Thermal degradation kinetics of anthocyanin and visual colour of plum puree

Thermal degradation kinetics of anthocyanin and visual colour (tristimulus L, a and b values) of plum puree were studied at selected temperatures (50–90 °C) for a residence time of 20 min. Results indicated that the thermal degradation of anthocyanin, tristimulus colour a value (representing redness) and L×a×b value (representing total colour) followed first-order reaction kinetics. The activation energy values for anthocyanin, red colour and total colour were 37.48, 25.86 and 30.68 kJ/mol respectively. Higher activation energy signified higher thermal sensitivity of anthocyanin during heat processing of plum puree. A linear relationship described well the variation of total visual colour (L×a×b) with anthocyanin content of plum puree during thermal processing.     

桑葚果浆中花色苷及其色泽的热降解动力学

为了研究桑葚果浆加工中花色苷和色泽的热降解规律,测定了不同温度(75、80、85、90℃)下桑葚果浆花色苷含量和色泽值的影响,并建立了花色苷与色泽值的相关性。结果表明:桑葚果浆中花色苷的热降解符合一级动力学反应,L*、a*和TCD*值的热降解符合联合动力学反应,b*值的热降解符合零级动力学反应。花色苷的降解与L*、a*和TCD*值正相关,与b*值负相关。     

Degradation kinetics and colour of anthocyanins in aqueous extracts of purple- and red-flesh potatoes (Solanum tuberosum L.)

The effect of pH and temperature on the stability and visual colour of aqueous anthocyanin (ACY) extracts from purple- and red-flesh potatoes was evaluated and compared to commercial ACY extracts from grape and purple carrot. Extracts from purple carrot and red-flesh potatoes showed higher stability than grape and purple-flesh potato extracts. Stability to pH (?3) and thermal degradation of extracts (pH 3) followed first-order kinetics. Changes in lightness and hue followed zero-order kinetics, while changes in chroma followed first-order kinetics. Degradation parameters such as t_1/2, k-, D-, z- and Q₁₀-values were determined. Extracts from red- and purple-flesh potatoes at pH 3 showed similar hues to FD&C Red #40 and red cabbage extracts, respectively. The visual colour of both potato ACY extracts was also affected by tinctorial strength. The use of purple- and red-flesh potatoes as a source of natural colorants shows potential use in the pH region around 3.     

Thermal degradation kinetics of aqueous anthocyanins and visual color of purple corn (Zea mays L.) cob

Purple corn cob was the byproduct during the corn processing. Thermal degradation kinetics and Hunter color parameters (a, b, C, h° and ΔE) of aqueous anthocyanins from purple corn cob were studied at selected temperatures (70 °C, 80 °C and 90 °C) at pH 4.0. The results indicated that the thermal degradation of anthocyanin and Hunter color C, a and ΔE parameters followed the first-order reaction kinetics, while Hunter color h° and b parameters followed zero-order reaction kinetics. The calculated values of activation energies (Ea) were 18.3, 35.9, 37.1, 31.6, 34.9 and 30.0 kJ/mol for anthocyanins, C, a, ΔE, h° and b parameters, respectively. The higher Ea indicated that greater temperature sensitivity of visual color as compared to anthocyanins content. The degradation of anthocyanins showed positive correlation with C (R² > 0.909), a (R² > 0.860) and ΔE (R² > 0.940), while the degradation of anthocyanins showed negative correlation with h° (R² > 0.828) and b (R² > 0.735) during heating.

Industrial relevance

Purple corn cob was the byproduct during the corn processing. Purple corn cob is dark purple to almost black color due to its high content of anthocyanins, which makes this byproduct a good source of anthocyanins. In this study, the excellent linear correlation between Hunter color parameters (a, b, C, h° and ΔE) and content of anthocyanins showed that the Hunter color parameters may also be used instead of anthocyanins content during heating. The advantage of using the visual Hunter color parameters may be measured as on-line quality control parameters during thermal processing of food industry.     

桑葚汁花色苷及其色泽热降解动力学研究

对热处理过程中桑葚汁中花色苷及其色泽降解动力学进行了研究。结果显示桑葚汁中花色苷及其色泽的热降解动力学都是符合一级反应动力学,并且均可用Arrhenius方程表示,其反应活化能分别为44.1、50.51kJ/mol。同时结果表明,热处理过程中色泽和花色苷含量之间有很好的线性关系,可表示为a/a0=0.8806(c/c0)+0.1124(R2=0.9714)。这表明生产中采用色度仪即时测得的色泽值代替费时的光谱法测定的花色苷含量可以用来监测加工过程中花色苷的降解情况,以利于在线品质控制。     

Vc与Cu2+的耦合氧化对桑葚花色苷的降解作用

研究通过构建含Vc和Cu2+的桑葚汁模拟体系,研究这两个内源因子对花色苷的降解作用。研究表明Vc能显著促进花色苷的降解,而在果汁所含Cu2+浓度下,Cu2+对花色苷具有一定的保护作用,但当在体系中与Vc共存时,则能大大促进花色苷的降解。因此,可以得出一个花色苷被Vc和Cu2+耦合氧化的降解机制:低浓度时,Cu2+自身不催化花色苷的降解,但当有Vc存在时,它能先通过促进Vc的氧化降解,使Vc转化为对花色苷降解有显著促进作用的氢过氧化物,从而加速花色苷的降解。     

Thermal kinetics on antiradical capacity of mulberry fruit extract

The effects of temperature and pH on the kinetics of the antiradical capacity of mulberry fruit extract were investigated. The browning index (A₄₂₀/A₅₁₀) increased as pH increased. The change in browning index at pH 2.0 was less than that at pH 4.0. The antiradical capacity increased as browning index increased. The correlation values (slop) of antiradical capacity and browning index were 135.8 (80 °C), 164.4 (90 °C), and 179.7 (100 °C). The antiradical capacity variation was adequately described by both first order and zero order kinetics; however, a zero order kinetic model was proposed because of a better fit. According to the Arrhenius model, the activation energies for antiradical capacity in the range 80–100 °C for the three different pH values were 82.0 kJ/mol for pH 2.0, 70.8 kJ/mol for pH 3.0, and 41.1 kJ/mol for pH 4.0.     

Chemical composition of white (Morus alba), red (Morus rubra) and black (Morus nigra) mulberry fruits

In this study, the chemical composition of white (Morus alba L.), red (Morus rubra L.) and black (Morus nigra L.) mulberry fruits grown in the East Anatolia Region of Turkey was investigated. The highest total phenolic and flavonoid contents were observed in black mulberry (1422 mg gallic acid equivalents/100 g fresh matter and 276 mg quercetin equivalents/100 g fresh matter). M. alba had the highest total fat content (1.10%), followed by M. nigra (0.95%) and M. rubra (0.85%), respectively. The major fatty acids in mulberry fruits were linoleic acid (54.2%), palmitic acid (19.8%) and oleic acid (8.41%), respectively. The total soluble solids content of mulberry species varied between 15.9% (M. rubra L.) and 20.4% (M. alba L.), acidity between 0.25% (M. alba L.) and 1.40% (M. nigra L.), pH between 3.52 (M. nigra L.) and 5.60 (M. alba L.), ascorbic acid 19.4 mg/100 g (M. rubra L.) and 22.4 mg/100 g (M. alba L.), respectively. Mineral compositions of the mulberry species were 0.83% N, 235 mg/100 g P, 1141 mg/100 g K, 139 mg/100 g Ca, 109 mg/100 g Mg, 60 mg/100 g Na, 4.3 mg/100 g Fe, 0.4 mg/100 g Cu, 4.0 mg/100 g Mn and 3.1 mg/100 g Zn, respectively.     

Thermal degradation of anthocyanins and its impact on color and in vitro antioxidant capacity

The aim of the current study was to thoroughly investigate the structural changes of anthocyanins at pH 3.5 in purified fractions from black carrot, elderberry and strawberry heated over 6 h at 95 degrees C. Degradation products were monitored by HPLC-DAD-MS(3 )to elucidate the prevailing degradation pathways. In addition, alterations of color and antioxidant properties observed upon heating were scrutinized. Most interestingly, the degradation pathways at pH 3.5 were found to differ from those at pH 1. Among others, chalcone glycosides were detected at 320 nm in heat-treated elderberry and strawberry pigment isolates, and opening of the pyrylium ring initiated anthocyanin degradation. In the case of acylated anthocyanins, acyl-glycoside moieties were split off from the flavylium backbone, first. Finally, for all pigment isolates, phenolic acids and phloroglucinaldehyde were the terminal degradation products as remainders of the B- and A-ring, respectively. Maximum and minimum antioxidant stabilizing capacities were found in black carrot and strawberry, respectively, which was explained by the high degree of acylation in the former. After heating, decline of trolox equivalent antioxidant capacity (TEAC) was observed in all samples, which was attributed to both anthocyanins and their colorless degradation products following thermal exposure. As deduced from the ratio of TEAC value and anthocyanin content, the loss of anthocyanin bioactivity could not be compensated by the antioxidant capacity of newly formed colorless phenolics upon heating.     

Thermal characterization of the anthocyanins from black soybean (Glycine max L.) exposed to thermogravimetry

One anthocyanin compound, cyanin-3-glucoside, was isolated and identified by high performance liquid chromatography tandem mass spectrometry (HPLC_MS/MS) from seed coat of black soybean variety, Heizi to assess its thermal characterization in vitro. The thermal characterization of anthocyanin was studied by thermogravimetry (TG) analysis. The results from the TG curves showed the decomposition of anthocyanin occurred in three stages. Glucose cleaved from the cyanin-3-glucoside occurred in the first stage. Degradation of cyanin and small amounts of cyanin-3-glucoside appeared mainly in the second stage. The sugar in the anthocyanin was decomposed in the third stage. Thermodynamic analysis was applied by free dynamic model. TG-isothermal experiments for the anthocyanins from black soybean seed coats confirmed the correct of the thermodynamic analysis.     

Clarification and pasteurisation effects on monomeric anthocyanins and percent polymeric colour of black carrot (Daucus carota L.) juice

Black carrots (BCs) are a rich source of stable anthocyanins (ACNs). The purpose of this study was to evaluate the effects of clarification and pasteurisation on ACNs of black carrot juice (BCJ). Monomeric ACNs, ACN profile and percent polymeric colour were determined during processing of BCJ. While depectinisation and bentonite treatments resulted in 7% and 20% increases in monomeric ACN content of BCJ, respectively, gelatine–kieselsol treatment and pasteurisation resulted in 10% and 3–16% reduction. Percent polymeric colour decreased after clarification, but substantially increased in samples subjected to heat. ACNs of BCJ samples were identified by HPLC–MS. Unclarified BCJ contained cyanidin-3-galactoside-xyloside-glucoside-ferulic acid as the major ACN, followed by cyanidin-3-galactoside-xyloside-glucoside-coumaric acid, and cyanidin-3-galactoside-xyloside-glucoside. After depectinisation, two more ACNs (cyanidin-3-galactoside-xyloside and cyanidin-3-galactoside-xyloside-glucoside-sinapic acid) were also identified. These results indicated that depectinisation and bentonite treatment had positive effect on the colour of BCJ, while gelatin–kieselsol treatment and pasteurisation had negative effect.     

Aqueous two-phase extraction,identification and antioxidant activity of anthocyanins from mulberry (Morus atropurpurea Roxb.)

Aqueous two-phase extraction (ATPE), identification and antioxidant activity of anthocyanins from mulberry (Morus atropurpurea Roxb.) were investigated in this study. The optimal differential partitioning of mulberry anthocyanins (MAY) and sugars was achieved in a system (pH 4.5, temperature = 35 ± 1 °C) composed of 30% (w/w) ethanol, 20% (w/w) concentration of ammonium sulphate, 10% (w/w) mulberry juice and 40% (w/w) water. The multiple partitioning indicated a single ATPE step could isolate the majority of anthocyanins, while removing near to 90% of the free sugars. The composition of the MAY extracted by ATPE had no obvious changes, and five anthocyanins were identified by HPLC–ESI-MS/MS. The ATPE extract showed a relatively high antioxidant ability compared to that by the conventional extraction. Our results indicated that ATPE was a valuable method for the removal of the majority of free sugars, which held great promise in the purification of natural anthocyanin pigments.     

Isolation and viscometric characterization of hydrocolloids from mulberry (Morus alba L.) leaves

Hydrocolloid in mulberry leaves was extracted with water or sodium bicarbonate, and characterized rheologically in a highly dilute to a semi-dilute regime. Mulberry leaf hydrocolloid was composed of mainly carbohydrate with high levels of uronic acid. The hydrodynamic behavior of mulberry leaf hydrocolloid in deionized water demonstrated a typical polyelectrolyte behavior in the dilute domain, as indicated by a nonlinear Huggins' plot. Intrinsic viscosity value for alkaline-extracted (Alk) and water-extracted (Hw) hydrocolloid was around 7.25 dL/g and 3.61 dL/g, respectively. The specific viscosity versus concentration plot for both Alk and Hw exhibited a power-law dependence on concentration, with an onset of molecular entanglement occurring at a concentration of around 0.6 g/dL and 1.8 g/dL, respectively. Coil-overlap parameter for Alk and Hw was in the range of 4.35–6.61. The relative chain stiffness parameter (B) for Alk and Hw was in the range of 0.004–0.013, indicating a stiff backbone.     

Antioxidant properties of various solvent extracts of mulberry (Morus indica L.) leaves

The antioxidant properties and total phenolic contents of methanol, acetone and water extracts of mulberry (Morus indica L.) leaves were examined. Various experimental models including iron (III) reducing capacity, total antioxidant capacity, DPPH radical scavenging activity and in vitro inhibition of ferrous sulphate-induced oxidation of lipid system were used for characterization of antioxidant activity of extracts. The three extracts showed varying degrees of efficacy in each assay in a dose-dependent manner. Methanolic extract with the highest amount of total phenolics, was the most potent antioxidant in all the assays used. In addition, the effect of temperature (50 °C and 100 °C), pH (3, 5, 7, 9 and 11) and storage (5 °C) on the antioxidant activity of methanolic extract was investigated. The antioxidant activity of the extract remained unchanged at 50 °C and was maximum at neutral pH. The extract stored at 5 °C in the dark was stable for 30 days after which the antioxidant activity decreased (p ? 0.05) gradually. On the basis of the results obtained, mulberry leaves were found to serve as a potential source of natural antioxidants due to their marked antioxidant activity.     

Dietary supplementation with purified mulberry (Morus australis Poir) anthocyanins suppresses body weight gain in high-fat diet fed C57BL/6 mice

We present our experiment about adding anthocyanins to the daily food of mice. Three kinds of anthocyanins (cyanidin-3-glucoside, cyanidin-3-rutinoside and pelargonidin-3-glucoside) purified from Chinese mulberry (Morus australis Poir) were evaluated for suppressing body weight gain of the male C57BL/6 mice fed with high-fat diet (HFD). The results from a 12-week experiment show that consumption of purified mulberry anthocyanins (MACN) of 40 or 200 mg/kg can significantly inhibit body weight gain, reduce the resistance to insulin, lower the size of adipocytes, attenuate lipid accumulation and decrease the leptin secretion. Thus, dietary supplementation with MACN can protect against body weight gain of the diet-induced obese mice.     

紫甘蓝花色苷的热降解动力学研究

探讨在不同温度和pH条件下紫甘蓝花色苷的热稳定性和降解动力学。以80%乙醇浸提,D-101大孔吸附树脂分离纯化制备紫甘蓝花色苷,在50、60、70、80 ℃温度范围内,于不同pH(2.0~6.0)体系中测定不同时间点的花色苷含量,研究其热降解动力学参数和褐变指数。结果表明,紫甘蓝花色苷热稳定性和褐变反应受温度和pH的影响,且其降解速率与时间呈良好线性关系,符合一级动力学模型。随着温度的升高,不同pH下花色苷的半衰期t_1/2均呈下降趋势,最大值为83.51 h(50 ℃,pH3.0),最小值为4.43 h(80 ℃,pH6.0),且各pH(2.0~6.0)体系的活化能E_a依次为42.30、45.31、38.85、26.83、31.20 kJ/mol。此外,其褐变指数随热处理时间延长、温度升高及pH增大而增大。     

Effect of ripeness and postharvest storage on the evolution of colour and anthocyanins in cherries (Prunus avium L.)

The relationship between colour parameters and anthocyanins of four sweet cherry cultivars, Burlat, Saco, Summit and Van was studied. The colour (L^∗, a^∗, b^∗, chroma and hue angle parameters) and anthocyanins were analysed during two different years at two different ripening stages (partially ripe, and ripe, respectively). The cherries were analysed at harvest and after storage at 1.5 ± 0.5 °C and 15 ± 5 °C for 30 and 6 days, respectively. The colour was measured by tristimulus colourimetry (CIELAB system) directly on the fruits, while anthocyanins were quantified by HPLC-DAD analysis on methanolic extracts of freeze-dried samples of the fresh cherries and on the differently stored cherries. L^∗, chroma, and hue angle values were always lower for the ripe than for the partially ripe cherries. All of the cultivars were found to contain cyanidin-3-rutinoside and cyanidin-3-glucoside as the major anthocyanins. The total anthocyanin content in fruits of the different cultivars varied in the order Burlat > Saco > Van > Summit. The concentration of anthocyanins increased at both temperatures of storage in both ripe and partially ripe cherries, but the extent of increase varied among cultivars. Cherries stored at 15 ± 5 °C showed higher reduction of L^∗, chroma and hue angle than fruits stored at 1.5 ± 0.5 °C. L^∗, a^∗, b^∗, chroma and hue angle correlated negatively (P < 0.001) with the total anthocyanins levels, but not with the total phenols. These results show that chromatic functions of chroma and hue correlate closely with the evolution of colour and anthocyanins levels during storage of sweet cherries and indicate that colour measurements can be used to monitor pigment evolution and anthocyanin contents of cherries (and vice versa).     

Influence of alcoholic fermentation process on antioxidant activity and phenolic levels from mulberries (Morus nigra L.)

The aim of the present study was to evaluate the profile of the phenolic constituents of Morus nigra fruits and their antioxidant activity (DPPH) and to compare their contents before and after fermentation. Antioxidant phenolics of black mulberry (M. nigra L.) samples grown in Galicia (NW Spain) were extracted with methanol/formic acid/water (MFW) and determined by high performance liquid chromatography (HPLC). Two major anthocyanins (cyanidin 3-glucoside and cyanidin 3-rutinoside) and two flavonols (quercetin 3-glucoside and rutin) were isolated, together with caffeic acid and other hydroxycinnamic and ellagic acid derivatives. Their chemical structures were identified by spectral analyses with diode array detection (DAD), but also with alkaline saponification and acid hydrolysis of the mulberry phenolics. Good correlations (r² = 0.6229) were observed among total flavonols contents and the IC₅₀ radical scavenging capacities of mulberry fruits. Anthocyanins are the major flavonoids present in mulberry. It would be expected that anthocyanins contribute significantly to their antioxidant activity; nevertheless, alcohol generated during fermentation may also contribute to antioxidant activity. Our results provide useful antioxidant nutritional information of fresh and fermented mulberry fruits.     

Composition and colour stability of anthocyanins extracted from fermented purple sweet potato culture

The components and colour stability of anthocyanins in purple sweet potato were investigated. Anthocyanins were extracted from fermented purple sweet potato culture fermented by Suzhou wine starter (Rhizopus 3.851, 3.866 and Saccharomyces cerevisiae). In these purple sweet potato anthocyanins (PSPAs), five major anthocyanins were detected by high performance liquid chromatography (HPLC). Cyanidin and peonidin were found to be the major anthocyanidins in PSPAs by acid hydrolysis of anthocyanins. PSPAs were more stable under the acid conditions (pH 2.0-4.0) than the subacid conditions (pH 5.0-6.0) as per UV-Vis absorption spectra and CIELAB colour coordinates.     

Antioxidant flavonol glycosides in mulberry (Morus alba L.) leaves isolated based on LDL antioxidant activity

Oxidation of low-density lipoprotein (LDL) has been implicated in atherogenesis. Antioxidants that prevent LDL from oxidation may reduce atherosclerosis. We investigated LDL antioxidant activity and extracted compounds of mulberry (Morus alba L.) leaves. The LDL antioxidant activity of 60% ethanol extracted of mulberry leaves, which inhibits human LDL oxidation induced by copper ion, was determined on the basis of oxidation lag time and calculated as epigallocatechin 3-gallate equivalents (58.3 μmol of EGCG equivalent/g of dry weight). Three flavonol glycosides [quercetin 3-(6-malonylglucoside), rutin (quercetin 3-rutinoside) and isoquercitrin (quercetin 3-glucoside)] were identified as the major LDL antioxidant compounds by LC-MS and NMR. The amounts of these flavonol glycosides in mulberry leaves and mulberry-leaf tea were determined by HPLC. Our results showed that quercetin 3-(6-malonylglucoside) and rutin were the predominant flavonol glycosides in the mulberry leaves.