Exploration of reaction mechanisms of anthocyanin degradation in a roselle extract through kinetic studies on formulated model media

The promising stability of carboxylpyranocyanidin-3-O-glucoside during food processing and simulated digestion and its bioavailability research

BACKGROUND

Pyranoanthocyanins are stable anthocyanin derivatives. Carboxylpyranoanthocyanin is one of the simplest pyranoanthocyanin, among which the production of carboxylpyranocyanidin-3-O-glucoside (crboxyl-pycy-3-gluc) is most feasible as a result of the abundance of its reactant, cyanidin-3-O-glucoside (Cy-3-gluc).

RESULTS

In the present study, carboxyl-pycy-3-gluc was synthesized and its stability during processing and after ingestion as well as its bioavailability in vivo were comprehensively evaluated. Our results indicated that the color of carboxyl-pycy-3-gluc remained more stable compared to Cy-3-gluc when facing the large-span pH variation. The high retention of anthocyanin symbolized the superb stability under thermal processing, sulfur dioxide bleaching and ultrasonic treatment of carboxyl-pycy-3-gluc. Because of the stability under the alkaline condition, carboxyl-pycy-3-gluc is more stable after oral-gastrointestinal digestion. After in vitro gut microbiota fermentation, the retention of carboxyl-pycy-3-gluc was significantly higher than that of Cy-3-gluc. The larger molecular size made absorption of carboxyl-pycy-3-gluc into blood more difficult than its precursor.

CONCLUSION

The present study demonstrated the promising stability of carboxyl-pycy-3-gluc during food processing and after digestion, confirming the potential of carboxyl-pycy-3-gluc as a colorant. © 2023 Society of Chemical Industry.

Optimization of Bioactive Compound Extraction from Eggplant Peel by Response Surface Methodology: Ultrasound-Assisted Solvent Qualitative and Quantitative Effect

Anthocyanin pigments, which the peel of eggplant is rich in, contribute to food quality because of their function in color, appearance, and nutritional advantages. For the first time, this study aimed to optimize the composition of the extracting solvent as three factors: factor A (ratio of ethanol to methanol 0-100% v/v), factor B (ratio of water to alcohol 0-100% v/v), and factor C (citric acid in the final solvent 0-1% w/v) using response surface methodology (RSM), central composite design (CCD) with α 2, and two repeats in axial and factorial points and four central points, for maximum total phenolic content, total anthocyanin content, extraction yield, antioxidant activity in terms of DPPH radical scavenging activity and ferric reducing antioxidant power (FRAP) assay of the eggplant peel dry extract assisted by ultrasound (200 watts power, frequency of 28 kHz) in 60 °C for 45 min has been investigated. The best optimal formulas determined using RSM for the final solvent comprised optimal formula 1 (i.e., ethanol-to-methanol ratio 59% and water-to-alcohol ratio 0%, and citric acid in final solvent 0.47%), and optimal formula 2 (i.e., ethanol-to-methanol ratio 67% and water-to-alcohol ratio 0%, and citric acid in final solvent 0.56%). In general, an alcoholic-acidic extract of eggplant peel made with an ethanol-methanol solvent including citric acid can be used in the food industry as a natural source of antioxidants and pigment.

Antioxidative Properties and Acrylamide Content of Functional Wheat-Flour Cookies Enriched with Wild-Grown Fruits

This study aimed to evaluate the impact of widely grown fruits (wild roses, elderberries, sea buckthorns, rowans, chokeberries, and hawthorns) as a functional ingredient in wheat-flour cookie formulation on antioxidative properties with a simultaneous reduction of the carcinogen-like compound acrylamide. The organoleptic features of the cookies were assessed by a panel of consumers. The following parameters were measured: chemical composition, total polyphenols, polyphenolic profile, antioxidant activity, and acrylamide content. The overall ratings of the tested cookies with the addition of chokeberries, hawthorns, sea buckthorns, and elderberries were more than satisfactory, while wild rose and rowan cookies were the most widely accepted and best rated by the panelists. The antioxidant activity of the tested cookies was 1.1−15.22 μmol trolox·g−1 dm and 2.46−26.12 μmol Fe (II)·g−1 dm as measured by the ABTS and FRAP methods, respectively. All the fruit-enriched cookies had significantly higher antioxidative properties (p < 0.05) in comparison to the control cookies, but among the fruit-enriched cookies, there were differences in the quality and quantity of particular polyphenols. The acrylamide content was significantly decreased by 59% (hawthorn), 71% (rowan), 87% (wild rose), 89% (sea buckthorn), 91% (elderberry), and 94% (chokeberry) compared with the control cookies (p < 0.05). Cookies enriched with wild-grown fruits could constitute a promising novel snack food.

Updated insights into anthocyanin stability behavior from bases to cases: Why and why not anthocyanins lose during food processing

Anthocyanins have received considerable attention for the development of food products with attractive colors and potential health benefits. However, anthocyanin applications have been hindered by stability issues, especially in the context of complex food matrices and diverse processing methods. From the natural microenvironment of plants to complex processed food matrices and formulations, there may happen comprehensive changes to anthocyanins, leading to unpredictable stability behavior under various processing conditions. In particular, anthocyanin hydration, degradation, and oxidation during thermal operations in the presence of oxygen represent major challenges. First, this review aims to summarize our current understanding of key anthocyanin stability issues focusing on the chemical properties and their consequences in complex food systems. The subsequent efforts to examine plenty of cases attempt to unravel a universal pattern and provide thorough guidance for future food practice regarding anthocyanins. Additionally, we put forward a model with highlights on the role of the balance between anthocyanin release and degradation in stability evaluations. Our goal is to engender updated insights into anthocyanin stability behavior under food processing conditions and provide a robust foundation for the development of anthocyanin stabilization strategies, expecting to promote more and deeper progress in this field.

Degradation of cyanidin-3-O-glucoside induced by antioxidant compounds in model Chinese bayberry wine: Kinetic studies and mechanisms

The degradation kinetic of cyanidin-3-O-glucoside was determined in combination with different antioxidants, namely ascorbic acid, cysteine, reduced glutathione, and sodium sulfite at different concentrations and temperatures (4, 20, and 37 °C) in model Chinese bayberry wine. Ascorbic acid, cysteine, and reduced glutathione accelerated cyanidin-3-O-glucoside degradation; half-life times decreased by ca. 46 ∼ 93%, 0.39 ∼ 88%, and 1.6 ∼ 92% respectively when the concentrations of antioxidants were 0.1 ∼ 5 mM. Thiols with more -SH groups lead to faster degradation of cyanidin-3-O-glucoside. Interactions of oxidized cyanidin-3-O-glucoside with antioxidants were evaluated in aqueous solution and methanol to investigate the degradation mechanism of anthocyanin after oxidation. An anthocyanin-cysteine adduct was identified by LC-MS and formation pathways are proposed, along with mechanisms of anthocyanin degradation induced by antioxidants.

A New Insight into the Degradation of Anthocyanins: Reversible versus the Irreversible Chemical Processes

The kinetics and thermodynamics of the pH-dependent reversible and irreversible processes leading to color fading of pelargonidin-3-O-glucoside, peonidin-3-O-glucoside, malvidin-3-O-glucoside, and cyanidin-3-O-glucoside dyes in aqueous solutions are reported. Following the addition of base to the flavylium cation, the quinoidal bases disappear by three distinct steps: (i) in an acidic medium by a biexponential process, in which the faster step is controlled by the hydration reaction and the slower one by cis-trans isomerization; the degradation process occurs essentially from the anionic quinoidal base; (ii) in a basic medium (pH > 9.5), in which the disappearance of the anionic bases is monoexponential, with the rate proportional to the hydroxyl concentration (hydroxyl attack), leading to anionic chalcones (cis and trans) at equilibrium─the slower degradation step occurs from the di- and trianionic chalcones; and (iii) in the pH region circa 7.7 < pH < 9.5, in which hydration and hydroxyl attacks are much slower than anionic quinoidal base degradation (which is the rate-controlling step) and the equilibrium cannot be attained.

DFT study of the stabilization effect on anthocyanins via secondary interactions

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Mechanisms and thermodynamic computations of anthocyanins degradation were performed using DFT.

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Secondary interactions and all energies of anthocyanins and dietary stabilizers were quantified.

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Binding free energy change was a good indicator of stabilization effect on aqueous anthocyanin.

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The screening method for dietary stabilizers was confirmed with reported experimental data.

Anthocyanins, which are the labile flavonoid pigments in botanical food, are attracting intensive attention because they can reduce the risk of noncommunicable diseases. Thus, many dietary molecules have been explored to minimize anthocyanin degradation. This study developed a novel model based on the density functional theory (DFT) and conceptual density functional theory (CDFT) to screen small dietary compounds that can stabilize aqueous anthocyanins. The progression of anthocyanin degradation, which was modeled as an aqueous food system, was illustrated using thermodynamic computation and relaxed scanning. The nucleophilic index and dipole moment were applied to quantify van der Waals interaction between anthocyanins and stabilizers. Two equations based on first-order kinetics were established to demonstrate that the equilibrium constant and free energy of the binding reaction between anthocyanins and stabilizers were theoretically important. The change in binding free energy change (ΔG) may be the best indicator of the protection offered by dietary stabilizers on anthocyanins, which was demonstrated by comparisons of computational ΔG with the thermal half time from the previous study on the effects of gallic/ferulic/caffeic acids on anthocyanin stability. Based on established forecasting methods, trans-resveratrol (ΔG = −35.63 kJ/mol) was found to be the best stabilizer among dietary compounds.

Cranberry (Vaccinium macrocarpon) Juice Precipitate Pigmentation Is Mainly Polymeric Colors and Has Limited Impact on Soluble Anthocyanin Loss

Anthocyanins degrade in fruit juice during storage, reducing juice color quality and depleting the health-promoting components of juice. Common water-soluble products of anthocyanins' chemical degradation are known, but little is known about the contribution of the insoluble phase to loss processes. Cranberry juice and isolated anthocyanins were incubated at 50 °C for up to 10 days to determine polyphenol profiles and degradation rates. Anthocyanin-proanthocyanidin heteropolymers were analyzed via Matrix Assisted Laser Desorption/Ionization (MALDI)- Time of Flight (TOF) Mass Spectrometry (MS). Formation of soluble protocatechuic acid accounted for 260 ± 10% and insoluble materials for 80 ± 20% of lost soluble cyanidin-glycosides in juice, over-representations plausibly due to quercetin and (epi)catechin in cranberry juice and not observed in the values of 70 ± 20% and 16 ± 6% in the purified anthocyanin system. Loss processes of soluble peonidin-glycosides were better accounted for, where 31 ± 2% were attributable to soluble vanillic acid formation and 3 ± 1% to insoluble materials in cranberry juice and 35 ± 5% to vanillic acid formation and 1.6 ± 0.8% to insoluble materials in the purified anthocyanin system. Free anthocyanins were below quantifiable levels in precipitate, implying most anthocyanins in precipitate were polymeric colors (PCs). PCs in the precipitate included cyanidin- and peonidin-hexosides and -pentosides covalently bonded to procyanidins. Therefore, formation of cranberry juice precipitate does not deplete a large portion of soluble anthocyanins; rather, the precipitate's pigmentation results from PCs that are also present in the soluble phase.

Incorporation of polyphenols in baked products

Bakery foods, including breads, cakes, cookies, muffins, rolls, buns, crumpets, pancakes, doughnuts, waffles, and bagels, etc., have been an important diet of humans for thousands of years. As the nutraceuticals with various biological activities, polyphenols, especially polyphenol-enriched products are widely used in bakery foods. The polyphenol-enriched products are mainly from fruits and vegetables, including fruits in whole, juice, puree, jam, and the powder of dried fruits, pomace, and peels. Incorporation of these products not only provide polyphenols, but also supply other nutrients, especially dietary fibers for bakery products. This chapter discussed the thermal stability of different types of polyphenols during baking, and the effect of polyphenols on the sensory attributes of baked foods. Moreover, their role in mitigation of reactive carbonyl species and the subsequent formation of advanced glycation end products, antioxidant and antimicrobial activities have been also discussed. Since polyphenols are subjected to high temperature for dozens of minutes during baking, future works need to focus on the chemical interactions of polyphenols and their oxidized products (quinones) with other food components, and the safety consequence of these interactions.

Multiple co-pigments of quercetin and chlorogenic acid blends intensify the color of mulberry anthocyanins: insights from hyperchromicity, kinetics, and molecular modeling investigations

BACKGROUND

The effect of multiple co-pigments on the color intensification of mulberry anthocyanins (ACs) using spectroscopic techniques in combination with a molecular docking study was studied. The hyperchromicity of ACs co-pigmented with chlorogenic acid (CH) and quercetin (Q) blends was measured and their color stability in liquid and encapsulated particle models was evaluated.

RESULTS

Multiple co-pigments exhibited higher hyperchromicity, pK_H -values, and heat-stability than their individual counterparts. Surflex-docking findings confirmed that stronger binding occurred between multiple ligands and AC than single ones due to their extra -OH, -COOH groups, and delocalization systems. The binding was allowed by increased H-bonding, van der Waals forces, and π-π sites by the extra groups of the multiple co-pigments with AC in aqueous juice and whey particle-based models.

CONCLUSION

This is the first report of the ternary mixture of phenolic acid-flavonol-anthocyanin which could be used as promising food red-colorants. © 2020 Society of Chemical Industry.

Methodologies in the Analysis of Phenolic Compounds in Roselle (Hibiscus sabdariffa L.): Composition, Biological Activity, and Beneficial Effects on Human Health

Roselle (Hibiscus sabdariffa L.), as an edible flower, has long provided an array of positive effects on human health. This benefit is a result of phenolic compounds that are naturally present mainly in the calyx. Plentiful medicinal remedies and functional foods based on this flower are available worldwide, as supported by the studies of phenolic compounds in recent decades. This paper aims to provide a comprehensive review of the composition, biological activity, and beneficial effects on human health of phenolic compounds in roselle. This review was performed in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. A structured search in the published literature for phenolics compositions in roselle was required prior to the evaluation on the validity of the reported analytical methods. Reliable identification and quantification of phenolic compounds in roselle can be achieved by employing the proper extraction and separation methods. With ample alternative analytical methods discussed here, this review provided an aid for comprehending and selecting the most appropriate method for a particular study. The applications of the analytical methods highlighted indicated that phenolic acids, flavonoids, and their derivatives have been identified and quantified in roselle with a range of biological activities and beneficial effects on human health. It was also disclosed that the composition and concentration of phenolic compounds in roselle vary due to the growth factors, cultivars, and environmental influence. Finally, apart from the research progress carried out with roselle during the last ten years, this review also proposed relevant future works.

Anthocyanins extraction from Hibiscus sabdariffa and identification of phenolic compounds associated with their stability

BACKGROUND

One of the main disadvantages of red pigments used in foods is their low extraction yield and storage stability. Roselle flowers are sources of anthocyanins; however, these are unstable during storage, but this could be improved with phenolic compounds, which establish bonds with the anthocyanins. The aim of this work was to identify conditions to improve the extraction efficiency and color stability of Hibiscus sabdariffa extract and, furthermore, to identify the phenolic compounds associated with color stability of roselle.

RESULTS

The temperature of extraction (35 and 75 °C), the time of extraction (15 and 60 min), type of acid (acetic and citric), percentage of acid (0.5 and 2.0%) and the water:ethanol ratio (20:80 and 80:20) did not affect the yield of anthocyanins; only the solid:solvent ratio had an effect in the anthocyanin extraction yield. The extraction with 80% ethanol decreased up to 50% the anthocyanin degradation in the extracts stored at 4, 25, 35, 45, and 80 °C. Phenolic acids and flavonoids were quantified by ultrahigh-performance liquid chromatography coupled with triple quadrupole electrospray ionization mass spectrometry. These compounds were analyzed using principal component analysis, and the H. sabdariffa extract, with greater stability, was found to be associated with the presence of quercetin, myricetin, kaempferol 3-O-glucose, ellagic acid, and rutin.

CONCLUSION

H. sabdariffa extract with increased color stability was extracted with a higher proportion of ethanol and the improvement in the color stability was attributed to the co-extraction of phenolic compounds, principally flavonoids that could interact with anthocyanins and stabilize them. © 2020 Society of Chemical Industry.

Anthocyanin Metabolites in Human Urine after the Intake of New Functional Beverages

Sugar intake abuse is directly related with the increase of metabolic diseases such as type 2 diabetes, obesity, and insulin resistance. Along this line, the development of new beverages using alternative sweeteners could help with combatting the pathophysiological disorders associated to the consumption of sugar. To provide evidence on this issue, in the present work, the bioavailability of anthocyanins was evaluated after the acute ingestion of a new maqui-citrus-based functional beverage rich in polyphenols, and supplemented with a range of sweeteners including sucrose (natural high caloric), stevia (natural non-caloric), and sucralose (artificial non-caloric), as an approach that would allow reducing the intake of sugars while providing bioactive phenolic compounds (anthocyanins). This approach allowed the evaluation of the maximum absorption and the diversity of metabolites excreted through urine. The beverages created were ingested by volunteers (n = 20) and the resulting anthocyanin metabolites in their urine were analyzed by UHPLC-ESI-MS/MS. A total of 29 degradation metabolites were detected: Caffeic acid, catechol, 3,4-dihidroxifenilacetic acid, hippuric acid, trans-ferulic acid, 2,4,6-trihydroxybenzaldehyde, trans-isoferulic acid, and vanillic acid derivatives, where peak concentrations were attained at 3.5 h after beverage intake. Sucralose was the sweetener that provided a higher bioavailability for most compounds, followed by stevia. Sucrose did not provide a remarkably higher bioavailability of any compounds in comparison with sucralose or stevia. The results propose two sweetener alternatives (sucralose and stevia) to sucrose, an overused high calorie sweetener that promotes some metabolic diseases.

Phytochemicals and Traditional Use of Two Southernmost Chilean Berry Fruits: Murta (Ugni molinae Turcz) and Calafate (Berberis buxifolia Lam.)

Murta and calafate have been traditionally used by indigenous and rural peoples of Chile. Research on murta and calafate has gained interest due to their attractive sensory properties as well as a global trend in finding new fruits with potential health benefits. The objective of this review was to summarize the potential use of murta and calafate as sources of nutraceuticals regarding both the traditional and the up-to-date scientific knowledge. A search of historical documents recorded in the Digital National Library as well as scientific articles in the Web of Science database were performed using combinations of keywords with the botanical nomenclature. Peer-reviewed scientific articles did meet the inclusion criteria (n = 38) were classified in phytochemicals (21 papers) and biological activity (17 papers). Murta and calafate are high oxygen radical absorbance capacity (ORAC)-value fruits and promising sources of natural antioxidants, antimicrobial, and vasodilator compounds with nutraceutical potential. The bioactivity of anthocyanin metabolites in murta and calafate must continue to be studied in order to achieve adequate information on the biological activity and health-promoting effects derived for the consumption of murta and calafate fruit.

The Multifunctional Benefits of Naturally Occurring Delphinidin and Its Glycosides

Delphinidin (Del) and its glycosides are water-soluble pigments, belonging to a subgroup of flavonoids. They are health-promoting candidates for pharmaceutical and nutraceutical uses, as indicated by exhibiting antioxidation, anti-inflammation, antimicroorganism, antidiabetes, antiobesity, cardiovascular protection, neuroprotection, and anticancer properties. Glycosylation modification of Del is associated with increased stability and reduced biological activity. Del and its glycosides can be the alternative inhibitors of CBRs, ERα/β, EGFR, BCRP, and SGLT-1, and virtual docking indicates that the sugar moiety may not effectively interact with the active sites of the targets. Structure-based characteristics confer the multifunctional properties of Del and its glycosides. Because of their health-promoting effects, Del and its glycosides are promising and have been developed as potential pharmaceuticals. However, more investigation on the underlying mechanisms of Del and its glycosides in mediating cellular processes with high specificity are still needed. The research progression of Del and its glycosides over the last 10 years is comprehensively reviewed in this article.

Positive and negative effects of polyphenol incorporation in baked foods

Polyphenols are hot research topics worldwide owing to their physiological and pharmaceutical activities. Polyphenols and polyphenol-enriched by-products have been widely used in bakery foods because of their neutraceutical properties. This review summarizes the classification, biosynthesis, main source and analysis of polyphenols and intensively discusses the effects of their incorporation in baked foods. The positive effects of polyphenol incorporation include elevation of antioxidant activity of baked foods, scavenging of food-borne toxins produced during thermal processing and decreasing postprandial serum glucose level. Meanwhile, polyphenol incorporation negatively influences colour, texture and flavour of baked foods and bioavailability of the added polyphenols. Most polyphenols are thermally sensitive and reactive. Thus far, few studies have investigated on neoformed compounds from the reaction of polyphenols or their oxidised products (quinones) with other food components. Before launching polyphenol-incorporated bakery foods in the market, future work should focus on full toxicological evaluation of newly derived compounds from polyphenols.

Complex of polyphenols sorbed on buckwheat flour as a functional food ingredient

An innovative approach to creating a new generation of specialised foods for dietary therapy of type 2 diabetes can involve planned adding of plant polyphenols to their formulafions. The marked antioxidant properties of polyphenols largely determine their potential antidiabetic effects. However, the use of food polyphenols for prophylactic purposes is limited by their low bioavailability, which makes it expedient to search for technological approaches aimed at obtaining polyphenolic matrices with high biological activity, increased digestibility, and stability. This study objective was to purposely extract and concentrate the polyphenols by sorbing them from an aqueous solution of the bilberry leaf extract (BLE) on buckwheat flour and to assess their storage stability. A number of experiments on optimal parameters selection for sorbing polyphenols from the BLE on buckwheat flour were performed. The parameters included the concentration of the extract solution, the solution/sorbent ratio, the pH of the solution, the temperature and the time of sorption. The sorption on the polyphenol matrix was determined from the difference in their contents in the initial solution of the extract and in the supernatant after centrifugation by the Folin-Ciocalteu method. The effects of exposure to light, temperatures, and humidity on the polyphenol compounds in the dry BLE and in the food matrix contents during storage was analysed by the FTIR spectroscopy. The experiments determined the optimal conditions for the BLE polyphenol sorption on buckwheat flour by incubation of a 2% BLE solution pH = 3.6 with the portion of buckwheat flour at the ratio of 1g/50 cm3 solution for 45 minutes at 25°C. When storing the food matrix, there was no significant degradation of the polyphenolic compounds in the food matrix, which indicates an increase in the stability of the polyphenols sorbed on buckwheat flour. This paper presents the results that are scientifically and practically relevant for the nutritiology experts who devise promising technological approaches to expanding the range of functional food ingredients of the antidiabetic character.

Monitoring anthocyanin degradation in Hibiscus sabdariffa extracts with multi-curve resolution on spectral measurement during storage

This study aims to monitor composition changes in an anthocyanin-rich beverage during storage by the means of UV-VIS measurements associated with a multi-curve resolution procedure. Hibiscus sabdariffa extract was stored at 37 °C for 50 days and UV-VIS spectra were measured on the extract and the fractions of the extract every 5 days. MCR was carried out in two steps, first with the fraction and then the extract spectra. The results enabled the main polyphenols initially present to be identified, anthocyanins and chlorogenic acid, but also found the nature of the main degradation products: the polymers from anthocyanin condensation and scission products. In addition, comparison with HPLC analysis results showed that the MCR procedure recovered the correct shapes of the concentration profiles particularly of anthocyanin and polymer kinetics during storage. This work gives perspective for the use of a rapid and efficient technique to monitor pigment-rich beverage processing or storage.

Browning Index of Anthocyanin-Rich Fruit Juice Depends on pH and Anthocyanin Loss More Than the Gain of Soluble Polymeric Pigments

Browning index (BI, ABS_{520 nm} /ABS_{420 nm} ) is a measure of anthocyanin-rich fruit juice pigmentation quality. This study sought to determine the extent to which BI describes anthocyanin quality and degradation in fruit juices. Commercial fruit juices were assayed for monomeric anthocyanin (MA) content, percent polymeric color (%PC), pH, and BI. BI varied, 0.29 to 1.72, among cranberry, cherry, grape, aronia, and pomegranate juices. Principal component analysis (PCA) revealed that BI was strongly inversely associated with %PC, and positively correlated with MAs to a lesser extent. The BI of grape and cherry juices varied linearly with pH from 2.0 to 4.0 in pH-adjusted juices. Cherry and grape juices at pH approximately 2.0 to 4.0 were incubated at 50 °C to induce juice browning. BI and MA decreased, and %PC increased, but the amount of MA degradation was not explained by %PC. In the aged juices, BI and MA were strongly correlated using PCA. In aged grape juice, chromatographic analysis was used characterize anthocyanins, proanthocyanidins, and anthocyanin scission products. Anthocyanin loss and a gain of unresolved components absorbing at 420 nm decreased BI. Proanthocyanidins and co-eluting pigments with varying BI decreased during aging. Scission products did not account for anthocyanin loss. Thus, MA loss more so than the gain in pigments associated with juice proanthocyanidins contribute to the increase in %PC and decline of the BI during accelerated aging of grape juice. Thus, BI is a useful marker of fruit juice quality within juices of the same pH and anthocyanin composition.

PRACTICAL APPLICATION

Fruit juice pigmentation depends on anthocyanins, pH, and other matrix components. Spectrophotometric methods to determine pigmentation include the browning index (ABS_{520 nm} /ABS_{420 nm} ), pH differential method for monomeric anthocyanin (MA) content, and bisulfite bleaching to determine percent polymeric color (%PC). In this study, anthocyanin-rich fruit juice browning index was strongly dependent on pH and MA content. MA loss, and to a lesser extent, a gain in newly-formed pigments at 420 nm contributed to the browning index change during aging. Therefore, browning index is strongly associated with MA content and is useful for assessing fruit juice quality.