Application of a Rapid and Simple Technological Process to Increase Levels and Bioccessibility of Free Phenolic Compounds in Annurca Apple Nutraceutical Product

Insoluble bound polyphenols (ISBP) are polyphenolic compounds linked to the food matrix with different interactions limiting both their water extractability and consequent bioaccessibility. The health-promoting potential of polyphenols is historically known and well-demonstrated; specifically, Annurca apple polyphenols were studied both in vitro and in vivo for their effect in controlling cholesterol plasma levels. The aim of the study was the preparation of nutraceutical products based on Annurca apple polyphenolic fraction through the application of a technological process (acid treatment) able to release the ISBP from Annurca apple food matrix and increase polyphenol bioaccessibility. Lyophilized annurca apple (LAA) underwent acid treatment (ATLAA), and differences in released polyphenol levels were analysed by DAD-HPLC. Free-polyphenol levels in samples treated under acid conditions were higher than in untreated ones; in particular, for oligomeric flavan-3-ols (+168% procyanidin B2, +42.97% procyanidin B1 and B2, +156.99% procyanidin C1), catechin (+512.20%), and gallic acid (+707.77%). Furthermore, ATLAA underwent an in vitro gastrointestinal digestion to evaluate the bioaccessibility of contained polyphenols, in comparison to the untreated Annurca apple. The bioaccessibility study indicates a valuable preservation of polyphenolic fraction compared to the control.