Sensory properties of foods are perceived through the five senses: sight, smell, hearing, taste, and touch. These senses collectively enable the evaluation of a food item.
Sensory properties include color, appearance, taste, aroma, flavor, consistency, and texture. Color, aroma, and taste are major factors affecting quality perception and consumer acceptance of food.
Color and appearance are the initial quality attributes that attract attention, but flavor, which combines oral and nasal stimulation, often has the greatest impact on acceptability and the desire to consume a food again.
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Appearance and Its Role in Food Choice
Appearance refers to how a food is perceived visually. For instance, encountering blue-colored tomatoes in a market would likely cause surprise and hesitation, as tomatoes are typically associated with a red color.
This illustrates the critical role of color and appearance in food choice and acceptability. If a food does not look appetizing, it is often rejected.
The appearance of a product, including its color and visual appeal, significantly influences whether it is deemed acceptable or unacceptable for purchase or consumption.
1. Attributes of Food Appearance
i. Color: Color involves both physical and psychological components, perceived by the visual system through light wavelengths: 400–500 nm (blue), 500–600 nm (green and yellow), and 600–800 nm (red). Many foods are identified by their characteristic colors, and deviations from expected colors can lead to rejection, even if the food remains wholesome.
For example, orange drinks are expected to have an orange color, aligning with the fruit’s typical hue, despite variations in natural orange fruit colors. Color changes often indicate food deterioration, aiding consumers in assessing freshness, such as perceiving dark brown meat as spoiled.
ii. Size and Shape: Attributes like length, thickness, width, particle size, geometric shape (e.g., square, circular), and distribution of pieces (e.g., in vegetables, pasta, or prepared foods) serve as indicators of product quality.
iii. Surface Texture: Characteristics such as dullness, shininess, roughness, or evenness, and surface properties like wet, dry, soft, hard, crisp, or tough, reflect quality.
iv. Clarity: The haze or opacity of transparent liquids or solids, and the presence or absence of visible particles, are important quality indicators.
Odor, Aroma, and Fragrance as Sensory Attributes
1. Definition of Odor, Aroma, and Fragrance
Odor, aroma, and fragrance are quality parameters perceived by the nose, with olfactory perception playing a greater role in overall flavor than taste. Food products are smelled for aroma immediately after opening a package, before tasting.
Odor is detected when volatiles enter the nasal passage and are perceived by the olfactory system, typically through sniffing. Aroma refers specifically to the odor of a food product, while fragrance is associated with perfumes or cosmetics.
The release of volatiles is influenced by temperature and the nature of the compounds, with volatility affected by surface conditions—more volatiles escape from soft, porous, humid surfaces than from hard, smooth, dry ones.
2. Descriptive Words for Odor
Table 1: Words Describing Odor with Examples
| Words | Example |
|---|---|
| Aromatic | Onions |
| Floral | Hibiscus flavor |
| Perfumed | Some food flavors |
| Rotten | Rotten meat |
| Acrid | Vinegar |
| Pungent | Pepper |
| Bland | Unsweetened foods |
| Rancid | Deteriorated oil |
| Tart | Yoghurt |
| Spicy | Spiced foods |
| Savory | Monosodium glutamate |
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Taste and Flavor as Sensory Properties
1. Definition of Taste
The tongue detects five basic tastes: bitter, salty, sour, sweet, and umami. Taste may be described by association with specific foods, such as meaty, minty, or fruity.
i. Bitterness: Caused by alkaloids, glycosides, organic compounds, or inorganic salts. For example, naringin in grapefruit is a non-toxic glycoside, while amygdalin in bitter almonds contains cyanide and is toxic. Quinine, strychnine, nicotine, and caffeine (in coffee and tea) are bitter alkaloids. Phenolic compounds like tannin and some flavonoids combine bitterness with astringency.
ii. Salty: Sodium chloride is the only salt with a pure salty taste, serving as both a flavor enhancer and an essential nutrient. Other salts, such as iodides and bromides, may taste bitter, while some lead and beryllium salts are sweet.
iii. Sweet: Sugars primarily impart sweetness. Fructose in honey is the sweetest, followed by sucrose and glucose, while lactose in milk is slightly sweet with minimal flavor. Natural sweet compounds, such as polyhydroxy compounds (e.g., sugars, mannitol, sorbitol), saccharin, peptides, and cyclamates, also contribute sweetness.
iv. Sourness: Attributed to organic acids like citric, tartaric, and malic acids, common in fruits, as well as acetic acid from alcohol fermentation and ascorbic acid in fruits and vegetables. Oxalic acid in spinach and phosphoric acid in food industry applications also contribute.
The hydrogen ion primarily drives sour taste, though most acids (except oxalic) are weak, and sourness does not directly correlate with hydrogen ion concentration.
2. Definition and Classification of Flavor
Flavor is a sensory phenomenon combining taste, odor or aroma, heat, cold, and texture or “mouthfeel.” While appearance is important, flavor ultimately determines a food’s quality and acceptability. Flavor can be classified into:
i. Natural Flavors: Derived from herbs, spices, aromatic seeds, fruits, and vegetables.
ii. Processed Flavors: Resulting from processes like fermentation, baking, toasting, roasting, or caramelization.
iii. Added Flavors: Including natural extracted flavors (e.g., herbs and spices) and synthetic flavors.
Texture as a Sensory Property
1. Definition of Texture
Texture is assessed through touch, particularly when food is placed in the mouth, where the tongue and other sensitive skin react to its surface, a sensation known as mouthfeel. Different sensations arise during chewing, influenced by resistance (e.g., chewiness, springiness) and viscosity (e.g., runny, thick).
Temperature also plays a role, as in cold ice cream, warm bread, or hot soup. Texture evaluation involves multiple parameters, perceived during mastication through various receptors and tissues, rather than a single specific receptor.
2. Textural Characteristics
| Textural Characteristics | Definition |
|---|---|
| Hardness | Force required to compress a food between molar teeth (solids) or tongue and palate (semi-solids). Examples: palm kernel, coconut. |
| Cohesiveness | Extent to which a food can be deformed before rupturing, dependent on internal bond strength. Example: chewing gum. |
| Tenderness, Chewiness, Toughness | Energy required to masticate a solid food to a state ready for swallowing, involving compression and shearing. Example: chocolates (tender). |
| Brittleness, Crunchiness, Crumbliness | Result of high hardness and low cohesiveness. Example: biscuits (brittle). |
Sound as a Sensory Property
1. Definition of Sound in Food
The sounds produced during the preparation, cooking, serving, and eating of food influence preferences. Mastication sounds, such as those from crispy, crunchy, or crackly foods, provide cues about texture. For example, plantain chips that lack a crunchy sound are poorly accepted, highlighting the role of auditory cues in food acceptability.
This article has explored the sensory properties appearance, odor, taste, flavor, texture, and sound that significantly influence food choice. These attributes, perceived through sight, smell, taste, touch, and hearing, determine consumer acceptance and quality perception, guiding decisions to purchase or consume food products.
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