Food Texture

Food Texture
Texture refers to those qualities of a food that can be felt with the fingers, tongue, palate, or teeth. Foods have different textures, such as crisp crackers or potato chips, crunchy celery, hard candy, tender steaks, chewy chocolate chip cookies and creamy ice cream, to name but a few.

Texture is also an index of quality. The texture of a food can change as it is stored, for various reasons. If fruits or vegetables lose water during storage they wilt or lose their turgor pressure, and a crisp apple becomes unacceptable and leathery on the outside.

Bread can become hard and stale on storage. Products like ice cream can become gritty due to precipitation of lactose and growth of ice crystal in the freezer temperature is allowed to fluctuate, allowing thawing and refreezing.

Evaluation of texture involves measuring the response of a food when it is subjected to forces such as cutting, shearing, chewing, compressing or stretching. Food texture depends on the rheological properties of the food. Rheology is defined as the science of deformation and flow of matter or in other words, reaction of a food when a force is applied to it.

Does it flow, bend, stretch or break? From a sensory perspective, the texture of a food is evaluated when it is chewed. The teeth, tongue and jaw exert a force on the food, and how easily it breaks or flows in the mouth determines whether it is perceived as hard, brittle, thick, runny, and so on. The term mouthfeel is a general term used to describe the textural properties of a food as perceived in the mouth.
Food Texture

Carbohydrates: Sugars

Carbohydrates: Sugars
Sugars, important in nutrition, consist of monosaccharides, having the general formula C6H12O6, and disaccharides, having the general formula C12H22O11.

Although the monosaccharides consists of 3-carbon sugars (trioses), 4 carbon sugars (tetroses), 5-carbon sugars (pentoses), and 6-carbon sugars (hexoses), only the latter are important in human nutrition as sources of energy.

Glucose, a 6-carbon sugar, is one of the simplest carbohydrates found in foods. While many foods contain traces of glucose, it is found in significant amounts only in fruits, such as grapes. Fructose, also a 6-carbon sugar, is found in fruits and honey. Both of these sugars can be utilized by the body as a source of energy.

Sucrose (the ordinary table sugar derived from sugar and beets) is a 12-carbon sugar that is broken down in the intestine to glucose and fructose, hence utilized as a source of energy.

Lactose, the 12-carbon sugar present in milk, is broken down in the intestine to glucose and galactose (6-carbon sugars), both of which can be used as sources of energy.
Carbohydrates: Sugars

Fat Processing

Fat Processing
Plant Oils
The oils are usually removed from plant tissues by three methods. In the first method, cells containing oil are ruptured by heat and mechanical methods. In the past, cottonseeds free of lint were hulled, then flaked between rollers, and cooked with lived steam prior to hydraulic pressing to separate the oil. A second method, called screw pressing, involves heating the flakes or cracked meats, followed by passage through closed-fitting cages of screws to press out the oil. The third method involves solvent extraction using petroleum hydrocarbons at 60 – 70 degree Celsius. This method, which is a continuous one, has a capacity of processing of hundreds of tons of oil per day. The by-products of these methods are proteins, which are used in animal feeds.

Animal Fats
Animal fats are separated from fatty tissues by wet or dry rendering. In wet rendering, the fatty tissue is heated under steam pressure, thus rupturing the cells and liberating the fat. In dry rendering, the fatty tissue is heated in jacketed drums with agitation until the fats is released. Presently, centrifuges are used to separates the fat from water and protein.

Hydrogenation
Hydrogenation of unsaturated fats and oils increase their melting point and hardness, this process often used in the production of shortenings, which are generally defined as plastic materials made wholly from fats and oils. Hardness can be controlled by varying the ratio of solid to liquid glycerides. The shortenings are made by blending the desired oils and/or fats, deodorizing the mixture, chilling, and finally packaging.

Interesterification
When fats and oils are heated in the presence of certain catalysts, the fatty acids attached to glycerol rearrange in a process called interesterification. While vegetable oils are randomly distributed, animal fats generally are not. For example, at a level of 0.4% tin in standard hydroxide added to fat at 140 degree Celsius, then heated to 225 degree Celsius for 90 min in a vacuum, the distribution pattern of fatty acids will become random. In similar process, the melting point of soybean oil can be increased from -7 degree to +5.5 degree Celsius and its softening form -13 degree to -0.5 degree Celsius.

Interesterification is used in the industry to produced standard oils, which may be blended with others for use in the margarine and cooking fat trade. During interesterification, if the temperature is lowered, a certain amount of the higher melting triglycerides crystallize out. This has a dramatic effect on the remaining portion of liquid oil and alters the course of esterification. This is called directed interesterification.
Fat Processing