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 arguably one of the most important organoleptic features of food, as it contributes to visual appeal to the consumer, and serves as a gauge of ripeness, freshness, and potential for full flavor. In the current clean label-focused marketplace, where discerning consumers try to avoid artificial or synthetic ingredients, the presence of visually-attractive natural anthocyanins in foods offers a market advantage. 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.

Anthocyanin-rich food is associated with protection against cardiovascular disease, thrombosis, diabetes, cancer, microbial-based disorders, neurological disorders, and vision ailments. However, the real health value of anthocyanin pigments, whether as natural colorants or functional ingredients, 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:

The review addresses anthocyanin properties in food processing and digestion, anthocyanin–protein complexes used in food matrices, and changes in the bioaccessibility and bioavailability of anthocyanins when bound with various plant or animal protein carriers to create anthocyanin–protein complexes in foods. Current evidence suggests that anthocyanin bioavailability may be far greater than initially assumed, particularly due to the role of the gut microbiome in anthocyanin catabolism and release of active phenolic metabolites. Protein binding to anthocyanins has been reported to enhance bioactivity, bioaccessibility, and bioavailability compared to anthocyanins delivered without a protein carrier.

Data Summary:

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, indicative of low bioavailability. Innovative food processing/encapsulation technologies have attempted to improve stabilization of anthocyanin molecules in the gastrointestinal tract to allow intact delivery for colonic uptake.

Conclusions:

The review concludes that protein-binding approaches are a promising strategy to improve the bioaccessibility and bioavailability of anthocyanins. The authors finally summarize the challenges and prospects of this delivery system for anthocyanin pigments.

Practical Significance:

Real-world applications include the use of anthocyanins as natural colorants in processed food products such as beverages, confections, dairy, and bakery goods, where they offer a market advantage in the clean-label marketplace. Additionally, anthocyanin-rich foods provide health benefits associated with protection against cardiovascular disease, diabetes, cancer, and other disorders, making protein-bound anthocyanin complexes valuable for functional food development.