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Levels of benzene, toluene, ethylbenzene, xylenes and styrene (BTEXS) find their way into olive trees and hence into the olives and olive oil mainly as a result of the presence of vehicle exhaust in ambient air. Although there is widespread concern about the presence of these carcinogenic compounds in olive oil, no definitive methods or limits have yet been prescribed. Various methods have been developed to detect and quantify these compounds down to levels of 5ng/g (5 ppb w/w). In this work, we have developed a simple method to determine these components in olive oil using headspace (HS) extraction and gas chromatography/mass spectrometry (GC/MS). Sample preparation simply comprises dispensing and sealing 10g of olive into a standard 22-mL headspace vial and sampling the headspace vapor after being equilibrated at 90°C. The vapor is introduced into a Carbowax capillary column for chromatographic separation. Detection, identification and quantification is performed using a quadrupole MS system with a novel ionizer and detection system that enables detection limits, in single ion monitoring (SIM) mode, down to below 0.5ng/g without the need for headspace vapor preconcentration. The analysis is fully automated and takes just 10.5 minutes for the chromatography and an additional 3.5 minutes for cool-down and equilibration between analyses. Excellent quantitative performance has been demonstrated and the system is easily able to see concentrations of these compounds in the range 0.9ng/g to 126.1ng/g in olive oil bought from a local supermarket. Examples of the chromatography and quantitative performance will be presented.
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April 13, 2023
© 2009 PerkinElmer
Practical Food Applications by Thermal AnalysisPeng Ye
Types of Food Characterized By Thermal Analysis
Oils
Starches
Proteins
Chocolate
Lactose
Page 2
TYPE OF SAMPLES TYPE OF INFORMATIONOils, fats and spreads onset temp of melt / crystallisation /polymorphic
behaviour/oxidation stability
Flour and rice starch gelatinization /glass transition Tg
Vegetable powders glass transition TgPastes and gels containing polysaccharides or gums
specific heat Cp, onset temp of melt and crystallisation
Protein denaturation/aggregation
Heat influence on emulsifier
Time influence on palm kernel oil melting behavior
Gelantinization of Starches by DSC
At gelatinization temperature, hydrogen bonding which holds amylopectin and amylose will be broken and the polysaccharides undergoes order-disorder transition, “Gelatinization”
DSC can be used to understand the gelatinization temperature and allows food technologist to mix different starch to achieve certain digestive and textural behavior in final food products
Requires use of sealed DSC containers
Page 5
20%wt/wt Starch in Water
En
do
http://food.oregonstate.edu/starch/temp.html
Page 6
Effect of Starch/Water Content on Gelatinization by DSC
Generally, gelatinization temperature will decrease with the increase in water content
It was found that at high and intermediate water contents, loss of crystallinity occurred over the gelatinization temperature range as determined by DSC.
When sufficient water is provided, gelatinization endotherm occur as a single peak (Biliaderis et al 1998).
When insufficient water is present, gelatinization endotherm may exist as two peaks.
Page 7
Gelatinization of CMC Derived from Palm Tree
Page 8
Gelatinization is a non reversible process
APPLICATION : wet Tg of Potato Starch by HyperDSC
Page 9
Denaturation of Egg Proteins by DSC
Protein denaturation is a phenomenon where the protein molecules undergoes irreversible structural rearrangment
Protein denaturation temperature will depend on the pH of the medium and water content.
Generally, protein denaturation temperature will increase with the reduction of water content
Heat of denaturation is important in the formation of food structure and the inhibition of enzymatic and microbial activity in food
Page 10
Shelf Life of Eggs by DSC
DSC can be used to assess shelf lifetimes of proteins
Storage will affect protein denaturation
For eggs, storage at 30’C causes transformation of ovalbumin to S-ovalbumin (undesired)
Page 11
Denaturation of Meat Proteins by DSC
Meat proteins undergo several conformational changes during heating
DSC curves are ‘fingerprints’ of the various meat proteins
Useful for quality assurance
Useful for shelf-life estimates
Page 12
DSC of Chocolate
Textural properties of chocolate are related to melting characteristics
Cocoa butter can exist in different polymorphic forms affecting textural properties
Different thermal history induced via tempering conditions will produce different polymorphic ratio and give it different textural properties
Page 13
Effects of Aging on Melting of Cocoa Butter
Cocoa butter will change its crystalline structure as it is physically aged at room temperature due to polymorphism
The melting process of the cocoa butter will affect the textural ‘feel’ of the butter
Page 14
Spray dried Lactose …
Page 15
----- 500 °C/min
----- 400 °C/min
----- 250 °C/min
----- 100 °C/min
----- 20 °C/min
… at various scan rates
Tg data of spray dried Lactose …
Page 16
----- 500°C/min Onset 79.3°C
----- 400°C/min Onset 80.1°C
----- 500°C/min Onset 80.5°C
----- 250°C/min Onset 79.8°C
----- 100°C/min Onset 78.0°C
…Tg Onset values little affected by scan rate
Mixtures of Amorphous and Crystalline Lactose
Page 17
----- 100% Amorphous
----- 11% Amorphous
----- 5% Amorphous
----- 4% Amorphous
----- 3% Amorphous
----- 1.5% Amorphous
… scanned at 500°C/min
Tg height as a Function of Amorphous Content …
0
2
4
6
8
10
12
0 50 100 150
% Amorphous Content
Hei
gh
t o
f T
G
Page 18 … to 100% amorphous
Tg height as a Function of Amorphous Content …
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12
% Amorphous Content
Heig
ht
of
Tg
Page 19 … below 12% amorphous
Conclusion
DSC is a useful analytical tool to study food system.
The information from DSC study can be used to understand the thermal transitions during food process or storage.
DSC is easy to operate and both liquid and solid food samples can be studied.
DSC can be used for both QA/QC and R&D purpose for food.
New DSC technique like HyperDSC has significantly improved the application of DSC for food system.
