Regarding percentage
of elongation,
only WWF was improved from 2.5 to 10.5, P B B
0.001. The water absorption was reduced in both
whole flour plastic compounds BWF, 17, and WWF, 20.
4. Discussion
It has been demonstrated in Fig. 1 that the protein black bean compound BP reaches the
higher percentage elongation and the higher ten- sile strength, which are not attained by the other
materials studied. These results can be attributed to the chemical characteristics inherent in the
cultivars under study.
The interpretation requires having into account the remarkable difference in chemical composition
existing between the soluble protein preparations BP, or WP and the defatted whole flours com-
pounds BWF or WWF. These latter materials have 21.3 and 18 of cellulose content respec-
tively, which is absent of the BP and WP materi- als. It should be remarked that the protein quality
inherent to the vegetal species would have an influence on the gelatinization process considering
that among proteins, the properties of hydration dampness or absorption and retention of water
depend on the interactions protein – water which depend also on pH and ionic strength.
The much higher elongation in BP can be un- derstand by the improved protein-protein interac-
tions with better possibility of plasticization when the cellulose content is absent. However, the im-
proved tensile strength, also suggests the influence of the typically quality protein of each cultivar,
because of the WP compound has similar but reduced behaviour.
Fig. 3. Effect of gamma radiation on the mechanical properties of protein soluble preparation of black bean BP and white bean WP; black whole flour bean BWF, and white whole flour bean WWF. Tensile strength expressed in MPa. Elongation .
Irradiation of the blend at 50 kGy.
Moreover, the presence of lecithin in the solu- ble protein fraction based on black bean seeds
would be contribute to the plasticization process actually in study at the laboratory.
It is known besides, that the starch structure determines the properties of starch material, such
as stability, degradability, texture, mechanical and thermal properties. There is a diversity of molecu-
lar and supramolecular structures in processed starch materials depending on starch source, par-
ticularly amyloseamylopectin ratio, moisture and plasticizer content Van Soest, 1996.
The starches in study possess different ratio of amyloseamylopectin, 7030 and 955, in white
and black bean respectively. This work shows a highly hydrophilic carbohy-
drate chains in the case of predominant amylose structure that would have better influence on the
gelatinization process in the presence of water and consequently in the mechanical properties of the
BP plastic material.
Irradiation of blends produced an appreciable effect regarding tensile strength and water absorp-
tion capacity of whole flour products. We did not found an effect of plasticization that would have
resulted in
case of
degradation of
starch molecules. This effect would have been noticeable
as an improvement in elongation. The cellulose material present in the defatted
whole flour could be affected by radiation through breaking of chains and introducing radi-
olytic products. Both effects would enhance the reactivity of the cellulose material Stepanik et al.,
1998.
The improvement in tensile strength and water absorption observed could be attributed to inter-
actions among cellulose chains, proteins and the amylopectin starch structure.
Fig. 2 shows that boric acid only has chemical effect on materials based on white beans; this
effect improves the mechanical properties, which was associated with the presence of different kind
of starch.
The plastic products of beans studied absorb not more than 30 of water. These values are
four times lower than that of the soy whole flour and two times lower than the protein soy isolate
respectively, treated
in similar
conditions. Salmoral et al., 1999.
At the moment of this presentation biodegrad- ability essays have begun at our laboratory. Fur-
ther experiments with the purpose to improve the presented plastics are to be carried on, among
them the elucidation of the protein quality of the beans.
5. Conclusion
