Formal Food Analysis Laboratory Report
February 7, 2013
By Carla Reed
Lab partner: Nina Jung
Total Phenolic Content of Grape Juice using Visible Spectrophotometry Abstract
The health benefits of red wine are well known and consumption has been encouraged more over the years because of the populations increasing obesity rates and the inherent complications thereof; including coronary heart disease and high blood pressure. Since the phenolic compounds in wine combats these negative effects and originate from the grape itself the focus of this study was the total phenolic content in red and white grape juice; measured in gallic acid equivalents (GAE). This entire lab class found 105mg GAE per 100 milliliters of phenolic compounds in white grape juice and 226 mg GAE per 100 milliliters in red grape juice. The variance in the values is to be expected since different components of the grape are retained or discarded during white grape and red grape processing procedures. Introduction
The data base of nutritional information has grown exponentially in the last decade and with it the population’s knowledge of what a beneficial diet encompasses. It is a well researched topic that heart disease is linked to the excessive consumption of dietary fat and cholesterol. Hectic lifestyles and the abundance of convenient high fat foods are contributing to health issues facing Americans today including complications due to obesity. A study preformed in the early 1990’s found that in some regions of France, despite their higher intake levels of saturated fat, the incidence of coronary heart disease remains low1. Frankel’s study correlated moderate red wine consumption with lower occurrences of coronary heart disease1. More specifically, he attributed the inhibition of oxidizing human low density lipoproteins (LDL) to the phenolic compounds and antioxidant properties found in red wine1. Since that time more research has been compiled and it is now widely accepted and promoted to drink a glass of wine each day to take advantage of its powerful antioxidant properties. The benefits of consuming alcohol moderately include short-term lowering of blood pressure and reducing platelet aggregation in blood vessels2. When combined with the additional benefits of the polyphenols contained in grapes it is thought to reduce susceptibility to vascular damage, decrease the activity of a particular hormone that causes blood vessel constriction (angiotensin), and increase the production of nitric oxide; a vasodilator hormone that signals to the surrounding smooth muscle tissue to relax2. The polyphenolic antioxidants present in red wine provide cardiovascular protection by their ability to function in the tissues as antioxidants while alcohol by itself imparts cardiovascular protection by adapting the heart to oxidative stress3. The natural phenols in grapes are mostly contained in the pulp, skin, and seeds. There are varying degrees of the different phenols in each component. Red wines will have higher concentration in the phenols from the skin and seeds because they are fermented along with the juice before being separated4. The phenols in white wine come mostly from the pulp and contain a lower concentration of phenolic content than in red wines4. The most abundant derivative of hydrobenzoic acid found in wine, both red and white, is gallic acid5. This is because it originates from the grape itself and it is also formed by the hydrolysis of condensed tannins5. The levels of gallic acid concentration vary with grape variety and growing conditions5, and will be passed on, if not increased during the process of fermenting the juice into wine. Since gallic acid is the most abundant phenolic acid in grape juice, it is used as a standard by which the total phenolic content of a juice or wine sample is measured. The antioxidant potential in grape juice, while not as...