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
how is food preserved by irradiation
-Radiation= Gamma rays from Co60, Electron beam irradiation. And microbes killed by free radicals
-Food can be packaged!
-No recontamination possible
-Pasteurization of meat, poultry, cheese
- No alteration of food- controversial claim
uses ionizing rays (gamma) and nonionizing (UV) radiation
what is MAP
Modified atmosphere packaging- o bacteria requires oxygen- modified atmosphere packaging- when it contains a lot of oxygen to prevent organism growth controls gas mixture and slows down shelf life
what is the high oxygen in MAP
70% O2 20-30 CO2 and 0-10% N2
what is the low oxygen in MAP
10% O2 20-30 CO2 and 70 % N2
what can foods naturally contain
Foods may naturally contain antimicrobial substances including, complex chemical inhibitors and enzymes
what are examples of foods with antimicrobial substances
–coumarins – fruits and vegetables
–lysozyme – cow’s milk and eggs
–aldehydic and phenolic compounds – herbs and spices such as cinnamon
–allicin – garlic
–polyphenols – green and black teas
what does carbon monoixde do to meat
interacts with myoglobin to forms a stable, bright red colour but this reaction prevents meat from browning naturally with age so it is difficult to tell how fresh the meat is (Brooks, 2008). For this reason, the use of CO for meats stored under MAP is banned in the European Union, but is still permitted in the United States and is used in small concentrations (<1%) for some New Zealand meats.
are GRAs safe
they are generally considered safe
what bacterium mainly spoils milk
bacterium Bacillus cereus is the main cause of spoilage of milk. The presence of psychotropic bacteria present in milk is exposed to heat and oxygen and reacts to become spoiled. The relation between temperature and growth of bacteria in dairy products are mainly responsible for defects of milk- this has been exploited commercially
what foods have reduced Aw
salted fish, dry fermented sausage, dry fish, cheeses, flour and cereals
what does teperature affect
affects storage time, and food deteriorates faster at higher temperatures
what is the temp for a cupboard
50-70 F
what is the temp for a fridge
34-40 F
what is the temp for a freezer
0 F or below
