Development of sensory tools for green rooibos (Aspalathus linearis (Burm.f.) R.Dahlgren) and changes in quality attributes during shelf-life storage.

BACKGROUND: Green rooibos (Aspalathus linearis (Burm.f.) R.Dahlgren) herbal tea is popular due to its health-promoting properties. Information on its characteristic sensory profile is scarce and sensory tools to define product variation are needed. The storage conditions and time during its shelf-life are hypothesized to affect the product quality. RESULTS: Production batches from two producers spanning 5 years (n = 57) were analyzed using descriptive sensory analysis. Primary attributes (>30 median intensity; 100% occurrence frequency) included 'hay/dried grass', 'cooked oats', 'tobacco', 'honey' and 'caramel' aromas, and astringent mouthfeel. 'Cooked vegetables', 'green grass', 'stewed fruit', 'rooibos-woody', 'marmalade' and 'cardboard' aromas, sweet taste and bitter taste were secondary attributes (10-20 median intensity; 100% occurrence frequency). The same flavor attributes were present, except for sweet-associated and fruity notes. A sensory lexicon and sensory wheels for aroma and palate attributes were constructed from the data. The shelf-life stability of green rooibos was evaluated in moisture-impermeable (pouches) and moisture-permeable (sachets) packaging at 25 and 40 °C at 60% relative humidity over 24 weeks. Green rooibos samples stored in pouches at 4 °C were also evaluated. Storage in sachets led to moisture uptake (~10 g (100 g)-1 dry basis) and an increase in water activity (>0.6), causing degradation of chlorophyll and dihydrochalcones. Changes in color and sensory profile (decreased vegetal, cereal and cardboard aromas and increased sweet-associated and fruity aromas) were evident and more pronounced at the higher storage temperature. CONCLUSIONS: Storage at ≤25 °C in moisture-impermeable packaging material is recommended for green rooibos herbal tea. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Food-grade phytosome vesicles for nanoencapsulation of labile C-glucosylated xanthones and dihydrochalcones present in a plant extract matrix-Effect of process conditions and stability assessment.

Phytosomes consist of a phytochemical bound to the hydrophilic choline head of a phospholipid. Their use in food products is gaining interest. However, literature on the use of food-grade solvents, crude plant extracts as opposed to pure compounds, and unrefined phospholipids to prepare phytosomes is limited. Furthermore, studies on compound stability are lacking. This study aimed to develop nano-phytosome vesicles prepared from inexpensive food-grade ingredients to improve the stability of polyphenolic compounds. Cyclopia subternata extract (CSE) was selected as a source of phenolic compounds. It contains substantial quantities of C-glucosyl xanthones, benzophenones, and dihydrochalcones, compounds largely neglected to date. The effect of process conditions on the complexation of CSE polyphenols with minimally refined food-grade fat-free soybean lecithin (PC) was studied. The PC:CSE ratio, sonication time, and reaction temperature were varied. This resulted in phytosomes ranging in vesicle size (113.7-312.7 nm), polydispersity index (0.31-0.48), and zeta potential (-55.0 to -38.9 mV). Variation was also observed in the yield (93.5%-96.0%), encapsulation efficiency (3.7%-79.0%), and loading capacity (LC, 1.3%-14.7%). Vesicle size and LC could be tailored by adjusting the sonication time and PC:CSE ratio, respectively. Chemical interaction between the lipid and the phenolic compounds was confirmed with nuclear magnetic resonance. Phytosomal formulation protected the compounds against degradation when freeze-dried samples were stored at 25 and 40°C for 6 months at low relative humidity. The study provided valuable information on the importance of specific process parameters in producing food-grade phytosomes with improved phenolic stability.

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-ß-D-glucopyranosyleriodictyol and (S/R)-8-ß-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.

Stability of labile xanthones and dihydrochalcones in a ready-to-drink honeybush beverage during storage.

BACKGROUND: The shelf-life of a functional herbal tea-based beverage is important not only for consumer acceptability, but also for the retention of bioactive compounds. The present study aimed to clarify the role of common iced tea beverage ingredients (citric and ascorbic acids) on the shelf-life stability of an herbal tea-based beverage. A hot water extract of green Cyclopia subternata, also used as honeybush tea, was selected as the main ingredient because it provides different types of phenolic compounds associated with bioactive properties (i.e. xanthones, benzophenones, flavanones, flavones and dihydrochalcones). RESULTS: The model solutions were stored for 180 and 90 days at 25 and 40 °C, respectively. Changes in their volatile profiles and color were also quantified as they contribute to product quality. 3',5'-Di-ß-d-glucopyranosyl-3-hydroxyphloretin (HPDG; dihydrochalcone) and, to a lesser extent, mangiferin (xanthone), were the most labile compounds. Both compounds were thus identified as critical quality indicators to determine shelf-life. The stability-enhancing activity of the acids depended on the compound; ascorbic acid and citric acid enhanced the stability of HPDG and mangiferin, respectively. However, when considering all the major phenolic compounds, the base solution without acids was the most stable. This was also observed for the color and major volatile aroma-active compounds [α-terpineol, (E)-ß-damascenone, 1-p-menthen-9-al and trans-ocimenol]. CONCLUSION: The addition of acids, added for stability and taste in ready-to-drink iced tea beverages, could thus have unwanted consequences in that they could accelerate compositional changes and shorten the shelf-life of polyphenol-rich herbal tea beverages. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

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-ß-d-glucopyranosyl-3-hydroxyphloretin (2), 3',5'-di-ß-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.

Electrospraying as a suitable method for nanoencapsulation of the hydrophilic bioactive dihydrochalcone, aspalathin.

The bioactive hydrophilic dihydrochalcone, aspalathin, has poor stability and bioavailability hampering its use in functional food ingredients with standardised aspalathin content. The aim of the study was to produce nanoparticles with controlled release to overcome these obstacles. Nanoencapsulation was investigated using both natural (chitosan and lecithin) and synthetic (poly(lactide-co-glycolide) and Eudragit S100® (ES100)) polymers by suitable conventional methods and electrospraying for all polymers. All polymer-method combinations produced particles smaller than 1.1 µm. Electrospraying produced more favourable results than conventional methods for the synthetic polymers, resulting in spherical particles with higher (p < 0.05) encapsulation efficiencies (>50%) and loading capacities (>10%). Opposite trends were observed for natural polymers. An in vitro release study revealed biphasic aspalathin release profiles at pH 7.4 with ES100 electrosprayed nanoparticles having the slowest (p < 0.05) release rate (1.67 h-1). Overall, ES100 electrosprayed nanoparticles showed the most favourable combination of parameters.