PerkinElmer: Practical Food Applications by Thermal Analysis
 

PerkinElmer: Practical Food Applications by Thermal Analysis

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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 ...

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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  • it can be observed that a α-modification is formed after a heat-cool treatment. This will be transformed into a β’-modification and after a certain time at room temperature partially to the β-modification. In Figure 2 the influence of storage time at room temperature is shown. The first heating of day 8 shows a better resolved peaks due to the transition of the less stable β’ to a more stable polymorphic fraction, as it was also confirmed by XRD.
  • In Figure 2 the influence of storage time at room temperature is shown. The first heating of day 8 shows a better resolved peaks due to the transition of the less stable β’ to a more stable β form polymorphic fraction, as it was also confirmed by XRD.
  • This figure shows the effect of analyzing the same spray-dried sample of lactose by conventional and HyperDSC methods. Conventional DSC is represented by the data collected with scan rates of 20°C/min and 100°C/min shown in brown and green, and the HyperDSC data are collected at scan rates of 250, 400, and 500°C/min (blue, red and black). As you can see in the temperature range below 120C, the fast heating and cooling rates associated with the HyperDSC method lead to a dramatically increased heat flow signal and increased sensitivity for the detection of the glass transition Tg. You can also see the excellent signal resolution of the double peaks of the melt, even at rates of 500C/minute. Further reduction of sample weight at this rate would further improve resolution.
  • Now lets rescale the data to just look at the glass transition area. There are several important points here: First notice again the increase of the glass transition step with scanning rate (i.e. the increased sensitivity). Note the very good reproducibility obtained on two different samples when using a fast rate of 500C/min. And finally, Unlike with Polymers (different molecular weights), the Tg here is only little affected by the scanning rate.
  • Comparing the results of a 100% amorphous material (the top curve, which is allowed to go offscale because of its large size) to various mixtures with as low as 1.5% amorphous component lead to these curves. As you can see, it was possible to reduce the amorphous content down to 1.5% and still detect clearly the Tg due to the great sensitivity of the HyperDSC method. It has previously been reported that the DSC detection sensitivity for amorphous content in crystals was 10% w/w (saleki-Gerhardt et al,1994). So there is no doubt that HyperDSC is a huge improvement and extends the capability of DSC to detection of very low amorphous content - HyperDSC increases detectability by almost a factor of 10.

PerkinElmer: Practical Food Applications by Thermal Analysis PerkinElmer: Practical Food Applications by Thermal Analysis Presentation Transcript

  • Practical Food Applications by Thermal Analysis Peng Ye March 20, 2012© 2009 PerkinElmer
  • Types of Food Characterized By Thermal Analysis Oils Starches Proteins Chocolate Lactose TYPE OF SAMPLES TYPE OF INFORMATION Oils, fats and spreads onset temp of melt / crystallisation /polymorphic behaviour/oxidation stability Flour and rice starch gelatinization /glass transition Tg Vegetable powders glass transition Tg Pastes and gels containing specific heat Cp, onset temp of melt and polysaccharides or gums crystallisation Protein denaturation/aggregation
  • Heat influence on emulsifier
  • Time influence on palm kernel oil melting behavior
  • Gelantinization of Starches by DSC At gelatinization temperature, 20%wt/wt Starch in Water 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 Endo Requires use of sealed DSC containers
  • http://food.oregonstate.edu/starch/temp.html
  • 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.
  • Gelatinization of CMC Derived from Palm Tree Gelatinization is a non reversible process
  • APPLICATION : wet Tg of Potato Starch by HyperDSC
  • 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
  • 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)
  • 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
  • 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
  • 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
  • Spray dried Lactose … ----- 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 … ----- 500°C/min Onset 79.3°C ----- 500°C/min Onset 80.5°C ----- 400°C/min Onset 80.1°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 ----- 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 … 12 10 Height of TG 8 6 4 2 0 0 50 100 150 % Amorphous Content … to 100% amorphous
  • Tg height as a Function of Amorphous Content … 1.2 1 Height of Tg 0.8 0.6 0.4 0.2 0 0 2 4 6 8 10 12 % Am orphous Content … 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.