Integrated Assignment 02
Quality control in food processing
The subject of this assignment is any pickle, consisting of a thick sauce containing chunks of vegetables.
Students should already have experience of following some of the standard procedures listed. In particular they should have the skills necessary to prepare a solution of known concentration by dilution, and carry out a titration accurately. They should also have some previous experience of using aseptic techniques and handling micro-organisms.
Depending on the time available, this could be tackled with individuals or pairs of students working through the whole assignment. Alternatively a group of students could share the tasks so that different students developed different tests. The group could come together at the end to draw up their chosen quality control instructions and standards.
Practical tips
- The ripeness of fruit could be tested using a system similar to part 2 (compressibility) of SP 0012:2005 Methods of testing strengths of materials. A ‘squashability’ requirement could be set for each type of fruit tested. Or a system as shown in the ITDG document (see Further information) could be set up to test the impact resistance of the fruit, and a limit set.
- The crispness of the vegetables could be measured with a similar adaptation of SP 0012:2005 but this time setting opposite limits. Where ripe fruit needed to be soft and squashable, the vegetables need to be firm and unsquashable, and snap cleanly.
- The vinegar titration should be straightforward. Several different brands should be available to test. Most vinegars are in the region of 4-5% ethanoic acid. It is important for the preservation process that the concentration of vinegar in the final product is sufficient, so dilute batches of vinegar would be a problem for the manufacturer.
- The micro-organism count should be low, even after storage at room temperature. Students should be encouraged to think of ways of providing standard conditions for storage tests so that results can be compared. The intention of the test is to find out how well the pickle keeps even when it is exposed to micro-organisms from the air (but conditions should be devised so that contamination by flies or other animals is avoided).
Health and safety note
Some students may think that biting food samples is a sensible way to test softness / crispness. They should be reminded that putting anything in their mouth in a laboratory is neither sensible nor permissible.
Solid sodium hydroxide, and solutions above 1 mol dm-3, are corrosive. A 0.1 mol dm-3 solution is mildly irritant. It is not advisable for students to handle solid sodium hydroxide, but they can prepare their 0.1 mol dm-3 solution by accurately diluting standard 1.0 mol dm-3.
Apparatus and reagents
- Standard Procedures: o SP 0003:2005 A method for counting micro-organisms in dairy products
- SP 0007:2005 Method for preparing a titration reagent
- SP 0008:2005 Method for determining the salt content of butter
- SP 0012:2005 Methods of testing strengths of materials
For testing fruit and vegetables:
- impact testing apparatus from SP 0012-2
(adapted as required by students for testing ‘squashability’) - selection of tomatoes, apples, carrots and cucumbers
(with varying degrees of ripeness / softness / crispness)
For titrating vinegar
- 250 c3 volumetric flask
- 25 cm-3 pipette and pipette filler
- 50 cm3 burette
- 250 cm3 conical flask
- phenolphthalein indicator solution
- 0.100 mol dm-3 solution of sodium hydroxide
Caution: corrosive
For testing keeping quality
- sterile apparatus:
- 15 cm3 (1 tbsp) measuring spoon
- sample bottle
- rack of 5 test tubes plugged with cotton wool
- 10 cm3 graduated pipette and filler, or syringe
- 1 cm3graduated pipette, or syringe
- fine dropper (to deliver about 50 drops per cm3)
- Petri dish of nutrient agar
- marker pen to write on glass
- 5 cm3 or 10 cm3measuring cylinder
- adhesive tape
- incubator set at 30 ± 1oC
- sterile saline-peptone solution (0.1% peptone, 0.85% NaCl)
(available commercially as ‘Oxoid’ MRD [Maximum Recovery Diluent] CM0733)