5. FoodIndustrial Products (Testing)

Exercise 5.1

• (a) What is the difference between unprocessed and processed foods?• unprocessed – no cooking, cleaning/cutting only• raw meats• fresh fruit & vegetables• (b) What should unprocessed foods be tested for?• freshness• contaminants (especially by organisms – moulds, insects)• (c) Is there anything else that processed foods should be tested for?• additive levels• required physical properties• (d) Are all food product types tested before consumption?• yes, but unprocessed foods only get visual inspection

Shelf life

Exercise 5.2(a) less tasty• baked products, e.g. bread, biscuits

(b) unsafe• raw meat• dairy products

• baked-for date – a date not later than 12 hours after the time the bread was baked

• baked-on date – the date on which the bread was baked• best-before date – will retain any specific qualities • use-by date – not safe afterwards

Water

CLASS EXERCISE 5.3Why is it necessary to test for water?• measure of freshness/processing

CLASS EXERCISE 5.4What are the limitations of the oven drying method?• not good for samples with:• high viscosity (eg honey)• high levels of other volatiles (eg essences)• low water content

CLASS EXERCISE 5.5(a) bread (b) honey(c) olive oil(d) vanilla essence

ovenKF, D&SKF

GC

Triglycerides and other lipids

• major component of fats in food

Exercise 5.6What is the structure of a typical triglyceride?

Analysis of fats

• total – solvent extraction (Soxhlet extractor)

• individual triglycerides can’t be analysed• too many different types• too similar to each other for chrom. separation

• to obtain a "fat profile" by the Fatty Acid Methyl Ester Method (FAME)1. hydrolysis of the triglycerides in methanolic KOH to produce the fatty

acid salts2. conversion of the fatty acids to their corresponding methyl esters using

methanol and the catalyst BF3

3. analysis of the esters by GC

CLASS EXERCISE 5.7(a) Write the equations for steps 1 & 2. (b) Explain why this gets around the problem described for the triglycerides.• fatty acid methyl esters differ by FW• only 10-20 of them

Simpler QC tests

• saponification value => average chain length• hydrolysis of the triglycerides under reflux with a known amount of KOH• excess KOH is back-titrated with standardised HCl• SV is the mass of KOH in mg that reacts with 1 g of food• shorter chains mean more triglyceride molecules per gram, therefore more

reaction with KOH

• iodine value => degree of unsaturation• reaction of the triglycerides with iodine monochloride (Wij’s reagent) in the

dark for 1 hour• C=C undergoes an addition reaction with the ICl• excess ICl is then back-titrated with standardised sodium thiosulfate• IN is the mass of iodine that reacts with 100 g of sample• more C=C => more reaction

Proteins

CLASS EXERCISE 5.8What is the structure of a typical protein?

NHNH

NH

O R1

O R2

O

Kjeldahl N analysis

• oxidation of the sample in hot concentrated sulfuric acid • converts the bound nitrogen into ammonium ions• addition of strong base to the solution converts the ammonium ions to

ammonia gas• collected by distillation• in a known volume of standard acid, then back titrated or • in a solution of excess unstandardised boric acid• borate ion produced is a stronger base than ammonia and is titrated with

standardised acid

• 1 mole of N gives 1 mole NH3

• amount N related to amount of protein by factor which is the proportion of N in typical protein of given material, eg flour, milk

Exercise 5.9/10

Calculate the %N & %protein in a sample of meat if 1.0589 g of sample, after the Kjeldahl procedure, gave a titre of 15.8 mL of 0.103 M HCl. FW of N is 14. Protein factor is 6.25.

• moles HCl = 15.8 x 10-3 x 0.103 = 1.63 x 10-3 = moles NH3 = moles N• mass N = 1.63 x 10-3 x 14 = 0.0228g• %N = 0.0228 x 100 ÷ 1.0589 = 2.15%• %protein = 2.15 x 6.25 = 13.4%

• Read remainder of chapter yourself