Download 9. Laboratory methods of food analysis

9. LABORATORY METHODS OF FOOD ANALYSIS
Food is analysed for many reasons. Some of the key applications of food testing; food
chemical analysis (e.g. moisture, fat, protein, pH, salt, minerals, sugar, contaminants, etc.),
food microbiology analysis (e.g. Lactobacillus, Salmonella, Pseudomonas, Listeria, E. coli,
Staphylococcus aureus, yeast, mould, etc.), food allergen analysis (e.g. peanut, egg, soy,
etc.), food nutrition analysis (determining the nutritional content), natural food toxin
analysis (e.g. histamine), food shelf life studies and food quality control determination (e.g.
GMO analysis, wheat adulteration, etc.).
Food analysis is often provided to ensure food safety. It would be very undesirable
for the both consumer and the manufacturer if unwholesome or toxic products were sold,
hence it is essential that the harmful substances like microorganisms, toxic chemicals or
extraneous matter are absent or effectively eliminated. This should be achieved by observing
good manufacture practice and regulations laid down by the government for specific food
products, as well as using analytical techniques that are capable of detecting unauthorized
substances. Sometimes it is necessary to employ high sensitivity analytical techniques that
can reliably detect very low levels of harmful substances.
Food analysis is conducted by scientists in all major sectors of the food industry
including food manufacturers, ingredient suppliers and by many types of laboratories
(analytical service, national or university research). Different analytical methods are
available for various purposes. They are chosen according to the property to be measured,
the type of foodstuff to be analysed or the reason for testing.
Typically, foods are tested in laboratories to determine their safety for consumption,
composition or to help food manufacturers in understanding the shelf life and stability of a
food product or ingredient. Every laboratory should be lit and ventilated properly, with
appropriate room temperature for a consistent environment and large enough to
accommodate all the necessary equipment as well as to provide a comfortable work area.
Although there are many types of laboratories corresponding to various purposes, every
laboratory has certain components that are common to all. Such equipment includes sinks
with a source of running water where specimens and reagents are rinsed, drained or stained,
and fluids are discarded. Sufficient storage space such as drawers and cabinets must be
available for reagents and supplies, to prevent clutter on the laboratory counter space. As
some reagents or specimens must be kept cool or frozen, a refrigerator and freezer are
essential. One of the necessary things for a laboratory in the 21st century is Internet access,
as it offers the possibility of e-mail to report the critical results of submitted diagnostic tests
or send photographic images. The Internet may also serve as a diagnostic aid in laboratories
with digital camera attachments to compound microscopes. Another important category of
laboratory equipment comprises laboratory glassware such as beakers, graduated cylinders,
flasks, thermometers, reagent bottles, test tubes, glass rods, evaporating dishes, watch
glasses and the like. Central to food testing analysis are spectrometers, alcohol analyzers,
refractometers, titrators, moisture analyzers, and other standard lab equipment. Specialized
analyzers and meters are also available for specific methods and applications, while others
can be used for various food analysis requirements.
The analysis of food products for the presence of pathogenic microorganisms is one
of the basic steps to control the safety and quality of food. Most of the microorganisms
encountered in the laboratory are potentially pathogenic, thus all specimens should be
handled as potentially contagious. The safety of every person working in the laboratory
depends on strict observance of safety and hygiene rules. Staff must wear personal
protective equipment (PPE) during their work and materials contaminated with potentially
infectious agents must be decontaminated before disposal. Moreover, all accidents must be
reported immediately to the laboratory supervisor or other competent authority.
The first stage of microbiological analysis of food consists in taking and preparing a
sample for testing. Incorrect sampling may result into obtaining false negative or false
positive results. The “representative sample” should reflect the profile of the product from
which it originates as accurately as possible.
There are a variety of methods used for microbe detection; some of them being more
traditional, like culture collection, whereas, others are newer and faster and include e.g.
polymerase chain reaction (PCR), infrared devices that detect bacteria in food, and rapid
scans that detect bacterial contamination in blood platelets. One traditional technique of
bacterial detection is to take a sample, grow a bacteria culture, and count the bacteria that
grow. This method is effective but can take hours or days to show results and may miss
some types of bacteria. Another traditional culture method detects changes in oxygen levels
indicating the presence of bacteria but obtaining results can take seven days.
Among the newer, more rapid systems to detect bacteria are: solid-phase cytometry
which detects and counts all fluorescently labelled bacteria within three minutes, or PCR
(polymerase chain reaction) typically required for high sensitivity, specificity, and rapid
results. It is an enzymatic reaction replicating a DNA molecule, thus a critical condition of the
PCR course is the presence of an enzyme, thermostable DNA polymerase. Variants of the
conventional PCR method are a real-time PCR (an improved method observed in real time)
and multiplex PCR (two or more loci are simultaneously amplified in the same reaction).
 Task. Answer the following questions.
What types of food analysis do you know?
___________________________________________________________________________
Who conducts food analysis?
___________________________________________________________________________
What is a laboratory and how should it be equipped?
___________________________________________________________________________
What typical equipment and instruments can you name?
___________________________________________________________________________
Are there some tools or appliances necessary for food testing?
___________________________________________________________________________
What does the abbreviation PPE stand for?
___________________________________________________________________________
What is a “representative sample”?
___________________________________________________________________________
Can you name some rapid methods of detecting microorganism in food?
___________________________________________________________________________
What does the word “thermostable” mean?
___________________________________________________________________________
Useful phrases and expressions
Basic laboratory equipment /ˈbeɪsɪk ləˈbɒrət(ə)ri ɪˈkwɪpmənt/Základní vybavení
laboratoře
balance/scales
/ˈbæləns/ /skeɪls/
váhy
beaker
/ˈbiːkə(r)/
kádinka
boiling flask
/ˈbɔɪlɪŋ flɑːsk/
varná baňka
Bunsen burner
/ˌbʌns(ə)n ˈbɜː(r)nə(r)/
Bunsenův kahan
burette
/bjuəˈret/
byreta
crucible
/ˈkruːsəb(ə)l/
tavicí kelímek
Erlenmeyer flask/conical flask/ˈɜːlənˌmaɪə flɑːsk / /ˈkɒnɪk(ə)l…/ Erlenmeyerova baňka
evaporating dish
/ɪˈvæpəreɪtɪŋ ˌdɪʃ/
odpařovací miska
forceps
/ˈfɔː(r)seps/
kleště
funnel
/ˈfʌn(ə)l/
nálevka
glass rod
/ɡlɑːs rɒd/
skleněná tyčinka
graduated cylinder
/ˈɡrædʒuˌeɪtɪd ˈsɪlɪndə(r)/
odměrný válec
hand lens/magnifying glass /hænd lenz/ /ˈmæɡnɪfaɪŋ ɡlɑːs/
lupa
microscope
/ˈmaɪkrəˌskəʊp/
mikroskop
mortar and pestle
/ˈmɔː(r)tə(r) ənd ˈpes(ə)l/
třecí miska s tloučkem
pipette/chemical dropper
/pɪˈpet/ /ˈkemɪk(ə)l ˈdrɒpə(r)/
pipeta
ring stand/clamp stand
/rɪŋ stænd / /klæmp stænd/
laboratorní stojan
test tube holder
/test tjuːb ˈhəʊldə(r)/
držák na zkumavky
test tube
/test tjuːb/
zkumavka
thermometer
/θə(r)ˈmɒmɪtə(r)/
teploměr
tongs
/tɒŋz/
kleště
tripod
/ˈtraɪpɒd/
trojnožka
wash bottle
/wɒʃ ˈbɒt(ə)l/
střička
watch glass
/wɒtʃ ɡlɑːs/
hodinové sklíčko
wire gauze
/ˈwaɪə(r) ɡɔːz/
drátěná síťka
Equipment and instruments specific
Zařízení a nástroje specifické
for the microbiology laboratory
pro mikrobiologické laboratoře
syringe and needle
/sɪˈrɪndʒ ˈniːd(ə)l/
stříkačka a jehla
inoculating loops
/ɪˈnɒkjʊleɪtɪŋ luːps/
očkovací kličky
scissors and forceps
/ˈsɪzə(r)z ənd ˈfɔː(r)seps/
nůžky a kleště
sterile cotton-tipped swabs /ˈsteraɪl ˈkɒt(ə)n tɪpt swɒb/
sterilní štětička
collection tube
/kəˈlekʃ(ə)n tjuːb/
odběrové zkumavka
glass slide and cover tip
/ɡlɑːs slaɪd ənd ˈkʌvə(r) tɪp/
podložní a krycí sklíčko
various culture media
/ˈveəriəs ˈkʌltʃə(r) ˈmiːdiə/
různá kultivační média
gram stain
/ɡræm steɪn/
Gramovo barvení
incubator
/ˈɪŋkjʊˌbeɪtə(r)/
inkubátor
discard jar with disinfectant
odpadní nádoba s
/dɪsˈkɑː(r)d dʒɑː(r) wɪð ˌdɪsɪnˈfektənt/
Lab. personal protective equipment (PPE)
desinfekcí
Osobní ochranné pomůcky
laboratory coat/gown
/ləˈbɒrət(ə)ri kəʊt / /...ɡaʊn/
laboratorní plášť
safety goggles
/ˈseɪfti ˈɡɒɡ(ə)lz/
ochranné brýle
face shield
/feɪs ʃiːld/
ochranný štít
disposable gloves
/dɪˈspəʊzəb(ə)l ɡlʌvz/
jednorázové
rukavice
face mask/respirator
/ feɪs mɑːsk//ˈrespəˌreɪtə(r)/
Units used to describe lab results
obličejová maska
Jednotky užívané pro popis lab. výsledků
g/L or g/l (gram per litre/liter)/ɡræm pə(r) ˈliːtə(r)/
gram na litr
L/L (litres per litre)
/ˈliːtə(r) pə(r) ˈliːtə(r)/
litr na litr
U/L (unit per litre)
/ˈjuːnɪts pə(r) ˈliːtə(r)/
jednotka na litr
mmol/L (millimole per litre) /ˈmɪləˌmoːl pə(r) ˈliːtə(r)/
milimol na litr
umol/L (micromols per litre) /ˈmaɪkrəʊˌməʊl pə(r) ˈliːtə(r)/
mikromol na litr
Terms used to describe lab values
Termíny užívané pro popis lab. výsledků
within normal limits/normal /wɪðˈɪn ˈnɔː(r)m(ə)l ˈlɪmɪts/
v normě/normální
elevated/raised/increased
/ˈeləˌveɪtɪd/ /reɪzd/ /ɪnˈkriːst/
zvýšený
reduced/decreased
/rɪˈdjuːst//diːˈkriːst/
snížený
Vocabulary practice
1. Label the following laboratory equipment.
a long thin glass container that is open at one end and is used in laboratories
T……. T……….
a glass tube marked with a scale and with a tap at the bottom
B………………..
a tube wide at the top and narrow at the bottom, used for pouring liquid
F………………..
a piece of equipment used for weighing people or things
S…………………
a glass or plastic container with straight sides
B………………..
a bowl in which you crush substances into a powder
M………………
a container used for heating substances or melting metals
C………………..
special glasses that protect your eyes
G……………….
a piece of equipment producing a gas flame, used for scientific experiments
B………B………
an object with three legs that is used for supporting something
T…………………
2. Translate the following phrases into English.
provádět pokusy a výzkum
………………………………………………………………………………..
objevit nebezpečné bakterie
………………………………………………………………………………..
zkoumat přítomnost enzymu
………………………………………………………………………………..
řádně odebrat vzorek
………………………………………………………………………………..
zvýšené hodnoty bílkovin
………………………………………………………………………………..
analýza na potravinové alergeny
………………………………………………………………………………..
vypěstovat bakteriální kulturu
………………………………………………………………………………..
sledovat změny v hodnotách kyslíku ………………………………………………………………………………..
získat výsledky během pár minut
………………………………………………………………………………..
nebezpečí falešně pozitivních výsledků.……………………………………………………………………………..
3. Below are the steps describing the procedure for operating a microscope. Put them into
the correct order.
1. Place the slide on the stage.
2. Lower the stage to its lowest point.
3. Turn on the light.
4. Move the objective into position by turning the turret or revolving nosepiece.
5. Go home
6. Use the coarse and fine adjustment knobs to get the image into focus.
7. Remove the slide.
8. Adjust the condenser and the diaphragm following the manufacturer’s instructions.
9. Check the eyepieces, objectives and condenser lens and clean them if necessary.
10. Turn the light off and lower the stage completely.
Grammar. Reported speech
Transform the following sentences into reported speech.
Example: He said: “I'm hungry!”
He said that he was hungry.
o Josh said: “Twelve panellists have evaluated all six of the bread samples.
Josh said that _____________________________________________________________
o All supervisors concluded: “The artisanal gluten free breads are associated with
more negative characteristics than that of industrially processed breads.”
All supervisors concluded that _______________________________________________
________________________________________________________________________
o The lecturer informed us: “Wheat bread consumption has been declining possibly
due to changing eating patterns and availability of alternative grain products such
as breakfast cereals.”
The lecturer informed us that ________________________________________________
________________________________________________________________________
o The report said: “To satisfy the demand of GF consumers for high quality bread
products companies must produce GF bread that has characteristics similar to
that of wheat flour bread.”
The report said that ________________________________________________________
________________________________________________________________________
o The reporter asked: “How many participants does this study consist of?”
The reported asked_________________________________________________________
________________________________________________________________________
o The study director asked: “Were participants yesterday instructed that the more
similar two samples were, the closer they were placed together on the paper?”
The study director asked____________________________________________________
________________________________________________________________________
o The manager ordered: Offer more printed publications relating to the wine and
gastronomy sector!”
The manager ordered_______________________________________________________
___________________________________________________________________________
Vocabulary
accommodate (v)
/əˈkɒmədeɪt/
vyhovovat, přizpůsobit
adjust (v)
/əˈdʒʌst/
seřídit, nastavit
agar (n)
/ˈeɪɡɑː(r)/
agar
allergen (n)
/ˈælə(r)ˌdʒen/
alergen
analyser (n)
/ˈænəlaɪzə/
analyzátor, analytik
beaker (n)
/ˈbiːkə(r)/
kádinka
cabinet (n)
/ˈkæbɪnət/
skříňka
clutter (n)
/ˈklʌtə(r)/
nepořádek
contaminant (n)
/kənˈtæmɪnənt/
znečišťující látka
count (n)
/kaʊnt/
množství, počet ve vzorku
counter space (phr)
/ˈkaʊntə(r) speɪs/
pracovní prostor
current (n)
/ˈkʌrənt/
proud
cylinder (n)
/ˈsɪlɪndə(r)/
válec
decontaminate (v)
/ˌdiːkənˈtæmɪˌneɪt/
dekontaminovat, odmořit
demonstrate (v)
/ˈdemənˌstreɪt/
prokázat, předvést
discard (v)
/dɪsˈkɑː(r)d/
vyhodit
disposal (n)
/dɪˈspəʊz(ə)l/
likvidace
drain (v)
/dreɪn/
drawer (n)
/ˈdrɔːə(r)/
zásuvka, šuplík
encounter (v)
/ɪnˈkaʊntə(r)/
setkat se s, narazit na
extraneous (adj)
/ɪkˈstreɪniəs/
nepodstatný; vnější
eyepiece (n)
/ˈaɪˌpiːs/
okulár (mikroskop)
flask (n)
/flɑːsk/
baňka
harmful (adj)
/ˈhɑː(r)mf(ə)l/
škodlivý
histamine (n)
/ˈhɪstəmiːn/
histamin
image (n)
/ˈɪmɪdʒ/
snímek, obrázek
Lactobacillus
/ˌlæktəʊbəˈsɪləs/
laktobacil
Listeria
/lɪsˈtɪərɪə/
listerie
meter (n)
/ˈmiːtə(r)/
měřicí přístroj
moisture (n)
/ˈmɔɪstʃə(r)/
vlhkost
peanut (n)
/ˈpiːˌnʌt/
arašíd
odtéct, vylít
platelet (n)
/ˈpleɪtlət/
krevní destička
polymerase (n)
/pəˈlɪməreɪz/
polymeráza
Pseudomonas
/sjuːˈdɒmənəs/
pseudomonáda
reagent (n)
/riˈeɪdʒ(ə)nt/
činidlo, reagens
reflect (v)
/rɪˈflekt/
odrážet
revolving nosepiece (phr)
/rɪˈvɒlvɪŋ ˈnəʊzˌpiːs/
otočná hlavice mikroskopu
rinse (v)
/rɪns/
opláchnout
rod (n)
/rɒd/
tyčinka
running water (phr)
/ˈrʌnɪŋ ˈwɔːtə(r)/
tekoucí voda
sink (n)
/sɪŋk/
umyvadlo, výlevka
slide (n)
/slaɪd/
podložní sklíčko
specimen (n)
/ˈspesəmɪn/
vzorek
spectroscopy (n)
/spekˈtrɒskəpɪ/
spektroskopie
stage (n)
/steɪdʒ/
stolek (mikroskop)
stain (v)
/steɪn/
vybarvovat (preparáty)
Staphylococcus aureus
/ˌstæfɪləʊˈkɒkəs ˈɔːrɪəs/
zlatý stafylokok
submit (v)
/səbˈmɪt/
předložit, podat, odevzdat
test tube (n)
/test tjuːb/
zkumavka
thermometer (n)
/θə(r)ˈmɒmɪtə(r)/
teploměr
thermostable (adj)
/ˌθɜːməʊˈsteɪbəl/
odolný proti teplu
tripod (n)
/ˈtraɪpɒd/
stativ, trojnožka
turret (n)
/ˈtʌrɪt/
revolverová hlava (mikroskop)
unwholesome (adj)
/ʌnˈhəʊls(ə)m/
nezdravý, zdravý škodlivý
wagon (n)
/ˈwæɡən/
nákladní vagón, vůz