Abstract Flaxseed (Linum usitatissimum L.), one kind of common oilseeds, has many biologically active compounds including α-linolenic acid (ALA), lignan and dietary fiber. At present, the research of flaxseed is focused on biological and clinical studies of its compounds. However, the studies of flaxseed protein obtained generally from flaxseed cake, are relatively limited. As many other kinds of plant proteins, flaxseed protein presents many excellent functionalities which can be used for food applications. Many evidence have showed that flaxseed protein hydrolysates can provide health benefits to our body, such as anti-bacterial activity, antioxidant capacity and angiotensin-converting enzyme inhibition ability. Therefore, in order to make better use of flaxseed protein in foods, the extraction, functionalities and applications of flaxseed protein were reviewed in this paper. In addition, the preparation of flaxseed protein hydrolysates was discussed.

Background: To identify the critical amino acid residues that contribute to the high enzyme activity and good thermostability of Yersinia enterocolitica subsp. palearctica (Y. NSN), 15 mutants of Y. NSN were obtained by site-directed mutagenesis in this study. And their enzyme activity and thermostability were assayed. Effect of several factors on the enzyme activity and thermostability of Y. NSN, was also investigated. Results: The results showed that the I203F and D264E mutants retained approximately 75% and 70% enzyme activity, respectively, compared to the wild-type enzyme. In addition to the I203F and D264E mutants, the mutant E202A had an obvious influence on the thermostability of Y. NSN. According to the analysis of enzyme activity and thermostability of Y. NSN, we found that Glu202, Ile203 and Asp264 might be the key residues for its high enzyme activity and good thermostability. Conclusions: Among all factors affecting enzyme activity and thermostability of Y. NSN, they failed to explain the experimental results well. One reason might be that the enzyme activity and thermostability of Y. NSN were affected not only by a single factor but also by the entire environment.

ABSTRACTIn this work, the mixture of alginate and soy protein isolate used as a wall material was developed to encapsulateEnterococcus faecalis HZNU P2 (E. faecalis HZNU P2). The survival ability in the simulated gastric fluid (SGF) and bile salt solution, storage stability at different temperatures and release properties in the simulated intestinal fluid (SIF) of encapsulated cells were assessed. The results showed that encapsulation could offer sufficient protection toE. faecalis HZNU P2. The viability of encapsulatedE. faecalis HZNU P2 did not decrease in SGF at pH 2.5 or 2.0 after 2 h incubation, while free cells were reduced from 11 to 9.85 log CFU/mL in SGF (pH 2.5) at the same exposure time. Only minor viability of encapsulatedE. faecalis HZNU P2 lost in 1.0 or 2.0% bile salt solution for 1 or 2 h exposure, compared with no survival of freeE. faecalis HZNU P2 under the same conditions. EncapsulatedE. faecalis HZNU P2 was completely released from the microspheres in SIF within 1 h. The viability of encapsulatedE. faecalisHZNU P2 stored for two weeks at 4°C was fully retained. Viabilities of encapsulatedE. faecalis HZNU P2, 9.6 and 9.0 Log CFU/g were obtained at 25 and 37°C after 21 days storage, respectively. However, around 1.0 log CFU/mL of free cells was reduced after two weeks storage at 4°C. EncapsulatedE. faecalis HZNU P2 using soy protein isolate and alginate as wall materials could play an important role in food applications.

In this work, alginate-whey protein was used as wall materials for encapsulating Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus). The characteristics of encapsulated and free L. bulgaricus showed that the free L. bulgaricus lost viability after 1 min exposure to simulated gastric fluid (SGF) at pH 2.0 and 2.5. However, the viability of encapsulated L. bulgaricus did not decrease in SGF at pH 2.5 for 2 h incubation. The viable numbers of encapsulated L. bulgaricus decreased less than 1.0 log unit for 2 h incubation in SGF at pH 2.0. For bile stability, only 1.2 log units and 2.0 log units viability of the encapsulated L. bulgaricus was lost in 1 and 2% bile for 1 h exposure, respectively, compared with no survival of free L. bulgaricus under the same conditions. Encapsulated L. bulgaricus was completely released from the microspheres in simulated intestinal fluid (SIF, pH 6.8) in 3 h. The viability of the encapsulated L. bulgaricus retained more 8.0 log CFU/g after stored at 4°C for four weeks. However, for free L. bulgaricus, only around 3.0 log CFU/mL was found at the same storage conditions. Results showed that the encapsulation could improve the stability of L. bulgaricus.

Date is the most popular fruit in middle-east countries. However, the date production process is accompanied by a substantial increase of loss during picking, storage, commercialization and conditioning process. Date and their byproducts have many essential elements for the growth of microorganisms. Thus, they can be converted into value-added compounds through biotechnology. In this paper, date and their processing byproducts used as substrates for producing value-added products such as organic acids, exopolysaccharide, antibiotics, date flavored probiotic fermented dairy, bakery yeast, etc, were reviewed.

Bacterial pollution is a great risk for human health. Nanotechnology offers a way to develop new inorganic antibacterial agents. Nano-inorganic metal oxide has a potential to reduce bacterial contamination. MgO is an important inorganic oxide and has been widely used in many fields. Many studies have shown that MgO nanoparticles have good antibacterial activity. Therefore, in this paper, the main synthesis methods, antibacterial activity and antibacterial mechanisms of MgO nanoparticles are reviewed.

The effect of calcination conditions on the size and killing activity of CaO nanoparticles towards L. plantarum was studied in this paper. The results showed that CaO nanoparticles with a diameter of 20 nm could be obtained under the investigated conditions. The lethal effect of CaO nanoparticles after incubation of 6 or 24 h increased with increasing calcination time. Using CaO-SA, CaO-SB, and CaO-SC after a 24-h exposure, 2.25, 3.37, and 5.97 log L. plantarum were killed, respectively, at a concentration of 100 ppm. The current results show that the use of CaO nanoparticles as antibacterial agents has significant potential in food-relevant industries.

The antibacterial activity of MgO nanoparticles prepared by a sonication method was evaluated in this paper. The effect of calcination conditions on the size and antibacterial activity of MgO nanoparticles was investigated. MgO nanoparticles were characterized for purity (TGA), crystallinity and crystal size (XRD), particle size and morphology (TEM) and surface area (BET). Results showed that the smallest size of 6 nm could be obtained. The lethal effects of nanocrystalline MgO were evaluated on Lactobacillus plantarum. At a concentration of 100 ppm, the killing effect of MgO was close to 1 log reduction for L. plantarum after 24 h exposure. At 1000 ppm and 24 h exposure, the killing effect of MgO was more than a 2.8 log reduction. With the increase of calcination time, the lethal effect of MgO nanoparticles increased after 6 h or 24 h exposure at 100 ppm or 1000 ppm. 2.86 log and 2.89 log were killed at 1000 ppm after 24 h exposure using the sample MgO, sonication, A, and the sample MgO, sonication, B, respectively. When the sample MgO, sonication, C, was used, the lethal quantity of L. plantarum was increased to a 3.36 log reduction.

Encapsulation and immobilization technology is important for the food processing and bioengineering industries. Chitosan is a natural polysaccharide prepared by the N - deacetylation of chitin. It has been widely used in food and bioengineering industries, including the encapsulation of active food ingredients, in enzyme immobilization, and as a carrier for controlled drug delivery, due to its significant biological and chemical properties such as biodegradability, biocompatibility, bioactivity, and polycationicity. In this work, chitosan nanoparticles and nanofibers used to encapsulate bioactive substances and immobilize enzymes were reviewed. Preparation of chitosan nanoparticles and nanofibers, including the work achieved in our group on chitosan nanoparticles for enzyme immobilization, were also introduced. Some problems encountered with nano - structured chitosan carriers for bioactive substance encapsulation and enzyme immobilization were discussed, together with the future prospects of such systems.

Effects of various factors, such as pH, ionic strength, glutaraldehyde concentration, enzyme amount and immobilization time, on enzyme activity were investigated. The immobilization conditions were optimized by orthogonal experiments. Characterizations of immobilized nuclease p1 were also evaluated. Through orthogonal optimization, the optimal immobilization conditions were as follows: pH 5.6, ionic strength 0.125, glutaraldehyde concentration 0.20% and immobilization time 2.0 h. Optimal pH of immobilized enzyme was 5.8. Optimal temperature of immobilized enzyme was 70ºC. Thermal, operational and storage stabilities of the enzyme were improved after it was immobilized on DEAE cellulose. Michaelis constant Km of immobilized enzyme at 69ºC was found to be 27.21 g/l by the Lineweaver-Burk plot.

The sorption of nuclease P1 onto chitosan nano-particles is studied in this paper. The effect of some adsorption kinetics factors such as nuclease P1 concentration, chitosan nano-particles solution concentration, adsorption temperature, chitosan nano-particles size, solution pH, etc. is investigated. Adsorption of nuclease P1 onto chitosan nano-particles is fitted into Lagergren first-order equation at initial nuclease P1 concentration of 3.0 mg/mL. The first-order constant for nuclease P1 is 22.98 h-1. When nuclease P1 concentration is controlled into certain region, the adsorption fits into Freundlich isothermal linear equation. A mechanism of adsorption for nuclease P1 is proposed by analyzing IR spectra. The IR spectra shows that the hydrogen bond might be the main force between the hydroxyl group, the NH2 group and the nuclease P1.

MgO is an important inorganic material, which can be used in many aspects, such as catalyst, toxic-waste remediation agent, adsorbent, and others. In order to make use of MgO, nano-MgO was prepared by ultrasonic method using Mg (CH3COO)2.2H2O as precursor, NaOH aqueous solution as precipitant in this paper. Effect factors on MgO nano-particle size were investigated. Characteristics of samples were measured by TGA, XRD, TEM, and others techniques. The results showed that the size of nano-MgO about 4 nm could be obtained under the following conditions (ultrasonic time 20 min, ultrasonic power 250 W, titration rate of NaOH 0.25 mL/min, NaOH concentration 0.48 mol/L, calcinations temperature 410 °C, calcination time 1.5 h, heating rate of calcination 5 °C/min). It was a very simple and effective method to prepare nano-MgO.