Search: hydride technique

The hydride technique is used to determine the concentration of arsenic ions in the water sample. In this process, arsenic ions are reduced by sodium tetrahydroborate in an acidic medium to arsine. This compound is then transferred using an inert gas into a heated quartz cuvette, is pyrolyzed and measured using AAS.

The absorbance is determined at a wavelength of 193.7 nm, and the arsenic concentration is calculated using a reference curve.

Terms

Aroma:
Aroma represents the overall sensory impression encompassed by the olfactory organs, some of which is perceived in the mouth and thus partly attributed to the sense of taste.

Flavor/Off-flavor:
For the sake of thoroughness, these two terms, which are defined in DIN 10950 part 2 Sensorische Prüfung, allgemeine Grundlagen, are mentioned here. According to definition put forth by DIN, flavor is defined as the “sum of olfactory, gustatory, temperature-related and/or trigeminal and tactile sensations in the mouth”. Off-flavors are sensory stimuli, which are perceived as unpleasant.

Odor:
Organoleptic properties perceived with the olfactory organ(s), whereby certain volatile substances are breathed in through the nose.

Flavour:
The overall sensory impression perceived through the sense of taste in the mouth, throat and nose. The sense of taste can be influenced by thermal or tactile stimuli, through pain or kinesthesia or any combination thereof. According to DIN, flavor is defined as the “sum of olfactory, gustatory, temperature-related and/or trigeminal and tactile sensations in the mouth”.

Mouthfeel:
Aside from the basic tastes, tactile stimuli – detected through haptic perception in the oral cavity – play a role in the sensory perception of comestibles as they are ingested. Tactile stimuli can be divided into the following:

• tactile (touch)

• kinesthetic (perception of weight, movement, resistance, etc.)

• trigeminal (pain)

• temperature-dependent

The term “mouthfeel” is often employed to describe haptic perception in the oral cavity. The following sensory attributes of beverages can be detected primarily by means of mouthfeel:

• viscosity, rheological properties

• liberation of gas, bubble formation, foaming (carbon dioxide)

• general after-effects in the mouth (refreshing, warming, thirst-quenching)

Aftertaste:
The sensory impression, which remains in the mouth, once a beverage has been swallowed. This is often employed as a criterion for the sensory evaluation of beverages.
An aftertaste described as “harmonious” provides incentive to continue drinking.

Orthonasal perception of odors:
Sensory perception commonly referred to as “smelling”. Odorants in the air enter the nasal cavity through the external nares, or nostrils, during the act of breathing. From there, the odorants are transported to the receptor cells where olfactory perception occurs.

Retronasal perception of odors:
Retronasal (lat. retro: “backwards, back”, nasal: “pertaining to the nose”) perception describes the transport of odorants from the oral cavity into the pharynx, then up through the internal nares and nasal cavity to the olfactory receptor cells. Odors are liberated through the mastication of food and beverages, thus providing olfactory (lat. olfacere: “to smell”) stimulus. The retronasal aroma profile of comestibles may differ from the orthonasal aroma profile owing to various factors (e.g. mastication or saliva).

Fullness:
Fullness is a kinesthetic sensation in the oral cavity, which – as it relates to beer – may range from “watery” to “satiating/excessive”. A frequently used synonym for fullness in beer is the term “body”.

Liveliness:
Liveliness as it pertains to beer is the tactile sensation in the oral cavity induced through the action of carbon dioxide, which may range from “flat/stale” to “gassy”.
A synonym often encountered for liveliness is “effervescence”.

In the beverage and food industries, sensory analysis is an essential part of a quality control program; for example, it serves as a valuable tool in determining the flavor stability of a beverage, in detecting any aberrations in quality, in promptly discovering fluctuations in a beverage or even in measuring the quality and intensity of certain flavor and aroma impressions. These aspects of sensory analysis represent points whereupon testing performed using laboratory equipment produces either inadequate results or fails to provide results at all. Sensory evaluation of products also affords a rapid, sensitive and specific means of assessing them. Many aroma compounds can be more readily detected with the human odor receptor cells, for the simple reason that these cells are more sensitive to such compounds than physico-chemical detectors. Results obtained from the chemical or biological analysis of finished products generally first become significant when they are consistent with results from sensory evaluation.

Therefore, before foods are introduced on the market, they should undergo sensory testing. As part of this testing, the internal and external features of the food are evaluated with the assistance of human sense organs regarding their character (e.g., sweetness) and expression (intensity as a function of time). Visual, olfactory (odor), gustatory (taste), tactile (e.g., tingling), trigeminal (e.g., burning, stabbing), kinesthetic (e.g., crispy, chewy), auditory (acoustic) impressions in addition to temperature (temperature sense) and nociception (pain perception, sensation) are differentiated.

In the case of beer, beer-based beverages, soft drinks and mineral water, the assessment is typically restricted to olfactory, gustatory, tactile and trigeminal characteristics, because other analysis methods, for example, for determining the foam stability of beer, are more accurate than a visual assessment.

Sensory analysis of food differs significantly from organoleptic evaluations for determining a person’s perceived sensitivity to certain odors and flavors. Organoleptic testing is considered a subjective sensory assessment, the results of which cannot be verified statistically. With sensory analysis, by contrast, precise procedures are employed in evaluating foods, and results are statistically assessed. The test methods in sensory analysis are standardized at an international level and include, for example, techniques for calibrating devices, which measure the physico-chemical attributes of foods, in order to obtain accurate results. Likewise, a sensory panel must be subject to certification, training and constant testing, with the ultimate goal of providing objective, accurate and reproducible results. These, in turn, allow conclusions to be made regarding the technology, raw materials and storage conditions. However, sensory analysis in the beverage industry is not only pertinent for the final product but also extends to the raw materials (e.g. brewing water, malt, hops, carbon dioxide), intermediate products (e.g. seasoning, natural lactic acid, green beer), processing aids and operating supplies (e.g., filter aids, stabilizing agents, air), auxiliary equipment and associated paraphernalia (e.g., closures, containers). Sensory analysis should comprise roughly one-third of the total analytical testing in a quality assurance program.

A distinction exists between simple sensory tests, which are part of the periodic monitoring in routine analysis of production processes, and up or down judgments, which must be reached in making ad hoc decisions. The latter are most often made by the person responsible for a particular production area, because a verdict is required quickly. Analysis of the finished product, however, must be performed by a sensory panel, because the opinion of one individual – regardless of their position – has little value. Due to ordinary inconsistencies in a person’s health, psychological condition and perception over the course of a day, a single individual is not capable of performing this function. For this reason, results from tastings by one person are always questionable and of no value for reliable quality control. The larger the number of participants on the sensory panel, the less influence the aforementioned sources of error have on the mean. Because differences also exist in the perceptive abilities of individuals, this requires that a sufficient number participate in the sensory analysis. Only an overall evaluation of the sensory panel’s results, especially if they can be expressed in a statistical form, can be considered reliable or plausible. Methods for conducting sensory analysis should therefore be selected only if they permit a statistical assessment of the results.
 

One of the basic prerequisites for properly conducting sensory analysis is motivating the members of the tasting panel.