Structure of the zein protein as treated with subcritical water

In the present study, we investigated the structure and selected functional properties of zein protein as treated with subcritical water. The results showed that subcritical water treatment, with different time (20–120 min) and temperatures (110–170°C), increased the solubility, foam capacity, and foam stability of zein protein significantly (p < 0.05). Analyses of particle size analysis, differential scanning calorimetry, circular dichroism spectra, scanning electron microscopy, and atomic force microscopy indicated that subcritical water treatment improved the thermal stability and the denaturation temperature of zein protein, as well as increased slightly in the percentage of ordered structural elements within the protein molecule. In addition, the particle size of zein protein increased and the surface became rough significantly. All these suggested that subcritical water is a potential green chemical, which could highly be used to change the structure and improve the functional properties of zein protein.     

亚临界水水解脱脂高温芝麻饼粕中蛋白与糖类研究

亚临界水是一种绿色化学反应介质,已经应用于农副产品加工。为拓展芝麻饼粕的利用途径,采用亚临界水将脱脂高温芝麻饼粕中的水不溶性蛋白与糖分别水解为水溶性小分子物质。以上清液中蛋白、多肽和氨基酸、还原糖浓度为指标,考察亚临界水温度、时间与pH对降解芝麻饼粕中蛋白与糖的影响。电泳结果显示亚临界水可以有效将因高温变性形成的高分子蛋白降解成低分子蛋白;亚临界水温度、加热时间与pH是芝麻蛋白和糖类水解的显著影响因素;选择适宜的亚临界水条件可以将原上清液中(0.08±0.01)mg/mL、(6.40±0.08)mg/mL、(1.2±0.1)μmol/L、(0.36±0.01)mg/mL的蛋白、多肽、氨基酸与还原糖浓度增加到(5.29±0.08)mg/mL、(22.28±0.05)mg/mL、(185.5±2.7)μmol/L和(4.28±0.12)mg/mL。     

Decomposition kinetics of monoacyl glycerol and fatty acid in subcritical water under temperature-programmed heating conditions

The decompositions of monocaprylin, monocaprin, monolaurin and their corresponding fatty acids in subcritical water were measured under temperature-programmed heating conditions where the reaction temperature was linearly increased from room temperature to 350 °C at specified rates to estimate the activation energies E_i and the frequency factors k_i0 for the decompositions. The decompositions of both monoacyl glycerol and fatty acid obeyed first-order kinetics, and the decomposition of a monoacyl glycerol proceeded consecutively to form its constituent fatty acid and then further decomposition compounds. There was a tendency for both the E_i and k_i0 values for a monoacyl glycerol or fatty acid with a longer acyl chain to be smaller, and it was shown that the enthalpy–entropy compensation held for the decompositions of monoacyl glycerols and fatty acids as well as for those of fatty acid esters with various acyl and alkyl chains in subcritical water.     

Capillary electrophoresis separation of rosemary antioxidants from subcritical water extracts

In this work, the possibilities of the combined use of subcritical water extraction (SWE) and capillary electrophoresis (CE) are established through the separation of antioxidants from rosemary (Rosmarinus officinalis L.). A new CE method is developed that allows the separation of different antioxidants found in the SWE fractions. The CE method is reproducible, efficient and fast, allowing the analysis of complex rosemary extracts in less than 16 min. The CE method is compared with a published reversed-phase high-performance liquid chromatography (RP-HPLC) procedure, both using diode-array detection. The main advantages of CE compared with HPLC are its higher resolving power and its different selectivity, which is demonstrated to be useful for the detection of some very polar compounds that cannot be analyzed by RP-HPLC. Moreover, the possibilities of the CE approach for following the degradation of antioxidants is also demonstrated. To our knowledge, this is the first work showing the high potential of the combined use of SWE and CE.     

Facts about the formation of new antioxidants in natural samples after subcritical water extraction

Subcritical water extraction (SWE) is a very promising technique for obtaining bioactives (mainly antioxidants) from natural sources; even if sometimes the high operation temperatures have been suggested as responsible for thermal degradation of bioactives, the fact is that this type of extraction processes may generate new bioactive (antioxidant) compounds. The present study involved the analysis of antioxidants either naturally found in raw samples and/or those formed during extraction via Maillard reaction and other chemical events. Samples of different nature like microalgae (Chlorella vulgaris), algae (Sargassum vulgare, Porphyra spp., Cystoseira abies-marina, Sargassum muticum, Undaria pinnatifida, and Halopitys incurvus) and plants (rosemary, thyme and verbena) were studied. Amino acid availability, sugar content, fluorescence and absorbance at different wavelengths were determined to follow chemical changes due to reactions such as Maillard, caramelization and thermoxidation. Folin reaction also provided information related to total phenol content of the samples. ABTS⁺, peroxyl as well as superoxide radical scavenging assays were used to measure the antioxidant capacity of the extracts. Results obtained from this study suggest that neoformed compounds derived from Maillard, caramelization and thermoxidation reactions affect the overall antioxidant capacity of water subcritical extracts depending on the nature of the sample. The brown algae U. pinnatifida was the sample in which these chemical events contributed to a higher extent to improve the antioxidant capacity (from 0.047 to 1.512 mmol/g and from 45.356 to 1522.692 μmol/g for the TEAC and ORAC_FL methods, respectively) when the extraction temperature was raised from 100 to 200 °C. To the best of our knowledge, this is the first work supporting the formation of neoantioxidants in natural complex matrices during subcritical water extraction.     

Effects of sodium chloride on the degradation of hexoses and the hydrolysis of sucrose in subcritical water

The effects of sodium chloride on the degradation of hexoses at 220 °C and the hydrolysis of sucrose at 170 °C in subcritical water were examined. Sodium chloride accelerated the degradation at 220 °C of any hexose, especially the degradation of galactose which significantly accelerated depending on the sodium chloride concentration. On the other hand, the hydrolysis of sucrose at 170 °C was not affected by sodium chloride.     

Thermal decomposition and oxidation of β-caryophyllene in black pepper during subcritical water extraction

Subcritical water extraction is an efficient technique for extracting components from various plants by changing the polarity of water. β-caryophyllene is a natural bicyclic sesquiterpene with the highest content found among black pepper essential oils. In this study, the efficiency of extraction and yield of β-caryophyllene from black pepper were investigated using a subcritical water extraction technique. The optimal conditions of β-caryophyllene (1.19 ± 0.38 mg/g), and caryophyllene oxide (0.82 ± 0.38 mg/g) were obtained from black pepper under extraction conditions of 170 °C/10 min, and 200 °C/15 min, respectively. As the extraction temperature was increased, β-caryophyllene oxidation proceeded and the extraction content of caryophyllene oxide increased. It is anticipated that both β-caryophyllene and caryophyllene oxide with high biological activity can be used to selectively extract compounds using subcritical water extraction, which will be helpful in industrial applications.     

High antioxidant activity of coffee silverskin extracts obtained by the treatment of coffee silverskin with subcritical water

Coffee silverskin (CS) is a thin tegument of the outer layer of green coffee beans and a major by-product of the roasting process to produce roasted coffee beans. CS extracts obtained by the treatment of CS with subcritical water at 25-270°C were investigated for their antioxidant activity using hydrophilic oxygen radical absorption capacity (H-ORAC) and DPPH radical scavenging capacity assays. The antioxidant activity increased with increasing the extraction temperature and the highest activity was observed with the extracts obtained at 270°C. The H-ORAC and DPPH values of the extracts were 2629±193 and 379±36μmol TE/g of CS extract, respectively. High correlation (R=0.999) was observed between H-ORAC and DPPH values for the CS extracts. High correlation of the antioxidant activity was also observed with protein and phenolic contents in the extracts. The CS extracts could be useful as a good source of antioxidative materials.     

Production of functional substances from black rice bran by its treatment in subcritical water

Black rice bran was treated by water and subcritical water at temperatures ranging from 20 to 260 °C for 5 min and at 200 and 260 °C for 5-120 min. The bran extracts were analyzed for their radical scavenging activity, protein and carbohydrate contents, molecular-mass distribution, antioxidation activity, emulsifying activity, and emulsion-stabilizing activity. The radical scavenging activity and the protein content of the extract were higher at higher treatment temperature. The carbohydrate content also increased with increasing temperature up to 200 °C, then steeply decreased at the temperatures higher than 200 °C. The bran extracts treated at 260 °C for 5 min exhibited a suppressive activity toward autoxidation of linoleic acid with the increasing the weight ratio of the bran extract to linoleic acid. The bran extracts prepared at 40-200 °C for 5 min showed the emulsifying- and emulsion-stabilizing activities, while the extracts prepared at 220-260 °C were low in the activities.     

Continuous preparation of O/W nano-emulsion by the treatment of a coarse emulsion under subcritical water conditions

A coarse oil-in-water (O/W) emulsion, the oil phase of which was octanoic acid, was prepared at a very low surfactant concentration using a rotor/stator homogenizer. The emulsion was passed in a stainless steel tube immersed in an oil bath at 220 °C at a residence time of 60 s, and then mixed with the surfactant solution to produce a finely dispersed emulsion. The diameter of oil droplets in the fine emulsion was ca. 40 nm at the weight ratio of surfactant to oil of ca. 0.35 or higher.     

Enhanced extraction of flavanones hesperidin and narirutin from Citrus unshiu peel using subcritical water

Flavanones including hesperidin and narirutin constitute the majority of the flavonoids that occur naturally in citrus fruits. The main purpose of this study was to extract valuable natural flavanones from agricultural by-products such as citrus peels using subcritical water extraction (SWE). Thus, the application of SWE to extraction of flavanones hesperidin and narirutin from Citrus unshiu peel was evaluated, and the effect of key operating conditions was determined by varying the extraction temperature (110–200 °C) and time (5–20 min) under high pressure (100 ± 10 atm). The maximum yields of hesperidin (72 ± 5 mg/g C. unshiu peel) and narirutin (11.7 ± 0.8 mg/g C. unshiu peel) were obtained at an extraction temperature of 160 °C for an extraction time of only 10 min. These yields accounted for approximately 99% of the total amount of these flavanones in the original material. The SWE was compared with three conventional extraction methods in terms of the extraction time and recovery yields for hesperidin and narirutin. The hesperidin yield by SWE was more than 1.9-, 3.2-, and 34.2-fold higher than those obtained by extraction methods using ethanol, methanol, or hot water, respectively, and the narirutin yield was more than 1.2-, 1.5-, and 3.7-fold higher.     

Solubility and emulsifying properties of barley protein concentrate

Protein concentrates were produced from the flours of two barley cultivars (Bülbül and Tokak) by alkaline extraction procedure. The flour samples and their protein concentrates were examined by SDS-PAGE. Solubility properties of protein concentrates were investigated as a function of pH, NaCl concentration and protein concentration, whereas emulsifying properties were determined as a function of pH and protein concentration. The highest solubility was observed in water among the solvents studied, especially at pH values of 2, 10 and 11 as compared to the other ones. A decrease in solubility was determined with increasing ionic strength of NaCl solutions. The results suggested that emulsifying behavior of protein concentrates generally resembled their solubility behavior in water. Minimum solubility and emulsifying values were observed at pH 6, which is close to the isoelectric point of barley proteins. Both of these functional properties were improved below and above the isoelectric pH.     

Recovery of hesperidin and narirutin from waste Citrus unshiu peel using subcritical water extraction aided by pulsed electric field treatment

The objective of this study was to identify whether the efficacy of extracting hesperidin and narirutin from Citrus unshiu peel by-products can be increased by combining pulsed electric field (PEF) and subcritical water extraction (SWE). The samples were treated with a PEF at a strength of 3 kV/cm for 60 and 120 s. Subsequent SWE was conducted at extraction temperatures of 110–190 °C for 3–15 min. The concentration of hesperidin was highest at 46.96 ± 3.37 mg/g peel (dry basis) after PEF treatment at 120 s, combined with SWE at 150 °C for 15 min, while that of narirutin peaked at 8.76 ± 0.83 mg/g after PEF treatment at 120 s, integrated with SWE at 190 °C for 5 min. The concentrations of both hesperidin and narirutin increased with PEF treatment time. The PEF increased the amounts of hesperidin and narirutin extracted by 22.1% and 33.6%, respectively. This study demonstrate the potential of PEF pretreatment for enhancing the SWE of flavonoids from C. unshiu peel.     

Microstructural properties of fat during the accelerated ripening of ultrafiltered-Feta cheese

A commercial pregastric lipase was used to accelerate lipolysis of Iranian ultrafiltered-Feta (UF-Feta) cheese. Scanning electron microscopy images showed that with an increase in lipase levels from 2.0 to 6.0 g 100 kg⁻¹ of retentate, disruption of fat globules increased significantly. On day 3 of ripening and enzyme level of 2.0 g 100 kg⁻¹ of retentate, individual fat globules and fat aggregates were clearly observed on the cheese samples. An increase in the lipase level or ripening period resulted in an increase in the rate of disappearance of fat globules. After 20 days of ripening, no apparent fat globules were observed and fewer fingerprints and voids of free fat were detected, compared to when no enzyme was used.     

亚临界水萃取麦胚蛋白及其功能特性的研究

以小麦胚芽为原料,通过单因素和响应面分析实验对亚临界水萃取麦胚蛋白的工艺条件进行优化,并对其功能特性进行评价。结果表明,麦胚蛋白最佳提取条件为:萃取温度130℃,萃取时间15 min,料水比1∶20 g/m L,p H为9.4。在此条件下,麦胚蛋白的提取得率达42.25%,乳化活性为113.63 m~2/g,乳化稳定性为82.16%,起泡性为71.45%,起泡稳定性为36.05%,持水性为4.21%,持油性为4.49%,溶解度为60.93%。与传统碱溶酸沉法相比,亚临界水萃取麦胚蛋白在提取时间、提取率等方面均具有明显优势。      

Surface properties and behaviour on abiotic surfaces of Staphylococcus carnosus, a genetically homogeneous species

This work aimed to characterize the surface properties of Staphylococcus carnosus and the influence of different media on their ability to adhere and grow on industrial supports. As their colonization could be dependant of the strain, the genetic diversity of the strains was studied. The diversity of 13 strains analysed by pulsed-field gel electrophoresis revealed that the S. carnosus strains formed a homogeneous genetic group. Their surface properties, characterized by studying their affinity to solvents, were hydrophilic with a strong negative surface charge. The S. carnosus strain CIT 833 hardly adhered to polytetrafluoroethylene (PTFE) and stainless steel chips. Tryptic soy broth (TSB) was the most favourable medium for growth on stainless steel support while TSB/NaCl was better for growth on PTFE. Scanning electron microscopy (sem) showed that this strain weakly colonized both supports and did not form cell aggregates. Indeed, the strain did not synthesize polysaccharides. These results showed that S. carnosus adhered on different abiotic surfaces which are used in food factories but was not able to accumulate on these surfaces. The inability of S. carnosus to form biofilm could explain why S. carnosus is rarely isolated in meat processing environment.     

Development and evaluation of a novel biodegradable film made from chitosan and cinnamon essential oil with low affinity toward water

Combining antimicrobial agents such as plant essential oils directly into a food packaging is a form of active packaging. In this work chitosan-based films containing cinnamon essential oil (CEO) at level of 0.4%, .0.8%, and 1.5% and 2% (v/v) were prepared to examine their antibacterial, physical and mechanical properties. Scanning electron microscopy was carried out to explain structure–property relationships. Incorporating CEO into chitosan-based films increased antimicrobial activity. CEO decreased moisture content, solubility in water, water vapour permeability and elongation at break of chitosan films. It is postulated that the unique properties of the CEO added films could suggest the cross-linking effect of CEO components within the chitosan matrix. Electron microscopy images confirmed the results obtained in this study.     

亚临界水中甘油酯型鱼油水解工艺研究

研究亚临界水中鱼油水解制备游离型EPA和DHA,本试验以甘油酯型鱼油为原料,采用亚临界水作为其水解的反应介质,分别探讨了反应温度、反应时间、油水体积比和反应压力对其水解率的影响。在此基础上,采用正交试验对其水解工艺进行优化。结果表明,其较优水解工艺条件为反应温度330℃,反应时间30 min,油水体积比1∶3,反应压力15 MPa。在此条件下,甘油酯型鱼油水解率可达(91.04±0.39)%。水解产物经RP-HPLC检测分析,游离型EPA和DHA的得率分别为96.31%和83.85%。