Abstract
There are a number of laboratory methods that could be used to estimate the adequacy of full-fat soybean (FFSB) heat treatment. The protein despersibility index (PDI) has been claimed to have the most constant response to the heating of FFSBs. In this study, the PDI method has been subjected to an inter-laboratory test, including the participation of eight laboratories. Seven FFSB samples were processed by dry extrusion at temperatures ranging from 110 to 164 °C and analysed on the PDI. Processed FFSB samples were also assessed in a growth trial of broilers. The analysis of the FFSBs by the PDI method generated adequately-processed FFSB values of between 8.49% and 10.3%. Values above 10.3% described under-processed and below 8.49% over-processed FFSBs. The PDI method generated a good repeatability limit of 2.1%, but the reproducibility limit (7.73%) was too wide when taking into account the narrow range (8.5 – 10.3%) for adequately heat-treated FFSBs. Despite its simplicity and initial indications that it might be the best indicator of FFSB heat treatment, the PDI method did not prove that in this inter-laboratory study.Keywords: Broilers, processing, extrusion, repeatability, reproducibility
Highlights
Soybeans contain highly valuable proteins and oils which make them good feed alternatives to animal proteins and oils
There are a number of laboratory methods that could be used to estimate the adequacy of full-fat soybean (FFSB) heat treatment
The best performance was achieved by chickens that were fed the FFSB processed at 136 °C, 140 °C and 145 °C, and there was no significant difference between them (P >0.05)
Summary
Soybeans contain highly valuable proteins and oils (crude protein ranging from 390 – 410 g/kg and oil from 180 – 210 g/kg) which make them good feed alternatives to animal proteins and oils. Raw soybeans contain several factors with anti-nutritional properties and must be processed prior to inclusion in animal diets. The anti-nutritional factors (ANFs) contained in soybeans may cause unfavourable physiological effects (Buttle et al, 2001; Vasconcelos et al, 2001) and may decrease weight gain in animals (Palacios et al, 2004). The processing of raw full-fat soybeans (FFSB) by means of heat and mechanical treatment destroys the anti-nutrients, making the soybean fit for use in monogastric diets. The underprocessing of the FFSBs limits amino acid availability due to the partial destruction of the anti-nutritional factors. Over-processing, on the other hand, decreases the amino acid availability as a result of the Maillard reaction that occurs between aldehyde groups of sugar and free amino groups (Vohra & Kratzer, 1991)
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