Antioxidant Activities of Konjac Glucomannan Hydrolysates of Different Molecular Weights at Different Values of pH

Konjac glucomannan (KGM) is a high-molecular-weight polysaccharide that was originally extracted from the corms (underground storage organs) of Amorphophallus konjac. KGM and its oligomers have been reported as dietary fibers that exhibit an array of health benefits. The depolymerization of KGM via enzymatic hydrolysis at different conditions gives products of low viscosity and can be used for coating materials in microencapsulation. In the present study, konjac glucomannan hydrolysates (KGMHs) were produced by enzymatic hydrolysis using commercial mannanase at pH 4.5 at 70 °C for 5-120 min, then KGMHs' molecular weight (Mw), Degree of Polymerization (DP) and their bioactivities were determined. A longer hydrolysis time resulted in KGMH of a lower DP. Oligoglucomannans (Mw < 10,000) could be obtained after hydrolysis for 20 min. The DP of KGMH rapidly decreased during an early stage of the hydrolysis (first 40 min); DP reached around 7 at the end of the hydrolysis. Antioxidant activities were determined by the DPPH radical scavenging and FRAP assays of KGMHs prepared at pH 4.5 and evaluated at pH 2.0-8.0 depending on pH. KGMH having lower Mw exhibited higher antioxidant activities. KGMHs having the smallest molecular weight (Mw = 419) exhibited the highest DPPH radical scavenging activity. Mw and pH have a greater impact on KGMHs' bioactivities which can be useful information for KGMHs as functional ingredients.

Production and characterization of nanofibrillated cellulose gels simultaneously exhibiting thermally stable green color and oil-in-water emulsion stabilizing capability from Centella asiatica

Nanofibrillated cellulose (NFC) gels simultaneously exhibiting Pickering stabilizing capability and thermally stable green color were developed for use as food additive in thermally processed food emulsion requiring the expression of color. Chopped Centella asiatica plant was mixed with zinc amino acid chelate solution and subject to autoclaving at 130°C for 2 h to form zinc-chlorophylls complex and to remove noncellulosic components. Autoclaved sample was high-shear homogenized at 26,000 rpm for 15 min and microfluidized at either 80, 120, or 160 MPa for 5 passes. An increase in microfluidization pressure resulted in a decrease in NFC diameters; microfluidization at 160 MPa did not nevertheless yield any further reduction in the diameters when compared with that at 120 MPa. From energy consumption point of view, microfluidization at 120 MPa for 5 passes was then noted as optimal condition for preparation of NFC coloring gel; NFC with diameters of 8-42 nm and crystallinity index of 35% was obtained. Freshly prepared gel exhibited gel-like behavior and dark green color. Heating at 121°C for 1 h did not affect diameters, viscoelasticity, and color of the gel. Addition of the gel at 0.9% or 1.2% (w/w) into soybean oil-in-water emulsion, in combination with high-shear homogenization at 18,000 rpm for 5 min, resulted in adequate emulsion stability. The emulsion exhibited stable dark green color and no phase separation after heating at 121°C for 1 h and during storage for 8 weeks. PRACTICAL APPLICATIONS: Information presented here can serve as a guideline for further development of a multifunctional food ingredient exhibiting thermally stable green color and oil-in-water emulsion stabilizing capability. In other words, one simple ingredient can serve at the same time as both natural food colorant and emulsion stabilizer.

Production of salad dressings via the use of economically prepared cellulose nanofiber from lime residue as a functional ingredient

Production of cellulose nanofiber (CNF) via the use of a more economical and less energy-intensive means is desirable. Once formed, it is necessary to determine whether or not the prepared CNF would be capable of forming a Pickering emulsion as in the case of traditionally prepared nanofiber. In the present study, oil-in-water emulsions, namely, salad dressings, with CNF as a functional ingredient, were prepared. Lime residue powder as the source of dietary fiber was subject to high-shear homogenization to form CNF suspension, which was then mixed with other ingredients. Different contents of fat (20%-40%), egg yolk (0%-4%), and lime residue powder (0%-4%) were tested. The formed CNF successfully acted as a Pickering emulsifier and allowed the production of salad dressings with desirable characteristics at 30%-40% fat, 2% egg yolk, and 2% lime residue powder. The dressings exhibited adequate physicochemical properties and remained stable throughout the storage period of 28 days. PRACTICAL APPLICATION: The presently proposed means would allow the industry to produce cellulose nanofiber (CNF) in a more economical and less energy-intensive manner. The so-produced CNF exhibits comparable properties as traditionally prepared nanofiber and can be used as a stabilizer in food emulsions.

Microstructures of encapsulates and their relations with encapsulation efficiency and controlled release of bioactive constituents: A review

Vitamins, peptides, essential oils, and probiotics are examples of health beneficial constituents, which are nevertheless heat-sensitive and possess poor chemical stability. Various encapsulation methods have been applied to protect these constituents against thermal and chemical degradations. Encapsulates prepared by different methods and/or at different conditions exhibit different microstructures, which in turn differently influence the encapsulation efficiency as well as retention of encapsulated core materials. This review provides a summary of various microstructures resulted from the use of selected encapsulation methods or systems, namely, spray coating; co-extrusion; emulsion-, micelle-, and liposome-based; coacervation; and ionic gelation encapsulation, at different conditions. Subsequent effects of the different microstructures on encapsulation efficiency and retention of encapsulated core materials are mentioned and discussed. Encapsulates having compact microstructures resulted from the use of low-surface tension and low-viscosity encapsulants, high-stability encapsulation systems, lower loads of core materials to total solids of encapsulants and appropriate solidification conditions have proved to exhibit higher encapsulation efficiencies and better retention of encapsulated core materials. Encapsulates with hollow, dent, shrunken microstructures or thinner walls resulted from inappropriate solidification conditions and higher loads of core materials, on the other hand, possess lower encapsulation efficiencies and protection capabilities. Encapsulates having crack, blow-hole or porous microstructures resulted from the use of high-viscosity encapsulants and inappropriate solidification conditions exhibit the lowest encapsulation efficiencies and poorest protection capabilities. Compact microstructures and structures formed between ionic biopolymers could be used to regulate the release of encapsulated cores.

Color and molecular structure alterations of brazilein extracted from Caesalpinia sappan L. under different pH and heating conditions

Brazilein extract from sappan wood (Caesalpinia sappan L.) has potential for use as natural food colorant since it has no unique flavor and taste. Although brazilein has long been applied in several traditional foods and beverages, information on its stability, which is of importance for practical application, is still limited. In this work, brazilein was isolated from sappan wood; its purity was confirmed by nuclear magnetic resonance spectroscopy. Relations between molecular structures and color as well as thermal stabilities of brazilein in aqueous solutions at pH 3, 7 and 9 were for the first time investigated. At the lowest pH, zero net-charge structure of brazilein, which exhibited yellow color, was predominantly found. The deprotonated and fully deprotonated structures of brazilein, which exhibited orange and red colors, respectively, were found when pH of the aqueous solutions increased. The forms of brazilein existing at the higher pH suffered extensive degradation upon heating, while the form existing at the lowest pH possessed higher stability. Heat-induced deprotonation and degradation were confirmed by UV-visible and Fourier-transform infrared spectra as well as losses of brazilein content.

Correction: Evolution of important glucosinolates in three common Brassica vegetables during their processing into vegetable powder and in vitro gastric digestion

Correction for 'Evolution of important glucosinolates in three common Brassica vegetables during their processing into vegetable powder and in vitro gastric digestion' by Thitima Kuljarachanan et al., Food Funct., 2020, DOI: 10.1039/c9fo00811j.

Evolution of important glucosinolates in three common Brassica vegetables during their processing into vegetable powder and in vitro gastric digestion

Evolution of important glucosinolates (GLSs), namely, sinigrin, glucoraphanin, glucoerucin and glucobrassicin, in three commonly consumed Brassica vegetables viz. white cabbage, Chinese cabbage and bok choy during their processing into vegetable powder was investigated. Drying was noted to be a major processing step causing significant losses of GLSs. Interestingly, different GLSs and even the same GLSs in different vegetables showed different thermal stabilities during drying. The stability of GLSs in vegetable powder during in vitro gastric digestion was also studied. Glucoraphanin exhibited the highest stability while glucobrassicin was the most vulnerable GLS under in vitro gastric conditions. White cabbage is found to be a promising material for the production of vegetable powder as it contains high contents of GLSs, especially glucoraphanin and glucoerucin, which are important precursors of anticarcinogenic compounds, namely sulforaphane and erucin. These two GLSs were also noted to be stable during in vitro gastric digestion.

On the use of microwave pretreatment to assist zero-waste chemical-free production process of nanofibrillated cellulose from lime residue

Microwave (MW) pretreatment as an energy-efficient method to enhance the production of nanofibrillated cellulose (NFC) from lime (Citrus aurantifolia Swingle) residue after juice extraction is proposed. NFC was prepared by subjecting lime residue to MW pretreatment for up to 3 rounds; this was followed by high-shear and high-pressure homogenization. Repeated application of MW pretreatment helped remove non-cellulosic components and resulted in an increased cellulose content and crystallinity index but a decrease in fiber diameter. Freshly prepared NFC sample exhibited gel-like behavior. G' and G″ of suspension prepared from dried NFC markedly decreased, indicating the loss of gel-like property upon drying. Proper pectin molecular weight as well as pectin content were noted to play an important role in controlling aggregation of NFC during drying and hence water redispersibility of dried NFC. Significant amounts of pectin and limonin could be recovered and utilized as co-products after the first round of MW pretreatment.

Use and Understanding of the Role of Spontaneously Formed Nanocellulosic Fiber from Lime (Citrus aurantifolia Swingle) Residues to Improve Stability of Sterilized Coconut Milk

Feasibility of using nanocellulosic fiber (NF) from lime residues as a stabilizer for oil-in-water emulsion was investigated. One-step process to simultaneously prepare an emulsion and NF is proposed. NF could spontaneously form by adding appropriately prepared fiber powder into the test emulsion viz. coconut milk, which was subsequently subject to homogenization and sterilization. Properties of the samples, that is, microstructure, rheological properties, emulsion stability, and color, after sterilization and after 8-week storage at 30 °C were determined. Sterilized samples exhibited pseudoplastic behavior. Samples containing higher NF concentrations exhibited higher viscosity; viscosity remained constant throughout the whole storage period. High emulsion stabilities (>97%) were observed for samples containing 0.4 to 0.8% (w/v) of NF. L^* , C^* , and h^* of the samples were 79 to 80, 8 to 10, and 90, respectively. Three-dimensional network of NF (diameters < 50 nm) attached to fat globule surfaces formed during homogenization is postulated to help stabilize the emulsions. PRACTICAL APPLICATION: One-step process to simultaneously prepare oil-in-water emulsion as well as nanocellulosic fiber (NF) is proposed. Such a formed NF can serve as natural ingredient to stabilize the emulsion. The proposed procedures should be of great interest to an industry producing oil-in-water emulsions (for example, canned coconut milk) that is looking for a natural alternative to synthetic stabilizer.

Enhanced production of sulforaphane by exogenous glucoraphanin hydrolysis catalyzed by myrosinase extracted from Chinese flowering cabbage (Brassica rapa var. parachinensis)

Sulforaphane formation via endogenous route is known to be less effective. Exogenous hydrolysis of the sulforaphane precursor is therefore of interest. Here, myrosinase activity was first determined to identify a suitable source of the enzyme from selected Brassica vegetables. Extracted enzyme was then evaluated for its thermal stability to establish a condition for extraction. Chinese flowering cabbage was selected as the source of myrosinase; suitable extraction condition was at 40 °C for 90 min. Enzyme extract was used to hydrolyze glucoraphanin standard into sulforaphane at 30 °C and pH 6. Exogenous hydrolysis reached the equilibrium with the reverse reaction after 30 min; sulforaphane concentration remained unchanged afterward. Molar fractional conversion of glucoraphanin into sulforaphane at 30-min hydrolysis was around 48%. In comparison with exogenous hydrolysis by myrosinase extracted from broccoli, which indeed exhibits higher activity than the enzyme extracted from Chinese flowering cabbage, no conversion of glucoraphanin into sulforaphane was unexpectedly observed.

Characterization of Nanofibrillated Cellulose Produced by Different Methods from Cabbage Outer Leaves

The potential use of cabbage outer leaves as a starting material for the production of nanofibrillated cellulose (NFC) was investigated. Chemical-free pretreatment methods, namely, autoclaving, ultrasonication (US), and high-shear homogenization (HS), were applied to remove noncellulosic components from cabbage cell walls prior to defibrillation, which was conducted by subjecting a pretreated sample to HS and then high-pressure homogenization. The sample undergone autoclaving at 130 °C for 2 hr was noted to contain a significantly higher cellulose content (36.5% dry mass) compared with the fresh leaves (12.48% dry mass). This led to an increase in the crystallinity index (CI) of the autoclaved cabbages from 30.8% to 50.7%. Further increase in the cellulose content (47.0% to 49.2% dry mass) was observed when subjecting the autoclaved sample to either US at 37 kHz for 1 hr, HS at 3800 × g for 15 min or HS followed by US at the aforementioned conditions. After pretreatment and defibrilllation, a suspension of NFC with the diameters of 4 to 50 nm was obtained, with the CI of 59.1% to 66.7%. Such a suspension exhibited a gel-like behavior with tan δ in the range of 0.12 to 0.13; the suspension exhibited a similar behavior to that prepared by the conventional chemical pretreatment method.

PRACTICAL APPLICATION

NFC could be produced from cabbage outer leaves, which are an abundantly available by-product of a vegetable processing plant, via the combined hydrothermal and mechanical pretreatment without the use of any chemicals. This chemical-free preparation process is highly desirable as it leaves no residues in the product and causes no chemical waste that needs to be treated. Cabbage-based NFC also exhibits similar characteristics to that prepared via a chemically treated route.

Natural colorants: Pigment stability and extraction yield enhancement via utilization of appropriate pretreatment and extraction methods

Natural colorants from plant-based materials have gained increasing popularity due to health consciousness of consumers. Among the many steps involved in the production of natural colorants, pigment extraction is one of the most important. Soxhlet extraction, maceration, and hydrodistillation are conventional methods that have been widely used in industry and laboratory for such a purpose. Recently, various non-conventional methods, such as supercritical fluid extraction, pressurized liquid extraction, microwave-assisted extraction, ultrasound-assisted extraction, pulsed-electric field extraction, and enzyme-assisted extraction have emerged as alternatives to conventional methods due to the advantages of the former in terms of smaller solvent consumption, shorter extraction time, and more environment-friendliness. Prior to the extraction step, pretreatment of plant materials to enhance the stability of natural pigments is another important step that must be carefully taken care of. In this paper, a comprehensive review of appropriate pretreatment and extraction methods for chlorophylls, carotenoids, betalains, and anthocyanins, which are major classes of plant pigments, is provided by using pigment stability and extraction yield as assessment criteria.

Molecular structure, stability and cytotoxicity of natural green colorants produced from Centella asiatica L. leaves treated by steaming and metal complexations

Stability of extracts from Centella asiatica L. leaves treated by steaming and metal-chlorophylls complexations against combined acid-heat was compared with that from untreated leaves and synthetic colorant. Formation of metal-chlorophylls complexes was confirmed by FTIR spectroscopy. Molecular structure changes during stability test and cytotoxicity of the extracts against Vero cells were evaluated. Utilization of the extracts as colorant was also assessed in selected beverage ingredient and food. Copper-chlorophylls extracts exhibited similar green hue to those from untreated and steamed leaves, while zinc-chlorophylls extracts exhibited yellow-green color. Metal-chlorophylls extracts possessed higher stability against combined acid-heat than those from untreated and steamed leaves. Use of metal-chlorophylls extracts in beverage ingredient led to increased hue value due to their structural rearrangement, which was confirmed by changes in Q band of VIS spectra. Cytotoxicity of zinc- and copper-chlorophylls extracts was slightly different and higher than those of extracts from untreated/steamed leaves and synthetic colorant.

Evolution of antioxidants in dietary fiber powder produced from white cabbage outer leaves: effects of blanching and drying methods

White cabbage outer leaves, which are usually discarded both during industrial processing and selling in a consumer market, have proven to be a good source of dietary fiber (DF) as well as antioxidants and can be effectively transformed into functional DF powder. In the past, however, only hot air drying was used to prepare DF powder from cabbage outer leaves although it is well recognized that this drying technique could lead to much quality degradation of a dried product. This work was therefore aimed at studying the evolution of selected important antioxidants, e.g., phenolic compounds and vitamin C, in white cabbage outer leaves during vacuum drying at 60, 70 and 80 °C. The effect of pretreatment viz. steam blanching was also evaluated. The results showed that there were losses of antioxidants during steam blanching; vacuum dried blanched leaves nevertheless contained higher antioxidant contents and activity than dried unblanched leaves. Losses of antioxidants during vacuum drying were also noted to be less than those during hot air drying. Overall, the results showed that there were no differences in the antioxidants retention among all the tested conditions performed in this study. Therefore, the most suitable condition for the production of antioxidant DF powder from cabbage outer leaves is vacuum drying at 80 °C as this condition requires the minimum specific energy consumption.

Desalination of fish sauce by electrodialysis: effect on selected aroma compounds and amino acid compositions

Fish sauce is an ingredient that exhibits unique flavor and is widely used by people in Southeast Asia. Fish sauce, however, contains a significant amount of salt (sodium chloride). Recently, electrodialysis (ED) has been successfully applied to reduce salt in fish sauce; however, no information is available on the effect of ED on changes in compounds providing aroma and taste of ED-treated fish sauce. The selected aroma compounds, amino acids, and sensory quality of the ED-treated fish sauce with various salt concentrations were then analyzed. The amounts of trimethylamine, 2,6-dimethylpyrazine, phenols, and all carboxylic acids except for hexanoic acid significantly decreased, whereas benzaldehyde increased significantly when the salt removal level was higher. The amounts of all amino acids decreased with the increased salt removal level. Significant difference in flavor and saltiness intensity among ED-treated fish sauce with various salt concentrations, as assessed by a discriminative test, were observed.

PRACTICAL APPLICATION

Information obtained in this work can serve as a guideline for optimization of a process to produce low-sodium fish sauce by ED. It also forms a basis for further in-depth sensory analysis of low-sodium fish sauce.

Thermal resistance of Salmonella enterica serovar Anatum on cabbage surfaces during drying: effects of drying methods and conditions

The effects of selected drying methods, i.e., hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD), on the heat resistance of Salmonella attached on vegetable surface, which are data that have never been reported elsewhere, were investigated at drying temperatures of 50-70 °C; vacuum drying and LPSSD were carried out at an absolute pressure of 10 kPa. The selected Salmonella serovar, i.e., S. Anatum, was used as a test organism. Cabbage was used as a vegetable model to represent uneven natural surface. The results showed that drying methods had a significant effect on the drying kinetics as well as the destruction rate of Salmonella. Higher drying temperatures resulted in higher destruction rates of S. Anatum. Hot air drying was noted to be the slowest drying process, while vacuum drying and LPSSD could be used to shorten the drying time. By considering the reduction in the number of Salmonella at the end of drying, LPSSD is recommended as it has proved to yield the highest degree of S. Anatum inactivation.

Electrodialysis desalination of fish sauce: electrodialysis performance and product quality

Fish sauce has a unique, pleasant flavor, but contains high levels of sodium chloride, which is nowadays not desirable for health-conscious consumers. Although many researchers have attempted to solve this problem by substituting sodium with potassium in fish sauce, potassium-based products are still unsuitable for patients with kidney disease. Thus, electrodialysis (ED) desalination of fish sauce was carried out. The rate of salt removal, evolution of total soluble solids, and electrical conductivity of the electrodialysis-treated fish sauce were investigated. Moreover, the system performance in terms of yield, energy consumption, and current efficiency were examined. Density, viscosity, ion concentrations (that is, Na(+), K(+)), total nitrogen, amino nitrogen, and color were investigated at various values of input voltage (6, 7, and 8 V) and remaining salt concentration (22%, 18%, 14%, 10%, 6%, and 2%[w/w]). The results indicated that an increase in the input voltage led to an increase in the rates of salt removal, electrical conductivity, and total soluble solids. The energy consumption increased whereas current efficiency and yield decreased significantly with an increase in input voltage and the salt removal level. Physicochemical properties of the treated fish sauce, in terms of the total soluble solids, density, viscosity, ion concentrations (that is, Na(+), K(+)), total nitrogen, and color were significantly affected by the input voltage and the salt-removal level.

Effects of drying temperature and surface characteristics of vegetable on the survival of salmonella

The heat resistance of Salmonella Anatum inoculated on the surface of a model vegetable as affected by hot-air drying temperature (50 to 70 degrees C) and surface characteristics was determined in this study. Cabbage was selected as a model vegetable to demonstrate the effect of topographical feature of vegetable surface on the Salmonella attachment ability. An image analysis technique was developed to monitor the change of cabbage surface during drying and the specific surface characteristics were described in terms of the roughness factor (R). It was found that the water activity of the vegetable decreased while R-value increased with longer drying time and higher drying temperature. However, the changes of both parameters during drying did not show a significant effect on the susceptibility of Salmonella attached on the cabbage surface. Drying temperature was found to be a major factor influencing the heat resistance of Salmonella during drying.

Effect of water activity on thermal resistance of Salmonella krefeld in liquid medium and on rawhide surface

The thermal resistivity of Salmonella krefeld at 60 and 65 degrees C as affected by water activity (0.99-0.60) was investigated in a liquid medium viz. Trypticase Soy Broth (TSB) and on rawhide surface. A reduction of the a(w) of the liquid medium resulted in an increase in the heat resistance of Salmonella krefeld. At a particular water activity the type of solute played a significant role with Salmonella krefeld exhibiting much higher heat sensitivity in the media with glycerol compared to the media with sucrose. The heat resistance of Salmonella krefeld inoculated onto the surface of rawhide was also investigated during hot air drying at 60 and 65 degrees C at two initial levels of a(w), 0.99 and 0.90, prior to drying as determined at 250 degrees C. The rate of water loss or a(w) decrease during drying was not significantly influenced by the initial water activity but was clearly dependent on the drying temperature with all survival curves displaying an upward concavity. Salmonella on rawhide with an initial a(w) of 0.90 exhibited higher heat tolerance than with an initial a(w) of 0.99 during a prolonged heating period with the initial a(w) significantly affecting the heat resistance particularly at higher drying temperatures.