M. Adília Lemos

Influence of cooking on the levels of bioactive compounds in Purple Majesty potato observed via chemical and spectroscopic means

Tubers rich in phytochemicals can exhibit a potential health benefit. This work aims at studying the relative effect of different domestic cooking techniques by monitoring the level of total phenolic compounds (TP), total anthocyanins (TA) and anti-oxidant activity (AOA) on a variety of pigmented potatoes. Raw purple potatoes are a good source of anthocyanins (219 mg/kg FW) and the level of these compounds increased using different cooking techniques, with the exception of baking. However, the levels of phenolic compounds (originally 209 mg GAE/100 g FW) decreased in the cooked potatoes. Although potatoes contain different antioxidants in this work the antioxidant activity seems to be related to the levels of phenolic compounds present in the pigmented potato. The fact that some of the compounds present fluoresce enabled both steady state and time-resolved fluorescence techniques to be assessed as a non destructive means of monitoring. This elucidated the presence of different components (via spectral deconvolution and time-resolved emission spectra). Their relative contribution to the fluorescence emission was found to be affected by the different cooking process, with a longer wavelength emission appearing to relate to reflect the presence of anthocyanins.

Effect of ultrasound on the extraction of total anthocyanins from Purple Majesty potato

This study examined anthocyanin extraction using the application of ultrasound to raw freeze dried, microwaved and raw sliced Purple Majesty potato, a new pigmented potato variety rich in anthocyanins. A 20 kHz probe was used for the sonication at 3 different amplitudes (30%, 50% and 70%) and ethanol in water at different ratios (50:50 and 70:30 v/v) was used for the extraction. Anthocyanin extraction from raw freeze dried purple potato was optimal at an ethanol:water ratio (70:30; v/v) after 5 min of ultrasonication, while the least amount of anthocyanins was extracted from raw sliced potatoes. The application of microwaves (as a pre-treatment) before the UAE resulted in an increase in the amount of anthocyanins extracted and a decrease in the amount of solvent used. Analysis of variance showed that potato form, ultrasonication time, ultrasonication amplitude and solvent ratio as well as two and three way interactions between some of these factors had a very significant effect (p<0.000) on the amount of anthocyanins extracted.

Use of Time-Resolved Fluorescence to Monitor Bioactive Compounds in Plant Based Foodstuffs

The study of compounds that exhibit antioxidant activity has recently received much interest in the food industry because of their potential health benefits. Most of these compounds are plant based, such as polyphenolics and carotenoids, and there is a need to monitor them from the field through processing and into the body. Ideally, a monitoring technique should be non-invasive with the potential for remote capabilities. The application of the phenomenon of fluorescence has proved to be well suited, as many plant associated compounds exhibit fluorescence. The photophysical behaviour of fluorescent molecules is also highly dependent on their microenvironment, making them suitable probes to monitor changes in pH, viscosity and polarity, for example. Time-resolved fluorescence techniques have recently come to the fore, as they offer the ability to obtain more information, coupled with the fact that the fluorescence lifetime is an absolute measure, while steady state just provides relative and average information. In this work, we will present illustrative time-resolved measurements, rather than a comprehensive review, to show the potential of time-resolved fluorescence applied to the study of bioactive substances. The aim is to help assess if any changes occur in their form, going from extraction via storage and cooking to the interaction with serum albumin, a principal blood transport protein.

The binding of Curcuma longa extract with bovine serum albumin monitored via time-resolved fluorescence.

Turmeric (Curcuma longa L.) is obtained from the rhizome of the Zingberaceae family and has a long history as an ingredient in cooking. It has been used as a dye and recently research has concentrated on its possible health benefits, specifically because of its antioxidant activity. The principal compound that is responsible for this activity is curcumin, which is present with the other curcuminoids; demethoxycurcumin and bisdemethoxycurcumin. Curcumin exhibits fluorescence and its photophysics are markedly affected by the polarity, hydrogen bonding and pH. This provides a means to examine its interaction with proteins, which is important if its potential health role is to be fully investigated. In this work, we monitor the binding kinetics using time‐resolved fluorescence measurements, enabled by the use of low dead time electronics coupled with a high repetition rate excitation source and time‐resolved emission spectra of the extracted curcuminoids upon interaction with bovine serum albumin. From these measurements the decay‐associated spectra of the different lifetime components were obtained, which is consistent with reports of more than one binding site. Monitoring changes in these spectra with increasing temperature also allows for the denaturing of the serum albumin to be inferred.

Use of time-resolved spectroscopy as a method to monitor carotenoids present in tomato extract obtained using ultrasound treatment.

INTRODUCTION Compounds exhibiting antioxidant activity have received much interest in the food industry because of their potential health benefits. Carotenoids such as lycopene, which in the human diet mainly derives from tomatoes (Solanum lycopersicum), have attracted much attention in this aspect and the study of their extraction, processing and storage procedures is of importance. Optical techniques potentially offer advantageous non-invasive and specific methods to monitor them. OBJECTIVES To obtain both fluorescence and Raman information to ascertain if ultrasound assisted extraction from tomato pulp has a detrimental effect on lycopene. METHOD Use of time-resolved fluorescence spectroscopy to monitor carotenoids in a hexane extract obtained from tomato pulp with application of ultrasound treatment (583 kHz). The resultant spectra were a combination of scattering and fluorescence. Because of their different timescales, decay associated spectra could be used to separate fluorescence and Raman information. This simultaneous acquisition of two complementary techniques was coupled with a very high time-resolution fluorescence lifetime measurement of the lycopene. RESULTS Spectroscopic data showed the presence of phytofluene and chlorophyll in addition to lycopene in the tomato extract. The time-resolved spectral measurement containing both fluorescence and Raman data, coupled with high resolution time-resolved measurements, where a lifetime of ~5 ps was attributed to lycopene, indicated lycopene appeared unaltered by ultrasound treatment. Detrimental changes were, however, observed in both chlorophyll and phytofluene contributions. CONCLUSION Extracted lycopene appeared unaffected by ultrasound treatment, while other constituents (chlorophyll and phytofluene) were degraded.

Time-resolved fluorescence observation of di-tyrosine formation in horseradish peroxidase upon ultrasound treatment leading to enzyme inactivation

The application of ultrasound to a solution can induce cavitional phenomena and generate high localised temperatures and pressures. These are dependent of the frequency used and have enabled ultrasound application in areas such as synthetic, green and food chemistry. High frequency (100kHz to 1MHz) in particular is promising in food chemistry as a means to inactivate enzymes, replacing the need to use periods of high temperature. A plant enzyme, horseradish peroxidase, was studied using time-resolved fluorescence techniques as a means to assess the effect of high frequency (378kHz and 583kHz) ultrasound treatment at equivalent acoustic powers. This uncovered the fluorescence emission from a newly formed species, attributed to the formation of di-tyrosine within the horseradish peroxidase structure caused by auto-oxidation, and linked to enzyme inactivation.

Effect of sucrose on thermal and pH stability of Clitoria ternatea extract

The aim of this work was to investigate the effect of sucrose on the stability of Clitoria ternate extract against thermal and pH degradations. Lyophilised extract of the flower (1 mg/ml) was added into a series of sucrose solutions with concentrations ranging from 0.1% to 20% at pH7. The thermal stability of the extract in the solutions at 60C was monitored using a UV-VIS spectrophotometer over 24 days. High temperature (60C) accelerated degradation of the anthocyanin-rich extract but the presence of sucrose appeared to have slowed down the degradation process. However, sucrose asserted no protective effect against pH even at a concentration of 20%. It was thought that sucrose enhanced the thermal stability of anthocyanins by reducing water activity, partially preventing nucleophilic attack at the pyrylium ring of anthocyanins by water molecules. The present work provides some useful information for evaluating the potential of C. ternatea extract on food applications.