Food Microbiology

List 6 things that can cause food spoilage

* Rodents, insects, physical injury due to bruising or freezing (texture changes), tissue enzyme activity (flavour changes), non-enzymatic chemical changes, micro-organisms

How do you detect food spoilage? (give 5 ways)

* Appearance, Texture, Odour, Flavour and Slime production

Contrast perishable, semi-perishable and non-perishable foods

Stable or non-perishable

* long shelf life, no special storage requirements.

* eg. flour, rice - due to low aw, or heat treatment ... canned food.

Semi-perishable

* limited shelf life: potatoes, apples, etc.

Perishable

* require some sort of preservation

* majority of foods are in this group

* milk, meat, eggs, etc.

What is the main bacterium for Bacterial soft rot?

* Erwinia species (Enterobacteriaceae): Erwinia caratovora, Pseudomonas marginalis (and Bacillus & Clostridium sometimes).

What causes gray mould rot? Why is it gray?

* Botrytis cinerea produces a gray mycelium on certain vegetables when stored in high RH. and warm temperatures ...grows on decayed areas and forms a prominent gray mold rot.

* Geotrichum candidum ... produces a watery soft rot or sour rot ... this fungus is carried by Fruit Flies to cracks or wounds on other vegetables.

* Rhizopus stolonifer causes soft rot on various vegetables ... it makes them soft and mushy and also shows a nice cottony growth with small black dots

What does pectinase have to do with soft rot or sour rot?

* Fruits have a little less water than vegetables, but more sugar.

* pH is lower than bacterial levels ... thus molds will tend to spoil fruits instead of bacteria.

Why does Pseudomonas grow on meat surfaces but Clostridium does not?

* Most bacteria don't grow fast enough to COMPETE with Pseudomonas at refrigerator temps.

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