Effects of dietary n-3 polyunsaturated fatty acids and ... - FINS

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1 st WorkshopXIII International Feed Technology SymposiumPROTEIN DISPERSIBILITY INDEX AS AN INDICATOR OFTHE DEGREE OF FULL FAT SOYBEAN HEAT TREATMENTDragan Palić 1 , Sophia Elisabeth Coetzee 2 , Kedibone Yvonne Modika 2 , Slavko Filipović 11 Institute for Food Technology, Bulevar cara Lazara 1, 21 000 Novi Sad, Serbia2 Animal Production Institute, Agricultural Research Council, Irene 0062, South AfricaABSTRACTFull fat soybeans (FFSB) intended for use in monogastric nutrition need to undergo heattreatment, so that present anti-nutritional factors can be inactivated. Under- or overtreatmentwill decrease the level of amino acids available to the animal. There are anumber of laboratory methods that can be used to estimate the adequacy of FFSBprocessing, one of them being the Protein Dispersibility Index (PDI). In this paper, theresults of an inter-laboratory study have been presented, with an aim to confirm the PDIglobally accepted values of between 15 and 28 for adequately processed soybean. SevenFFSB samples were dry extruded at temperatures from 110°C to 164°C and assessed inthe trial with chickens. Eight laboratories have been determining the PDI according tothe official AOCS method. PDI range of 8.50 - 10.30 has been obtained for describingadequately extruded full fat soybean. Repeatibility limit r=2.11 and reproducibility limitR=7.73 were obtained.Key words: full fat soybean, extrusion, degree of processing, protein dispersibility index,inter-laboratory studyINTRODUCTIONFull fat soybeans (FFSB) contain anti-nutritional factors (ANFs) which limit its use inmonogastric diets (10). The ANFs can be inactivated by heat treatment. However, overtreatmentwill damage the protein and decrease amino acid availability (6). There istherefore an optimum range of temperatures where the ANFs are sufficiently removedwithout damage to reactive amino acids. Amongst other authors, Holmes (7), Ruiz et al.(8) and Zarkadas et al. (11) showed that moderate heating is necessary to increase thedigestibility of soybean protein for non-ruminants. A comparatively mild heating leadsto denaturation of tertiary and quaternary structures, allowing more effective penetrationof digestion enzymes.There are a number of laboratory methods that can be used to estimate the adequacy ofFFSB heat treatment. Commonly used methods for assessing the processed FFSB qualityare those for the determination of urease activity andex (UAI), trypsin inhibitor (TI),protein solubility in KOH (PSKOH), nitrogen solubility index (NSI) and proteindispersibility index (PDI). In a critical assessment of methods, Palic et al. (7) concludedthat protein solubility is the best indicator for FFSB quality control and that therefore187
1 st WorkshopXIII International Feed Technology SymposiumPSKOH, NSI and PDI are the prefered methods. Batal et al. (4) reported that the PDIdisplayed the most constant response to heating of FFSB and that it may better indicateprocessed FFSB quality compared to other methods, and thus the PDI would be the firstchoice.For adequately heat treated soybeans globally accepted values for PDI are between 15and 28 (6). However, these values PDI are not specified in the description of the officialAOCS method (3). In fact, no values were specified. Attempts to source originalpublication(s) which cited the PDI values of 15 - 28 for adequately-processed FFSB,have failed. It was therefore the aim of this study to confirm that globally acceptedrange.MATERIALS AND METHODSRaw soybeans were processed by dry extrusion at 7 temperatures: 110°C, 127°C, 136°C,140°C 145°C, 151°C and 164°C and fed to chickens.In vivo trialA total of 384 male Ross broilers were randomly allocated to 48 pens, each containing 8birds. On arrival all broilers were sorted into equal weight groups, and assigned atrandom to the different treatment pens, so that initial average weight and weightdistribution were similar for all pens. They were allocated to one of seven dietarytreatments containing the processed FFSB, with five replicates per treatment. Theaverage body weight gain (ADWG) in the period from day 0 to 14 and feed conversionratio (FCR) on day 14 were monitored as production parameters.Data were analyzed using the statistical programme SAS/STAT (9).Protein Dispersibility Index (PDI)Protein dispersibility index (PDI) was determined according to the official AOCSmethod (3). It was subjected to an inter-laboratory study, which was conductedaccording to the Collaborative Study Procedures (1) and in which participated 8laboratories. Seven FFSB samples which were assessed in the in vivo trial with chickenswere analysed for PDI in duplicate. A “Hamilton Beach” Commercial Blender, modelG936, (constructed according to requirements of the official AOCS method) was used byall laboratories. The speed of the blender was 8500 rpm. Repeatibility limit (absolutedifference between two single results of analysis of the same sample obtained in onelaboratory) and reproducibility limit (absolute difference between single results ofanalysis of the same sample obtained in different laboratories) were determinedaccording to the AOCS procedure (2).188
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