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Home > News & Events > Spectroscopy Techniques for Food Analysis

Spectroscopy Techniques for Food Analysis

Applying Absorbance, Reflectance and More to Food Applications

Ocean Optics offers a full menu of spectrometers and accessories for applications involving food and beverage processing, authentication and packaging. Spectroscopy techniques including absorbance, reflectance and fluorescence reveal information ranging from the fat content of milk and grains to the purity of olive oil and honey. Additional examples include: Absorbance, Reflectance, NIR, Fluorescence, and SERS.
Absorbance

Absorbance measurements explore the chemical composition of a food directly via the wavelengths absorbed when light is transmitted through it. Absorbance is most often used for liquids, as Beer’s Law simplifies quantitative analysis.

Samples with high absorption or scatter like colloids (milk) or suspensions (mixed vegetable juice) may require chemometric analysis. Temperature is also important for aqueous samples, and for oils that might be solid at ambient conditions. Also, it is possible to look at the light transmitted through whole foods, which has proven a viable method for inspecting fruit for ripeness, internal rot, pests and defects.

  • Fruit juices: soluble solids content, pH, color, adulteration
  • Milk: fat, protein and casein content
  • Saffron: ISO 3632 quality method to measure crocin, picrocrocin and safranal
  • Vegetable oils: identity, adulteration, acid value, peroxide value
  • Wine: quality, phenols, tannins, methanol content

Reflectance

Reflection yields information similar to absorbance when applied to solid foods, with the depth of penetration being dependent on factors such as the wavelengths used, sample composition and structure, and illumination source intensity. Reflectance has the benefit of being non-contact and noninvasive, and can be configured for a wide range of samples.

Bulk samples like meats and fruit are usually measured in a stand-off configuration, but a window is typically used for measurement of ground samples and powders. The greatest amount of information often can be extracted about food quality or integrity when visible and NIR reflectance measurements are combined to cover 400-2500 nm, which can be achieved using an Ocean Optics tungsten halogen lamp with Flame-S-VIS-NIR and NIRQuest512-2.5 spectrometers for detection.

  • Crabmeat: substitution with surimi-based imitations and lower-grade crabmeat
  • Fruit: variety, ripeness, sugar content, soluble solid content, internal pests
  • Meat: distinguishing pasture-fed from concentrate-fed livestock
  • Purees: adulteration of strawberry or raspberry with lower-cost apple
  • Whole grains: protein, moisture, oil content

NIR

Near infrared spectroscopy is well-suited to nondestructive analysis of bulk, high-moisture samples like fruit, fish, meat and grains. While challenging to interpret and analyze, NIR spectroscopy probes the vibrational overtone absorption of chemical bonds, and is sensitive to most chemical constituents in foods. The resulting spectra are often broad, overlapping and complex, necessitating chemometric analysis to unlock their secrets.

Light at NIR wavelengths penetrates fairly deeply with less scattering, allowing internal composition to be analyzed via nondestructive reflectance and through-sample transmission techniques. When processed using a well-developed chemometric model, a simple NIR reflectance spectrum can be used to predict complex characteristics, such as an apple’s ripeness, sweetness or storage duration.

  • Adulterated ground beef: detecting mutton, pork, organs and fillers
  • Chicken quality: detecting thawed versus fresh cuts; artificially boosted water content
  • Fraudulent labeling of fish: identification of fish species without DNA testing
  • Fruit quality: screening for core rot, internal pests and ripeness
  • Gluten screening: sorting unprocessed grains with NIR and machine vision

Fluorescence

Fluorescence spectroscopy utilizes the native fluorophores in food products to detect the presence or concentration of those components. Fluorescence is already used as a detection method for HPLC and CE in chemical analysis, but offers a wealth of information when used as a standalone analytical technique.

Fluorescence spectra are composed of broad, overlapping emission bands containing information about the sample components. Fluorescence analysis may look for peaks to change in intensity, or to shift in wavelength or bandwidth. Different excitation wavelengths may be used to build up a fluorescence excitation-emission matrix that can be reduced to a 3D component space for correlation to concentration via chemometrics. Fluorescence can be performed in right angle or front-face configurations, adapting to provide rapid, sensitive, nondestructive analysis of a wide variety of food types.

  • Cheese: variety, manufacturing method, geographic origin and degree of aging
  • Eggs: freshness
  • Food and animal feed: mycotoxins in nuts, grains, dried fruits and spices
  • Fruit: fecal matter contamination of peel
  • Meat: quantification of fat, bone, cartilage and connective tissue

SERS

Surface-enhanced Raman spectroscopy can be used for trace detection of harmful compounds in foods, from pathogens to antifungal dyes, antibiotics and pesticides. Trace contaminants and residues used in the growth, processing and storage of food products have been shown to be toxic to humans, with effects ranging from digestive problems to death.

SERS substrates may be gold, silver or gold-silver alloy-based, and can be made even more specific through functionalizing ligands specific to a particular pathogen. Ocean Optics SERS substrates offer better performance than expensive patterned substrates at a fraction of the price, and are compatible with our IDRaman mini and modular Raman detection systems for rapid, on-site testing of food products with little to no sample preparation.

  • Banned antifungal agents used in aquaculture: crystal violet and malachite green
  • Food dyes: Sudan 1, a carcinogenic, mutagenic dye used to boost color of chili powder
  • Pathogens: Salmonella enterica and Staphylococcus aureus on fresh spinach
  • Pesticides: organophosphorus and sulfur-containing pesticides, tricyclazole, malathion, imidacloprid
  • Restricted antibiotics: enrofloxacin, ciprofloxacin and chloramphenicol