Decreasing pH results in a reduction of anthocyanin coprecipitation during cold stabilization of purple grape juice.

David Manns,Passaporn Siricururatana,Gavin Sacks,Olga Padilla-Zakour

doi:10.3390/molecules20010556

David Manns, Passaporn Siricururatana + Show 2 more

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https://doi.org/10.3390/molecules20010556

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Abstract

Anthocyanin pigments in grape juice can coprecipitate with potassium bitartrate (KHT) crystals during cold stabilization, but factors that reduce these adsorptive losses are not well understood. We hypothesized that coprecipitation on a % w/w basis should be decreased at lower pH. In initial experiments, model juice solutions containing an anthocyanin monoglucoside extract and varying pH values were subjected to cold-storage to induce KHT crystallization, and anthocyanins in the resulting precipitant were characterized by HPLC. The pH of the model juice was directly correlated with the % w/w concentration of anthocyanins in the KHT crystals, with a maximum observed at pH 3.40 (0.20% w/w) and a minimum at pH 2.35 (0.01% w/w). A pH dependency was also observed for anthocyanin-KHT coprecipitation in purple Concord grape juice, although the effect was smaller. Coprecipitation was significantly greater for anthocyanin monoglucosides and acylated anthocyanins as compared to anthocyanin diglucosides at pH > 3.05, but coprecipitation of mono- and acylated forms declined more sharply at lower pH values.

Highlights

While a wide range of phenolic compounds have been detected in juices from Concord grape juices and related grape cultivars, including hydroxycinnamates, flavan-3-ols, flavonols, and stilbenes [1,2], the major species are the anthocyanins [1]
The current study investigated the effects of pH on coprecipitation of anthocyanins with KHT, in both a model juice system and a purple Concord grape juice
As an initial evaluation of this hypothesis, a model juice containing a blackcurrant anthocyanin extract was prepared with potassium (0.02–0.04 M) and tartaric acid (0.02–0.04 M) concentrations within the range ordinarily encountered in grape juice: 0.01–0.06 M for potassium [14,15] and 0.01–0.07 M for tartaric acid [13]

Summary

Introduction

While a wide range of phenolic compounds have been detected in juices from Concord grape juices and related grape cultivars, including hydroxycinnamates, flavan-3-ols, flavonols, and stilbenes (e.g., resveratrol) [1,2], the major species are the anthocyanins [1] These anthocyanins are the major compounds responsible for the pigmentation of red and purple grapes and are critical to consumer acceptance of grape-derived products like juices and wines [3]. The anthocyanins along with other polyphenols and their metabolites have been implicated as important phytonutrients capable of reducing the incidence of chronic disease [4,5] Due to their overall importance to the acceptability of fruit juices and related products, several publications have considered the impact of production practices on anthocyanin stability, acid-catalyzed hydrolysis and polymerization reactions [6,7,8]. To prevent formation of KHT crystals in finished products, a cold-stabilization step is usually performed on grape juices and wines prior to bottling [18]

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