| Drying Objectives | can be used to retain the viability of starter culture bacteria for use in bioprocessing
- prevent growth of vegetative cells
- prevent germination and outgrowth of microbial spores
- prevent toxin production by toxigenic molds and bacteria |
| Natural Dehydration | - uncontrolled, slow process
- water removed by heat of sun (solar drying)
- low cost method
- used for grains and some foods
- spoilage and pathogenic bacteria/yeasts/molds can grow during the process |
| Mechanical drying | ex: tunnel drying, roller drying, spray drying
- controlled process
- rapid; eliminates risk of microbial growth
- foods dried within a few seconds to hours
- liquids may be partially concentrated before drying
- some microbes die during drying, some sub-lethally injured
- spores generally survive |
| Freeze drying | - acceptance quality of foods least affected: little/no effect on shape/size of food
- relatively costly
- foods rapidly frozen then exposed to high vacuum
- water removed by sublimation, ice transformed directly to water vapor
- some cells die, some sub-lethally injured
- spores unaffected |
| Foam drying | - vigorous whipping or injecting gas (air/nitrogen) in liquid food to produce foam, food usually concentrated prior to whipping
- surface area increased
- foam dried by warm air (50-80C)
- some foods don't have foaming properties --> addition of foaming agents and foam stabilizers (ex. egg albumen, gelatin, carboxymethyl cellulose, maltodextrin
- food to be foam dried should be of high microbial quality, process has little lethal effect on microbial cells and spores |
| Smoking | - food product exposed to low heat and smoke
- smoke deposited on surface during heating
- many low-heat processed meat products produced this way (dry and semi-dry sausages and smoked fish)
- some antimicrobials in smoke like phenolic compounds, carbonyls, and organic acids |
| Smoking antimicrobial components | - phenols: disrupt bacterial membranes
- carbonyls (ketones and aldehydes): sequester low MW nutrients
- organic acids: inhibit microbial energy production |
| Intermediate moisture foods | - foods with aw = 0.7-0.9, typ 10-40% MC
- can be eaten without rehydration
- shelf stable for relatively long periods without refrigeration
- considered microbiologically safe --> water binding solutes and hydrophilic colloids added to bind water
- microbes can survive but low aw prevents bacterial growth
- yeasts and molds can grow --> preservatives added to control (potassium sorbet, sodium benzoate)
- ex: jam/jelly, honey, candies, salami, baked foods, dried fruits, jerky |
