Effects of different cooking methods on chemical compositions,in vitro starch digestibility and antioxidant activity of taro (Colocasia esculenta) corms

The impacts of different cooking methods (boiling, steaming, baking, microwaving and frying) on chemical compositions, starch digestibility and antioxidant activity of taro corms were investigated. Compared with raw taro, boiling and frying reduced crude protein and ash contents. Frying significantly increased crude fat and fibre contents but decreased carbohydrate content. All cooking methods reduced oxalate content, especially frying. Among the cooked products, the boiled taro had the highest rapidly digestible starch (RDS) but the lowest resistant starch (RS) contents. In contrast, the fried taro provided the lowest RDS but the highest RS contents. All cooking methods reduced the total phenolic content and antioxidant activity of taro. The boiled taro had the lowest antioxidant activity but the fired taro provided the highest. Frying was able to retain most of the health-promoting compounds with the lowest oxalate content; however, the high consumption of high-fat fried taro may adversely affect human health.     

Bioreactors Based on Monolith‐Supported Ionic Liquid Phase for Enzyme Catalysis in Supercritical Carbon Dioxide

Bioreactors with covalently supported ionic liquid phases (SILP) were prepared as polymeric monoliths based on styrene–divinylbenzene or 2‐hydroxyethyl methacrylate–ethylene dimethacrylate, and with imidazolium units loadings ranging from 54.7 to 39.8 % wt IL per gram of polymer. The SILPs were able to absorb Candida antarctica lipase B (CALB), leading to highly efficient and robust heterogeneous biocatalysts. The bioreactors were prepared as macroporous monolithic mini‐flow systems and tested for the continuous flow synthesis of citronellyl propionate in supercritical carbon dioxide (scCO₂) by transesterification. The catalytic activity of these mini‐flow‐bioreactors remained practically unchanged for seven operational cycles of 5 h each in different supercritical conditions. The best results were obtained when the most hydrophobic monolith, M‐SILP‐ 8 ‐CALB, was assayed at 80 °C and 10 M Pa, reaching a total turnover number (TON) of 35.8×10⁴ mol product/mol enzyme. The results substantially exceeded those obtained for packed‐bed reactors with supported silica‐CALB‐Si‐4 catalyst under the same experimental conditions.     

Argon Plasma Treatment of Tapioca Starch Using a Semi-continuous Downer Reactor

To develop a novel modification process of tapioca starch using low-pressure argon plasma treatment in a large-scale production, a semi-continuous downer reactor was designed to provide a production rate of 0.1–0.5 kg per cycle. Physicochemical and rheological properties of plasma-treated starch were investigated in order to predict the phenomena occurred during the plasma treatment. Native tapioca starch (NTS) was plasma-treated for 1, 3, or 6 cycles, which were referred to as PTS-1, PTS-3, or PTS-6 samples, respectively. Plasma treatment of the NTS resulted in a significant decrease (P?<?0.05) in paste clarity and Rapid Visco Analyzer (RVA) breakdown viscosity, and an increase in gel strength of starch. The PTS-1 had the lowest paste clarity of 39.85 %T at 650 nm and breakdown viscosity of 29.71 Rapid Visco Unit (RVU), and the highest gel strength, e.g., G′?=?5.47ω ^0.32. With increasing the number of treatment cycles, i.e., the PTS-3 and PTS-6, the paste clarity and breakdown viscosity significantly increased (P?<?0.05), while the gel strength decreased. The Fourier transform infrared (FTIR) spectroscopy via relative areas of C–O–C peaks indicated that the PTS-1 had a significant increase (P?<?0.05) in the C–O–C cross-linked bonds compared to the NTS, but the effect of depolymerization could further suppress the cross-linking reaction when the number of treatment cycle was increased. Taking an advantage of a very short residence time (less than 0.3 s) in the plasma downer reactor, the semi-continuous process of starch modification could be developed for a commercial production of non-chemically modified starch with a relatively low degree of cross-linking.     

Zeta Potential (ζ) Analysis for the Determination of Protein Content in Rice Flour

Zeta potential (ζ) analysis was investigated as a means of rapid determination of residual protein content of rice flour during processing of rice starch. A rice flour sample was suspended in 0.3% sodium hydroxide solution to obtain rice flour slurry which was subjected to protein extraction by a decanter for five cycles. The samples from all cycles were collected, neutralized, dried, sieved through a 200 mesh sifter and subjected to ζ analysis. The data from ζ values (y) and chemical analysis of protein content (x) from six samples of rice flour were used in a regression analysis to develop an empirical equation to express the protein content of rice flour based on ζ value alone. The result of ζ value obtained from six samples of different protein contents suspended in a buffer solution of pH 12 yielded a standard linear equation of y = –1.29x–12.51. In another method of ζ analysis, the sample was suspended in DI (deionized) water without buffer by varying pH from 2 to 8 for the ζ measurement. A linear relationship between ζ and pH was obtained together with the constant value k (slope) which could be converted into protein content (x) of rice flour by a standard linear equation of k = –1.15x –4.90.     

Physicochemical properties and in vitro digestibility of flours and starches from taro cultivated in different regions of Thailand

This research aimed to study physicochemical properties and in vitro digestibility of flours and starches from taro cultivated in different regions of Thailand, that is, Kanchanaburi (KB), Chiang Mai (CM), Phetchaburi (PB) and Saraburi (SB). Taro starches were extracted from taro flours using either water or alkaline extraction. The taro flours had significantly (P ≤ 0.05) larger particle size, higher pasting and gelatinisation temperatures, and resistant starch content but lower total starch content, whiteness (L* value), paste viscosities and clarity than their corresponding extracted starches. All the taro starches exhibited polygonal and irregular granules and gave A-type X-ray diffraction pattern. The alkaline-extracted taro starches had significantly (P ≤ 0.05) higher extraction yield, total starch content, L* value, pasting and gelatinisation temperatures, and paste clarity but lower granular size, amylose content, resistant starch content, paste viscosities and relative crystallinity than their water-extracted counterparts.