Analysis and Identification of Major Organic Acids in Wine and Fruit Juices by Paper Chromatography

Abstract

A simple and inexpensive paper chromatography experiment that separates and identifies major organic acids in wine and fruit juices has been developed for introductory organic undergraduate students to teach the basics of chromatography. This experiment reinforces several concepts for students such as compound separation via extraction and chromatography, intermolecular forces and acidity, and a comparison of organic acid polarities related to structure. In addition, the separation of acids within wine and/or fruit juices enhances student understanding of real-world organic acids present in foods. Citric, malic, tartaric, and lactic acids, all potential components of fruit juices and wine samples, are the focus of this experiment that includes a description of the malolactic fermentation occurring in wine samples. A mobile phase mixture of n-butanol, formic acid, acetone, and ethanol along with bromocresol green indicator allows for fast separation and visualization of the acids of interest. Retention factor calculation and identification of acid types present in selected samples encourage student understanding of overall acidity and the relationship of pK a values to acid structure. This analysis helped students understand the impact of intermolecular forces, pH, and the application of paper chromatography in real-world situations.

From Soybeans to Tofu: The Underlying Chemistry

“…This neutralization decreases the electrostatic repulsion between protein molecules, which results in intermolecular aggregation through either hydrophobic interactions or short-range interactions. Organic acids such as tartaric acid and malic acid, which are present in grapes (the most abundant constituents in grape), , citric acid, and malic acid (found in oranges and lemons, respectively) have also been used as acid coagulants. The addition of grape, orange, and lemon juice in soymilk coagulates the protein, as shown in Figure E–G.…”

Research and Service Learning in a Garden of Chemistry

“…Simple extraction procedures using green and affordable solvents make this type of project accessible to students with a wide range of lab skills and backgrounds. Different instrumentation, such as thin layer chromatography, liquid chromatography, gel electrophoresis, or fluorescence spectrophotometry could be used to analyze plant extracts, depending on compounds of interest. − Without a mass spectrometer, positive identification of extract components will be limited, but antioxidant activity can be evaluated, and classes of compounds can be quantified. For those interested in antioxidant-rich plants, further activity assays could be conducted using commercial kits .…”

Color, Candy, and Chromatography: A Combined TLC and HPLC Activity for the General Chemistry Laboratory

“…Prior to the introduction of HPLC, students gain understanding of the principles of chromatography, polarity, and separation through carrying out hands-on activities with thin layer chromatography (TLC), which is more commonly seen not only in general chemistry laboratories but throughout the wider curriculum, 23−28 with examples of past work looking specifically at analysis of real world systems including plant pigments, 29,30 spices, 31 and organic acids in beverages. 32 making TLC an ideal introduction for HPLC as part of an effort designed to prevent students simply seeing the HPLC as a black box. In addition, the use of a common material (food dyes) for both the TLC and HPLC experiments serves to strengthen the connections between the two techniques.…”