The interactions between anthocyanin and whey protein: A review

Anthocyanins (ACN) are natural pigments that produce bright red, blue, and purple colors in plants and can be used to color food products. However, ACN sensitivity to different factors limits their applications in the food industry. Whey protein (WP), a functional nutritional additive, has been shown to interact with ACN and improve the color, stability, antioxidant capacity, bioavailability, and other functional properties of the ACN-WP complex. The WP's secondary structure is expected to unfold due to heat treatment, which may increase its binding affinity with ACN. Different ACN structures will also have different binding affinity with WP and their interaction mechanism may also be different. Circular dichroism (CD) spectroscopy and Fourier transform infrared (FTIR) spectroscopy show that the WP secondary structure changes after binding with ACN. Fluorescence spectroscopy shows that the WP maximum fluorescence emission wavelength shifts, and the fluorescence intensity decreases after interaction with ACN. Moreover, thermodynamic analysis suggests that the ACN-WP binding forces are mainly hydrophobic interactions, although there is also evidence of electrostatic interactions and hydrogen bonding between ACN and WP. In this review, we summarize the information available on ACN-WP interactions under different conditions and discuss the impact of different ACN chemical structures and of WP conformation changes on the affinity between ACN and WP. This summary helps improve our understanding of WP protection of ACN against color degradation, thus providing new tools to improve ACN color stability and expanding the applications of ACN and WP in the food and pharmacy industries.

Background:

Color is an important characteristic of food, and over the last 15 years, more attention has been paid to natural colorants because of the rising demand for clean-label food products. Anthocyanins, which are a group of phytochemicals responsible for the purple, blue or red hues of many plants, offer a market advantage. In addition, anthocyanin-rich foods are associated with protection against cardiovascular disease, thrombosis, diabetes, cancer, microbial-based disorders, neurological disorders, and vision ailments. However, the real health value of anthocyanins, whether as a natural colorant or a functional ingredient, is dependent on the ultimate bioaccessibility and bioavailability in the human body. Many animal and human clinical studies revealed that, after intake of anthocyanin-rich foods or anthocyanin extracts, only trace amounts (< 1% of ingested content) of anthocyanins or their predicted metabolites were detected in plasma after a standard blood draw, which was indicative of low bioavailability of anthocyanins. Protein binding to anthocyanins is a strategy that has recently been reported to enhance the ultimate bioactivity, bioaccessibility, and bioavailability of anthocyanins as compared to anthocyanins delivered without a protein carrier.

Methods:

N/A - Review article.

Results:

Key findings from the reviewed literature indicate that only trace amounts (< 1% of ingested content) of anthocyanins or their predicted metabolites are detected in plasma after intake, demonstrating low bioavailability. In contrast, protein binding to anthocyanins has been reported to enhance the ultimate bioactivity, bioaccessibility, and bioavailability of anthocyanins compared to delivery without a protein carrier. The review addresses anthocyanin properties in food processing and digestion, anthocyanin–protein complexes used in food matrices, and changes in bioaccessibility and bioavailability when anthocyanins are bound with various plant or animal protein carriers.

Data Summary:

Quantitative evidence from many animal and human clinical studies shows that less than 1% of ingested anthocyanins or their predicted metabolites are detected in plasma after a standard blood draw, indicating low bioavailability. No additional quantitative results were provided in the excerpt.

Conclusions:

The review concludes that protein binding is a promising strategy to improve the bioaccessibility and bioavailability of anthocyanins, though challenges remain. Current evidence suggests that anthocyanin bioavailability may be far greater than initially assumed, and innovative food processing/encapsulation technologies, including protein binding, aim to improve stabilization in the gastrointestinal tract. The review summarizes challenges and prospects of this delivery system for anthocyanin pigments.

Practical Significance:

By using functional fruit- or vegetable-derived anthocyanins extracted from traceable natural sources as ingredients to naturally offset color lost in processed food products (including beverages, confections, dairy, and bakery goods), potential consumer backlash against artificial colorants is mitigated. The “health halo” associated with anthocyanins offers additional market advantage, and protein-binding approaches can enhance the real health value of these pigments by improving their bioaccessibility and bioavailability in food applications.