Course:FNH200/Lessons/Lesson 11/Page 11.2

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)
• storage
  • 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.

Want to learn more?

You are welcome to visit: the USDA Table of Nutrient Retention Factors for several foods cooked and/or processed under different conditions.

Critical Thinking

After reading the article by Newsome, Make a list of benefits versus risks (or "advantages and disadvantages") of food processing. Try to answer the following questions: What are the main factors that affect the extent of nutrient loss as a result of processing? Can you describe some of the factors that might contribute to the different extents of nutrient losses observed for thiamin and pyridoxine, as shown in Table 5 of the article by Newsome? What strategies can be used to minimize the potential loss of nutritional value in processed foods? What about in terms of home cooking or food storage conditions?