Sensory properties

The sensory properties are the characteristics of foods perceived by the senses of sight, smell, taste, touch and hearing, such as flavour, texture and appearance. The human sensory organs are a remarkably sensitive means of measuring sensory properties. 

In addition to the compounds that provide aroma and taste, two other types of molecule can affect flavour molecules that affect the trigeminal (touch) receptors, and flavour enhancers. Trigeminal sensations in the nose, lips, mouth and throat are responsible for the coolness of menthol, the bite of mustard and pepper, and the warmth of cloves. 

Flavour enhancers and suppressers are used in low concentrations to enhance or suppress other flavours. Examples include maltol and ethylmaltol, which have a low caramel taste and enhance the sugary feeling of products furaneol, which is used with red fruits or wild fruit flavours and vanillin, which softens bitter chocolate and fruit flavours and can also enhance the perception of sweetness. In general, sucrose suppresses bitter, sour and salty tastes, for example in chocolate, and enhances fruit flavours. A further important point for ice cream is that the perception of flavour is affected by temperature flavours are less intense at low temperatures. For this reason, ice cream and water ices are generally more strongly flavoured than products consumed at warmer temperatures, such as soft drinks (Experiment 17 in Chapter 8 demonstrates this). 

The sensory perception of texture is produced by a combination of the neural signals from pressure sensors in the tongue and mouth and from the sensors in the muscles involved in mastication that sense their forces and displacements. The perception of texture arises not only from the properties of the original sample, but also from how the sample breaks down in the mouth as it is eaten. 

Heresztyn (1986) reports that fermentations utilizing B, intermedius and B, anomalus produced substantial amounts of the volatile phenols 4-ethyl 

Among the volatile phenol compounds identified, 4-ethyl phenol (produced from / -coumaric acid) was reported to be present in the highest concentration. This suggests its utility as a general sensory marker in Bret-tanomyceAnfecied wines. 

It is believed that these compounds, characteristic of Brettanomyces and Dekkera, result from decarboxylation of hydroxycinnamic acids, yielding vinyl phenol intermediates and subsequent reduction to produce the ethyl analog (Steinke and Paulson, 1964). As seen in Fig. 3-3 initial decarboxylation is mediated by cinnamate decarboxylase, whereas the reduction step utilizes a vinyl phenol reductase. 

Dubourdieu (1992) points out that wine yeasts Saccharomyces cerevisiae also contains the cinnamate decarboxylase and thus are capable of producing the vinyl phenol intermediate. However, flavonoid phenols (tannins) inhibit its activity hence, the formation of volatile phenols in red and rose wines is significantly less than that seen in white wine fermentations. Activity of cinnamate decarboxylase in the case of Brettanomyces and Dekkera, however, is not inhibited by polymeric phenols. 

Muller and Fugelsang (1995 1996) have shown that carbon monoxide, at levels of 420 mg/L, is effective in the control of Zygosaccharomyces. Sacchro-myces, by comparison, was not effected by levels of CO 1000 mg/L. 

Free amino acids can contribute to the flavor of protein-rich foods in which hydrolytic processes occur (e. g. meat, fish or cheese). 

The taste intensity of a compound is reflected in its recognition threshold value. The recognition threshold value is the lowest concentration needed to recognize the compound reliably, as assessed by a taste panel. Table 1.12 shows that the taste intensity of amino acids is dependent on the hydrophobicity of the side chain. 

L-Tryptophan and L-tyrosine are the most bitter amino acids with a threshold value of Ct bitter = 4—6mmol/l. D-Tryptophan, with Ct sweet = 0.2—0.4 mmol/1, is the sweetest amino acid. A comparison of these threshold values with those of caffeine (ctbi = 1 —1.2mmole/l) and sucrose (ctsw = 10—12 mmol/1) shows that caffeine is about 5 times as bitter as L-tryptophan and that D-tryptophan is about 37 times as sweet as sucrose. 

L-Glutamic acid has an exceptional position. In higher concentrations it has a meat broth flavor, while in lower concentrations it enhances the characteristic flavor of a given food (flavor enhancer, cf. 8.6.1). L-Methionine has a sulfur-like flavor. 

The bitter taste of the L-amino acids can interfere with the utilization of these acids, e. g., in chemically defined diets. 

---

Sensory perception is both quaUtative and quantitative. The taste of sucrose and the smell of linalool are two different kinds of sensory perceptions and each of these sensations can have different intensities. Sweet, bitter, salty, fmity, floral, etc, are different flavor quaUties produced by different chemical compounds the intensity of a particular sensory quaUty is deterrnined by the amount of the stimulus present. The saltiness of a sodium chloride solution becomes more intense if more of the salt is added, but its quaUty does not change. However, if hydrochloric acid is substituted for sodium chloride, the flavor quahty is sour not salty. For this reason, quaUty is substitutive, and quantity, intensity, or magnitude is additive (13). The sensory properties of food are generally compHcated, consisting of many different flavor quaUties at different intensities. The first task of sensory analysis is to identify the component quahties and then to determine their various intensities. 

The relationship between molecular stmcture and sensory properties is very unclear for compounds with odor. It seems likely that there is a set of odors that could be called primaries, but a widely accepted Hst of such primary odor quahties has not been devised. Molecular size and shape have been used to... 

This example demonstrates the most challenging problem of flavor chemistry, ie, each flavor problem may require its own analytical approach however, a sensory analysis is always required. The remaining unknown odorants demand the most sensitive and selective techniques, and methods of concentration and isolation that preserve the sensory properties of complex and often dehcate flavors. Furthermore, some of the subtle odors in one system will be first identified in very different systems, like o-amino acetophenone in weasels and fox grapes. 

Reverse Osmosis. A reverse osmosis (RO) process has been developed to remove alcohol from distilled spirits without affecting the sensory properties (14). It consists of passing barrel-strength whiskey through a permeable membrane at high pressure, causing the alcohol to permeate the membrane and concentrating the flavor components in the retentate. 

Occurrence and sensorial properties of alkoxypyrazines contained in foodstuffs and wines 98CLY402. 

Commercial interest in the sensory properties of foods during the past decade has led to a great increase in basic knowledge of the phenomenon. 

For more details about the sensory properties of the pectin preparations additional sizes such as thixotropy and viscosity have to be referred to (see figure 6). Fruit preparations with apple pectin Classic AY 901 have a relatively high yield point after shearing, a small thixotropic area, and a relatively high viscosity. This supports the statement, that their texture is weakly elastic and highly reversible. The apple pectin Classic AY 905 gives products with a sufficiently high yield point at 35 % soluble solids and a pronounced area of thixotropy. 

The determination and analysis of sensory properties plays an important role in the development of new consumer products. Particularly in the food industry sensory analysis has become an indispensable tool in research, development, marketing and quality control. The discipline of sensory analysis covers a wide spectrum of subjects physiology of sensory perception, psychology of human behaviour, flavour chemistry, physics of emulsion break-up and flavour release, testing methodology, consumer research, statistical data analysis. Not all of these aspects are of direct interest for the chemometrician. In this chapter we will cover a few topics in the analysis of sensory data. General introductory books are e.g. Refs. [1-3]. 

In paired comparison tests two different samples are presented and one asks which of the two samples has most of the sensory property of interest, e.g. which of two products has the sweetest taste (Fig. 38.3). The pairs are presented in random order to each assessor and preferably tested twice, reversing the presentation order on the second tasting session. Fairly large numbers (>30) of test subjects are required. If there are more than two samples to be tested, one may compare all possible pairs ( round robin ). Since the number of possible pairs grows rapidly with the number of different products this is only practical for sets of three to six products. By combining the information of all paired comparisons for all panellists one may determine a rank order of the products and determine significant differences. For example, in a paired comparison one compares three food products (A) the usual freeze-dried form, (B) a new freeze-dried product, (C) the new product, not freeze-dried. Each of the three pairs are tested twice by 13 panellists in two different presentation orders, A-B, B-A, A-C, C-A, B-C, C-B. The results are given in Table 38.3. 

The experimental designs discussed in Chapters 24-26 for optimization can be used also for finding the product composition or processing condition that is optimal in terms of sensory properties. In particular, central composite designs and mixture designs are much used. The analysis of the sensory response is usually in the form of a fully quadratic function of the experimental factors. The sensory response itself may be the mean score of a panel of trained panellists. One may consider such a trained panel as a sensitive instrument to measure the perceived intensity useful in describing the sensory characteristics of a food product. 

Onwulata, C. 1. and Heymann, H. (1994). Sensory properties of extruded corn meal related to the spatial distribution of process conditions.. Sens. Stud. 9,101-112. 

In the conventional vision, product quality is mainly based on external, nutritive and sensory properties and is strongly directed by traders and trends. Besides tastiness and ripeness, organic consumers expect products to have properties such as vitality and coherence , which are not easy to define and thus to explain and transfer. In the past, experimental parameters have been proposed to estimate vitality and coherence , but they were neither scientifically validated nor related to a validated quality concept with relation to human health. 

Sensory quality can be defined as texture, flavour (taste), aroma and visual aspect. The sensory properties of milk are highly influenced by its fat content (Phillips et al., 1995a). As a result, research has examined the effects of various food additives on sensory quality when used as a substitute for fat in milk (Philips et al., 1995b). Frpst et al. (2001) showed that a combination of thickener, whitener and cream aroma in 0.1% fat milk was successful in mimicking the sensory quality of 1.3% fat milk. With the interest in the production of milk enriched with cis-9, trans-l 1 CLAs, owing to their relevance to human health (Tricon et al., 2004), recent research has examined the effects of CLA on the sensory quality of dairy products and found that it is possible to produce CLA-enriched dairy products with acceptable sensory characteristics (Jones et al., 2005). 

Buchin S, Martin D, Dupont D, Bomard A and Achilleos C (1999), Influence of the composition of Alpine highland pasture on the chemical, rheological and sensory properties of cheese , Journal of Dairy Research, 66, 579-588. 

Jones E L, Shingfield K J, Kohen C, Jones A K, Lupoli B, Grandison A S, Beever D E, Williams C M, Calder P C and Yaqoob P (2005), Chemical, physical, and sensory properties of dairy products enriched with conjugated linoleic acid , Journal of Dairy Science, 88, 2923-2937. 

Phillips L G, McGiff M L, Barbano D M and Lawless H T (1995a), The influence of fat on the sensory properties, viscosity, and color of lowfat milk , Journal of Dairy Science, 78, 1258-1266. 

Di Cagno R, Surico RF, Paradiso A, De Angelis M, Salmon JC, Buchin S, De Gara L and Gobbetti M. 2009. Effect of autochthonous lactic acid bacteria starters on health-promoting and sensory properties of tomato juices. Int JFood Microbiol 128(3) 473-483. 

Schmidt, S.J. 1999. Probing the physical and sensory properties of food systems using NMR spectroscopy. In Advances in Magnetic Resonance in Food Science (P.S. Belton, B.P. Hills, and G.A. Webb, eds), pp. 79-94. Royal Society of Chemistry, Cambridge, UK. 

The main unique feature of osmotic dehydration, compared to other dehydration processes, is the penetration of solutes into the food material. Through a calculated incorporation of specific solutes into the food system, it is possible, to a certain extent, to change nutritional, functional, and sensory properties, making it more suitable to processing by... 

Some experiments have been conducted to verily the feasibility of the process shown in Figure 5 on pilot plant scale. With the correct level of El post-dosed, a similar product microstructure could be obtained. And more importantly, the physico-chemical and sensory properties of the product produced with the new process were found to be similar to the product properties from the original process. 

Yang NC, Chang S, Suh DH (2003) Synthesis and optically acid-sensory properties of novel polyoxadiazole derivatives. Polymer 44 2143-2148... 

In summary, there have been several physical/mechanical means developed to improve the functionality, safety, and sensory properties of psyllium. These previous investigations have indicated the possibility to improve the physicochemical, sensory, biological properties of psyllium for its optimal applications in foods. However, none of them could sufficiently solve the strong gelling and extreme water-uptake problems of psyllium. 

---