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Stability of flavonoids in grape seed and grape marc meal extract (GSGME)
Introduction
A secure food supply is crucial to all consumers. The use of a plant derived component poses a challenge for quality control: environmental factors lead to variations of plant composition, regarding the desired active substances, during the growth period. After harvest the active component should stay stable.
The following study investigates the processing and storage stability of plant derived components, using the example of plant derived flavonoids in GSGME (Anta®OxE, Dr. Eckel GmbH, Niederzissen, Germany). Flavonoids have shown anti-inflammatory properties and are effective for animal nutrition (Gessner et al., 2013; Fiesel et al., 2013).
Material
The stability of flavonoids in GSGME was studied under common processing conditions with different stressors: time of storage (9 months), standard packaging material and temperature stress to simulate manufacturing processes. Flavonoid content was analysed using the Folin-Ciocalteu-method (Waterhouse, 2003). It was decided to compare storage characteristics in bags which were shut and sewn or open, stored under cool to room temperature (22°C) conditions. Each measurement was taken in triplicate. The samples, with an initial flavonoid concentration of about 86g/kg ±0.9g/kg, were analysed every three months. To rule out light as a potential influence, some samples were stored in daylight and some in darkness. Heat stability of flavonoids was tested in a cabinet dryer (Heraeus) at different temperatures, ranging from room temperature to 140°C for four hours.
Results
In the present study, the analysis of the flavonoid content after three months of storage showed a higher concentration (up to 156g/kg ±1.6g/kg) than before. This increase in flavonoid concentration may be caused by isomerisation. We found no influence of sealing and packaging on flavonoid activity. For the samples stored under daylight conditions, we analysed an increase in flavonoid content of maximum 25% compared to the other groups after 9 months.
For temperatures of 50°C, 75°C and 100°C, the samples showed flavonoid contents above the initial concentration of 86g/kg ±0.9g/kg. At 120°C and 140°C, the flavonoid content decreased to 70-82g/kg.
Conclusion
The study showed that both storage up to nine months or temperatures up to 120°C did not lead to a reduction of the initial concentration of flavonoids in GSGME. It even had a positive influence on concentrations. The results indicate that GSGME can be used without any concern with regard to flavonoids. Further studies should be conducted to explain the increase of flavonoids during storage and which molecules are modified during that time.
Keywords: flavonoids, stability, Anta®OxE