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Single use food packaging made from expanded polystyrene (EPS) is generally discarded after use and, since it is a difficult material to recycle, generates a large amount of waste. The EPS can be replaced by thermoplastic starch (TPS) foams, which are made from renewable sources and are biodegradable. However, TPS foams are hydrophilic and absorb large amounts of water, which makes it difficult to use. An alternative to this problem is to chemically modify the starch to make it more hydrophobic. Two modifications for potato starch were evaluated: acetylation and esterification with maleic anhydride. Foams with 6.67%, 13.34%, 20% and 26.67% (modified starch weight/ total starch paste mass) of modified starch were prepared. While TPS foams without modified starch absorbed 75 g water /100 g solids, foams with 13% acetylated starch and 20% esterified starch presented lower absorption results (42 g and 45 g water/100 g solids, respectively), which represents an improvement in water resistance.

This study was designed to investigate the effect of a thermostable α-glucanotransferase (TSαGT) originated from Thermus scotoductus on the rheological properties, molecular weight distribution, thermo-reversibility, and freeze-thaw stability of rice starch paste. Rice starch paste samples (5%) were incubated at 70 °C with TSαGT and a commercial α-amylase, respectively, until reduction of moduli leveled off. The TSαGT-modified rice starch paste showed a yield stress. After the enzymatic treatment, both enzyme-treated pastes showed considerably low moduli with higher G ″ than G ′, indicating a significant liquefaction. However, when stored at 4 °C, both moduli of a TSαGT-treated sample dramatically increased with significantly higher G ′ than G ″, confirming that a solid gel structure formed. This transition was found to be reversible, when temperature fluctuated between 70 and 4 °C. The control starch gel did not show thermo-reversibility, and α-amylase-treated starch paste was incapable of forming a solid gel. The size distribution of the starch polymers, as measured by MALLS, revealed that average M w reduced to about 5×10 5 after the TSαGT treatment, which was a significant decrease, but possibly high enough to form a solid gel matrix at low temperatures. The TsαGT-treated gel demonstrated highly improved freeze-thaw stability.

Swelling and pasting properties of 15 starches from different plant origins were studied to elucidate their relationship with structural features using simple and multiple regression analyses. Avoidance of additional effects of starch minor components showed that swelling power and pasting parameters were associated with the ratio of the relative molar distribution of amylopectin branch-chains with a degree of polymerization (DP) of 6–12 to that of chains with DP 6–24 (amylopectin unit-chain (APC) ratio). Swelling power of starch granules increased with APC ratio. Multiple regression analysis revealed that the peak viscosity (PkV) of starch paste increased with low APC ratio, low amylose content (AC) and large average granule size (AGS). At a high starch concentration, pasting temperature (PT) was reduced by a high APC ratio and large AGS. Peak time (PkT) decreased with increasing APC ratio and AC. Percentage of breakdown viscosity (BD%) and setback viscosity (SB) were primarily affected by APC ratio. At a low concentration, AC and AGS had more profound effects on BD%. SB was also reduced by higher AC. Models of pasting profile, which is influenced by individual factors, were also proposed.