Effect of steam processing temperature and time on the protein nutritional value of Phaseolus vulgaris beans for swine

Protein structural changes during processing of vegetable feed ingredients used in swine diets: implications for nutritional value

Protein structure influences the accessibility of enzymes for digestion. The proportion of intramolecular β-sheets in the secondary structure of native proteins has been related to a decrease in protein digestibility. Changes to proteins that can be considered positive (for example, denaturation and random coil formation) or negative (for example, aggregation and Maillard reactions) for protein digestibility can occur simultaneously during processing. The final result of these changes on digestibility seems to be a counterbalance of the occurrence of each phenomenon. Occurrence of each phenomenon depends on the conditions applied, but also on the source and type of the protein that is processed. The correlation between denaturation enthalpy after processing and protein digestibility seems to be dependent on the protein source. Heat seems to be the processing parameter with the largest influence on changes in the structure of proteins. The effect of moisture is usually limited to the simultaneous application of heat, but increasing level of moisture during processing usually increases structural changes in proteins. The effect of shear on protein structure is commonly studied using extrusion, although the multifactorial essence of this technology does not allow disentanglement of the separate effects of each processing parameter (for example, heat, shear, moisture). Although most of the available literature on the processing of feed ingredients reports effects on protein digestibility, the mechanisms that explain these effects are usually lacking. Clarifying these mechanisms could aid in the prediction of the nutritional consequences of processing conditions.

The digestibility in piglets of faba bean (Vicia faba L.) as affected by breeding towards the absence of condensed tannins

Seed samples from two near-isogenic faba bean (Vicia faba L.) lines were examined for the levels of so-called anti-nutritional factors (ANF). From the ANF known to be present in faba beans, trypsin inhibitor activity, functional lectins, condensed tannins and pyrimidine glycosides were analysed. It was concluded that the lines differed only in the content of condensed tannins being < 0.5 g/kg and 5.2 (SD 0.2) g/kg for the low (LT)- and high (HT)-tannin lines respectively. In addition, the level of pyrimidine glycosides in the LT line was slightly higher than that in the HT line. The LT line showed a reduced proportion of the seed coat (105 v. 119 g/kg) and a lower seed weight (0.85 v. 1.01 g). The apparent ileal and faecal digestibility values of dry matter and nitrogen from the HT and LT line were determined for piglets which were fed on diets containing chromium oxide as a marker. The mean apparent ileal and faecal digestibility values for dry matter for the LT line were 0.694 and 0.889 and for N 0.828 and 0.879 respectively. For the HT line, these values were approximately 0.05 and 0.10 lower (P > 0.05). A multienzyme technique was used to predict the in vitro protein digestibility (IVPD) of the two lines. The IVPD of the LT line was 0.965 and about 0.05 higher than the HT line, confirming the difference in digestibility as measured in vivo. The present study shows the positive effects on digestibility of removal of condensed tannins in faba beans which was achieved by plant breeding.

True protein digestibility and amounts of endogenous protein measured with the 15N-dilution technique in piglets fed on peas (Pisum sativum) and common beans (Phaseolus vulgaris)

The faecal and ileal true protein digestibilities of the raw pea (Pisum sativum) varieties finale and frijaune and the ileal true protein digestibility of steam-processed common beans (Phaseolus vulgaris) were measured in piglets using the 15N-dilution technique. The faecal true protein digestibility of both pea varieties was about 97. The ileal true protein digestibility was between 93 and 95, indicating that the pea protein is almost completely enzymically digested in the small intestine. The faecal apparent protein digestibility was 85 for both varieties while at the ileal level it was 79 and 74 respectively. The lower ileal apparent protein digestibility of peas can be attributed completely to the excretion of endogenous protein. The ileal apparent protein digestibility of toasted common beans was about zero (-4); the ileal true protein digestibility was about 66. This indicates that the protein of the common bean, although toasted, was highly resistant to enzymic digestion. It was calculated that per kg ingested bean protein, 340 g undigested bean protein and 700 g endogenous protein passed the terminal ileum. The results of the present study explain why in previous experiments a strongly reduced weight gain and even weight loss was observed in piglets fed on raw and toasted common beans.