Effect of heat on aspalathin, iso-orientin, and orientin contents and color of fermented rooibos (Aspalathus linearis) iced tea

Assessment of the stability of compounds belonging to neglected phenolic classes and flavonoid sub-classes using reaction kinetic modeling

Phenolic compounds are known to degrade and/or undergo changes during food production and storage. Reaction kinetic modeling is generally used to define kinetic parameters of a food system and predict changes during thermal processing and storage. Data for phenolic acids and flavonoids, such as anthocyanins and flavan-3-ols, have been reviewed in detail, but the flavonoid sub-classes, dihydrochalcones and flavanones, have been mostly neglected. Other neglected phenolic classes are xanthones and benzophenones. The stability of these types of compounds is important as they are present in fruits and exposed to heat when processed into juice and jam. Other sources of the compounds are herbal teas, which are also subjected to thermal processing, either during the primary processing of the plant material, or the production of extracts for use as food ingredients. The theoretical background is given to understand the review of literature on these classes/sub-classes. Results of research on kinetic modeling are discussed in detail, while research on compound stability without the application of reaction kinetic modeling is briefly mentioned to provide context. The studies discussed included those focusing on heating during the processing and storage of model solutions, liquid foods, plant material, dried extracts, and extracts formulated with other food ingredients.

Reaction kinetics of aspalathin degradation and flavanone isomer formation in aqueous model solutions: Effect of temperature, pH and metal chelators

The poor stability of aspalathin in aqueous solutions is a major challenge in delivering a shelf-stable ready-to-drink (RTD) green rooibos iced tea. The kinetics of aspalathin degradation and the formation of eriodictyol glucoside isomers [(S/R)-6-β-D-glucopyranosyleriodictyol and (S/R)-8-β-D-glucopyranosyleriodictyol] in aqueous buffers were modeled to understand and predict aspalathin losses during heat processing. The effects of temperature and pH on the rate constants of aspalathin degradation and eriodictyol glucoside isomer formation were determined in a 0.1 M phosphate buffer with 5.7 mM citric acid. The zero-order model best described the reaction kinetics of aspalathin degradation and eriodictyol glucoside isomer formation. Increasing the temperature and pH increased the reaction rate constants. The activation energies of the reactions were much lower at pH 6 than at pH 4, indicating that pH affected the temperature dependence of the reactions. The 8-C-glucosyl eriodictyol derivatives (RE8G and SE8G) formed at much lower rates than the 6-C-glucosyl eriodictyol derivatives (RE6G and SE6G). The metal chelators, citric acid, citrate and EDTA, drastically reduced the reaction rate constants, indicating the catalytic role of metal ions in aspalathin autoxidation. The results of the study could assist manufacturers to improve the shelf life of rooibos RTD beverages by changing the formulation and adjusting heat processing conditions.

Extraction optimization, structural characterization and potential alleviation of hyperuricemia by flavone glycosides from celery seeds

Celery seeds are commonly used as condiments and in herbal teas with high medicinal value. In the present study, we investigated the contents of extracts derived under different extraction conditions and determined the optimal conditions for only extracting flavone glycosides from celery seeds. The compositional analysis identified three primary flavone glycosides in the ethanolic extract, and apiin, graveobioside A, and graveobioside B were isolated. Apigenin, luteolin, and chrsyeriol were obtained by the acid hydrolysis of flavone glycosides under high-temperature conditions. Here we investigated the inhibitory activity of apigenin and apiin on xanthine oxidase by reducing the rate of oxidative cytochrome C and found that both apigenin and apiin reduced cytochrome C production, except for low concentrations of apiin. In vivo analysis with hyperuricemia mice and rats showed that apiin had excellent uric acid-lowering effects and high dose-dependence, while apigenin was relatively slightly uric acid-lowering. In addition, the flavone glycoside extracts from celery seeds exhibited similar effects of reducing uric acid with apiin. Surprisingly, in hyperuricemia rats, the uric acid-lowering effects of high-dose apiin and flavone glycoside extracts were almost comparable to that of allopurinol. Besides, our experimental results showed that apigenin could improve uric acid clearance by increasing the glomerular filtration capacity, which was reflected in reducing the renal function parameters SUN and SCr; also, apiin showed better results. This study also showed that celery seeds have a unique medicinal value in treating hyperuricemia and that the flavone glycoside extracts from celery seeds can be developed as medicine for hyperuricemia.

Shelf-Life Stability of Ready-to-Use Green Rooibos Iced Tea Powder-Assessment of Physical, Chemical, and Sensory Properties

Green rooibos extract (GRE), shown to improve hyperglycemia and HDL/LDL blood cholesterol, has potential as a nutraceutical beverage ingredient. The main bioactive compound of the extract is aspalathin, a C-glucosyl dihydrochalcone. The study aimed to determine the effect of common iced tea ingredients (citric acid, ascorbic acid, and xylitol) on the stability of GRE, microencapsulated with inulin for production of a powdered beverage. The stability of the powder mixtures stored in semi-permeable (5 months) and impermeable (12 months) single-serve packaging at 30 °C and 40 °C/65% relative humidity was assessed. More pronounced clumping and darkening of the powders, in combination with higher first order reaction rate constants for dihydrochalcone degradation, indicated the negative effect of higher storage temperature and an increase in moisture content when stored in the semi-permeable packaging. These changes were further increased by the addition of crystalline ingredients, especially citric acid monohydrate. The sensory profile of the powders (reconstituted to beverage strength iced tea solutions) changed with storage from a predominant green-vegetal aroma to a fruity-sweet aroma, especially when stored at 40 °C/65% RH in the semi-permeable packaging. The change in the sensory profile of the powder mixtures could be attributed to a decrease in volatile compounds such as 2-hexenal, (Z)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, (E,Z)-2,6-nonadienal and (E)-2-decenal associated with "green-like" aromas, rather than an increase in fruity and sweet aroma-impact compounds. Green rooibos extract powders would require storage at temperatures ≤ 30 °C and protection against moisture uptake to be chemically and physically shelf-stable and maintain their sensory profiles.

Identification of a novel di-C-glycosyl dihydrochalcone and the thermal stability of polyphenols in model ready-to-drink beverage solutions with Cyclopia subternata extract as functional ingredient

Heat processing of ready-to-drink beverages is required to ensure a microbiologically safe product, however, this can result in the loss of bioactive compounds responsible for functionality. The objective of this study was to establish the thermal stability of a novel dihydrochalcone, 3',5'-di-β-d-glucopyranosyl-3-hydroxyphloretin (2), 3',5'-di-β-d-glucopyranosylphloretin (3) and other Cyclopia subternata phenolic compounds, in model solutions with or without citric acid and ascorbic acid. The solutions were heated at 93, 121 and 135 °C, relevant to pasteurisation, commercial sterilisation and ultra-high temperature (UHT) pasteurisation, respectively. For most compounds, the acids decreased the second order reaction rate constants, up to 27 times. Compound 2 (46.29 ± 0.53 (g/100 g)^-1 h^-1), and to a lesser extent compound 3 (5.94 ± 0.01 (g/100 g)^-1 h^-1) were the most thermo-unstable compounds when treated at 135 °C without added acids. Even though differential effects were observed for compounds at different temperatures and formulations, overall, the phenolic compounds were most stable under UHT pasteurisation conditions.

Further isolation and identification of anti-diabetic principles from root bark of Myrianthus arboreus P. Beauv.: The ethyl acetate fraction contains bioactive phenolic compounds that improve liver cell glucose homeostasis

ETHNOPHARMACOLOGICAL RELEVANCE

We recently reported that ethanol extract of Myrianthus arboreus P. Beauv. root bark demonstrated antidiabetic activity by modulating hepatocyte glucose homeostasis. This activity was associated significantly to the ethyl acetate (EAc) fraction. The current study sought to identify the active compounds responsible of the antidiabetic effect of M. arboreus in the EAc fraction using bioassay-directed sub-fractionation.

MATERIALS AND METHODS

EAc fraction was sub-fractionated using Flash chromatography. Preparative HPLC was used to isolate the pure compounds. The structures of the isolated compounds were confirmed by analysis of NMR spectroscopic and mass spectrometric data. Hepatic (H4IIE, HepG2) cells were treated with maximum non-toxic concentrations of ethanol extract, its EAc fraction and isolated compounds thereof. Glucose-6-phosphatase (G6Pase) activity was measured using the glucose oxidase method. To measure glycogen synthase (GS) activity, radioactive assays were used. Phosphorylation of AMP-activated protein kinase (AMPK) and Glycogen Synthase Kinase-3 (GSK-3) were probed by Western blot.

RESULTS

Six sub-fractions were obtained, and the antidiabetic activity was found in two sub-fractions (SFE1 and SFE2). For the first time, two known C-glycosylflavone regio-isomers, isoorientin (1) and orientin (2) were detected and isolated from M. arboreus plant, especially from SFE2 as well as protocatechuic acid, 3,4-dihydroxybenzaldehyde (4), and chlorogenic acid isolated from SFE1. The compounds 1, 2, 4 were determined to decrease the activity of G6Pase by increasing AMPK phosphorylation and to stimulate GS through GSK-3 phosphorylation. Isoorientin which is one of the main compounds of EAc fraction, expressed the strongest effect in all bioassays, similar to that of the EAc fraction. A significant and linear correlation was found between the phosphorylation of AMPK and the activity of G6Pase modulated by all samples (R² = 0.54; p < 0.05). Similar to G6Pase assay, a correlation was determined between the capacity of M. arboreus extracts/fractions/compounds to stimulate GS activity and to phosphorylate GSK-3 (R² = 0.57, p < 0.01).

CONCLUSION

Results demonstrate that 1, 2, 4 are responsible, at least in part, for the antidiabetic activity of M. arboreus. These compounds can be used to ensure the quality and efficacy of M. arboreus antidiabetic preparations and standardize such preparations.

Dietary Flavonoids for Immunoregulation and Cancer: Food Design for Targeting Disease

Flavonoids, one of the most abundant phytochemicals in a diet rich in fruits and vegetables, have been recognized as possessing anti-proliferative, antioxidant, anti-inflammatory, and estrogenic activities. Numerous cellular and animal-based studies show that flavonoids can function as antioxidants by preventing DNA damage and scavenging reactive oxygen radicals, inhibiting formation of DNA adducts, enhancing DNA repair, interfering with chemical damage by induction of Phase II enzymes, and modifying signaling pathways. Recent evidence also shows their ability to regulate the immune system. However, findings from clinical trials have been mixed with no clear consensus on dose, frequency, or type of flavonoids best suited to elicit many of the beneficial effects. Delivery of these bioactive compounds to their biological targets through "targeted designed" food processing strategies is critical to reach effective concentration in vivo. Thus, the identification of novel approaches that optimize flavonoid bioavailability is essential for their successful clinical application. In this review, we discuss the relevance of increasing flavonoid bioavailability, by agricultural engineering and "targeted food design" in the context of the immune system and cancer.

Process for production of ready to drink iced teas from sage (Salvia officinalis L.) and linden (Tilia cordata): pressurized hot water extraction and spray drying

The aim of this study was to produce ready to drink (RTD) iced teas from sage and linden. For this purpose, phenolics of sage and linden were extracted by pressurized hot water extraction (PHWE) and then the extracts obtained were spray dried by the addition of maltodextrin. The powders produced by spray drying were processed into RTD sage and linden iced teas by adding sucrose and citric acid. The optimum conditions of PHWE of sage and linden were at 160 °C and for 10 min and 5 min, respectively. The solubility and microencapsulation efficiency of spray dried powders were found to be greater than 97%. In addition, total phenolic content and antioxidant activity of RTD iced teas are parallel with those of microencapsulated sage and linden powders after pasteurization at 80 °C for 5 min. The sensory analysis of RTD iced teas showed that products were well-accepted by the panelists.

Flavones: Food Sources, Bioavailability, Metabolism, and Bioactivity

Flavones are a class of flavonoids that are a subject of increasing interest because of their biological activities in vitro and in vivo. This article reviews the major sources of flavones and their concentrations in food and beverages, which vary widely between studies. It also covers the roles of flavones in plants, the influence of growing conditions on their concentrations, and their stability during food processing. The absorption and metabolism of flavones are also reviewed, in particular the intestinal absorption of both O- and C-glycosides. Pharmacokinetic studies in both animals and humans are described, comparing differences between species and the effects of glycosylation on bioavailability. Biological activity in animal models and human dietary intervention studies is also reviewed. A better understanding of flavone sources and bioavailability is needed to understand mechanisms of action and nutritional intervention.

Evaluation of capillary electrophoresis for the analysis of rooibos and honeybush tea phenolics

Rooibos and honeybush are popular herbal teas produced from the shrubs of Aspalathus linearis and Cyclopia spp., respectively, which are indigenous to South Africa. Both herbal teas are rich in polyphenols and their consumption is associated with several health benefits, partly ascribed to their phenolic constituents. Quantification of phenolics in extracts and teas for quality control and research purposes is generally performed using HPLC, although dedicated and often species-specific methods are required. CE offers an attractive alternative to HPLC for the analysis of phenolics, with potential benefits in terms of efficiency, speed and operating costs. In this contribution, we report quantitative CZE methods for the analysis of the principal honeybush and rooibos phenolics. Optimal separation for honeybush and rooibos phenolics was achieved in 21 and 32 min, respectively, with good linearity and repeatability. Quantitative data for extracts of "unfermented" and "fermented" rooibos and two honeybush species were statistically comparable with those obtained by HPLC for the majority of compounds. The developed methods demonstrated their utility for the comparison of phenolic contents between different species and as a function of manufacturing processes, thus offering cost effective, although less sensitive and robust, alternatives to HPLC analysis.

Oxidative stability of blesbok, springbok and fallow deer droëwors with added rooibos extract

Abstract The addition of rooibos extract (RBE) (0%, 0.25%, 0.50%, 1.0% RBE) to improve the oxidative stability of blesbok, springbok and fallow deer droëwors (dried sausage) was studied. RBE treatments had no effects (p more than 0.05) on the lipid and protein oxidation of the dried product. With the addition of RBE 0.25%, lipid stability after drying showed the malonaldehydes decreased considerably. Haem-iron concentration increased after drying and differed (p less than 0.05) between RBE treatments within the dried stage within species. There were no differences (p more than 0.05) between the moisture, protein and fat contents between treatments within a specific processing stage. With the high polyunsaturated fatty acid content of the sausages, a high level of oxidation occurred. Even though RBE addition did not reduce oxidation significantly during the drying process, it could be a successful addition to the traditional South African meat product if it is shown to impart positive flavour attributes.

Anti-oxidative effects of Rooibos tea (Aspalathus linearis) on immobilization-induced oxidative stress in rat brain

Exposure to chronic psychological stress may be related to increased reactive oxygen species (ROS) or free radicals, and thus, long-term exposure to high levels of oxidative stress may cause the accumulation of oxidative damage and eventually lead to many neurodegenerative diseases. Compared with other organs, the brain appears especially susceptible to excessive oxidative stress due to its high demand for oxygen. In the case of excessive ROS production, endogenous defense mechanisms against ROS may not be sufficient to suppress ROS-associated oxidative damage. Dietary antioxidants have been shown to protect neurons against a variety of experimental neurodegenerative conditions. In particular, Rooibos tea might be a good source of antioxidants due to its larger proportion of polyphenolic compounds. An optimal animal model for stress should show the features of a stress response and should be able to mimic natural stress progression. However, most animal models of stress, such as cold-restraint, electric foot shock, and burn shock, usually involve physical abuse in addition to the psychological aspects of stress. Animals subjected to chronic restraint or immobilization are widely believed to be a convenient and reliable model to mimic psychological stress. Therefore, in the present study, we propose that immobilization-induced oxidative stress was significantly attenuated by treatment with Rooibos tea. This conclusion is demonstrated by Rooibos tea's ability to (i) reverse the increase in stress-related metabolites (5-HIAA and FFA), (ii) prevent lipid peroxidation (LPO), (iii) restore stress-induced protein degradation (PD), (iv) regulate glutathione metabolism (GSH and GSH/GSSG ratio), and (v) modulate changes in the activities of antioxidant enzymes (SOD and CAT).

Variation in phenolic content and antioxidant activity of fermented rooibos herbal tea infusions: role of production season and quality grade

Data are required to calculate the dietary exposure to rooibos herbal tea flavonoids and phenolic acids. Representative content values for the principal phenolic compounds and total antioxidant capacity of fermented rooibos infusion, taking into account variation caused by production seasons (2009, 2010, and 2011) and quality grades (A, B, C, and D), were determined for samples (n = 114) from different geographical areas and producers. The major phenolic constituents were isoorientin and orientin (>10 mg/L), with quercetin-3-O-robinobioside, phenylpyruvic acid glucoside, and aspalathin present at >5 mg/L. Isovitexin, vitexin, and hyperoside were present at <3 mg/L. Rutin, ferulic acid, and isoquercitrin were present at <2 mg/L. Nothofagin was present at <1 mg/L. Only traces of luteolin-7-O-glucoside and the aglycones quercetin, luteolin, and chrysoeriol were present. Substantial variation was observed in the individual content values of the phenolic compounds and total antioxidant capacity within production seasons and quality grades.

Enhancing aspalathin stability in rooibos (Aspalathus linearis) ready-to-drink iced teas during storage: the role of nano-emulsification and beverage ingredients, citric and ascorbic acids

BACKGROUND

The effects of citric and ascorbic acids on the stability of aspalathin in rooibos (Aspalathus linearis) ready-to-drink (RTD) formulations containing fermented rooibos extract (FR), aspalathin-enriched green rooibos extract (GR) and aspalathin-enriched green rooibos extract ascorbic acid solubilisate (GR-solubilisate) were investigated during storage (12 weeks at 25 °C).

RESULTS

Storage of iced tea formulations containing FR and GR extracts reduced their flavonoid content. The aspalathin content of FR iced tea without citric or ascorbic acid was reduced to undetectable levels by week 8 of storage. Addition of citric acid resulted in improved stability of aspalathin, but ascorbic acid did not impart additional stability. Iso-orientin and orientin were less affected than aspalathin, presumably owing to partial conversion of aspalathin to these flavones. Similar results were obtained for GR iced tea formulations. Improved stability of aspalathin was noted in iced tea containing GR-solubilisate with or without citric acid. Lower pH was shown to favour stability, especially for fermented rooibos iced teas.

CONCLUSION

Citric and ascorbic acids contribute to the stability of rooibos flavonoids during storage. Differences in stability between formulations are not due to pH differences but may be related to the matrix.

Use of green rooibos (Aspalathus linearis) extract and water-soluble nanomicelles of green rooibos extract encapsulated with ascorbic acid for enhanced aspalathin content in ready-to-drink iced teas

Heat-induced changes in aspalathin, iso-orientin, and orientin content of ready-to-drink (RTD) green rooibos iced tea formulations were investigated. An organic-solvent-based aspalathin-enriched extract prepared from green rooibos was used "as-is" or encapsulated with ascorbic acid in a water-soluble nanomicelle-based carrier system. The common iced tea ingredients, ascorbic acid, and/or citric acid were added to the iced tea containing green rooibos extract. Only citric acid was added to the iced tea containing the nanomicelles. Heat treatments consisted of pasteurization (93 °C/5 min and 93 °C/30 min), normal-temperature sterilization (NTS; 121 °C/15 min), and high-temperature sterilization (HTS; 135 °C/4 min). Pasteurization had little or no effect on the flavonoid content. NTS and HTS induced significant losses in the flavonoids. The addition of citric and ascorbic acids improved the stability of the flavonoids, but encapsulation of green rooibos extract with ascorbic acid in nanomicelles did not offer additional stability. The only benefit of using the water-soluble nanomicelles was the improved clarity of the RTD product. Iso-orientin and orientin contents were substantially less affected than aspalathin by the heat treatments, partially because of conversion of aspalathin to these flavones, which countered losses. 5-Hydroxymethylfurfural (HMF), a known dehydration product of hexoses under mild acidic conditions and also a degradation product of ascorbic acid, was observed in formulations containing citric and/or ascorbic acids.