the rumen microflora.

Isoflavones

“…Furthermore, other factors, like the nutrient contents, are involved in isoflavone metabolism. Generally, higher equol production is connected to hay diets than to concentrate-rich diets [49]. Equol was the dominant isoflavone found in the digesta of both cattle [47] and sheep [11].…”

In vitro metabolism of red clover isoflavones in rumen fluid

“…Higher levels of extract added into the incubations resulted in a decline in equol production that was almost negligible (0.08-1.76 µg/ml). One possible explanation is an inhibitory effect of higher isoflavone concentrations on ruminal bacteria, as discussed in details in our previous study (Trnková et al, 2018). However, this inhibitory effect has been connected primarily with genistein (Harlow, Flythe, & Aiken, 2017;Verdrengh, Collins, Bergin, & Tarkowski, 2004).…”

“…Different profile of isoflavones in soybean and red clover and their glycosylation pattern may influence the course of their metabolism and their bioavailability (Lipovac et al, 2015). In our previous in vitro study with soybean extract (Trnková et al, 2018), daidzein, genistein and glycitein were metabolized from the very beginning of the experiment. On the other hand, during the incubations with clover extract, increases in the isoflavone concentrations preceded their metabolism (Figure 2).…”

“…Experimental design, preparation of samples and analytical procedure were the same as in our previous study (Trnková et al, 2018).…”

“…This could be due to gradual dissolution of the isoflavones, as after incubation, excess amounts of undissolved isoflavones were discarded by centrifugation. The isoflavone solubility was discussed in more detail in our previous study (Trnková et al, 2018).…”