14-Preservation-11 - FST 10 Preservation Fermentation...

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FST10 ©GFR/GMS 2011 FST 10 Preservation, Fermentation, Spoilage FST10 ©GFR/GMS 2011 Harvest vs. Consumption ! Harvest once a year ! but you have to eat all year ! Slaughter a 1000lb animal (any time of year) ! but you can’t eat 1000 lbs of meat ! Have to store food for future use ! must retain nutritional value ! must remain safe ! would be nice if it remains palatable FST10 ©GFR/GMS 2011 Food “Goes Bad” by ! Oxidation ! esp. fatty acids (rancidity), proteins ! Hydrolysis ! loss of texture, milk (hydrolytic rancidity) ! Loss or migration of moisture (sogging out, drying out) ! Crystallization ! honey, jams, retrogradation of starch ! But it “ Spoils ” by microbial action FST10 ©GFR/GMS 2011 In order to understand how microorganisms grow and don’t grow, we need to understand THREE things water content acidity temperature FST10 ©GFR/GMS 2011 Preservation of foods: T ! High Temperature - kills microorganisms ! Thermal processing - high heat in sealed can ! Aseptic packaging ! sterilize product ! place in a sterile package in a sterile environment ! Pasteurization - heating short of sterilization ! Low temperature ! Refrigeration - impedes bacterial growth ! Freezing - Stops growth, impedes chemical changes FST10 ©GFR/GMS 2011 Preservation of foods: a w , pH Other important ways that foods are preserved and made safe to consume are by controlling: ! (1) Water content ! (2) Acid content
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FST10 ©GFR/GMS 2011 (1) Water content ! Originally, scientists tried to measure the moisture content as a percentage ! Tried to relate to spoilage and safety ! It just didn’t work well ! Eventually, they found a measurement of the ‘availability’ of the water ! Related to a physical chemistry term called “water activity” or a w ! A low a w usually means bacteria (especially pathogens) won’t grow FST10 ©GFR/GMS 2011 How do we lower a w ? ! Dry the food ! Such as sun-dried tomatoes, grapes, plums ! Beef jerky (doesn’t kill trichina cysts) ! ! Add salt ! Such as salted meats ! Treatment with brine ! Add sugar ! FST10 ©GFR/GMS 2011 Familiar example ! Butter ! a w/o emulsion ! ~16% water (composition, not a w ) ! subject to microbial spoilage ! Solutions? Lower the a w by making ! salted butter ! longer shelf life, different flavor
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This note was uploaded on 03/18/2012 for the course FST 10 taught by Professor Jack during the Spring '08 term at UC Davis.

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14-Preservation-11 - FST 10 Preservation Fermentation...

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