Lecture 3: Sample Preparation

Why is important to sample pre treatment and during sample processing?

1. reduce sample size

When sampling from a group of apples containing green and red apples, what type of sampling would you like to employ?

Stratified random sampling, whichtinvolves the division of a population into smaller subgroups known as strata. the strata are formed based on members' shared attributes or characteristics

What are the four objectives of sample pretreatment?

to reduce sample size, make samples homogenous, prevent changes in samples like contamination and deterioration, and avoice matrix interference during analysis

What type of sampling method are used for sampling spices?

coning and quartering, which is used for powder samples.

A 1kg lab sample must be reduced to what type of sample? What is the approximate amss of this sample?

Laboratory samples needs to be reduced to analytical samples of small quantity e.g. 2-5g.

Are the samples obtained from a population heterogenous or homogenous?

heterogenous. The distribution of attributes in a can of tomatoes, for example, may not be equal throughout the entire can.

What types of samples are homogenized by knives or blades?

high fat, high moisture content.

What types of samples are homogenized by grinders or mills?

low moisture samples

Why arent grinders or mills used for high fat or high moisture samples?

grinders and mills generate heat, which can alter moisture content and degrade fats.

Describe cryogenic grinding.

Cryogenic grinding: Grinding frozen samples in liquid nitrogen

Whata re three ways sample can be lost during preparation?

losses as 1. dust or particulates, 2. through volatization, or 3. adsorption.

Give three examples of sample Losses as Dust or Particulates

1. Dry dust powder during `ashing` by passing a stream of gas over the sample during heating to assist in combustion. 2. Air flows are generated by changes in temperature e.g., opening the furnace while it is hot. 3. Breathing onto dry powder sample.

Give four measures to mitigate sample losses and dust or particulates.

1. Never open the door of a hot furnace. 2. Use a plug of glass or quartz wool to collect particulates when combustion is aided by stream of gas. 3. Ash or finely ground samples should be covered before they are moved. 4. Add reagents slowly to prevent losses as spray

When do losses of sample through volatilization happen?

it happens during heating of samples, e.g. during wet ashing. This decreases water content during grinding solids because of localized heating.

Give examples of elements that may volatilize.

Examples of elements that may volatilize include arsenic, antimony, tin, polonium, lead, selenium, mercury, germanium, and boron.

How can chromium be volatized?

chromium is volatilized under oxidizing conditions in the presence of chloride.

How can carbon, phosphorus, and silicon be volatilized?

Carbon, phosphorus, and silicon may be volatilized as hydrides

How do you mitigate sample loss through volatilization?

Use properly sealed vessels for wet ashing.

Describe sample losses due to adsorption.

loss of sample is caused by the adsorption of molecules to plastic or glass containers

How do you mitigate sample loss through adsorption? List two ways.

1. Use pretreated glassware with an established hydrated layer. 2. Soak new glassware overnight in a dilute nitric or hydrochloric acid solution

What are five ways unpreserved samples can be changed?

1. Enzymatic degradation 2. Lipid oxidation 3. Microbial growth 4. Physical Change 5. Contamination

What is the only substance that can dissolve glass?

Hydrofluoric acid

Give examples of degradation enzymes in a food, and how this can alter accuracy in analysis.

proteases, amylases, lipases, peroxidases, oxidases and hydrolases can break down compounds.

What type of enzymes cause browning in apples? What is happening during this reaction?

phenoloxidase, or PPO, reacts with the phenolic compounds and turns them brown through oxidation. This is not ideal when testing for antioxidant activity in apples.

How do you mitigate PPO degradation in apples?

you can add citric acid and/or salt to the exposed areas.

Give four examples of ways to mitigate enzymatic degradation in foods.

blanching to denture through heat, storage in -20 or -30 freezer, adjusting pH, and adding reducing agents such as citric acid.

Why must oils be stored in a closed opaque bottle from the light?

Unsaturated lipids are sensitive to oxidative degradation, and exposure to light can accelerate lipid peroxidation.

What are two ways to mitigate lipid oxidation in a high lipid sample?

1. Storing under nitrogen or vacuum, 2. Use antioxidant

Why does fish oil spoil faster than olive oil?

fish oil spoils faster because it has more unsaturated fatty acids, while olive oil contains more monounsaturated FAs and also naturally contains antioxidants.

What are four ways in mitigating microbial growth in samples?

Addition of preservative (e.g. sodium azide). Low-temperature storage. Freeze drying. Storage under modified atmosphere

What are the three causes of change in the physical structure of a sample? What are two ways to mitigate this?

drying, fluctuating storage temperatures, fluctuating gas pressures. To mitigate this, store samples in air-tight humidity-controlled containers, and maintain temperature.

What are 5 sources of contaminants?

Airborne (moisture and dust). Reagents. Glassware/equipment. Facilities. Cross-contamination

What is the objective of the AOAC's triangle scheme?

?

What are two main ways, conceptually, to prepare a sample to reduce matrix interference?

extract target analytes from the matrix or remove the interfering substances

What are four main methods of analyte extraction?

1. Digestion, 2. Solvent extraction, 3. Sorbent extraction, 4. Membrane extraction

Give 2 examples of digestion.

microwave, UV photolysis

Give 3 examples of solvent extraction.

pressurized liquid extraction PLE, supercritical fluid extraction SFE, microwave-assisted extraction MAE

Give 2 examples of sorbent extraction.

solid phase extraction SPE, headspace sorptive extraction HSSE,

Give 2 examples of membrane extraction.

dialysis, membrane extraction with a solvent interface MESI

Describe magnetic resonance imaging, or MRI.

MRI allows the structure of foods to be imaged noninvasively and nondestructively. Magnetic resonance images can present information about several processes and material properties in foods.

Describe the Computrac Vapor Pro XL from Arizona Instrument Inc

it is a chemical free alternative to Karl Fischer titration.

Describe the InfraLab-e-series (NDC Tecjnologies)

Infra red spectroscopy based instruments for measuring of moisture, fat, protein, and collagen content of meat products

Describe the MCT466-QuickCheck

on-line NIR tester for moisture, fat and seasoning contents.

Describe the SpectraStar-XT NIR Analyser (Unity Scientific)

measures moisture, fat , protein etc of food such as snacks, cereals, bakery mixes.

Describe the OPTi handheld and RFM340 Lab refractometer

for measuring Brix of beverages, sugars edible oil and flavors

Describe the Luminar 4030 & 5030 from Brimrose Corp

For real time evaluation of sugar in crackers and other products

Describe the ORACLE Universal Fat Analyzer from CEM Corp

for lab or at-line determination of fat content of any food product with in 30 sec.

Describe the Higuchi Inc.éIntlligent Sensor Technology-

Taste sensing system TS-5000Z which uses lipid membrane sensors to mimic human tongue.

Describe the MW 4300 (TEWS of America Cop.)

Microwave based at-line moisture determination instrument.

What is the equation of the regression line?

y=mx+b

What do the confidence bands on a standard curve represent?

they define the statistical uncertainty of the regression line

What does the correlation coefficient r on a standard curve represent?

r defines how well the data fits a straight line. Ideally, we want an r of +1 or -1, meaning that all data points represent the relationship between the x and y values.

What are the three effects of having outlier data?

1.Increase error variance 2. Reduce the power of statistical tests. 3. Decrease normality

What is the dixon Q test used for?

it is an objective way to determine outlier values.

What is the equation for finding the Q value?

x2-x1 / W, where x1 is the suspencted outlier value, x2 is the next closest value to x1, and W is the total spread of all values, obtained by subtracting the lowest value from the highest value

What are two main reasons outlier data occurs?

Outliers could be because of Errors in the data, human error, such as errors in data collection, recording, or entry, or from the inherent variability of the data

For a method to be precise, what should the coefficient of standard deviation be?

For a method to be considered precise, the coefficient of SD should be

What is a sample T test used for?

The One Sample t Test determines whether the sample mean is statistically different from a known or hypothesized population mean. It is a parametric test.

In a single sample t test, The variable used in this test is known as what?

the test variable

What are the 6 requirements data must meet for conducting a sample t test?

values must be 1. Continuous 2. Independent of observations 3. Random 4. Normally distributed 5. Homogenous 6. No outliers

What does it mean for the data to be independent of observations? What happens to the t test if this requirement is not met?

There is no relationship between scores on the test variable. Violation of this assumption will yield an inaccurate p value

Why are non-normal distributions of data non ideal?

Non-normal population distributions, especially those that are thick-tailed or heavily skewed, considerably reduce the power of the test. However, for moderate or large samples, a violation of normality may still yield accurate p values

What does it mean to have homogeneity of variances?

variances approximately equal in both the sample and population

Summarize the sample T test and how it is conducted.

In a One Sample t Test, the test variable is compared against a "test value", which is a known or hypothesized value of the mean in the population.