Previous studies have demonstrated that certain flavonoids can have an inhibitory effect on angiotensin-converting enzyme (ACE) activity, which plays a key role in the regulation of arterial blood pressure. In the present study, 17 flavonoids belonging to five structural subtypes were evaluated in vitro for their ability to inhibit ACE in order to establish the structural basis of their bioactivity. The ACE inhibitory (ACEI) activity of these 17 flavonoids was determined by fluorimetric method at two concentrations (500 µM and 100 µM). Their inhibitory potencies ranged from 17 to 95% at 500 µM and from 0 to 57% at 100 µM. In both cases, the highest ACEI activity was obtained for luteolin. Following the determination of ACEI activity, the flavonoids with higher ACEI activity (i.e., ACEI >60% at 500 µM) were selected for further IC₅₀ determination. The IC₅₀ values for luteolin, quercetin, rutin, kaempferol, rhoifolin and apigenin K were 23, 43, 64, 178, 183 and 196 µM, respectively. Our results suggest that flavonoids are an excellent source of functional antihypertensive products. Furthermore, our structure-activity relationship studies show that the combination of sub-structures on the flavonoid skeleton that increase ACEI activity is made up of the following elements: (a) the catechol group in the B-ring, (b) the double bond between C2 and C3 at the C-ring, and (c) the cetone group in C4 at the C-ring. Protein-ligand docking studies are used to understand the molecular basis for these results.

A study was made of the texture, composition, appearance, colour and descriptive sensory analysis of low-fat chocolate muffins in which part of the oil ingredient (25%, 50% and 75%) had been replaced by soluble cocoa fibre and full-fat (no fat replacement) control sample to which cocoa powder had been added for comparison purposes. The rheology of the batter was studied with a rheometer. The height of the baked product fell as the fat replacement percentage rose, but no weight loss differences were observed after 1-h cooling. The texture of the fat replacement muffins showed lower values for hardness, chewiness and resilience than those of the control sample and retained greater moisture. The chocolate colour of samples with the highest level of fat replacement was scored similar to the full-fat control formulation indicating a good colour development without adding cocoa powder. The sponginess and springiness of the samples with the lowest fat replacement were scored similar to the full-fat control formulation. In general, muffins containing cocoa fibre were increasingly more cohesive and more difficult to chew and swallow when higher level of cocoa fibre was added. A certain degree of stickiness and a bitter taste different from that of cocoa were found.