10. LABORATORY ANALYSIS OF FOOD
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).
Ø Task. Answer the following questions.
What types of food analysis do you know?
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Who conducts food analysis?
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What is a laboratory?
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What typical equipment and instruments can you name?
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Are there some tools or appliances necessary for food testing?
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What does the abbreviation PPE stand for?
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What is a “representative sample”?
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Can you name some rapid methods of detecting microorganism in food?
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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/ desinfekcí
Lab. personal protective equipment (PPE) 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)/ obličejová maska
Units used to describe lab results 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.……………………………………………………………………………..
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 homeJ
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 Practice - Reported (Indirect) Speech
Key points:
Ø Back shift: Tenses shift back in time after a past tense reporting verb.
Present
present simple / past simpleI work in a laboratory.
Pracuji v laboratoři. / He said he worked in a laboratory.
Řekl, že pracuje v laboratoři.
present continuous / past continuous
I am working in a laboratory. / He said he was working in a laboratory.
present perfect simple / past perfect simple
I have worked in a laboratory. / He said he had worked in a laboratory.
present perfect continuous / past perfect continuous
I have been working in a laboratory. / He said he had been working in a laboratory.
Past
past simple / past perfect simple/past simpleI worked in a laboratory.
Pracoval jsem v laboratoři. / He said he had worked/ worked in a laboratory.
Řekl, že pracoval v laboratoři.
past continuous / past perfect continuous
I was working in a laboratory. / He said he had been working in a laboratory.
past perfect simple/continuous / past perfect simple/continuous - NO CHANGE!!!
I had worked/been working in a laboratory. / He said he had worked/been working in a laboratory.
Future
Will / WouldI will work in a laboratory.
Budu pracovat v laboratoři. / He said he would work in a laboratory.
Řekl, že bude pracovat v laboratoři.
“be going to” / “was/were going to”
I am going to work in a laboratory. / He said he was going to work in a laboratory.
Modal verbs
can / couldI can work in a laboratory. / He said he could work in a laboratory.
may / might
I may work in a laboratory. / He said he might work in a laboratory.
will / would
I will work in a laboratory. / He said he would work in a laboratory.
shall / would
I shall work in a laboratory. / He said he would work in a laboratory.
must / must or had to
I must work in a laboratory. / He said he must/had to work in a laboratory.
needn’t / needn’t/didn’t have to
I needn’t work in a laboratory. / He said he needn’t/didn’t have to work in a laboratory.
Reference words (place and time adverbials, pronouns, etc.)
Direct speech / Reported speechnow / then, at the moment
today, this week, this month, etc. / that day, that week, that month
yesterday, last week, last year, etc. / the day before, the previous week, the previous year
tomorrow, next week / the following day, the following week
ago / before
here / there
· Indirect questions
Reporting questions - Yes/No questions are reported using if. The verb does not have a question form but has the form of a normal statement. There is no question mark.
e.g. “Do I have to wear a lab coat during the experiment?”
He asked me if he had to wear a lab coat during the experiment.
Wh- questions are reported using the question word. The verb has the form of a normal statement. There is no question mark.
e.g. Why do I have to wear a lab coat during the experiment?”
He asked me why he had to wear a lab coat the experiment.
Ø No back shift:
· If the reporting verb is in the present tense.
e.g. “I sample the blood if necessary.”
The doctor says he samples the blood if necessary.
· If the present (e.g. today) in the direct speech is still the present in the reported speech.
e.g. “I am in a lab.”
He said he is in a lab today.
· If the future in the direct speech is still the future in the reported speech.
e.g. “I will phone you the results.”
He said he will phone me the results. (I am still waiting for his phone call).
· If the reported words are always true.
e.g. “Salmonellosis is an infection with bacteria called Salmonella.”
He said salmonellosis is an infection with bacteria called Salmonella.
· If the sentences are commands (imperatives) or requests; they are reported with tell or ask + infinitive.
e.g. “Avoid distress and suffering to the experimental animals!”
He told us to avoid distress and suffering to the experimental animals.
SAY x TELL
We say something – e.g. I said I could treat his wound.
We tell somebody – e.g. I told him I could treat his wound.
1. Rewrite each sentence as reported speech. Start with “the supervisor said/asked/ordered, etc”.