FNH 200 final

how does food deteriorate

• Reaction with oxygen/ light

• Time

• Physical stress/ abuse

• Inappropriate temperatures

• Infestation by insects, parasites, rodents

• food enzymes and other chemical reactions within the food 

• microorganisms like yeast, bacteria, and mould

• Gain or loss of moisture

• Physical causes

• Chemical causes

• Biochemical (enzymatic) causes

• Biological causes

what are perishable foods

• Not processed or are only minimally processed and have a shelf life of less than 60 days.

what are semi-perishable foods

• Last between 2 to 6 months as a result of some form of preservation method.

• examples: ice cream, cheeses, and dry snack foods.

what does shelf stable mean 

• have a shelf life greater than 6 months.

• Examples: cereal grains, dehydrated pasta, some frozen foods, canned foods, and dehydrated vegetables.

• Cutoff for needing date marking is 90 days or less

Which one of the mentioned classifications needs date labelling as mandatory core labelling requirements?

• Perishable foods 

• Some semi perishable foods

explain micro organism classification

• Type: Bacteria, Yeast, Mould- 

• function: good- probiotic (yogurt), bad- spoilage formers (spoil food), ugly- (pathogens)

• temperature requirement: Psychrophiles, Psychrotrophs (cold loving), Mesophiles, Thermophiles

• Psychotrophs can grow and multiply in refrigerated temperatures, most of them are spoilage formers 

• oxygen requirement: Aerobic, Anaerobic, Facultative, anaerobe

explain viruses 

• Pseudo-organisms- (Not true organisms)

• Obligated parasites require living hosts to propagate

• Do not ferment or spoil food, use food as vehicle to get into our bodies

• Can cause foodborne illnesses

• although not considered true microorganisms can be agents of foodborne disease but do not cause food spoilage, nor are they used to produce fermented foods.

explain bacteria

• has fastest growth

• vegetative cells (active)- are actively metabolizing cells, consume nutrients and produce waste products.

• spores (dormant)- dormant form of the bacterial cell. The spore is analogous to the seed of a green plant. All of the genetic material is contained within the spore

• germinating cells (transition from spores to vegetative)- When favourable conditions are encountered, the spore germinates and produces an actively metabolizing bacterial cell capable of cell division).

• Not all bacteria can form spores

• aerobic (needs oxygen) and anaerobic  (needs there to be no oxygen)

• FACULTATIVE ANAEROBE- can grow in the presence or absence of oxygen

explain Yeast

• Yeasts are commonly found in many foods of agricultural and aquatic origin.

• Yeasts reproduce by budding.

• slower growth than bacteria but more tolerant of severe environments 

• canTolerate lower pH and lower water activity

• aerobic (needs oxygen)

• Some yeasts are used to produce fermented foods and beverages.

• FACULTATIVE ANAEROBE- can grow in the presence or absence of oxygen

explain moulds

• Moulds are filamentous and are also found on most foods of agricultural and aquatic origin. Most moulds produce spores.

• even more tolerant of low pH and low  water activity

• Strictly aerobic (need oxygen)

• Microbial spores are very resistant to a variety of conditions (heat, dehydration, ionizing radiation, antimicrobial agents) that can inhibit or cause death of the vegetative cell.

explain enzymatic reaction in foods

• can catalyze reactions leading to chemical changes in foods

• enzymes may continue to catalyze chemical reactions within foods even after slaughter or harvest.

• Enzymes in the apple tissue degrade pectins that cement the cells together, leading to textural change.

• enzymatic browning: Polyphenol oxidase- found in plant tissue, catalyzes the oxidation of colorless phenols in the tissues to brown colored compounds

• Once you cut plant tissue it gets released and leads to brown pigment

• Can avoid enzymes by avoiding exposure to oxygen/ gases, inactivating enzyme with acid/ chemicals, or inactivating enzyme with heat 

explain issues with parasites

• can cause damage to food quality.

• An example is the visible appearance of parasitic cysts in fish flesh which lowers the quality and market value of infested products.

• Parasites such as Trichinella spiralis in pork and Anisakis species in some types of fish can also cause health problems in humans if they are ingested through inadequately cooked or improperly processed foods, infested with those parasites.

Factors Affecting Microbial Growth, Enzyme Activity and Chemical Reactions in Foods

• temperature effects

• gain or loss of moisture

• oxygen effects

• physical deterioration

• time

explain temperature effects in relation to affecting microbial growth, enzyme activity, and chemical reactions in foods

• Rates of reactions generally increase as the temperature increases until an optimum is achieved, after which any further increase in temperature, causes the rates of reaction to decrease because of the inactivation of microorganisms or enzymes or because of inhibitory effects on chemical reactions.

• Excessive heat also denatures proteins, breaks emulsions, removes moisture from foods (drying out), and destroys vitamins.

• Cold temperatures can also deteriorate food. A well-known example is "chill injury", the change in texture and discolouration of fruits and vegetables when they are exposed to freezing temperatures.

• Freezing temperatures can deteriorate liquid foods such as milk, causing emulsions to break and fat to separate, and denaturing protein causing it to curdle or coagulate.

• "Freezer burn" due to loss of moisture can occur in solid and liquid foods.

explain gain or loss of moisture in relation to effecting microbial growth, enzyme activity, and chemical reactions in foods

• Water loss during storage (e.g. wilting of lettuce in the refrigerator), or water uptake (e.g. by dehydrated foods) can lead to deterioration.

• Retrogradation of starch, resulting in staling of bread, is caused by packing of linear starch molecules leading to the exclusion of water that was previously absorbed during gelatinization. The bread becomes tough and develops a dry texture.

• Changes in water activity (free versus bound water) can influence chemical and enzymatic reactions and microbial growth.

explain oxygen effects in relation to effecting microbial growth, enzyme activity, and chemical reactions in foods

• Oxygen is an important factor in food quality since many oxidative reactions lead to deterioration in the quality of food and, in some cases, to losses in nutritive value. Oxidative deterioration is often accelerated by light.

• deterioration frequently occurs because of lipid oxidation in food products. The development of rancidity in breakfast cereals, vegetable oils and oil-based products, and deep-fried foods is due to the reaction of oxygen with fats, particularly those with high unsaturated fatty acid content.

• This type of rancidity is known as oxidative rancidity. This is in contrast to rancidity induced in foods upon the release of free fatty acids by very high temperatures or by the action of lipase enzymes, either endogenous or produced by spoilage-causing microorganisms. The latter rancidity is known as hydrolytic or lipolytic rancidity.

• Oxidation of vitamins and colour pigments can lead to the deterioration of nutritive quality and aesthetic appeal of foods.

explain physical deterioration in relation to effecting microbial growth, enzyme activity, and chemical reactions in foods

• Physical abuse causes tissue disruption and release of enzymes into tissues which can lead to changes such as enzymatic browning

• improper packaging, can cause crushing and tissue damage, making foods such as fruits and vegetables particularly susceptible to microbial invasion as well as enzymatic and chemical reactions.

explain time in relation to effecting microbial growth, enzyme activity, and chemical reactions in foods

• For the majority of foods, quality will decrease with time.

• Food preservation, packaging and storage practices are aimed to maintain this quality for as long as possible (shelf life); however, eventually the quality of any food will decrease with time.

what are old preservation methods

• Dehydration

• Smoking

• Fermentation

• Salting

• Sweetening

• cause noticeable changes in the food (i.e. fresh salmon vs. smoked salmon, grapes vs. wine, milk vs. cheese);

• Without these "old" preservation methods we wouldn't have the variety of desirable food products such as cheese, bread, wine, smoked meats, etc

explain modern preservation methods

• Canning- Canned foods will not undergo microbial or enzymatic spoilage as long as the physical integrity of the can is maintained, but foods may spoil as a consequence of chemical reactions such as Maillard browning which can proceed slowly even at ambient temperature.

• Freezing

• UHT

• Irradiation

• cause little change to food (freezing, pasteurization)

• No method can completely eliminate spoilage phenomena indefinitely.

explain list of preservation methods to know in depth

• Dehydration

• Fermentation

• Low-temperature preservation

• Thermal processing

• Irradiation

• Addition of chemicals- combined with other methods 

explain dehydration

• Removal of water to control chemical, enzymatic and microbial activity

• Complete removal of water (Drying)

• Partial removal (Concentration)

• Condensed milk uses concentration and canning 

explain fermentation

• Use of the desired microorganism to delay the growth of non-desirable ones

• Production of acid

• Production of Antimicrobial

• Requires other forms of preservation (eg. vacuum or modified atmosphere packaging)

explain low temperature used for preservation 

• Slowing down the rate of chemical, enzymatic and microbial activity

• Refrigeration- mild, lower temperature to control and slow down chemical, enzymatic and microbial reaction  

• Can be combined with other preservation methods to extend the shelf life

Freezing:

• More severe

• Control temperature to the point where chemical, enzymatic, and microbial activity stops

• Should be blanched- chemical and thermal processing blanching 

• Freezer burn can occur

explain thermal processing

Blanching

• Inactivate the enzymes

Pasteurization

• Destroy the disease-causing microorganism

• Putrefaction microorganism survive

• More mild than commercial sterilization but more severe than blanching 

Commercial sterilization (Botulinum cook)

• Destroys almost disease-causing and spoilage causing microorganisms

• Destroys both pathogens and spoilage formers 

• Spores are NOT destroyed unless boiled at a temperature of 121°C for 15 minutes or longer.

explain irradiation

• Controversial and not often used

• Using Ionization energy to inactivate microorganisms or biological systems

• General public concern

• Required dose is regulated

explain addition of chemicals for preservation

• Acids- lower pH to below 4.6

• Sugar and Salt- Lower water activity

• Antioxidants- Vitamin C and E, Butylated hydroxyanisole (BHA)

• Preservatives- Sodium propionate (important anti fungal preservative), Sodium benzoate (used in beverages)

give summary of roles of preservation

• Eliminate any potential microbiological harm to the consumer

• Maintain nutritional value within limits dictated by the production of a safe food product

• Maintain quality of Food

what are the principles of thermal preservation 

• Refers to regulated processes using heat that are performed commercially to control chemical, enzymatic and microbial reactions

• Highly regulated

what are the types of thermal preservation 

• Blanching

• Pasteurization

• Commercial sterilization

explain blanching

• Type of process: mild - intensity heat process

• Exposing fruit/vegetables to boiling water or steam for a short period of time

Preservation principle:

• Inactivate enzymes in plant tissues so that enzymatic degradation does not occur in the interval between packaging and thermal processing or during frozen storage or in the early stages of food dehydration and after reconstitution of dehydrated plant foods.

• wilt vegetable products to enable packing of the products into containers so that proper fill weights can be achieved.

• drive off inter-and intracellular oxygen and other gases from plant tissues so that containers are not deformed by excessively high internal pressures due to expanding gases within the container and to permit the formation of a vacuum in the container after thermal processing

explain pasteurization

• Type of process: moderate-intensity heat process

• Temperature below boiling point of water 60-80C E.g. (milk)

• 30-40 min at 60C, low temp, long time – LTLT- can change taste of milk

• 15 sec at 72C, high temp, short time- HTST (flash pasteurization), does not change taste of food

• many spoilage-causing MOs can survive pasteurization especially in low acid foods

• Because pasteurization does not kill all the psychrotrophic spoilage-causing bacteria in milk, pasteurized milk must be refrigerated to maintain shelf life quality.

Combined with other forms of preservation:

• refrigeration–“durable life date” at < 4C

• psychrotrophic bacteria

• putrefactive spoilage (protein)

• lipolytic spoilage – (lipid)

• (lactic acid bacteria – usually lead to souring of raw milk, cannot survive thermal processing)

Preservation principle:

• 2 objectives:

• 1) Low-acid foods (milk, eggs) to destroy pathogenic (disease-causing) bacteria & viruses and To inactivate enzymes

• 2) Acid foods (beer, wine, fruit juices) To extend product shelf-life, Destroy spoilage-causing MOs & enzymes

• Acid Foods not a source of pathogens (except E. coli0157:H7)

• pasteurized vs. unpasteurized juices…

why select pasteurization

• for Foods that will be consumed within a short period of time after processing

• storage life partially extended by a combination of pasteurization and refrigerated storage…milk, some cured meat products, smoked salmon…

what is commercial sterilization

• Type of process: high-intensity heat process

• Also known as “canning” (if it is used in canned product)

• Requires a minimum of 121°C moist heat for 15 min.

• CS conducted once the food is packaged in suitable containers

• Containers must withstand the high Temp. and pressure used

Containers must be hermetically sealed:

• impermeable to transmission of gases, liquids and microorganisms

• CS products have a shelf life of 2 years or more (eg. Canned food)

Preservation principle:

• Destroys spoilage-causing & disease-causing MOs

• Free from viable forms of MOs (including spores) (Attainable?)

• Ensures that the spores of Clostridium botulinum are destroyed = “botulinum cook”

• Survive: Small number of heat-resistant spores (do not cause disease) BUT not able to multiply (germinate) in the food product even if held at room temperature