Hanhua Liang

Investigation on ultrasound assisted extraction of saikosaponins from Radix Bupleuri

n Abstractn n Ultrasound assisted extraction (UAE) of saikosaponins from Radix Bupleuri (Bupleurum Chinense DC) was studied. The effects of various factors such as time (t), temperature (T), ultrasound power (I), particle size (S), solvent to solid ratio (R) and solvent concentration (C) on the yield of target components were investigated. The experimental results indicated that the extraction by UAE is six times faster than those by conventional thermal extraction. It is also found that fast extraction rate was obtained in the first 30min of sonication. Prolonged sonication did not give a proportional increase in the yield. For the effect of ultrasound power, the maximum yield was obtained at the power level of around 21W. Scanning electron microscope (SEM) images of the plant cells after UAE treatment were obtained to provide visual evidence of the sonication effect. The effects of particle size, solvent to solid ratio and solvent concentration on the yield are also discussed. The preliminary optimum conditions for UAE of saikosaponins were found at time of 30min, temperature of 80°C, power of 21W, particle size <0.3mm, solvent to solid ratio of 25ml/g and solvent concentration of 50%.n n

Properties of tea-polyphenol-complexed bromelain

Tea polyphenols extracted from Chinese green tea were used to complex and separate bromelain from pineapple juice. The antioxidant activity of tea polyphenols and their effects on the properties of bromelain were studied. The thermal stability of bromelain was enhanced after complexing with tea polyphenols. By complexing, the activity half-life of bromelain at 60°C was lengthened from 60 to 105 min. The improved thermal stability of the tea-polyphenol-complexed (TPC) bromelain is attributed to the antioxidant activity of tea polyphenols. Iso-electric focusing showed that six iso-enzymes fractions of bromelain could complex tea polyphenols with no change in their iso-electric points. Complexing with tea polyphenols did not change the optimum temperature (60°C) for the enzyme activity but the optimum pH value range was narrowed down from pH 6.8–9.0 to around 7.8. The Michaelis constant (K) of the TPC bromelain for casein substrate was determined to be 1.42×10−5 mol/l, higher than that of free bromelain (8.06×10−6 mol/l). Tea polyphenols were found to act as a competitive inhibitor on bromelain in the hydrolysis of casein.

Size-dependent colorimetric visual detection of melamine in milk at 10 ppb level by citrate-stabilized Au nanoparticles

In this paper, we demonstrate a colorimetric visual detection of melamine in milk simply using citrate-stabilized Au nanoparticles (NPs). Due to strong interaction between melamine and Au NPs, all of the Au NPs sensors present a significant and sensitive color change in the presence of ppb-level melamine, which can be directly observed by the naked eye and monitored by UV-vis absorbance spectra. Au NPs size dependence on the visual detection sensitivity of melamine is firstly studied in detail. The visual detection sensitivity can be significantly improved from 15 ppb to 5 ppb when increasing the Au NPs size from 15 to 30 nm, and the optimized Au NPs size of the visual detecting sensor was determined to be 30 nm. The pH effect on the sensitivity results show that the optimal pH value was 3–4 and this approach shows excellent selectivity for melamine over the use of other molecules. More importantly, this size- and pH-optimized Au NPs sensor was successfully applied to visually detect a milk sample. As low as 10 ppb melamine in milk could be distinguished upon a color change of solution within five minutes.

Modeling of supercritical fluid extraction from Hippophae rhamnoides L. seeds

Modeling of supercritical CO2 extraction of Hippophae rhamnoides L. seed oil was studied at 15 to 30 MPa and 30 to 45°C. Four mean Hippophae rhamnoides L. particle sizes raging from 0.4 to 1.0 mm were tested. CO2 flow rate ranged between 0.05 and 0.2 m3 h− 1. A new method that can be used for the simulation of SCFE process was presented. The model was based on differential mass balances along the extraction bed. The equilibrium between the solid and the fluid phase appeared to be the controlling step during the extraction fast period. By a series of transforms and derivatives, the explicit expression of the oil yield, q(z,t), was obtained. It can be used for the SCFE process simulation. In this model, only one adjustable parameter was used: the equilibrium constant between the solvent and the free solute phase, K. A fairly good fitting of the experimental data was obtained by setting K = 10. The Hippophae rhamnoides L. seed oil extraction process was modeled as a desorption process from the seed matter plus a small mass‐transfer resistance.

Modeling and fouling mechanisms for ultrafiltration of Huanggi (Radix astragalus) extracts

A semi-empirical model has been developed in ultrafiltration of huanggi (Radix astragulus) extracts. Three major fouling resistances were quantified with transmembrane pressure (TMP) ranged from 0.4 to 0.8 bar and process time lasted for 120 min. Adsorption grew fast at the initial 15 min and its contribution was more significant at 0.4 bar, nearly 50%. Pore blocking almost kept the same values of 1.28, 1.84, and 2.39 at pressures of 0.4, 0.6, and 0.8 bar, respectively. Cake layer grew linearly at 0.4 bar but it increased rapidly as the TMP arose. With the TMP increased, the contribution of cake layer became more significant, almost 75% at 0.8 bar which was triple of that at 0.4 bar. Prediction of flux decline fitted quite well with the experimental data, all within 5% errors. It demonstrates that adsorption, pore blocking, and cake layer are the main mechanisms for membrane fouling during the process.

Multiresponse optimization by a normalized function approach

Abstract A simple new method, called Normalized Function Approach (NFA), was developed for simultaneously optimizing systems defined by several output variables (response functions) and a common set of input variables (factors). For each original response function the difference between the estimated response and its individual optimum was evaluated and normalized over the experimental space. The individually normalized functions were then weighted for their importance and combined into an overall function using a “sum of squares” approach. Simultaneous optimization was completed by minimizing the overall function. Some numerical examples were considered to introduce the new method and several reported applications in the food area were used for verification and comparison with other multiresponse optimization methods.

Ultrasonic inactivation of soybean trypsin inhibitors

Abstract Soybean trypsin inhibitors (TI) in soymilk were treated by heat and ultrasound of 20 kHz. The influence of several factors (temperature, time of treatment, pH, ultrasonic power, soymilk concentration, and ionic strength) on inactivation of TI was investigated. The results of the experiment shown that temperature was the major factor to affect the inactivation of TI, and treatment time was the next important factor. Under the experimental conditions of temperature 80°C, ultrasonic power of 150 w, and pH 7.0 for 5 min treatment, TI in soymilk sample could be inactivated by 73%. The retained 27% TI was difficult to inactivate. This residual component is mainly Bowman-Birk inhibitor (BBI) which is extremely stable to heat as well as ultrasound of 20 kHz.