Introduction to Human Nutrition

328 Introduction to Human Nutrition

Table 14.1

Characteristics of food-borne bacterial intoxications

Bacteria

Comment

Food-borne illness

(a) Min. temp (b) Opt. temp (c) Min. pH

a

(d) Min. A

bw

Forms spores

Heat resistance

(a) Gram stain(b) Aerobic/

anaerobic

(a) Source(b) Associated foods

b

(a) Onset(b) Duration

(a) Symptoms(b) Infectious dose

Bacillus cereus

(Emetic)

Vegetative cells are

inactivated by normal cooking temperatures; however, spores are quite heat resistant. Emetic illness is caused by consumption of heat-stable emetic toxin produced by cells growing to high numbers in food. This is most likely to happen when cooked foods are not served while hot or not cooled rapidly

(a) 1–5 h(b) 6–24 h

(a) Nausea and

vomiting

(b)

>^10

5 cells

(12–32

μg

toxin/kg)

(a) 10°C(b) 30–35°C(c) 4.3(d) 0.95

Yes

Heat-sensitive,

but can form heat-resistant spores (D

121

=

0.03–2.35 min)

Emetic toxin:

extremely heat resistant (can withstand 121°C for 90 min)

(a) Gram

positive

(b) Facultative

anaerobe

(a) Soil, dust and

vegetation

(b) Cooked rice, cereals

and cereal-based products, herbs and spices

Clostridium

botulinum

Group I

(proteolytic)

Group II (nonproteolytic)

Food-borne botulism is

caused when food becomes contaminated with spores from the environment, which are not destroyed by initial cooking or processing. If the food is packaged anaerobically and provides a suitable environment for growth, spores will germinate, leading to toxin production. The toxin is heat sensitive, so further heat treatment of the food would prevent illness. The so called “botulinum cook” (heat treatment to 121°C for 3 min or equivalent) is used for low acid canned food products to destroy these spores

(a) 12–36 h,

but may be as long as 8 days

(b) Variable

(from days to months)

(a) Blurred and/or

double vision, dryness of the mouth followed by diffi culties swallowing and fi nally breathing. Vomiting and mild diarrhea may occur in the early stages

(b) 0.005–0.5

μg

toxin

Group I(a) 10°C(b) 30–40°C(c) 4.6(d) 0.94Group II(a) 3.3°C(b) 25–37°C(c) 5.0(d) 0.97

Yes

Toxin: destroyed by

5 min at 85°C

Group ISpores: D^100

= 25 min

D^121

=

<0.001 min

0.1–0.2 minGroup IISpores: D^100

<

0.1 min

D^121

=

<0.001 min

(a) Gram

positive

(b) Obligate

anaerobe

(a) Soil, sediment,

intestinal tract of fi sh and mammals

(b) Canned foods,

smoked and salted fi sh, honey