Blueberry polyphenols as natural antimicrobial agents against foodborne viruses: Towards understanding their mechanism and applications in food systems

Foodborne viruses are recognized as public health concerns worldwide and therefore effective strategies to control their spread are being researched. Blueberries are known for their health benefits and antimicrobial properties. This study aimed to (1) determine the antiviral effects of blueberry juice (BJ) and blueberry proanthocyanidins (B-PAC) against the infectivity of hepatitis A virus (HAV), Aichi virus (AiV) and human norovirus surrogates (feline calicivirus (FCV-F9) and murine norovirus (MNV-1)) at 37^oC over 24-h using standard plaque assays; (2) evaluate antiviral effects in model foods (apple juice (AJ) and 2% milk) and simulated gastrointestinal conditions at 37^oC; and (3) determine the mechanism of action of B-PAC by comparing activity of monomeric catechins, procyanidin B2, B-type PAC from blueberries (B-PAC) and A-type PAC from cranberries (C-PAC), effects on viral structure using transmission electron microscopy, and on adsorption and replication. FCV-F9, MNV-1, HAV and AiV titers were reduced to undetectable levels after 5 min, 3-h, 30 min and 3-h with 1, 1, 2, and 5 mg/ml B-PAC, respectively. BJ reduced FCV-F9, MNV-1, AiV to undetectable levels and HAV by ~2 log PFU/ml after 3, 6, 24 and 24-h, respectively. All tested viruses were reduced to undetectable levels within 15 min with B-PAC (1, 2 and 5 mg/ml) in AJ (pH 3.6). B-PAC effects decreased in milk, where FCV-F9, MNV-1, HAV and AiV were reduced by ~1 log PFU/ml with 5 mg/ml after 24-h. B-PAC at 5 mg/ml in simulated intestinal fluid reduced all tested viruses to undetectable levels within 30 min. Monomeric catechins and procyanidin B2 were less effective than the polymeric B-PAC. Time of addition assays indicated that B-PAC had modest effects in preventing viral adsorption, with no significant effect on viral replication. TEM observations revealed moderate effects on virus structure with either damaged viral capsid or virus binding to B-PAC, possibly preventing virus attachment to host cells. Overall, this study demonstrated the ability of BJ and B-PAC to reduce viral titers in model food systems and under simulated gastric conditions, suggesting their potential as preventive and therapeutic options against foodborne viral illnesses.