Scanning electron microscopy in frozen foods

Scanning electron microscopy in frozen foods

1. SCANNING ELECTRON
MICROSCOPY IN
FROZEN FOODS

2. INDEX
What is Scanning electron microscopy?
Principle and working
SEM in frozen foods
Sample Preparation
Microstructural analysis
Case study of ice cream
conclusion

3. 3
INTRODUCTION
SEM providesvaluableinsightsinto
themicrostructureandcompositionof
frozenfoods,enablingresearcherstoanalyze
icecrystalformation,foodtexture,and
structuralchangesduringfreezingandstorage.
ScanningElectronMicroscopy(SEM)isapowerful
imagingtechniquethatusesafocusedbeamof
electronstogeneratedetailed,high-resolution
imagesofthesurfacestructureofmaterials,
includingfrozenfoodsamples.

4. 4
Why SEM in
Frozen Food?
Defect
Detection
Quality
Assurance
Shelf Life
Prediction
Microstructural
Analysis
Early Warning
System
Research and
Development

5. 5
Working and Principle of SEM in
Frozen Food Analysis
TheprinciplesofSEMrelyontheinteractionbetween
theelectronbeamandthesample'ssurface.Asthe
beamscansacrossthesample,itgeneratesvarious
signalsthataredetectedandtranslatedintoadigital
image.Thisallowsresearcherstoanalyzethesize,
shape,anddistributionoficecrystals,aswellas
changesinthefood'scellularstructureduringfreezing
andstorage.

6. Sample
Preparation
6
Cryogenic
Fixation
•Rapidly freeze the samples in liquid nitrogen
or a cryogenic chamber to preserve the
microstructure and prevent ice crystal
formation during sample preparation.
Freeze
Drying
•Lyophilize the frozen samples to remove
water content while maintaining the original
structure and morphology of the food matrix.
Sputter
coating
•Apply a thin layer of conductive material, such
as gold or platinum, to the sample surface to
enhance contrast and prevent charging during
SEM imaging.

7. Microstructural
Analysis
•Microstructuralanalysisinvolvesthe
examinationoftheinternalstructure
andarrangementofcomponents
withinamaterialatamicroscopic
level.
•Inthecontextoffrozenfoods,
microstructuralanalysisaimsto
characterizethearrangementof
variouscomponentssuchasice
crystals,cellstructures,airpockets,
andotherconstituentspresentinthe
sample

8. 8
Types of Structures Observed in Frozen Foods
Ice Crystals
•Ice crystals form during the freezing process
and can vary in size, shape, and distribution.
The size and distribution of ice crystals have a
significant impact on the texture, appearance,
and overall quality of frozen foods.
Cell Walls
•Cell Walls: In plant-based frozen foods (e.g.,
fruits, vegetables), the cell walls of plant cells
may undergo changes during freezing,
affecting the texture and integrity of the food.
Microstructural analysis can reveal alterations
in cell morphology and cell wall integrity.
Air Pockets
•Air pockets or void spaces may be present within
frozen foods, particularly in products with a
porous structure (e.g., baked goods, ice cream).
The distribution and size of air pockets influence
factors such as texture, mouthfeel, and sensory
attributes.
Protein
Matrix
•In frozen foods containing proteins (e.g., meat,
seafood), the protein matrix undergoes structural
changes during freezing, such as denaturation and
aggregation. Microstructural analysis can provide
insights into protein-protein interactions and their
effects on product quality.

9. MICROSTRUCTURAL
ANALYSIS OF ICE CREAM
UNDER SEM
9
Themicrostructureoficecreamiscomplex,consisting
ofmultiplephasesincludingicecrystals,airbubbles,fat
globules,andaserumphasecontainingdissolved
and/orcolloidalcomponents.
Icecreamexhibitsafour-phasestructureconsistingof
icecrystals,aircells,fatinanemulsifiedform,anda
continuousserumphase.Theicecrystalsareseparated
fromairbubblesbyathinseruminterface.
Airbubblesinicecreamaresphericalandsmooth,
surroundedbyfatglobulesandtheserumphase.Aircell
diametersrangefromabout10to60µm,andfat
globulesaredisproportionatelydistributedattheair
bubble/seruminterface
Fatglobulesrangefrom0.5to2.5µmindiameterand
arefoundbothwithinairbubblesanddispersed
throughouttheserumphase.

10. 10
Images Under SEM
Four-phasestructureconsistingoficecrystals,aircells,
fatinanemulsifiedform,andacontinuousserumphase
containingdissolvedand/orcolloidalsugars,salts,
proteinsandstabilizers(Fig.2).
Athinseruminterfaceseparatedtheicecrystalsfrom
airbubbles(Fig.3a).
Atlowermagnifications,airbubblesweresphericaland
smoothandcontainedfatglobuleswhereasicecrystals
weremorerectangularwithanetworkstructure(Fig.2).
Thestructuredenotedby"C"inFig.2isthespaceonce
4occupiedbyanicecrystalpriortofreeze-etching.

11. 11
Role of SEM in Quality Control
•Itallowsfortheexaminationoftheinternalstructure
offrozenfoodsatamicroscopiclevel,enablingthe
detectionofdefects,abnormalities,andchangesthat
mayoccurduringprocessing,storage,and
transportation.
•ByanalyzingSEMimages,manufacturerscanassess
theoverallquality,integrity,andsafetyoffrozenfood
productsandidentifyanypotentialissuesthatmay
affectconsumersatisfactionorcompliancewith
regulatorystandards.
•SEMenablesthedetectionofdefectsandabnormalities
infrozenfoodproductsthatmaynotbevisibletothe
nakedeyeorthroughconventionalqualitycontrol
methods.Commondefectsandabnormalitiesthatcanbe
detectedinclude:
•Structuraldamage
•Contamination
•Physicalirregularities
•SEMallowsforthemonitoringofchangesthatoccurin
frozenfoodproductsduringstorageandtransportation.
•ByperiodicallyanalyzingSEMimagesoffrozenfood
samplesthroughoutthestorageandtransportation
process,manufacturerscantrackchangesin
microstructure,identifysignsofdeteriorationorspoilage.
•SEMcanprovidevaluableinsightsintotheeffectsof
temperaturefluctuations,moisturemigration,packaging
defects.

12. CONCLUSION
12
SEMservesasapowerfultoolforqualitycontrolin
thefrozenfoodindustry,enablingthedetectionof
defects,abnormalities,andchangesinmicrostructure
thatmayaffectproductqualityandsafety.By
leveragingSEManalysis,manufacturerscanensure
theintegrity,stability,andcomplianceoffrozenfood
productswithregulatorystandardsandconsumer
expectationsthroughouttheproduction,storage,and
transportationprocess.