Head Space sampling –
- Static Headspace: Direct analysis of the equilibrium headspace above a food product would appear to be an ideal method for aroma studies. It is very simple, gentle, and easily automated. In this method, one places a food sample into a vessel, closes the vessel with an inert septum (Teflon-lined), allows equilibration (between the food and the sample headspace — 30 to 60 min), and then draws a few ml of headspace above the food into a gas-tight syringe and makes a direct injection into gas chromatography (GC).
- Dynamic Headspace: Headspace methods employing some type of gas stripping and concentration are commonly called dynamic headspace methods. In these methods, the sample is purged with inert gas, such as nitrogen or helium, which strips aroma constituents from the sample. The volatiles in the purge gas must then be trapped (somehow removed) from the gas stream. The aroma constituents may be trapped via a cryogenic, Tenax (or alternative adsorptive polymer), charcoal, or another suitable trapping system.
- Thermal Desorption/ Sorptive Extraction: Sorptive extraction (Solid Phase Micro Extraction [SPME] and Stir Bar extraction) are relatively new techniques for the isolation of food aromas. In this technique, an inert fiber is coated with an adsorbent (several choices). The adsorbent-coated fiber is placed in the headspace of a sample, or the sample itself if liquid, and allowed to adsorb volatiles. The loaded fiber is then thermally desorbed into a GC carrier gas flow, and the released volatiles are analyzed.
Solid Phase Extraction (SPE): The principle of SPE is similar to that of liquid-liquid extraction (LLE), involving a partitioning of solutes between two phases. However, instead of two immiscible liquid phases, as in LLE, SPE involves partitioning between a liquid (sample matrix or solvent with analytes) and a solid (sorbent) phase. SPE is typically performed by loading the complex sample onto a preconditioned extraction cartridge containing a chromatographic sorbent.
Steam Distillation: Distillation can be defined broadly to include high vacuum molecular distillation, steam distillation, or simple heating of the food and sweeping the distilled aroma constituents into a GC. Many organic compounds tend to decompose at high sustained temperatures. Separation by normal distillation would then not be an option, so water or steam is introduced into the distillation apparatus. By adding water or steam, the boiling points of the compounds are depressed, allowing them to evaporate at lower temperatures, preferably below the temperatures at which the deterioration of the material becomes appreciable. If the substances to be distilled are very sensitive to heat, steam distillation can also be combined with vacuum distillation. After distillation the vapors are condensed, as usual, usually yielding a two-phase system of water and organic compounds, allowing for decantation.
Solvent Extraction: Solvent Extraction: One of the simplest and most efficient approaches for aroma isolation is direct solvent extraction. Solvent extraction is a selective separation procedure for isolating and concentrating a valuable material from an aqueous solution with the aid of organic acids. The extraction process depends on the solubility of the flavoring compounds in the solvent. A compound can be separated from impurities in a solution by extracting the compound from the original (or first) solvent into a second solvent. For the process to be selective, the compound must be more soluble in the second solvent than in the first solvent, and the impurities must be insoluble in the second solvent.
Additionally, the two selected solvents must be immiscible, or not soluble in one another, so that they produce two separate solvent layers. After dissolving the mixture in the first solvent, the solution is added to a second solvent. The major limitation of this method is that it is most useful for foods that do not contain any lipids. If the food contains lipids, the lipids will also be extracted along with the aroma constituents, and they must be separated from each other prior to further analysis. Aroma constituents can be separated from fat-containing solvent extracts via techniques such as molecular distillation, steam distillation, and dynamic headspace.
Supercritical fluid extraction: A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be altered. Supercritical fluids are suitable as a substitute for organic solvents in a range of industrial and laboratory processes. Carbon dioxide and water are the most commonly used supercritical fluids.
- Explain the techniques for flavor analysis briefly
Flavor analysis: Flavor may be evaluated with either instrumental or sensory methods. Instrumental techniques may determine that tens or hundreds of compounds are present in a particular food product, but such methods do not give a measure of the contribution of that specific compound unless they are accompanied by a sensory measurement of odor or flavor activity. For this reason, the flavor may be the most challenging quality attribute to both measures and correlate to consumer acceptability.
They include identifying flavor components in natural foods and beverages, such as fruits, vegetables, meat, milk, etc., so that particular components can be enhanced, reduced, eliminated, or duplicated; identifying sources of off-flavors and off-odors; monitoring the quality of foods and beverages; determining the shelf life of products; analyzing for contaminants and adulteration; checking raw materials before formulating products and checking finished products before shipping them, and other applications.
- Sensory Analysis:
Analytical intensity rating tests
- Instrumental Methods
Gas Chromatography (GC) or Gas Chromatography-Mass Spectrometry (GC-MS): The primary technique used in flavor analysis is gas chromatography, with and without mass spectrometry and olfactometry. Since most flavor and fragrance compounds are volatile, GC is the method of choice. As a flavor or food sample passes through a heated capillary column, the chemical components are evaporated and separated, producing peaks according to the time it takes to reach a detector, such as a flame ionization detector (the most common type). Passing the effluent from the GC into a mass spectrometer (MS) allows the identification and quantification of the chemical components detected by the GC. GC/Olfactometry (GC/O) or Gas Chromatography-Mass Spectrometry/Olfactometry (GC-MS/O): GC/O and GC-MS/O are techniques uniquely applied to aroma studies. In olfactometric techniques, the nose is used as a GC detector. Here, regions of the gas flow from the gas chromatograph can be split, and sent to a mass spectrometer and to a sniff port, where the effluent can be sniffed to identify the particular odor.
Electronic nose: An electronic nose functions by analyzing a sensor array response to a complete aroma, i.e., there is no separation of aroma components. The sensor array response to any given aroma is correlated (pattern recognition software) to sensory panel data.
Flavor Identification by Spectrometric Methods Ultra Violet Spectrometry Infrared Spectrometry-FTIR Nuclear Magnetic Resonance Spectrometry Mass Spectrometry.
- What are flavor emulsions and how are prepared? Explain with an example.
Emulsions are typically used in the flavor industry to carry product flavor (e.g., beverage or baker’s emulsions) or impart turbidity (cloud emulsion) to a product.
This technique employs a conventional three-phase system: the manufacturing vehicle (solvent), the flavor carriers (wall materials), and the flavor (core material).
While there are several types of coacervation, complex coacervation is most commonly used in the food/flavor Industry
The basic principle involved in this method is to form an emulsion and then precipitate components of the continuous phase around the droplets of the discontinuous phase to form a wall (capsule).
DEHYDRATION: While any method of dehydration (tray, vacuum tray, freeze, or drum) can and is used for some applications, spray drying is by far the major process used for flavor encapsulation.
SPRAY DRYING: The initial step in spray drying a flavor is the selection of a suitable carrier (or encapsulating agent). The ideal carrier should have good emulsifying properties, be a good film former, have low viscosity at high solids levels (<300 cps at >35% solids levels), exhibit low hygroscopicity, release the flavor when reconstituted in a finished food product, be low in cost, bland in taste, stable in supply, and afford good protection to the encapsulated flavor.
FREEZE, DRUM, TRAY DRYING:
Alternative dehydration processes for the encapsulation of flavors include drum (contact) drying, tray drying, and freeze drying.
While these processes do not find major use in the industry, they are used in certain applications.
Extrusion, as applied to flavor encapsulation, may be used in a broader sense in that a molten flavor emulsion is forced through a die.
However, unlike the high temperatures and pressures used in cereal processing, traditionally pressures were typically less than 100 psi and temperatures seldom exceeded 120°C.
- Differentiate flavor extracts and flavor emulsions
Flavor emulsions- concentrated water soluble flavoring
– can withstand high temperatures
-hold favor integrity at high temperatures
– taste purer
– can be blended into food products easily
Flavor extract- concentrate suspended in a base made of alcohol
– flavor last longer in the shelf life and have a powerful flavor
– lose their intensity during baking
– lose flavor at high temperature as the alcohol evaporates
- Explain the stability of flavors during food processing.
- Maillard reaction
- Strecker degradation
- Physical and chemical reactions
- AUTHENTICATION OF FLAVOURS:
Food authentication is a rapidly growing field due to increasing public awareness concerning food quality and safety.
The isotopic methods used for vanilla authentication involve a variety of analytes, 14C,
13C, 12C, H, D, 16O, 18O, 3H, as well as a number of techniques, liquid scintillation (LS),
stable isotope ratio analysis (SIRA), gas proportional counting (GPC), nuclear magnetic
resonance (NMR) including site‐specific nuclear isotopic fractionation (SNIF‐NMR)
and accelerator mass spectrometry (AMS).
Nuclear Magnetic Resonance (NMR)
Nuclear Magnetic Resonance (NMR) can be used to determine the source of aroma extraction based on the hydrogen isotopic ratios. The method is known as SNIF-NMR (site-specific natural isotope fractionation by NMR). This method allows characterization of all the main sources of commercial vanillin and detection of undeclared mixtures. It is based on the fact that the amounts of deuterium at various positions in the vanillin molecule are significantly different from one source to another. The proportions of isotopomers monodeuterated at each hydrogen position of the molecule are recorded, and the corresponding (D/H) ratios are determined by using certified reference material.
- A specific natural isotopic fraction can be measured for each position in the vanillin molecule to improve antibacterial potency
- A straightforward method for identification of incorrectly declared food flavorings
Mass spectrometry is an analytical technique whose purpose is to discover new molecules, determine quantities of known components, and determine the structural and chemical properties of a molecule.
The detection capability in mass spectrometry is very small, at about 10−12 grams and its application field is multifaceted, being used in industries such as chemical, pharmaceutical, biotechnology, and food, among others. It is frequently used in environmental and medical sciences, and in molecular biology.
A mass spectrometer is an instrument with the capability of measuring the mass of a molecule after it has been ionized. Due to the extremely small mass of a molecule expressed in grams or kilograms, it is more convenient to measure its molecular mass, expressed as mols; for example, the mass of a hydrogen atom is 1.66 x 10−24 grams, but its mol is approximately 1 gram, or if it is desired in Daltons, considering that this unit is equivalent to 1/12 of the mass of an isotope carbon-12.
The spectrometry does not directly measure the mass of an isotope, but rather its mass-to-charge ratio of the ions that are formed (m/z), where z is the charge, most of the ions formed in the mass spectrometry have a value of the charge of z = 1.
The mass spectrometers are constituted by various components, namely: 1) system for introducing the sample, 2) ionization source, 3) mass analyzer, 4) detection system and 5) data analysis system.