food spoilage Flashcards
what is food spoilage
process or change which renders a product undesirable or unacceptable for consumption- can cause water loss, increase in moisture of dry foods, freezer burn and recrystallisation of frozen foods
what can microorganisms cause in food (agents of…)
agents of food production, agents of disease and agents of food spoilage
what is microbial food spoilage
Microbial growth introducing unwanted alterations in food-appearance, smell and taste
o Changes not necessarily harmful!
what is hakarl
fermented shark
what are examples of highly perishable foods
meat, fruit, milk, vegetables
(wet foods)
what are examples of semi- perishable foods
potatoes and nuts
what are examples of stable foods
rice, flour and dry beans (dry foods)
what defines each food group (the amounts of…)
the amounts of water
explain spoilage in milk
o Bacterial growth on milk sugars
o (Lactobacillus spp., Lactococcus spp.)
o pH reduction due to lactic acid build-up
o Change in bacterial population
o further pH reductions and much more lactic acid, continues until all sugars depleted
o Yeasts and moulds dominate and use lactic acid for growth.
o pH rise allowing further bacterial growth
o Bacteria use proteins as major nutrient
o (Primary amines produced- Smelly!!!!!)
look diagrams in booklet
What factors influence spoilage
-Moisture content
-Environmental conditions- temp and atmosphere
-Nature of the food –Chemical composition, Ph, Indigenous microflora and Introduced microflora
what occurs in the preservation of food
-Removal or killing of all microbes from a food will prevent spoilage!
-Removal or killing of all microbes from a food will drastically alter the food taste, texture and nutritional content
-Compromise needed: reduce overall numbers!
why are a number of parameters manipulated
to slow down mirobial growth
what is One of the most important parameters for controlling growth
Moisture content {water activity (Aw)} because bacteria favour wet conditions
what is the Aw of pure water
1
what foods have a high Aw and how are they perserved
perishable foods- preserved by lowering Aw
how are foods preserved by reducing water activity
-Drying- sun, heat, freeze - dried (expensive!)
-addition of salt or sugar- water needed to keep salt and sugar in solution- salt is a dehydrating agent
how are foods preserved by controlling pH
-pH- very few bacteria grow below pH 5.0
-How to make food acidic?- Add acid e.g. acetic acid, Allow bacteria to make acid from natural food components, lactic acid bacteria
-understanding lactic acids bacteria is a major aim of food production companies
how are foods preserved by controlling temperature
-storage at 4oC degrees- rate of spoilage decreased
-storage at -20oC degrees- rate of spoilage extremely slow
-need -70oC to eliminate spoilage- to eliminates growth u need -70 degrees- very expensive
how are foods preserved by canning
-Canning- sterilization by heat, 115oC for up to 100 minutes, Milder conditions also used, bacteria and endospores killed
-canning gets rid of everything- basically autoclaving- seal food in airtight container and apply conditions to get rid of endospores and organisms
-canning removes texture
what is pasteurisation
-Pasteurization= a mild heat treatment, disinfection by heat, overall microbial population is reduced and pathogens are eliminated since these tend to be more heat sensitive than other organisms
-we don’t need to kill everything- reduce numbers is pasteurisation
-if you increase dose you reduce time you need to contact
what temperature is pasteurisation
63 degrees for 30 min
what temperature is flash pasturisation
72 degrees for 15 seconds- expensive
what is flash past
-HTST- High temperature –Short Time
-Industry standard: milk and other beverages
-flash pasteurisation- continuous process- milk flows over heat
