Raw materials and processing

Small differences in the ash, protein and fat composition of legumes and wheat among the processing treatments could be attributed to normal variations in the analytical methods. Extrusion did not affect either pea or faba bean protein values in other studies (Alonso et al., 2000a; Alonso et al., 2000b) or ash and ether extract of extruded peas (Alonso et al., 2000b). Protein and ash were also measured in raw and extruded peas, chickpeas and faba beans by Abd El-Hady and Habiba (2003) and no differences were found again for any of the legumes before and after processing, while the absolute concentration of protein and ash was slightly higher in the present study only for faba beans.

Starch analysis showed an overall increase in the processed materials that could be related to composition changes in the resistant starch. Resistant legume starch corresponds to physically inaccessible starch that is entrapped in the cellular matrix (Englyst et al., 1992) that in most cases is destroyed by processing (Gonzalez-Soto et al., 2006). Thermal processing such as cooking has been proven to cause a significant reduction of resistant and poorly digestible starch and an increase in rapidly digestible starch in peas (Periago et al., 1996), chickpeas and common beans (Marconi et al., 2000). However, in some cases (potato and banana starch) amylose retrogradation may occur resulting in resistant starch when raw materials are either freeze dried or autoclaved (Gonzalez-Soto et al., 2006). In this respect, highly digestible starch may have increased and this is possibly reflected in the final starch values, while resistant starch formation is less likely to occur in legume starches. The increased values

CHAPTER 3.EXTRUSION OF PEAS, CHICKPEAS & FABA BEANS

observed for total starch in processed legumes could be possibly attributed to the easier breakage of extruded starch granules by amylase during analysis.

Total NSP were reduced in all extruded faba beans and peas compared to respective raw product values. Extruded chickpeas also had lower values but the reduction was smaller and these results are in agreement with the results of Alonso et al.

(2000b) for extruded peas. A redistribution of S-NSP and I-NSP has been found in rice after press cooking (Sagum and Arcot, 2000) or in cooked chickpeas and common beans (Marconi et al., 2000) with increase of S-NSP and decrease of I-NSP (reduction of ratio I/S-NSP) after treatment. This may be comparable to the results for the extruded chickpeas and peas in the present study although total NSP were not affected in the case of pressure cooking (Marconi et al., 2000). Anguita et al. (2006) also noted that extrusion can increase solubilization of pea NSP, however, solubilisation is less and absolute numbers are higher in the present study and this may be attributed to differences in field pea variety. The redistribution of S-NSP and I-NSP fractions could be attributed to the partial solubilization or depolymerization of hemicellulose and insoluble pectic substances (Vidal-Valverde et al., 1992). Faba bean and wheat flour that underwent drying processing in the present study showed decreased values of S-NSP as opposed to peas, chickpeas and the results of the aforementioned authors but, when faba bean flour was not dried, S-NSP increased. Different behaviours amongst legumes could be attributed to differences in the synthesis of the NSP fraction; for example pea uronic acids and mannose seem to increase, while xylose does not change under extrusion and rhamnose and arabinose are stable (Alonso et al., 2000b). Different results were reported by Periago et al. (1996) between raw and cooked peas NSP fractions, indicating that differences could be expected in the results.

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Alonso et al. (2000b) found that pea sucrose, raffinose and verbascose were increased after extrusion processing, but significant differences were only observed for verbascose values, while stachyose values significantly decreased. In a later work the same authors (Alonso et al., 2001) found that pea and kidney bean sucrose, stachyose and verbascose did not differ before and after extrusion, while raffinose significantly decreased in kidney beans. In addition, autoclaving rapeseed for 1.5 hours resulted in decreased levels of sucrose and stachyose (Mansour et al., 1993). In this respect the result of extrusion on total oligosaccharides could also be dependent on the fraction composition that could be variable among different pulses or seed parts such as hulls, dehulled seeds or protein concentrates (Knudsen, 1997).

Phytic acid values in processed ingredients vary in the literature. For instance, Alonso et al. (1998; 2000a; 2000b; 2001) found significant reduction in peas (5.9%), in faba beans (29%) and kidney beans (4%) after extrusion at 150˚C (in outer die).

However, according to Abd El-Hady and Habiba (2003) findings much lower reduction of phytate was observed between raw and extruded legumes at 140˚C or 180˚C (barrel temperature). Gualberto et al. (1997) showed that extrusion did not affect cereal bran phytate content. In the present study extruded peas, chickpeas and faba bean phytate values either remained the same or decreased up to 17.5, 17.5 and 22.5% respectively compared to the raw legumes. The reduction of phytate though was not consistent for the different processing methods and thus further investigation is imperative.

Francis et al. (2001) in their review of antinutrients mentioned that the effect of thermal treatment on substances like tannins is still not clear. Total tannins in the current study did not seem to be affected drastically, with most of the values in processed legumes being slightly lower than the values in raw materials. In some cases though that was not the case. In this respect the results are partially in accordance with

CHAPTER 3.EXTRUSION OF PEAS, CHICKPEAS & FABA BEANS

those of Abd El-Hady and Habiba (2003) who found a slight decrease in tannins in peas, chickpeas and faba beans after different extrusion temperatures. Nonetheless Alonso et al. (1998, 2000a, 2000b) presented significant reduction in both tannins and polyphenols in peas and faba beans when extruded at 150˚C and this reached 92% when compared to the raw legumes. Reduction of condensed tannins was also observed for peas and kidney beans by Alonso et al. (2001) under the same extrusion conditions.

Differences in tannin reduction could be attributed to higher temperatures or to the duration of processing methods and these are not always clear especially for the extrusion appliance. It has also been suggested that heat treatment possibly reduces extractability by increasing polymerisation of tannins and thus showing lower values after analysis (van der Poel et al., 1991).

TI are known to be heat sensitive (Francis et al., 2001) and they can be reduced or completely destroyed in different plant materials and under different processing methods (Marquez and Alonso, 1999; Frias et al., 2000; Romarheim et al., 2005). High values of TI in raw chickpeas, similar to the present study, have also been reported from other authors (Abd El-Hady and Habiba, 2003). The highest reduction of TI among legumes was noted in chickpeas reaching 92%, while for faba beans it was up to 44%, for peas up to 59% and in wheat TI was not detected in the extrudates. Reduction of 95% in peas was found by Alonso et al. (2000a; 2000b) and 99% in faba beans (Alonso et al., 1998), while in another study (Abd El-Hady and Habiba, 2003) no TI was detected in any of the tested legumes after extrusion processing no matter the initial quantity of the ANF in the raw seeds or the temperature applied. Complete inactivation of TI in the present study was only observed for wheat flour, even though no high temperatures were applied to this material.

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