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

1 st WorkshopXIII International Feed Technology Symposiumalready being utilized for ash determination in different kinds of food (such as coffee,milk powders, starches, flours, oil seeds etc.) since it requires shorter analysis times,smaller sample masses and no sample pretreatment [3, 9, 10, 13]. The application ofTGA method for feed quality control has not been reported so far. Thermogravimetricanalysis (TGA) is considered to be one of the five basic thermal analysis techniques. Itinvolves the measurement of change of sample mass with change of temperature. InTGA, mass loss is observed if a thermal event involves loss of a volatile component.Chemical reactions, such as combustion, involve mass losses, whereas physical changes,such as melting, do not. The purpose of this study was to compare the gravimetric andthermogravimetric methods used for determination of ash content in feedstuffs.MATERIALS AND METHODSA total of 143 feed samples were collected for the study. Ash contents were determinedby dry ashing in a muffle furnace at 550 C until the constant weight was reached. Thethermogravimetric analyses (TGA) were performed using thermogravimetric analyzerTGA701 (Leco) with ceramic crucibles and sample mass of about 1.0 ± 0.1 mg, withdynamic air atmosphere at high flow rate (10 lpm) and ramp rate of 20ºC per minute inthe temperature interval of 25-550ºC until the constant weight was reached. Themeasurements were carried out in replicates. The statistical approach applied in thisstudy suggested by Pojić et al. (2009) [8] for the comparison of different analyticalmethods with each other included descriptive statistics (mean, standard deviation (SD),minimum and maximum, coefficient of variance (CV) and confidence interval),multivariate analysis of variance (MANOVA), discriminant analysis and analysis ofvariance (ANOVA).RESULTS AND DISCUSSIONValues for crude ash content measured by the TGA method ranged from 6.6 to 15.5 %,whilst values for crude ash content measured by the gravimetric method ranged from5.6 to 13.2 %, being narrower in comparison to the TGA values (Tab. 1). The normal ashcontent of feed is from 7.0 to 13.0 depending on the type, so it was impossible to identifywhich method was more accurate [4, 6, 11]. The spread in ash content is representativeof the values likely to be encountered in practice. The distribution of these results isshown in Figure 1 and 2.193