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The impact of flours and product storage on the thiamin content of Asian noodles

The impact of flours and product storage on the thiamin content of Asian noodles
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  LWT 41 (2008) 262–269 The impact of flours and product storage on thethiamin content of Asian noodles Lan T.T. Bui  , Darryl M. Small School of Life Sciences and Technology, Victoria University, Werribee Campus, PO Box 14428 MCMC, Victoria 8001, Australia Received 23 October 2006; received in revised form 21 December 2006; accepted 1 March 2007 Abstract Thiamin is essential for human health and wheat foods are generally considered to be a good source of thiamin. However, dietarylevels may be limited because of losses during processing. The aim of this study was to investigate the level of thiamin in a variety of wheat flour products along with the factors impacting on the thiamin content of Asian noodles particularly during storage. A standardfluorometric procedure was selected for the determination of thiamin in flours and noodle samples. White salted, yellow alkaline andinstant noodles were prepared and the impact of storage conditions on thiamin levels analysed. Noodle pH appeared to be directlyrelated to the amount of alkaline salt added and this in turn influenced the thiamin stability. The losses varied between the different styleswith the greatest decreases occurring in the fresh yellow alkaline noodles. Prolonged drying at 40 1 C for up to 9 days had no adverseinfluence on the ultimate thiamin status of these products. Storage of dried noodles for up to 4 months did not result in any further lossof thiamin. It is concluded that the potential of Asian noodles to contribute to dietary thiamin intakes appears to be limited in thosewhere alkaline salts are included in the formulation. r 2007 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords:  Asian noodles; Nutrients; Thiamin 1. Introduction There are two groups of noodle products made fromwheat. These are pasta products typically prepared fromdurum wheat ( Triticum durum ) by an extrusion process aswell as Asian wheat flour noodles. The latter are basedupon fine flour milled from bread wheat ( Triticumaestivum ) and the processing involves sheeting and cuttinginto strands using a series of rolls. The three main styles of Asian wheat noodles are white salted, yellow alkaline andinstant. Selection of suitable flour depends on the type of product as well as the specific preferences of the consumers.Generally, the flour should have fine granularity, low ash,good colour, reasonable degree of extensibility and rapidwater absorption in a short mixing time. The requirementsfor specific noodle types have been described by Nagao(1996) and Crosbie and Ross (2004). The ingredients of Asian noodles include wheat flour,water and either common salt (sodium chloride) or alkalinesalts (often referred to as lye water, kan swi (kansui) andare typically mixtures of sodium and potassium carbo-nates) (Moss, Miskelly, & Moss, 1986). The classification of noodles is based on the ingredients and manufacturingmethod. There are a variety of processes which might beapplied depending upon the style of noodles, consumerpreferences and the form in which the noodles arepurchased. Generally speaking, a white, soft and elasticnoodle texture is characteristic of white salted noodles(Nagao, 1996). A bright, clear yellow colour with a firm,chewy texture and a smooth surface is typical of yellowalkaline noodles. The alkaline salt in yellow alkalinenoodles inhibits enzyme activity and changes the flourpigments, flavonoids to yellow. This results in a productwith a desirable bright yellow colour, favourable noodlestrength and palatability (Lorenz, Martin, & Stewart, 1994). The processing of instant noodles involves precook-ing of the fresh noodle strands by steaming and then deep-frying which gives a texture distinct from that of white ARTICLE IN PRESS$30.00 r 2007 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.lwt.2007.03.001  Corresponding author. Tel.: 61363526606; fax: 61363523044. E-mail address: (L.T.T. Bui).  salted and yellow alkaline noodles. Instant noodles areincreasingly popular due to ease of preparation (Hoseney,1994).In recent studies (Bui & Small, 2007a) it has been shown that the thiamin contents of Asian noodles prepared in thelaboratory under controlled conditions were lower thanexpected. This reflects the relative instability of the thiaminmolecule. It has previously been shown that the levels of Bgroup vitamins decline during the preparation of durum-based products (Dexter, Matsuo, & Morgan, 1982; Watanabe & Ciacco, 1990). Further investigation has demonstrated that the thiamin levels in samples of commercial noodles vary quite widely (Bui & Small,2007b).Wheat flour represents one of the primary potentialsources of thiamin in the diet of many individuals aroundthe world (Batifoulier, Verny, Chanliaud, Re ´me ´sy, &Demigne ´, 2005; Ottaway, 1993). However, the losses found for Asian noodles are a cause for concern because theyrepresent a staple food globally and can be considered as apotential vehicle for thiamin fortification.Asian noodles may be sold as a fresh product, in themoist form following partial cooking, or they may be driedprior to packaging. In the context of the various optionsavailable both for formulation and varied processing stepsapplied in noodle manufacture, the purpose of the currentstudy has been to investigate the levels of thiamin in arange of wheat flour products; the stability of thiaminduring processing and particularly, to compare the impactof different storage conditions. 2. Material and methods  2.1. Materials All chemicals used in this study were of analytical grade.Thiamin hydrochloride used as a standard was the purestgrade available from Sigma, St. Louis, MO, USA. A widerange of wheat flours were obtained from AgrifoodTechnology, Werribee, Melbourne and from retail outletsin Melbourne. Flours used to make noodles in thelaboratory were Maximus strong bakers and ContinentalFarina, from Weston Milling, Melbourne. Commercialnoodles were purchased from retail outlets in Melbourne.AACC standard reference sample (VMA 339) wasobtained from AACC, St. Paul, MN, USA.  2.2. Methods 2.2.1. Noodle preparation Noodle samples were prepared using procedures basedon those described by Moss, Gore, and Murray (1987). Allsteps in the preparation of noodles were carried out insubdued lighting conditions in order to minimise theimpact of light on thiamin retention. In general, the noodlemaking methods for the three styles have four commonsteps: mixing, sheeting, cutting and drying. However, forinstant noodles, after cutting, steaming and frying stepswere also required. The preparation of each of the threestyles of noodles is described briefly as follows: Preparation of white salted noodles.  White saltednoodles were prepared from Continental Farina flour as ithad processing characteristics generally suitable for thisstyle of noodles. The basic ingredients used for making allwhite salted noodles were: 300.0g flour, 96.0g water and9.0g common salt. The salt was first dissolved in the waterand this solution was added to the flour during mixing.After mixing, the resultant dough had a crumbly consis-tency similar to that of moist breadcrumbs. Then thedough was first formed into a dough sheet by a process of folding and passing the crumbly dough through the rollersof the noodle machine several times. The thickness of thesheet was reduced stepwise by passing between the rollersof the noodle machine before cutting into strands. Thefresh noodles were arranged upon trays lined withaluminium foil. The noodles were placed loosely in orderto facilitate effective drying and the trays were stored in adehydrator at 40 1 C for 24h. The product was then allowedto cool for 30min in the ambient conditions of thelaboratory prior to being placed in airtight plastic bagsor containers for storage. Preparation of yellow alkaline noodles.  The flourused for preparation of yellow alkaline noodles wasMaximus. The ingredient formulation was: 300.0g flour,96.0g water and 3.0g sodium carbonate. The procedure formaking yellow alkaline noodles was the same as thatdescribed above for white salted noodles. Preparation of instant noodles.  Maximus wasused to prepare instant noodles. The ingredients used tomake instant noodles were: 200.0g flour, 60.0g water, 0.2gsodium carbonate. Palm oil was used to deep fry thenoodles. The procedure for making instant noodles was thesame as that for yellow alkaline noodles at the mixing androlling steps. However, additional steps were steaming(2min) over vigorously boiling water, frying (45s/150 1 C),draining (30s) and cooling in the air flow for 20min priorto packing and storage.  2.2.2. Noodle storage In order to assess the impact of extended drying of noodles at 40 1 C in a dehydrator, multiple batches of bothwhite salted and yellow alkaline noodle strands wereprepared. Samples were placed in the dehydrator forextended periods of up to 9 days. Sub-samples were takenat 1-day intervals and analysed for thiamin content.Prepared noodles (white salted, yellow alkaline andinstant) were stored in a cupboard at room temperature forperiods of up to 4 months. White salted and yellow alkalinefresh noodle were dried in a dehydrator at 40 1 C for 24hprior to storage at room temperature. Fresh yellow alkalinenoodles were also stored for 24h under different storage ARTICLE IN PRESS L.T.T. Bui, D.M. Small / LWT 41 (2008) 262–269  263  conditions: in the dehydrator at 40 1 C, room temperatureand refrigeration temperatures.  2.2.3. Thiamin analysis Sampling.  For analysis purposes, flours did notrequire pretreatment, while noodle products were preparedprior to analysis. When dried noodles were stored for up to4 months, noodles samples were analysed each month. Inaddition, sub-samples were cooked to the optimumcooking time which was established for each style of noodles as the time when the central core of uncookedmaterial had just disappeared. Grinding:  All the dried/fried noodles investigated wereground to pass through a 35-mesh screen (i.e., sieveaperture: 500 m m) before the extraction of thiamin. Cooking:  The noodle samples were cooked by placing asmall amount (approximately 10g) into a saucepan of gently boiling water (300mL). After every minute, a strandof noodle was removed, placed in cold water and thensqueezed between two microscope slides. The noodle wasdetermined to be fully cooked if a uniform colour wasobtained, indicating that the uncooked core had disap-peared. The optimum cooking time depended on the sizeand type of the noodle product. Homogenising.  Sufficient quantities of each sam-ple (including flours, cooked and uncooked noodles) wereweighed (approximately 3.2g) and blended with 50mLdilute acid (0.1M HCl) for a short period. The resultingslurries were highly homogeneous. If much fat was present(instant noodles), the fat was excluded during the samplingstep following autoclaving as it contained insignificantquantities of thiamin. In addition, if the assay could not befinished in 1 day, after autoclaving the filtrate was storedunder refrigeration (Ellefson, 1985). AOAC procedure for thiamin analysis.  The ex-traction and assay of thiamin were performed according tothe fluorometric method (Association of Official AnalyticalChemists (AOAC) procedure number 953.17) (AOAC,1990a). This involved: preparation of samples, acidification(homogenised with 0.1M HCl), autoclaving (20min/109 1 C), centrifugation (20min/3500rpm), oxidation usingK 3 Fe(CN) 6 , extraction ( iso butanol) and determination of thiochrome (fluorescence measurements (Perkin-ElmerLS50) using excitation wavelength set at 365nm andemission wavelength at 435nm). Quinine sulfate solutionwas also used to assess reproducibility. In all cases multipleanalyses were performed.All thiamin values are expressed in units of mg per 100gand have been calculated to a dry weight basis. Thepurpose was to facilitate the direct comparison of theresults particularly for different sample types. All samplesanalysed for thiamin were also tested for pH and moisturecontents. The American Association of Cereal Chemists(AACC) method 02–52 and AOAC method 925.10,respectively were used (AACC, 1994; AOAC, 1990b).  2.2.4. Measurement of instant noodle colour The colour of instant noodles was measured with aMinolta Chroma Meter (Model CR300). For analysis, thethree different colour parameters,  L * (degree of whiteness/darkness),  a * (redness and greenness) and  b * (yellownessand blueness) were recorded. For  a * and  b * readings,values closer to zero indicate less intense colour whereasreadings further from zero correspond to more intensechroma characteristics (Hutchings, 1999). Multiple sets of readings ( n X 10) were taken on all samples randomly andthe mean values reported. 3. Results and discussion 3.1. Measurement of thiamin in flour samples In order to establish the reliability of the thiaminanalysis for noodles samples, a series of flours, noodlesand a reference sample were repeatedly analysed (Table 1).These results demonstrate that the repeatability andaccuracy were good. It is noted that the higher level of thiamin in Maximus reflects the fortification in accordancewith Australian regulations for breadmaking flours.It is known that a number of factors influence the use of wheat flours such as variation in the milling extractionrates, inherent flour quality characteristics as well as thenutritional value (Kent-Jones & Amos, 1967; Ranhotra, 1994). Therefore, in this phase of the study, the first stepwas to examine the thiamin contents of commercial floursamples which might be used for further experimentation.The moisture contents, thiamin and pH values of 5commercial flour samples are presented in Table 2.The results highlight the variability in thiamin content of commercial flour depending on whether fortification withthiamin had been carried out. In order to facilitateinterpretation of these results, a further series of flourswere also analysed. These flours were obtained fromlaboratory millings of wheat grown in different regions of Australia. These provide information on the levels of thiamin present in flours that had not been fortified and the ARTICLE IN PRESS Table 1The results of repeatability studies for thiamin analyses using commercialflours, noodle samples and AACC reference materialSamples Thiamin content (mg/100g)Range of results Mean SD CV (%)Continental Farina* 0.197–0.219 0.210 0.007 3.49Maximus flour* 1.081–1.196 1.146 0.031 2.69Dragon noodles 0.147–0.162 0.156 0.009 5.54Thin Kan to noodles 0.072–0.083 0.077 0.004 4.69Tomoshiraga noodles 0.118–0.132 0.126 0.005 3.78Mai Hong noodles 0.025–0.031 0.028 0.002 7.82AACC reference material** 0.637–0.787 0.781 0.065 9.03 Note : (1) Thiamin values are presented in units of mg/100g and expressedon an as-is moisture basis. (2) Flour samples (*),  n ¼ 10. Noodle sample, n ¼ 6, AACC reference material (**),  n ¼ 12. L.T.T. Bui, D.M. Small / LWT 41 (2008) 262–269 264  results are presented in Table 3. Firstly, the results showtypical moisture contents as might be expected for milledflours. These values have been used in calculating thecorrected thiamin results.The results for commercial flours in Table 2 show thatthe pH of typical flours is similar to that of white saltednoodles. The only higher value was seen for the self-raisingflour in which the addition of aerating agents has probablyraised the pH of the sample. The results are consistent withthe inherent flour characteristics having no direct influenceon the pH of noodles.In relation to the thiamin contents in commercial flours,there is considerable variation with the range being0.21–1.39mg/100g. Clearly the higher values reflect for-tification of the flour at the mill. In Australia, since 1992 ithas been a legal requirement for all flours for breadmakingto be fortified with thiamin (Food Standards AustraliaNew Zealand, 2006) to a minimum level of 0.64mg/100g.Thus the breadmaking flour analysed here complies withthe standard with a value well in excess of that required.Flours for purposes other than breadmaking are notrequired to be fortified. Of the samples analysed here(Table 2) the pizza flour appears to have been fortified andthis is consistent with the declared ingredient list on thepackaging. On the other hand, the flour with the lowestthiamin levels (Continental Farina—0.209mg/100g) waslabelled as having being fortified.The laboratory milled flours showed thiamin contents of 0.085–0.183mg/100g. These flours had been milled to 75%extraction rates from wheats grown in different Australianstates. The wheats included the full range of wheat typesavailable in Australia representing each of the differentcommercial grades of wheat and both soft and hardgrained wheats. Therefore the range found here demon-strates the range of thiamin contents that might beencountered in straight-run flours which have not beenfortified.In comparing the results for the laboratory andcommercial flours, the latter are higher. The results leadto the conclusion that all of the commercial flours had beenfortified to some extent at the flour mill (Tables 2 and 3). Ithas been reported in early studies that wheat from differentcountries may vary in thiamin levels (Kent-Jones & Amos, 1967). Some of the early data also indicated that Australianwheats may have had higher thiamine levels. There is norecent data to confirm this and further studies may bewarranted to clarify these issues.Two of the flours analysed for thiamin were then selectedfor further studies. Continental Farina was selected forpreparation of white salted noodles in the laboratory andMaximus was chosen for yellow alkaline and instantnoodles. These choices were based upon the knowncharacteristics of the flours, particularly protein contents,and their suitability for the specific products (Crosbie,Huang, & Barclay, 1998). 3.2. The relationship between colour and thiamin content of instant noodles Thiamin is generally known to be thermally labile andwe have recently reported losses of 24% during the fryingof noodles (Bui & Small, 2007a). In the current study, the extent of loss has been related to the product colour as thismay indicate the extent of exposure to heat. To investigatethis, a range of commercial instant noodles was selectedalong with samples prepared in the laboratory. The latter ARTICLE IN PRESS Table 2Thiamin contents, moistures and pH levels of different types of commercial milled floursBrand Flour type Thiamin (mg/100g) pH Moisture (%)Continental Farina Specialist cake production 0.209 5.95 12.1Maximus Strong breadmaking 1.196 6.05 13.1Defiance Plain 0.573 5.84 13.6Mc.Alpin’s Wholemeal selfraising 0.337 6.67 11.7Milano Pizza 1.386 5.92 13.1 Note : Thiamin values are presented in units of mg/100g and expressed on an as-is moisture basisTable 3Thiamin contents of flours milled in the laboratory from a variety of wheat typesSample type Port zone Thiamin content (mg/100g) Moisture content (%)Australian Soft Albany, WA 0.088 13.6Australian Premium White Port Adelaide, SA 0.183 13.7Australian Premium White Brisbane, Qld. 0.175 13.8Australian Premium White Geelong, Vic. 0.137 14.6Australian Prime Hard Port Kembla, NSW 0.180 13.8Australian Hard Newcastle, NSW 0.085 13.7 Note : Thiamin values are presented in units of mg/100g and expressed on an as-is moisture basis L.T.T. Bui, D.M. Small / LWT 41 (2008) 262–269  265  were fried in oil for 45s at 150 1 C and colour characteristicswere assessed, both visually and instrumentally (Table 4).These results firstly show considerable variation in visualappearance. In addition, there is considerable variation inall three colour parameters with lighter appearancecorresponding to lower  L *  a * and  b * values. The thiamincontent of the laboratory noodles was much higher,reflecting the fortification of the flour used for noodlepreparation. The results for the commercial samples showthat the lowest thiamin content in the deep fried noodleswas found for the Wai Wai sample which also showed thelowest  L * and highest  a * and  b * values. It is noted thatdeep frying is very widely used in the drying of instantnoodles, although some products may be dried by sprayingwith hot oil. From the limited number of samples assessedit appears that some samples with darker colour showedlower thiamin contents. However, MaMa Mien hadcreamy appearance and also had low amount of thiamin.These results did not clearly demonstrate a significantrelationship between colour and thiamin content. 3.3. The impact of the drying procedure A series of experiments was carried out to study changesin thiamin contents for white salted and yellow alkalinenoodles which were subjected to a longer duration of drying conditions.White salted noodle doughs contained an average of 0.207mg/100g thiamin (Fig. 1). Drying at 40 1 C for 24hresulted in a decrease in moisture content from 33.4% inthe dough to 9.8% and there was no corresponding loss inthiamin. Extended drying for periods of up to 9 daysresulted in no decline in thiamin content. Minor variationsobserved reflect inherent variability associated with themeasurement of thiamin.For yellow alkaline noodles there was considerable lossof thiamin due to the drying at 40 1 C where the moisturedropped from 35.5% to 9.8% during the first 24h. Theaverage loss of thiamin from the prepared dough was0.89mg/100g with the level in the dried noodles atapproximately 0.10mg/100g (Figs. 1 and 2). It is alsonoted that the flour used for yellow alkaline noodles hadhigher thiamin levels due to the mandatory fortification of flours for breadmaking in Australia. Again some minorvariation in levels was observed upon extended drying at40 1 C for up to 9 days (Fig. 1). However, there was no cleartrend of further loss during extended dehydration and thevariability again reflected minor variations related to theanalysis procedure. The results for white salted noodlesappear to be similar to those reported for fortified pastaproducts (Dexter et al., 1982; Watanabe & Ciacco, 1990). On the other hand, the overall losses for the alkalinenoodles are much higher. 3.4. Effect of storage conditions on thiamin in fresh yellowalkaline noodles In this study, the yellow alkaline noodle dough pH wasaround 10.4. Considerable loss of thiamin occurred in thedough at the mixing and the drying stages (Fig. 2). Anadditional issue of relevance here is that yellow alkalinenoodles may be either dried soon after dough preparation,or alternatively, may be stored and sold fresh. Suchnoodles may also then be stored by a consumer prior tocooking and eating. Accordingly an experiment wasconducted in order to compare the effect of storage of both fresh and dried yellow alkaline noodles and the resultsare presented in Fig. 2. ARTICLE IN PRESS Table 4The colour characteristics and thiamin contents of instant noodlesSample type Brand Visual colour assessment Colour parameter Thiamin content (mg/100g) L *  a *  b *Commercial Mama Brownish 59.96 3.25 25.10 0.083Ma Ma Mien Creamy 66.67   0.99 17.11 0.084Trident Creamy 64.26   0.94 15.18 0.152Wai Wai Brown 58.51 3.98 26.87 0.066Indomie Yellowish 69.11   3.22 22.61 0.146Laboratory Creamy 62.15   1.80 17.69 0.918 Note : Thiamin values are presented in units of mg/100g and expressed on an as-is moisture basis. 00.511.522.51 2 3 4 5 6 7 8 9 Drying time (day)    T   h   i  a  m   i  n   l  e  v  e   l  s   (  m  g   /   k  g   ) Fig. 1. The influence of drying time at 40 1 C on thiamin contents of whitesalted (upper) and yellow alkaline noodles (lower). L.T.T. Bui, D.M. Small / LWT 41 (2008) 262–269 266
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