In countries where food is abundant, people choose foods based on a number of factors which can in sum be thought of as “quality.” Quality has been defined as degree of excellence and includes such things as taste, appearance, and nutritional content. We might also say that quality is the composite of characteristics that have significance and make for acceptability. Acceptability, however, can be highly subjective. Quality and price need not go together, but food manufacturers know that they generally can get a higher price for or can sell a larger quantity of products with superior quality. Often “value” is thought of as a composite of cost and quality. More expensive foods can be a good value if their quality is very high. The nutrient value of the different grades of canned fruits and vegetables it similar for all practical purposes, yet the price can vary as much as threefold depending on other attributes of quality. This is why processors will go to extremes to control quality.
When we select foods and when we eat, we use all of our physical senses, including sight, touch, small, taste, and even hearing. The snap of a potato chip, the crackle of a breakfast cereal, and crunch of celery are textural characteristics, but we also hear them. Food quality detectable by our senses can be divided into three main categories: appearance factors, textural factors, and flavor factors.
Appearance factors include such things as size, shape, wholeness, different form of damage, gloss, transparency, color, and consistency. For example, apple juice is sold both as cloudy and clear juice. Each has a different appearance and is often thought of as a somewhat different product.
Textural factors include hand feel and mouth feel of firmness, softness, juiciness, chewiness, grittiness. The texture of a food is often a major determinant of how little or well we like a food. For example, many people do not like cooked liver because of its texture. Texture of foods can be measured with sophisticated mechanical testing machines such as the one shown in Fig. 6.1.
Flavor factors include both sensations perceived by the tongue which include sweet, salty, sour, and bitter, and aromas perceived by the nose. The former is often referred to as “flavors” and the latter “aromas,” although these terms are often used interchangeably. Flavor and aroma are often subjective, difficult to measure accurately, and difficult to get a group of people to agree. A part of food science called sensory science is dedicated to finding ways to use humans to accurately describe the flavors and other sensory properties of foods. There are hundreds of descriptive terms that have been invented to describe flavor, depending on the type of food. Expert tea tasters have a language all of their own, which has been passed down to members of their guild from generation to generation. This true of wine tasters as well.
Since we generally experience the properties of food in the order of appearance, texture, and flavor, it is logical to discuss quality factors in this order now.
APPEARANCE FACTORS
In addition to size, shape, and wholeness, pattern (e.g., the way olives are laid out in a jar or sardines in a can) can be an important appearance factor. Wholeness refers to degree of whole and broken pieces; the price of canned pineapple goes down from the whole rings, to chunks, to bits. Appearance also encompasses the positive and negative aspects of properly molded blue-veined cheeses, and the defect of moldy bread, as well as the quality attribute of ground vanilla bean specks in vanilla ice cream, and the defect of specks and sediment from extraneous matter. Although some ice cream manufacturers have added ground vanilla bean as a mark of highest quality, others have concluded that as often as not a less-sophisticated consumer misinterprets these specks and rejects are product.
Size and shape
Size and shape are easily measured and are important factors in federal and state grade standards. Fruits and vegetables can be graded for size by the openings they will pass through. The simple devices shown in Fig 6.2 were the forerunners of current high-speed automatic separating and grading machines, although they are still used to some extent in field grading and in laboratory work.
Size also be approximated by weight after rough grading, for example, determining the weight of a dozen eggs.
Shape may have more than visual importance, and the grades of certain types of pickles include the degree of curvature (Fig 6.3). Such curiosities can become quite important, especially in the design of machines to replace hand operations. When an engineer attempts to design a machine for automatically filling pickles into jars at high speeds, it must be recognized that all pickles are not shaped the same, and a machine that will dispense round objects like olives or cherries can be totally inadequate. Mechanized kitchen, restaurant, and vending systems for rapid mass feeding have become commonplace.
Some of the most difficult engineering problems encountered in such facilities were in designing equipment that would dispense odd-shaped food pieces into moving dishes.
Color and Gloss
Food color not only helps to determine quality; it can tell us many things. Color is commonly an index of ripeness or spoilage. Potatoes darken in color as they are fried and we judge the endpoint of frying by color. The bleaching of dried tomato powder on storage can be indicative of too high an oxygen level in the headspace of the package, whereas the darkening of dried tomato can reflect too high a final moisture level in the power. The color of a food foam or batter varies with its density and can indicate a change in mixing efficiency. The surface color of chocolate is a clue to its storage history. These and many other types of color changes can be accurately measured in the laboratory and in the plant-all influence or reflect food quality.
If the food is a transparent liquid such as wine, beer, or grape juice, or if a colored extract can be obtained from the food, then various types of colorimeters or spectrophotometers can be used for color measurement. With these instruments, a tube of the liquid is placed in a slot and light of selected wavelength is passed through the tube. This light will be differentially absorbed depending on the color of the liquid and the intensity of this color. Two liquids of exactly the same color and intensity will transmit equal fractions of the light directed through them. If one of the liquids is a juice and the other is the same juice somewhat diluted with water, the latter sample will transmit a greater fraction of the incoming light and this will cause a proportionately greater response on the instrument. Such an instrument can also measure the clarity or cloudiness of a liquid depending on the amount of light the liquid lets pass. There are several other methods for measuring the color of liquids.
If the food is liquid or a solid, we can measure its color by comparing the reflected color to defined colored tiles or chips. The quality control inspector changes tiles until the closest color match is made and then defines the color of the food as being identical to the matching tile or falling between the two nearest tiles. Working with tomato products, one would need to have only a few green and disks to cover the usual range of tomato color. The grade standards for tomatoes have been based on such a method.
Color measurement can be further quantified. Light reflected from a colored object can be divided into three components; which have been termed value, hue, and Chroma. Value refers to the lightness or darkness of the color or the amount of white versus black; hue to the predominant wavelength reflected, which determines what the perceived color is (red, green, yellow, blue, etc.); and Chroma refers to the intensity strength of the color. The color of an object can be precisely defined in terms of numerical values of these three components. Another three-dimensional coordinate scale for describing color utilizes the attributes of lightness-darkness, yellowness-blueness, and redness-greenness. These dimensions of color, used in tri-stimulus colorimeter, can be quantified by instruments such as the Hunter lab color and color Difference Meter (Fig. 6.4). Food samples having the same three numbers have the same color. These numbers, as well as numbers representing value, hue, and chroma, vary with color in a systematic fashion that can be graphed to produce a chromaticity diagram (Fig. 6.5). The color chemist and quality controller can relate these numbers to color, and through changes in the numbers can follow gross or minute changes in products that may occur during ripening, processing, or storage. In similar fashion a quality controller can define the color of a product and relate this information to distant plants to be matched at any future date. This is particularly useful where the food color is so unstable as to make the forwarding of a standard sample unfeasible.
As with color, there are light-measuring instruments that quantitatively define the shine or gloss, of a food surface. Gloss is important to the attractiveness of gelatin desserts, buttered vegetables, and the like.
Consistency
Although consistency may be considered a textural quality attribute, in many instances we can see consistency and so it also is another factor in food appearance. A chocolate syrup may be thin-bodied or thick and viscous; a tomato sauce can be thick or thin. Consistency of such foods is measured by their viscosity, higher viscosity products being of higher consistency and lower viscosity being lower consistency.
The simplest method to determined consistency is to measure the time it takes for the food to run through a small hole of a known diameter; or one can measure the time it takes for more viscous foods to flow down an inclined plane using the Bostic Consistometer (Fig 6.6). This device might be used for ketchup, honey, or sugar syrup. These devise are called viscometers. There are several other types of viscometers using such principles as the resistance of the food to a falling weight such as a ball, and the time it takes the ball to travel a defined distance; and resistance to the rotation of a spindle, which can be measured by the power requirements of the motor or the amount of twist on a wire suspending the spindle. Viscometers range from the quite simple as shown above to highly sophisticated electronic instruments.
TEXTURAL FACTORS
Texture refers to those qualities of food that we can feel either with the fingers, the tongue, the palate, or the teeth. The range of textures in foods is very great, and a departure from an expected texture is a quality defect.
We expect chewing gum to be chewy, crackers and potato chips to be crisp, and steak to be compressible and sharable between the teeth. The consumer squeezes melons and bread as a measure of texture which indicates the degree of ripeness and freshness. In the laboratory, more precise methods are available. However, the squeezing device in Fig. 6.7 gives only an approximation of freshness, since the reading also depends on the stiffness of the wrapping and the looseness with which the bread slices are packed.
Measuring Texture
Food texture can be reduced to measurements of resistance to force. If food is squeezed so that it remains as one piece, this is compression as with the squeezing of bread. If a force is applied so that one part of the food slides past another, it is shearing –as in the chewing of gum. A force that goes through the food so as to divide it causes cutting-as in cutting an apple. A force applied away from the material results in tearing or pulling apart, which is a measure of the food’s tensile strength –as in pulling apart a muffin. When we chew a steak, what we call toughness or tenderness is really the yielding of the meat to a composite of all of these different kinds of forces. There are instruments to measure each kind of force, many with appropriate descriptive manes but none exactly duplicate what occurs in the mouth.
Many specialized test instruments have been devised to measure some attribute of texture. For example, a succulometer (Fig. 6.8) uses compression to squeeze juice out of food as a measure of succulence. A tenderometer applies compression and shear to measure the tenderness of peas. A universal testing machine fitted with the appropriate devices can measure firmness and crispness and other textural parameters (Fig.6.9). This and similar instruments frequently are connected to a moving recording chart. The time-force curve traced on the chart gives a graphic representation of the rheological properties of the food item. When an apple half is tested, the tracing would show an initial high degree of force required to break the skin, and then a change in force as the compressing-shearing element enters and passes through the apple pulp.
Various forms of penetrometers are in use. These generally measure the force required to move a plunger a fixed distance through a food material. A particular penetrometer used to measure gel strength is the Bloom Gelometer. In this device, lead shot is automatically dropped into a cup attached to the plunger. The plunger positioned above the surface move a fixed distance through the gel unit it makes contact with a switch that cuts off the flow of lead shot.
The weight of shot in grams, which is proportional to the firmness of the gel, is reported as degrees Bloom. This is one way of measuring the “strength” of gelatin and the consistency of gelatin desserts. Another kind of penetrometer, also referred to as a tenderometer, utilizes a multiple-needle probe that is pressed into the rib eye muscle of raw beef (Fig.6.10). The force needed is sensed by a transducer and displayed on a meter. The carefully engineered needle probe was designed to give readings that correlate with the tenderness of the meat after cooking, while at the same time not altering the raw meat for further use.
Several of the above methods for measuring texture alter the food sample being tested, so that it cannot be returned to a production batch. Since there are correlations between color and texture in some instances, there are applications where color may be used as an indication of acceptable texture. Under controlled conditions automatic color measurement may then be used as a nondestructive measure of texture; this is done in the evaluation of the ripeness of certain fruits and vegetables moving along conveyor belts. Another nondestructive indication of texture is obtained by the experienced cheesemaker who thumps the outside of a cheese and listens to the sound.
Testing the rheological properties of food using a sophisticated mechanical spectrometer. Courtesy of Cornell University Photo Services.
Evaluating the tenderness of beef with the Armour meat tenderometer. Source: Anon, Food Technology 27:1 1973.
This gives a rough indication of the degree of eye formation during ripening of Swiss cheese. One of the newer methods of nondestructive texture measurement makes use of sonic energy, which is absorbed to different extents depending on the firmness of an object.
Texture Changes
The texture of foods, like shape and color, does not remain constant. Water changes play a major role. Foods also can change texture on ageing. Texture of fresh fruit and vegetables becomes soggy as the cell walls break down and the cells lose water. This is referred to as loss of turgor. As more water is lost from the fruit, it becomes dried out, tough, and chewy. This is desirable in the case of dried apricots, prunes, and raisins. Bread and cake in the course of becoming stale lose some water and this is a quality defect. Steaming the bread refreshes it somewhat by softening the texture. Crackers, cookies, and pretzels must be protected against moisture pickup that would soften texture.
Quite apart from changes in the texture of unprocessed foods, there are the textural aspects of processed foods. For example, lipids are softeners and lubricants that the baker blends into a cake formula to tenderize cake. Starch and numerous gums are thickeners; they increase viscosity. Protein in solution can be a thickener, but if the solution is heated and the protein coagulates, it can form a rigid structure as in the case of cooked egg white or coagulated gluten in baked bread. Sugar affects texture differently depending on tis concentration. In dilute solution it adds body and mouthfeel to soft drinks. In concentrated solution it adds thickening and chewiness. In still higher concentrations it crystallizes and adds thickening and chewing. In still higher concentrations it crystallizes and adds brittleness as in hard candies.
The food manufacturer not only can blend food constituents into an endless number of mixtures but may use countless approved ingredients and chemicals to help modify texture.
FLAVOR FACTORS
As noted already, flavor is a combination of both taste and smell and is largely subjective and therefore hard to measure. This frequently leads to differences of opinion between judges of quality. This difference of opinion is to expected since people differ in their sensitivity to detect different tastes and odors, and even where they can detect them people differ in their preference. In some cultures, strong smelling fish is desirable, whereas in others such fish would be unacceptable.
The flavor of a given food is determined by both the mixture of salt, sour, butter, and sweet tastes and by the endless number of compounds which give foods characteristic aromas. Thus, the flavor of a food is quite complex and has not been completely described for most foods. Adding to this complexity is the fact that the same food is often perceived differently by different individuals. This difference is due to cultural and biological differences between people.
Influence of Color and Texture
Judgments about flavor often are influenced by color and texture. For example, we associate such flavors as cherry, raspberry, and strawberry with the color red. Actually, the natural flavor essences and the chemicals they contain are color less. But in nature they occur in foods of typical color and so we associate orange flavor with the orange color, cherry with red, lime with green, chicken flavor with yellow, and beef flavor with brown.
If gelatin type desserts are prepared without color, inexperienced tasters will find it hard to distinguish lime from cherry. If we color the lime-flavored item red and the cherry-flavored item green, then the challenge becomes still greater. Butter and margarine may be colored by the addition of a dye. Many consumers will agree that of two samples, the yellow one has the stronger butter flavor, but this may not actually be the case. This is the reason “blind” testing is often employed in flavor evaluation, colored lighting being the means of masking out an influencing color.
Texture can be equally misleading. When one of two identical samples of gravy is thickened with a tasteless starch or gum, many will judge the thicker sample to have the richer flavor. This can be entirely psychological. However, the line between psychological and physiological reactions is not always easy to draw. Our taste buds respond in a complex fashion not yet fully understood. Many chemicals can affect taste response to other compounds. It is entirely possible for texturizing substances to influence taste and flavor in a fashion that is not imaginary. If a thickener affects the solubility or volatility of a flavor compound, its indirect influence on the nose or tongue could be very real.
Taste Panels
We can measure flavor in various ways depending on our purpose. The use of gas chromatography to measure specific volatile compounds has already been mentioned. Some flavor-contributing substances can be measured chemically or physically with other instruments. Examples are salt, sugar, and acid. Salt concentration can be measured electrically by its effect on the conductivity of a food solution. Sugar in solution can be measured by its effect on refractive index. Acid can be measured by titration with alkali, or by potentiometric determination of hydrogen ion concentration as in determining Ph. (negative logarithm of the hydrogen ion concentration). All of these are largely research or quality control tools. When it comes to consumer quality acceptance, there is still no substitute for measurements made by having people taste products.
We may use individuals, but groups are better because differences of opinion tend to average out. We may use trained individuals as is common in federal and state grading of agricultural products such as butter and cheese. We may employ consumer percentage groups-panels that are not specifically trained but can provide a good insight into what customers generally will prefer. We can use panels of highly trained people who are selected on the basis of their flavor sensitivity and trained to recognize attributes and defects of a particular product such as coffee or wine.
A typical taste panel room is provided with separate booths to isolate tasters so that they do not influence one another with conversation or by facial expressions. The booths may be equipped with colored lights when appropriate. The food sample is given to the taste through a closed window so the taster will not see how it was prepared and thus, be influenced. The samples are coded with letters or numbers to avoid terms or brand names that might be influential.
The tasters are given an evaluation form, of which there are many kinds. One kind has columns for samples with descriptive terms such as like definitely, like mildly, neither like nor dislike, dislike mildly, and dislike definitely. The taster checks an opinion for each sample and may make additional comments. The terms are given number rankings by the taste panel leader, such as 5 for like definitely down to 1 for dislike definitely. When all evaluation forms are complete, the taste panel leader tabulates and averages the results. A number ranking scale for flavor or for other quality factors is known as a hedonic scale.
Often taste panelists are asked to choose between two samples in a preference test. Given just two samples, tasters me choose one even though they are really unable to distinguish between them. Given the same two samples again, they might choose in reverse order quite by chance. To avoid this and gain more meaningful data on samples that are quite close in the attribute being studied, preference tests often involve three samples. In this case, tasters are given two samples that are identical and one that is different, all at the same time and appropriately coded. Tasters are asked which two samples are similar, which sample is different, and which is preferred. If a taster cannot correctly pick the odd sample, then his or her preference loses significance. This is known as a triangle test. There are various ways of interpreting triangle tests and different kinds of preference tests; statistical analysis of results is commonly employed.
The number of samples tasters can reliably judge at one sitting without their taste perception becoming dulled is quite limited and depends on the product; generally, no more than about four or five samples can be reliably tested at one time. Taste panel booths often are provided with facilities for rinsing the mouth between samples, or unsalted crackers may be eaten to accomplish a similar effect.
Taste panels used in research product development and for purposes of evaluating new and competitive products are nor restricted to evaluating flavor. Texture, color, and many other quality factors can be meaningfully measured with this technique. Further, evaluation forms can be devised to measure the reactions of the very young (Fig.6.11), or any other special group.
ADDITIONAL QUALITY FACTORS
Three very important quality factors that may not always be apparent by sensory observation are nutritional quality, sanitary quality, and keeping quality.
Nutritional quality frequently can be assessed by chemical or instrumental analyses for specific nutrients. In many cases this is not entirely adequate and animal feeding tests or equivalent biological tests or equivalent biological tests must be used. Animal feeding tests are particularly common in evaluating the quality of protein sources. In this case, the interacting variables of protein level, amino acids all contribute to determine biological value. Whereas the commercial feeding of livestock is done very largely on a nutritional quality basis, unfortunately people do not choose their food on this basis.
Sanitary quality usually is measured by counts of bacteria, yeast, mold, and insect fragments, as well as by sediment levels. X-rays can be used to reveal inclusions like glass chips, stones, and metal fragments in raw materials and finished products moving at high speeds through a plant.
Keeping quality or storage stability is measured under storage and handling conditions that are set up to simulate or somewhat exceed the conditions the product is expected to encounter in normal distribution and use. As normal storage tests may require a year or longer to be meaningful, it is common to design accelerated storage tests. These usually involve extremes of temperature, humidity, or other variables to show up developing quality defects in a shorter time. Accelerated storage tests must be chosen with considerable care because an extreme temperature or other variable frequently will alter the pattern of quality deterioration.
The major quality factors of appearance, texture, and flavor are referred to as organoleptic, or sensory, properties since they are perceived by the senses.
There are hundreds of specific quality attributes unique to particular foods and sometimes they do not seem to make much sense, unless we accept the fact that they are traditional and people have become used to them and expect them.
The foam or head on a glass of beer is a quality factor, and its size, bubble structure, and stability are all important quality attributes. But the slightest head foam at the top of a glass of wine or a cup of tea is a quality defect. A slight cloudiness or turbidity is desirable in orange juice and is a quality attribute, but cloudiness in apple juice may be considered a defect by some but desirable by others. The quality of Swiss cheese is judged by the size, shape, gloss, and distribution of its eye or holes, but eye in Cheddar cheese is a defect.
These and many other quality attributes make our foods different and interesting and in many cases the quality attribute that seems arbitrary really is associated with a more fundamental quality factor. The eye in Swiss cheese, for example, are an indication of flavor through proper bacterial fermentation and of a proper cheese texture capable of holding the carbon dioxide formed during fermentation.
QUALITY STANDARDS
To help ensure food quality, many types of quality standards have come into existence. These include research standards, trade standards, and various kinds of government standards.
Research standards are internal standards set up by a company to help ensure that excellence of its products in a highly competitive market. Trade standards generally are set up by members of an industry on a voluntary basis to assure at least minimum acceptable quality and to prevent the lowering of standards of quality for the products of that industry. Government set many types of standards. Some are mandatory these are the standards developed to protect health and prevent deception of the consumer. More will be said about them in later chapters. Other government standards known as Federal Grade Standards are largely optional and have been set up mainly to help producers, dealers, wholesalers, retailers, and consumers in marketing food products. The Federal Grade Standards provide a common language among producers, dealers, and consumers for trading purposes.
Federal Grade Standards
The Federal Grade Standards are standards of quality administered by the USDA Agricultural Marketing Service and the Food Safety and Inspection Service. To give meaning and uniformity to the standards, the USDA established on official system of food inspection and grading. The difference between inspection and grading must be understood. Inspection is often mandatory and assures the wholesomeness of products, particularly meats. Grading is voluntary and determines the quality of products such as meats. Inspectors and graders are trained in the accepted quality factors, and there are inspectors and graders for each major food category. Uniform grades of quality have been established for over 100 foods, including meat, dairy, poultry, fruit, vegetable, and seafood products.
Taking meat products as an example, a federal meat grader evaluates the overall quality of beef, taking into account such factors as shape of the animal carcass, quality and distribution of the fat, age of the animal, firmness and texture of the flesh, and color of the lean meat. The grader stamps the meat in such a repetitive way that the grade stamp will be present on all cuts even after the carcass is butchered for retail sale.
The federal grade marks for beef (Fig.6.12), in order of decreasing quality, are Prime, Choice, Select, Standard, Commercial, Utility, Cutter, and Canner. The first three are generally found on meat cuts in retail stores or used in restaurants; the other grades are more commonly used in processed meat products. These grade standards are quality standards that do not reflect differences in wholesomeness, cleanliness, or freedom from disease. All meat must pass such inspection regardless of Federal Grade Standards. The quality level indicated by a standard sometimes is changed for reasons of limited availability or economics. The Federal Grade Standards for beef were first instituted in the 1920s and the most recent changes in the beef grading system occurred in 1980.
In similar fashion, other foods for which grade standards have been established are graded. Detailed brochures are published on each food, and quality control tests for the different quality factors are precisely defined. Liberal use of pictures is made where the quality factor is difficult to describe in worlds.
Insert Figure 6.12. The relationship between fat marbling, animal maturity (i.e., age) and the USDA federal grade standard for beef. “A” maturity animals are 9-30 months of age, whereas “E” are more than 96 months. Source: Muscle Foods: Meat, Poultry and Seafood Technology. D.M. Kinsman. A.N. Kotula, and B.C. Breidenstein (editors), 1994 Chapman & Hall, New York.
In the grading of eggs, for example, the freshness quality is fairly accurately measured by the visual condition of the egg white and the egg yolk (Fig. 6.13). A fresh egg has a high percentage of thick white next to the yolk and a small amount of thin white beyond the thick white. As the egg ages, the thick white breaks down and the proportion of the thick white to thin white decreases. Ultimately all of the white is thin water white and no thick white will be seen. There is also flattening of the yolk with ageing and loss of freshness.
Quality defects of fruits and vegetables are of many kinds. The grade standards for asparagus recognize slight differences in development in the head and bracts. The standards for sweet potatoes consider the shape that yields “usable pieces” for processing. A usable piece means a segment of such size and shape that it will be recognizable as a sweet potato after canning or freezing. The quality attributes for fresh whole tomatoes (ripeness, color, freedom from cracks and blemishes, size, etc.) also include limited “puffiness.” This is the amount of air void or open space between the tomato wall and the central pulp (Fig.6.14).
Federal Grade Standards for shelled pecans include degree of shriveling, color of nut kernels, degree of chipping of nut halves, moldiness, decay, rancidity, broken shells, and so on.
Typically, the final grade of a product is given after weighing each of the quality factors and giving each a numerical value. The values are then added up to give a total score. The Federal Grade Standard for canned concentrated orange juice allows 40 points for color, 40 points for flavor, and 20 points for absence of defects; the latter includes freedom from seeds, excessive orange oil, proper reconstitution with water, absence of settling out, and so on. The relative importance given in Federal Grade Standards to different quality factors for a wide range of processed fruit and vegetable products is listed in Table 6.1.
Many kinds of score sheets are devised for special quality control purposes. The score sheets for quality control of military rations may include well over 100 quality factors, ranging from specific requirements for packaging materials to storage stability and performance of the packaged food under unique environmental conditions.
Planned Quality Control
Regardless of whether quality is to be maintained on agricultural raw materials or on manufactured food products, a systematic quality control program is essential. These program begins with customer specifications and market demand. What level of quality is demanded and can be produced for the price the customer can afford to pay? Additionally, what legal requirements must be met? With these specifications agreed upon, appropriate testing methods and control stations can be set up. Nearly all food manufacturing facilities have a formal quality control or quality assurance department.
Figure; 6.14the defect of puffiness in tomatoes. Courtesy of U.S. Department of Agriculture.
The functions of a quality control department are diverse and far ranging, as can be seen in Fig. 6.15 for a department organized to control quality of tomato products. Such a department not only is charged with quality control, which implies detection and correction of defects, but also with the broader concept of quality assurance, which encompasses anticipation and prevention of potential defects. In a food processing or manufacturing plant, quality control testing must start with the raw materials. Sampling and testing of the raw materials will provide a basis for accepting or rejecting these raw materials and will give useful information on how to handle the material in order to obtain a finished product of the desired quality and shelf life. Quality control tests on the processed products through manufacturing, packaging, and warehousing operations are then essential to ensure that customer demands and legal requirements are satisfied.
The diversity of testing indicated in Fig. 6.15 is further complicated by the variations that may be expected between units or batches of raw materials, as well as the fluctuations that occur when any processing condition is repeatedly measured over time. Are variations of a magnitude that is within an acceptable range and within the intrinsic capability of the manufacturing process or is the variation indicative of a process truly out of control? Such questions are answered by applying statistics to repeated measurements of a given quality attribute or processing condition. Repeated measurement will provide data for determination of the mean, range, and normal frequency distribution of the variable under consideration. Such data then can be used to develop quality control charts, one type of which is shown in Fig. 6.16. This chart graphs the variation of a measured attribute from a mean value (x) with time. The attribute might be weight of filled cans coming from the filling machine prior to can seaming. The chart also provides a range bounded by an upper control limit (UCL) and a lower control limit (LCL) based on the measured attribute’s normal frequency distribution. Filled cans with weights beyond this range would be unacceptable and could be removed for adjustment prior to seaming. This type of chart also reveals trends during processing that may call for filler machine adjustment depending on the direction of the drift. Statistical quality control charts are of many kinds and can be devised on monitor specific measurements of size, color, texture, flavor, ingredient composition, nutrients, microbial counts, and numerous types of processing variables. These and other measurements are increasingly being performed continuously by automated instrumentation systems, which can detect deviations from specification and, through computer controls, initiate process adjustment. Thus, on-line measurement of carbon dioxide levels in soft drinks, and of alcohol and carbohydrates as an index of calories in “light” beer, is currently being performed by infrared analyzers as part of the quality control programs for these products.
The influence of market demand on quality specifications cannot be overemphasized. Whereas such factors as nutritional quality and sanitary quality ought not be permitted to vary from well-established standards, organoleptic quality factors are by no means rigid. White eggs are preferred in New York, but brown egg have been very popular in Boston. Quality bread means different formulas, textures, and shapes in many markets of the United States and indeed all over the world.
Two newer concepts in product quality and safety have been developed and widely adopted in recent years. Total Quality Management (TQM) and Hazard Analysis and Critical Control Point (HACCP) are quality and management “systems” designed to assure the highest quality and safest foods possible. TQM is a management system which strives to continuously improve the quality of products by making small but incremental changes in a product’s ingredients, manufacture, handling, or storage which result in overall improvement.
Relation of the ẋ control chart to a normal frequency distribution: (A) frequency distribution with frequency scale vertical: (B) frequency distribution with frequency scale horizontal: (C) control chart. Frequency distribution extended into a time series. Source: Kramer and Twigg, Quality Control in the Food Industry, 3rd ed. AVI Publishing Co., Westport, CT, 1973.
All workers in plants which employ TQM techniques have joint responsibility for product quality and routinely meet in “quality circles” or similar groups to discuss potential improvements. This concept has been widely applied with success in other industries such as automobile manufacturing. HACCP is a preventative food safety system in which a process for manufacturing, storing, and distributing a food product is carefully analyzed step-by-step. Points at which tight control of the process will result in elimination of a potential hazard are identified and appropriate control measures taken before a problem occurs the principles and practices of such a system will be presented in greater detail in food safety hazards.