翻译原文.pdf

Biosystems Engineering (2004) 89(2), 151158doi:10.1016/j.biosystemseng.2004.05.007Available online at PHPostharvest TechnologyDevelopment and Performance Evaluation of an Automatic Vacuum Packer of theContinuous TypeT.Y. Yan; J.H. ChungDepartment of Biosystems and Agricultural Engineering, Inst. of Ag. Sci. and Tech., Chonnam National University, 300 Yongbong-dong,Puk-gu, Gwangju 500-757, Republic of Korea; e-mail of corresponding author: jhchungchonnam.ac.kr(Received 19 November 2003; accepted in revised form 18 May 2004; published online 28 July 2004)The objectives of this study were to develop an automatic vacuum packer of continuous type and to evaluateits performance for packing white rice with embryo. The vacuum packer consisted of a pressing boardassembly, a vibrating conveyor assembly, a tape adhering assembly, and a gas lling system. The processingcapacity of the vacuum packerwas 6pouchminC01. The success rate of the vacuum packaging of the machinewas 92C16%. The changes of the whiteness, moisture content, peroxide value, and acid value of non-vacuum-packed and vacuum-packed samples were investigated to analyse the preservation effects of vacuum packagingon rice quality during the storage of 3 months. The results obtained from the storage experiment were asfollows: (1) the whiteness of the non-vacuum-packed and vacuum-packed rice decreased by 4 and 2,respectively; (2) the moisture content of the non-vacuum-packed and vacuum-packed rice decreased by 1C13and 0C18% (w.b.), respectively; (3) the peroxide value of the non-vacuum-packed rice increased by3C145meqkgC01and then dropped moderately; but the value of the vacuum-packed samples increased by1C189meqkgC01; (4) the acid values of the non-vacuum-packed and vacuum-packed rice increased by 0C198 and0C171mgg,C01respectively; (5) The vacuum packaging suffocated all the insects in the pouches.# 2004 Silsoe Research Institute. All rights reservedPublished by ElsevierLtd1. IntroductionHigh-quality rice should be produced to make nativeagricultural industry more competitive and to satisfy theconsumers requirements. Recently, several kinds ofspecialised rice products, such as white rice withembryo, germinated brown rice, pre-washed white ricethat can be cooked without washing, rice fortied withother nutrients, and functional rice are produced andsold in some superstores in Korea. Rice in storagerespires by consuming nourishment. As white rice withembryo has more nutrients, enzymes, and bres thannormal white rice (Houston, 1972), many consumers areattracted by white rice with embryo in market surveys.However, the embryos of white rice are easily deterio-rated due to high temperature in hot seasons. Evenmildews and insects are sometimes found in white rice.Non-vacuum packaging not only shortens the shelf-lifeof rice products but also decreases the rice qualitybecause chemical components such as carbohydrate andfat in rice are dissolved and oxidised, and consequentlyfree fatty acid and various organic acids are generatedduring the storage period. It is widely known thatvacuum packaging can prolong the shelf-life of agricul-tural products and maintain their quality and freshnessbecause it can attenuate their biological respiration rate(Hosokawa et al., 1995; Murcia et al., 2003).Preventing insect pests in rice products is one of theimportant factors in producing high-quality rice. Stored-product insects, which outbreak in high temperature andhumidity, are usually found in rice products. They areIndian meal moth (larval period), lesser grain borer, andrice weevil. Vacuum packaging is one of the effectivephysical methods of insect control. Dendy and Elk-ington studied that the lack of oxygen in hermeticstorage was the major cause of insect death (Calderon &Barkai-Golan, 1990).In this study, an automatic vacuum packerdesignedwith virtual prototyping technology (Yan et al., 2003;Erdman et al., 2001) to prolong the shelf-life ofwhite rice with embryo was manufactured and evalu-ated. The specic objectives of this research were: (1) toARTICLE IN PRESS1537-5110/$30.00 151 # 2004 Silsoe Research Institute. All rights reservedPublished by ElsevierLtdmanufacture an automatic vacuum packer of contin-uous; (2) to conduct packing tests forevaluating theperformance of the vacuum packer; (3) to analyse therelationship between vacuum time and vacuum level atdifferent pouch sizes; (4) to investigate the preservationeffects of vacuum packaging on white rice with embryoin physical and chemical changes.2. Materials and method2.1. Development of a vacuum packerThe function of the proposed vacuum packer was toremove the air from a pouch of rice by a needle in ashort time and to seal the vacuum hole with a piece oftransparent tape quickly. The vacuum packer (Fig. 1)consisted of the following three assemblies was designedand manufactured: (1) a pressing board assembly thataccelerates the air removing process; (2) a vibratingconveyorassembly that shapes the vacuum-packed riceproducts for a good appearance; and (3) a tape adheringassembly that puts a transparent 5cm by 3cm tape pieceon a pouch. All the moving parts of the vacuum packerwere operated according to the developed controlalgorithm (Fig. 2) of a programmable logical controller(PLC) of the vacuum packer. The acting sequence forthe vacuum packerwas also designed. The vacuumpacker was designed to pack cereal products of varioussizes according to vacuum time, shape-forming time,and the intended position of the vacuum-hole on apouch. The vacuum time and shape-forming time of theARTICLE IN PRESSFig. 1. The configuration of an automatic vacuum packer; all dimensions in mmStartPosition settingVacuum-time settingVibration-time settingEndShape formingAir removing and tapingIs a pouch detected?Finished or not?NoNoYesTape cuttingYesFig. 2. Control algorithm of an automatic vacuum packerT.Y. YAN; J.H. CHUNG152vacuum packer were controlled with an accuracy of0C101s. As modied atmosphere packaging can prolongthe shelf-life of agricultural products, the function of gaslling was embedded in the proposed automatic vacuumpacker. The gas-lling time of the developed packer wasadjusted with an accuracy of 0C101s. This study mainlycovers the effects of vacuum packaging on white ricewith embryo as chemical experiments related to gaslling were not nished.2.1.1. Pressing board assemblyThe pressing board assembly consisted of a camfollowermechanism shown in Fig. 3. The followerof thecam mechanism was a roller-type follower. It was drivenbya0C11kW geared motor with a reduction rate of 1:25(model GM-H2B-RL, Mitsubishi Co., Japan). The camwas pivoted with the output shaft of the motor. As theshaft of the geared motor rotates, the pressing boardundergoes an up-down translational movement. Whenthe thickness of a pouch was too large, the cam and thefollower were disconnected each other to suit differentsized pouches. The 550mm by 280mm rectangularpressing board was utilised to accelerate the airremoving speed. A 3mm thick rubber plate with thesame shape of the pressing board was attached to itsdown surface to protect the packaging lm of a pouchduring the vibrating process for shape forming. Thepressing board was screwed onto two supports thatmounted on two 522mm linearmotion guides.2.1.2. Vibrating conveyor assemblyA vibrating conveyor (Fig. 4) mounted on two linearguides was used to make the vacuum-packed rice inshape forits commercial value. The airin the pouch wasremoved by a needle during the vibrating. The vibratingconveyorassembly was also a camfollowermechanism.The eccentricity of the cam mechanism was 1mm. A90W induction motor(model 51K91A-SF, OrientalMotor Co., Japan) was used to drive the vibrating boardassembly. Another 90W geared motor with a reductionrate of 1:10 (model GM-JB, Mitsubishi Co., Japan) wasused to drive the belt conveyor for transferring pouchesto a proper position. As soon as a pouch is positionedproperly, the motor for driving the vibrating boardstarts to shape the pouch on the belt for a set time.2.1.3. Tape adhering assemblyThe tape adhering assembly had a slidercrankmechanism. The schematic view of this mechanism isshown in Fig. 5. The tape adhering assembly consistedof a tape holdercontaining 24 tiny holes of 1mm inARTICLE IN PRESSFig. 3. Schematic view of the pressing board assemblyFig. 4. Schematic view of the vibrating board assemblyFig. 5. Schematic view of the tape adhering assemblyAUTOMATIC VACUUM PACKER DEVELOPMENT AND PERFORMANCE 153diameter, a 170mm long crank, a 300mm long coupler,and a 25W geared motor with a reduction rate of 1:50(model GM-JB, Mitsubishi Co., Japan). The crank waspivoted with the shaft of the motor. The coupler waspivoted with the crank and the tape holder through tworevolute joints. The tape holder was mounted on twolinear guides through two prismatic joints. As the motorshaft rotates, the tape holder performs an up-downlinear movement for tape adhering. When a rice pouch istoo thick, then the tape holdercan be separated into twoparts to adjust it to different sized pouches. The gearedmotor was used to drive the slidercrank mechanism. Asa exible plastic hose was used to connect the tapeholderto a vacuum pump (model KRX3-SS-4001-G3,Orion Machinery Co., Japan) through a solenoid valve,The tape holder could tightly hold a piece of transparenttape supplied by an electronic tape dispenser during ataping operation.2.2. Performance experimentsWhite rice with embryo was produced at a rice mill ofChonnam National University. The milled white ricewith embryo adherence rate of 52% and moisturecontent of 16C11% (w.b.) was used as experimentalmaterials. The material was pre-packaged in 5kgpouches with the lm of nylon (15mm)/polyethylene(95mm) using an automatic vinyl packer. One hundredand eight vacuum-packed pouches of white rice withembryo were randomly selected to investigate theperformance of the vacuum packer. The 108 poucheswere left alone for1 day fordiscriminating the pouchesthat were unsuccessfully packaged by the vacuumpacker.Among the 108 pouches, 100 pouches were success-fully vacuum-packed (55C13C60C1293kPa). Eight vacuum-packed pouches and one non-vacuum-packed pouchwere randomly chosen and stored at 258C to investigatethe effects of vacuum packaging on the moisturecontent, whiteness, peroxide value, and acid value.Five vacuum-packed pouches initially contaminated bythe three kinds of insects were chosen for an insectcontrol experiment to evaluate the effect of vacuumpackaging on insect control. The insects alive in eachpouch were counted before the experiment. The numberof the initial insects in each pouch ranged from 5 to 20.The developed vacuum packerwas tested to packpouches of 2kg (pouch size of 25cm by 30cm), 3kg(pouch size of 30cm by 35cm), and 5kg (pouch size of30cm by 45cm). The relationship between vacuum leveland vacuum time at the different pouches was investi-gated to improve the productivity and efciency of thevacuum packer.2.2.1. Measurement of vacuum levelA digital vacuum gauge (model KVC-700, range0C113199kPa, Vacuum Research Co., USA) withC613C133Pa accuracy was used to measure the vacuumlevel in a pouch. The digital vacuum gauge consistedof a 16-bit analogue-to-digital converter, a sensor ofdiaphragm type, a 4-bit digital displayer, and a needle.A piece of 5cm by 5cm by 0C15cm rubber plate waspressed on the pouch to be measured to prevent airleakage as shown in Fig. . Measurement of whitenessThe whiteness of the samples for the storage experi-ment was measured using a whiteness meter (modelC-300-3, Kett Electric Laboratory, Japan). Before eachmeasurement, the whiteness meter was calibrated usinga standard whiteness disk provided by the manufac-turer.2.2.3. Measurements of peroxide value and acid valueThe peroxide value is a common measure thatindicates the degree of oxidation of white rice withembryo, i.e. the amount of peroxides in the white ricewith embryo by determining the milliequivalents (meq)of active oxygen perkilogramme of fat. The peroxidevalue was determined using the method of AOCS Cd 8-53 (AOCS, 1973). The acid value is the amount of freeacid present in fat as measured by the milligrams ofpotassium hydroxide needed to neutralise it. The acidvalue was measured by the method of AOCS Cd 3a-63(AOCS, 1973).2.2.4. Measurement of moisture contentThe moisture content of white rice is considered as afactor that directly related to the taste of cooked rice.The change of moisture content of the vacuum-packedwhite rice with embryo was investigated during thestorage period. A moisture meter (model Riceter K305,Kett Electric Laboratory, Japan) with an accuracy ofC60C11%, was used formeasuring the moisture content.ARTICLE IN PRESSFig. 6. The measurement of the vacuum level in a pouchT.Y. YAN; J.H. CHUNG1543. Results and discussion3.1. Development of an automatic vacuum packerof continuous typeAn automatic vacuum packerof the continuous typewas designed with virtual prototyping and manufac-tured with a PLC control system (Fig. 7). An actingsequence forthe developed vacuum packeris shown inFig. 8. The maximum capacity of the vacuum packerwas 6pouchesminC01when packing 5kg rice pouches.The vacuum packercould be set according to vacuumtime for removing air, vibrating time for forming shape,and pouch position on the belt. Among the 108 pouchesof rice products produced by the developed packer, 100pouches were vacuum-packed successfully, and theothereight pouches failed. The failure of vacuumpackaging could be classied into type I and type IIfailures. The type I failure was caused by an inappropri-ate taping of the automatic vacuum packer. Theunsuccessful sealing of a vinyl packer, on the otherhand, caused the type II failure. Among the failed eightpouches, six pouches were categorised to the type Ifailure and other two pouches to the type II failure.Through this experiment, it was observed that thesuccess rate, type I failure rate, and type II failure ratewere 92C16, 5C16, and 3C17%, respectively.3.2. Relationship between vacuum time and vacuum levelThe relationship between vacuum level and vacuumtime at pouches of different sizes was investigated as shownin Fig. 9. During the beginning period of vacuumpackaging, the air pressures in pouches increased tocertain extent due to the pressing effect of the pressingboard. The maximum air pressures in 2, 3, and 5kgpouches were 106C19kPa,107C12kPa,and106C19kpa, respec-tively. As the air removing process continued, the vacuumlevels in the pouches decreased gradually. When thevacuum time was 11s, the vacuum level of a 5kg pouchreached to the minimum value of 45C14kPa.Inthecasesof2 and 3kg pouches, the minimum vacuum levels of43C13kPaand45C11kPa reached in 6s and 8s, respectively.3.3. Whiteness of white riceForboth the vacuum-packed and the non-vacuum-packed rice, it was shown that the longer the storageARTICLE IN PRESSFig. 7. The changes of acid values of differently packed whiterice with embryo: *, vacuum-packed white rice with embryo;&, non-vacuum-packed white rice with embryoFig. 8. The flowchart of acting sequence for an automaticvacuum packer; (1) motor for driving the pressing boardassembly; (2) motor for driving the taping assembly; (3)vacuuming time; (4) motor for driving the vibrating assembly20406080100120023 681011213Time, sVacuum level, kPa1 4 5 7 9Fig. 9. Relationship between vacuum level and vacuum time atdifferently sized pouches: *, 2 kg; &, 3 kg;4,5kgAUTOMATIC VACUUM PACKER DEVELOPMENT AND PERFORMANCE 155time was, the more the whiteness of milled rice decreased(Fig. 10). The whiteness of the vacuum-packed and non-vacuum-packed rice rapidly decreased from the originalwhiteness of 35C19 to the values of 33C19 and 31C19,respectively, in 95 days. However, the whiteness of thenon-vacuum-packed rice decreased more rapidly thanthat of the vacuum-packed rice. It is mainly due to thefact that the non-vacuum-packed rice was exposed tooxygen, which accelerated the whiteness change. Incontrast, the whiteness of the vacuum-packed ricechanged moderately. An equation for the whiteness ofthe vacuum-packed rice versus storage time wasexpressed asWvC00C1024t 36C113 1where: Wvis the whiteness of the vacuum-packed rice; tis storage time in days; The coefcient of determinationis 0C1923. Anotherequation forthe whiteness of the non-vacuum-packed versus storage time was presented asWnC00C1047t 35C198 2where, Wnis the whiteness of the non-vacuum-packedrice. The coefcient of determination is 0C1968.3.4. Moisture contentThe moisture content of the vacuum-packed samplesdecreased slowly during the experimental period, but themoisture content of the non-vacuum-packed rice de-creased rapidly. The moisture content of the vacuum-packed rice decreased form 16C11to15C13%, while themoisture content of the non-vacuum-packed rice quicklydecreased from 16C11to14C18%. The changes of themoisture content of the samples are shown in Fig. 11.An equation forthe change of moisture content ofvacuum-packed rice versus storage time wasMvC00C10078t 16C109 3where Mvis the moisture content of the vacuum-packedrice in % (w.b.). The coefcient of determination is0C1988. The equation expressing the change of moisturecontent of the non-vacuum-packed rice versus storagetime wasMnC00C10145t 16C103 4where Mnis the moisture content of the non-vacuum-packed rice in % (w.b.). The coefcient of determinationis 0C1974.3.5. Peroxide valueUnfavourable smells were sensed in the non-vacuum-packed sample, and moulds were found on the surfaceof rice kernels in 45 days. The peroxide values versusstorage time are shown in Fig. 12. The peroxide value ofthe vacuum-packed rice increased slightly,1C189meqkgC01, over the entire experimental period.However, the peroxide value of the non-vacuum-packedrice increased to 10C122meqkgC01rapidly until the 80thday in storage and then dropped moderately to6C167meqkgC01. The shelf-life of the vacuum