Regulation on the quality of yogurt by phenolic fraction of mulberry pomace supplemented before and after fermentation

The effects of phenolic fraction of mulberry pomace on yogurt quality were investigated. Polyphenol-enriched extract of mulberry pomace (MPPE), rich in phenols, anthocyanins and proanthocyanidins, was incorporated to yogurt before and after fermentation at 0.50%, 0.75%, 1.00% and 1.25% (w/v), respectively. The addition either before or after fermentation decreased L* and b* values, increased a* value, reduced syneresis and changed textural properties. MPPE added before fermentation inhibited lactic acid bacteria (LAB) growth, increased particle size, inhibited protein hydrolysis and active peptide release, and reduced ACE-I activity of yogurt. When added after fermentation, MPPE at moderate levels (within 1.00%) promoted LAB growth, reduced pH value and increased total acid content, decreased particle size, promoted protein hydrolysis and active peptide release, and increased ACE-I activity. Phenolics in mulberry pomace exert unique effects on the physicochemical and textural properties of yogurt and adding MPPE after fermentation was more beneficial to improve yogurt quality.