Blanching• A mild heat treatment designed to inactivate enzymes that may cause deterioration during storage• Primary concerns are browning and off flavor production• Blanching treatments vary substantially from product to product
Blanching• Hot Water – Product added to water and pumped through a pipe for a specific time – Product added to water and conveyed through the water for a specific time (similar to our chip fryer)• Steam – Product is moved quickly through a zone of steam
Heat-processed foodsPasteurizedCommercially sterile – retort and aseptically packaged Microbial destruction by heat: D-value, F0 High vs. low acid foods 12-D process for low acid foodsBlanchedHot-filled
BlanchingPrimary purpose: inactivate specific enzymes withina solid food product to improve quality.Enzymes can cause…Off-flavors Vitamin lossColor loss Texture softeningIf not blanched, enzyme activity can occur evenunder refrigerated, frozen and dried conditions.Enzymes can also be active during the come uptime for retorted canned products.
BlanchingMost frequently used for processed fruits andvegetables.Process: Heat the product using boiling water orsteam until thoroughly heated.Will reduce the population of vegetative cells.Safety of product depends on secondary barrier.
Hot-filled foods• Product is heated ( typically 180°F) - Mild heat treatment kills some vegetative cells• Product is filled into container• On cooling of the container, a vacuum is formed – Anaerobic environment – prevents growth of some microorganisms• Dependent upon another barrier to make the product safe
Hot-filled foods • Multiple barriers to provide safety – Mild heat treatment & anaerobic environment + – Low pH or – Low water activity or – Addition of antimicrobial agents
Typical hot-filled foods• Jams and Jellies (low pH and low aw)• Syrups (low aw)• Dessert sauces (low aw)• Other sauces or juices (low pH or low a w)
Hot-filled foods – after opening • Molds and some yeasts will not grow because of anaerobic conditions as long as container is sealed • After opening – Generally advised to refrigerate – Anti-microbial agents can be used to extend shelf life after opening
Heat processing Additional barrierProcess Temp. range required?Pasteurization 161°F (71.5°C), 15 s yes or equivalentHot-filling ~ 180°F (82°C) yesBlanching 212°F (100°C) yes – short timeCommercial no ≥ 212°F (100°C)sterilization (higher temps for low acid)
Removing waterRemove water that is available for microbialgrowth.Bound vs. free water:Molecules and ions in foods bind some water,making it unavailable for other reactions. Freewater is not bound and is available.Total water content = bound + free water
Water activity• Water activity (aw) is a measurement of the “free” water.• aw = Relative humidity of the product Relative humidity of pure water – Most bacteria can’t grow below aw = 0.85 – Most yeasts & molds can’t grow below aw = 0.65
Reducing water activityDrying or concentrating: remove water fromthe food• drying with heat - evaporation• freeze-drying – sublimation• concentration by evaporation• concentration by filtrationAdd solutes to the food: Bind “free” water:• Sugar, salt, proteins, and others
Water activity and microbial growthRelative growth or reaction rate 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Water activity –Most bacteria can’t grow below aw = 0.85 –Most yeasts & molds can’t grow below a = 0.65
Typical water activity of some foods Aw – examples 0.95 – fruits, vegetables, meat, fish, milk 0.91 – some cheeses, ham 0.87 – salami, pepperoni, dry cheeses, margarine, 0.80 – fruit juice concentrates, sweetened condensed milk, syrups, flour, rice, high sugar cakes 0.75 – jam, marmalade 0.65 – oatmeal, fudge, marshmallows, jelly, molasses, sugar, nuts 0.60 – dried fruits, honey 0.50 – dried pasta, dried spices 0.30 – cookies, crackers 0.03 – dry milk, dehydrated soups, corn flakes