Chen Jianchu

Optimization of vacuum cooling treatment of postharvest broccoli using response surface methodology combined with genetic algorithm technique

Abstract In this paper, the effects of vacuum cooling factors on the weight loss of postharvest broccoli were initially investigated. In sequence, the vacuum cooling treatment conditions were optimized using the response surface methodology (RSM) combined with the genetic algorithm (GA) technique. Fresh broccoli samples were harvested from a Chinese farm, and the green heads of selected samples were cut into smaller pieces, with diameters approximately 3–4 cm, and sequentially equilibrated to room temperature. Pressure (200–600 Pa), broccoli weight (200–500 g), water volume (2–6%, v/v) and time (20–40 min) were used as factors, and weight loss and end temperature were recorded as responses. The GA was employed to find the optimal condition for processing broccoli, and its initial solution was obtained from the RSM. The results demonstrate a good performance of the GA for the optimization of the broccoli cooling process. The best conditions of vacuum cooling process were as follows: a weight between 273.5 g and 278.0 g, a water volume of 3.0% v/v, a processing time of 40 min, a pressure of 200 Pa, and a weight loss and end temperature of 0.34 ± 0.01% and 2.0 ± 0.0 °C, respectively, leading to a percentage of profit of 99.66 ± 0.01%.

Detection of ten biogenic amines in Chinese commercial soybean paste by HPLC

ABSTRACT This paper aimed to develop a high-performance liquid chromatography (HPLC) method that can simultaneously detect ten biogenic amines (BAs) in commercially available soybean paste and to determine the contents of BAs in these products. Heptylamine (Hep) was used as the internal standard reagent and benzoyl chloride as the sample derivatization reagent; Inertsil ODS-3 chromatographic column was set as the stationary phase while the acetonitrile and 5 mmol/L ammonium acetate solution as the mobile phases; the samples were treated with gradient elution and detected at 254 nm (UV). Perchloric acid solution (0.4 mol/L) was employed as the sample extraction solvent to determine the contents of ten BAs in soybean paste products. All BAs were separated within 20 min. The methodological validation suggested good linearity, whereas the linear correlation coefficient of all standards was greater than 0.99 with the linear range of 0.1–80 μg/g, detection limits of 0.01–0.03 μg/g, and quantitation limits of 0.03–0.10 μg/g. For 17 commercially available soybean paste products involved in our study, different samples were distinguished from each other not only by the dramatic differences in the contents of BAs but also by the variance in BA types. Of these BAs, tyramine (Tyr) and agmatine (Agm) were found to be the highest contents in soybean paste products; the contents of histamine (His), 2-phenylethylamine (Phe), serotonin (Ser), spermidine (Spd), and putrescine (Put) were lower, followed by cadaverine (Cad), tryptamine (Try), and spermine (Spm). This method proved to be highly sensitive and effective in determining the contents of BAs in soybean paste products; there was a dramatic difference in the contents of ten BAs among different soybean paste products.

Studies on cathepsin L in the surimi of southern blue whiting.

According to the conventional method,actomyosin was extracted from the surimi of southern blue whiting (Micromesistius australias). After Sepharose-6B gel filtration of the actomyosin obtained,cathepsin L activity was monitored in each of the fractions collected. The results showed that the activity values in the actomyosin samples were much higher than that in the washing water,suggesting that cathepsin L could not be removed completely during conventional leaching and still remained in actomyosin sample. Further purification of actomyosin by dilution-precipitation could not remove cathepsin L effectively,indicating that cathepsin L might be dissolved together with actomyosin in the presence of high ion-strength solutions. The profile of the gel filtration showed hat the main peak of cathepsin L was obviously separated from that of actomyosin,suggesting that cathepsin L was non-binding with actomyosin. Fractions that showing the main peak of cathepsin L were pooled to be called L_ mix ,partially purified cathepsin L. L_ mix could strongly hydrolyze Z-Phe-Arg-MCA,a specific substrate for cathepsin L,rather than Z-Arg-Arg-MCA,spcefic substrate for cathepsin B,nor Arg-MCA,substrate for cathepsin H,as well as Boc-Gln-Ala-Arg-MCA,substrate for trypsin and trypsin-like proteases. The above results indicate that L_ mix was a crude cathepsin L. Cathepsin L specific inhibitors,such as E-64,specific inhibitor for cathepsins,and leupeptin,inhibitor for both cathepsins and trypsin-like proteases,could suppress the activity of L_ mix completely. Activators for cathepsin L,such as DTT,EDTA+DTT,could effectively improve the activity of L_ mix . As a result,the effect of activators and inhibitors confirmed the partially purified crude enzyme,L_ mix ,to be a thiol-type cysteine protease. The temperature dependence and pH dependence of the activity of L_ mix were also investigated. L_ mix had optimum temperature of 45 ℃ which was right in the temperature range of modori phenomena. L_ mix had optimum pH of 5.5,but kept high residue activity near neutral pH,and the pH range of surimi processing,suggesting its high potential ability in modori phenomena.