Lecture 3 - Sample Prep Flashcards Preview

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Flashcards in Lecture 3 - Sample Prep Deck (38)
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1

describe the general flow of food analysis

sampling, pre-processing, processing, testing

2

what's the purpose of pre-treatment and sample processing?

- reduce sample size
- homogenize
- prevent changes (contamination, deterioration)
- avoid matrix interference

3

name some methods of reducing sample size

- blenders
- coning and quartering (spice)

4

sample obtained from populations are usually (homogeneous/heterogeneous)

heterogenous

5

variations in properties of different units within the sample causes what?

sample heterogeneity

6

name some methods for homogenizing samples

- grinders
- mixers
- slicers
- blenders

7

mechanical homogenization often results in the undesirable production of _____

heat

8

grinding frozen samples in liquid nitrogen using a pre-cooled mortar and pestle is known as:

cryogenic grinding

9

what are 3 causes of sample loss?

- dust/particulates
- volatilization
- adsorption

10

list sources of loss of dust/particulates

- dry dust powder
- air flows generated by changes in temp
- breathing

11

how do you avoid loss of dust/particulates?

- never open the door of a hot furnace
- use a plug of glass or quartz wool to collect particulates when combustion is aided by stream of gas
- ash or finely ground samples should be covered before they are moved
- add reagents slowly to prevent losses as spray

12

list sources of loss via volatilization

- during heating of samples
- heat generated in grinding (lose water)
- volatile metals: As, Sb, Sn, Po, Pb, Se, Hg, Ge, B
- Cr volitized in oxidizing chloride media
- C, P, Si volitized as hydrates

13

how do you mitigate loss from volatilization?

use properly sealed vessels for wet ashing

14

how do you get loss from adsorption?

molecules adsorb to plastic or glass containers

15

how do you mitigate adsorption losses?

- use pre-treated glassware with an established hydrated layer
- soak new glassware overnight in a dilute nitric or hydrochloric acid solution

16

when sampling, we want to (prevent/enable) change

prevent, duh

17

what are some causes of changes in samples? (5)

- enzymes
- lipid oxidation
- microbial growth
- physical change
- contamination

18

how do you prevent enzymatic changes?

- heat denaturation
- storage in freezer
- pH
- adding reducing agents to prevent oxidative enz

19

(saturated/unsaturated) lipids are sensitive to oxidative degredation

unsaturated

20

exposure to _____ can accelerate lipid peroxidation

light

21

how do you mitigate lipid oxidation of samples?

- store under nitrogen or vacuum
- use antioxidant if not interfering with analysis

22

what badness do microbes bring to your samples?

- degradation of food components
- introduction of microbial components

23

how do you mitigate microbial changes to your sample?

- addition of preservative (sodium azide)
- low temp storage
- freeze drying
- storage under modified atmosphere

24

what kind of conditions cause physical changes?

- drying
- fluctuating storage temp
- fluctuating gas pressure

25

how d you mitigate physical changes?

- storage in airtight humidity controlled containers
- maintaining temperature

26

what are sources of contamination?

- airborne
- reagents
- glassware/equipment
- facilities
- cross-contamination

27

how do you reduce matrix interference?

- extraction of target analytes
- removal of interfering substances

28

methods of extracting analytes (4)

- digestion
- solvent extraction
- sorbent extraction
- membrane extraction

29

read slide 18 and 19

ok

30

what's a confidence band?

defines statistical uncertainty of regression line