Lecture 4

1795, the idea for food preservation started 1874 Retort for pressure canning was developed in the U.S.

Canning involves heat treatment of foods to destroy enzyme actions and spoilage microorganisms Food is sealed in sterile, airtight containers to prevent it from contamination by new sources

Acid Foods (pH < 4.5) Fruits, tomatoes, pickles, sauerkraut, jams, jellies Yeast and Molds : Heat Sensitive Process in boiling water bath

Low Acid Foods (pH> 4.5) Meat, seafood, chicken, milk, fresh vegetables Bacteria grow well C. botulinum (spore former): Heat Resistant Pressure Canner (120C)

Safety Preservation (increase shelf life) Increase sensory and nutritional quality

Micro-Organisms ↓ Natural Toxic Factors ↓ Trypsin Inhibitor (Raw Soy Beans) -Protein inhibits action of trypsin that helps with the digestin of protien Avidin (Raw Eggs bind with Biotin) -Biotin B vitamin, whn cook eggs avidin is inactiavted and no loner available for binding

Fresh Milk – 3 days Past. Milk – 10- 14 days Sterilized Milk – 1 year

Wet Heat • Moisture is a good conductor of heat • Water penetrate into microbial cells and spores

Mocroorganism overed by a layer of fat High fat food dry heat is more effective

Heat is directly transmitted through a substance when there is a difference of temperature between adjoining region

The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under which consequently results in transfer of heat.

When starch is heated in presence of water= geletanization (liquid to semi liquid) When starch is in the system, and presense of water, becomes more viscous, moree dense and would slow down the heat transfer because the heat condiction is by conduction and not convextion (convection is faster but it turns to conduction bwhich is slower)

Heating food in steam or hot water Until the temperature of food reaches 82-87 0C Then lowering temp. by adding cold water

Shrinks the product and provides a better fill of the container Removes gases and provides a better vacuum after sealing Destroys enzymes in foods Fixes the natural colour of vegetables (Chlorophyll)

Lipoxygenase: Off-Flavour Polyphenol Oxidase: Browning Rxn Ascorbic Acid Oxidase

Pasteurization (↑ shelf-life) Sterilization • In-Container • Continuous (Aseptic Packaging)

Food is sterilized outside of the cans and then aseptically placed in sterilized containers and sealed in an aseptic environment Processed outside of the can and packaged into container and sealed

Complete destruction of microorganisms not achievable in food processing

There might be a few bacterial spores left in the food after heat processing, but they are inactivated and cannot grow or produce any toxins.

Time needed at a given temp to decrease the microbial population by one log cycle or 90%

Temp. change required to change D-value by factor of 10

Time at specific temp. to destroy a specific number of M.O.

F = (Sv) (D)

Pressure cooker Simplest Method Temp. must be less than 1210C Longer Time Best for Solid Foods