How to Carry Out Acidity Analysis on Food and Drinks

 

ACIDITY

The acidity of a substance is the amount of hydrogen ion (H+) or hydroxonium ion (H3O+) concentration in the substance.

Acidic foods and drinks can have several negative health effects when consumed in excess. It can be difficult to avoid acidic foodstuffs in our diets, ranging from salad dressing, soda to fruit juices typically have high acidity in addition to eating acidic foods. The acidity of the body fluid can also be increased by eating meat products, low consumption of fruit and vegetable. EFFECTS OF HIGH ACIDITY

(i)                 Bone thinning: Consumption of acidic diets  can lead to decrease in bone density

(ii)               Stomach pain: Acidic foods and drinks can cause stomach irritation. In high concentration can lead to denaturation of proteins in the stomach wall leading to soreness of the stomach, which can lead to ULCER

(iii)             Dental erosion: Excess acid in the system can lead to teeth erosion. This can occur due to excessive consumption of fruit juices.

AIM: To determine the total acidity of food.

Principle: The reaction between an acid and a base is term Neutralization. Hence using sodium hydroxide (NaOH) as our base we can neutralize all the acids present in a sample by simple titration. Most acids in food samples are organic acids which are generally weak in strength thus we use Phenolphthalein as our indicator.

Equations

HOOCCH2COOH + 2NaOH--- Na+O-OCCH2COO-Na+ + 2H2O

Malic acid                                     Disodium Malate

HOOCCH (OH) CH (OH) COOH + 2NaOH --- Na+O-OCCH(OH)CH(OH)COO-Na+ + 2H₂O

Tartaric acid                                                          Disodium Tartarate

APPARATUS: conical flask, spatula, burette, retort stand.

REAGENT: 0.1M NaOH, 1% Phenolphthalein (indicator)

For Solid Samples

PROCEDURE: 2g of the sample is weighed into a conical flask, 50ml of distilled water is added and then 2-3 drops of 1% phenolphthalein as indicator. The setup is titrated against 0.1M NaOH in the Burette until pink colour appears.

For Liquid Samples

Procedure: 10ml of the liquid sample is measured into a Cornical flask, 2-3 drops of 1% phenolphthalein were added and titrated against 0.1M NaOH in the Burette until a pink colouration appears.

CALCULATION:

Percentage Acidity =  TV× standard (0.009)  ×  100%

                                    Volume of sample taken

Exampled RESULT

Volume taken = 10ml

Titre value= 6ml

Therefore

Percentage Acidity= 6*0.009     *  100  = 0.54%

                                    10

Hence sample passed because it contain wheat

 

LIMITS: 0.5% maximum for ice cream, 0.5% for baker’s fat, 1% garri, Wheat 1%, 0.5% maximum for sweets, fruit and fruit juices, honey and refined granulated sugar.