Abstract:
The use of full fat soybeans (FFSB) in animal feeds has, to date, been limited due to the presence of anti-nutritional factors (ANF). It is, therefore, increasingly recognized that, if the full potential of full fat soybeans for the use in diets is to be realized, reliable analytical procedures must be available for the quality control of processed FFSB which would enable feed manufactures to determine the degree of soybean processing. Results of currently available analytical techniques vary widely between laboratories, causing uncertainty and confusion among soybean processors, feed manufacturers and end users. A collaborative study was conducted to standardize a number of existing analytical procedures used for determining the effects of heat treatment on FFSB and to generate South African ranges for standardized laboratory procedures. Raw soybeans, in a mixture of cultivars, were processed by dry extrusion at eight different temperatures (110ºC, 120ºC, 127ºC, 136ºC, 140ºC, 145ºC, 151ºC and 164ºC). In vivo trials were conducted on broiler chicks which were fed the eight extruded FFBB. Their performance was monitored with regard to average daily gain (ADG) and feed conversion ratio (FCR). The Protein Solubility in KOH (PSKOH) and the Protein Dispersibility index (PDI) procedures were used for standardization in an inter-laboratory study with the participation of ten South African analytical laboratories. Statistical analysis of the in vivo trials with broilers showed no significant difference (P>0.05) between broilers fed FFSB processed at 136 ºC, 140 ºC and 145 ºC. In addition, samples processed at those temperatures (136 ºC, 140 ºC and 145 ºC) showed the best chick performance with regard to average daily gain (ADG) and the feed conversion ratio (FCR). There was a significant difference (P<0.05) between broilers fed FFSB processed at 110 ºC, 120 ºC and 120 ºC as well as those fed FFSB processed at 151 ºC and 164 ºC. In vitro results showed that the PSKOH and PDI values corresponding to temperatures which showed the best chicken performance were between 67-77% and 10.3-8.5 index units respectively. Therefore, the South African ranges for describing the degree of soybean processing using the PSKOH method are 66-77% with repeatability and reproducibility limits of 3.5 and 10.9 respectively and, when using the PDI method, are 8.5-10.3 index units with repeatability and reproducibility limits of 2.1 and 7.7 respectively. A very good correlation was established between the animal production parameters and the PSKOH values, while a poor correlation between animal production parameters (ADWG and FCR) and PDI values was established. The PSKOH method was found to be the most reliable method for FFSB quality control under standardized South African conditions.
