The commercial approach to food quality is undergoing both an evolution and a revolution. Quality evaluation systems are evolving from a perspective of quality control to quality Assurance to Quality Management. These changes have necessitated revolutionary switches of emphasis from inspecting quality to improving processes that result in enhanced quality. Food science has generally regarded quality as a tool to evaluate other objectives (e.g., food process development, food product development, new package assessment). Thus, food quality is still generally defined by the investigator in terms of clearly measurable characteristics rather than in terms of consumer acceptability. Within a food process, trade offs frequently occur such that quality can be optimized and not maximized. Thus, changes in quality of a specific product undergoing a specific process are described in relative changes of specific characteristics
QUALITY OF FRESH AND PROCESSED PRODUCTS
Quality is an increasingly important factor in the production andmarketing of biological products. The term ‘quality’ is one of the mostdefined terms in use in food industry today. Quality may be defined as‘The totality of features and characteristics of a product ………….’Concerns objective factors related to the product. The second part, ‘……….To satisfy a given need’, concern subjective factors related to user orconsumer of goods.In general sense, quality is defined as degree of excellence. Fromthe strategic point of view, there is wide agreement on the quality definitionfor the goal of product development products and services that satisfy orexceed the customers’ requirements (Surak and Mc Anelly, 1992) whileaccording to Oliver (1997) quality means to exceed the customer’sexpectations. From the biochemistry corner, the meaning of quality is stillvague, and is not yet able fully to explain the difference between high andlow quality product.To the consumer, the quality of any produce is well defined andthe difference is in subjective terms between a high and a low qualityproduct. An average consumer may accept even the inferior sample butthere is a wide difference between “accept” and “prefer”. Although the‘optimum quality range’ is determined primarily with the views of 75%(approximately) of the people when would consider (not to be confusedwith the word “prefer”) a fruit / vegetable / any product being acceptable.However, when the quality of a fresh commodity in the market is measuredagainst on optimum quality range, the result are extremely disappointingin terms of consumer satisfaction, which is beyond the optimum quality
137range. In an attempt to develop ways of defining fruit and vegetable qualityin terms of consumer, it has been necessary to challenge some of the widelyheld assumptions of quality both by food scientists and post-harvestphysiologist (Shewfelt, 1999). The Quality Enhancement (QE) model hasbeen proposed to redefine quality in terms of the consumer and thus leadto improve quality of fresh fruits and vegetables
Natural contaminantsThese includes cyanogenic in limabean and cassava, oxalates inrhubarb and spinach, thioglucosides in cruciferous vegetables andglycoalkaloids (Solanine) in potatoes.ii. Microbial contaminationConsumers are giving less priority to it compared to chemicaltoxicants. Bacteria can be introduced on to fresh fruits and vegetablesthrough use of untreated organic fertilizers (e.g., manure), or throughinsufficiently treated waste water. Inadequate hygiene standards in packingsheds and anywhere else in food chain and also cause problems. Problemis excerbated because fruit and vegetables often are eated fresh. Washingfresh produce is a help, but water used should be clean and free ofcontaminants.iii. Synthetic toxicantsIn many countries, consumers are very much concerned about levelsof chemical spray deposits found in and on fresh products. Evidence ofpesticide residues above acceptable levels, or presence of unapproved orbanned spray deposits, renders entire shipments or otherwise sound cropsunsaleable.1.7.
Measurement of product qualityEating quality can be assessed most accurately by using taste panelsor consumers. These consist of a selection of customers from market whoare trained to assess quality attributes being examined. Taste panel can notbe used easily as part of production process. Instead, it is necessary toresort to readily usable test methods, which may involve simple or complexequipment. Various methods used for evaluation are: instrumental,immunoassay and sensory evaluation.i. InstrumentalOne ideal instrumental method for measuring quality would becheap, non destructive to sample, easy to use and not subject to variationor fatigue with a rapid response and wide application. In addition,instrumental methods must be linked to assessment made by a trainedsensory panel. Quality is assessed with the help of measuring parameterslike colour, flavour, texture etc. Colour may be measured by using colourmeters such as Gardner or Hunterlab colour meters. Other instrument forcolour measurement are Munsell discs and Lovibond Tintometer.
141Flavour of food is caused by chemical substances present in foodand consists of a combination of taste, odour and other sensations. This ismeasured by using a gas chromatograph coupled to a massspectrophotometer by identifying flavour constituting compounds present.Textural characteristics which consumers appear to value in fruitsand vegetables are crispness and firmness. Different texture measuringdevices are available which comprise penetrometers, texture analyzer andinstron universal testing machines.These instrumental methods are further classified broadly intodestructive and non-destructive methods, The destructive indices are againclassified into mechanical destructie tests. Non-destructive measurementsare sub divided into mechanical non-destructive and visual non-destructivetests.
2. Destructive Tests
2.1. Mechanical destructive measurementa. PenetrometerThe most common device used to asses firmness is thepenetrometer. This has a cylindrical probe, end of which is pushed into theobject to be measured. The force required to give a preset penetration isnoted. The penetrometer gives an index of the firmness of the producttissue e.g., Magness Taylor penetrometer, Effigi penetrometer.b. Universal testing machineThis is another modified version of penetrometer and textureanalyzer. Unlike penetrometer, in the case of universal testing machine,the plunger is moved automatically and it removes the operator biasaltogether. The cross head speed of plunger can be varied and forced appliedis expressed in Newton. However this device is costlier and lacks portabilitydue to its heavy weight.c. Texture analysersIt is an instrument that measures the response of a sample to tension,compression, penetration and bend. Texture analyzer is a highly versatileand useful instrument, which can replace many other existing texturemeasuring instruments.d. TenderometerThis device is generally used to measure pea tenderness. It consist
142of a grid assembly which stimulates jaw action in eating of peas. Upperand lower sets of grid are hinged together and sample is first compressedand then sheared and extruded. It is operated hydraulically and force isshown by an indicator.e. Denture tenderometerIt is designed to stimulate denture surfaces and motion ofmastication in mouth. A complete set of human dentures is used formechanical chewing. An electronic modification of this device was adoptedfor the measurement of tenderness of peas.f. Twist testerAn alternative destructive tester is developed in which fruit ispushed onto a blade mounted on a spindle, so that blade enters fruit at apredetermined depth under skin. Fruit is determined either by readingmaximum angle to which pendulum weight is lifted or by recording angleas a function of time electronically. It is used successfully to measure thetexture of apples, kiwifruit, mangoes, plums and other fruits.g. Warner bratzlerThis instrument is primarily designed for meat texture. This canalso be used to assess texture of some stem vegetables.h. SuccolumeterIt measures volume of extractable juice under controlled conditionsof time and pressure. Its measurements are correlated with maturity of setcorn, storage quality of apple, and oil and water contents of products.3. Visual Destructive Tests3.1. Physiological change
A. ColourFlesh colour is an important determinant of quality and maturityin many crops including melons, mangoes and squash. Chemical analysisdoes not enable colour estimation. Yellowing in vegetables and fruits isoften a result of disappearance in chlorophylls, which allows yellow –orange xanthophylls and carotenes to become more visible. Bluberry colouris determined by anthocyanins, which are red when extracted.
B. RefractometerA measurement of chemical composition, level of soluble solids
143in fruits and vegetable juices can be determined by measuring refractiveindex of juices. Laboratory and field devices require a small of juice placedon a glass cover. Refraction of light produces on indication on a scale thatgives a measure of soluble solids directly. This is useful indicator of maturityat harvest time expecially in kiwifruits. Refractometer are low in cost butrequire calibration. Measurement may be affected by temperature anddelays in carrying out the test after exposing fresh juice.
- Chemical tests
4.1. General chemical assessmentRelative proportions of chemicals in juices of fruits and vegetableare often good indicator of quality. Particularly during maturation, thereare significant change in chemical composition, and these can be measuredby appropriate analytical means.
4.2. Starch testA common maturity test is the starch level in a fruit (particularlyapple and pears), found by cutting the fruit in half along equator and placingcut surface in an iodine solution (4% potassium iodide and 1% iodine).Iodine stains the section in regions of high starch but does not affect sugars.The resulting stain pattern can be compared against photographs of standardpattern, and a stand index determined.
4.3. Chemical residuesNormal analytical chemical tests can be used to test for sprayresidues. Gas chromatographs also are used extensively. These detectcharacteristics distribution of molecular weights associated with targetedorganic substances.
4.4. Moisture content measurementIn addition to electrical measurement, moisture content can bedetermined accurately by gravimetric method (oven drying), to establishdry weight after removal of moisture.
4.5. Biological destructive testerPresence of pathogen and bacteria can be determined by a rangeof cell culture techniques. Samples of skin or tissue are placed in a suitablegrowth media and incubated for several days, Pathogens reproduce to levelsat which they can be detected and counted. - Non-destructive testing methodsWe can save in numbers of fruits and vegetables wasted, but thereare other advantages: first, the same fruit can be retestd several timesthroughout its lifetime, giving a reduction in variability as a result of randomsampling of fruit in growth and storage traits. Other advantages are thatsamples taken from packed fruit do not need to be replaced. This has majoradvantages for quality control inspection procedures. In scientificexperiments, because the same fruit can be used again and again withoutinterrupting its normal life cycle, number of samples required can bereduced.
- Mechanical nondestructive tests5.1. Mass and bulk densityMass is one of the most obvious quality indices and is easy tomeasure. Density can be measured using Archimedes principle. Fruit isweighed in air and then suspended in water. The apparent loss in mass isequal to the volume of the fruit multiplied by the density of water.
5.2. Quasistafic low-pressure indentersA large number of different techniques involve applying low-pressure compression to intact fruit and vegetables. Some are quasistatic,and in general these can be set up using a modern texture analyzer.
5.3. Dynamic low-pressure indentersOther indenters involve impart devices using small accelerometersto measure impact parameters. In soft-sense system, fruits are droppedfrom a small height onto a force transducer.
Typical analysis involvesmeasurement of dwell time (the period that impact force remains above50% or 80% of the pack value), or area under force time curve.
5.4. Nondestructive use of texture analyzerA wide range of non-destructive measurements can be taken.Measurements made include compressibility, energy absorption during aloading cycle, and whole fruit modules of elasticity determined bycompression between flat platters. This test is suited to cherries and othersoft fruits.
5.5. Acoustic methods Acoustic-response method is used for estimation of overall orglobal texture of fruits that are approximately spherical. Acoustic impulse
145response method makes use of sound signal imitted by fruit as it vibratesin response to a gentle short duration shock, produced by tapping with asmall rod or pendulum. A microphone captures the signal, and the principlefrequency of vibration is then calculated by means of a fast Fouriertransform