Changes of gallic acid mediated by ultrasound in a model extraction solution

Abstract

Ultrasound has been widely used as a new kind of auxiliary extraction technique in food industry, but its effect cannot be ignored on the potential degradation of the extracted target compound. In this paper, a model extraction solution was constructed with the standard gallic acid as target compound to be extracted, and its change was monitored by using high performance liquid chromatography (HPLC) under different ultrasonic extraction conditions, namely, solvent types, extractant concentrations, extraction time, extraction temperature, ultrasound power and frequency, in order to understand the effect of ultrasound on the extract during ultrasonic extraction and provide an objective evaluation of ultrasonic extraction of polyphenols. The results indicate that ultrasonic parameters had definite effect on the degradation of gallic acid during ultrasonic extraction, which implies that the extraction yield should not be over-focused in actual extraction applications of ultrasound, more attention should be paid to the potential degradation of the extracted target compound induced by ultrasound.

Free radical generation induced by ultrasound in red wine and model wine: An EPR spin-trapping study

“…ultrasound power has a strong influence on the amounts of free radicals generated, which is in accordance with that reported by other authors [25]. As a rule, Ultrasonic intensity is defined by the power, and it increases at the same reactor area with power [24]. Gogate and pandit (2004) [25] have pointed out that the ultrasonic intensity has a strong effect on the pressures of bubble collapses and local temperatures as well as the number of free radicals generated in the studied solution.…”

“…3, the application of higher ultrasound frequencies led to an increase in the intensity of DMPO / 1-hydroxylethyl free radical spin adducts, which may be attributed to the amounts increasing of the collapsing bubbles of ultrasound caviation as reported by other authors [19][20][21]. Generally, the effect of ultrasound cavitation could be reduced at higher ultrasonic frequency, since either the rarefaction cycle of the sound wave produces a great negative pressure which is insufficient in its duration and/or intensity to initiate cavitation, or the compression cycle occurs faster than the time for the microbubble to collapse [22][23][24]. As a consequence, the collapse of bubbles occurs much more rapidly, resulting in the amounts of cavitation bubbles increased and more hydroxyl free radicals released from the bubbles, finally inducing the increase of 1-hydroxylethyl free radical and its spin adducts in model wine.…”

“…We do need the free radicals, which is easier to be generated by high power ultrasound, to accelerate aging and oxidation of wine [9]. But according to our results [24,27], higher ultrasonic power would lead the degradation of phenolic compounds in red wine, and these compounds are beneficial to health as well known by now. Besides that, Zheng [5] argued that ultrasonic conditions of 300 W could improve the maturation of wine.…”

“…5, the intensity of free radical spin adducts in model wine increased with the increase of ultrasonic temperature from 20°C to 50°C, then followed by a decrease at 60 ºC. Generally, the effect of the ultrasonic temperature on the reactions in solution is a rather complicated phenomenon, since the temperature can affect the gas solubility, surface tension and the vapor pressure of the solutes [24].…”

“…Regarding the slowly increasing stage from 40 to 80 min, the major inducement may be attributed to the limiting amounts of free radicals ultrasonically generated, and the ultrasonic-induced spontaneous degradation of DMPO / free radical spin adducts and DMPO [6,24].…”