Physical and light oxidative properties of eugenol encapsulated by molecular inclusion and emulsion–diffusion method

The aim of this research was to study the encapsulation of eugenol as a volatile active substance by inclusion with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD), and by an emulsion–diffusion method with polycaprolactone (PCL). After formulation of each type of complex, size, zeta-potential, and thermal properties were determined by using Nanosizer®, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Overall, the mean sizes of encapsulated eugenol were the same at 320 nm. However, the size distribution of the β-CD and 2-HP-β-CD inclusion complex was poly-disperse as compared with eugenol encapsulated with polycaprolactone (PCL). TGA analysis revealed the encapsulation efficiency of PCL, β-CD eugenol and 2-HP-β-CD eugenol inclusion complexes were 100%, 90.9% and 89.1%, respectively. The study of oxidation stability revealed the emulsion–diffusion method was more efficient than the molecular inclusion method resulting from high stability depending on storage time. On the other hand, β-CD was more effective than 2-HP-β-CD for eugenol encapsulation. It is supposed that the side chain of hydroxypropyl group of 2-HP-β-CD might interrupt eugenol inclusion within the cavity of 2-HP-β-CD molecule. From our experiments, we concluded that the emulsion–diffusion method was the most effective for eugenol encapsulation to protect from light oxidation during storage time due to their complete wrapping of eugenol by PCL layer from TEM analysis.     

Isolation and characterisation of a novel Podoviridae-phage infecting Weissella cibaria N 22 from Nham, a Thai fermented pork sausage

A novel Podoviridae lactic acid bacteria (LAB) phage from Nham, a Thai fermented pork sausage, is reported. From a total of 36 samples, 41 isolates of LAB were obtained and employed as hosts for the isolation of phages. From these LAB, only one phage, designated Φ 22, was isolated. The lactic acid bacterial isolate named N 22, sensitive to phage Φ 22 infection was identified by an API 50 CHL kit and N 22’s complete sequence of the 16S rDNA sequence. BLASTN analysis of the 16S rDNA sequence revealed a 99% similarity to the 16S rDNA sequence of Weissella cibaria in the GenBank database. Electron micrographs indicated that the phage head was icosahedral with head size and tail length of 92 × 50 nm and 27 nm, respectively. On the basis of the morphology, this phage belongs to the family Podoviridae. Host-range determination revealed that the phage Φ 22 was not capable of infecting the other 40 isolates of LAB and referenced Weissella strains used. A one-step growth experiment showed that the latent period and burst size were estimated at 110 min and 55 phage particles/infected cell, respectively. Furthermore, the phage was infective over a wide range of pH (pH 5.0-8.0) and the D time of Φ 22 was calculated as 88 s at 70 °C and 15 s at 80 °C. Phage titers decreased below the detection limit (20 PFU/ml) after heating for more than 60 s at 80 °C, or 20 s at 90 °C or less than 10 s at 100 °C. The results from the study of Nham revealed that Φ 22 was active against the potential starter culture (W. cibaria N 22) for Nham fermentation. Phage infection could adversely affect the fermentation process of Nham by delaying acidification when using W. cibaria N 22 as a starter. However, the results from a sensory test revealed that the panelists did not detect any defects in the final products. This is the first report on the isolation of W. cibaria phage.     

Partial characterisation of bacteriocins produced by lactic acid bacteria isolated from Thai fermented meat and fish products

Lactic acid bacteria (LAB) from Thai fermented meat and fish products were isolated. From a total of 93 samples, 152 isolates of lactic acid bacteria were obtained. Antimicrobial activity screening was performed using the agar spot test and the agar well diffusion method. Of the six isolates which produced antimicrobial activities against Weissella confusa N31, only isolate N23 was identified as Weissella cibaria (GenBank accession number AB494716.1) with 99% similarity by 16S rDNA sequence analyses. Complete inactivation of antimicrobial activity produced by W. cibaria N23 was observed after treatment of the bacteriocins with trypsin, actinase, protease XIII, ficin, trypsin from porcine pancreas, α-chymotrypsin and pepsin. In addition, the inhibitory activities were not affected by the addition of catalase. Taken together, these results confirmed that the inhibitory compounds produced by this strain were proteinaceous in nature and possessed typical characteristics of bacteriocins. The highest yield of bacteriocin produced by W. cibaria N23 was recorded at 20 h. The bacteriocin N23 remained stable after 2 h of incubation at pH values between 2.0 and 8.0, and also for 15 min at 121 °C. The bacteriocin produced by W. cibaria N23 was found to have a narrow antibacterial spectrum, being able to inhibit only W. confusa N31. In addition, bacteriocin N23 did not adhere to the surface of the producer cells. The results produced from this study will contribute to the existing body of knowledge and enhance the databases of bacteriocin-producing Weissella.     

Effect of Amylose Content on Gelatinization,Retrogradation and Pasting Properties of Flours from Different Cultivars of Thai Rice

Presently, rice cultivars are categorized according to amylose content into three groups: low, medium and high amylose content cultivars. The correlation of amylose content with gelatinization properties, retrogradation, and pasting properties of eleven cultivars of Thai rice were investigated. Rice flour was prepared from milled rice by the wet grinding process. Onset (T_o), peak (T_p) and conclusion (T_c) temperatures of gelatinization, (determined by DSC) were found to be highly positively correlated with amylose levels. This correlation could be used for prediction of amylose content of rice flour. Low amylose starch could also be characterized by low degree of retrogradation (%R). The data obtained from RVA‐viscograms (peak viscosity, breakdown, setback, and pasting temperature) can be used only for characterization of the group of low amylose starches (waxy rice). It was demonstrated that low amylose rice starch provided the highest peak viscosity and breakdown and the lowest setback and pasting temperature among the groups investigated.     

Influence of biopolymer emulsifier type on formation and stability of rice bran oil-in-water emulsions: whey protein, gum arabic, and modified starch

Rice bran oil (RBO) is used in foods, cosmetics, and pharmaceuticals due to its desirable health, flavor, and functional attributes. We investigated the effects of biopolymer emulsifier type and environmental stresses on the stability of RBO emulsions. Oil-in-water emulsions (5% RBO, 10 mM citrate buffer) stabilized by whey protein isolate (WPI), gum arabic (GA), or modified starch (MS) were prepared using high-pressure homogenization. The new MS used had a higher number of octenyl succinic anhydride (OSA) groups per starch molecule than conventional MS. The droplet diameters produced by WPI and MS were considerably smaller (d < 300 nm) than those produced by GA (d > 1000 nm). The influence of pH (3 to 8), ionic strength (0 to 500 mM NaCl), and thermal treatment (30 to 90 °C) on the physical stability of the emulsions was examined. Extensive droplet aggregation occurred in WPI-stabilized emulsions around their isoelectric point (4 < pH < 6), at high salt (> 200 mM, pH 7), and at high temperatures (>70 °C, pH 7, 150 mM NaCl), which was attributed to changes in electrostatic and hydrophobic interactions between droplets. There was little effect of pH, ionic strength, and temperature on emulsions stabilized by GA or MS, which was attributed to strong steric stabilization. In summary: WPI produced small droplets at low concentrations, but they had poor stability to environmental stress; GA produced large droplets and needed high concentrations, but they had good stability to stress; new MS produced small droplets at low concentrations, with good stability to stress. Practical Application: This study showed that stable rice bran oil-in-water emulsions can be formed using biopolymer emulsifiers. These emulsions could be used to incorporate RBO into a wide range of food products. We compared the relative performance of whey protein, GA, and a new MS at forming and stabilizing the emulsions. The new OSA MS was capable of forming small stable droplets at relatively low concentrations.     

Physicochemical investigation and molecular modeling of cyclodextrin complexation mechanism with eugenol

The inclusion complexes between a series of cyclodextrins (CDs), which are αCD, βCD, γCD and hydroxypropyl-β-CD (HPβCD), and eugenol was studied by spectroscopy, thermal analysis and in silico molecular modeling. Molecular modeling provided conformation and thermodynamic data, and also confirmed experimental observations that, in aqueous phase, the complex formation was found at 1:1 mole ratio of eugenol and all CDs except those of γCD. Free energy of solvation of CDs and its cavity size are the most crucial factors for complex formation. The aromatic portion of eugenol was partially incorporated in αCD hydrophobic cavity whereas for βCD and HPβCD their aromatic parts could completely translocate inside. Moreover, a presence of free eugenol absorbed on CD hydrophilic surface were found as the following order, βCD < HPβCD < αCD, resulting in varying extents of eugenol release profiles. The intermolecular forces were found primarily due to intermolecular hydrogen bonding, resulting in stable complexes.     

Changes in colour,antioxidant activities and carotenoids (lycopene, β-carotene,lutein) of marigold flower (Tagetes erecta L.) resulting from different drying processes

Marigold (Tagetes erecta L.) flower has long been used as a food colourant and ingredient in human food and animal feed. Drying is one of the most important processes for producing marigold powder. Therefore the effects of different drying processes, namely freeze drying (FD), hot air drying (HA) and combined far-infrared radiation with hot air convection (FIR-HA), on the colour, carotenoids (lycopene, β-carotene and lutein) and phenolic compounds of marigold flowers were evaluated. The results indicate that colour changes were less for FIR-HA dried marigold than after FD and HA drying. Different drying methods resulted in changes in the content of individual bioactive compounds. HA gave the highest content of β-carotene (15.5 mg/100 g dry weight (DW)), while FIR-HA and FD provided the highest levels of lutein and lycopene. The predominant phenolic acids in all samples of marigold are p-coumaric acid, ferulic acid and sinapic acid. Gallic, protocatechuic, caffeic, syringic, p-coumaric and ferulic acid showed the highest content in marigold after FIR-HA drying. These results demonstrate that FIR-HA should be considered as a suitable drying method for marigold with respect to preserving its colour, antioxidant properties and bioactive compounds and provided useful information for industrial production of marigold powder.     

Freezing and Thawing Conditions Affect the Gel Stability of Different Varieties of Rice Flour

The freeze‐thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze‐thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour < Jasmine rice flour < amylose rice flour. The syneresis values and the appearance of starch gels, which had gone through the freeze‐ thaw process, suggested that the order of freeze‐thaw stability of gels for the three types of rice flour was waxy > Jasmine > amylose rice flour.