Vitamins and food product shelflife

As the tendency to include nutritional information on the labels of food products has increased, so have the liabilities of the manufacturers. For many, if not most, foods the inclusion of nutrition information is optional but any statements made on the label come under the force of law. A company making an inaccurate voluntary nutritional declaration can be subject to prosecution. Within a nutritional information statement, vitamins are the main category of declared nutrients where the quantities can significantly decrease during the shelf life of the food. The vitamin content of processed foods can decrease during storage and it has already been pointed out that losses of vitamin C can occur in frozen vegetables stored at -23°C (page 259).

If declarations of vitamin levels are required on the label, whether voluntary or statutory, the manufacturer needs to carry out suitable stability trials to deter mine the stability of each vitamin claimed on the label over the duration of the declared shelf life. The actual procedures used for the study will depend on the composition of the food, the processing and the form in which it is presented and stored. The type of packaging can have a significant effect on vitamin stability and the quality of the barriers to oxygen, moisture and light is very important. A requirement for label claims for vitamins can influence the selection of the form of packaging. The need to retain the vitamins often means that a compromise has to be achieved between the length of required shelf life and the barrier quality of the packaging.

Due to the wide variety of products, processes and packaging, it is not possible to give specific procedures for the determination of the shelf life of vitamins in a food. However, guidelines have been established for the determinations and predictions of shelf life.20 The determination of the vitamin levels at each stage of the shelf life study should be built into the protocol. As the degradation of most of the vitamins follow 'first order' or 'zero order' kinetics, it is possible for shelf life predictions to be made using a classical Arrhenius model on the assumptions that the model holds for all the reactions being studied; that the same reaction mechanism occurs throughout the temperature range of the study; that the energy of activation is between 10 and 20kcal/mole and that the effects of moisture at ambient temperature are equivalent to maintaining the same relative humidity at the higher temperatures.18

Where it is possible to add vitamins to a food either to restore losses during processing or to fortify the food, it is common practice to add an amount above the label claims to compensate for losses during storage. This additional amount is called an overage and is normally quoted as a percentage of the claimed level. For example, if a label claim is made for 60 mg/serving of vitamin C and it is determined that a 10% overage is required to achieve a stored shelf life of one year, the input of vitamin C would be 110% of label claim, or 66mg/serving. The amount of overage added should be reasonable and well within any safety concerns for the vitamin.

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