Irradiation of maize and bean flours: effects on starch physicochemical properties

Abstract

In an earlier study (Rombo GO et al, J Sci Food Agric 81: 497-502 (2001)) it was found that the in vitro starch digestibility of raw and cooked maize and bean flours was increased by irradiation of the flours at 2.5 kGy, but there was a reduction in starch digestibility at doses above 2.5 kGy. Experiments were performed to determine what effects irradiation had on the molecular properties of the starch in maize and bean flours. Increasing irradiation dose caused an increased proportion of β(1-3)-and β(1-4)-bonded starch in bean and maize flours. Starch containing β-bonds is only partially digestible by porcine pancreatic α-amylase, and this may in part explain the reduction in starch digestibility at higher doses. Size exclusion-high-performance liquid chromatography showed that higher irradiation doses led to a reduction in the molecular size of amylopectin in both bean and maize starches, which presumably involved debranching and an increase in the production of short, straight-chain molecules. With increased irradiation dose there was an increase in the crystallinity of the amylopectin fraction of the bean starch as shown by differential scanning calorimetry, presumably at least in part due to β-bonding and amylopectin depolymerisation. These two factors and their interrelated effects are probably responsible for the observed slight reduction in maize and bean porridge starch digestibility reported previously.

Characterization of Physical Properties of Flour and Starch Obtained from Gamma-Irradiated White Rice

“…Our previous results also showed that gamma irradiation decreased the T p (27C decrease) and DH of rice flour, after being irradiated at 50 kGy [2]. Increases in T o and T p after irradiation were reported in wheat and potato starches [11,15] and bean flour [17]. However, the T p of wheat starch decreased after being irradiated with 446 kGy [11].…”

“…However, the T p of wheat starch decreased after being irradiated with 446 kGy [11]. Rombo et al [17] also reported that the T o decreased in maize flour after gamma irradiation. The DH was reported to decrease in potato and wheat starches [11,15] and bean flour [17], but to increase in maize flours [17] after irradiation.…”

“…Hence, work has been documented on irradiation of starches of rice [2,[8][9][10], wheat [11][12][13], maize [14], potato [15], and beans [16,17]. Tomasik and Zaranyika [1] and Sohkey et al [18] have reviewed the molecular changes in starches resulting from gamma irradiation.…”

“…Increase in irradiation dosage decreases viscosity and increases water solubility and acidity of starches [8,13,[18][19][20][21][22]. The gelatinization enthalpy was reported to increase [16,17] or decrease [2,11,15] gradually with increasing irradiation dosage. Bachman et al [22] reported that a dosage of 2 kGy irradiation resulted in decreased and increased retrogradation of Lasco triticale and Grana wheat starches, respectively.…”

Effect of gamma irradiation on the condensed state structure and mechanical properties of konjac glucomannan/chitosan blend films

“…Gamma irradiation had been applied to modification of the properties of konjac glucomannan (Prawitwonga, Takigamia, & Phillips, 2007), starch (Abu, Duodu, & Minnaar, 2006;Bao, Ao, & Jane, 2005;Rombo, Taylor, & Minnaar, 2004), chitosan (Chen, Song, Liu, & Fang, 2007;Choi, Ahn, Lee, Byun, & Park, 2002;Huang, Shen, Sheng, & Fang, 2005) and its blend film (Zhai, Zhao, Yoshii, & Kume, 2004). The effects of irradiation on these polysaccharides had been shown to include depolymerisation and degradation (Sokhey & Hanna, 1993), resulting in decreased viscosity or cross-linking (Nagasawa et al, 2004;Rombo, Taylor, & Minnaar, 2001), increased water solubility and acidity (Bao, Shu, Xia, Bergman, & McClung, 2001), and the gelatinization enthalpy was reported to increase (Rayas-Duarte & Rupnow, 1993;Rombo et al, 2001), or decrease (Bao & Corke, 2002).…”