Determination of Sugars and Organic Acid Concentration in Apple Juices Using Infrared Spectroscopy

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1 Jurnal f Scientific & Industrial Research Vl. 8, January 1999, pp 194 Determinatin f Sugars and Organic Acid Cncentratin in Apple Juices Using Infrared Spectrscpy Jagdish Tewari, Mna Jshi, Alka Gupta, Ranjana Mehrtra* and Subhas Chandra Natinal Physical Labratry, Dr K S Krishnan Rad, New Delhi I IO 1 Received: July 1998; accepted: 17 September 1998 Ptential f Furier Transfrm IR spectrscpy as an analytical methd fr determinatin f sugars and rganic acid cncentratin in apple juice is investigated. Calibratin is perfrmed n synthetic samples in midir regin using Attenuated Ttal Reflectance (A TR) mde. Partial Least Square () and Principle Cmpnent Regressin () methds are used t btain these calibratins fr mixtures f sucrse, glucse, fructse, and citric acid in cncentratin ranges, typically encuntered in real apple juices. A cmparisn is given between the actual values and the predicted values. The calibratins are used t determine the cncentratin f these cmpnents in real samples. The present study assesses the feasibility f the technique fr nline applicatin in fruit prcessing industries. Intrductin The mst imprtant criterin fr the final prduct quality f fruits and their byprducts in fruit prcessing industry is their sugar cntent. The labratry methds fr the quantitative determinatin f sugars and rganic acids in fruits have been develped and refined ver the years. The traditinal gravimetric and wet chemical methds are destructive, expensive, and timecnsuming. These methds have prven t be inefficient fr a prcess cntrl in any industry.. The use f sphisticated techniques like High Perfrmance Liquid Chrmatgraphy (HPLC), Magnetic Resnance Imaging (MRI) and high reslutin Nuclear Magnetic Resnance (NMR) fr mnitring sugars and rganic acids fr quality cntrl has been reprted in literature 1 4. These techniques, hwever, require trained persnnel and are unecnmical t perfrm. Near IR spectrscpy has been well established as a rapid and nndestructive analytical technique in many agr fd industries. 6. Althugh NIR technique is fast and suitable fr prcess cntrl applicatins, a majr disadvantage lies in the intrinsically brad, verlapping bands encuntered in NIR spectra f sugar slutin, which limits the accuracy. IR spectrscpy in mid IR regin has shwn great advantages in predicting sugar cntents in bth agriculture and fd prducts 7 1. The paper illustrates the ptential f Furier Transfrm IR Spectrscpy, in mid infrared regin, fr determinatin f cncentratins f sugars and rganic acids in apple juices and als assesses the feasibility f technique fr nline applicatins in industries. Bth, Principle Cmpnent Regressin () and Partial Least Square () methds have been used t btain calibratin fr sucrse, * Authr fr crrespndence glucse, fructse, and citric acid, based n synthetic samples. The calibratin has been applied t predict the cncentratins f different sugars and citric acid in real samples. Materials and Methds All the FTIR measurements were carried ut n a Bi Rad 17C (Century series) spectrphtmeter equipped with a deuterated triglycine sulphate (DTGS) detectr, perating at 4cm 1 reslutin and.3 cm/s mirrr velcity. Tw hundred and fifty six interfergrams were taken and Furier Transfrmed. The instrument was purged with nitrgen gas (grade 1) prir t acquisitin f spectra in rder t minimize spectral cntributin due t atmspheric carbn dixide and water vaprs. ATR was adpted as the sampling methd fr which a hrizntal ATR cntact sampler equipped with a Zinc Selenide (ZnSe) crystal was used. The sampler affrds six reflectins t the sample due t 4 angle between beam and the crystal surface. Single beam spectra were btained fr all the samples and were rtied against a backgrund spectrum f water t present the spectra in absrbence units. After each sample the A TR cell was thrughly washed with water. Fr calibratin, twentyfur standard mixtures f sucrse, glucse, fructse, and citric acid were prepared. Precautin was taken s that the synthetic mixtures represented the real juices and entire cncentratin range was cvered (Table 1 and ). The samples used fr calibratin were als used as test samples in rder t check the validity f the analysis. A cmparisn is presented between the results btained using and methds, emplyed fr quantitative analysis.

2 J SCI IND RES VOL 8 JANURY 1999 Five different cmmercially available apple juices were prcured fr analysis. These samples were used undiluted with n further preparatin. Results and Discussin Figure 1 shws the FTIR spectra f sucrse, glucse, fructse, and citric acid, the prime cmpnents f apple juice. The bands fr different sugars, as well as fr citric acid are well defined, narrw and distinct. These vibratinal mde bands fr sucrse, glucse, fructse and citric aci d were identified using pure slutins f each individual cmpnent. After careful examinatin, the regin between 9 cm 1 t 1 cm 1 was chsen fr calibratin.figure depicts the family f spectra f synthetic mixtures used fr calibratins. Partial least square methd and principal cmpnent regressin methd were emplyed t develp a multivariate mdel. Multivariate calibratins are useful in spectral analysis because the simultaneus inclusin f Table I multiple spectral intensity can greatly imprve the precisin and predictive ability. Twentyfur standard samples were used fr calibratins. In rder t mdel the system withut verfitting the cncentratin data, a crss validatin methd, leaving ut ne sample at a time was used. Given the set f 4 calibratin spectra, the per and calibratins n 3 spectra were perfrmed, and using this calibratin, the cncentratins f the cmpunds in the sample left ut during calibratin were predicted. The values f the rt mean square deviatin (RMSD), which is an indicatin f the average errr in the analysis, fr each cmpnent is: RMSD = N [l/n r i=1 (Ai r Bi)]O., and the square f the crrelatin cefficient (R ), which is an indicatin f the quality f fit, is: cncentratins f different cmpnents f synthetic mixture with respect t actual values using methd Glucse, er cent Sucrse, er cent SI N. Fructse, Citric acid, er cent >:

$1 C VV I\Kl er at.: I\YYLC J UILC;:) Table cncentratins f different cmpnents f synthetic mixture with respect t actual values using methd '1 A Glucse, Sucrse, SI N. l :t l Fructse, Citric acid, 1.. 1. 1. 1.........3.$

3 1 C VV I\Kl er at.: I\YYLC J UILC;:) Table cncentratins f different cmpnents f synthetic mixture with respect t actual values using methd '1 A Glucse, Sucrse, SI N. l :t l Fructse, Citric acid, N R = I, i=1 N (A i C)/I, i=1 (Bi C), where A i is the actual cncentratin f the analyte in the sample i, Bi represents the estimated cncentratin f the analyte in the sample i, C is the mean f the actual cncentratins in the predictin set and N is the ttal number f the samples used in the predictin set. In Table 3, RMSD and R values have been summarized. The values f RMS D and R are bserved t be sme what simi lar fr per and methd in all instances. The values btained fr R is satisfactry fr all the cases. N significant advantages were fund with the applicatin f tw different methds used fr calibratin. The predicted cncentratins, using PeR and f synthetic samples with reference t the actual values are given in Table I and Table, respectively. The predicted values agree clsely with the actual values. Figure 3 (ad) shws the plts f actual cncentratins f sucrse, glucse, fructse, and citric acid in synthetic mixture vs the cncentratins determined using the methd. The linearity f the plts btained nce again highlights the validity f technique used. In rder t test the feasibility f quantitative analysis five real samples f apple juices (AP I t AP) were taken and analyzed. A typical ATR spectrum in the range 9 I I cm t 1 cm f real apple juice is shwn in Figure 4. The spectrum very well matches with thse f synthetic mixtures used fr calibratin. The cncentratins f different cmpnents as determined by and methds are shwn in Table 4. The values indicate the quality f fruit taken as far as cncentratin f varius sugars and citric acid is cncerned.

J SCI IND RES VOL 8 JANURY 1 999.8. 8.7 III c. ' III <t ).7.6.6.....!.4 13 1 1 1 1 1 1 1,... 1 /.

acid; FFructse; GGlucse; and SSucrse) y.9.8 III c. ' 1/1 <t. 7.6.

4 J SCI IND RES VOL 8 JANURY III c. ' III <t ) ! ,... 1 / Wavenum b e r ( cm I ) Figure I FfIR spectra f different cmpnents f apple juice (CCitric acid; FFructse; GGlucse; and SSucrse) y.9.8 III c. ' 1/1 <t Waven u m b er ( e mi ) Figure Family f FfIR spectra f synthetic mixture with different cncentratins f cmpnents

$1. 1.4 1.6 L 1.8...4 : g lucse A c t ua l : sucrse 3.. '«I\) U)... t. Q.. 1. " I\) " I\). :E O c.. ' ':;.. 'u goa... 1. 1... 3..3 A c tual : f r u c t se.$ 3.4.4. : ci t ri c a c id Figure 3 Plts f actual cncentratin f cmpnent vs the predicted cncentratins using methd 1.

3.4.4. : ci t ri c a c id Figure 3 Plts f actual cncentratin f cmpnent vs the predicted cncentratins using methd 1.

5 3 TEWARI et al.: APPLE JUICES 4. U). u :;, " Q)...U " a u 3. L8 :,; , a L L : g lucse A c t ua l : sucrse 3.. '«I\) U)... t. Q.. 1. " I\) " I\). :E O c.. ' ':;.. 'u goa A c tual : f r u c t se : ci t ri c a c id Figure 3 Plts f actual cncentratin f cmpnent vs the predicted cncentratins using methd 1. r '=:: J. I t..9 c.x Wavenumber (cm I ) Figure 4 Typical FfIR spectra f real apple juice 9

4 1 SCI IND RES VOL 8 Table 3 Statistical parameters f and methds RMSD R.7 1.99

6 4 1 SCI IND RES VOL 8 Table 3 Statistical parameters f and methds RMSD R Cmpnents RMSD R Sucrse.69 Glucse.1 Fructse Citric acid landry than the synthetic mixtures s that the cntributin f all the cmpnents in apple juices can be incrprated in calibratin. Once the technique is autmated, it will be manyfld faster than ther methds. The imprtant characteristic f the present study is that the cmpnents f apple juices can be determined withut any physical r chemical separatin. The technique hlds tremendus ptential fr fruit prcessing industry. The ptential f this type f calibratin fr nline analysis is being explred using a fibre ptic prbe. The preliminary tests indicate quite prmising results. ) Table 4 results fr different variety f apple juices Sucrse, Glucse, Fructse,peCitric acid, r cent AP AP Sample Methd name AP I AP4 AP Cnclusins IR technique appears t be a suitable methd fr accurate and fast determinatin f sugar cntent in apple juices. The results are highly prmising and the apprach can be develped int a cmpletely autmated n line technique where n sample preparatin is required. Hwever, the calibratin is needed t be perfrmed n real samples rather References 1 Me Feeters R F, Thmpsn R L & Fleming H P, J Fd Sci, 8(4) ( 1 993) pp 834. Ni Q X & Eads T M, Ch S I, Strshine R L, Baianu I C & Kurtz G W, Trans ASAE, 36(4) ( 1 993) p p Ni Q X & Eads T M, Delwieh S R & Nrris K H, 93. Cereal Chern, 6 Isakssn T & Kwalski B, 79. Appl Spectrsc, 7 De Lene M, Bulu J C, Dupuy N, Meurens M, Huvenne J P & Legrand P, Appl Spectrsc, 47(8) ( 1993) pp J Agric Fd Chern, J Agric Fd Chern, 41(7) ( 1 993) pp 'r 41(7) (1993) pp 7(1 ) ( 1 993) pp 47 ( 1 993) pp Kemsley E K, Wilsn R H, Pulter G & Day I L, ( 1 993) pp Appl Spectrsc, 47( 1 ) 9 Kellner R, Lendl B, Wells 1 & Wrsefld P J, AppfSpectrsc, 1() ( 1 997) pp Dupuy N, Huvenne J P & Legrand P, 11(1 ) ( 1 993) pp 1. lnd Alirnent Agric, Y

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