Water activity and types of food based on water activity
- 1. WATER ACTIVITY Water activity is a fundamental property of aqueous solutions, and by definition is the ratio of the vapour pressure of the water in the substrate (p) to that of pure water at the same temperature (p0) 13-09-2018prepared by SAPTADEEP SANYAL 1
- 2. Water activity (aw) concept • Water has been called the universal solvent as it is a requirement for growth, metabolism, and support of many chemical reactions occurring in food products. • Free water in fruit or vegetables is the water available for chemical reactions, to support microbial growth and to act as a transporting medium for compounds. • In the bound state water is not a available to participate in these reactions as it is bound by water soluble compounds such as sugar, salt gums, etc. 13-09-2018prepared by SAPTADEEP SANYAL 2
- 3. How does activity effect a food material ? • If a product is kept below a certain water activity, then mold growth is inhibited. • This results in a longer shelf life. 13-09-2018prepared by SAPTADEEP SANYAL 3
- 4. Food stability as a function of water activity. (From Rockland, L. B. and Beuchat, L. R. 1987. In: Introduction, Water Activity: Theory and Applications to Food. Rockland, L. B. and Beuchat, L. R. eds. Marcel Dekker, New York. p. v.) 13-09-2018prepared by SAPTADEEP SANYAL 4
- 5. Hypothetical curves showing effects of water activity reduction on bacterial growth. (From Troller, J. A. 1987. In: Water Activity: Theory and Applications to Food. Rockland, L. B. and Beuchat, L. R. eds. Marcel Dekker, New York. pp. 101–117.) 13-09-2018prepared by SAPTADEEP SANYAL 5
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- 7. Water Activity of Some Foods 13-09-2018prepared by SAPTADEEP SANYAL 7
- 8. Change Water Activity • Increase • ↑ temperature • ↑ pressure • Decrease • ↓ temperature • ↓ pressure 13-09-2018prepared by SAPTADEEP SANYAL 8
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- 10. Sorption Isotherm The moisture sorption isotherm is the dependence of moisture content on the water activity of one of the samples at a specified temperature. It is usually presented in a graphical form. Brunauer et al. classified adsorption isotherms of materials into five general types • Sugars or salt, the isotherm appears as concave shape type III. • Most other foods result sigmoid isotherm type II. The inflection point of the isotherm indicates the change of water-binding capacity or of the relative amounts of free and bound water. • Type I is indicative of a non-swelling porous solid, such as slicate anticaking agents. 13-09-2018prepared by SAPTADEEP SANYAL 10
- 11. Hysteresis • The difference in the equilibrium moisture content between the adsorption and desorption curves is called hysteresis and is shown in figure below. • In region II of this figure, the water is held less tightly and is usually present in small capillaries, whereas in region III, the water is held loosely in large capillaries or is free. Hysteresis in sorption has important theoretical and practical implications in foods. • The practical implications deal with the effects of hysteresis on chemical and microbiological deterioration and its importance on low- and intermediate-moisture foods 13-09-2018prepared by SAPTADEEP SANYAL 11
- 12. Factors Affecting Hysteresis • Types of Foods Affecting Hysteresis • Temperature Effects on Hysteresis • Effects of Physicochemical Nature 13-09-2018prepared by SAPTADEEP SANYAL 12
- 13. Food Product Design • Food designers use water activity to formulate shelf-stable food. If a product is kept below a certain water activity, then mold growth is inhibited. This results in a longer shelf life. • Water activity values can also help limit moisture migration within a food product made with different ingredients. If raisins of a higher water activity are packaged with bran flakes of a lower water activity, the water from the raisins migrates to the bran flakes over time, making the raisins hard and the bran flakes soggy. Food formulators use water activity to predict how much moisture migration affects their product. 13-09-2018prepared by SAPTADEEP SANYAL 13
- 14. Shelf-stable food • Shelf-stable food (sometimes ambient food) is food of a type that can be safely stored at room temperature in a sealed container. This includes foods that would normally be stored refrigerated but which have been processed so that they can be safely stored at room or ambient temperature for a usefully long shelf life. 13-09-2018prepared by SAPTADEEP SANYAL 14
- 15. Shelf life • Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. • In other word it might be defined as time period in which a food material remains in desirable colour, texture, flavour and nutritional composition. • It applies to foods and beverages, medicines, pharmaceutical drugs etc. 13-09-2018prepared by SAPTADEEP SANYAL 15
- 16. Food safety • Water activity is used in many cases as a critical control point for Hazard Analysis and Critical Control Points (HACCP) programs. • Samples of the food product are periodically taken from the production area and tested to ensure water activity values are within a specified range for food quality and safety. 13-09-2018prepared by SAPTADEEP SANYAL 16
- 17. Equilibrium Relative Humidity (ERH) • The ERH of a food product is defined as the relative humidity of the air surrounding the food at which the product neither gains nor loses its natural moisture and is in equilibrium with the environment. • The definition of moisture conditions in which pathogenic or spoilage microorganisms cannot grow is of paramount importance to food preservation. It is well known that each microorganism has a crystal aw below which growth cannot occur. • For instance, pathogenic microorganisms cannot grow at aw < 0.62. • The so called intermediate moisture foods (IMF) have aw values in the range of 0.65 - 0.90. 13-09-2018prepared by SAPTADEEP SANYAL 17
- 18. A relationship between ERH and aw • A relationship exists between ERH and aw. since both are based on vapor pressure. 13-09-2018prepared by SAPTADEEP SANYAL 18
- 19. Typical equilibrium of water content vs. water activity in foods 13-09-2018prepared by SAPTADEEP SANYAL 19
- 20. Intermediate Moisture Food (IMF) • Traditional intermediate moisture foods (IMF) can be regarded as one of the oldest foods preserved by man. • The mixing of ingredients to achieve a given aw, that allowed safe storage while maintaining enough water for palatability, was only done, however, on an empirical basis. • The work done by food scientists approximately three decades ago, in the search for convenient stable products through removal of water, resulted in the so-called modern intermediate moisture foods. 13-09-2018prepared by SAPTADEEP SANYAL 20
- 21. Intermediate Moisture Food (IMF) • These foods rely heavily on the addition of humectants and preservatives to prevent or reduce the growth of microorganisms. • IMF in terms of aw values and moisture content vary within wide limits (0.6- 0.90 aw, 10-50% moisture), and the addition of preservatives provides the margin of safety against spoilage organisms tolerant to low aw. • Of the food poisoning bacteria, Staphylococcus aureus is one of the organisms of high concern since it has been reported to tolerate aw as low as 0.83-0.86 under aerobic conditions. 13-09-2018prepared by SAPTADEEP SANYAL 21
- 22. Intermediate Moisture Food (IMF) • Many of the considerations on the significance of microorganisms in IMF are made in terms of aw limits for growth. • However, microbial control in IMF does not only depend on aw but on pH, time, preservatives, temperature and other envirormental conditions etc., which also exert an important effect on colonizing flora. 13-09-2018prepared by SAPTADEEP SANYAL 22
- 23. Examples of IMFs • Jam and Jellies • Candies • Baked foods 13-09-2018prepared by SAPTADEEP SANYAL 23
- 24. Advantages of IMF preservation • Intermediate moisture foods have an aw range of 0.65-0.90, and thus water activity is their primary hurdle to achieving microbial stability and safety. • IMF foods are easy to prepare and store without refrigeration. • They are energy efficient and relatively cheap. • They are not readily subject to spoilage, even if packages have been damaged prior to opening, as with thermostabilized foods, because of low aw. • This is a plus for many developing countries, especially those in tropical climates with inadequate infrastructure for processing and storage, and offers marketing advantages for consumers all over the world. 13-09-2018prepared by SAPTADEEP SANYAL 24
- 25. Disadvantages of IMF preservation • Some IMF foods contain high levels of additives (i.e., nitrites sulphites, humectants, etc.) that may cause health concerns and possible legal problems. • High sugar content is also a concern because of the high calorific intake. Therefore, efforts are been made to improve the quality of such foods by decreasing sugar and salt addition, as well as by increasing the moisture content and aw, but without sacrificing the microbial stability and safety of products if stored without refrigeration. 13-09-2018prepared by SAPTADEEP SANYAL 25
- 26. Disadvantages of IMF preservation • Fruit products from intermediate moisture foods (IMF) appear to have potential markets. • Application of this technology to produce stable products at ambient temperature is limited by the high concentration of solutes required to reduce water activities to safe levels. • This usually affects the sensory properties of the food. 13-09-2018prepared by SAPTADEEP SANYAL 26
- 27. Types of Food based on Water Activity (aw ) or Moisture Content • Perishable Foods • Semi Perishable Foods • Non-Perishable Foods 13-09-2018prepared by SAPTADEEP SANYAL 27
- 28. Perishable Foods • They have high moisture content. • It includes meat, poultry, fish, milk, eggs and many raw fruits and vegetables. All home cooked foods are considered perishable foods. To store these foods for any length of time, perishable foods need to be held at refrigerator or freezer temperatures. If refrigerated, perishable foods should be used within several days. 13-09-2018prepared by SAPTADEEP SANYAL 28
- 29. Perishable Foods 13-09-2018prepared by SAPTADEEP SANYAL 29
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- 31. Semi Perishable Foods • Intermidiate Moisture Content • if properly stored and handled, may remain unspoiled for six months to about one year. Flour, grain products, dried fruits and dry mixes are considered semi-perishable. 13-09-2018prepared by SAPTADEEP SANYAL 31
- 32. Semi Perishable Foods 13-09-2018prepared by SAPTADEEP SANYAL 32
- 33. Non Perishable Foods • Very low moisture content. • such as sugar, dried beans, spices, etc. do not spoil unless they are handled carelessly. These foods will lose quality, however, if stored over a long time, even if stored under ideal conditions. 13-09-2018prepared by SAPTADEEP SANYAL 33
- 34. Non Perishable Foods 13-09-2018prepared by SAPTADEEP SANYAL 34
- 35. Techniques of Reducing Water Activity •Drying •Dehydration 13-09-2018prepared by SAPTADEEP SANYAL 35
- 36. Drying • Food drying is a method of food preservation in which food is dried. • Drying inhibits the growth of bacteria, yeasts, and moldthrough the removal of water. • Water is traditionally removed through evaporation (air drying, sun drying, smoking or wind drying), although today electric food dryers or freeze- drying can be used to speed the drying process and ensure more consistent results. 13-09-2018prepared by SAPTADEEP SANYAL 36
- 37. Dehydration • Dehydration, in food processing, means by which many types of food can be preserved for indefinite periods by extracting the moisture, thereby inhibiting the growth of microorganisms. • Dehydration is one of the oldest methods of food preservation and was used by prehistoric peoples in sun-drying seeds. 13-09-2018prepared by SAPTADEEP SANYAL 37
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- 39. Reference • http://moisturecontrol.weebly.com/intermediate-moisture-food-imf.html • Julie A. Albrecht, Extension Food Specialist-University of Nebraska,lincoln • National Center for Home Food Preservation, drying section • Rockland, L.B.; Beuchat, L.R. (1987). Water Activity:Theory and Applications to Food (2nd ed.). New York: Marcel Dekker. • Fennema, O.R., ed. (1985). Food Chemistry (2nd ed.). New York: Marcell Dekker, Inc. • Handbook of Food Preservation, Second Edition by M. Shafiur Rahman • WATER ACTIVITY CONCEPT AND ITS ROLE IN FOOD PRESERVATION by Sandulachi E., Dr., assoc. prof. Technical University of Moldova. 13-09-2018prepared by SAPTADEEP SANYAL 39
- 40. THANK YOU PRESENTED BY SAPTADEEP SANYAL Msc Food Science & Technology SPECIAL THANKS DR. BARINDERJIT SINGH 13-09-2018prepared by SAPTADEEP SANYAL 40