Effects of Oven Drying Temperature and Drying Time on Rough Rice Moisture Content Determination

Transcription

1 Effets of Oven Drying Temperature and Drying Time on Rough Rie Moisture ontent Determination V. K. Jindal, T. J. Siebenmorgen MEMBER ASAE ASSO. MEMBER ASAE ABSTRAT HE effets of oven drying temperature and drying T time on whole-kernel, long-grain rough rie moisture ontent determination were investigated for different moisture ontent levels ranging from approximately 9 to 22% (w.b.). The results showed that a simplified oven method an be used for rapid moisture measurement with auray omparable to that of a standard Assoiation of Offiial Analytial hemists (AOA) method. An equation was developed that relates the apparent moisture ontent determined using a given drying time and temperature to the moisture ontent determined by the standard AOA method. INTRODUTION Aurate measurement of rough rie moisture ontent is important during harvesting, drying, storage and proessing operations. It is often neessary to speify and use a standard moisture ontent for seed ertifiation and storage, as well as for marketing and milling ontrats. Grain moisture ontent (% wet basis) is defined as the ratio of the weight of water that an be removed without hanging the grain hemial struture to the initial weight of the grain. The basi referene methods for moisture ontent determination suh as the Karl Fisher tehnique (Hart and Neustadt, 1957) and the method outlined by the International Organization for Standardization (ISO) (1978) have been used to standardize simplified oven methods that are then regarded as pratial working methods. Referene methods are time onsuming and tedious but were formulated to obtain aurate moisture values for alibration purposes. It is assumed in the use of referene methods that omplete drying of material is ahieved without any loss or deomposition of organi material. Pratial methods developed on the basis of alibration against referene methods are used to reliably determine grain moisture ontent in a reasonable time and are orreted for any possible deomposition ourring during a test. There are several pratial air-oven proedures that have been standardized to determine moisture ontent of grains (Hart et ai., 1959; United States Department of Artile was submitted for publiation in November, 1986; reviewed and approved for publiation by the Food and Proess Engineering Institute in April, Published with approval of the Diretor. Agriultural Experiment Station, University of Arkansas. The authors are: V. K. JINDA, Assoiate Professor, Division of Agriultural and Food Engineering, Asian Institute of Tehnology, Bangkok. Thailand; and T. J. SIEBENMORGEN, Assistant Professor, Agriultural Engineering Dept., University of Arkansas, Fayetteville. Agriulture (USDA), 1971; Assoiation of Offiial Analytial hemists (AOA), 198; Amerian Soiety of Agriultural Engineers (ASAE), 1982). These methods are based on drying whole or ground grain in an oven over a fixed period of time. The drying temperature and time are usually speified for a partiular type of grain on the basis of moisture ontent omparison with a referene method. ASAE Standard S352.1 (ASAE, 1982), whih was adopted in 1972 based on the reommendations of Hart et al. (1959), emphasizes the use of whole-grain samples primarily due to simpliity and avoiding possible moisture loss during grinding. Various proedures for measuring moisture ontent of grains are listed in Table 1 for relative omparison. Moisture ontent determinations made with different oven methods and different grains may not be the same due to the empirial nature of the methods. Oven exposure time depends upon the type of grain and the method used (Hart et ai., 1959; Warner and Browne, 1963; Young et ai., 1982; Bowden, 1984). Hart et al. (1959) showed that drying flaxseed in a moisture ontent range of 7.6 to 8.2/ wet basis (w.b.), wheat at 12. to 12.3% and orn at 1.5 to 11.4% to a onstant weight at TABE 1. PROEDURES FOR MEASURING MOISTURE ONTENT OF GRAJNS. Method Referene methods InternationalOrg<lnization for Standardization (1978) Karl Fisher (Hart and Neustadt, 1957) Standard methods International Organization for Standardization (1979) Assoiation of Offiial Analytial hemists (198) Unitd States Deparment of Agriulture (1971) Amerian Soiety of Agriultural Engineers (1982) Details Reommendation ISO R 711, vauum oven (1-2 mm Hg), 5, 3-4 g ground sample in presene of phosphofuspentoxide ( onstant weight. Extration with dry methanol and water determined by titration. Reommendation ISO R712, air oven, , 2 h, 5 g ground sample. (a) Vauum oven (;;;:; 25 mm Hg), 98 1 o e,5 h. 2 g ground sample through a 2 mesh sreen. (b) Air ovel1. 13 ±3, 1 h, 2 g ground sampie. (a) Air oven one-stage (for samples ontaining 16% or less moisture ontent. 13% for rough rie) e, 1 h. 2-3 g ground sample through a 2 mesh sren. *Drying time and temperature are not speitid for rough rie. (b) Air oven two-stag. unground sample redued to] 6'."%, (lys, for rough rie) or less moisture ontenr in first stage. Moist ure ontent determined as in first-stage rrodure. Standard: ASAE SJ52.1, air oven, temperatur and time speified for various grains for unb'tound samples weighing a minimum of 15 g.'" Vol. 3(4)uly-August Amerian Soiety of Agriultural Engineers /87/ $2, 1185

2 respetive oven temperatures in ranges of 1 to l3 D, 1 to 1lDe, and 94 to 15 D resulted in small but signifiantly different moisture ontents. Suh differenes ould further inrease over wider ranges of grain moisture ontents. This is supported by Bowden (1984), who ompared three routine oven methods for moisture ontent determination of wheat and barley. He onluded that the variation of moisture ontent within the repliates inreased with moisture ontent level. Other differenes in methods were reported by Matthews (1962), who observed disrepanies of up to.3/ w.b. when using a l3 D -16 h method for whole grain and up to.5<t/o w.b. for a l3 D -1 h ground sample method. Random errors in grain moisture ontent determinations repliated two or three times may range from.2 to.5% w.b. depending upon the sample loation within an oven and/or the use of different ovens (Warner and Browne, 1963). Drying whole grain in a fored-onvetion air-oven aording to ASAE Standard S352.1 (ASAE, 1982) is the most widely used method of moisture ontent determination and yields highly reproduible results under seleted onditions of time and temperature. The disadvantage of this method is a long drying time requirement. Therefore a rapid moisture ontent determination method using high-temperature, shorttime guidelines would be valuable in time savings if proven aurate. Though air-oven proedures have been standardized for moisture determination of several ommon whole grains, there exists no suh standard for rough rie. Noomhorm and Verma (1982) have ompared rough rie moisture ontent determinations using the l3 D -16 h whole-grain method based on the work of Matthews (1962). They used the AOA (198) method as a standard, inorporating two-stage drying over the moisture ontent range of approximately 1-19% w.b. They onluded that the whole-grain oven method gave signifiantly higher moisture ontents ompared to the AOA method. Thus, there is a need to develop a standard oven proedure for whole-grain rough rie moisture ontent determination that would be aurate, rapid and easy to use. OBJETIVES The objetives of this study were: 1. to determine the effets of oven drying temperature and time on the moisture ontent determination of unground (whole-grain), long-grain rough rie in the 9 to 22% w.b. moisture ontent range 2. to develop a standard reommendation of drying temperature and time for general use in determining rough rie moisture ontent, patterned after the proedure outlined in ASAE standard S352.1 (ASAE, 1982). MATERIAS AND METHODS Overall Proedure This study began as a laboratory exerise to explore the overall effets of oven drying temperatures and times in determining the moisture ontent of unground, longgrain rough rie. As suh, a preliminary study was onduted in whih the moisture ontent of samples varying in moisture ontent from approximately 1 to 19% w.b. was determined using an air onvetion oven 1186 held at l3 D in one set of tests and at 2 D in a subsequent test. Drying times for the l3 D setting were 1,6 and 2 h; for the 2 D setting. only a 1 h time was used. The results of this determination revealed a trend that indiated a possible relationship between the moisture ontents attained with the various drying temperature/time ombinations. This, oupled with the fat that a standard whole-grain air-oven proedure did not exist for rough rie, prompted a omprehensive study of this subjet. The omprehensive study was onduted in the following phases: 1. Eight lots of rie taken from the same, single soure were dried to moisture ontents ranging from 9 to 22% w.b. 2. The variability in moisture ontent determination attributed to sample loation in the oven used in this study was determined. 3. The moisture ontent of the eight lots of rie was determined by various standard moisture ontent determination proedures to establish the atual moisture ontent of eah lot. 4. The moisture ontent of samples taken from eah of the eight moisture ontent lots was determined by oven drying samples at seleted temperatures and times. 5. A relationship between the apparent moisture ontent determined at eah drying temperature/time ombination and the moisture ontent determined by a standard proedure was established. Experimental Proedure ong-grain rough rie (Tebonnet variety) was ombine harvested at the Rie Researh and Extension enter, Stuttgart, AR. at an approximate moisture ontent of 25% w.b. Immediately after ombining, the rie was leaned in an A. T. Farrel* Model 2B leaner to remove immature kernels and foreign material. The lean rie was plaed in plasti bags and stored at 1D for about 2 months prior to testing. Rie was onditioned to eight moisture ontent levels ranging from 9.2 to 22.3% w.b. Eah lot was dried to the appropriate moisture ontent level by plaing rie on trays onstruted of light wooden frames with metal sreen bottoms and exposing the rie to room onditions averaging 26 D and 6% RH. It was neessary to dry two bathes of rie to lower moisture ontents in an air oven set at 4 D e, Samples were then sealed in polyethelene bags and stored at 1D for several days until testing. The drying oven was a Blue M Model OV-49A-2 having two heaters eah with a rating of 16.4 amps at 12 volts and employing fored-air irulation and temperature ontrol within ± 1D. Only two shelves loated near the oven enter were used to minimize errors due to temperature variations within the oven. The temperature of air in the viinity of the sample ontainers was monitored using a preision merury bulb thermometer. The sample ontainers had a diameter of 5 mm, a depth of 4 mm and were onstruted of light gage sheet metal. Prior to a given moisture ontent determination, the oven was preheated to a desired temperature using *Mention of a ommerial name does not imply endorsement by the University of Arkansas. TRANSATIONS of the ASAE

3 TABE 2. APPARENT MOISTURE ONTENT (%, w.b.) OF ROUGH RIE SAMPES FOR DIFFERENT DRYING TEMPERATURES AND TIMES. Oven drying temperature and time 13 2 Moisture level 1 h 6h 2 h 1h Slope* Interept* R MSEt *Values were determined by linear regression of moisture ontents in eah method to those attained at 13 and 2 h. t Mean square error. fored-air irulation with the oven side vents open. Test portions of whole rough rie weighing 25 g were obtained from large lots of rie using a Boerner divider. All moisture ontent determinations were dupliated. Samples were randomly plaed in the oven and were periodially removed. immediately weighed and returned to the oven within a total time of about 3 to 5 min. All mass measurements were made to the nearest.1 g on a top-loading open pan balane. The loations of sample ontainers on the oven shelves as well as the loations of the oven shelves were routinely hanged during the ourse of the experiment to redue the unwanted effet of sample loation in determining moisture ontent. Determination of Variability Due To Sample oation The variation in moisture ontent as affeted by sample loation within the oven was determined by seleting 18 samples from the lowest moisture ontent lot and randomly plaing them in the oven, nine on eah shelf. Using the proedure for weighing as outlined above, the apparent moisture ontent of the samples was determined at 4 and 2 h using an oven temperature of 13..Apparent' moisture ontents were omputed based on the sample weights at seleted drying times for the orresponding oven temperature. Standard Moisture ontent Determination Proedure The methods used to determine the atual moisture ontent of the eight moisture ontent lots of rie were the vauum oven and air oven standard methods reommended by AOA (198) and outlined in Table 1. A two-stage proedure was used whenever sample moisture ontents exeeded 13% w.b. (USDA, 1971). Variations of these methods as to oven temperature, oven drying time and whole samples versus ground samples were also used and are listed in Table 4. Drying Time and Temperature Test Proedure Dupliate samples from eah of the eight lots were dried in the air oven using the sampling and weighing proedure desribed above. The samples were plaed in the oven and subsequently weighed at 1, 2, 4, 8, 2 and 72 h from the start of drying. The oven temperatures used were 11, 13, 15 and 17. Apparent moisture ontent for eah drying temperature/time ombination was alulated based on the mass removed by drying as determined by the sample masses at eah weighing. RESUTS AND DISUSSION Exploratory Analysis The data from the exploratory tests of the effet of drying temperature and time on moisture ontent determination are shown in Table 2. It was observed that a moisture ontent value determined by a given drying temperature and time at a given moisture ontent level was ditterent from the moisture ontent value determined by another drying temperature and time by a onsistent amount over the range of moisture ontent levels. This observane led to an analysis in whih eah set of moisture ontent values determined at a given drying temperature and time was regressed against the TABE 3. APPARENT MOISTURE ONTENT (% w.b.) OF ROUGH RIE SAMPES FOR DIFFERENT OATIONS AND DRYING PERIODS AT 13. Drying period, Upper shelf ower shelf h eft enter Right eft enter Right olumn mean (standard deviation) (.61) (.46) (.138) (.23) (.23) (.122) Shelf mean (standard deviation) (.1) (.7) olumn mean (standard deviation) (.46) (.) (.83) (.) (.) (.92) Shelf mean (standard deviation) (.6) (.5) Vol. JO(4)uly-August

4 TABE 4. APPARENT MOISTURE ONTENTS (%, w.b.) OF ROUGH RIE AT VARIOUS MOISTURE ONTENT EVES DETERMINED BY DIFFERENT MEASUREMENT METHODS. Measurement method Moisture level 13 -lh ground 13-2h ground Air oven 13-2h whole 7-2h ground h whole Vauun1ven - 1 _5h ground 1-2h whole Slope * Interept* R2 MSEt ~ *Values were determined by linear regression of moisture ontents in eah method to those attained at 13 and 1 h in an air oven. tmean square error. set of moisture ontents determined at l3 and 2 h. The results of this analysis are shown at the bottom of Table 2. The high values of the oeffiient of determination and low values of the mean square error for eah regression indiated a strong orrelation between the values determined by eah method and that at 13 and 2 h. An F-test (Neter and Wasserman, ]974) was used to show that the slope values for the regression lines were equal (alpha=.5). This strong orrelation indiated that a rapid moisture ontent determination based on a very high drying temperature and short time (e.g., 2 and 1 h) might be used to estimate the moisture ontent attained at l3 and 2 h. However, sine moisture ontent depended upon oven drying temperature and time, it was neessary to identify a standard oven proedure for estimating the atual moisture ontent of rough rie. Aordingly, a hypothesis was postulated and investigated that a relationship between standard and apparent moisture ontents existed. Sample oation Effets Table 3 gives the apparent moisture ontent determinations of whole-grain rough rie samples made at different loations on the two shelves after drying for 4 and 2 h in an oven set at 13. The standard deviation of moisture ontent on both the upper and lower shelves for eah drying time was less than.1 % w.b. However, individual moisture ontents showed a deviation from the assoiated shelf/drying period mean of up to.24% w.b. It was observed that an inrease in the drying time from 4 to 2 h resulted in lower standard deviations in mean moisture ontents. Moisture ontent Determination by Standard Methods Table 4 shows the rough rie moisture ontents determined by different measurement methods at various moisture ontent levels. In this part of the study, the AOA air oven method (l3, ] h, ground sample) was seleted as standard and ompared with other moisture ontent measurement methods. This standard method gave slightly higher moisture ontents than the 1188 vauum oven method (loo, 5 h). Drying of wholegrain rough rie at 13 for 2 h over-estimated the moisture ontents in omparison to those attained with the standard method over the moisture ontent range of 9 to 22% w.b. A omparison of the results of eah method was made using a regression analysis in whih eah set of moisture ontent values obtained with a given method was regressed against the moisture ontents obtained with the aepted standard method. The results of this analysis are shown in Table 4. As in the exploratory analysis, the moisture ontents determined by a standard method ould be predited aurately (see Table 4 for oeffiients of determination and mean square error values for eah ase) based on the moisture ontents attained with the other methods. These results further veritied the hypothesis that apparent moisture ontents determined by different oven methods over a wide range of moisture levels are linearly related to standard moisture ontents. Development of Drying Temperature and Time Relationship Figs. 1 to 4 show the relationship between the standard (AOA method; air oven, 13, 1 h, ground sample) and apparent moisture ontents based on the drying of whole rough rie samples for seleted times at 11, 13, 15 and 17, over a moisture ontent range of about 9 to 22% w.b. These relationships were represented by the following equation: M stan ==a()+a1 M app [1] M,ran standard moisture ontent, % w.b. M app apparent moisture ontent, % w.b. au, at regression oeffiients. The parameters obtained from linear regression of eah temperature/time ombination are given in Table 5. The slopes of the relationships in Figs. 1 to 4 appeared to be independent of the oven drying temperatures and times. The interepts, however, were linearly related to TRANSATIONS of the ASAE

5 "j b. One Hour o Two Hours Ii,. o Four Hours EIght Hours ~ henty Hours Seventy-tlo Hours J IB / " b. Onli! Hour i o Tlo Hours,. o Four Hours Eight Hours t) Twenty Hours 18 J <J) 15 a ::>: u u If") II, ')" I <J) 15 a ::>: u u If") II S Apparent MOIsture ontent (Yo 2D 2. w. b.) S Apparent MOIsture ontent (Yo w. b. ) 24 Fig. I-Effets of drying time at node on apparent moisture ontent. Fig. 3-Effets of drying time at ISO on apparent moisture ontent. Ii,. /I.e. One Hour o T1 Hours o Four Hours... EIght Hours t; 21 henty Hours J IB <J) 15 a ::>: u u If") 11 4///,):: // / ~ /I 4:1. One Hour o Two Hours Ii,. o Four Hours... T.enty Hours ~ J 11 IB <J) 15 a ::>: u u If") 11 S Apparent MOIsture ontent (Yo w. b. ) Fig. 2-Effets of drying time at BoDe on apparent moisture ontent. the logarithm of drying times as shown in Fig. 5. The following equation form was used to desribe this relationship: a o = b o + b 1 (In t) where: a o interept in equation [1] b o ' b l regression oeffiients t drying time. h. Table 6 gives the parameters of equation [2] for eah temperature. The slopes were similar. However, the interepts of the relationships represented by equation [2] were related to the oven drying temperature in the [2] 's Apparent MOisture ontent (Yo w. b.) Fig. 4-Effets of drying time at l7 on apparent moisture ontent. following manner and as illustrated in Fig. 6:... [3] where: o,, = regression oeffiients T = drying temperature, d. Using linear regression, the values of o and, were found to be 1.33 and -.625, respetively. Equations [1] to [3] were ombined using mean slopes of relationships shown in Figs. 1 to 5 to give: M stan = T n t M app.... [4] TABE 5. REGRESSION OEFFIIENTS OF EQUATION [1]. Time l h Temperature. D ao a1 ao a1 ao a1 ao a1 1 * * * * * * * * * * Average slope *Data was not olleted at the extreme temperature/time ombinations. Vol. 3(4)uly August

6 o.9 " U.": -I o., o T W ~ 11 [ o 13"[ o 15 O[ 17 "[ l Fig. S-Relationship between equation [1] interept (a o ) and time. Equation [4] was developed on the basis of the preeding least squares analysis, whih yields a funtional relationship among the experimental variables. Based on these exploratory alulations and observations, a general relationship was subsequently developed through regression of the data shown in Figs. 1 to 4 based on the form of equation [4] as follows: M stan = T - 1.2Sln t M app '...[5] The oeffiient of determination and standard error of estimate for equation [5] were.992 and.39, respetively. Relative Effets of Time and Temperature Though equation [5] was adequate for general use, the interations and relative ontributions of experimental variables on estimated moisture ontents were further investigated by onsidering the following model: 1 " U N 1 o o W "1., ~I Temperature (D Fig. 6-Relationship between equation [2] interept (bol and temperature. and standard error of estimates for the model variables were: b o s(b o ).7877 b l.919 s(b l ).521 b 2.14 s(b 2 ).12 b J s(b J ).54 b s(b 4 ).1779 bs.128 s(bs).63 bb.683e-3 S(bb).3457E-3 I ----J 17 The experimental variables and their interations listed in equation [6] aounted for about 99.2% of the total variane and an be used to estimate the standard moisture ontent aurately. Among the single fators, In t had the least effet in improving the model. The interations, M ; In t and M ' T, did not ontribute api app greatly despite their being statistially signifiant. Therefore a simpler form of Equation [6] ould be adopted without any pereptible loss of auray using only the most signifiant variable terms with the following regression oeffiients:... [6] where: b", b l, b 2, b j, b 4, bs' and br, are regression oeffiients. The pertinent results of a step-wise multiple regression analysis using equation [6] and the data of Fig. 1 through 4 are shown in Table 7 with the model variables listed in the order of their relative ontributions. It was found that all of the model variables of equation [6] suffiiently improved the model to warrant inlusion in the model at a level of signifiane of 5%. The regression oeffiients TABE 6. REGRESSION OEFFIIENTS OF EQUATION [2]. Temperature,o bo bi Average slope where: b o s(b o ).3631 b l s(b l ).75 b 2.22 s(b 2 ).12 b j s(b J ).25 b s(b 4 ) Equation [7] provides a simple means of adjusting apparent moisture ontent determinations for various oven drying temperatures and times to the moisture TABE 7. RESUTS OF THE STEP-WISE MUTIPE REGRESSION ANAYSIS. Variables in model Mean square error M* M, T ln t M, TIn t, T M, T ln t, T, In t M, TIn t, T, In t, M ln t M, T ln t, T, In t, M ln t. M T *'M' is the abbreviation of 'M app '. 119 TRANSATIONS of the ASAE

7 TABE 8. ESTIMATED OVEN DRYING TIMES (h) FOR ROUGH RIE SAMPES OF DIFFERENT MOISTURE EVES AT SEETED OVEN TEMPERATURES. Oven drying temperature, Moisture level %w.b Average time (Standard deviation) (2.32) (.94) (.35) (.12) TABE 9. OMPARISON OF EXPERI MENTA (NOOMHORM AND VERMA, 1982) AND PREDITED (PRESENT STUDY) MOISTURE ONTENTS OF ROUGH RIE SAMPES. Moisture ontent, % w.b. Experimental Predited 13, 16 h AOA Equation [7] ontents determined by the standard AOA method. ~quation [.1] an be used to show that the oven drying time required at a given temperature to math the apparent and standard moisture ontents would be influened by the sample moisture level. Table 8 shows the oven drying times predited by equation [7] assuming apparent and standard moisture ontents to be the same for sample moisture levels ranging from 9 to 23% w.b. It is obvious that low moisture rough rie samples would requi:e shorter drying times at any set oven temperature and vie versa. These findings indiated that, in order to attain the most aurate possible results, a ommon dry~ng time annot be speified over a wide range of moisture levels. This supports the view that a two-stage drying proedure is required to determine the moisture ontent of high moisture ontent grains (USDA, 1971). Reommended Proedure The dependene of average drying time (Table 8) on oven temperature in the range of moisture ontent levels used ~n this experiment was expressed by the following equation: t =e( TJ; R 2 =.998 [8J Equation [8] gives estimates of drying time at different oven drying temperatures for apparent moisture ontent determination of whole rough rie samples relative to the standard AOA method. This equation an thus be used to ~stimate the approximate drying time required for a desired oven temperature when the moisture ontent is unknown. ~in~ equation [8] was developed using average drymg times over a range of moisture ontent levels, the apparent moisture ontent determined after drying for the time period estimated by equation [8] should be used as an input to equation [7] for a more aurate determination of moisture ontent. This proedure aounts for the signifiant differenes that ould result due to varying sample moisture ontent levels. In summary, equation [8], or the values of Table 8, an be used as a first step in estimating an approximate drying time for a desired oven temperature. The apparent moisture ontent from the drying test is then used as an input to equation [7] to determine the moisture ontent that would have been attained with the standard AOA method. The results in Table 8 show that drying rie for about 11.5 h at a onventional oven drying temperature of 13 a an be adopted as a general standard oven proedure for rough rie moisture ontent determination, although the subsequent use of equation [7] to aount for varying initial sample moisture ontents is reommended. Alternately. a rapid moisture ontent determination proedure based on the use of equation [7] and higher oven temperatures also proved to be reliable. The results of this study support the hypothesis that apparent moisture ontents determined at different drying temperatures and times with an oven proedure over a wide range of moisture levels are related to the atual moisture ontents of rough rie samples. Validation ~he proposed approah was validated using the moisture ontent determination data of rough rie reported by Noomhorm and Verma (1982). They found that 13 a -16 h drying of rough rie resulted in signifiantly higher moisture ontents ompared to the sta?dard AOA method. Using equation [7], the moisture ontents of rough rie samples were omputed by entering the experimental moisture ontent values determined at 13 a and 16 h by Noomhorm and Verma as apparent moisture ontents. Table 9 shows that the experimental AOA (Noomhorm and Verma, 1982) and omputed (present study) moisture ontents were lose generally within.5% w.b. exept for a few ases. A lose examination of the experimental data of Noomhorm and Verma revealed that moisture ontent differenes between the two methods varied up to 1.72% w. b., perhaps due to experimental disrepanies. This was ontrary to the observations made in the present study, whih showed a more onsistent pattern in moisture differene values when omparing various methods of moisture measurement (Table 4). SUMMARY AND ONUSIONS A study of the effets of oven drying temperature and time on whole-grain rough rie moisture ontent determination showed that the moisture ontent determined by a standard AOA method ould be aurately estimated from the apparent moisture ontent determined by oven drying at various oven temperatures Vol. JO(4);July-August,

8 for various times at moisture ontents ranging from approximately 9 to 22% w.b. More speifially, the following onlusions were drawn: 1. Oven proedures involving various oven drying temperatures and times resulted in onsistent moisture ontent differenes relative to a standard AOA method in the moisture ontent range of approximately 9 to 22% w.b. 2. A relationship between standard (atual) and apparent moisture ontents was developed to quantify the effets of oven drying temperatures and times. This relationship an be used as the basis for rapid moisture ontent determination using high-temperature. shorttime (e.g., 2 a, 1 h) drying of rough rie in an oven. 3. Oven drying times for moisture ontent determination of whole-grain rough rie depended upon the sample moisture level. ow moisture samples required shorter drying times than high moisture samples required. A l1.s-h drying time at l3 a appears to be satisfatory for general use in the moisture ontent range of approximately 9 to 22/ w.b. However, subsequent use of an expression relating apparent to standard moisture ontent is reommended to aount for varying sample moisture ontents. Referenes I. Amerian Soiety of Agriultural Engineers Standard: ASAE S Moisture measurement-grains and seeds. 2. Assoiation of Otliial Analytial hemists Offiial methods of analysis. 13th Edition, AOA, Washington, D.. 3. Bowden, P. J omparison of three routine oven methods for grain moisture ontent determination. Journal of Stored Produts Researh 2(2): Hart, J. R... Feinstein and. Golumbi Oven methods for preise measurement of moisture ontent of seeds. Marketing Researh Report No. 34 (USDA-AMS), US Government Printing Otlie, Washington, D.. 5. Hart, J. R. and M. H. Neustadt Appliation of the Karl Fisher method of grain moisture determination. ereal hemistry 34: International Organization for Standardization Reommendation IS (E). ereals and ereal produts-determination of moisture ontent (Basi referene method). 7. International Organization for Standardization Reommendation IS (E). ereals and ereal produts-determination of moisture ontent (Routine referene method). 8. Matthews, J The auray of measurement of known hanges in moisture ontent of ereals by typial oven methods. Journal of Agriultural Engineering Researh 7(3): Neter, J. and W. Wasserman Applied linear statistial models. Rihard D. Irwin, In., Homewood, I. 1. Noomhorm, A. and. R. Verma A omparison of mirowave, air oven and moisture meters with the standard method for rough rie moisture determination. TRANSATIONS of the ASAE 25(5): II. United States Department of Agriulture Oven methods for determining moisture ontent of grain and related agriultural ommodities, hapter 12, Equipment Manual, GR Instrution onsumer and Marketing Servie, Grains Division, Hyattsville, MD. 12. Warner, M.G.R. and D.A. Browne Investigations into oven methods of moisture ontent measurement of grain. Journal of Agriultural Engineering Researh 8(4): Young, J. H., T. B., Whitaker, P. D. Blankenship, G. H. Brusewitz, J. M. Troeger, J.. Steele and N. K. Person, Jr Effet of oven drying time on peanut moisture determination. TRANSATIONS of the ASAE 25(2): TRANSATIONS of the ASAE