The effects of six phenolic acids and tannic acid on colour stability and the anthocyanin content of mulberry juice during refrigerated storage

Formation of vinylphenolic pyranoanthocyanins by selected indigenous yeasts displaying high hydroxycinnamate decarboxylase activity during mulberry wine fermentation and aging

The color of mulberry wine is difficult to maintain since the main chromogenic substances, anthocyanins, are severely degraded during fermentation and aging. This study selected Saccharomyces cerevisiae I34 and Wickerhamomyces anomalus D6, both displaying high hydroxycinnamate decarboxylase (HCDC) activity (78.49% and 78.71%), to enhance the formation of stable vinylphenolic pyranoanthocyanins (VPAs) pigments during mulberry wine fermentation. The HCDC activity of 84 different strains from eight regions in China was primarily screened via the deep well plate micro fermentation method, after which the tolerance and brewing characteristics were evaluated via simulated mulberry juice. The two selected strains and a commercial Saccharomyces cerevisiae were then inoculated individually or sequentially into the fresh mulberry juice, while the anthocyanin precursors and VPAs were identified and quantified via UHPLC-ESI/MS. The results showed that the HCDC-active strains facilitated the synthesis of stable pigments, cyanidin-3-O-glucoside-4-vinylcatechol (VPC3G), and cyanidin-3-O-rutinoside-4-vinylcatechol (VPC3R), highlighting its potential for enhancing color stability.

Effects of organic acids on color intensification, thermodynamics, and copigmentation interactions with anthocyanins

Anthocyanins are attractive alternatives to synthetic colorants, but their low stability impedes practical applications. Intermolecular copigmentation can enhance both color intensity and stability. Herein, the copigmentation interactions of Kyoho grape skin anthocyanins (KSA) or cyanidin-3-O-glucoside (Cy-G) with organic acids were investigated. Color enhancement was evaluated at different acid molar ratios and treatment temperatures. The optimal copigmentation effects were observed for KSA/tannic acid (1:150) and Cy-G/tannic acid (1:100). Based on enthalpy variation, KSA/ferulic acid and Cy-G/ferulic acid exhibited the highest stability. The distinct color differences observed in the presence of different acids were attributed to structural effects. The influence of ferulic acid on various anthocyanins was also evaluated using theoretical approaches. Owing to steric hindrance, the acyl groups in KSA affected the spatial conformation, hydrogen bonding, and van der Waals interactions of the complexes. Further, hydroxyl groups decreased complex stability. These findings contribute to furthering the understanding of copigmentation effects.

Effects of different antioxidants combined with high hydrostatic pressure on the color and anthocyanin retention of a blueberry juice blend during storage

Blueberry juice has been found to undergo severe browning after treatment and cold storage, such as processing by high hydrostatic pressure (HHP) at 550 MPa/10 min/25°C followed storage at 4°C for 4 days. This browning may be due to the degradation of anthocyanin (AC) in the berries. Therefore, in this study, gallic acid (GA), ferulic acid (FA), ascorbic acid (VC), citric acid (CA), tea polyphenol (TP) and α-tocopherol (VE) were compared to determine their ability to improve the stability of the AC in HHP-treated blueberry juice. The juice was combined with the six abovementioned antioxidants at different concentrations, then treated by HHP at 550 MPa/10 min/25°C and stored at 4°C for 20 days. Thereafter, the pH levels, degrees °Brix (°Bx), color parameters, total AC content and polyphenol oxidase (PPO) activity of the blueberry juice blend were measured and compared. Gallic acid at 2 g/L was found to be the most effective antioxidant to protect against AC degradation. After storage at 4°C for 20 days, the AC content of the juice with no added antioxidants had decreased by 62.27% with a PPO relative activity of 50.78%, while the AC content of juice supplemented with 2 g/L GA had decreased by 13.42% with a PPO relative activity of 28.13%. The results of this study, thus, suggest that GA can stabilize the structure of AC in blueberry juice and reduce PPO activity, which may be beneficial in guiding the production of blueberry juice with high AC retention.

Effects of Ultrasound Irradiation on the Co-Pigmentation of the Added Caffeic Acid and the Coloration of the Cabernet Sauvignon Wine during Storage

In this paper, experiments were conducted to investigate the effects of ultrasound irradiation on the co-pigmentation of caffeic acid added in wine and the coloration of wine during storage. The wine color, chroma, level of the monomeric, combined and polymerized anthocyanins and the concentrations of malvidin-3-O-glucoside and syringic acid in wines were determined by the high-performance liquid chromatography (HPLC), ultraviolet-visible spectroscopy, respectively. The results indicate that ultrasound irradiation could definitely affect the color characteristic of wine to a certain extent. Compared with the wine without addition of caffeic acid, the co-pigmentation effects of wine added with caffeic acid could be significantly promoted by ultrasound irradiation, such as the wine color, color density and the polymerized anthocyanins. Furthermore, ultrasound irradiation had a continuous effect on the co-pigmentation of caffeic acid and wine coloration with the extended storage time. In summary, ultrasound could significantly modify the color properties of wine by enhancing the co-pigmentation between caffeic acid and monomeric anthocyanins in the wine, resulting in the improvement of wine quality.

Functionalization of whey protein isolate fortified with blackcurrant concentrate by spray-drying and freeze-drying strategies

A solution of whey protein isolate was combined with blackcurrant concentrate via spray-drying and freeze-drying techniques separately to develop novel protein ingredients, (SWB and FWB). Chemical compositions, colour profiles, total anthocyanin content and encapsulation efficacy of the protein ingredients were evaluated. An in vitro digestion process was employed to observe the changes in total phenolic content, antioxidant activity, and predictive in vitro glycaemic response of the protein ingredients. The half maximal inhibitory concentration (IC₅₀) towards α-Amylase, and a molecular docking study on the interactions of α-Amylase with anthocyanins, were both performed to investigate the potential mechanisms of hypoglycaemic properties of these protein ingredients. The protein contents of SWB and FWB were 67.94 ± 0.47% and 68.16 ± 0.77%, respectively. Blackcurrant concentrate significantly (p < 0.001) changed the colour profiles of whey protein isolate. SWB obtained a higher total phenol content (3711.28 ± 4.36 μg/g), total anthocyanin content (85390.80 ± 162.81 μg/100 g), and greater encapsulation efficacy (99.64 ± 0.16%) than those of FWB (3413.03 ± 20.60 μg/g, 64230.24 ± 441.08 μg/100 g, and 95.43 ± 0.14%, respectively). Total phenolic content and antioxidant activities of SWB and FWB decreased after the in vitro digestion. The reducing sugar released during the in vitro digestion from SWB and FWB decreased compared with their corresponding controls (SWC and FWC). FWB (IC₅₀ = 73.46 μg/mL) exhibited stronger α-Amylase inhibitory activity than SWB (IC₅₀ = 81.46 μg/mL). Different anthocyanins differed from binding affinities to bind with the active sites of α-Amylase via formation of hydrogen bonds. This study suggested whey protein encapsulated-blackcurrant concentrate might be an innovative food product with improved nutritional profiles. Both spray- and freeze-drying are potential options to this encapsulation.

Comparison of Metabolome and Transcriptome of Flavonoid Biosynthesis Pathway in a Purple-Leaf Tea Germplasm Jinmingzao and a Green-Leaf Tea Germplasm Huangdan reveals Their Relationship with Genetic Mechanisms of Color Formation

Purple-leaf tea is a phenotype with unique color because of its high anthocyanin content. The special flavor of purple-leaf tea is highly different from that of green-leaf tea, and its main ingredient is also of economic value. To probe the genetic mechanism of the phenotypic characteristics of tea leaf color, we conducted widely targeted metabolic and transcriptomic profiling. The metabolites in the flavonoid biosynthetic pathway of purple- and green-leaf tea were compared, and results showed that phenolic compounds, including phenolic acids, flavonoids, and tannins, accumulated in purple-leaf tea. The high expression of genes related to flavonoid biosynthesis (e.g., PAL and LAR) exhibits the specific expression of biosynthesis and the accumulation of these metabolites. Our result also shows that two CsUFGTs were positively related to the accumulation of anthocyanin. Moreover, genes encoding transcription factors that regulate flavonoids were identified by coexpression analysis. These results may help to identify the metabolic factors that influence leaf color differentiation and provide reference for future research on leaf color biology and the genetic improvement of tea.