FS Unit 5 FCS-FS-5: Students will discuss why water and pH are important factors in food preparation and preservation

» The measure of how acidic/basic water is. » pH is the measure of free hydrogen and hydroxyl ions in water. ˃ Less than 7 is acidic ˃ More than 7 is basic ˃ 7 neutral

» The pH of water determines the solubility » Solubility – the amount of that substance that will dissolve in a given amount of solvent ˃ pH can also determine if the water can be used by aquatic life. ˃ pH can tell us the affect and how much and in what form of phosphorus is most abundant in water.

» Dissociate (in relation to water)- molecules that are dissolved in water may separate.

» A water molecule ionizes when one of its two hydrogen atoms leaves its electron behind and, as a hydrogen ion, joins a different water molecule. » Two ions are produced by this reaction, a hydroxide ion and a hydronium ion.

» If there are more hydrogen ions than hydroxide ions in the solution the solution is ACIDIC. » If there are more hydroxide ions than hydrogen ions the solution is BASIC. » If the concentration of Hydrogen ions equals the concentration of hydroxide ions the solution is NEUTRAL.

» Increasing the acidity of food, either through fermentation or the addition of weak acids, has been used as a preservation method since ancient time. ˃ Most meat in their natural state are slightly acidic. ˃ Most fruits moderately acidic ˃ Few foods like egg whites are alkaline.

» pK a describes the state of dissociation of an acid. » pk a is the pH at which the concentration of dissociated and undissociated acids are equal. - strong acids have very low pK a, almost entirely dissociated. *this is extremely important when using acidity as a preservation method for foods.

» Microorganisms have pH optimum, minimum and maximum for growth in foods. » The buffering capacity of a food is its ability to resist changes in pH. ˃ Foods with low buffering capacity will change pH quickly in response to acidic or alkaline compounds produced by microorganisms as they grow.

» Pathogens do not grow or grow more slowly, at pH levels below 4.6. (there are exceptions) » Many pathogens can survive in foods at pH levels below their growth minimum. » C. Botulinum has been reported to be able to produce a toxin as low as pH4.2