Characterisation of a milk-clotting extract from Balanites aegyptiaca fruit pulp

Milk-clotting proteases were extracted and characterised from Balanites aegyptiaca fruit pulp traditionally used in sub-Saharan countries to thicken gruel. The aim was to improve the extraction conditions and milk-clotting in the context of future cheese making. B. aegyptiaca fruits were disinfected, husked and soaked in different buffers and saline solutions. The extracts obtained were diafiltered, concentrated and decoloured with active charcoal. The effects of extract concentration, milk pH and temperature on clotting-time were studied. The use of specific inhibitors showed that the B. aegyptiaca extract contains two types of proteases: an aspartic protease and a serine protease, with an optimum activity at pH 5.0 and pH 8.0, respectively, and an optimal temperature at 50 °C. The proteolytic activity is more thermostable than bovine chymosin at pH 5.0. Partial purification by anion exchange chromatography and sodium docecylsulphate polyacrylamide gel electrophoresis allowed separation of the two milk-clotting proteases.     

Effect of High Pressure and/or Temperature over Gelation of Isolated Hake Myofibrils

High hydrostatic pressure (HHP) processing was used to determine its ability to induce protein gelation. Isolated hake myofibrils were processed by HHP at 0, 150, 250, and 500 MPa (10?ºC/10 min) and/or by heating (90?ºC/20 min). The results were analyzed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), determination of sulfhydryl group contents, and dynamic rheometry measurements. FTIR data indicated that secondary protein structures exhibited a reduction in α-helix together with an increase in β-sheet as a result of protein denaturation caused by HHP. DSC showed that HHP induced a reduction in myosin denaturation temperature (T _peak) indicating protein unfolding. Protein gelation after HHP is based on physical (non-covalent) interactions which make more sulfhydryl groups available, while after heating, it is based on the formation of covalent (disulfide) bonds as a consequence of protein denaturation reducing the sulfhydryl groups. The combination of HHP and heating, particularly the latter, improved network stabilization. These results were reflected in the rheological changes, in which heated gels showed more elastic, cohesive, and time-stable networks than pressurized (non-heated) gels. The HHP effect provided softer, more flexible networks. The gel at 500 MPa was the most elastic and time-stable and exhibited the highest level of connectivity.     

Extraction of Antioxidants from Aloe vera Leaf Gel: a Response Surface Methodology Study

Extraction of antioxidants from aloe gel powder with water–ethanol solvents was studied using response surface methodology. The independent variables were solvent composition, temperature, extraction time, and the liquid-to-solid (L/S) ratio. The concentrations of potentially antioxidant compounds (aloin A and B, aloesin, total phenolics, and total carbohydrates) and a few indicators of antioxidant capacity (DPPH, FRAP, CUPRAC) served as the response functions. It was found that aloe gel contains both phenolic and non-phenolic antioxidants, and it was supposed that the phenolic fraction consists almost exclusively of chromones and anthrones. Different approaches to the optimization of extraction procedures are discussed, and here, the maximum recovery yield of antioxidants is achieved with 34 % ethanol at 60 °С and a L/S ratio of 46 in 1 h. The use of 90 % ethanol results in a higher antioxidant capacity of the product, but also results in a much lower extraction yield, decreasing the overall productivity of the process.     

Heat-induced gel formation of a protein-rich extract from the microalga Chlorella sorokiniana

Microalgae proteins are an underutilized biomass source for foods with unknown technofunctionalities. Heat-induced gel formation was used in this study to investigate the gelation properties of a protein-rich extract from the microalga Chlorella sorokiniana. Gel formation was achieved at a minimum protein concentration of 9.9 g/100 mL and a temperature of 61 °C was necessary to produce a stable gel network. Small-amplitude oscillatory shear measurements revealed that a weak gel was formed with tan δ > 0.1, which was also evident during backward extrusion measurements. The elasticity of the gels increased when the final T_set was increased and a maximum gel elasticity was obtained at T_set = 80 °C and a heating rate of 1 °C min⁻¹. Increasing the heating rate to 5 and 15 °C min⁻¹ negatively affected the gel strength. Additionally, increasing the ionic-strength and increasing or decreasing the pH negatively affected the gel network, which was related to a change in electrostatic interactions. The results obtained showed that it is possible to produce protein gels from water-soluble protein-rich extracts from Chlorella sorokiniana, which may simplify application of protein extracts from this microalga in foods.     

Gloss of thermally densified alder (Alnus glutinosa Goertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) wood veneers

Thermo-mechanical densification of wood is performed to improve physical and mechanical properties of wood. During this treatment aesthetic properties of wood, including gloss, also change. Therefore, the purpose of this study was to determine the effect of short-term thermo-mechanical (STTM) densification in different wood species (alder (Alnus glutinosa Goertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.)) on their gloss changes. Commercial wood veneers were densified in a hot plate press for 4 min at temperatures of 100, 150 and 200 °C, pressures of 4, 8 and 12 MPa. Gloss was evaluated at 20°, 60° and 85° angles of incident light using PICO GLOSS 503. Gloss measurements showed an enhancement of aesthetic properties of densified wood. Findings of this study indicated that both densification temperature and pressure have a significant effect on wood gloss. Gloss values of densified wood increased with increasing densification temperature and pressure for all investigated species. Compared to non-densified wood, gloss (85°) values (across/along the grain) for alder, beech, birch and pine increased after treatment to 2109.1/2376.9, 1728.6/2311.1, 2787.5/3000, and 2591.7/1216.7 %, respectively. The greatest gloss values were recorded at 200 °C and pressure of 12 MPa for all tested angles of incident light and for all densified wood samples. Gloss changes for birch were the highest, but the glossiest surface was observed for pine among all investigated species after wood densification.     

THE FORMATION OF HEAT AND ENZYME INDUCED (PLASTEIN) GELS FROM PEPSIN-HYDROLYZED SOY PROTEIN ISOLATE1

A gel prepared by heating pepsin-hydrolyzed soy protein isolate (HSPI) had a higher turbidity and viscosity and less solubility than did its starting hydrolyzate. The gelling characteristics of the heated hydrolyzate were possibly due to hydrophobic interactions, as opposed to peptide bond reformation. The presence of pepsin was found to be necessary for gel formation at 37°C but could be successfully replaced by heat. Incubation of the concentrated HSPI at 95°C for 30 min was optimal for heat-induced gel formation. When soy protein isolate (SPI) was hydrolyzed with papain or bacterial protease, little gelation occurred (either by heat or enzyme induced gelation treatments).     

Phytosanitary treatment of European pallets by microwave: developing a program to ensure compliance with ISPM 15 and monitoring its efficacy on the house longhorn beetle (Hylotrupes bajulus L.)

Microwave heating was recently approved by the FAO as a significantly effective phytosanitary treatment for wood packaging material. According to ISPM 15 (FAO 2009), the target organisms are eradicated if a temperature higher than 60 °C is maintained for 60 s across the entire profile of the board (i.e. 60 °C/60 s). A study using pallet boards was carried out in order to set up a treatment program that would meet ISPM 15 requirements in terms of wood temperature and insect mortality. A 4 m-long industrial tunnel oven (maximum power of 28.8 kW) was used to carry out the experiments. Temperature was measured by means of a VarioCAM^® infrared camera. The most relevant results found were: (i) achieving a mean temperature of 63.2 °C (Populus sp.) or 64.8 °C (Pinus sylvestris L.) on the upper surface of 22 mm-thick boards enabled compliance with FAO requirements (i.e. 60 °C/60 s), whatever the moisture content, basic density and initial temperature of the wood (provided the latter exceeded 0 °C); (ii) larvae >150 mg represented the most microwave-resistant life stage of Hylotrupes bajulus L.; (iii) the mortality rate of the larvae was influenced by the moisture content of the boards. Using the Gompertz model, the upper surface temperature was estimated that would be needed to achieve a 99.99683 % mortality rate (the Probit 9 mortality level of efficacy) for the most microwave-resistant life stage of H. bajulus. This temperature was estimated to be 46.8 and 57 °C for wood with >50 and <25 % moisture content, respectively.     

Isolation of angiotensin I-converting enzyme inhibitor from pepsin hydrolysate of porcine hemoglobin

Angiotensin I-converting enzyme (ACE) inhibitors have been widely used as antihypertensive agents. However, most synthetic ACE inhibitors ineluctably have severe side effects. Researchers have focused on various ACE-inhibitory peptides derived from dietary food. In the present study, we reported peptides produced from porcine blood, an important food in Asian countries. Through enzymatic hydrolysis, we found that peptides from this animal compound have ACE-inhibitory effects. Porcine hemoglobin was hydrolyzed using ordinary proteases, including alcalase, trypsin, neutral, papain, protamex, and pepsin. Results showed that pepsin was the most efficient protease in producing active peptides, and the pepsin hydrolysate of porcine hemoglobin showed the highest activity (IC₅₀ = 1.53 ± 0.03 mg/mL). Combining DA 201-C macroporous resin chromatography, Sephadex LH-20 gel chromatography, and reversed-phase high-performance liquid chromatography, the fraction 2-IV was purified from pepsin hydrolysis of porcine hemoglobin; this compound exhibited the highest ACE-inhibitory activity (IC₅₀ = 0.02 ± 0.01 mg/mL). Through Edman degradation, we also found that the exact amino acid sequence of fraction 2-IV was Gln–Glu–Leu–Pro–Gly. The results indicated that porcine hemoglobin peptides possessed significant ACE-inhibitory effect in vitro, which is an important complement of the previous work.     

Roles of components of rice-based fat substitute in gelation

The roles of maltodextrin, protein and fat in the gelation of the rice-based fat substitute were investigated. Rheological properties and gel strength of samples were measured. Results showed that the rising rates of both G′ and G″ of rice starch-based fat substitute were higher than those of rice-based fat substitute when temperature was lower than 35 °C. G′ was equal to G″ at 60 °C for 25% rice-based fat substitute whilst it was at 35 °C for rice starch-based fat substitute. The presence of rice protein and fat increased G′ and G″. Gel strength of rice-based fat substitute was lower than that of starch-based fat substitute at 25% solid content. However, gel strength of a fat substitute increased in the presence of protein. SEM showed that protein particles aggregated to gel. Therefore, protein in rice-based fat substitute gelled firstly, followed by maltodextrin which formed the main matrix of the rice-based fat substitute gel. Fat benefited for gel formation.     

Novel bioconversion of sodium glutamate to γ-amino butyric acid by co-culture of Lactobacillus plantarum K154 in Ceriporia lacerata culture broth

Co-cultivation was performed for optimization of microbial GABA production in Ceriporia lacerata cultures. C. lacerata was grown in a defined medium containing 3% glucose, 3% soybean flour, 0.15% MgSO₄, and 5% rice bran for 7 days at 25°C in a shaking culture, resulting in production of a culture with 0.63% (w/v) acidity, 11.2 g/L of mycelia, 3.0 g/L of exopolysaccharides, 6.24 unit/mL of α-amylase, 45.6 unit/mL of protease and 4.1 unit/mL of cellulase. Viable cell counts of Lactobacillus plantarum K154 co-cultured in C. lacerata culture broth were increased by 1×10¹⁰ CFU/mL. In co-cultivation with L. plantarum K154, 15.53 mg/mL of GABA was produced from sodium glutamate. A 40 kDa molecular weight protein co-produced with GABA by L. plantarum K154 was confirmed to be GAPDH based on protein sequencing. Co-cultivation of L. plantarum K154 in C. lacerata culture broth efficiently produced functional ingredients, including GABA, peptides, polysaccharides, and probiotics.     

Antimicrobial Properties of Ethylene Vinyl Alcohol/Epsilon-Polylysine Films and Their Application in Surimi Preservation

Polymer films based on ethylene vinyl copolymers (EVOH) containing a 29 % (EVOH 29) and a 44 % molar percentage of ethylene (EVOH 44), and incorporating ε-polylysine (EPL) at 0 %, 1 %, 5 % and 10 % were successfully made by casting. The optical properties and the amount of EPL released from the films to phosphate buffer at pH 7.5 were evaluated, films showing great transparency and those of EVOH 29 copolymer releasing a greater amount of EPL. The antimicrobial properties of the resulting films were tested in vitro against different foodborne microorganisms and in vivo in surimi sticks. With regard to the antimicrobial capacity tested in vitro in liquid medium at 37 °C and 4 °C against Listeria monocytogenes and Escherichia coli over a period of 72 h, films showed a considerable growth inhibitory effect against both pathogens, more notably against L. monocytogenes, and being EVOH 29 more effective than EVOH 44 films. At 37 °C, total growth inhibition was observed for EVOH 29 films incorporating 10 % EPL against both microorganisms whereas the copolymer EVOH 44 did show total inhibition against L. monocytogenes and the growth of E. coli was reduced by 6.64 log units. At 4 °C, no film was able to inhibit completely bacterial growth. Scanning electron microscopy micrographs showed corrugated cell surfaces with blisters and bubbles, and collapse of the cells appearing shorter and more compact after treatment with EPL. Finally, the films were successfully used to increase the shelf life of surimi sticks. The results show the films developed have a great potential for active food packaging applications.     

Changes in the antioxidant capacity and phenolic compounds of <Emphasis Type="Italic">maesil</Emphasis> extract during one-year fermentation

This study aimed to identify the effects of soaking time and fermentation temperature and period on the total phenolics, total flavonoids, and antioxidant activity of maesil extract. Green maesil fruits were fermented with brown sugar at 15 or 25°C for one year. After soaking maesil for 90 days, the fruits were removed and the remaining liquid was further ripened for 275 days, whereas other samples continued to ferment with maesil until 365 days. Total phenolics, total flavonoids, and antioxidant activities of the extracts fermented with maesil for one year were higher compared with those wherein the fruits were removed at day 90. The total phenolic and total flavonoid contents were relatively higher at 15°C, whereas the ABTS and ferric-reducing antioxidant power (FRAP) activities were significantly higher at 25°C. The total phenolic and total flavonoid contents highly correlated with the antioxidant activities. These results show that fermentation temperature plays a critical role in enhancing the phenolic compounds and antioxidant activity of maesil extract.     

Characterization of proso millet starches from different geographical origins of China

The influence of geographical origin (Lvliang, Baotou, Gulang, and Jilin) on the physicochemical properties of proso millet (Panicum miliaceum L.) starches from China, and starch chemical compositions were studied. Scanning electron microscopy showed that starch granules from millet starches were polygonal and spherical with smooth surfaces with sizes ranging from 2.5 to 12 μm. X-ray diffraction showed that millet starches were typical of A-type starch granules with a mean crystallinity of 35.81%. The transition temperatures (T _o , T _p , and T _c ) and enthalpy of gelatinization (ΔH) of Lvliang, Baotou, Gulang, and Jilin proso millet starches were 66.81 to 70.01°C, 72.79 to 76.55°C, 78.30 to 82.44°C, and 10.4 to 14.46 J/g, respectively. Significant differences (p<0.05) were observed for the amylose content, granule size, peak temperature, gelatinization enthalpy, and peak viscosity temperature among the millet starches. Millet starches may have potential applications in production of puffed starch food products and other food items.     

Assessment of the production of Bacillus cereus protease and its effect on the quality of ultra-high temperature-sterilized whole milk

Bacillus cereus is one of the most important spoilage microorganisms in milk. The heat-resistant protease produced is the main factor that causes rotten, bitter off-flavors and age gelation during the shelf-life of milk. In this study, 55 strains of B. cereus were evaluated, of which 25 strains with protease production ability were used to investigate proteolytic activity and protease heat resistance. The results showed that B. cereus C58 had strong protease activity, and its protease also had the highest thermal stability after heat treatment of 70°C (30 min) and 100°C (10 min). The protease was identified as protease HhoA, with a molecular mass of 43.907 kDa. The protease activity of B. cereus C58 in UHT-sterilized whole milk (UHT milk) showed an increase with the growth of bacteria, especially during the logarithmic growth phase. In addition, the UHT milk incubated with protease from B. cereus C58 at 28°C (24 h) and 10°C (6 d) were used to evaluate the effects of protease on the quality of UHT milk, including protein hydrolysis and physical stability. The results showed that the hydrolysis of casein was κ-CN, β-CN, and α_S-CN successively, whereas whey protein was not hydrolyzed. The degree of protein hydrolysis, viscosity, and particle size of the UHT milk increased. The changes in protein and fat contents indicated that fat globules floated at 28°C and settled at 10°C, respectively. Meanwhile, confocal laser scanning microscopy images revealed that the protease caused the stability of UHT milk to decrease, thus forming age gelation.     

Modeling Gelation of Egg Albumen and Ovalbumin

The Flory gelation theory and a new protein gelation model were used to investigate the aggregation reactions of egg albumen and ovalbumin. Results showed that 178 to 267 ovalbumin monomers were required to establish the initial ovalbumin gel at the gel point temperature, 81°C. The gel point temperature for egg albumen was 72°C by the Instron and 60°C by protein solubility. The values of the activation energy rate constants for the formation of the different aggregates in the pre-gel stage suggested that the larger ovalbumin aggregates were more reactive than the smaller ones.     

Quality evaluation of probiotic pasta produced with Bacillus coagulans GBI-30

Nowadays, the production of non-dairy and heat-treated probiotic foods has been gaining high interest. With this aim, due to its spore-forming ability Bacillus coagulans has been widely used in research studies. In this study, probiotic pasta production was accomplished with the addition of Bacillus coagulans GBI-30 spores into semolina. Samples were packed in zip-lock bag and stored at room temperature for 6 months. The microbiological characteristics, cooking behavior, texture, color and sensory attributes of pasta samples were investigated at 0 and 6 months of storage. Results showed that B. coagulans GBI-30 count of pasta samples decreased from 7.20 to 6.08 log CFU/g during cooking and storage showed statistically significant effect on B. coagulans GBI-30 count. At the end of the cooking in boiling (100 °C) distilled water for 8 min, B. coagulans GBI-30 did not negatively affect the sensorial quality of pasta according to the sensory panel of 7 experts. Therefore, it was concluded that the pasta can be considered as a probiotic product after 6 months of storage at room temperature due to the fact that B. coagulans GBI-30 count was above 6 log CFU/g.     

The Release of Carotenoids from a Light-Protected Antioxidant Active Packaging Designed to Improve the Stability of Soybean Oil

An antioxidant active packaging was developed by coextruding two layers of high-density polyethylene (HDPE). Bags were made with the film in which the inner layer, designed to be in contact with food, contained marigold flower (Tagetes erecta) extract rich in carotenoids. The outer layer of the film was added with titanium dioxide (TiO₂) to decrease the effect of commercial lighting on the degradation of carotenoids. Four bilayer films were produced: added with TiO₂ and carotenoids, added with carotenoids, added with TiO₂, and with no additives at all (control film). Degradation of color and astaxanthin in the films was delayed by the addition of the TiO₂ when they were stored under commercial lighting at 25 °C. Bags made of these films produced an improvement on the soybean oil stability at 25 °C as a result of a synergic effect of light protection by TiO₂ and carotenoids release. This release was measured as diffusion coefficients of carotenoids from the films toward soybean oil at 10, 25, and 40 °C (2.10–19.26?×?10^?11 cm² s^?1) with activation energy of 53.66 kJ mol^?1. In conclusion, the combination of the two layers of HDPE added with TiO₂ and carotenoids introduced opacity and permitted to extend the active effect of the films in contact with soybean oil. Moreover, the effect of temperature on the diffusion of carotenoids showed that this new active packaging is able to exert its function in conditions of transport, storage, and commercialization of food.     

The probiotic characteristics and GABA production of Lactobacillus plantarum K154 isolated from kimchi

In order to identify strains with a high GABA production ability and glutamate decarboxylase activity, 273 bacteria were isolated from kimchi. K154 produced 154.86 μg/mL of GABA in an MRS broth containing 1% MSG, 170.42 μg/mL of GABA in an MRS broth containing 2% MSG, and 201.78 μg/mL of GABA in an MRS broth containing 3% MSG. K154 was identified as Lactobacillus plantarum based on API carbohydrate fermentation pattern testing. The 16s rDNA sequence was investigated in order to determine physiological characteristics. The optimum growth temperature of K154 was 37°C. K154 was more sensitive to novobiocin and bacitracin than to other antibiotics, and exhibited greater resistance to polymyxin B and vancomycin. K154 was comparatively tolerant to bile juice and acid, and displayed resistance to Escherichia coli, Salmonella Typhimurium, and Staphylococcus aureus at rates of 19.0, 18.9, and 13.6% respectively.     

The Effects of High-Pressure Processing at Low and Subzero Temperatures on Inactivation of Microorganisms in Frozen and Unfrozen Beef Mince Inoculated with Escherichia coli Strain ATCC 25922

Frozen and unfrozen beef mince inoculated with Escherichia coli strain ATCC 25922 were exposed to a pressure of 300 MPa for 5 min at different temperatures (?10, ?5, 0, 10 and 20 °C). A maximum reduction of 1.5 log in total aerobic count (TAC) was obtained in unfrozen samples at ?5 °C, whereas at 20 °C, the reduction was only 0.6 log. Microbial inactivation in beef mince was enhanced by freezing the beef mince prior to pressurization. An average log reduction of 3.0 (SD?=?0.2) in both E. coli and TAC was obtained in frozen beef mince treated at ?5 °C. The highest bacterial reductions were observed in frozen samples. The extent of bacterial injury was substantially less in frozen samples than unfrozen samples, indicating that the damage inflicted on microorganisms in frozen beef mince by high pressure was irreversible. Lightness (L ^*), redness (a ^*) and yellowness (b ^*) values measured in accordance of Commission Internationale de l’Eclairage (CIE) for all the pressure-treated frozen and unfrozen samples differed slightly from unfrozen control samples (average total colour change, ΔE?=?6.1, SD?=?1.1). Water-holding capacity (WHC) measured by “high-pressure expressed moisture”, a new method proposed in this study, showed that freezing the samples prior to pressurization could increase WHC of minced beef. The results suggest that high-pressure processing could be used to make safer traditional raw minced meat products, such as steak tartare and cig kofte, a traditional Turkish dish made with minced beef, bulgur and spices.     

Quality Changes and Establishment of Predictive Models for Bighead Carp (Aristichthys nobilis) Fillets During Frozen Storage

The objectives of this study were to investigate quality changes of bighead carp fillets during frozen storage by measuring free fatty acids (FFA), salt extractable protein (SEP) content, Ca²⁺-ATPase activity, and total sulfhydryl (SH) content and to develop predictive models based on them. FFA increased with the extension of storage time. Meanwhile, SEP content, SH content, and Ca²⁺-ATPase activity all decreased during storage. A marked inhibition (p?2+-ATPase activity and SH content decrease was observed during storage of bighead carp fillets at ?30 °C, compared to those stored at ?10 and ?20 °C. Additionally, the relative errors of models based on Ca²⁺-ATPase and SH were all below 10 %. Thus, the lower frozen temperature can inhibit quality damage effectively, and a reliable estimation of quality changes could be performed by models based on Ca²⁺-ATPase and SH.