Effects of Processing on Nutritive Values of Foods
In this lesson you will learn about the effects of various preservation technologies on selected nutrients in foods. The effects of handling foods in processing plants, in retail stores, in the food service industry and in the home will be also discussed.
The goal of this lesson is to provide you with an appreciation of the fact that, nutrient loss may occur during any type of food preservation. However the losses are not always substantial and they occur whether food is preserved in a processing plant or in your home. More specifically, upon completion of this lesson you will be able:
- outline the main factors that affect the extent of nutrient loss as a result of processing
- distinguish between the benefits and drawbacks of food processing
- discuss the strategies that can be used to minimize the potential loss of nutritional value in processed foods
11.1 Effects of Preservation Practices on nutrient content of foods
One of the main objectives of food preservation is the prevention of normal spoilage of perishable foods with maximum retention of food quality which includes retention of aesthetic characteristics of the food as well as its nutritional properties. Spoiled or deteriorating food is not only unsafe to eat, but it will also lose its nutritional value. All food types inevitably deteriorate from the time they are made. Along with deterioration comes the loss of nutrients. The rate of deterioration and nutrient loss depends on several factors reviewed in Lesson 5, such as light, oxygen, temperature, pH, etc.
We often hear comments made that processed foods have all the "goodness" removed from them during processing. It is true that nutrients are lost during the processing of foods that extends their storage life, whether that processing occurs at home or manufacturing plant. However, it is important to note that the extent of nutrient loss depends on the particular nutrient and the conditions of processing. Although food processing and preservation practices do lead to some losses in nutrient content, it provides the opportunity to preserve the food for a longer period of time. In contrast, when a food spoils, the loss of nutrients is 100% because that food is no longer used for human consumption. In most cases, a significant proportion of nutrients is retained after processing. Keep in mind that nutrient losses can also occur in fresh foods even during storage in the refrigerator and during normal cooking processes commonly used at home.
11.2 Factors affecting the extent of nutrient loss due to food preservation methods
Generally, the extent of nutrient loss depends on the following factors:
- the specific nutrient
- chemical and physical properties, e.g. water- or fat-soluble? double bonds? etc
- the properties of the food
- e.g. solid or liquid, acidity, moisture, chemical composition, presence of food additives or preservatives etc
- the processing method and conditions
- type of process (thermal processing, low temperature preservation, dehydration, fermentation; physical processes such as milling and grinding, etc)
- severity of the process (e.g. blanching versus pasteurization versus commercial sterilization) and the exact conditions (e.g. HTST and UHT versus slow batch heating; e.g. boiling in water, steaming, microwave-cooking, stir-frying, baking or broiling)
- environmental conditions (temperature, light, oxygen, moisture, ...)
- type of packaging
Table 2 of the article shows the effects of food pH and food environment (air or oxygen, light, and heat) on the stability of different vitamins and mineral salts in foods. For example, vitamin C is unstable under neutral and alkaline pH conditions; but stable in acidic conditions. In comparison, vitamin E remains relatively stable under a relatively broad pH range.
The following information could be added to that table to indicate the stability of those same nutrients to ionizing radiation (U = unstable; S = stable):
- Vitamin A (U), vitamin C (U), biotin (S), ß-carotene (U), choline (S), vitamin B12 (U), vitamin D (S), vitamin K (U), niacin (S), pantothenic acid (S), pyridoxine (U), riboflavin (S), thiamin (U), vitamin E (U).
Nutrients vary in their sensitivity to destruction by ionizing radiation as they do to the traditional forms of food preservation such as exposure to heat. Thiamine (vitamin B1) is the most vulnerable of the micronutrients to ionizing radiation. The losses are minimized by irradiating in the absence of oxygen or when vacuum packaging is used.
High temperature, short time (HTST) processes accelerate the destruction of microorganisms and their spores, but nutrient destruction occurs at a lower rate than lower temperature longer time processes. Thus, HTST processes result in improved nutrient retention while still providing the safety factors required from a microbiological point of view. For example, the nutrient levels in UHT sterilized milk are similar to those in pasteurized milk even though the UHT milk has been exposed to much higher temperatures, whereas milk sterilized within a bottle has significantly less nutrient retention because of the need for exposing the milk to high temperatures for long times in order to achieve the 12D thermal process with respect to Clostridium botulinum.
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11.3 Summary of Lesson 11
The important point to note is that, although each type of food preservation method causes some loss of some nutrients, the losses vary with the type of food and nutrient, and this in many respects reflects the pH value of the foods and the inherent sensitivity of the nutrient in question to destruction under the conditions of processing.
Generally speaking, thermally processed foods have the highest nutrient loss, however the loss highly depends on the time, temperature combination used for the process.
Supplemental Video: How does food irradiation work?
|After reading the article by Newsome, you should be able to:
Bonus: Name a food additive that was once often added to food to preserve the product's colour, but is now recognized as a major source of food sensitivity. As of August 4, 2012 in Canada, products containing more than 10 ppm of this additive must declare it on the labels.
FNH 200 Course content on this wiki page and associated lesson pages was originally authored by Drs. Brent Skura, Andrea Liceaga, and Eunice Li-Chan. Ongoing edits and updates are contributed by past and current instructors including Drs. Andrea Liceaga, Azita Madadi-Noei, Nooshin Alizadeh-Pasdar, and Judy Chan.