Effects of Processing on Nutritive Values of Foods
Overview In this lesson we will consider the effects of food processing on nutrients in foods, including the effects of different preservation technologies, as well as the handling of foods in processing plants, in retail stores, in the food service industry and in the home.
Objectives The goal of this lesson is to provide you with an appreciation of the fact that, although nutrient losses occur during food preservation, the losses are not always large 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:
- to describe the variations in nutrient losses depending on the food, its chemical and physical properties, and the food preservation or preparation method used.
The journal article below provides a great summary of how different food processing affect nutritive values of food. As a bonus, it serves as a great review of the many processes described in Lesson 06 to 10. Please obtain an hard copy from the WOODWARD LIBRARY Stacks; Call Number TX341 .F63. General trends described in the article remain valid today.
- Newsome, 1986: "Effects of food processing on nutritive values". (A scientific status summary). Food Technology, 40(12): 109-116.
- Posted on the homepage on Connect.
- Or, try this DIRECT LINK
The USDA Table of Nutrient Retention Factors for several foods cooked and/or processed under different conditions. (pdf file) http://www.nal.usda.gov/fnic/foodcomp/Data/retn6/retn06.pdf
Why Process Foods?
Processing delays food deterioration. 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 inevitably deteriorates from the time it is harvested, slaughtered, or manufactured. Along with deterioration comes 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.
Some Loss is Inevitable
Note from your reading of the article "Effects of food processing on nutritive values" that all food preservation methods lead to a certain degree of loss of some nutrients.
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 processing of foods that extends their storage life, whether that processing occurs in the home or on an industrial scale. It is important to note, however, 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 has been found that food processing methods that favour maximum retention of aesthetic attributes of food, also favour retention of nutrients. In most cases, a significant proportion of nutrients is retained after processing. In contrast, when a food spoils, the loss of nutrients is 100% because that food is no longer used for human consumption. Keep in mind also that nutrient losses occur in fresh foods even during storage in the refrigerator and during normal cooking processes commonly used in the home.
Factors Affecting Nutrient Loss
Generally, the extent of nutrient loss depends on the following factors:
- Specific nutrient: chemical and physical properties, e.g. water- or fat-soluble? double bonds? etc
- Properties of the food: e.g. solid or liquid, acidity, moisture, chemical composition, presence of food additives or preservatives etc
- 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
- 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, etc.
- 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).
You will note that the 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.
The important point to note in the article "Effects of food processing on nutritive values" 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.
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.
|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.